Advances in universal scaling for broadband turbulent noise in internal flow devices
Violato, D.; Jong, A.T. de; Golliard, J.
2014-01-01
This paper focuses on the scalability of broadband turbulent noise in internal pipe flows. It discusses a universal scaling approach for broadband turbulent noise that is based on surface acoustic power modeled by ANSYS Fluent. This investigation proposes a strategy for amplitude scaling at
Alhamdi, Sabah F. H.; Bailey, Sean C. C.
2017-11-01
Measurements of the small-scale dissipation statistics of turbulent boundary layer flows with and without free-stream turbulence are reported for Reτ ≈ 1000 (Reθ ≈ 2000). The scaling of the dissipation scale distribution is examined in these two boundary conditions. Results demonstrated that the local large-scale Reynolds number based on the measured longitudinal integral length scale fails to properly normalize the dissipation scale distribution near the wall in these two free-stream conditions due to the imperfect characterization of the upper bound of the inertial cascade by the integral length scale. A surrogate found from turbulent kinetic energy and mean dissipation rate only moderately improved the scaling of the dissipation scales, relative to the measured integral length scale. When a length scale based on the distance from the wall [as suggested by Bailey and Witte, "On the universality of local dissipation scales in turbulent channel flow," J. Fluid Mech. 786, 234-252 (2015)] was utilized to scale the dissipation scale distribution, in the region near the wall, there was a noticeable improvement in the collapse of the normalized distribution of dissipation scales. In addition, unlike in channel flows, in the outer layer of the turbulent boundary layer, the normalized distributions of the local dissipation scales were observed to be dependent on the wall-normal position. This was found to be attributable to the presence of external intermittency in the outer layer as the presence of free-stream turbulence was found to restore the scaling behavior by replacing the intermittent laminar flow with turbulent flow.
International Nuclear Information System (INIS)
Blum, Daniel B; Voth, Greg A; Bewley, Gregory P; Bodenschatz, Eberhard; Gibert, Mathieu; Xu Haitao; Gylfason, Ármann; Mydlarski, Laurent; Yeung, P K
2011-01-01
We present a systematic comparison of conditional structure functions in nine turbulent flows. The flows studied include forced isotropic turbulence simulated on a periodic domain, passive grid wind tunnel turbulence in air and in pressurized SF 6 , active grid wind tunnel turbulence (in both synchronous and random driving modes), the flow between counter-rotating discs, oscillating grid turbulence and the flow in the Lagrangian exploration module (in both constant and random driving modes). We compare longitudinal Eulerian second-order structure functions conditioned on the instantaneous large-scale velocity in each flow to assess the ways in which the large scales affect the small scales in a variety of turbulent flows. Structure functions are shown to have larger values when the large-scale velocity significantly deviates from the mean in most flows, suggesting that dependence on the large scales is typical in many turbulent flows. The effects of the large-scale velocity on the structure functions can be quite strong, with the structure function varying by up to a factor of 2 when the large-scale velocity deviates from the mean by ±2 standard deviations. In several flows, the effects of the large-scale velocity are similar at all the length scales we measured, indicating that the large-scale effects are scale independent. In a few flows, the effects of the large-scale velocity are larger on the smallest length scales. (paper)
Onset of meso-scale turbulence in active nematics
Doostmohammadi, Amin; Shendruk, Tyler N.; Thijssen, Kristian; Yeomans, Julia M.
2017-05-01
Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at low Reynolds number in fluidized biological systems. This spatiotemporal disordered flow radically changes nutrient and molecular transport in living fluids and can strongly affect the collective behaviour in prominent biological processes, including biofilm formation, morphogenesis and cancer invasion. Despite its crucial role in such physiological processes, understanding meso-scale turbulence and any relation to classical inertial turbulence remains obscure. Here we show how the motion of active matter along a micro-channel transitions to meso-scale turbulence through the evolution of locally disordered patches (active puffs) from an ordered vortex-lattice flow state. We demonstrate that the stationary critical exponents of this transition to meso-scale turbulence in a channel coincide with the directed percolation universality class. This finding bridges our understanding of the onset of low-Reynolds-number meso-scale turbulence and traditional scale-invariant turbulence in confinement.
Scaling, Intermittency and Decay of MHD Turbulence
International Nuclear Information System (INIS)
Lazarian, A.; Cho, Jungyeon
2005-01-01
We discuss a few recent developments that are important for understanding of MHD turbulence. First, MHD turbulence is not so messy as it is usually believed. In fact, the notion of strong non-linear coupling of compressible and incompressible motions along MHD cascade is not tenable. Alfven, slow and fast modes of MHD turbulence follow their own cascades and exhibit degrees of anisotropy consistent with theoretical expectations. Second, the fast decay of turbulence is not related to the compressibility of fluid. Rates of decay of compressible and incompressible motions are very similar. Third, viscosity by neutrals does not suppress MHD turbulence in a partially ionized gas. Instead, MHD turbulence develops magnetic cascade at scales below the scale at which neutrals damp ordinary hydrodynamic motions. Forth, density statistics does not exhibit the universality that the velocity and magnetic field do. For instance, at small Mach numbers the density is anisotropic, but it gets isotropic at high Mach numbers. Fifth, the intermittency of magnetic field and velocity are different. Both depend on whether the measurements are done in a local system of reference oriented along the local magnetic field or in the global system of reference related to the mean magnetic field
Large-scale turbulence structures in shallow separating flows
Talstra, H.
2011-01-01
The Ph.D. thesis “Large-scale turbulence structures in shallow separating flows” by Harmen Talstra is the result of a Ph.D. research project on large-scale shallow-flow turbulence, which has been performed in the Environmental Fluid Mechanics Laboratory at Delft University of Technology. The
Beyond scale separation in gyrokinetic turbulence
International Nuclear Information System (INIS)
Garbet, X.; Sarazin, Y.; Grandgirard, V.; Dif-Pradalier, G.; Darmet, G.; Ghendrih, Ph.; Angelino, P.; Bertrand, P.; Besse, N.; Gravier, E.; Morel, P.; Sonnendruecker, E.; Crouseilles, N.; Dischler, J.-M.; Latu, G.; Violard, E.; Brunetti, M.; Brunner, S.; Lapillonne, X.; Tran, T.-M.; Villard, L.; Boulet, M.
2007-01-01
This paper presents the results obtained with a set of gyrokinetic codes based on a semi-Lagrangian scheme. Several physics issues are addressed, namely, the comparison between fluid and kinetic descriptions, the intermittent behaviour of flux driven turbulence and the role of large scale flows in toroidal ITG turbulence. The question of the initialization of full-F simulations is also discussed
Multiple-scale turbulence and bifurcation
Energy Technology Data Exchange (ETDEWEB)
Yagi, M.; Itoh, S.-I.; Kawasaki, M. [Kyushu Univ., Research Institute for Applied Mechanics, Kasuga, Fukuoka (Japan); Itoh, K. [National Inst. for Fusion Science, Toki, Gifu (Japan); Fukuyama, A. [Kyoto Univ., Department of Nuclear Engineering, Kyoto (Japan)
2003-01-01
In this paper, we analyze the turbulence composed of collective modes with different scale lengths. The hierarchical model for multiple-scale turbulence is developed. Nonlinear interactions between different scale length are modeled as turbulent drag, nonlinear noise and nonlinear drive and a set of Langevin equations is formulated. Using this model, a case where two driving mechanisms coexist (one for the micro mode and the other for semi-micro mode) is investigated. It is found that a new type of turbulence transition and a cusp-type catastrophe exist in some parameter regime. Numerical simulations are also performed for neighboring multiple-scale turbulence such as ion temperature gradient driven drift wave (ITG) (k{sub y}{rho}{sub i} < 1) and short wavelength ITG (k{sub y}{rho}{sub i} > 1) modes in the shearless slab geometry. The cascade and inverse cascade in multiple-scale turbulence are investigated. The cascade is mainly observed in k sub(parallel) space. On the other hand, the cascade and the inverse cascade are observed in K sub(perpendicular) space. Another interesting result is that the particle flux is negative (inward pinch) due to the short wavelength ITG modes, while the ion and electron heat flux are positive, which indicates nonlinear interaction between different scale length mode might affect transport. (author)
Speculation about near-wall turbulence scales
International Nuclear Information System (INIS)
Yurchenko, N F
2008-01-01
A strategy to control near-wall turbulence modifying scales of fluid motion is developed. The boundary-layer flow is shown to respond selectively to the scale of streamwise vortices initiated, e.g. with the spanwise regular temperature distribution over a model surface. It is used to generate sustainable streamwise vortices and thus to optimize integral flow characteristics.
Environmental turbulence and climate-weather scaling
Ben Mahjoub, Otman; Cherubini, Claudia; Jebbad, Raghda; Mosso, Cessar; Benjamin, Juan Jose; Jorge, Joan; Diez, Margarita; Redondo, Jose M.
2017-04-01
Climate changes in Harbours, coastal areas and ROFI are key to Environmental flows. Ocean and Atmospheric turbulence is an energetic, eddying state of motion that disperses material at rates far higher than those of molecular processes alone; The role of intermittency and understanding of how turbulence is modified at Climatic and Weather scales in shallow seas, the deep ocean, and in the mixed layers is of great importance and practical applications. The larger-scale and time coherent structures associated with large Stommel diagram processes akin to turbulence that also have intermittency. With the aid of remote sensing we also use surface signatures[1,2] that can be detected and used to infer ocean parameters. Such effects dominate mesoscale vorticity, the role of Rossby deformation radius, Spiral eddies, convective cells, or the spacing of Langmuir turbulence, related to the depth of the mixed layer, or to cloud tops. The dominant instability processes can generate different intermittency , detected often as bursts or in variations in the scale to scale transfer of turbulence. We include climatic scales where Extended Self Simmilarity is used also in these scales in a fractal way. Global experiments, even with a wide range of new configurations are possible[3-6]. Such complex flows are known to generate nonequilbrium and non-local turbulence which produces different turbulence properties and varying intermittency. Applications to enhanced mixing and drag reduction are still being investigated [6, 7], and how do the turbulence and mixing properties change in Lagrangian and Eulerian descriptors with generalized Rayleigh, Rossby, Richardson and Reynolds numbers? in complex Poincare like, parameter spaces. [1]. Redondo J.M., Mixing efficiencies of different kinds of turbulent processes and instabilities, Applications to the environment in Turbulent mixing in geophysical flows. Eds. Linden P.F. and Redondo J.M. 131-157. 2002. [2]. Ben Mahjoub, Redondo J
Universal equations and constants of turbulent motion
Baumert, H. Z.
2013-07-01
This paper presents a parameter-free theory of shear-generated turbulence at asymptotically high Reynolds numbers in incompressible fluids. It is based on a two-fluids concept. Both components are materially identical and inviscid. The first component is an ensemble of quasi-rigid dipole-vortex tubes (vortex filaments, excitations) as quasi-particles in chaotic motion. The second is a superfluid performing evasive motions between the tubes. The local dipole motions follow Helmholtz' law. The vortex radii scale with the energy-containing length scale. Collisions between quasi-particles lead either to annihilation (likewise rotation, turbulent dissipation) or to scattering (counterrotation, turbulent diffusion). There are analogies with birth and death processes of population dynamics and their master equations and with Landau's two-fluid theory of liquid helium. For free homogeneous decay the theory predicts the turbulent kinetic energy to follow t-1. With an adiabatic wall condition it predicts the logarithmic law with von Kármán's constant as 1/\\sqrt {2\\,\\pi }= 0.399 . Likewise rotating couples form localized dissipative patches almost at rest (→ intermittency) wherein under local quasi-steady conditions the spectrum evolves into an ‘Apollonian gear’ as discussed first by Herrmann (1990 Correlation and Connectivity (Dordrecht: Kluwer) pp 108-20). Dissipation happens exclusively at scale zero and at finite scales this system is frictionless and reminds of Prigogine's (1947 Etude Thermodynamique des Phenomenes Irreversibles (Liege: Desoer) p 143) law of minimum (here: zero) entropy production. The theory predicts further the prefactor of the 3D-wavenumber spectrum (a Kolmogorov constant) as \\frac {1}{3}(4\\,\\pi )^{2/3}=1.802 , well within the scatter range of observational, experimental and direct numerical simulation results.
Scale-locality of magnetohydrodynamic turbulence
Energy Technology Data Exchange (ETDEWEB)
Aluie, Hussein [Los Alamos National Laboratory; Eyink, Gregory L [JOHNS HOPKINS UNIV.
2009-01-01
We investigate the scale-locality of cascades of conserved invariants at high kinetic and magnetic Reynolds numbers in the 'inertial-inductive range' of magnetohydrodynamic (MHD) turbulence, where velocity and magnetic field increments exhibit suitable power-law scaling. We prove that fluxes of total energy and cross-helicity - or, equivalently, fluxes of Elsaesser energies - are dominated by the contributions of local triads. Corresponding spectral transfers are also scale-local when defined using octave wavenumber bands. Flux and transfer of magnetic helicity may be dominated by nonlocal triads. The magnetic stretching term also may be dominated by non-local triads but we prove that it can convert energy only between velocity and magnetic modes at comparable scales. We explain the disagreement with numerical studies that have claimed conversion non locally between disparate scales. We present supporting data from a 1024{sup 3} simulation of forced MHD turbulence.
Sahraoui, F.; Huang, S.
2017-12-01
Large surveys of power spectral density (PSD) of the magnetic fluctuations in the solar wind have reported different slopes distributions at MHD, sub-ion and sub-electron scales; the smaller the scale the broader the distribution. Several explanations of the variability the slopes at sub-ion scales have been proposed. Here, we present a new one that has been overlooked in the literature, which is based on the relative importance of the dispersive effects w.r.t. the Doppler shift due to the flow speed. We build a toy model based on a dispersion relation of a linear mode that matches at high frequency (ω ≳ ω ci) the Alfvén (resp. whistler) mode at high oblique (resp. quasi-parallel) propagation angles θ kB. Starting with double power-law spectrum of turbulence {k⊥}-1.66 in the inertial range and {k⊥}-2.8 at the sub-ion scales, the transformed spectrum (in frequency f) as it would be measured in the spacecraft frame shows a broad range of slopes at the sub-ion scales that depend both on the angle θ kB and the flow speed V. Varying θ kB in the range 10o-100o and V in the range 400-800 km/s, the resulting distribution of slopes at the sub-ion scales reproduces quite well the observed one in the solar wind. Fluctuations in the solar wind speed and the anisotropy of the turbulence may explain (or at least contribute to) the variability of the spectral slopes reported in the solar wind.
Universal Probability Distribution Function for Bursty Transport in Plasma Turbulence
International Nuclear Information System (INIS)
Sandberg, I.; Benkadda, S.; Garbet, X.; Ropokis, G.; Hizanidis, K.; Castillo-Negrete, D. del
2009-01-01
Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this Letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density fluctuations observed in plasma edge of several magnetic confinement devices and the remarkable scaling between their skewness S and kurtosis K. Similar statistical characteristics of variabilities have been also observed in other physical systems that are characterized by convection such as the x-ray fluctuations emitted by the Cygnus X-1 accretion disc plasmas and the sea surface temperature fluctuations.
Reinterpreting aircraft measurements in anisotropic scaling turbulence
Directory of Open Access Journals (Sweden)
S. J. Hovde
2009-07-01
Full Text Available Due to both systematic and turbulent induced vertical fluctuations, the interpretation of atmospheric aircraft measurements requires a theory of turbulence. Until now virtually all the relevant theories have been isotropic or "quasi isotropic" in the sense that their exponents are the same in all directions. However almost all the available data on the vertical structure shows that it is scaling but with exponents different from the horizontal: the turbulence is scaling but anisotropic. In this paper, we show how such turbulence can lead to spurious breaks in the scaling and to the spurious appearance of the vertical scaling exponent at large horizontal lags.
We demonstrate this using 16 legs of Gulfstream 4 aircraft near the top of the troposphere following isobars each between 500 and 3200 km in length. First we show that over wide ranges of scale, the horizontal spectra of the aircraft altitude are nearly k^{-5/3}. In addition, we show that the altitude and pressure fluctuations along these fractal trajectories have a high degree of coherence with the measured wind (especially with its longitudinal component. There is also a strong phase relation between the altitude, pressure and wind fluctuations; for scales less than ≈40 km (on average the wind fluctuations lead the pressure and altitude, whereas for larger scales, the pressure fluctuations leads the wind. At the same transition scale, there is a break in the wind spectrum which we argue is caused by the aircraft starting to accurately follow isobars at the larger scales. In comparison, the temperature and humidity have low coherencies and phases and there are no apparent scale breaks, reinforcing the hypothesis that it is the aircraft trajectory that is causally linked to the scale breaks in the wind measurements.
Using spectra and structure functions for the wind, we then estimate their exponents (β, H at small (5/3, 1/3 and large scales (2
Non-equilibrium turbulence scalings in turbulent planar jets
Cafiero, Gioacchino; Vassilicos, John Christos; Turbulence, Mixing; Flow Control Group Team
2017-11-01
A revised version of the Townsend George theory, as proposed by Dairay et al. 2015, is applied to the study of turbulent planar jets (Cafiero and Vassilicos 2017). Requiring the self-similarity of only few quantities along with the non-equilibrium dissipation scaling law (Vassilicos 2015), it implies new mean flow and jet width scalings. In particular, the ratio of characteristic cross-stream to centreline streamwise velocities decays as the -1/3 power of streamwise distance in the region where the non-equilibrium dissipation scaling holds. In the definition of Cɛ both in Dairay et al. 2015 and in Cafiero and Vassilicos 2017 the local Reynolds number is based on the local flow width rather than on the integral lengthscale. We verify that the ratio of the integral lengthscale to the flow width is constant, thus enabling the use of the integral flow width in place of the integral lengthscale for defining Cɛ. The importance of this result is twofold: firstly it further strengthens the scalings obtained in the works of Dairay et al. 2015 and Cafiero and Vassilicos 2017; secondly the flow width is immediately accessible by any mean flow measurement, whereas the estimation of the integral lengthscale often requires an additional hypothesis. ERC Advanced Grant 320560.
Universities scale like cities.
van Raan, Anthony F J
2013-01-01
Recent studies of urban scaling show that important socioeconomic city characteristics such as wealth and innovation capacity exhibit a nonlinear, particularly a power law scaling with population size. These nonlinear effects are common to all cities, with similar power law exponents. These findings mean that the larger the city, the more disproportionally they are places of wealth and innovation. Local properties of cities cause a deviation from the expected behavior as predicted by the power law scaling. In this paper we demonstrate that universities show a similar behavior as cities in the distribution of the 'gross university income' in terms of total number of citations over 'size' in terms of total number of publications. Moreover, the power law exponents for university scaling are comparable to those for urban scaling. We find that deviations from the expected behavior can indeed be explained by specific local properties of universities, particularly the field-specific composition of a university, and its quality in terms of field-normalized citation impact. By studying both the set of the 500 largest universities worldwide and a specific subset of these 500 universities--the top-100 European universities--we are also able to distinguish between properties of universities with as well as without selection of one specific local property, the quality of a university in terms of its average field-normalized citation impact. It also reveals an interesting observation concerning the working of a crucial property in networked systems, preferential attachment.
Universities scale like cities.
Directory of Open Access Journals (Sweden)
Anthony F J van Raan
Full Text Available Recent studies of urban scaling show that important socioeconomic city characteristics such as wealth and innovation capacity exhibit a nonlinear, particularly a power law scaling with population size. These nonlinear effects are common to all cities, with similar power law exponents. These findings mean that the larger the city, the more disproportionally they are places of wealth and innovation. Local properties of cities cause a deviation from the expected behavior as predicted by the power law scaling. In this paper we demonstrate that universities show a similar behavior as cities in the distribution of the 'gross university income' in terms of total number of citations over 'size' in terms of total number of publications. Moreover, the power law exponents for university scaling are comparable to those for urban scaling. We find that deviations from the expected behavior can indeed be explained by specific local properties of universities, particularly the field-specific composition of a university, and its quality in terms of field-normalized citation impact. By studying both the set of the 500 largest universities worldwide and a specific subset of these 500 universities--the top-100 European universities--we are also able to distinguish between properties of universities with as well as without selection of one specific local property, the quality of a university in terms of its average field-normalized citation impact. It also reveals an interesting observation concerning the working of a crucial property in networked systems, preferential attachment.
On spectral scaling laws for incompressible anisotropic magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
Galtier, Sebastien; Pouquet, Annick; Mangeney, Andre
2005-01-01
A heuristic model is given for anisotropic magnetohydrodynamics turbulence in the presence of a uniform external magnetic field B 0 e parallel . The model is valid for both moderate and strong B 0 and is able to describe both the strong and weak wave turbulence regimes as well as the transition between them. The main ingredient of the model is the assumption of constant ratio at all scales between the linear wave period and the nonlinear turnover time scale. Contrary to the model of critical balance introduced by Goldreich and Sridhar [Astrophys. J. 438, 763 (1995)], it is not assumed, in addition, that this ratio be equal to unity at all scales. This allows us to make use of the Iroshnikov-Kraichnan phenomenology; it is then possible to recover the widely observed anisotropic scaling law k parallel ∝k perpendicular 2/3 between parallel and perpendicular wave numbers (with reference to B 0 e parallel and to obtain for the total-energy spectrum E(k perpendicular ,k parallel )∼k perpendicular -α k parallel -β the universal prediction, 3α+2β=7. In particular, with such a prediction, the weak Alfven wave turbulence constant-flux solution is recovered and, for the first time, a possible explanation to its precursor found numerically by Galtier et al. [J. Plasma Phys. 63, 447 (2000)] is given.
Stellarator turbulence at electron gyroradius scales
Jenko, F.; Kendl, A.
2002-06-01
Electromagnetic gyrokinetic simulations of electron-temperature-gradient-driven modes on electron gyroradius scales are performed in the geometry of an advanced stellarator fusion experiment, Wendelstein 7-AS. Based on linear simulations, a critical electron-temperature-gradient formula is established which happens to agree quite well with a previously derived formula for tokamaks in the appropriate limit. Nonlinear simulations are used to study the turbulence and transport characteristics which are dominated by the presence of high-amplitude radially elongated vortices or `streamers'. The role of Debye shielding effects is also examined.
The theory of gyrokinetic turbulence: A multiple-scales approach
Plunk, Gabriel Galad
Gyrokinetics is a rich and rewarding playground to study some of the mysteries of modern physics -- such as turbulence, universality, self-organization and dynamic criticality -- which are found in physical systems that are driven far from thermodynamic equilibrium. One such system is of particular importance, as it is central in the development of fusion energy -- this system is the turbulent plasma found in magnetically confined fusion device. In this thesis I present work, motivated by the quest for fusion energy, which seeks to uncover some of the inner workings of turbulence in magnetized plasmas. I present three projects, based on the work of me and my collaborators, which take a tour of different aspects and approaches to the gyrokinetic turbulence problem. I begin with the fundamental theory of gyrokinetics, and a novel formulation of its extension to the equations for mean-scale transport -- the equations which must be solved to determine the performance of Magnetically confined fusion devices. The results of this work include (1) the equations of evolution for the mean scale (equilibrium) density, temperature and magnetic field of the plasma, (2) a detailed Poynting's theorem for the energy balance and (3) the entropy balance equations. The second project presents gyrokinetic secondary instability theory as a mechanism to bring about saturation of the basic instabilities that drive gyrokinetic turbulence. Emphasis is put on the ability for this analytic theory to predict basic properties of the nonlinear state, which can be applied to a mixing length phenomenology of transport. The results of this work include (1) an integral equation for the calculation of the growth rate of the fully gyrokinetic secondary instability with finite Larmor radius (FLR) affects included exactly, (2) the demonstration of the robustness of the secondary instability at fine scales (krhoi for ion temperature gradient (ITG) turbulence and krhoe ≪ 1 for electron temperature
Scale invariance from phase transitions to turbulence
Lesne, Annick
2012-01-01
During a century, from the Van der Waals mean field description (1874) of gases to the introduction of renormalization group (RG techniques 1970), thermodynamics and statistical physics were just unable to account for the incredible universality which was observed in numerous critical phenomena. The great success of RG techniques is not only to solve perfectly this challenge of critical behaviour in thermal transitions but to introduce extremely useful tools in a wide field of daily situations where a system exhibits scale invariance. The introduction of scaling, scale invariance and universality concepts has been a significant turn in modern physics and more generally in natural sciences. Since then, a new "physics of scaling laws and critical exponents", rooted in scaling approaches, allows quantitative descriptions of numerous phenomena, ranging from phase transitions to earthquakes, polymer conformations, heartbeat rhythm, diffusion, interface growth and roughening, DNA sequence, dynamical systems, chaos ...
On transition in plasma turbulence with multiple scale lengths
Energy Technology Data Exchange (ETDEWEB)
Itoh, K.; Spineanu, F.; Vlad, M.O. [National Inst. for Fusion Science, Toki, Gifu (Japan); Itoh, S.-I.; Kawasaki, M. [Kyushu Univ., Research Institute for Applied Mechanics, Kasuga, Fukuoka (Japan)
2003-05-01
A statistical theory of plasma turbulence which is composed of multiple-scale fluctuations is examined. Influences of statistical noise and variance of rapidly-changing variable in an adiabatic approximation are investigated. It is confirmed that the contributions of noise and variance remain higher order corrections. Transition rate of the turbulence with multiple scale lengths is obtained under the refined adiabatic approximation. (author)
Influence of small-scale turbulence on cup anemometer calibrations
Marraccini, M.; Bak-Kristensen, K.; Horn, A.; Fifield, E.; Hansen, S. O.
2017-11-01
The paper presents and discusses the calibration results of cup anemometers under different levels of small-scale turbulence. Small-scale turbulence is known to govern the curvature of shear layers around structures and is not related to the traditional under and over speeding of cup anemometers originating from large-scale turbulence components. The paper has shown that the small-scale turbulence has a significant effect on the calibration results obtained for cup anemometers. At 10m/s the rotational speed seems to change by approx. 0.5% due to different simulations of the small-scale turbulence. The work which this paper is based on, is part of the TrueWind research project, aiming to increase accuracy of mast top-mounted cup anemometer measurements.
Statistics and scaling of turbulence in a spatially developing mixing layer at Reλ = 250
Attili, Antonio
2012-03-21
The turbulent flow originating from the interaction between two parallel streams with different velocities is studied by means of direct numerical simulation. Rather than the more common temporal evolving layer, a spatially evolving configuration, with perturbed laminar inlet conditions is considered. The streamwise evolution and the self-similar state of turbulence statistics are reported and compared to results available in the literature. The characteristics of the transitional region agree with those observed in other simulations and experiments of mixing layers originating from laminar inlets. The present results indicate that the transitional region depends strongly on the inlet flow. Conversely, the self-similar state of turbulent kinetic energy and dissipation agrees quantitatively with those in a temporal mixing layer developing from turbulent initial conditions [M. M. Rogers and R. D. Moser, “Direct simulation of a self-similar turbulent mixing layer,” Phys. Fluids6, 903 (1994)]. The statistical features of turbulence in the self-similar region have been analysed in terms of longitudinal velocity structure functions, and scaling exponents are estimated by applying the extended self-similarity concept. In the small scale range (60 < r/η < 250), the scaling exponents display the universal anomalous scaling observed in homogeneous isotropic turbulence. The hypothesis of isotropy recovery holds in the turbulent mixing layer despite the presence of strong shear and large-scale structures, independently of the means of turbulence generation. At larger scales (r/η > 400), the mean shear and large coherent structures result in a significant deviation from predictions based on homogeneous isotropic turbulence theory. In this second scaling range, the numerical values of the exponents agree quantitatively with those reported for a variety of other flows characterized by strong shear, such as boundary layers, as well as channel and wake flows.
Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung
2012-11-01
In this work we clarify the role of Markstein diffusivity on turbulent flame speed and it's scaling, from analysis and experimental measurements on constant-pressure expanding flames propagating in near isotropic turbulence. For all C0-C4 hydrocarbon-air mixtures presented in this work and recently published C8 data from Leeds, the normalized turbulent flame speed data of individual mixtures approximately follows the recent theoretical and experimental ReT, f 0 . 5 scaling, where the average radius is the length scale and thermal diffusivity is the transport property. We observe that for a constant ReT, f 0 . 5 , the normalized turbulent flame speed decreases with increasing Mk. This could be explained by considering Markstein diffusivity as the large wavenumber, flame surface fluctuation dissipation mechanism. As originally suggested by the theory, replacing thermal diffusivity with Markstein diffusivity in the turbulence Reynolds number definition above, the present and Leeds dataset could be scaled by the new ReT, f 0 . 5 irrespective of the fuel considered, equivalence ratio, pressure and turbulence intensity for positive Mk flames. This work was supported by the Combustion Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences under Award Number DE-SC0001198 and by the Air Force Office of Scientific Research.
Vortex scaling ranges in two-dimensional turbulence
Burgess, B. H.; Dritschel, D. G.; Scott, R. K.
2017-11-01
We survey the role of coherent vortices in two-dimensional turbulence, including formation mechanisms, implications for classical similarity and inertial range theories, and characteristics of the vortex populations. We review early work on the spatial and temporal scaling properties of vortices in freely evolving turbulence and more recent developments, including a spatiotemporal scaling theory for vortices in the forced inverse energy cascade. We emphasize that Kraichnan-Batchelor similarity theories and vortex scaling theories are best viewed as complementary and together provide a more complete description of two-dimensional turbulence. In particular, similarity theory has a continued role in describing the weak filamentary sea between the vortices. Moreover, we locate both classical inertial and vortex scaling ranges within the broader framework of scaling in far-from-equilibrium systems, which generically exhibit multiple fixed point solutions with distinct scaling behaviour. We describe how stationary transport in a range of scales comoving with the dilatation of flow features, as measured by the growth in vortex area, constrains the vortex number density in both freely evolving and forced two-dimensional turbulence. The new theories for coherent vortices reveal previously hidden nontrivial scaling, point to new dynamical understanding, and provide a novel exciting window into two-dimensional turbulence.
Time change and universality in turbulence
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole Eiler; Schmiegel, Jürgen
experiment. Taylor Reynolds numbers range from Rλ = 80 for the wind tunnel experiment up to Rλ = 17000 for the atmospheric boundary layer experiment. Empirical findings strongly support the appropriateness of normal inverse Gaussian distributions for a parsimonious and universal description...... of universality in terms of a stochastic equivalence class that reformulates and extends the concept of Generalized Extended Self-Similarity....
Mixing in 3D Sparse Multi-Scale Grid Generated Turbulence
Usama, Syed; Kopec, Jacek; Tellez, Jackson; Kwiatkowski, Kamil; Redondo, Jose; Malik, Nadeem
2017-04-01
Flat 2D fractal grids are known to alter turbulence characteristics downstream of the grid as compared to the regular grids with the same blockage ratio and the same mass inflow rates [1]. This has excited interest in the turbulence community for possible exploitation for enhanced mixing and related applications. Recently, a new 3D multi-scale grid design has been proposed [2] such that each generation of length scale of turbulence grid elements is held in its own frame, the overall effect is a 3D co-planar arrangement of grid elements. This produces a 'sparse' grid system whereby each generation of grid elements produces a turbulent wake pattern that interacts with the other wake patterns downstream. A critical motivation here is that the effective blockage ratio in the 3D Sparse Grid Turbulence (3DSGT) design is significantly lower than in the flat 2D counterpart - typically the blockage ratio could be reduced from say 20% in 2D down to 4% in the 3DSGT. If this idea can be realized in practice, it could potentially greatly enhance the efficiency of turbulent mixing and transfer processes clearly having many possible applications. Work has begun on the 3DSGT experimentally using Surface Flow Image Velocimetry (SFIV) [3] at the European facility in the Max Planck Institute for Dynamics and Self-Organization located in Gottingen, Germany and also at the Technical University of Catalonia (UPC) in Spain, and numerically using Direct Numerical Simulation (DNS) at King Fahd University of Petroleum & Minerals (KFUPM) in Saudi Arabia and in University of Warsaw in Poland. DNS is the most useful method to compare the experimental results with, and we are studying different types of codes such as Imcompact3d, and OpenFoam. Many variables will eventually be investigated for optimal mixing conditions. For example, the number of scale generations, the spacing between frames, the size ratio of grid elements, inflow conditions, etc. We will report upon the first set of findings
Time Change and Universality in Turbulence and Finance
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole E.; Schmiegel, Jürgen; Shephard, Neil
Empirical time series of turbulent flows and financial markets reveal some common basic stylized features. In particular, the densities of velocity increments and log returns are well fitted within the class of Normal inverse Gaussian distributions and show a similar evolution across time scales ...
Turbulence Spreading into Linearly Stable Zone and Transport Scaling
International Nuclear Information System (INIS)
Hahm, T.S.; Diamond, P.H.; Lin, Z.; Itoh, K.; Itoh, S.-I.
2003-01-01
We study the simplest problem of turbulence spreading corresponding to the spatio-temporal propagation of a patch of turbulence from a region where it is locally excited to a region of weaker excitation, or even local damping. A single model equation for the local turbulence intensity I(x, t) includes the effects of local linear growth and damping, spatially local nonlinear coupling to dissipation and spatial scattering of turbulence energy induced by nonlinear coupling. In the absence of dissipation, the front propagation into the linearly stable zone occurs with the property of rapid progression at small t, followed by slower subdiffusive progression at late times. The turbulence radial spreading into the linearly stable zone reduces the turbulent intensity in the linearly unstable zone, and introduces an additional dependence on the rho* is always equal to rho i/a to the turbulent intensity and the transport scaling. These are in broad, semi-quantitative agreements with a number of global gyrokinetic simulation results with zonal flows and without zonal flows. The front propagation stops when the radial flux of fluctuation energy from the linearly unstable region is balanced by local dissipation in the linearly stable region
Turbulence of Weak Gravitational Waves in the Early Universe.
Galtier, Sébastien; Nazarenko, Sergey V
2017-12-01
We study the statistical properties of an ensemble of weak gravitational waves interacting nonlinearly in a flat space-time. We show that the resonant three-wave interactions are absent and develop a theory for four-wave interactions in the reduced case of a 2.5+1 diagonal metric tensor. In this limit, where only plus-polarized gravitational waves are present, we derive the interaction Hamiltonian and consider the asymptotic regime of weak gravitational wave turbulence. Both direct and inverse cascades are found for the energy and the wave action, respectively, and the corresponding wave spectra are derived. The inverse cascade is characterized by a finite-time propagation of the metric excitations-a process similar to an explosive nonequilibrium Bose-Einstein condensation, which provides an efficient mechanism to ironing out small-scale inhomogeneities. The direct cascade leads to an accumulation of the radiation energy in the system. These processes might be important for understanding the early Universe where a background of weak nonlinear gravitational waves is expected.
Turbulence of Weak Gravitational Waves in the Early Universe
Galtier, Sébastien; Nazarenko, Sergey V.
2017-12-01
We study the statistical properties of an ensemble of weak gravitational waves interacting nonlinearly in a flat space-time. We show that the resonant three-wave interactions are absent and develop a theory for four-wave interactions in the reduced case of a 2.5 +1 diagonal metric tensor. In this limit, where only plus-polarized gravitational waves are present, we derive the interaction Hamiltonian and consider the asymptotic regime of weak gravitational wave turbulence. Both direct and inverse cascades are found for the energy and the wave action, respectively, and the corresponding wave spectra are derived. The inverse cascade is characterized by a finite-time propagation of the metric excitations—a process similar to an explosive nonequilibrium Bose-Einstein condensation, which provides an efficient mechanism to ironing out small-scale inhomogeneities. The direct cascade leads to an accumulation of the radiation energy in the system. These processes might be important for understanding the early Universe where a background of weak nonlinear gravitational waves is expected.
A glimpse of fluid turbulence from the molecular scale
Komatsu, Teruhisa S.
2014-08-01
Large-scale molecular dynamics (MD) simulations of freely decaying turbulence in three-dimensional space are reported. Fluid components are defined from the microscopic states by eliminating thermal components from the coarse-grained fields. The energy spectrum of the fluid components is observed to scale reasonably well according to Kolmogorov scaling determined from the energy dissipation rate and the viscosity of the fluid, even though the Kolmogorov length is of the order of the molecular scale. © 2014 The Authors.
Transition in multiple-scale-lengths turbulence in plasmas
International Nuclear Information System (INIS)
Itoh, S.-I.; Yagi, M.; Kawasaki, M.; Kitazawa, A.
2002-02-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Statistical nonlinear interactions between semi-micro and micro modes are first kept in the analysis as the drag, noise and drive. The nonlinear dynamics determines both the fluctuation levels and the cross field turbulent transport for the fixed global parameters. A quenching or suppressing effect is induced by their nonlinear interplay, even if both modes are unstable when analyzed independently. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. The thermal fluctuation of the scale length of λ D is assumed to be statistically independent. The hierarchical structure is constructed according to the scale lengths. Transitions in turbulence are found and phase diagrams with cusp type catastrophe are obtained. Dynamics is followed. Statistical properties of the subcritical excitation are discussed. The probability density function (PDF) and transition probability are obtained. Power-laws are obtained in the PDF as well as in the transition probability. Generalization for the case where turbulence is composed of three-classes of modes is also developed. A new catastrophe of turbulent sates is obtained. (author)
Semi-local scaling and turbulence modulation in variable property turbulent channel flows
Patel, A.; Peeters, J.W.R.; Boersma, B.J.; Pecnik, R.
2015-01-01
We theoretically and numerically investigate the effect of temperature dependent density and viscosity on turbulence in channel flows. First, a mathematical framework is developed to support the validity of the semi-local scaling as proposed based on heuristic arguments by Huang, Coleman, and
Interaction of turbulent length scales with wind turbine blades
Torres-Nieves, Sheilla N.
Understanding the effects of free-stream turbulence (FST) and surface roughness on the flow around wind turbine blades is imperative in the quest for higher wind turbine efficiency, specially under stall conditions. While many investigations have focused on the aerodynamic loads on wind turbine airfoils, there are no studies that examine the effects of free-stream turbulence and surface roughness on the velocity field around a wind turbine airfoil. Hence, the aim of this investigation is to study the influence of high levels of FST on the flow around smooth and rough surfaces with pressure gradients. Moreover, of great importance in this study is the examination of how the length scales of turbulence and surface roughness interact in the flow over wind turbine airfoils to affect flow separation. Particle Image Velocimetry measurements were performed to analyze the overall flow around a S809 wind turbine blade. Results indicate that when the flow is fully attached, free-stream turbulence significantly decreases aerodynamic efficiency by 82%, yielding to higher loads and fatigue on the blades. On the contrary, when the flow is separated, the effect is reversed and aerodynamic performance is slightly improved (i.e., by 5%) by the presence of the free-stream turbulence. Analysis of the mean flow over the suction surface shows that, under stall conditions, free-stream turbulence delays separation, and surface roughness advances separation. Interestingly, the highly non-linear interaction between free-stream turbulence and surface roughness results in the further advancement of separation. Of particular interest is the study of the region closer to the wall (i.e., the boundary layer), where the flow interacts with both the surface of the blade and the free-stream. Turbulent boundary layer experiments subject to an external favorable pressure gradient (FPG) were performed to study the influence of FST, surface roughness and external pressure gradient (present around the
Logarithmic scaling in the near-dissipation range of turbulence
Indian Academy of Sciences (India)
physics pp. 315–321. Logarithmic scaling in the near-dissipation range of turbulence. K R SREENIVASAN1 and A BERSHADSKII1,2. 1The Abdus Salam International Center for Theoretical Physics, Strada Costiera 11,. 34100 Trieste, Italy. 2ICAR, P.O. Box 31155, Jerusalem 91000, Israel. E-mail: krs@ictp.it. Abstract.
Low-Level Turbulence Forecasts From Fine-Scale Models
2014-02-01
Obviously, it is the “big picture ” that influences the “small picture ” so additional development in model initialization and model physics will also serve...241–253. 15. Keller, J. L. Clear air turbulence as a response to meso- and synoptic -scale dynamic processes. Mon. Wea. Rev., 1990, 118, 2228–2242
Two-scale analysis of intermittency in fully developed turbulence
Energy Technology Data Exchange (ETDEWEB)
Badii, R.; Talkner, P. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)
1999-08-01
A self-affinity test for turbulent time series is applied to experimental data for the estimation of intermittency exponents. The method employs exact relations satisfied by joint expectations of observables computed across two different length scales. One of these constitutes a verification tool for the existence and the extent of the inertial range. (author) 2 figs., 13 refs.
Energy Technology Data Exchange (ETDEWEB)
Falceta-Gonçalves, D. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom); Kowal, G. [Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, Rua Arlindo Bettio, 1000, São Paulo, SP 03828-000 (Brazil)
2015-07-20
In this work we report on a numerical study of the cosmic magnetic field amplification due to collisionless plasma instabilities. The collisionless magnetohydrodynamic equations derived account for the pressure anisotropy that leads, in specific conditions, to the firehose and mirror instabilities. We study the time evolution of seed fields in turbulence under the influence of such instabilities. An approximate analytical time evolution of the magnetic field is provided. The numerical simulations and the analytical predictions are compared. We found that (i) amplification of the magnetic field was efficient in firehose-unstable turbulent regimes, but not in the mirror-unstable models; (ii) the growth rate of the magnetic energy density is much faster than the turbulent dynamo; and (iii) the efficient amplification occurs at small scales. The analytical prediction for the correlation between the growth timescales and pressure anisotropy is confirmed by the numerical simulations. These results reinforce the idea that pressure anisotropies—driven naturally in a turbulent collisionless medium, e.g., the intergalactic medium, could efficiently amplify the magnetic field in the early universe (post-recombination era), previous to the collapse of the first large-scale gravitational structures. This mechanism, though fast for the small-scale fields (∼kpc scales), is unable to provide relatively strong magnetic fields at large scales. Other mechanisms that were not accounted for here (e.g., collisional turbulence once instabilities are quenched, velocity shear, or gravitationally induced inflows of gas into galaxies and clusters) could operate afterward to build up large-scale coherent field structures in the long time evolution.
Radial and zonal modes in hyperfine-scale stellarator turbulence
Jenko, F.; Kendl, A.
2002-10-01
Electromagnetic plasma turbulence at hyperfine (i.e., electron gyroradius) scales is studied in the geometry of an advanced stellarator fusion experiment, Wendelstein 7-AS [H. Renner, Plasma Phys. Controlled Fusion 31, 1579 (1989)], by means of nonlinear gyrokinetic simulations. It is demonstrated that high-amplitude radial streamers may also exist in non-tokamak devices, raising the electron heat flux to experimentally relevant values. Moreover, some statistical characteristics of the fully developed turbulence are computed, highlighting the (co-)existence, nature, and role of self-generated zonal flows and fields.
Size scaling of turbulent transport in magnetically confined plasmas
International Nuclear Information System (INIS)
Lin, Z.; Ethier, S.; Hahm, T.S.; Tang, W.M.
2002-01-01
Transport scaling with respect to device size in magnetically confined plasmas is critically examined for electrostatic ion-temperature-gradient turbulence using global gyrokinetic particle simulations. It is found, by varying device size normalized by ion gyroradius while keeping other dimensionless plasma parameters fixed, that fluctuation scale length is microscopic in the presence of zonal flows. The local transport coefficient exhibits a gradual transition from a Bohm-like scaling for device sizes corresponding to present-day experiments to a gyro-Bohm scaling for future larger devices
Size Scaling of Turbulent Transport in Magnetically Confined Plasmas
International Nuclear Information System (INIS)
Z. Lin; S. Ethier; T.S. Hahm; W.M. Tang
2002-04-01
Transport scaling with respect to device size in magnetically confined plasmas is critically examined for electrostatic ion temperature gradient turbulence using global gyrokinetic particle simulations. It is found, by varying device size normalized by ion gyroradius while keeping other dimensionless plasma parameters fixed, that fluctuation scale length is microscopic in the presence of zonal flows. The local transport coefficient exhibits a gradual transition from a Bohm-like scaling for device sizes corresponding to present-day experiments to a gyro-Bohm scaling for future larger devices
Size scaling of turbulent transport in tokamak plasmas
International Nuclear Information System (INIS)
Lin Zhihong
2002-01-01
Transport scaling with respect to tokamak device size is critically examined for electrostatic ion temperature gradient (ITG) turbulence with adiabatic electrons using first-principles gyrokinetic particle simulations, which use up to one billion particles to address realistic parameters of reactor-grade plasmas. Results of these large scale simulations, varying ρ* (ion gyroradius normalized by tokamak minor radius) while keeping other dimensionless plasma parameters fixed, show that the fluctuation scale length is microscopic and transport is diffusive in the presence of zonal flows. The local transport coefficient exhibits a gradual transition from a Bohm-like scaling for device sizes corresponding to present-day tokamak experiments to a gyro-Bohm scaling for future larger devices. The device size where this transition occurs is much larger than that expected from linear ITG theory for profile variations. Our simulations include a heat bath/source to prevent profile relaxation and are in the strong turbulence regime far away from ITG marginality. The effects of kinetic electrons on electrostatic ITG-TEM (trapped electron mode) driven turbulence will also be presented. (author)
An investigation of small scales of turbulence in a boundary layer at high Reynolds numbers
Wallace, James M.; Ong, L.; Balint, J.-L.
1993-01-01
The assumption that turbulence at large wave-numbers is isotropic and has universal spectral characteristics which are independent of the flow geometry, at least for high Reynolds numbers, has been a cornerstone of closure theories as well as of the most promising recent development in the effort to predict turbulent flows, viz. large eddy simulations. This hypothesis was first advanced by Kolmogorov based on the supposition that turbulent kinetic energy cascades down the scales (up the wave-numbers) of turbulence and that, if the number of these cascade steps is sufficiently large (i.e. the wave-number range is large), then the effects of anisotropies at the large scales are lost in the energy transfer process. Experimental attempts were repeatedly made to verify this fundamental assumption. However, Van Atta has recently suggested that an examination of the scalar and velocity gradient fields is necessary to definitively verify this hypothesis or prove it to be unfounded. Of course, this must be carried out in a flow with a sufficiently high Reynolds number to provide the necessary separation of scales in order unambiguously to provide the possibility of local isotropy at large wave-numbers. An opportunity to use our 12-sensor hot-wire probe to address this issue directly was made available at the 80'x120' wind tunnel at the NASA Ames Research Center, which is normally used for full-scale aircraft tests. An initial report on this high Reynolds number experiment and progress toward its evaluation is presented.
ION-SCALE TURBULENCE IN THE INNER HELIOSPHERE: RADIAL DEPENDENCE
Energy Technology Data Exchange (ETDEWEB)
Comisel, H.; Motschmann, U.; Büchner, J.; Narita, Y.; Nariyuki, Y. [University of Toyama, Faculty of Human Development, 3190, Gofuku, Toyama, 930-8555 (Japan)
2015-10-20
The evolution of the ion-scale plasma turbulence in the inner heliosphere is studied by associating the plasma parameters for hybrid-code turbulence simulations to the radial distance from the Sun via a Solar wind model based mapping procedure. Using a mapping based on a one-dimensional solar wind expansion model, the resulting ion-kinetic scale turbulence is related to the solar wind distance from the Sun. For this purpose the mapping is carried out for various values of ion beta that correspond to the heliocentric distance. It is shown that the relevant normal modes such as ion cyclotron and ion Bernstein modes will occur first at radial distances of about 0.2–0.3 AU, i.e., near the Mercury orbit. This finding can be used as a reference, a prediction to guide the in situ measurements to be performed by the upcoming Solar Orbiter and Solar Probe Plus missions. Furthermore, a radial dependence of the wave-vector anisotropy was obtained. For astrophysical objects this means that the spatial scales of filamentary structures in interstellar media or astrophysical jets can be predicted for photometric observations.
SCALING OF THE ELECTRON DISSIPATION RANGE OF SOLAR WIND TURBULENCE
International Nuclear Information System (INIS)
Sahraoui, F.; Belmont, G.; Rétino, A.; Robert, P.; De Patoul, J.; Huang, S. Y.; Goldstein, M. L.
2013-01-01
Electron scale solar wind (SW) turbulence has attracted great interest in recent years. Considerable evidence exists that the turbulence is not fully dissipated near the proton scale, but continues cascading down to electron scales. However, the scaling of the magnetic energy spectra as well as the nature of the plasma modes involved at those small scales are still not fully determined. Here we survey 10 yr of the Cluster STAFF search-coil magnetometer waveforms measured in the SW and perform a statistical study of the magnetic energy spectra in the frequency range [1, 180] Hz. We found that 75% of the analyzed spectra exhibit breakpoints near the electron gyroscale ρ e , followed by steeper power-law-like spectra. We show that the scaling below the electron breakpoint cannot be determined unambiguously due to instrumental limitations that we discuss in detail. We compare our results to those reported in other studies and discuss their implications for the physical mechanisms involved and for theoretical modeling of energy dissipation in the SW
International Nuclear Information System (INIS)
Chapman, S. C.; Nicol, R. M.; Leonardis, E.; Kiyani, K.; Carbone, V.
2009-01-01
We perform statistical analysis of the fluctuating magnetic field observed in-situ by the Ulysses spacecraft, from the perspective of quantitative characterization of the evolving magnetohydrodynamic (MHD) turbulence. We focus on two successive polar passes around solar minimum which provide extended intervals of quiet, fast solar wind at a range of radial distances and latitudes: the south polar pass of 1994 and the north polar pass of 1995. Fully developed inertial range turbulence has a characteristic statistical similarity property of quantities that characterize the flow, such as the magnetic field components B k (t), so that the pth moment of fluctuations has power-law dependence on scale τ such that k (t + τ) - B k (t)| p > ∼ τ ζ(p) . We instead find a generalized similarity k (t + τ) - B k (t)| p > ∼ g(τ/τ 0 ) ζ(p) consistent with extended self-similarity; and in particular all of these Ulysses observations, from both polar passes, share the same single function g(τ/τ 0 ). If these observations are indeed characteristic of MHD turbulence evolving in-situ, then this quantifies for the first time a key aspect of the universal nature of evolving MHD turbulence in a system of finite size, with implications both for theoretical development, and for our understanding of the evolving solar wind.
The Effect of Large Scale Salinity Gradient on Langmuir Turbulence
Fan, Y.; Jarosz, E.; Yu, Z.; Jensen, T.; Sullivan, P. P.; Liang, J.
2017-12-01
Langmuir circulation (LC) is believed to be one of the leading order causes of turbulent mixing in the upper ocean. It is important for momentum and heat exchange across the mixed layer (ML) and directly impact the dynamics and thermodynamics in the upper ocean and lower atmosphere including the vertical distributions of chemical, biological, optical, and acoustic properties. Based on Craik and Leibovich (1976) theory, large eddy simulation (LES) models have been developed to simulate LC in the upper ocean, yielding new insights that could not be obtained from field observations and turbulent closure models. Due its high computational cost, LES models are usually limited to small domain sizes and cannot resolve large-scale flows. Furthermore, most LES models used in the LC simulations use periodic boundary conditions in the horizontal direction, which assumes the physical properties (i.e. temperature and salinity) and expected flow patterns in the area of interest are of a periodically repeating nature so that the limited small LES domain is representative for the larger area. Using periodic boundary condition can significantly reduce computational effort in problems, and it is a good assumption for isotropic shear turbulence. However, LC is anisotropic (McWilliams et al 1997) and was observed to be modulated by crosswind tidal currents (Kukulka et al 2011). Using symmetrical domains, idealized LES studies also indicate LC could interact with oceanic fronts (Hamlington et al 2014) and standing internal waves (Chini and Leibovich, 2005). The present study expands our previous LES modeling investigations of Langmuir turbulence to the real ocean conditions with large scale environmental motion that features fresh water inflow into the study region. Large scale gradient forcing is introduced to the NCAR LES model through scale separation analysis. The model is applied to a field observation in the Gulf of Mexico in July, 2016 when the measurement site was impacted by
Emergence of multi-scaling in fluid turbulence
Donzis, Diego; Yakhot, Victor
2017-11-01
We present new theoretical and numerical results on the transition to strong turbulence in an infinite fluid stirred by a Gaussian random force. The transition is defined as a first appearance of anomalous scaling of normalized moments of velocity derivatives (or dissipation rates) emerging from the low-Reynolds-number Gaussian background. It is shown that due to multi-scaling, strongly intermittent rare events can be quantitatively described in terms of an infinite number of different ``Reynolds numbers'' reflecting a multitude of anomalous scaling exponents. We found that anomalous scaling for high order moments emerges at very low Reynolds numbers implying that intense dissipative-range fluctuations are established at even lower Reynolds number than that required for an inertial range. Thus, our results suggest that information about inertial range dynamics can be obtained from dissipative scales even when the former does not exit. We discuss our further prediction that transition to fully anomalous turbulence disappears at Rλ < 3 . Support from NSF is acknowledged.
Energy Technology Data Exchange (ETDEWEB)
Pietri, L.; Amielh, M.; Anselmet, F.; Fulachier, L. [Institut de Recherche sur les Phinomenes Hors Equilibre Equipe Turbulence, 13 - Marseille (France)
1997-12-31
Turbulent flows with strong density variations, like helium jets in the ambient air, have specific properties linked with the difference of gas densities. This paper presents some experimental results of turbulence properties inside such flows: the Reynolds tensions and the associated turbulent viscosity, and some characteristics linked with the statistical properties of the different turbulence scales. These last results allows to show the complexity of such flows characterized by the influence of external parameters (Reynolds number, initial density ratio, initial momentum flux) that govern the evolution of these parameters inside the jet from the nozzle up to regions where similarity properties are reached. (J.S.) 12 refs.
Dynamic scaling and large scale effects in turbulence in compressible stratified fluid
International Nuclear Information System (INIS)
Pharasi, Hirdesh K.; Bhattacharjee, Jayanta K.
2016-01-01
We consider the propagation of sound in a turbulent fluid which is confined between two horizontal parallel plates, maintained at different temperatures. In the homogeneous fluid, Staroselsky et al. had predicted a divergent sound speed at large length scales. Here we find a divergent sound speed and a vanishing expansion coefficient at large length scales. Dispersion relation and the question of scale invariance at large distance scales lead to these results. - Highlights: • Turbulence in a stratified fluid has been studied in the Boussinesq approximation. • We extend this study to include density fluctuations due to pressure fluctuations. • For a homogeneous weakly compressible fluid the sound speed is known to become scale dependent. • For the stratified fluid we show that the expansion coefficient is also scale dependent. • Our results are based on general dynamic scaling arguments rather than detailed calculation.
Statistics and scaling in turbulent Rayleigh-Bénard convection
Ching, Emily SC
2013-01-01
This Brief addresses two issues of interest of turbulent Rayleigh-Bénard convection. The first issue is the characterization and understanding of the statistics of the velocity and temperature fluctuations in the system. The second issue is the revelation and understanding of the nature of the scaling behavior of the velocity temperature structure functions. The problem under the Oberbeck-Boussinesq approximation is formulated. The statistical tools, including probability density functions (PDF) and conditional statistics, for studying fluctuations are introduced, and implicit PDF formulae for
Intermittency in small-scale turbulence: a velocity gradient approach
Meneveau, Charles; Johnson, Perry
2017-11-01
Intermittency of small-scale motions is an ubiquitous facet of turbulent flows, and predicting this phenomenon based on reduced models derived from first principles remains an important open problem. Here, a multiple-time scale stochastic model is introduced for the Lagrangian evolution of the full velocity gradient tensor in fluid turbulence at arbitrarily high Reynolds numbers. This low-dimensional model differs fundamentally from prior shell models and other empirically-motivated models of intermittency because the nonlinear gradient self-stretching and rotation A2 term vital to the energy cascade and intermittency development is represented exactly from the Navier-Stokes equations. With only one adjustable parameter needed to determine the model's effective Reynolds number, numerical solutions of the resulting set of stochastic differential equations show that the model predicts anomalous scaling for moments of the velocity gradient components and negative derivative skewness. It also predicts signature topological features of the velocity gradient tensor such as vorticity alignment trends with the eigen-directions of the strain-rate. This research was made possible by a graduate Fellowship from the National Science Foundation and by a Grant from The Gulf of Mexico Research Initiative.
Multifractal scaling at the Kolmogorov microscale in fully developed compressible turbulence
International Nuclear Information System (INIS)
Shivamoggi, B.K.
1995-01-01
In this paper, some aspects of multifractal scaling at the Kolmogorov microscale in fully developed compressible turbulence are considered. These considerations, on the one hand, provide an insight into the mechanism of compressible turbulence, and on the other hand enable one to determine the robustness of some known results in incompressible turbulence. copyright 1995 Academic Press, Inc
A Parsimonious and Universal Description of Turbulent Velocity Increments
DEFF Research Database (Denmark)
Barndorff-Nielsen, O.E.; Blæsild, P.; Schmiegel, J.
boundary layer experiment with Taylor-Reynolds numbers Rλ = 80,190,17000, respectively. The application of a time change in terms of the scale parameter δ of the normal inverse Gaussian distribution reveals some universal features that are inherent to the pdf of all three data sets....
Bailly, Christophe
2015-01-01
This book covers the major problems of turbulence and turbulent processes, including physical phenomena, their modeling and their simulation. After a general introduction in Chapter 1 illustrating many aspects dealing with turbulent flows, averaged equations and kinetic energy budgets are provided in Chapter 2. The concept of turbulent viscosity as a closure of the Reynolds stress is also introduced. Wall-bounded flows are presented in Chapter 3, and aspects specific to boundary layers and channel or pipe flows are also pointed out. Free shear flows, namely free jets and wakes, are considered in Chapter 4. Chapter 5 deals with vortex dynamics. Homogeneous turbulence, isotropy, and dynamics of isotropic turbulence are presented in Chapters 6 and 7. Turbulence is then described both in the physical space and in the wave number space. Time dependent numerical simulations are presented in Chapter 8, where an introduction to large eddy simulation is offered. The last three chapters of the book summarize remarka...
Energy partitioning constraints at kinetic scales in low-β turbulence
Gershman, Daniel J.; F.-Viñas, Adolfo; Dorelli, John C.; Goldstein, Melvyn L.; Shuster, Jason; Avanov, Levon A.; Boardsen, Scott A.; Stawarz, Julia E.; Schwartz, Steven J.; Schiff, Conrad; Lavraud, Benoit; Saito, Yoshifumi; Paterson, William R.; Giles, Barbara L.; Pollock, Craig J.; Strangeway, Robert J.; Russell, Christopher T.; Torbert, Roy B.; Moore, Thomas E.; Burch, James L.
2018-02-01
Turbulence is a fundamental physical process through which energy injected into a system at large scales cascades to smaller scales. In collisionless plasmas, turbulence provides a critical mechanism for dissipating electromagnetic energy. Here, we present observations of plasma fluctuations in low-β turbulence using data from NASA's Magnetospheric Multiscale mission in Earth's magnetosheath. We provide constraints on the partitioning of turbulent energy density in the fluid, ion-kinetic, and electron-kinetic ranges. Magnetic field fluctuations dominated the energy density spectrum throughout the fluid and ion-kinetic ranges, consistent with previous observations of turbulence in similar plasma regimes. However, at scales shorter than the electron inertial length, fluctuation power in electron kinetic energy significantly exceeded that of the magnetic field, resulting in an electron-motion-regulated cascade at small scales. This dominance is highly relevant for the study of turbulence in highly magnetized laboratory and astrophysical plasmas.
Universal scaling in sports ranking
International Nuclear Information System (INIS)
Deng Weibing; Li Wei; Cai Xu; Bulou, Alain; Wang Qiuping A
2012-01-01
Ranking is a ubiquitous phenomenon in human society. On the web pages of Forbes, one may find all kinds of rankings, such as the world's most powerful people, the world's richest people, the highest-earning tennis players, and so on and so forth. Herewith, we study a specific kind—sports ranking systems in which players' scores and/or prize money are accrued based on their performances in different matches. By investigating 40 data samples which span 12 different sports, we find that the distributions of scores and/or prize money follow universal power laws, with exponents nearly identical for most sports. In order to understand the origin of this universal scaling we focus on the tennis ranking systems. By checking the data we find that, for any pair of players, the probability that the higher-ranked player tops the lower-ranked opponent is proportional to the rank difference between the pair. Such a dependence can be well fitted to a sigmoidal function. By using this feature, we propose a simple toy model which can simulate the competition of players in different matches. The simulations yield results consistent with the empirical findings. Extensive simulation studies indicate that the model is quite robust with respect to the modifications of some parameters. (paper)
Solar Wind Turbulence at Sub-Ion and Electron Scales
Alexandrova, O.; Lacombe, C.; Matteini, L.; Zaslavsky, A.; Orel, I.
2017-12-01
We study magnetic fluctuations at sub-ion scales and down to sub-electron scales (from 1 to 200Hz) using two complementary approaches: (i) a statistical study of the turbulent spectra of the different field components in the reference frame based on the quasi-local mean field B and velocity V; (ii) a detailed analysis of magnetic waveforms in the same reference frame. For this statistical study, we consider 93 10-minute intervals of Cluster/STAFF measurements. We find that the fluctuations are non-gyrotropic at a given frequency f, a property already observed at larger scales. This non-gyrotropy provides indications on the angular distribution of the wave vectors k: at f> k||, mainly in the fast wind; at f>10Hz, the k are more isotropic. We then consider the magnetic compressibility of the fluctuations: it increases with f and at electron scales the fluctuations become isotropic. From 1 to 20Hz, there is a strong correlation between the observed compressibility and the one expected for the kinetic Alfven waves (KAWs), which only depends on the total plasma beta. For f>20Hz, the observed compressibility is larger than the one expected for classical KAWs, and it is stronger in the slow wind: this could be an indication of the presence of a slow-ion acoustic mode of fluctuations, which is more compressive and is favoured by the larger values of the electron to proton temperature ratio generally observed in the slow wind. For the analysis of the magnetic waveforms, we use burst mode intervals in the solar wind and in the Earth's magnetosheath during the Cluster Guest Investigator campaign in 2015, when C3 and C4 were at 7km apart only. Time-frequency analysis using Morlet wavelets shows that the turbulence is non-homogeneous and filled in with intermittent events. A detailed study of magnetic fluctuations on C3 and C4 shows signatures of electron-scale magnetic vortices, but with strong compressible components, in agreement with our statistical study discussed above
The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence
Energy Technology Data Exchange (ETDEWEB)
Staebler, G. M.; Candy, J. [General Atomics, San Diego, California 92186 (United States); Howard, N. T. [Oak Ridge Institute for Science Education (ORISE), Oak Ridge, Tennessee 37831 (United States); Holland, C. [University of California San Diego, San Diego, California 92093 (United States)
2016-06-15
The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. The zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ion-scale gyrokinetic simulations.
Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations
Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung K.
2013-09-01
In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a ReT,f0.5 scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given ReT,f, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by ReT,M0.5 irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.
Intermittent structures at ion scales in the turbulent solar wind
Perrone, Denise; Alexandrova, Olga; Lion, Sonny; Roberts, Owen W.; Maksimovic, Milan; Escoubet, Philippe C.; Zouganelis, Yannis
2017-04-01
Understanding the physical mechanisms of dissipation, and the related heating, in turbulent collisionless plasmas (such as the solar wind) represents nowadays one of the key issues of plasma physics. Although the complex behavior of the solar wind has been matter of investigation of many years, some of the primary problems still remain a puzzle for the scientific community. Here, we study coherent structures responsible for solar wind intermittency around ion characteristic scales. We find that, in fast solar wind, intermittency is due to current sheets and Alfvén vortex-like structures. In slow solar wind, we observe as well compressive structures like magnetic solitons, holes and shocks. By using high-time resolution magnetic field data of multi-point measurements of Cluster spacecraft, we characterize the observed coherent structures in terms of topology and propagation speed. We show that all structures, both in fast and slow solar wind, are characterized by a strong wave-vector anisotropy in the perpendicular direction with respect to the local magnetic field and typical scales around ion characteristic scales. Moreover, some of them propagate in the plasma rest frame. Moreover, a further analysis on the ion velocity distribution shows a high variability; in particular, close to coherent structures the proton distribution function appears strongly deformed and far from the thermodynamic equilibrium. We discuss possible interpretation of the observed structures and their role in the heating process of the plasma.
The Effect of Small Scale Turbulence on the Physiology of Microcystis aeruginosa cyanobacterium
Wilkinson, Anne; Hondzo, Miki; Guala, Michele
2014-11-01
Microcystis aeruginosa is a single-celled blue-green alga, or cyanobacterium, that is responsible for poor water quality and microcystin production, which in high concentrations can be harmful to humans and animals. These harmful effects arise during cyanobacterium blooms. Blooms occur mainly in the summer when the algae grow uncontrollably and bond together to form colonies which accumulate on the surface of freshwater ecosystems. The relationship between fluid motion generated by wind and internal waves in stratified aquatic ecosystems and Microcystis can help explain the mechanisms of such blooms. We investigated the effect of small scale fluid motion on the physiology of Microcystis in a reactor with two underwater speakers. Different turbulent intensities were achieved by systematically changing the input signal frequency (30-50 Hz) and magnitude (0.1-0.2V) to the speakers. The role of turbulence is quantified by relating energy dissipation rates with the cell number, chlorophyll amount, dissolved oxygen production/uptake, and pH. The results suggest that turbulence mediates the physiology of Microcystis. The findings could be instrumental in designing restoration strategies that can minimize Microcystis blooms. This work was supported by the NSF Graduate Research Fellowship and University of Minnesota start-up funding.
Large Scale Organization of a Near Wall Turbulent Boundary Layer
Stanislas, Michel; Dekou Tiomajou, Raoul Florent; Foucaut, Jean Marc
2016-11-01
This study lies in the context of large scale coherent structures investigation in a near wall turbulent boundary layer. An experimental database at high Reynolds numbers (Re θ = 9830 and Re θ = 19660) was obtained in the LML wind tunnel with stereo-PIV at 4 Hz and hot wire anemometry at 30 kHz. A Linear Stochastic Estimation procedure, is used to reconstruct a 3 component field resolved in space and time. Algorithms were developed to extract coherent structures from the reconstructed field. A sample of 3D view of the structures is depicted in Figure 1. Uniform momentum regions are characterized with their mean hydraulic diameter in the YZ plane, their life time and their contribution to Reynolds stresses. The vortical motions are characterized by their position, radius, circulation and vorticity in addition to their life time and their number computed at a fixed position from the wall. The spatial organization of the structures was investigated through a correlation of their respective indicative functions in the spanwise direction. The simplified large scale model that arise is compared to the ones available in the literature. Streamwise low (green) and high (yellow) uniform momentum regions with positive (red) and negative (blue) vortical motions. This work was supported by Campus International pour la Sécurité et l'Intermodalité des Transports.
The Belonging to the University Scale
Karaman, Omer; Cirak, Yuksel
2017-01-01
The aim of the study is to develop a belonging to the university scale (BUS) in order to determine the level of fulfillment of the need to belong among university students at the higher education institutions they attend. The population of the investigation includes university students studying at the campus of Ordu University. A 5 point…
A simplified PDF parameterization of subgrid-scale clouds and turbulence for cloud-resolving models
Bogenschutz, Peter A.; Krueger, Steven K.
2013-06-01
Over the past decade a new type of global climate model (GCM) has emerged, which is known as a multiscale modeling framework (MMF). Colorado State University's MMF represents a coupling between the Community Atmosphere Model and the System for Atmospheric Modeling (SAM) to serve as the cloud-resolving model (CRM) that replaces traditionally parameterized convection in GCMs. However, due to the high computational expense of the MMF, the grid size of the embedded CRM is typically limited to 4 km for long-term climate simulations. With grid sizes this coarse, shallow convective processes and turbulence cannot be resolved and must still be parameterized within the context of the embedded CRM. This paper describes a computationally efficient closure that aims to better represent turbulence and shallow convective processes in coarse-grid CRMs. The closure is based on the assumed probability density function (PDF) technique to serve as the subgrid-scale (SGS) condensation scheme and turbulence closure that employs a diagnostic method to determine the needed input moments. This paper describes the scheme, as well as the formulation of the eddy length which is empirically determined from large eddy simulation (LES) data. CRM tests utilizing the closure yields good results when compared to LESs for two trade-wind cumulus cases, a transition from stratocumulus to cumulus, and continental cumulus. This new closure improves the representation of clouds through the use of SGS condensation scheme and turbulence due to better representation of the buoyancy flux and dissipation rates. In addition, the scheme reduces the sensitivity of CRM simulations to horizontal grid spacing. The improvement when compared to the standard low-order closure configuration of the SAM is especially striking.
Structure function scaling in a Reλ = 250 turbulent mixing layer
Attili, Antonio
2011-12-22
A highly resolved Direct Numerical Simulation of a spatially developing turbulent mixing layer is presented. In the fully developed region, the flow achieves a turbulent Reynolds number Reλ = 250, high enough for a clear separation between large and dissipative scales, so for the presence of an inertial range. Structure functions have been calculated in the self-similar region using velocity time series and Taylor\\'s frozen turbulence hypothesis. The Extended Self-Similarity (ESS) concept has been employed to evaluate relative scaling exponents. A wide range of scales with scaling exponents and intermittency levels equal to homogeneous isotropic turbulence has been identified. Moreover an additional scaling range exists for larger scales; it is characterized by smaller exponents, similar to the values reported in the literature for flows with strong shear.
Turbulence and other processes for the scale-free texture of the fast solar wind
Hnat, B.; Chapman, S. C.; Gogoberidze, G.; Wicks, R. T.
2012-04-01
The higher-order statistics of magnetic field magnitude fluctuations in the fast quiet solar wind are quantified systematically, scale by scale. We find a single global non-Gaussian scale-free behavior from minutes to over 5 hours. This spans the signature of an inertial range of magnetohydrodynamic turbulence and a ˜1/f range in magnetic field components. This global scaling in field magnitude fluctuations is an intrinsic component of the underlying texture of the solar wind which co-exists with the signature of MHD turbulence but extends to lower frequencies. Importantly, scaling and non- Gaussian statistics of fluctuations are not unique to turbulence and can imply other physical mechanisms- our results thus place a strong constraint on theories of the dynamics of the solar corona and solar wind. Intriguingly, the magnetic field and velocity components also show scale-dependent dynamic alignment outside of the inertial range of MHD turbulence.
Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales
International Nuclear Information System (INIS)
Howes, G. G.; TenBarge, J. M.; Dorland, W.; Numata, R.; Quataert, E.; Schekochihin, A. A.; Tatsuno, T.
2011-01-01
A three-dimensional, nonlinear gyrokinetic simulation of plasma turbulence resolving scales from the ion to electron gyroradius with a realistic mass ratio is presented, where all damping is provided by resolved physical mechanisms. The resulting energy spectra are quantitatively consistent with a magnetic power spectrum scaling of k -2.8 as observed in in situ spacecraft measurements of the 'dissipation range' of solar wind turbulence. Despite the strongly nonlinear nature of the turbulence, the linear kinetic Alfven wave mode quantitatively describes the polarization of the turbulent fluctuations. The collisional ion heating is measured at subion-Larmor radius scales, which provides evidence of the ion entropy cascade in an electromagnetic turbulence simulation.
Universal intermittent properties of particle trajectories in highly turbulent flows
DEFF Research Database (Denmark)
Arnèodo, A.; Benzi, R.; Berg, Jacob
2008-01-01
We present a collection of eight data sets from state-of-the-art experiments and numerical simulations on turbulent velocity statistics along particle trajectories obtained in different flows with Reynolds numbers in the range R-lambda is an element of [120740]. Lagrangian structure functions fro...
Turbulence Enhancement by Fractal Square Grids: Effects of the Number of Fractal Scales
Omilion, Alexis; Ibrahim, Mounir; Zhang, Wei
2017-11-01
Fractal square grids offer a unique solution for passive flow control as they can produce wakes with a distinct turbulence intensity peak and a prolonged turbulence decay region at the expense of only minimal pressure drop. While previous studies have solidified this characteristic of fractal square grids, how the number of scales (or fractal iterations N) affect turbulence production and decay of the induced wake is still not well understood. The focus of this research is to determine the relationship between the fractal iteration N and the turbulence produced in the wake flow using well-controlled water-tunnel experiments. Particle Image Velocimetry (PIV) is used to measure the instantaneous velocity fields downstream of four different fractal grids with increasing number of scales (N = 1, 2, 3, and 4) and a conventional single-scale grid. By comparing the turbulent scales and statistics of the wake, we are able to determine how each iteration affects the peak turbulence intensity and the production/decay of turbulence from the grid. In light of the ability of these fractal grids to increase turbulence intensity with low pressure drop, this work can potentially benefit a wide variety of applications where energy efficient mixing or convective heat transfer is a key process.
International Nuclear Information System (INIS)
Kleiner, S.C.; Dickman, R.L.
1985-01-01
The velocity autocorrelation function (ACF) of observed spectral line centroid fluctuations is noted to effectively reproduce the actual ACF of turbulent gas motions within an interstellar cloud, thereby furnishing a framework for the study of the large scale velocity structure of the Taurus dark cloud complex traced by the present C-13O J = 1-0 observations of this region. The results obtained are discussed in the context of recent suggestions that widely observed correlations between molecular cloud widths and cloud sizes indicate the presence of a continuum of turbulent motions within the dense interstellar medium. Attention is then given to a method for the quantitative study of these turbulent motions, involving the mapping of a source in an optically thin spectral line and studying the spatial correlation properties of the resulting velocity centroid map. 61 references
Multi-Spacecraft Study of Kinetic scale Turbulence Using MMS Observations in the Solar Wind
Chasapis, A.; Matthaeus, W. H.; Parashar, T.; Fuselier, S. A.; Maruca, B.; Burch, J.; Moore, T. E.; Phan, T.; Pollock, C. J.; Gershman, D. J.; Torbert, R. B.; Russell, C. T.; Strangeway, R. J.
2017-12-01
We present a study investigating kinetic scale turbulence in the solar wind. Most previous studies relied on single spacecraft measurements, employing the Taylor hypothesis in order to probe different scales. The small separation of MMS spacecraft, well below the ion inertial scale, allow us for the first time to directly probe turbulent fluctuations at the kinetic range. Using multi-spacecraft measurements, we are able to measure the spatial characteristics of turbulent fluctuations and compare with the traditional Taylor-based single spacecraft approach. Meanwhile, combining observations from Cluster and MMS data we were able to cover a wide range of scales from the inertial range where the turbulent cascade takes place, down to the kinetic range where the energy is eventually dissipated. These observations present an important step in understanding the nature of solar wind turbulence and the processes through which turbulent energy is dissipated into particle heating and acceleration. We compute statistical quantities such as the second order structure function and the scale-dependent kurtosis, along with their dependence on the parameters such as the mean magnetic field direction. Overall, we observe an overall agreement between the single spacecraft and the multi-spacecraft approach. However, a small but significant deviation is observed at the smaller scales near the electron inertial scale. The high values of the scale dependent kurtosis at very small scales, observed via two-point measurements, open up a compelling avenue of investigation for theory and numerical modelling.
Scaling of turbulence spectra measured in strong shear flow near the Earth’s surface
DEFF Research Database (Denmark)
Mikkelsen, Torben Krogh; Larsen, Søren Ejling; Ejsing Jørgensen, Hans
2017-01-01
Within the lowest kilometer of the Earth's atmosphere, in the so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to the ground, the turbulence is predominately generated by mechanical wall-bounded wind shear, whereas at higher altitudes turbulent mixing of heat......) their generation; (2) the cascade of energy across the spectrum from large- to small-scale; and (3) the eventual decay of turbulence into heat owing to viscosity effects on the Kolmogorov microscale, in which the eddy size is only a fraction of a millimeter. This paper addresses atmospheric turbulence spectra...... in the lowest part of the atmospheric boundary layer—the so-called surface layer—where the wind shear is strong owing to the nonslip condition at the ground. Theoretical results dating back to Tchen's early work in 1953 'on the spectrum of energy in turbulent shear flow' led Tchen to predict a shear production...
Sub-grid-scale description of turbulent magnetic reconnection in magnetohydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Widmer, F., E-mail: widmer@mps.mpg.de [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen (Germany); Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Büchner, J. [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen (Germany); Yokoi, N. [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan)
2016-04-15
Magnetic reconnection requires, at least locally, a non-ideal plasma response. In collisionless space and astrophysical plasmas, turbulence could transport energy from large to small scales where binary particle collisions are rare. We have investigated the influence of small scale magnetohydrodynamics (MHD) turbulence on the reconnection rate in the framework of a compressible MHD approach including sub-grid-scale (SGS) turbulence. For this sake, we considered Harris-type and force-free current sheets with finite guide magnetic fields directed out of the reconnection plane. The goal is to find out whether unresolved by conventional simulations MHD turbulence can enhance the reconnection process in high-Reynolds-number astrophysical plasmas. Together with the MHD equations, we solve evolution equations for the SGS energy and cross-helicity due to turbulence according to a Reynolds-averaged turbulence model. The SGS turbulence is self-generated and -sustained through the inhomogeneities of the mean fields. By this way, the feedback of the unresolved turbulence into the MHD reconnection process is taken into account. It is shown that the turbulence controls the regimes of reconnection by its characteristic timescale τ{sub t}. The dependence on resistivity was investigated for large-Reynolds-number plasmas for Harris-type as well as force-free current sheets with guide field. We found that magnetic reconnection depends on the relation between the molecular and apparent effective turbulent resistivity. We found that the turbulence timescale τ{sub t} decides whether fast reconnection takes place or whether the stored energy is just diffused away to small scale turbulence. If the amount of energy transferred from large to small scales is enhanced, fast reconnection can take place. Energy spectra allowed us to characterize the different regimes of reconnection. It was found that reconnection is even faster for larger Reynolds numbers controlled by the molecular
Scaling laws of turbulence and heating of fast solar wind: the role of density fluctuations.
Carbone, V; Marino, R; Sorriso-Valvo, L; Noullez, A; Bruno, R
2009-08-07
Incompressible and isotropic magnetohydrodynamic turbulence in plasmas can be described by an exact relation for the energy flux through the scales. This Yaglom-like scaling law has been recently observed in the solar wind above the solar poles observed by the Ulysses spacecraft, where the turbulence is in an Alfvénic state. An analogous phenomenological scaling law, suitably modified to take into account compressible fluctuations, is observed more frequently in the same data set. Large-scale density fluctuations, despite their low amplitude, thus play a crucial role in the basic scaling properties of turbulence. The turbulent cascade rate in the compressive case can, moreover, supply the energy dissipation needed to account for the local heating of the nonadiabatic solar wind.
Nickelsen, Daniel
2017-07-01
The statistics of velocity increments in homogeneous and isotropic turbulence exhibit universal features in the limit of infinite Reynolds numbers. After Kolmogorov’s scaling law from 1941, many turbulence models aim for capturing these universal features, some are known to have an equivalent formulation in terms of Markov processes. We derive the Markov process equivalent to the particularly successful scaling law postulated by She and Leveque. The Markov process is a jump process for velocity increments u(r) in scale r in which the jumps occur randomly but with deterministic width in u. From its master equation we establish a prescription to simulate the She-Leveque process and compare it with Kolmogorov scaling. To put the She-Leveque process into the context of other established turbulence models on the Markov level, we derive a diffusion process for u(r) using two properties of the Navier-Stokes equation. This diffusion process already includes Kolmogorov scaling, extended self-similarity and a class of random cascade models. The fluctuation theorem of this Markov process implies a ‘second law’ that puts a loose bound on the multipliers of the random cascade models. This bound explicitly allows for instances of inverse cascades, which are necessary to satisfy the fluctuation theorem. By adding a jump process to the diffusion process, we go beyond Kolmogorov scaling and formulate the most general scaling law for the class of Markov processes having both diffusion and jump parts. This Markov scaling law includes She-Leveque scaling and a scaling law derived by Yakhot.
Turbulence in rough-wall boundary layers: universality issues
Amir, Mohammad; Castro, Ian P.
2011-08-01
Wind tunnel measurements of turbulent boundary layers over three-dimensional rough surfaces have been carried out to determine the critical roughness height beyond which the roughness affects the turbulence characteristics of the entire boundary layer. Experiments were performed on three types of surfaces, consisting of an urban type surface with square random height elements, a diamond-pattern wire mesh and a sand-paper type grit. The measurements were carried out over a momentum thickness Reynolds number ( Re θ) range of 1,300-28,000 using two-component Laser Doppler anemometry (LDA) and hot-wire anemometry (HWA). A wide range of the ratio of roughness element height h to boundary layer thickness δ was covered (0.04 ≤ h/δ ≤ 0.40). The results confirm that the mean profiles for all the surfaces collapse well in velocity defect form up to surprisingly large values of h/δ, perhaps as large as 0.2, but with a somewhat larger outer layer wake strength than for smooth-wall flows, as previously found. At lower h/δ, at least up to 0.15, the Reynolds stresses for all surfaces show good agreement throughout the boundary layer, collapsing with smooth-wall results outside the near-wall region. With increasing h/δ, however, the turbulence above the near-wall region is gradually modified until the entire flow is affected. Quadrant analysis confirms that changes in the rough-wall boundary layers certainly exist but are confined to the near-wall region at low h/δ; for h/δ beyond about 0.2 the quadrant events show that the structural changes extend throughout much of the boundary layer. Taken together, the data suggest that above h/δ ≈ 0.15, the details of the roughness have a weak effect on how quickly (with rising h/δ) the turbulence structure in the outer flow ceases to conform to the classical boundary layer behaviour. The present results provide support for Townsend's wall similarity hypothesis at low h/δ and also suggest that a single critical roughness
The Effect of Stem- and Canopy-Scale Turbulence on Sediment Dynamics within Submerged Vegetation.
Tinoco, R. O.; San Juan Blanco, J. E.; Prada, A. F.
2017-12-01
Stem- and canopy-scale turbulence generated by submerged patches of vegetation plays a paramount role on sediment transport within aquatic ecosystems such as wetlands, marshes, mangrove forests, and coastal regions, as dense patches dampen velocities and mean bed stresses within the plants, while also increasing turbulence intensity through stem-scale wakes and canopy-scale eddies. To explore the interactions between such processes, laboratory experiments are conducted using rigid cylinders placed in a staggered configuration as vegetation elements, embedded on a non-cohesive sediment bed in a racetrack flume. Quantitative imaging is used to characterize the flow field and the associated suspended sediment concentration throughout the water column at different submergence ratios, defined as the ratio between water depth, H, and plant height, h, to investigate the role of canopy-scale eddies formed at the top of the canopy, and their interaction with near-bed flow structures, on sediment dynamics. Turbulent kinetic energy, turbulent intensity, and Reynolds stresses are quantified within and above the array to clearly identify the contributions from bed generated turbulence and vegetation generated turbulence, at both stem- and canopy-scale, as submergence ratio increases from emergent, H/h=1, to fully submerged, H/h=5, conditions. The experimental results are compared with transport models to highlight the need for a multi-scale approach to represent flow-vegetation-sediment interactions.
Siebert, H.; Shaw, R. A.; Ditas, J.; Schmeissner, T.; Malinowski, S. P.; Bodenschatz, E.; Xu, H.
2015-01-01
Mountain research stations are advantageous not only for long-term sampling of cloud properties, but also for measurements that prohibitively difficult to perform on airborne platforms due to the true air speed or adverse factors such as weight and complexity of the equipment necessary. Some cloud-turbulence measurements, especially Lagrangian in nature, fall into this category. We report results from simultaneous, high-resolution and collocated measurements of cloud microphysical and turbulence properties during several warm cloud events at the Umweltforschungsstation Schneefernerhaus (UFS) on Zugspitze in the German Alps. The data gathered was found to be representative of observations made with similar instrumentation in free clouds. The turbulence observed, shared all features known for high Reynolds number flows: it exhibited approximately Gaussian fluctuations for all three velocity components, a clearly defined inertial subrange following Kolmogorov scaling (power spectrum, and second and third order Eulerian structure functions), and highly intermittent velocity gradients, as well as approximately lognormal kinetic energy dissipation rates. The clouds were observed to have liquid water contents of order 1 g m-3, and size distributions typical of continental clouds, sometimes exhibiting long positive tails indicative of large drop production through turbulent mixing or coalescence growth. Dimensionless parameters relevant to cloud-turbulence interactions, the Stokes number and settling parameter, are in the range typically observed in atmospheric clouds. Observed fluctuations in droplet number concentration and diameter suggest a preference for inhomogeneous mixing. Finally, enhanced variance in liquid water content fluctuations is observed at high frequencies, and the scale break occurs at a value consistent with the independently estimated phase relaxation time from microphysical measurements.
Yamamoto, Keisuke; Nakayama, Katsuyuki
2017-11-01
Development or decay of a vortex in terms of the local flow topology has been shown to be highly correlated with its topological feature, i.e., vortical flow symmetry (skewness), in an isotropic homogeneous turbulence. Since a turbulent flow might include vortices in multi-scales, the present study investigates the characteristics of this relationships between the development or decay of a vortex and the vortical flow symmetry in several scales in an isotropic homogeneous turbulence in low Reynols number. Swirlity is a physical quantity of an intensity of swirling in terms of the geometrical average of the azimuthal flow, and represents the behavior of the development or decay of a vortex in this study. Flow scales are decomposed into three scales specified by the Fourier coefficients of the velocity applying the band-pass filter. The analysis shows that vortices in the different scales have a universal feature that the time derivative of swirlity and that of the symmetry have high correlation. Especially they have more stronger correlation at their birth and extinction.
Numerical simulation of a laboratory-scale turbulent V-flame
Energy Technology Data Exchange (ETDEWEB)
Bell, J.B.; Day, M.S.; Shepherd, I.G.; Johnson, M.; Cheng, R.K.; Grcar,J.F.; Beckner, V.E.; Lijewski, M.J.
2005-02-07
We present a three-dimensional, time-dependent simulation of a laboratory-scale rod-stabilized premixed turbulent V-flame. The simulations are performed using an adaptive time-dependent low Mach number model with detailed chemical kinetics and a mixture model for differential species diffusion. The algorithm is based on a second-order projection formulation and does not require an explicit subgrid model for turbulence or turbulence chemistry interaction. Adaptive mesh refinement is used to dynamically resolve the flame and turbulent structures. Here, we briefly discuss the numerical procedure and present detailed comparisons with experimental measurements showing that the computation is able to accurately capture the basic flame morphology and associated mean velocity field. Finally, we discuss key issues that arise in performing these types of simulations and the implications of these issues for using computation to form a bridge between turbulent flame experiments and basic combustion chemistry.
Phenomenology of two-dimensional stably stratified turbulence under large-scale forcing
Kumar, Abhishek
2017-01-11
In this paper, we characterise the scaling of energy spectra, and the interscale transfer of energy and enstrophy, for strongly, moderately and weakly stably stratified two-dimensional (2D) turbulence, restricted in a vertical plane, under large-scale random forcing. In the strongly stratified case, a large-scale vertically sheared horizontal flow (VSHF) coexists with small scale turbulence. The VSHF consists of internal gravity waves and the turbulent flow has a kinetic energy (KE) spectrum that follows an approximate k−3 scaling with zero KE flux and a robust positive enstrophy flux. The spectrum of the turbulent potential energy (PE) also approximately follows a k−3 power-law and its flux is directed to small scales. For moderate stratification, there is no VSHF and the KE of the turbulent flow exhibits Bolgiano–Obukhov scaling that transitions from a shallow k−11/5 form at large scales, to a steeper approximate k−3 scaling at small scales. The entire range of scales shows a strong forward enstrophy flux, and interestingly, large (small) scales show an inverse (forward) KE flux. The PE flux in this regime is directed to small scales, and the PE spectrum is characterised by an approximate k−1.64 scaling. Finally, for weak stratification, KE is transferred upscale and its spectrum closely follows a k−2.5 scaling, while PE exhibits a forward transfer and its spectrum shows an approximate k−1.6 power-law. For all stratification strengths, the total energy always flows from large to small scales and almost all the spectral indicies are well explained by accounting for the scale-dependent nature of the corresponding flux.
A MODEL FOR THE NON-UNIVERSAL POWER LAW OF THE SOLAR WIND SUB-ION-SCALE MAGNETIC SPECTRUM
International Nuclear Information System (INIS)
Passot, T.; Sulem, P. L.
2015-01-01
A phenomenological turbulence model for kinetic Alfvén waves in a magnetized collisionless plasma that is able to reproduce the non-universal power-law spectra observed at the sub-ion scales in the solar wind and the terrestrial magnetosphere is presented. The process of temperature homogenization along distorted magnetic field lines, induced by Landau damping, affects the turbulence transfer time and results in a steepening of the sub-ion power-law spectrum of critically balanced turbulence, whose exponent is sensitive to the ratio between the Alfvén wave period and the nonlinear timescale. Transition from large-scale weak turbulence to smaller scale strong turbulence is captured and nonlocal interactions, relevant in the case of steep spectra, are accounted for
Modeling subgrid-scale turbulent fluxes in the "Grey Zone"
De Roode, S. R.; Jonker, H. J.; Siebesma, P.
2017-12-01
The ever increasing computational power nowadays allows both weather and climate models to operate at a horizontal grid resolution that is high enough to resolve some part of the turbulent transport. Some of these models apply a Smagorinsky type TKE closure model including a buoyancy production term to compute the subgrid turbulent fluxes of heat, momentum and moisture. For a stable stratification an analytical solution for the eddy viscosity can be derived. From a comparison with similarity relations from field observations it is concluded that an anistropic grid, as measured by the ratio of the horizontal to the vertical grid mesh sizes (r=Dx/Dz>1), will yield excessive subgrid mixing and an erroneous dependency on the grid resolution. Secondly, in contrast to what is being used in many LES models, field observations suggest that for a stable boundary layer the turbulent Prandtl number is close to unity. The effect of grid anistropy is also investigated for the CONSTRAIN cold air outbreak model intercomparison case. Here opposite results are found. In the presence of convective stratocumulus clouds the Smagorinsky model appears to be well capable of compensating the gradual reduction of the resolved vertical fluxes with coarsening horizontal grid resolution, up to values Dx>3 km, in such a way that the total turbulent fluxes are hardly affected.
Turbulent Concentration of mm-Size Particles in the Protoplanetary Nebula: Scale-Dependent Cascades
Cuzzi, J. N.; Hartlep, T.
2015-01-01
estimated using a statistical model with properties inferred from large numerical simulations of turbulence. Nebula turbulence is described by its Reynolds number Re = (L/eta)(exp 4/3), where L = H alpha(exp 1/2) is the largest eddy scale, H is the nebula gas vertical scale height, alpha the turbulent viscosity parameter, and eta is the Kolmogorov or smallest scale in turbulence (typically about 1km), with eddy turnover time t(sub eta). In the nebula, Re is far larger than any numerical simulation can handle, so some physical arguments are needed to extend the results of numerical simulations to nebula conditions. In this paper, we report new physics to be incorporated into our statistical models.
Multi-scale-nonlinear interactions among micro-turbulence, magnetic islands, and zonal flows
International Nuclear Information System (INIS)
Ishizawa, A.; Nakajima, N.; Okamoto, M.; Ramos, J.J.
2006-10-01
We investigate multi-scale-nonlinear interactions among micro-instabilities, macro-scale tearing instabilities and zonal flows, by solving reduced two-fluid equations numerically. We find that the nonlinear interactions of these instabilities trigger macro-scale MHD activity after an equilibrium is formed by a balance between the micro-turbulence and zonal flow. This MHD activity breaks magnetic surfaces then this breaking spreads the micro-turbulence over the plasma. These multi-scale-nonlinear interactions can explain the evolution of fluctuation observed in torus plasma experiments because micro-turbulence and MHD instabilities usually appear in the plasma at the same time, in spite of the fact that effects of micro-turbulence and MHD instabilities on plasma confinement have been investigated separately. For instance, MHD activities are observed in reversed shear tokamak plasmas with a transport barrier related to zonal flows and micro-turbulence, and micro-turbulence is observed in Large Helical Device plasmas that usually exhibit MHD activities. (author)
Turbulent boundary layer over 2D and 3D large-scale wavy walls
Chamorro, Leonardo P.; Hamed, Ali M.; Castillo, Luciano
2015-11-01
In this work, an experimental investigation of the developing and developed flow over two- and three-dimensional large-scale wavy walls was performed using high-resolution planar particle image velocimetry in a refractive-index-matching flume. The 2D wall is described by a sinusoidal wave in the streamwise direction with amplitude to wavelength ratio a/ λx = 0.05. The 3D wall is defined with an additional wave superimposed on the 2D wall in the spanwise direction with a/ λy = 0.1. The flow was characterized at Reynolds numbers of 4000 and 40000, based on the bulk velocity and the flume half height. Instantaneous velocity fields and time-averaged turbulence quantities reveal strong coupling between large-scale topography and the turbulence dynamics near the wall. Turbulence statistics show the presence of a well-structured shear layer that enhances the turbulence for the 2D wavy wall, whereas the 3D wall exhibits different flow dynamics and significantly lower turbulence levels, particularly for which shows about 30% reduction. The likelihood of recirculation bubbles, levels and spatial distribution of turbulence, and the rate of the turbulent kinetic energy production are shown to be severely affected when a single spanwise mode is superimposed on the 2D wall. POD analysis was also performed to further understand distinctive features of the flow structures due to surface topography.
Stochastic time scale for the Universe
International Nuclear Information System (INIS)
Szydlowski, M.; Golda, Z.
1986-01-01
An intrinsic time scale is naturally defined within stochastic gradient dynamical systems. It should be interpreted as a ''relaxation time'' to a local potential minimum after the system has been randomly perturbed. It is shown that for a flat Friedman-like cosmological model this time scale is of order of the age of the Universe. 7 refs. (author)
Synergistic cross-scale coupling of turbulence in a tokamak plasma
Energy Technology Data Exchange (ETDEWEB)
Howard, N. T., E-mail: nthoward@psfc.mit.edu [Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, Tennessee 37831 (United States); Holland, C. [University of California - San Diego, La Jolla, California 92093 (United States); White, A. E.; Greenwald, M. [MIT - Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States); Candy, J. [General Atomics, P.O. Box 85608, San Diego, California 92186 (United States)
2014-11-15
For the first time, nonlinear gyrokinetic simulations spanning both the ion and electron spatio-temporal scales have been performed with realistic electron mass ratio ((m{sub D}∕m{sub e}){sup 1∕2 }= 60.0), realistic geometry, and all experimental inputs, demonstrating the coexistence and synergy of ion (k{sub θ}ρ{sub s}∼O(1.0)) and electron-scale (k{sub θ}ρ{sub e}∼O(1.0)) turbulence in the core of a tokamak plasma. All multi-scale simulations utilized the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] to study the coupling of ion and electron-scale turbulence in the core (r/a = 0.6) of an Alcator C-Mod L-mode discharge shown previously to exhibit an under-prediction of the electron heat flux when using simulations only including ion-scale turbulence. Electron-scale turbulence is found to play a dominant role in setting the electron heat flux level and radially elongated (k{sub r} ≪ k{sub θ}) “streamers” are found to coexist with ion-scale eddies in experimental plasma conditions. Inclusion of electron-scale turbulence in these simulations is found to increase both ion and electron heat flux levels by enhancing the transport at the ion-scale while also driving electron heat flux at sub-ρ{sub i} scales. The combined increases in the low and high-k driven electron heat flux may explain previously observed discrepancies between simulated and experimental electron heat fluxes and indicates a complex interaction of short and long wavelength turbulence.
Small-scale turbulence, marine snow formation, and planktivorous feeding
DEFF Research Database (Denmark)
Kiørboe, Thomas
1997-01-01
to demonstrate how phytoplankton cells may coagulate, how their stickiness may be measured, how coagulation determines the sedimentation of particulate matter in the ocean, and how it may control the population dynamics of phytoplankton. Subsequently the collision equations are used to describe how planktivorous......This paper examines how turbulence influences two very basic properties of planktonic ecosystems, namely trophic interactions and vertical flux of particulate material. It starts with a simple account of classical particle encounter theory which forms the basis of the substance of both problems....... Turbulent fluid motion will bring suspended particles to collide, and the basic equations describing the collision rate as a function of dissipation rate and particle size, concentration and motility will be presented. The classical (coagulation) theory is then applied to marine snow formation in the ocean...
Scaling laws and intermittent structures in solar wind MHD turbulence
Veltri, Pierluigi; Mangeney, André
1999-06-01
Thirteen months of velocity and magnetic field data from ISEE space experiment have been used to calculate spectra and structure functions using Haar wavelets technique in the range from 1 minute to about 1 day. Using conditioned structure function definition we have been able to eliminate the intermittency effects in the spectra and thus to evidentiate which kind of phenomenology of nonlinear cascade between Kolmogorov and Kraichnan is taking place in Solar Wind turbulence. By the same technique the most intermittent structures in solar wind turbulence can also be identified and they turn out to be either shock waves or one dimensional current sheets, at variance with ordinary fluid intermittency, where the most intermittent structures are two dimensional vortices.
PECASE - Multi-Scale Experiments and Modeling in Wall Turbulence
2014-12-23
amplitude and singular value. The SVD of the resolvent before Fourier decomposition is imposed would itself naturally result in a de- composition into the...the measurement location. The flow was conditioned by passing it through a perforated plate, a honey comb, three turbulence reducing screens and...and a small, well resolved, field from which a composite spectrum can be produced covering the whole wavenumber range, which is the focus of future
PLASMA TURBULENCE AND KINETIC INSTABILITIES AT ION SCALES IN THE EXPANDING SOLAR WIND
Energy Technology Data Exchange (ETDEWEB)
Hellinger, Petr; Trávnícek, Pavel M. [Astronomical Institute, CAS, Bocni II/1401, CZ-14100 Prague (Czech Republic); Matteini, Lorenzo [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Landi, Simone; Verdini, Andrea; Franci, Luca, E-mail: petr.hellinger@asu.cas.cz [Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze Largo E. Fermi 2, I-50125 Firenze (Italy)
2015-10-01
The relationship between a decaying strong turbulence and kinetic instabilities in a slowly expanding plasma is investigated using two-dimensional (2D) hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and vanishing correlation between the two fields. A turbulent cascade rapidly develops; magnetic field fluctuations exhibit a power-law spectrum at large scales and a steeper spectrum at ion scales. The turbulent cascade leads to an overall anisotropic proton heating, protons are heated in the perpendicular direction, and, initially, also in the parallel direction. The imposed expansion leads to generation of a large parallel proton temperature anisotropy which is at later stages partly reduced by turbulence. The turbulent heating is not sufficient to overcome the expansion-driven perpendicular cooling and the system eventually drives the oblique firehose instability in a form of localized nonlinear wave packets which efficiently reduce the parallel temperature anisotropy. This work demonstrates that kinetic instabilities may coexist with strong plasma turbulence even in a constrained 2D regime.
Towards an integrated multiscale simulation of turbulent clouds on PetaScale computers
International Nuclear Information System (INIS)
Wang Lianping; Ayala, Orlando; Parishani, Hossein; Gao, Guang R; Kambhamettu, Chandra; Li Xiaoming; Rossi, Louis; Orozco, Daniel; Torres, Claudio; Grabowski, Wojciech W; Wyszogrodzki, Andrzej A; Piotrowski, Zbigniew
2011-01-01
The development of precipitating warm clouds is affected by several effects of small-scale air turbulence including enhancement of droplet-droplet collision rate by turbulence, entrainment and mixing at the cloud edges, and coupling of mechanical and thermal energies at various scales. Large-scale computation is a viable research tool for quantifying these multiscale processes. Specifically, top-down large-eddy simulations (LES) of shallow convective clouds typically resolve scales of turbulent energy-containing eddies while the effects of turbulent cascade toward viscous dissipation are parameterized. Bottom-up hybrid direct numerical simulations (HDNS) of cloud microphysical processes resolve fully the dissipation-range flow scales but only partially the inertial subrange scales. it is desirable to systematically decrease the grid length in LES and increase the domain size in HDNS so that they can be better integrated to address the full range of scales and their coupling. In this paper, we discuss computational issues and physical modeling questions in expanding the ranges of scales realizable in LES and HDNS, and in bridging LES and HDNS. We review our on-going efforts in transforming our simulation codes towards PetaScale computing, in improving physical representations in LES and HDNS, and in developing better methods to analyze and interpret the simulation results.
Scale dependence of the alignment between strain rate and rotation in turbulent shear flow
Fiscaletti, D.; Elsinga, G.E.; Attili, A; Bisetti, F; Buxton, O.R.H.
2016-01-01
The scale dependence of the statistical alignment tendencies of the eigenvectors of the strain-rate tensor ei, with the vorticity vector ω, is examined in the self-preserving region of a planar turbulent mixing layer. Data from a direct numerical simulation are filtered at various length scales and
Realization of a Tunable Dissipation Scale in a Turbulent Cascade using a Quantum Gas
Navon, Nir; Eigen, Christoph; Zhang, Jinyi; Lopes, Raphael; Smith, Robert; Hadzibabic, Zoran
2017-04-01
Many turbulent flows form so-called cascades, where excitations injected at large length scales, are transported to gradually smaller scales until they reach a dissipation scale. We initiate a turbulent cascade in a dilute Bose fluid by pumping energy at the container scale of an optical box trap using an oscillating magnetic force. In contrast to classical fluids where the dissipation scale is set by the viscosity of the fluid, the turbulent cascade of our quantum gas finishes when the particles kinetic energy exceeds the laser-trap depth. This mechanism thus allows us to effectively tune the dissipation scale where particles (and energy) are lost, and measure the particle flux in the cascade at the dissipation scale. We observe a unit power-law decay of the particle-dissipation rate with trap depth, which confirms the surprising prediction that in a wave-turbulent direct energy cascade, the particle flux vanishes in the ideal limit where the dissipation length scale tends to zero.
Advancing Knowledge in Higher Education: Universities in Turbulent Times
Fitzgerald, Tanya, Ed.
2014-01-01
Over the last three decades, higher education institutions have experienced massive changes. In particular, institutions of higher education have been positioned as a means to contribute to the knowledge economy and gain a level of competitive advantage in the global marketplace. "Advancing Knowledge in Higher Education: Universities in…
Lee, Jin; Zaki, Tamer
2017-11-01
Transitional boundary layers feature long coherent motions of streamwise velocity fluctuation, u', in both the laminar and turbulent regions. In the former, Klebanoff streaks amplify and become seats for breakdown to turbulence. In the fully turbulent region, large-scale motions contribute appreciably to the turbulence energy and shear stresses. Direct numerical simulation (DNS) of boundary-layer bypass transition over a flat plate with a leading edge is performed. Instantaneous realizations of spatially and temporally resolved fields are stored in a database. Structure identification techniques are used to identify these coherent flow structures. The inception rate, lifetime and amplification rate of Klebanoff streaks are evaluated in the laminar region, and conditional averaging is used to examine the early stages of streak formation. Structure identification and tracking is also used to study the inception of large-scale coherent motion in the nascent turbulent spots and fully turbulent boundary layer downstream. This work has been partially supported by the National Science Foundation (NSF, Grant 1605404). The computations were performed using the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by NSF (Grant ACI-1053575).
International Nuclear Information System (INIS)
Reuss, J.D.; Misguich, J.H.
1996-02-01
An important point for turbulent transport consists in determining the scaling law for the diffusion coefficient D due to electrostatic turbulence. It is well-known that for weak amplitudes or large frequencies, the reduced diffusion coefficient has a quasi-linear like (or gyro-Bohm like) scaling, while for large amplitudes or small frequencies it has been traditionally believed that the scaling is Bohm-like. The aim of this work consists to test this prediction for a given realistic model. This problem is studied by direct simulation of particle trajectories. Guiding centre diffusion in a spectrum of electrostatic turbulence is computed for test particles in a model spectrum, by means of a new parallelized code RADIGUET 2. The results indicate a continuous transition for large amplitudes toward a value which is compatible with the Isichenko percolation prediction. (author)
Universal Scaling Relations in Scale-Free Structure Formation
Guszejnov, Dávid; Hopkins, Philip F.; Grudić, Michael Y.
2018-04-01
A large number of astronomical phenomena exhibit remarkably similar scaling relations. The most well-known of these is the mass distribution dN/dM∝M-2 which (to first order) describes stars, protostellar cores, clumps, giant molecular clouds, star clusters and even dark matter halos. In this paper we propose that this ubiquity is not a coincidence and that it is the generic result of scale-free structure formation where the different scales are uncorrelated. We show that all such systems produce a mass function proportional to M-2 and a column density distribution with a power law tail of dA/d lnΣ∝Σ-1. In the case where structure formation is controlled by gravity the two-point correlation becomes ξ2D∝R-1. Furthermore, structures formed by such processes (e.g. young star clusters, DM halos) tend to a ρ∝R-3 density profile. We compare these predictions with observations, analytical fragmentation cascade models, semi-analytical models of gravito-turbulent fragmentation and detailed "full physics" hydrodynamical simulations. We find that these power-laws are good first order descriptions in all cases.
Energetics of stratified turbulent mixing at geophysical scales
Scotti, Alberto; Passaggia, Pierre-Yves; White, Brian
2017-11-01
Energy-based arguments provide a fundamental diagnostic tool in turbulent flows. In stratified incompressible flows, there are two reservoirs of energy, the kinetic and potential energy. However, the standard expression Ep = ρgZ for the latter is not convex, and thus, within an energetic framework based on this definition, turbulent fluctuations have zero potential energy, a rather unsatisfactorily state of affairs. The solution is to modify the definition of potential energy to include only the portion that is effectively available. This introduces the concept of Available Potential Energy (APE). In this talk, we approach the problem of APE using a general framework which recovers the standard buoyancy-only dependent formulation in non-rotating systems. Unlike the standard formulation, rotation can be included in a natural way, in which case the Available Energy depends both on the buoyancy and potential vorticity distribution. We will show results from experiments of stratified mixing at oceanic values of the Gibson number conducted in our large flume. The goal of this experiments is to shed some light on the controversy surrounding the relationship between the mixing efficiency and the Gibson number. Funded by NSF-OCE-1155558 and OCE-1736989.
Anomalous scaling of structure functions and dynamic constraints on turbulence simulations
International Nuclear Information System (INIS)
Yakhot, Victor; Sreenivasan, Katepalli R.
2006-12-01
The connection between anomalous scaling of structure functions (intermittency) and numerical methods for turbulence simulations is discussed. It is argued that the computational work for direct numerical simulations (DNS) of fully developed turbulence increases as Re 4 , and not as Re 3 expected from Kolmogorov's theory, where Re is a large-scale Reynolds number. Various relations for the moments of acceleration and velocity derivatives are derived. An infinite set of exact constraints on dynamically consistent subgrid models for Large Eddy Simulations (LES) is derived from the Navier-Stokes equations, and some problems of principle associated with existing LES models are highlighted. (author)
A One-Dimensional Global-Scaling Erosive Burning Model Informed by Blowing Wall Turbulence
Kibbey, Timothy P.
2014-01-01
A derivation of turbulent flow parameters, combined with data from erosive burning test motors and blowing wall tests results in erosive burning model candidates useful in one-dimensional internal ballistics analysis capable of scaling across wide ranges of motor size. The real-time burn rate data comes from three test campaigns of subscale segmented solid rocket motors tested at two facilities. The flow theory admits the important effect of the blowing wall on the turbulent friction coefficient by using blowing wall data to determine the blowing wall friction coefficient. The erosive burning behavior of full-scale motors is now predicted more closely than with other recent models.
Horizontal Structure of Turbulence on Decimeter to 10m Scales in Fast Tidal Flows
Horwitz, R.; Hay, A. E.
2016-02-01
We characterize the structure of turbulence in a very fast tidal channel in the Bay of Fundy, Nova Scotia that has been identified for development as a commercial tidal power resource. A subsurface mooring that orients into the flow was equipped with a horizontally-aimed AD2CP, and upward- and downward-looking ADCPs. Two week-long deployments provide velocity measurements of tidal flows up to 4 m/s that are used to describe the spatial (lateral) and temporal structure of turbulent fluctuations on decimeter to 10m scales. The spatial scales and temporal intermittency vary with both speed of the flow and the effects of upstream topography.
SOLAR WIND TURBULENCE FROM MHD TO SUB-ION SCALES: HIGH-RESOLUTION HYBRID SIMULATIONS
Energy Technology Data Exchange (ETDEWEB)
Franci, Luca; Verdini, Andrea; Landi, Simone [Dipartimento di Fisica e Astronomia, Università di Firenze, Largo E. Fermi 2, I-50125 Firenze (Italy); Matteini, Lorenzo [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Hellinger, Petr [Astronomical Institute, AS CR, Bocni II/1401, CZ-14100 Prague (Czech Republic)
2015-05-10
We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers. The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm’s law.
Turbulent methane combustion in a laboratory-scale furnace
Energy Technology Data Exchange (ETDEWEB)
Oksanen, A.; Maeki-Mantila, E. [Tampere Univ. of Technology (Finland). Energy and Process Engineering
1996-12-31
Methane combustion in the 400 rotational symmetric test chamber by ENEL was investigated. The prediction of the reaction rates of methane and carbon monoxide was based on the models which are taking into consideration the effect of turbulence on the oxidation phenomena namely the eddy dissipation concept model (EDC) and the eddy dissipation model (EDM). The experimental results of the distributions of the different species concentrations, temperature, velocities, turbulence quantities etc. were measured in the chamber cross-sections. The formation of nitric oxide was modelled using the thermal- and prompt-NO formation mechanisms and the formulation was based on the chemical kinetics and the probability density function (pdf) with the {beta}- and {delta}-distributions. If more than one variable is taken into consideration in the use of pdf it is very difficult to find distribution for different variables and especially to solve them with the moderate amount of the computing time. Therefore, in this presentation the amount of the pdf variables was limited as small as possible i.e. only one variable namely the mixture fraction was used the variance of which was solved from the transport equation. The computational domain which was divided into about seven thousand cells includes areas where the mean values of the variables can be supposed to be known and where the distribution of the probability is very narrow. Because in every computational cell the probability distribution as accurate as possible is wanted the linearization of the integration was made. The effect of the local extinction on the reaction rates was also included in the paper
Logarithmic scaling in the near-dissipation range of turbulence
Indian Academy of Sciences (India)
From experimental data at moderate Reynolds numbers, it is shown that the logarithmic scaling, deduced from general considerations for the near-dissipation range, covers almost the entire range of scales (about two decades) of structure functions, for both velocity and passive scalar fields. This new scaling requires two ...
TURBULENCE-GENERATED PROTON-SCALE STRUCTURES IN THE TERRESTRIAL MAGNETOSHEATH
Energy Technology Data Exchange (ETDEWEB)
Vörös, Zoltán; Narita, Yasuhito [Space Research Institute, Austrian Academy of Sciences, Graz (Austria); Yordanova, Emiliya [Swedish Institute of Space Physics, Uppsala (Sweden); Echim, Marius M. [Belgian Institute for Space Aeronomy, Bruxelles (Belgium); Consolini, Giuseppe, E-mail: zoltan.voeroes@oeaw.ac.at [INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma (Italy)
2016-03-01
Recent results of numerical magnetohydrodynamic simulations suggest that in collisionless space plasmas, turbulence can spontaneously generate thin current sheets. These coherent structures can partially explain the intermittency and the non-homogenous distribution of localized plasma heating in turbulence. In this Letter, Cluster multi-point observations are used to investigate the distribution of magnetic field discontinuities and the associated small-scale current sheets in the terrestrial magnetosheath downstream of a quasi-parallel bow shock. It is shown experimentally, for the first time, that the strongest turbulence-generated current sheets occupy the long tails of probability distribution functions associated with extremal values of magnetic field partial derivatives. During the analyzed one-hour time interval, about a hundred strong discontinuities, possibly proton-scale current sheets, were observed.
COSMIC-RAY SMALL-SCALE ANISOTROPIES AND LOCAL TURBULENT MAGNETIC FIELDS
Energy Technology Data Exchange (ETDEWEB)
López-Barquero, V. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Farber, R. [Department of Physics and Astronomy, Wheaton College, Norton, MA 02766 (United States); Xu, S. [Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China); Desiati, P. [Wisconsin IceCube Particle Astrophysics Center (WIPAC), University of Wisconsin, Madison, WI 53703 (United States); Lazarian, A. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)
2016-10-10
Cosmic-ray anisotropy has been observed in a wide energy range and at different angular scales by a variety of experiments over the past decade. However, no comprehensive or satisfactory explanation has been put forth to date. The arrival distribution of cosmic rays at Earth is the convolution of the distribution of their sources and of the effects of geometry and properties of the magnetic field through which particles propagate. It is generally believed that the anisotropy topology at the largest angular scale is adiabatically shaped by diffusion in the structured interstellar magnetic field. On the contrary, the medium- and small-scale angular structure could be an effect of nondiffusive propagation of cosmic rays in perturbed magnetic fields. In particular, a possible explanation for the observed small-scale anisotropy observed at the TeV energy scale may be the effect of particle propagation in turbulent magnetized plasmas. We perform numerical integration of test particle trajectories in low- β compressible magnetohydrodynamic turbulence to study how the cosmic rays’ arrival direction distribution is perturbed when they stream along the local turbulent magnetic field. We utilize Liouville’s theorem for obtaining the anisotropy at Earth and provide the theoretical framework for the application of the theorem in the specific case of cosmic-ray arrival distribution. In this work, we discuss the effects on the anisotropy arising from propagation in this inhomogeneous and turbulent interstellar magnetic field.
The time scale for the transition to turbulence in a high Reynolds number, accelerated flow
International Nuclear Information System (INIS)
Robey, H.F.; Zhou Ye; Buckingham, A.C.; Keiter, P.; Remington, B.A.; Drake, R.P.
2003-01-01
An experiment is described in which an interface between materials of different density is subjected to an acceleration history consisting of a strong shock followed by a period of deceleration. The resulting flow at this interface, initiated by the deposition of strong laser radiation into the initially well characterized solid materials, is unstable to both the Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) instabilities. These experiments are of importance in their ability to access a difficult experimental regime characterized by very high energy density (high temperature and pressure) as well as large Reynolds number and Mach number. Such conditions are of interest, for example, in the study of the RM/RT induced mixing that occurs during the explosion of a core-collapse supernova. Under these experimental conditions, the flow is in the plasma state and given enough time will transition to turbulence. By analysis of the experimental data and a corresponding one-dimensional numerical simulation of the experiment, it is shown that the Reynolds number is sufficiently large (Re>10 5 ) to support a turbulent flow. An estimate of three key turbulence length scales (the Taylor and Kolmogorov microscales and a viscous diffusion scale), however, shows that the temporal duration of the present flow is insufficient to allow for the development of a turbulent inertial subrange. A methodology is described for estimating the time required under these conditions for the development of a fully turbulent flow
Below the Kolmogorov scale: the non-turbulent sex life of ...
African Journals Online (AJOL)
Below the Kolmogorov length scale there is no turbulence and phytoplankton gametes swim in order to encounter each other and achieve syngamy. An encounter rate model, Z = ð p2 R2 u N, is derived incorporating cell size (R), swimming speed (u) and cell concentration (N). Assuming Z = 1 day–1, calculations using this ...
Scaling and universality in magnetocaloric materials
DEFF Research Database (Denmark)
Smith, Anders; Nielsen, Kaspar Kirstein; Bahl, Christian R. H.
2014-01-01
-order phase transition within the context of the theory of critical phenomena. Sufficiently close to the critical temperature of a second-order material, the scaling of the isothermal entropy change will be determined by the critical exponents and will be the same as that of the singular part of the entropy......The magnetocaloric effect of a magnetic material is characterized by two quantities, the isothermal entropy change and the adiabatic temperature change, both of which are functions of temperature and applied magnetic field. We discuss the scaling properties of these quantities close to a second...... fields are not universal, showing significant variation for models in the same universality class. As regards the adiabatic temperature change, it is not determined exclusively by the singular part of the free energy and its derivatives. We show that the field dependence of the adiabatic temperature...
Scale-separation scheme for simulating superfluid turbulence: Kelvin-Wave cascade
International Nuclear Information System (INIS)
Kozik, Evgeny; Svistunov, Boris
2005-01-01
A Kolmogorov-type cascade of Kelvin waves--the distortion waves on vortex lines--plays a key part in the relaxation of superfluid turbulence at low temperatures. We propose an efficient numeric scheme for simulating the Kelvin-wave cascade on a single vortex line. This idea is likely to be generalizable for a full-scale simulation of different regimes of superfluid turbulence. With the new scheme, we are able to unambiguously resolve the cascade spectrum exponent, and thus to settle the controversy between recent simulations of Vinen, Tsubota, and Mitani [Phys. Rev. Lett. 91, 135301 (2003)] and recently developed analytic theory [Phys. Rev. Lett. 92, 035301 (2004)
Scaling and universality in urban economic diversification.
Youn, Hyejin; Bettencourt, Luís M A; Lobo, José; Strumsky, Deborah; Samaniego, Horacio; West, Geoffrey B
2016-01-01
Understanding cities is central to addressing major global challenges from climate change to economic resilience. Although increasingly perceived as fundamental socio-economic units, the detailed fabric of urban economic activities is only recently accessible to comprehensive analyses with the availability of large datasets. Here, we study abundances of business categories across US metropolitan statistical areas, and provide a framework for measuring the intrinsic diversity of economic activities that transcends scales of the classification scheme. A universal structure common to all cities is revealed, manifesting self-similarity in internal economic structure as well as aggregated metrics (GDP, patents, crime). We present a simple mathematical derivation of the universality, and provide a model, together with its economic implications of open-ended diversity created by urbanization, for understanding the observed empirical distribution. Given the universal distribution, scaling analyses for individual business categories enable us to determine their relative abundances as a function of city size. These results shed light on the processes of economic differentiation with scale, suggesting a general structure for the growth of national economies as integrated urban systems. © 2016 The Authors.
Time Resolved Scanning PIV measurements at fine scales in a turbulent jet
International Nuclear Information System (INIS)
Cheng, Y.; Torregrosa, M.M.; Villegas, A.; Diez, F.J.
2011-01-01
The temporal and spatial complexity of turbulent flows at intermediate and small scales has prevented the acquisition of full three-dimensional experimental data sets for validating classical turbulent theory and Direct Numerical Simulations (DNS). Experimental techniques like Particle Velocimetry, PIV, allow non-intrusive planar measurements of turbulent flows. The present work applied a Time Resolved Scanning PIV system, TRS-PIV, capable of obtaining three-dimensional two-component velocities to measure the small scales of a turbulent jet. When probing the small scales of these flows with PIV, the uncertainty of the measured turbulent properties are determined by the characteristics of the PIV system and specially the thickness of the laser sheet. A measurement of the particle distribution across the thickness of the laser sheet is proposed as a more detailed description of the PIV sheet thickness. The high temporal and spatial resolution of the TRS-PIV system allowed obtaining quasi-instantaneous volumetric vector fields at the far field of a round turbulent jet in water, albeit for a low Reynolds number of 1478 due to the speed limitations of the present camera and scanning system. Six of the nine components of the velocity gradient tensor were calculated from the velocity measurements. This allowed the visualization with near Kolmogorov-scale resolution of the velocity gradient structures in three-dimensional space. In general, these structures had a complex geometry corresponding to elongated shapes in the form of sheets and tubes. An analysis of the probability density function, pdf, of the velocity gradients calculated showed that the on-diagonal (off-diagonal) velocity gradient components were very similar to each other even for events at the tails of the pdfs, as required for homogeneous isotropy. The root mean square of the components of the velocity gradients is also calculated and their ratio of off-diagonal components to on-diagonal components
Turbulence-induced contact rates of plankton : the question of scale
DEFF Research Database (Denmark)
Visser, Andre; MacKenzie, Brian
1998-01-01
Modelling encounter rates between planktonic predators and prey in turbulent waters requires an estimate of a spatial scale. One spatial scale proposed in the literature based on prey concentration is shown to be systematically inconsistent and its use is shown to imply that plankton sampling met...... as the length scale produces encounter rates for small (e.g. 4 to 10 mm) fish larvae 2- to 3-fold lower than those using prey separation distance......Modelling encounter rates between planktonic predators and prey in turbulent waters requires an estimate of a spatial scale. One spatial scale proposed in the literature based on prey concentration is shown to be systematically inconsistent and its use is shown to imply that plankton sampling...... methodology can bias encounter rate estimates in turbulent situations. We show that a scale based on the predator's reactive distance is more appropriate, as it has clear theoretical support, and is consistent with other mathematical treatments of encounter problems. Applying the reactive distance...
The PVC technique a method to estimate the dissipation length scale in turbulent flows
Ho, Chih-Ming; Zohar, Yitshak
1997-12-01
A time-averaged length scale can be defined by a pair of successive turbulent-velocity derivatives, i.e. [dnu(x)/ dxn][prime prime or minute]/ [dn+1u(x)/ dxn+1][prime prime or minute]. The length scale associated with the zeroth- and the first-order derivatives, u[prime prime or minute]/u[prime prime or minute]x, is the Taylor microscale. In isotropic turbulence, this scale is the average length between zero crossings of the velocity signal. The average length between zero crossings of the first velocity derivative, i.e. u[prime prime or minute]x/u[prime prime or minute]xx, can be reliably obtained by using the peak-valley-counting (PVC) technique. We have found that the most probable scale, rather than the average, equals the wavelength at the peak of the dissipation spectrum in a plane mixing layer (Zohar & Ho 1996). In this study, we experimentally investigate the generality of applying the PVC technique to estimate the dissipation scale in three basic turbulent shear flows: a flat-plate boundary layer, a wake behind a two-dimensional cylinder and a plane mixing layer. We also analytically explore the quantitative relationships among this length scale and the Kolmogorov and Taylor microscales.
Can large-scale oblique undulations on a solid wall reduce the turbulent drag?
Ghebali, Sacha; Chernyshenko, Sergei I.; Leschziner, Michael A.
2017-10-01
Direct numerical simulations of fully developed turbulent channel flows with wavy walls are undertaken. The wavy walls, skewed with respect to the mean flow direction, are introduced as a means of emulating a Spatial Stokes Layer (SSL) induced by in-plane wall motion. The transverse shear strain above the wavy wall is shown to be similar to that of a SSL, thereby affecting the turbulent flow and leading to a reduction in the turbulent skin-friction drag. However, some important differences with respect to the SSL case are brought to light too. In particular, the phase variations of the turbulent properties are accentuated and, unlike in the SSL case, there is a region of increased turbulence production over a portion of the wall, above the leeward side of the wave, thus giving rise to a local increase in dissipation. The pressure- and friction-drag levels are carefully quantified for various flow configurations, exhibiting a combined maximum overall-drag reduction of about 0.6%. The friction-drag reduction is shown to behave approximately quadratically for small wave slopes and then linearly for higher slopes, whilst the pressure-drag penalty increases quadratically. The transverse shear-strain layer is shown to be approximately Reynolds-number independent when the wave geometry is scaled in wall units.
DEFF Research Database (Denmark)
Kiørboe, Thomas; MacKenzie, Brian
1995-01-01
Turbulent water motion has several effects on the feeding ecology of larval fish and other planktivorous predators. In this paper, we consider the appropriate spatial scales for estimating relative velocities between larval fish predators and their prey, and the effect that different choices...... of scales might have on encounter and ingestion rates. Four possible scaling choices have been used in the literature, giving rise to varying estimates of the effect of turbulence on encounter rate. We argue that the correct scale is that based on the larval reactive distance, and that this interpretation...... are more likely to benefit from turbulence-increased encounter than larger larvae. Overall ingestion rate probability (= probability of encounter x probability of successful pursuit) is likely to be highest at moderate-high levels of turbulence. In most larval fish habitats, turbulence levels appear to lie...
Keenan, Brett D; Ford, Alexander L; Medvedev, Mikhail V
2015-09-01
Plasmas with electromagnetic fields turbulent at sub-Larmor scales are a feature of a wide variety of high-energy-density environments and are essential to the description of many astrophysical and laboratory plasma phenomena. Radiation from particles, whether they are relativistic or nonrelativistic, moving through small-scale magnetic turbulence has spectral characteristics distinct from both synchrotron and cyclotron radiation. The radiation, carrying information on the statistical properties of the magnetic turbulence, is also intimately related to the particle diffusive transport. We have investigated, both theoretically and numerically, the transport of nonrelativistic and trans-relativistic particles in plasmas with high-amplitude isotropic sub-Larmor-scale magnetic turbulence, and its relation to the spectra of radiation simultaneously produced by these particles. Consequently, the diffusive and radiative properties of plasmas turbulent on sub-Larmor scales may serve as a powerful tool to diagnosis laboratory and astrophysical plasmas.
MMS Observations of Ion-Scale Magnetic Island in the Magnetosheath Turbulent Plasma
Huang, S. Y.; Sahraoui, F.; Retino, A.; Contel, O. Le; Yuan, Z. G.; Chasapis, A.; Aunai, N.; Breuillard, H.; Deng, X. H.; Zhou, M.;
2016-01-01
In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 di, where di is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma..
Scaling of turbulence spectra measured in strong shear flow near the Earth’s surface
Mikkelsen, T.; Larsen, S. E.; Jørgensen, H. E.; Astrup, P.; Larsén, X. G.
2017-12-01
Within the lowest kilometer of the Earth’s atmosphere, in the so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to the ground, the turbulence is predominately generated by mechanical wall-bounded wind shear, whereas at higher altitudes turbulent mixing of heat and moisture also play a role. The variance (square of the standard deviation) of the fluctuation around the mean wind speed is a measure of the kinetic energy content of the turbulence. This kinetic energy can be resolved into the spectral distributions, or spectra, as functions of eddy size, wavenumber, or frequency. Spectra are derived from Fourier transforms of wind records as functions of space or time corresponding to wavenumber and frequency spectra, respectively. Atmospheric spectra often exhibit different subranges that can be distinguished and scaled by the physical parameters responsible for: (1) their generation; (2) the cascade of energy across the spectrum from large- to small-scale; and (3) the eventual decay of turbulence into heat owing to viscosity effects on the Kolmogorov microscale, in which the eddy size is only a fraction of a millimeter. This paper addresses atmospheric turbulence spectra in the lowest part of the atmospheric boundary layer—the so-called surface layer—where the wind shear is strong owing to the nonslip condition at the ground. Theoretical results dating back to Tchen’s early work in 1953 ‘on the spectrum of energy in turbulent shear flow’ led Tchen to predict a shear production subrange with a distinct inverse-linear power law for turbulence in a strongly sheared high-Reynolds number wall-bounded flow, as is encountered in the lowest sheared part of the atmospheric boundary layer, also known as the eddy surface layer. This paper presents observations of spectra measured in a meteorological mast at Høvsøre, Denmark, that support Tchen’s prediction of a shear production subrange following a distinct power law of degree
International Nuclear Information System (INIS)
Maroteaux, Fadila; Pommier, Pierre-Lin
2013-01-01
Highlights: ► Turbulent time evolution is introduced in stochastic modeling approach. ► The particles number is optimized trough a restricted initial distribution. ► The initial distribution amplitude is modeled by magnitude of turbulence field. -- Abstract: Homogenous Charge Compression Ignition (HCCI) engine technology is known as an alternative to reduce NO x and particulate matter (PM) emissions. As shown by several experimental studies published in the literature, the ideally homogeneous mixture charge becomes stratified in composition and temperature, and turbulent mixing is found to play an important role in controlling the combustion progress. In a previous study, an IEM model (Interaction by Exchange with the Mean) has been used to describe the micromixing in a stochastic reactor model that simulates the HCCI process. The IEM model is a deterministic model, based on the principle that the scalar value approaches the mean value over the entire volume with a characteristic mixing time. In this previous model, the turbulent time scale was treated as a fixed parameter. The present study focuses on the development of a micro-mixing time model, in order to take into account the physical phenomena it stands for. For that purpose, a (k–ε) model is used to express this micro-mixing time model. The turbulence model used here is based on zero dimensional energy cascade applied during the compression and the expansion cycle; mean kinetic energy is converted to turbulent kinetic energy. Turbulent kinetic energy is converted to heat through viscous dissipation. Besides, in this study a relation to calculate the initial heterogeneities amplitude is proposed. The comparison of simulation results against experimental data shows overall satisfactory agreement at variable turbulent time scale
Scale dependence of the alignment between strain rate and rotation in turbulent shear flow
Fiscaletti, D.; Elsinga, G. E.; Attili, A.; Bisetti, F.; Buxton, O. R. H.
2016-10-01
The scale dependence of the statistical alignment tendencies of the eigenvectors of the strain-rate tensor ei, with the vorticity vector ω , is examined in the self-preserving region of a planar turbulent mixing layer. Data from a direct numerical simulation are filtered at various length scales and the probability density functions of the magnitude of the alignment cosines between the two unit vectors | ei.ω ̂| are examined. It is observed that the alignment tendencies are insensitive to the concurrent large-scale velocity fluctuations, but are quantitatively affected by the nature of the concurrent large-scale velocity-gradient fluctuations. It is confirmed that the small-scale (local) vorticity vector is preferentially aligned in parallel with the large-scale (background) extensive strain-rate eigenvector e1, in contrast to the global tendency for ω to be aligned in parallel with the intermediate strain-rate eigenvector [Hamlington et al., Phys. Fluids 20, 111703 (2008), 10.1063/1.3021055]. When only data from regions of the flow that exhibit strong swirling are included, the so-called high-enstrophy worms, the alignment tendencies are exaggerated with respect to the global picture. These findings support the notion that the production of enstrophy, responsible for a net cascade of turbulent kinetic energy from large scales to small scales, is driven by vorticity stretching due to the preferential parallel alignment between ω and nonlocal e1 and that the strongly swirling worms are kinematically significant to this process.
Global MHD Modelling of the ISM - From large towards small scale turbulence
de Avillez, M.; Breitschwerdt, D.
2005-06-01
Dealing numerically with the turbulent nature and non-linearity of the physical processes involved in the ISM requires the use of sophisticated numerical schemes coupled to HD and MHD mathematical models. SNe are the main drivers of the interstellar turbulence by transferring kinetic energy into the system. This energy is dissipated by shocks (which is more efficient) and by molecular viscosity. We carried out adaptive mesh refinement simulations (with a finest resolution of 0.625 pc) of the turbulent ISM embedded in a magnetic field with mean field components of 2 and 3 μG. The time scale of our run was 400 Myr, sufficiently long to avoid memory effects of the initial setup, and to allow for a global dynamical equilibrium to be reached in case of a constant energy input rate. It is found that the longitudinal and transverse turbulent length scales have a time averaged (over a period of 50 Myr) ratio of 0.52-0.6, almost similar to the one expected for isotropic homogeneous turbulence. The mean characteristic size of the larger eddies is found to be ˜ 75 pc in both runs. In order to check the simulations against observations, we monitored the OVI and HI column densities within a superbubble created by the explosions of 19 SNe having masses and velocities of the stars that exploded in vicinity of the Sun generating the Local Bubble. The model reproduces the FUSE absorption measurements towards 25 white dwarfs of the OVI column density as function of distance and of N(HI). In particular for lines of sight with lengths smaller than 120 pc it is found that there is no correlation between N(OVI) and N(HI).
Benchmarking and scaling studies of pseudospectral code Tarang for turbulence simulations
VERMA, MAHENDRA K
2013-09-21
Tarang is a general-purpose pseudospectral parallel code for simulating flows involving fluids, magnetohydrodynamics, and Rayleigh–Bénard convection in turbulence and instability regimes. In this paper we present code validation and benchmarking results of Tarang. We performed our simulations on 10243, 20483, and 40963 grids using the HPC system of IIT Kanpur and Shaheen of KAUST. We observe good ‘weak’ and ‘strong’ scaling for Tarang on these systems.
Plasma turbulence driven by transversely large-scale standing shear Alfvén waves
International Nuclear Information System (INIS)
Singh, Nagendra; Rao, Sathyanarayan
2012-01-01
Using two-dimensional particle-in-cell simulations, we study generation of turbulence consisting of transversely small-scale dispersive Alfvén and electrostatic waves when plasma is driven by a large-scale standing shear Alfvén wave (LS-SAW). The standing wave is set up by reflecting a propagating LS-SAW. The ponderomotive force of the standing wave generates transversely large-scale density modifications consisting of density cavities and enhancements. The drifts of the charged particles driven by the ponderomotive force and those directly caused by the fields of the standing LS-SAW generate non-thermal features in the plasma. Parametric instabilities driven by the inherent plasma nonlinearities associated with the LS-SAW in combination with the non-thermal features generate small-scale electromagnetic and electrostatic waves, yielding a broad frequency spectrum ranging from below the source frequency of the LS-SAW to ion cyclotron and lower hybrid frequencies and beyond. The power spectrum of the turbulence has peaks at distinct perpendicular wave numbers (k ⊥ ) lying in the range d e −1 -6d e −1 , d e being the electron inertial length, suggesting non-local parametric decay from small to large k ⊥ . The turbulence spectrum encompassing both electromagnetic and electrostatic fluctuations is also broadband in parallel wave number (k || ). In a standing-wave supported density cavity, the ratio of the perpendicular electric to magnetic field amplitude is R(k ⊥ ) = |E ⊥ (k ⊥ )/|B ⊥ (k ⊥ )| ≪ V A for k ⊥ d e A is the Alfvén velocity. The characteristic features of the broadband plasma turbulence are compared with those available from satellite observations in space plasmas.
Similarity Scaling for the Inner Region of the Turbulent Boundary Layer
2009-11-20
layers, this search for "similarity" was mostly unsuccessful. This led to the practice of dividing the turbulent profile into two regions, an inner...work over the whole profile. This led to the concept of an inner and outer layer. This has evolved to where it is now assumed the regions are...and George using the y-axis scale uluzs instead of (ue -u) luzs , then the profiles do not show good collapse as contended by Castillo and George
Turbulence descriptors for scaling fatigue loading spectra of wind turbine structural components
Energy Technology Data Exchange (ETDEWEB)
Kelley, N D
1994-07-01
The challenge for the designer in developing a new wind turbine is to incorporate sufficient strength in its components to safely achieve a 20- or 30-year service life. To accomplish this, the designer must understand the load and stress distributions (in a statistical sense at least) that the turbine is likely to encounter during its operating life. Sources of loads found in the normal operating environment include start/stop cycles, emergency shutdowns, the turbulence environment associated with the specific site and turbine location, and extreme or ``rare`` events that can challenge the turbine short-term survivability. Extreme events can result from an operational problem (e.g., controller failure) or violent atmospheric phenomena (tornadic circulations, strong gust fronts). For the majority of the operating time, however, the character of the turbulent inflow is the dominant source of the alternating stress distributions experienced by the structural components. Methods of characterizing or scaling the severity of the loading spectra (or the rate of fatigue damage accumulation) must be applicable to a wide range of turbulent inflow environments -- from solitary isolation to the complex flows associated with multi-row wind farms. The metrics chosen must be related to the properties of the turbulent inflow and independent of the nature of local terrain features.
Directory of Open Access Journals (Sweden)
R. André
2003-08-01
Full Text Available Unusual structures characterized by a very high-velocity divergence have been observed in the high-latitude F-region with SuperDARN radars (André et al., 2000. These structures have been interpreted as due to local demagnetization of the plasma in the ionospheric F-region, during very specific geophysical conditions. In this study, the collective wave scattering theory is used to characterize the decameter-scale turbulence (l approx 15 m inside the structures. The distribution function of the diffusion coefficient is modified when the structures are generated, suggesting that two regimes of turbulence coexist. A temporal analysis decorrelates the two regimes and gives access to the dynamics associated with the structures. It is shown that a high turbulent regime precedes the plasma demagnetization and should be related to an energy deposition. Then a second regime appears when the plasma is demagnetized and disappears simultaneously with the structures. This study is the first application of the collective wave scattering theory to a specific geophysical event.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities – Space plasma physics (turbulence
A Novel Multi-scale Simulation Strategy for Turbulent Reacting Flows
Energy Technology Data Exchange (ETDEWEB)
James, Sutherland [University of Utah
2018-04-12
Abstract In this project, a new methodology was proposed to bridge the gap between Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES). This novel methodology, titled Lattice-Based Multiscale Simulation (LBMS), creates a lattice structure of One-Dimensional Turbulence (ODT) models. This model has been shown to capture turbulent combustion with high fidelity by fully resolving interactions between turbulence and diffusion. By creating a lattice of ODT models, which are then coupled, LBMS overcomes the shortcomings of ODT, which are its inability to capture large scale three dimensional flow structures. However, by spacing these lattices significantly apart, LBMS can avoid the curse of dimensionality that creates untenable computational costs associated with DNS. This project has shown that LBMS is capable of reproducing statistics of isotropic turbulent flows while coarsening the spacing between lines significantly. It also investigates and resolves issues that arise when coupling ODT lines, such as flux reconstruction perpendicular to a given ODT line, preservation of conserved quantities when eddies cross a course cell volume and boundary condition application. Robust parallelization is also investigated.
Liu, Zhenping; Fox, Rodney; Hill, James; Olsen, Michael
2013-11-01
Flash Nanoprecipitation (FNP) is a technique to produce monodisperse functional nanoparticles. Microscale multi-inlet vortex reactors (MIVR) have been effectively applied to FNP due to their ability to provide rapid mixing and flexibility of inlet flow conditions. A scaled-up MIVR could potentially generate large quantities of functional nanoparticles, giving FNP wider applicability in industry. In the presented research, the turbulent velocity field inside a scaled-up, macroscale MIVR is measured by particle image velocimetry (PIV). Within the reactor, velocity is measured using both two-dimensional and stereoscopic PIV at two Reynolds numbers (3500 and 8750) based on the flow at each inlet. Data have been collected at numerous locations in the inlet channels, the reaction chamber, and the reactor outlet. Mean velocity and Reynolds stresses have been obtained based on 5000 instantaneous velocity realizations at each measurement location. The turbulent mixing process has also been investigated with passive scalar planar laser-induced fluorescence and simultaneous PIV/PLIF. Velocity and concentration results are compared to results from previous experiments in a microscale MIVR. Scaled profiles of turbulent quantities are similar to those previously found in the microscale MIVR.
Scale-Invariance and Intermittency in the Solar Wind Alfvénic Turbulence: Wind Observations
Salem, C. S.; Mangeney, A.; Bale, S. D.; Veltri, P.
2004-12-01
In the "Alfvénic" regime, i.e. for frequencies below the local proton cyclotron frequency, solar wind MHD turbulence exhibits what appears like an inertial domain, with power-law spectra and scale-invariance, suggesting as in fluid turbulence, a nonlinear energy cascade from the large "energy containing" scales towards the small scales where dissipation by kinetic effects is presumed to act. However, the intermittent character of solar wind fluctuations is much more important than in ordinary fluids. Indeed, the fluctuations consist of a mixture of random fluctuations and small-scale "singular" or coherent structures. This intermittency modifies significantly the scaling exponents of actual power-law spectra, which are directly related to the physical nature of the energy cascade taking place in the solar wind. The identification of the most intermittent structures and their relation to dissipation represents then a crucial problem in the framework of turbulence. We present here a new approach to study the scaling laws and intermittency based on the use of Wavelet transforms on simultaneous WIND 3s resolution particle and magnetic field data from the 3DP and the MFi experiments respectively. Using the Haar wavelet transform, spectra and structure functions are calculated. We show that this powerful technique allows: (1) for a systematic elimination of intermittency effects on spectra and structure functions and thus for a clear determination of the actual scaling properties in the inertial range, and (2) for a direct and systematic identification of the most active, singular structures responsible for the intermittency in the solar wind. We finally discuss the various effects which may be important for the formation of these structures in the absence of collisions.
Anomalous scaling and the role of intermittency in solar wind MHD turbulence: new insights
Salem, C.; Mangeney, A.; Bale, S. D.; Veltri, P.; Bruno, R.
2007-08-01
In the Alfvénic regime, i.e. for frequencies below the local proton cyclotron frequency, solar wind MHD turbulence exhibits what appears like an inertial domain, with power-law spectra and scale-invariance, suggesting as in fluid turbulence, a nonlinear energy cascade from the large ``energy containing'' scales towards much smaller scales, where dissipation via kinetic effects is presumed to act. However, the intermittent character of the solar wind fluctuations in the inertial range is much more important than in ordinary fluids. Indeed, the fluctuations consist of a mixture of random fluctuations and small-scale ``singular'' or coherent structures. This intermittency modifies significantly the scaling exponents of actual power-law spectra, which are directly related to the physical nature of the energy cascade taking place in the solar wind. The identification of the most intermittent structures and their relation to dissipation represents then a crucial problem in the framework of turbulence. We will discuss here recent results on scaling laws and intermittency based on the use of Wavelet transforms on simultaneous WIND 3s resolution particle and magnetic field data from the 3DP and the MFi experiments respectively. More specifically, the Haar Wavelet transform is used to compute spectra, structure functions and probability distribution functions (PDFs). We show that this powerful technique allows: (1) for a systematic study of intermittency effects on these spectra, structure functions and PDFs, thus for a clear determination of the actual scaling properties in the inertial range, and (2) for a direct and systematic identification of the most active, singular structures responsible for the intermittency in the solar wind. The analysis of structure functions and PDFs and new results on the nature of the intermittent coherent structures will be presented.
Derivation of Zagarola-Smits scaling in zero-pressure-gradient turbulent boundary layers
Wei, Tie; Maciel, Yvan
2018-01-01
This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations for zero-pressure-gradient turbulent boundary layers (ZPG TBLs). It has long been observed that the scaling of the mean streamwise velocity in turbulent boundary layer flows differs in the near surface region and in the outer layer. In the inner region of small-velocity-defect boundary layers, it is generally accepted that the proper velocity scale is the friction velocity, uτ, and the proper length scale is the viscous length scale, ν /uτ . In the outer region, the most generally used length scale is the boundary layer thickness, δ . However, there is no consensus on velocity scales in the outer layer. Zagarola and Smits [ASME Paper No. FEDSM98-4950 (1998)] proposed a velocity scale, U ZS=(δ1/δ ) U∞ , where δ1 is the displacement thickness and U∞ is the freestream velocity. However, there are some concerns about Zagarola-Smits scaling due to the lack of a theoretical base. In this paper, the Zagarola-Smits scaling is derived directly from a combination of integral, similarity, and order-of-magnitude analysis of the mean continuity equation. The analysis also reveals that V∞, the mean wall-normal velocity at the edge of the boundary layer, is a proper scale for the mean wall-normal velocity V . Extending the analysis to the streamwise mean momentum equation, we find that the Reynolds shear stress in ZPG TBLs scales as U∞V∞ in the outer region. This paper also provides a detailed analysis of the mass and mean momentum balance in the outer region of ZPG TBLs.
Cuzzi, Jeffrey N.; Hartlep, Thomas; Weston, B.; Estremera, Shariff Kareem
2014-01-01
The initial accretion of primitive bodies (asteroids and TNOs) from freely-floating nebula particles remains problematic. Here we focus on the asteroids where constituent particle (read "chondrule") sizes are observationally known; similar arguments will hold for TNOs, but the constituent particles in those regions will be smaller, or will be fluffy aggregates, and are unobserved. Traditional growth-bysticking models encounter a formidable "meter-size barrier" [1] (or even a mm-cm-size barrier [2]) in turbulent nebulae, while nonturbulent nebulae form large asteroids too quickly to explain long spreads in formation times, or the dearth of melted asteroids [3]. Even if growth by sticking could somehow breach the meter size barrier, other obstacles are encountered through the 1-10km size range [4]. Another clue regarding planetesimal formation is an apparent 100km diameter peak in the pre-depletion, pre-erosion mass distribution of asteroids [5]; scenarios leading directly from independent nebula particulates to this size, which avoid the problematic m-km size range, could be called "leapfrog" scenarios [6-8]. The leapfrog scenario we have studied in detail involves formation of dense clumps of aerodynamically selected, typically mm-size particles in turbulence, which can under certain conditions shrink inexorably on 100-1000 orbit timescales and form 10-100km diameter sandpile planetesimals. The typical sizes of planetesimals and the rate of their formation [7,8] are determined by a statistical model with properties inferred from large numerical simulations of turbulence [9]. Nebula turbulence can be described by its Reynolds number Re = L/eta sup(4/3), where L = ETA alpha sup (1/2) the largest eddy scale, H is the nebula gas vertical scale height, and a the nebula turbulent viscosity parameter, and ? is the Kolmogorov or smallest scale in turbulence (typically about 1km), with eddy turnover time t?. In the nebula, Re is far larger than any numerical simulation can
Solar Wind MHD Turbulence: Anomalous Scaling and Intermittency Effects in the Slow and Fast Wind
Salem, C.; Mangeney, A.; Bale, S. D.
2007-12-01
Although considerable progress has been made in the understanding of MHD turbulence over the past few decades through the analysis of in-situ solar wind data, two of the primary problems of solar wind MHD turbulence that still remain a puzzle are the nature of the nonlinear energy cascade, and the strong intermittent character of solar wind fluctuations in the inertial range. This intermittency modifies significantly the scaling exponents of actual power-law spectra, which are directly related to the physical nature of the energy cascade taking place in the solar wind. The identification of the most intermittent structures and their relation to dissipation represents then a crucial problem in the framework of turbulence. Anomalous scaling of both solar wind magnetic field and velocity fluctuations in the inertial range, as well as intermittency effects have recently been investigated in detail using Wavelet transforms on simultaneous WIND 3s resolution particle and magnetic field data from the 3DP and the MFi experiments respectively. Specifically, the Haar Wavelet transform is used to compute spectra, structure functions and probability distribution functions (PDFs). This powerful technique allows: (1) for a systematic study of intermittency effects on these spectra, structure functions and PDFs, thus for a clear determination of the actual scaling properties in the inertial range, and (2) for a direct and systematic identification of the most active, singular structures responsible for the intermittency in the solar wind. The analysis of structure functions and PDFs, as well as new results on the nature of the intermittent coherent structures will be presented. The turbulent properties and intermittency effects in different solar wind regimes will be also discussed.
Second-moment closures and length scales for weakly stratified turbulent shear flows
Baumert, Helmut; Peters, Hartmut
2000-03-01
For the special hydrodynamic situation of unbounded homogeneous shear layers, turbulence closure models of Mellor-Yamada type (MY) and k-ɛ type are put into a single canonical form. For this situation we show that conventional versions of MY and various k-ɛ versions lack a proper steady state, and are unable to simulate the most basic properties of stratified shear flows exemplified in, for example, the Rohr et al. [1988] experiments: exponential growth at sufficiently low gradient Richardson number (Rg), exponential decay at sufficiently large Rg, and a steady state in between. Proper choice of one special model parameter readily solves the problems. In the fairly general case of structural equilibrium (state of exponential evolution) in weakly to moderately stratified turbulence (Rg ≲ 0.25), the ratio between the Thorpe scale (or Ellison scale) and the Ozmidov scale varies like the gradient Richardson number (Rg) to the power 3/4, and the ratio of the Thorpe scale to the buoyancy scale varies like Rg1/2. Length scales predicted by our current model are consistent with laboratory measurements of Rohr et al. [1988], with large-eddy numerical simulations of Schumann and Gerz [1995], and with microstructure measurements from the 1987 Tropic Heat Experiment in the equatorial Pacific by Peters et al. [1995].
Statistical theory and transition in multiple-scale-lengths turbulence in plasmas
International Nuclear Information System (INIS)
Itoh, Sanae-I.; Itoh, Kimitaka
2001-06-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Nonlinear interactions in the same kind of fluctuations as well as nonlinear interplay between different classes of fluctuations are kept in the analysis. Nonlinear interactions are modelled as turbulent drag, nonlinear noise and nonlinear drive, and a set of Langevin equations is formulated. With the help of an Ansatz of a large number of degrees of freedom with positive Lyapunov number, Langevin equations are solved and the fluctuation dissipation theorem in the presence of strong plasma turbulence has been derived. A case where two driving mechanisms (one for micro mode and the other for semi-micro mode) coexist is investigated. It is found that there are several states of fluctuations: in one state, the micro mode is excited and the semi-micro mode is quenched; in the other state, the semi-micro mode is excited, and the micro mode remains at finite but suppressed level. New type of turbulence transition is obtained, and a cusp type catastrophe is revealed. A phase diagram is drawn for turbulence which is composed of multiple classes of fluctuations. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. Finally, the nonlocal heat transport due to the long-wave-length fluctuations, which are noise-pumped by shorter-wave-length ones, is analyzed and the impact on transient transport problems is discussed. (author)
Tokamak electron heat transport by direct numerical simulation of small scale turbulence
International Nuclear Information System (INIS)
Labit, B.
2002-10-01
In a fusion machine, understanding plasma turbulence, which causes a degradation of the measured energy confinement time, would constitute a major progress in this field. In tokamaks, the measured ion and electron thermal conductivities are of comparable magnitude. The possible sources of turbulence are the temperature and density gradients occurring in a fusion plasma. Whereas the heat losses in the ion channel are reasonably well understood, the origin of the electron losses is more uncertain. In addition to the radial velocity associated to the fluctuations of the electric field, electrons are more affected than ions by the magnetic field fluctuations. In experiments, the confinement time can be conveniently expressed in terms of dimensionless parameters. Although still somewhat too imprecise, these scaling laws exhibit strong dependencies on the normalized pressure β or the normalized Larmor radius, ρ * . The present thesis assesses whether a tridimensional, electromagnetic, nonlinear fluid model of plasma turbulence driven by a specific instability can reproduce the dependence of the experimental electron heat losses on the dimensionless parameters β and ρ * . The investigated interchange instability is the Electron Temperature Gradient driven one (ETG). The model is built by using the set of Braginskii equations. The developed simulation code is global in the sense that a fixed heat flux is imposed at the inner boundary, leaving the gradients free to evolve. From the nonlinear simulations, we have put in light three characteristics for the ETG turbulence: the turbulent transport is essentially electrostatic; the potential and pressure fluctuations form radially elongated cells called streamers; the transport level is very low compared to the experimental values. The thermal transport dependence study has shown a very small role of the normalized pressure, which is in contradiction with the Ohkama's formula. On the other hand, the crucial role of the
A model of the saturation of coupled electron and ion scale gyrokinetic turbulence
Staebler, G. M.; Howard, N. T.; Candy, J.; Holland, C.
2017-06-01
A new paradigm of zonal flow mixing as the mechanism by which zonal E × B fluctuations impact the saturation of gyrokinetic turbulence has recently been deduced from the nonlinear 2D spectrum of electric potential fluctuations in gyrokinetic simulations. These state of the art simulations span the physical scales of both ion and electron turbulence. It was found that the zonal flow mixing rate, rather than zonal flow shearing rate, competes with linear growth at both electron and ion scales. A model for saturation of the turbulence by the zonal flow mixing was developed and applied to the quasilinear trapped gyro-Landau fluid transport model (TGLF). The first validation tests of the new saturation model are reported in this paper with data from L-mode and high-β p regime discharges from the DIII-D tokamak. The shortfall in the predicted L-mode edge electron energy transport is improved with the new saturation model for these discharges but additional multiscale simulations are required in order to verify the safety factor and collisionality dependencies found in the modeling.
Kinetic-Scale Magnetic Turbulence and Finite Larmor Radius Effects at Mercury
Uritsky, V. M.; Slavin, J. A.; Khazanov, G. V.; Donovan, E. F.; Boardsen, S. A.; Anderson, B. J.; Korth, H.
2011-01-01
We use a nonstationary generalization of the higher-order structure function technique to investigate statistical properties of the magnetic field fluctuations recorded by MESSENGER spacecraft during its first flyby (01/14/2008) through the near-Mercury space environment, with the emphasis on key boundary regions participating in the solar wind - magnetosphere interaction. Our analysis shows, for the first time, that kinetic-scale fluctuations play a significant role in the Mercury's magnetosphere up to the largest resolvable timescale (approx.20 s) imposed by the signal nonstationariry, suggesting that turbulence at this plane I is largely controlled by finite Larmor radius effects. In particular, we report the presence of a highly turbulent and extended foreshock system filled with packets of ULF oscillations, broad-band intermittent fluctuations in the magnetosheath, ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail, and kinetic-scale fluctuations in the inner current sheet encountered at the outbound (dawn-side) magnetopause. Overall, our measurements indicate that the Hermean magnetosphere, as well as the surrounding region, are strongly affected by non-MHD effects introduced by finite sizes of cyclotron orbits of the constituting ion species. Physical mechanisms of these effects and their potentially critical impact on the structure and dynamics of Mercury's magnetic field remain to be understood.
Sahraoui, Fouad; Goldstein, Melvyn L.
2010-01-01
Over the past few decades, large-scales solar wind (SW) turbulence has been studied extensively, both theoretically and observationally. Observed power spectra of the low frequency turbulence, which can be described in the magnetohydrodynamic (MHD) limit, are shown to obey the Kolmogorov scaling, $k"{ -5/3 }$, down the local proton gyrofrequency ($C{ci} \\sim O.l$-Hz). Turbulence at frequencies above $C{ci}$ has not been thoroughly investigated and remains far less well understood. Above $C{ ci}$ the spectrum steepens to $\\sim f"{ -2.5}$ and a debate exists as to whether the turbulence has become dominated by dispersive kinetic Alfven waves (KA W) or by whistler waves, before it is dissipated at small scales, In a case study Sahraoui et al., PRL (2009) have reported the first direct determination of the dissipation range of solar wind turbulence near the electron gyroscale using the high resolution Cluster magnetic and electric field data (up to $10"2$-Hz in the spacecraft reference frame). Above the Doppler-shifted proton scale $C{\\rho i}$ a new inertial range with a scaling $\\sim f"{ -2.3}$ has been evidenced and shown to remarkably agree with theoretical predictions of a quasi-two-dimensional cascade into KA W turbulence. Here, we use a wider sample of data sets of small scale SW turbulence under different plasma conditions, and investigate under which physical criteria the KA W (or the whistler) turbulence may be observed to carry out the cascade at small scales, These new observations/criteria are compared to the predictions on the cascade and the (kinetic) dissipation from the Vlasov theory. Implications of the results on the heating problem of the solar wind will be discussed.
SOMAR-LES: A framework for multi-scale modeling of turbulent stratified oceanic flows
Chalamalla, Vamsi K.; Santilli, Edward; Scotti, Alberto; Jalali, Masoud; Sarkar, Sutanu
2017-12-01
A new multi-scale modeling technique, SOMAR-LES, is presented in this paper. Localized grid refinement gives SOMAR (the Stratified Ocean Model with Adaptive Resolution) access to small scales of the flow which are normally inaccessible to general circulation models (GCMs). SOMAR-LES drives a LES (Large Eddy Simulation) on SOMAR's finest grids, forced with large scale forcing from the coarser grids. Three-dimensional simulations of internal tide generation, propagation and scattering are performed to demonstrate this multi-scale modeling technique. In the case of internal tide generation at a two-dimensional bathymetry, SOMAR-LES is able to balance the baroclinic energy budget and accurately model turbulence losses at only 10% of the computational cost required by a non-adaptive solver running at SOMAR-LES's fine grid resolution. This relative cost is significantly reduced in situations with intermittent turbulence or where the location of the turbulence is not known a priori because SOMAR-LES does not require persistent, global, high resolution. To illustrate this point, we consider a three-dimensional bathymetry with grids adaptively refined along the tidally generated internal waves to capture remote mixing in regions of wave focusing. The computational cost in this case is found to be nearly 25 times smaller than that of a non-adaptive solver at comparable resolution. In the final test case, we consider the scattering of a mode-1 internal wave at an isolated two-dimensional and three-dimensional topography, and we compare the results with Legg (2014) numerical experiments. We find good agreement with theoretical estimates. SOMAR-LES is less dissipative than the closure scheme employed by Legg (2014) near the bathymetry. Depending on the flow configuration and resolution employed, a reduction of more than an order of magnitude in computational costs is expected, relative to traditional existing solvers.
Gorokhovski, Mikhael; Zamansky, Rémi
2018-03-01
Consistently with observations from recent experiments and DNS, we focus on the effects of strong velocity increments at small spatial scales for the simulation of the drag force on particles in high Reynolds number flows. In this paper, we decompose the instantaneous particle acceleration in its systematic and residual parts. The first part is given by the steady-drag force obtained from the large-scale energy-containing motions, explicitly resolved by the simulation, while the second denotes the random contribution due to small unresolved turbulent scales. This is in contrast with standard drag models in which the turbulent microstructures advected by the large-scale eddies are deemed to be filtered by the particle inertia. In our paper, the residual term is introduced as the particle acceleration conditionally averaged on the instantaneous dissipation rate along the particle path. The latter is modeled from a log-normal stochastic process with locally defined parameters obtained from the resolved field. The residual term is supplemented by an orientation model which is given by a random walk on the unit sphere. We propose specific models for particles with diameter smaller and larger size than the Kolmogorov scale. In the case of the small particles, the model is assessed by comparison with direct numerical simulation (DNS). Results showed that by introducing this modeling, the particle acceleration statistics from DNS is predicted fairly well, in contrast with the standard LES approach. For the particles bigger than the Kolmogorov scale, we propose a fluctuating particle response time, based on an eddy viscosity estimated at the particle scale. This model gives stretched tails of the particle acceleration distribution and dependence of its variance consistent with experiments.
Mininni, P D; Alexakis, A; Pouquet, A
2008-03-01
We analyze the data stemming from a forced incompressible hydrodynamic simulation on a grid of 2048(3) regularly spaced points, with a Taylor Reynolds number of R(lambda) ~ 1300. The forcing is given by the Taylor-Green vortex, which shares similarities with the von Kàrmàn flow used in several laboratory experiments; the computation is run for ten turnover times in the turbulent steady state. At this Reynolds number the anisotropic large scale flow pattern, the inertial range, the bottleneck, and the dissipative range are clearly visible, thus providing a good test case for the study of turbulence as it appears in nature. Triadic interactions, the locality of energy fluxes, and longitudinal structure functions of the velocity increments are computed. A comparison with runs at lower Reynolds numbers is performed and shows the emergence of scaling laws for the relative amplitude of local and nonlocal interactions in spectral space. Furthermore, the scaling of the Kolmogorov constant, and of skewness and flatness of velocity increments is consistent with previous experimental results. The accumulation of energy in the small scales associated with the bottleneck seems to occur on a span of wave numbers that is independent of the Reynolds number, possibly ruling out an inertial range explanation for it. Finally, intermittency exponents seem to depart from standard models at high R(lambda), leaving the interpretation of intermittency an open problem.
Scale dependence of the alignment between strain rate and rotation in turbulent shear flow
Fiscaletti, D.
2016-10-24
The scale dependence of the statistical alignment tendencies of the eigenvectors of the strain-rate tensor e(i), with the vorticity vector omega, is examined in the self-preserving region of a planar turbulent mixing layer. Data from a direct numerical simulation are filtered at various length scales and the probability density functions of the magnitude of the alignment cosines between the two unit vectors vertical bar e(i) . (omega) over cap vertical bar are examined. It is observed that the alignment tendencies are insensitive to the concurrent large-scale velocity fluctuations, but are quantitatively affected by the nature of the concurrent large-scale velocity-gradient fluctuations. It is confirmed that the small-scale (local) vorticity vector is preferentially aligned in parallel with the large-scale (background) extensive strain-rate eigenvector e(1), in contrast to the global tendency for omega to be aligned in parallelwith the intermediate strain-rate eigenvector [Hamlington et al., Phys. Fluids 20, 111703 (2008)]. When only data from regions of the flow that exhibit strong swirling are included, the so-called high-enstrophy worms, the alignment tendencies are exaggerated with respect to the global picture. These findings support the notion that the production of enstrophy, responsible for a net cascade of turbulent kinetic energy from large scales to small scales, is driven by vorticity stretching due to the preferential parallel alignment between omega and nonlocal e(1) and that the strongly swirling worms are kinematically significant to this process.
Power Spectra, Power Law Exponents, and Anisotropy of Solar Wind Turbulence at Small Scales
Podesta, J. J.; Roberts, D. A.; Goldstein, M. L.
2006-01-01
The Wind spacecraft provides simultaneous solar wind velocity and magnetic field measurements with 3- second time resolution, roughly an order of magnitude faster than previous measurements, enabling the small scale features of solar wind turbulence to be studied in unprecedented detail. Almost the entire inertial range can now be explored (the inertial range extends from approximately 1 to 10(exp 3) seconds in the spacecraft frame) although the dissipation range of the velocity fluctuations is still out of reach. Improved measurements of solar wind turbulence spectra at 1 AU in the ecliptic plane are presented including spectra of the energy and cross-helicity, the magnetic and kinetic energies, the Alfven ratio, the normalized cross-helicity, and the Elsasser ratio. Some recent observations and theoretical challenges are discussed including the observation that the velocity and magnetic field spectra often show different power law exponents with values close to 3/2 and 5/3, respectively; the energy (kinetic plus magnetic) and cross-helicity often have approximately equal power law exponents with values intermediate between 3/2 and 5/3; and the Alfven ratio, the ratio of the kinetic to magnetic energy spectra, is often a slowly increasing function of frequency increasing from around 0.4 to 1 for frequencies in the inertial range. Differences between high- and low-speed wind are also discussed. Comparisons with phenomenological turbulence theories show that important aspects of the physics are yet unexplained.
Bifurcation and phase diagram of turbulence constituted from three different scale-length modes
International Nuclear Information System (INIS)
Itoh, S.-I.; Kitazawa, A.; Yagi, M.; Itoh, K.
2002-04-01
Cases where three kinds of fluctuations having the different typical scale-lengths coexist are analyzed, and the statistical theory of strong turbulence in inhomogeneous plasmas is developed. Statistical nonlinear interactions between fluctuations are kept in the analysis as the renormalized drag, statistical noise and the averaged drive. The nonlinear interplay through them induces a quenching or suppressing effect, even if all the modes are unstable when they are analyzed independently. Variety in mode appearance takes place: one mode quenches the other two modes, or one mode is quenched by the other two modes, etc. The bifurcation of turbulence is analyzed and a phase diagram is drawn. Phase diagrams with cusp type catastrophe and butterfly type catastrophe are obtained. The subcritical bifurcation is possible to occur through the nonlinear interplay, even though each one is supercritical turbulence when analyzed independently. Analysis reveals that the nonlinear stability boundary (marginal point) and the amplitude of each mode may substantially shift from the conventional results of independent analyses. (author)
Energy spectrum scaling in an agent-based model for bacterial turbulence
Mikel-Stites, Maxwell; Staples, Anne
2017-11-01
Numerous models have been developed to examine the behavior of dense bacterial swarms and to explore the visually striking phenomena of bacterial turbulence. Most models directly impose fluid dynamics physics, either by modeling the active matter as a fluid or by including interactions between the bacteria and a fluid. In this work, however, the `turbulence' is solely an emergent property of the collective behavior of the bacterial population, rather than a consequence of imposed fluid dynamics physical modeling. The system is simulated using a two dimensional Vicsek-style model, with the addition of individual repulsion to simulate bacterial collisions and physical interactions, and without the common flocking or sensing behaviors. Initial results indicate the presence of k-1 scaling in a portion of the kinetic energy spectrum that can be considered analogous to the inertial subrange in turbulent energy spectra. This result suggests that the interaction of large numbers of individual active bacteria may also be a contributing factor in the emergence of fluid dynamics phenomena, in addition to the physical interactions between bacteria and their fluid environment.
International Nuclear Information System (INIS)
Ishizawa, A.; Nakajima, N.
2007-01-01
Micro-turbulence and macro-magnetohydrodynamic (macro-MHD) instabilities can appear in plasma at the same time and interact with each other in a plasma confinement. The multi-scale-nonlinear interaction among micro-turbulence, double tearing instability and zonal flow is investigated by numerically solving a reduced set of two-fluid equations. It is found that the double tearing instability, which is a macro-MHD instability, appears in an equilibrium formed by a balance between micro-turbulence and zonal flow when the double tearing mode is unstable. The roles of the nonlinear and linear terms of the equations in driving the zonal flow and coherent convective cell flow of the double tearing mode are examined. The Reynolds stress drives zonal flow and coherent convective cell flow, while the ion diamagnetic term and Maxwell stress oppose the Reynolds stress drive. When the double tearing mode grows, linear terms in the equations are dominant and they effectively release the free energy of the equilibrium current gradient
Reversing flow causes passive shark scale actuation in a separating turbulent boundary layer
Lang, Amy; Gemmell, Bradford; Motta, Phil; Habegger, Laura; Du Clos, Kevin; Devey, Sean; Stanley, Caleb; Santos, Leo
2017-11-01
Control of flow separation by shortfin mako skin in experiments has been demonstrated, but the mechanism is still poorly understood yet must be to some extent Re independent. The hypothesized mechanisms inherent in the shark skin for controlling flow separation are: (1) the scales, which are capable of being bristled only by reversing flow, inhibit flow reversal events from further development into larger-scale separation and (2) the cavities formed when scales bristle induces mixing of high momentum flow towards the wall thus energizing the flow close to the surface. Two studies were carried out to measure passive scale actuation caused by reversing flow. A small flow channel induced an unsteady, wake flow over the scales prompting reversing flow events and scale actuation. To resolve the flow and scale movements simultaneously we used specialized optics at high magnification (1 mm field of view) at 50,000 fps. In another study, 3D printed models of shark scales, or microflaps (bristling capability up to 50 degrees), were set into a flat plate. Using a tripped, turbulent boundary layer grown over the long flat plate and a localized adverse pressure gradient, a separation bubble was generated within which the microflaps were placed. Passive flow actuation of both shark scales and microflaps by reversing flow was observed. Funding from Army Research Office and NSF REU site Grant.
Onset and universality of turbulent drag reduction in von Karman swirling flow
Burnishev, Yuri; Steinberg, Victor
2012-10-01
We report the results of experiments on turbulent drag reduction (TDR) in swirling flow of water and water-sucrose polymer solutions, where Re and Wi as well as polymer concentration ϕ are varied. The friction coefficients Cf and Cp defined through average torque \\bar {\\Gamma } and rms of pressure fluctuations prms for different elasticity El = Wi/Re and ϕ vs. Re/Rec collapse onto universal curves in accord with theory, where Rec is Re at TDR onset. The transition lines to the TDR state, Rec - El and Rec - ϕ, are measured and relevant physics is discussed. Power spectra for Γ and p at Re/Rec > 1 show a drastic reduction of low-frequency noise and the emergence of a peak corresponding to the main vortex frequency in accord with TDR.
Experimental scaling law for the subcritical transition to turbulence in plane Poiseuille flow.
Lemoult, Grégoire; Aider, Jean-Luc; Wesfreid, José Eduardo
2012-02-01
We present an experimental study of the transition to turbulence in a plane Poiseuille flow. Using a well-controlled perturbation, we analyze the flow by using extensive particle image velocimetry and flow visualization (using laser-induced fluorescence) measurements, and use the deformation of the mean velocity profile as a criterion to characterize the state of the flow. From a large parametric study, four different states are defined, depending on the values of the Reynolds number and the amplitude of the perturbation. We discuss the role of coherent structures, such as hairpin vortices, in the transition. We find that the minimal amplitude of the perturbation triggering transition scales asymptotically as Re(-1).
Large- and small-scale turbulent spectra in MHD and atmospheric flows
Directory of Open Access Journals (Sweden)
O. G. Chkhetiani
2006-01-01
Full Text Available In the present review we discuss certain studies of large- and small-scale turbulent spectra in MHD and atmospheric flows performed by S. S. Moiseev and his co-authors during the last years of his life and continued by his co-authors after he passed away. It is shown that many ideas developed in these works have not lost their novelty and urgency until now, and can form the basis of future studies in this field.
Correlations at large scales and the onset of turbulence in the fast solar wind
International Nuclear Information System (INIS)
Wicks, R. T.; Roberts, D. A.; Mallet, A.; Schekochihin, A. A.; Horbury, T. S.; Chen, C. H. K.
2013-01-01
We show that the scaling of structure functions of magnetic and velocity fields in a mostly highly Alfvénic fast solar wind stream depends strongly on the joint distribution of the dimensionless measures of cross helicity and residual energy. Already at very low frequencies, fluctuations that are both more balanced (cross helicity ∼0) and equipartitioned (residual energy ∼0) have steep structure functions reminiscent of 'turbulent' scalings usually associated with the inertial range. Fluctuations that are magnetically dominated (residual energy ∼–1), and so have closely anti-aligned Elsasser-field vectors, or are imbalanced (cross helicity ∼1), and so have closely aligned magnetic and velocity vectors, have wide '1/f' ranges typical of fast solar wind. We conclude that the strength of nonlinear interactions of individual fluctuations within a stream, diagnosed by the degree of correlation in direction and magnitude of magnetic and velocity fluctuations, determines the extent of the 1/f region observed, and thus the onset scale for the turbulent cascade.
Magnetic Reconnection May Control the Ion-scale Spectral Break of Solar Wind Turbulence
Vech, Daniel; Mallet, Alfred; Klein, Kristopher G.; Kasper, Justin C.
2018-03-01
The power spectral density of magnetic fluctuations in the solar wind exhibits several power-law-like frequency ranges with a well-defined break between approximately 0.1 and 1 Hz in the spacecraft frame. The exact dependence of this break scale on solar wind parameters has been extensively studied but is not yet fully understood. Recent studies have suggested that reconnection may induce a break in the spectrum at a “disruption scale” {λ }{{D}}, which may be larger than the fundamental ion kinetic scales, producing an unusually steep spectrum just below the break. We present a statistical investigation of the dependence of the break scale on the proton gyroradius ρ i , ion inertial length d i , ion sound radius ρ s , proton–cyclotron resonance scale ρ c , and disruption scale {λ }{{D}} as a function of {β }\\perp i. We find that the steepest spectral indices of the dissipation range occur when β e is in the range of 0.1–1 and the break scale is only slightly larger than the ion sound scale (a situation occurring 41% of the time at 1 au), in qualitative agreement with the reconnection model. In this range, the break scale shows a remarkably good correlation with {λ }{{D}}. Our findings suggest that, at least at low β e , reconnection may play an important role in the development of the dissipation range turbulent cascade and cause unusually steep (steeper than ‑3) spectral indices.
DEFF Research Database (Denmark)
Kiørboe, Thomas; MacKenzie, Brian
1995-01-01
Turbulent water motion has several effects on the feeding ecology of larval fish and other planktivorous predators. In this paper, we consider the appropriate spatial scales for estimating relative velocities between larval fish predators and their prey, and the effect that different choices of s...... in the range in which turbulent intensity has an overall positive effect on larval fish ingestion rate probability. However, experimental data to test the model predictions are lacking. We suggest that the model inputs require further empirical study....
Energy Technology Data Exchange (ETDEWEB)
Pinson, F
2006-03-15
- This work deals with the macroscopic modeling of turbulence in porous media. It concerns heat exchangers, nuclear reactors as well as urban flows, etc. The objective of this study is to describe in an homogenized way, by the mean of a spatial average operator, turbulent flows in a solid matrix. In addition to this first operator, the use of a statistical average operator permits to handle the pseudo-aleatory character of turbulence. The successive application of both operators allows us to derive the balance equations of the kind of flows under study. Two major issues are then highlighted, the modeling of dispersion induced by the solid matrix and the turbulence modeling at a macroscopic scale (Reynolds tensor and turbulent dispersion). To this aim, we lean on the local modeling of turbulence and more precisely on the k - {epsilon} RANS models. The methodology of dispersion study, derived thanks to the volume averaging theory, is extended to turbulent flows. Its application includes the simulation, at a microscopic scale, of turbulent flows within a representative elementary volume of the porous media. Applied to channel flows, this analysis shows that even within the turbulent regime, dispersion remains one of the dominating phenomena within the macro-scale modeling framework. A two-scale analysis of the flow allows us to understand the dominating role of the drag force in the kinetic energy transfers between scales. Transfers between the mean part and the turbulent part of the flow are formally derived. This description significantly improves our understanding of the issue of macroscopic modeling of turbulence and leads us to define the sub-filter production and the wake dissipation. A
Turbulent cascade in the solar wind at kinetic scales and quasi-parallel whistler waves
Alexandrova, O.; Lacombe, C.; Mangeney, A.; Grappin, R.; Maksimovic, M.; Matteini, L.; Santolik, O.; Cornilleau-Wehrlin, N.; de Conchy, Y.
2014-12-01
The nature of the magnetic field fluctuations in the solar wind between the ion and electron scales is still under debate. Using the Cluster/STAFF instrument, we make a survey of the power spectral density and of the polarization of these fluctuations at frequencies 1-400 Hz, during five years (2001-2005) when Cluster was in the free solar wind, i.e. not magnetically connected to the Earth's bow-shock.In most of the analyzed time intervals, the fluctuations are non-polarized and they have a general spectral shape between the ion scales and a fraction of electron scales. The intensity of these spectra is well correlated to the ion thermal pressure. These non-polarized fluctuations seem to have a negligible frequency in the solar wind frame, and a wavevector anisotropy kperp>>k||. In the rest ~10% of the selected data, we observe narrow-band, right-handed, circularly polarized fluctuations, with wave vectors quasi-parallel to the mean magnetic field, superimposed on the spectrum of the permanent background turbulence. We interpret these coherent fluctuations as whistler mode waves. The life time of such waves varies between a few seconds and several hours. We analyze in details the long-lived whistler waves, i.e. with a life time longer than five minutes. We find several conditions for the appearance of such waves: (1) a low level of the background turbulence; (2) a low ion thermal pressure; (3) a slow solar wind speed; (4) an electron heat flux Qe>4μW/m2; (5) an electron mean free path larger than 0.5 AU, i.e., a low collisional frequency; (6) a change in the magnetic field direction. When the level of the background turbulence is high, we cannot affirm that whistler waves do not exist: they can be just masked by the turbulence. The six above conditions for the presence of parallel whistlers in the free solar wind are necessary but are not sufficient. When the electron parallel beta factor βe is larger than 3, the whistler waves are seen along the heat flux
Can one detect small-scale turbulence from standard meteorological radiosondes?
Directory of Open Access Journals (Sweden)
R. Wilson
2011-05-01
Full Text Available It has been recently proposed by Clayson and Kantha (2008 to evaluate the climatology of atmospheric turbulence through the detection of overturns in the free atmosphere by applying a Thorpe analysis on relatively low vertical resolution (LR profiles collected from standard radiosoundings. Since then, several studies based on this idea have been published. However, the impact of instrumental noise on the detection of turbulent layers was completely ignored in these works. The present study aims to evaluate the feasibility of overturns detection from radiosoundings. For this purpose, we analyzed data of two field campaigns during which high-resolution (HR soundings (10–20 cm were performed simultaneously with standard LR soundings. We used the raw data of standard meteorological radiosondes, the vertical resolution ranging from 5 to 9 m.
A Thorpe analysis was applied to both LR and HR potential temperature profiles. A denoising procedure was first applied in order to reduce the probability of occurrence of artificial overturns, i.e. potential temperature inversions due to instrumental noise only. We then compared the empirical probability density functions (pdf of the sizes of the selected overturns from LR and HR profiles.
From HR profiles measured in the troposphere, the sizes of the detected overturns range from 4 to ~1000 m. The shape of the size pdf of overturns is found to sharply decrease with increasing scales. From LR profiles, the smallest size of detected overturns is ~32 m, a similar decrease in the shape of the pdf of sizes being observed. These results suggest that overturns, resulting either from small-scale turbulence or from instabilities, can indeed be detected from meteorological radiosonde measurements in the troposphere and in the stratosphere as well. However they are rather rare as they belong to the tail of the size distribution of overturns: they only represent the 7 % largest events in the troposphere
Nickelsen, Daniel
2017-01-01
We derive the Markov process equivalent to She-Leveque scaling in homogeneous and isotropic turbulence. The Markov process is a jump process for velocity increments $u(r)$ in scale $r$ in which the jumps occur randomly but with deterministic width in $u$. From its master equation we establish a prescription to simulate the She-Leveque process and compare it with Kolmogorov scaling. To put the She-Leveque process into the context of other established turbulence models on the Markov level, we d...
Modification of large-scale motions in a turbulent pipe flow
Senshu, Kohei; Shinozaki, Hiroaki; Sakakibara, Jun
2017-11-01
We performed experiments to modify the flow structures in a fully developed turbulent flow in a straight round pipe. The modification of the flow was achieved by installing a short coaxial inner pipe. The inner pipe has ability to add continuous suction or blowing disturbance through its outer surface. The experiments were conducted at a Reynolds number of 44,000 with seven different disturbance patterns. The wall static pressure was measured and pipe friction coefficient was evaluated. The velocity distribution was measured with PIV and very large scale motions (VLSMs) were visualized. Pipe friction coefficient was increased by installing the inner pipe, while turbulence intensities over the cross section were reduced. Slight change of the friction was observed if the disturbance was added. We decomposed fluctuating velocity field in the azimuthal direction by a Fourier series expansion. As a result, we obtained that contribution of lower azimuthal mode numbers (m = 2, 3, 4) reduced while the higher modes increased. This was consistent with the observation of visualized very large scale motions.
International Nuclear Information System (INIS)
Li Feng-Chen; Wang Lu; Cai Wei-Hua
2015-01-01
A mixed subgrid-scale (SGS) model based on coherent structures and temporal approximate deconvolution (MCT) is proposed for turbulent drag-reducing flows of viscoelastic fluids. The main idea of the MCT SGS model is to perform spatial filtering for the momentum equation and temporal filtering for the conformation tensor transport equation of turbulent flow of viscoelastic fluid, respectively. The MCT model is suitable for large eddy simulation (LES) of turbulent drag-reducing flows of viscoelastic fluids in engineering applications since the model parameters can be easily obtained. The LES of forced homogeneous isotropic turbulence (FHIT) with polymer additives and turbulent channel flow with surfactant additives based on MCT SGS model shows excellent agreements with direct numerical simulation (DNS) results. Compared with the LES results using the temporal approximate deconvolution model (TADM) for FHIT with polymer additives, this mixed SGS model MCT behaves better, regarding the enhancement of calculating parameters such as the Reynolds number. For scientific and engineering research, turbulent flows at high Reynolds numbers are expected, so the MCT model can be a more suitable model for the LES of turbulent drag-reducing flows of viscoelastic fluid with polymer or surfactant additives. (paper)
New Methods of Presenting Scale the Universe Concepts
Adkins, J.
2012-12-01
Traditional scale of the universe activities involve building a scale model solar system, expressing distances in light travel time, and doing powers-of-ten animations. Free NASA materials will provide a sorting/ordering activity to teach this concept in a different way and at the same time introduce vocabulary and concepts involving some of the most distant objects in the universe. In addition, the author has used two novel methods of teaching universe scaling concepts: using a video of a drive representing the distance to a nearby star translates the distance concept into a more personal time-based experience, and a new version of a scale the universe powerpoint that uses power-of-1000 slides to compress each view of the universe into a single pixel of the next slide to help visualize the vast scales encompassing the universe and how far humanity's influence actually extends. Free NASA materials. Presented by NASA Fermi Education Ambassador.
Two-scale correlation and energy cascade in three-dimensional turbulent flows
International Nuclear Information System (INIS)
Huang, Y X; Schmitt, F G; Gagne, Y
2014-01-01
In this paper, we propose a high-order harmonic-free methodology, namely arbitrary-order Hilbert spectral analysis, to estimate the two-scale correlation (TSC). When applied to fully developed turbulent velocity, we find that the scale-dependent Hilbert energy satisfies a lognormal distribution on both the inertial and dissipation ranges. The maximum probability density function of the logarithm of the Hilbert energy obeys a power law with a scaling exponent γ ≃ 0.33 in the inertial range. For the measured TSC, we observe a logarithmic correlation law with an experimental exponent α ≃ 0.37 on both the inertial and dissipation ranges. The correlation itself is found to be self-similar with respect to the distance between the two considered scales and a central frequency ω c in the logarithm space. An empirical nonlinear and nonlocal triad-scale interaction formula is proposed to describe the observed TSC. This triadic interaction can be interpreted as experimental evidence of a small-scale nonlinear and nonlocal coupling inside the self-similarity of the Richardson–Kolmogorov phenomenological cascade picture. (paper)
Universal geometrical scaling of the elliptic flow
Directory of Open Access Journals (Sweden)
Andrés C.
2015-01-01
Full Text Available The presence of scaling variables in experimental observables provide very valuable indications of the dynamics underlying a given physical process. In the last years, the search for geometric scaling, that is the presence of a scaling variable which encodes all geometrical information of the collision as well as other external quantities as the total energy, has been very active. This is motivated, in part, for being one of the genuine predictions of the Color Glass Condensate formalism for saturation of partonic densities. Here we extend these previous findings to the case of experimental data on elliptic flow. We find an excellent scaling for all centralities and energies, from RHIC to LHC, with a simple generalization of the scaling previously found for other observables and systems. Interestingly, the case of the photons, difficult to reconcile in most formalisms, nicely fit the scaling curve. We discuss on the possible interpretations of this finding in terms of initial or final state effects.
Hill, Jon; Piggott, M. D.; Ham, David A.; Popova, E. E.; Srokosz, M. A.
2012-10-01
Research into the use of unstructured mesh methods for ocean modelling has been growing steadily in the last few years. One advantage of using unstructured meshes is that one can concentrate resolution where it is needed. In addition, dynamic adaptive mesh optimisation (DAMO) strategies allow resolution to be concentrated when this is required. Despite the advantage that DAMO gives in terms of improving the spatial resolution where and when required, small-scale turbulence in the oceans still requires parameterisation. A two-equation, generic length scale (GLS) turbulence model (one equation for turbulent kinetic energy and another for a generic turbulence length-scale quantity) adds this parameterisation and can be used in conjunction with adaptive mesh techniques. In this paper, an implementation of the GLS turbulence parameterisation is detailed in a non-hydrostatic, finite-element, unstructured mesh ocean model, Fluidity-ICOM. The implementation is validated by comparing to both a laboratory-scale experiment and real-world observations, on both fixed and adaptive meshes. The model performs well, matching laboratory and observed data, with resolution being adjusted as necessary by DAMO. Flexibility in the prognostic fields used to construct the error metric used in DAMO is required to ensure best performance. Moreover, the adaptive mesh models perform as well as fixed mesh models in terms of root mean square error to observation or theoretical mixed layer depths, but uses fewer elements and hence has a reduced computational cost.
International Nuclear Information System (INIS)
Horton, W.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates
Turbulent pipe flow at extreme Reynolds numbers.
Hultmark, M; Vallikivi, M; Bailey, S C C; Smits, A J
2012-03-02
Both the inherent intractability and complex beauty of turbulence reside in its large range of physical and temporal scales. This range of scales is captured by the Reynolds number, which in nature and in many engineering applications can be as large as 10(5)-10(6). Here, we report turbulence measurements over an unprecedented range of Reynolds numbers using a unique combination of a high-pressure air facility and a new nanoscale anemometry probe. The results reveal previously unknown universal scaling behavior for the turbulent velocity fluctuations, which is remarkably similar to the well-known scaling behavior of the mean velocity distribution.
1983-09-01
Shook Spray modelling in high turbulent swirling flow n.r. M.M. Elkotb, O.M.F. Elbahar, M.M.M. Abou-Ellail A two-equation turbulence model for two...energy evaluated by the following equation,0.1 -- "/U .. cc 15V3u / at9 u" The magnitude of the micro scale is o.3 0.7 roughly 1/3 times to the integral...adiabatic in which case the enthalpy is, for the 1= in spray flames (27) and in gaseous ones, as in the above specified reaction model, a linear function of
Ion-Scale Spectral Break in the Normal Plasma Beta Range in the Solar Wind Turbulence
Wang, X.; Tu, C.-Y.; He, J.-S.; Wang, L.-H.
2018-01-01
The spectral break (fb) of magnetic fluctuations at the ion scale in the solar wind is considered to give important clue on the turbulence dissipation mechanism. Among several possible mechanisms, the most notable two are related respectively to proton thermal gyroradius ρi and proton inertial length di. The corresponding frequencies of them are fρi=VSW/(2πρi) and fdi=VSW/(2πdi), respectively, where VSW is the solar wind speed. However, no definite conclusion has been given for which one is more reasonable because the two parameters have similar value when plasma beta β ˜ 1. Here we do a statistical study to see if the two ratios fb/fρi and fb/fdi have different dependence on β in the solar wind turbulence with 0.1 fdi is statistically not dependent on β, and the average value of it is 0.48 ± 0.06. However, fb/fρi increases with increasing β clearly and is significantly smaller than fb/fdi when β fdi, and the influence of β could be negligible in the studied β range. It indicates a preference of the dissipation mechanism associated with di in the solar wind with 0.1 < β < 0.8. Further theoretical studies are needed to give detailed explanation.
Buaria, D.; Yeung, P. K.
2017-12-01
A new parallel algorithm utilizing a partitioned global address space (PGAS) programming model to achieve high scalability is reported for particle tracking in direct numerical simulations of turbulent fluid flow. The work is motivated by the desire to obtain Lagrangian information necessary for the study of turbulent dispersion at the largest problem sizes feasible on current and next-generation multi-petaflop supercomputers. A large population of fluid particles is distributed among parallel processes dynamically, based on instantaneous particle positions such that all of the interpolation information needed for each particle is available either locally on its host process or neighboring processes holding adjacent sub-domains of the velocity field. With cubic splines as the preferred interpolation method, the new algorithm is designed to minimize the need for communication, by transferring between adjacent processes only those spline coefficients determined to be necessary for specific particles. This transfer is implemented very efficiently as a one-sided communication, using Co-Array Fortran (CAF) features which facilitate small data movements between different local partitions of a large global array. The cost of monitoring transfer of particle properties between adjacent processes for particles migrating across sub-domain boundaries is found to be small. Detailed benchmarks are obtained on the Cray petascale supercomputer Blue Waters at the University of Illinois, Urbana-Champaign. For operations on the particles in a 81923 simulation (0.55 trillion grid points) on 262,144 Cray XE6 cores, the new algorithm is found to be orders of magnitude faster relative to a prior algorithm in which each particle is tracked by the same parallel process at all times. This large speedup reduces the additional cost of tracking of order 300 million particles to just over 50% of the cost of computing the Eulerian velocity field at this scale. Improving support of PGAS models on
Zhou, Bowen; Xue, Ming; Zhu, Kefeng
2017-04-01
Compared to the representation of vertical turbulent mixing through various PBL schemes, the treatment of horizontal turbulence mixing in the boundary layer within mesoscale models, with O(10) km horizontal grid spacing, has received much less attention. In mesoscale models, subgrid-scale horizontal fluxes most often adopt the gradient-diffusion assumption. The horizontal mixing coefficients are usually set to a constant, or through the 2D Smagorinsky formulation, or in some cases based on the 1.5-order turbulence kinetic energy (TKE) closure. In this work, horizontal turbulent mixing parameterizations using physically based characteristic velocity and length scales are proposed for the convective boundary layer based on analysis of a well-resolved, wide-domain large-eddy simulation (LES). The proposed schemes involve different levels of sophistication. The first two schemes can be used together with first-order PBL schemes, while the third uses TKE to define its characteristic velocity scale and can be used together with TKE-based higher-order PBL schemes. The current horizontal mixing formulations are also assessed a priori through the filtered LES results to illustrate their limitations. The proposed parameterizations are tested a posteriori in idealized simulations of turbulent dispersion of a passive scalar. Comparisons show improved horizontal dispersion by the proposed schemes, and further demonstrate the weakness of the current schemes.
Scaling and universality in two dimensions
DEFF Research Database (Denmark)
Bellotti, Filipe Furlan; Frederico, T.; Yamashita, M. T.
2011-01-01
The momentum space zero-range model is used to investigate universal properties of three interacting particles confined to two dimensions. The pertinent equations are first formulated for a system of two identical and one distinct particle and the two different two-body subsystems are characterized...
Similarity and Scaling of Turbulent Flame Speeds for Expanding Premixed Flames of C4-C8 n -alkanes
Wu, Fujia; Saha, Abhishek; Chaudhuri, Swetaprovo; Yang, Sheng; Law, Chung K.
2013-11-01
We experimentally investigated the propagation speed of constant-pressure expanding flames in near isotropic turbulence using a dual-chamber, fan-stirred vessel. The motivation is to test whether the fuel similarity concept among C4-C8 n-alkanes on laminar flames also holds for turbulent flames. Previously it was found that the laminar flame speed and Markstein length are almost identical for C4-C8 n-alkanes. If this fuel similarity concept can also be shown for turbulent flames, it will suggest a canonical flame structure for large hydrocarbon fuels, i . e . , large fuels always decompose to small C0-C4 fuel fragments before being oxidized, and would significantly simplify the description of the flames. Preliminary results show that in the flamelet and thin-reaction zone, turbulent flame speeds of C4-C8 n-alkanes are indeed largely similar at various conditions, thereby suggesting the fuel similarity for turbulent flames. In addition, it is found that the normalized turbulent flame speed also approximately scales with the square root of an appropriately-defined Reynolds number recently found for C0-C4 fuels. This work was supported by the AFOSR under the technical monitoring of Dr. Chiping Li.
Kadum, Hawwa; Rockel, Stanislav; Holling, Michael; Peinke, Joachim; Cal, Raul Bayon
2017-11-01
The wake behind a floating model horizontal axis wind turbine during pitch motion is investigated and compared to a fixed wind turbine wake. An experiment is conducted in an acoustic wind tunnel where hot-wire data are acquired at five downstream locations. At each downstream location, a rake of 16 hot-wires was used with placement of the probes increasing radially in the vertical, horizontal, and diagonally at 45 deg. In addition, the effect of turbulence intensity on the floating wake is examined by subjecting the wind turbine to different inflow conditions controlled through three settings in the wind tunnel grid, a passive and two active protocols, thus varying in intensity. The wakes are inspected by statistics of the point measurements, where the various length/time scales are considered. The wake characteristics for a floating wind turbine are compared to a fixed turbine, and uncovering its features; relevant as the demand for exploiting deep waters in wind energy is increasing.
New insights into sub-ion scale turbulence in Earth's magnetosheath using MMS data
Breuillard, Hugo; Andriopoulou, Maria; Graham, Daniel; Le Contel, Olivier; Huang, Shiyong; Hadid, Lina; Sahraoui, Fouad; Alexandrova, Olga; Berthomier, Matthieu; Retino, Alessandro; Nakamura, Rumi; Baumjohann, Wolfgang
2017-04-01
On January 22nd 2016, MMS was located in Earth's magnetosheath and detected intense lion roars showing a secondary bandwidth. Detailed polarization analysis, using burst data from SCM and EDP instruments, and numerical simulation, using WHAMP, are performed in this study. They show that these mainly perpendicular fluctuations are highly nonlinear whistler wave packets, and that a high sampling rate is needed to pick up the peaks of the signal. As a result, their amplitude might have been underestimated in previous missions such as Cluster, which can have a significant impact on electron dynamics. Using FPI burst data, we show that electron velocity distribution functions exhibit a gyrophase-bunched signature in the presence of these lion roars. The analysis of magnetic and density fluctuations, inferred from spacecraft potential, also show the highly-compressible nature of turbulence up to electron scales.
Guala, Michele; Chamorro, Leonardo P.
2011-11-01
Turbulent boundary layer measurements in wind tunnels and in the near neutral atmospheric surface layer outlined a significant contribution of the large scale motions to turbulent kinetic energy and Reynolds stresses for a wide range of Reynolds number, providing evidence of complex scale interactions across the wall region. In order to understand the effect of the large scales on the near wall turbulence and extend the predictive models of amplitude modulation to more realistic atmospheric conditions, different thermal stability conditions must be explored. In this study, experiments are performed in the atmospheric wind tunnel of the St. Anthony Falls Laboratory independently controlling air flow and floor temperatures. Measurements of fluctuating temperature simultaneously with the streamwise and wall normal velocity components are obtained with an ad hoc calibrated and customized triple-wire sensor. Scaling quantities and the dominant terms in the turbulent kinetic energy and temperature variance budget equations are estimated and discussed. A comparative analysis of the weakly stable, convective and neutral conditions based on the power spectra of the streamwise, wall normal and Reynolds stress contributions is presented. Appreciable differences in the energetic contributions of the large scales were observed.
Zhong, J.Q.; Sterl, S.H.; Li, H.M.
2015-01-01
We present measurements of the azimuthal rotation velocity $\\dot{{\\it\\theta}}(t)$θ˙(t) and thermal amplitude ${\\it\\delta}(t)$δ(t) of the large-scale circulation in turbulent Rayleigh–Bénard convection with modulated rotation. Both $\\dot{{\\it\\theta}}(t)$θ˙(t) and ${\\it\\delta}(t)$δ(t) exhibit clear
Energy Technology Data Exchange (ETDEWEB)
Bogenschutz, Peter [National Center for Atmospheric Research, Boulder, CO (United States); Moeng, Chin-Hoh [National Center for Atmospheric Research, Boulder, CO (United States)
2015-10-13
The PI’s at the National Center for Atmospheric Research (NCAR), Chin-Hoh Moeng and Peter Bogenschutz, have primarily focused their time on the implementation of the Simplified-Higher Order Turbulence Closure (SHOC; Bogenschutz and Krueger 2013) to the Multi-scale Modeling Framework (MMF) global model and testing of SHOC on deep convective cloud regimes.
Felder, Stefan; Chanson, Hubert
2009-07-01
In high-velocity free-surface flows, air entrainment is common through the interface, and intense interactions take place between turbulent structures and entrained bubbles. Two-phase flow properties were measured herein in high-velocity open channel flows above a stepped chute. Detailed turbulence measurements were conducted in a large-size facility, and a comparative analysis was applied to test the validity of the Froude and Reynolds similarities. The results showed consistently that the Froude similitude was not satisfied using a 2:1 geometric scaling ratio. Lesser number of entrained bubbles and comparatively greater bubble sizes were observed at the smaller Reynolds numbers, as well as lower turbulence levels and larger turbulent length and time scales. The results implied that small-size models did underestimate the rate of energy dissipation and the aeration efficiency of prototype stepped spillways for similar flow conditions. Similarly a Reynolds similitude was tested. The results showed also some significant scale effects. However a number of self-similar relationships remained invariant under changes of scale and confirmed the analysis of Chanson and Carosi (Exp Fluids 42:385-401, 2007). The finding is significant because self-similarity may provide a picture general enough to be used to characterise the air-water flow field in large prototype channels.
Ghannam, Khaled
The atmospheric boundary-layer is the lowest 500-2000 m of the Earth's atmosphere where much of human life and ecosystem services reside. This layer responds to land surface (e.g. buoyancy and roughness elements) and slowly evolving free tropospheric (e.g. temperature and humidity lapse rates) conditions that arguably mediate and modulate biosphere-atmosphere interactions. Such response often results in spatially- and temporally-rich turbulence scales that continue to be the subject of inquiry given their significance to a plethora of applications in environmental sciences and engineering. The work here addresses key aspects of boundary layer turbulence with a focus on the role of roughness elements (vegetation canopies) and buoyancy (surface heating) in modifying the well-studied picture of shear-dominated wall-bounded turbulence. A combination of laboratory channel experiments, field experiments, and numerical simulations are used to explore three distinct aspects of boundary layer turbulence. These are: • The concept of ergodicity in turbulence statistics within canopies: It has been long-recognized that homogeneous and stationary turbulence is ergodic, but less is known about the effects of inhomogeneity introduced by the presence of canopies on the turbulence statistics. A high resolution (temporal and spatial) flume experiment is used here to test the convergence of the time statistics of turbulent scalar concentrations to their ensemble (spatio-temporal) counterpart. The findings indicate that within-canopy scalar statistics have a tendency to be ergodic, mostly in shallow layers (close to canopy top) where the sweeping flow events appear to randomize the statistics. Deeper layers within the canopy are dominated by low-dimensional (quasi-deterministic) von Karman vortices that tend to break ergodicity. • Scaling laws of turbulent velocity spectra and structure functions in near-surface atmospheric turbulence: the existence of a logarithmic scaling in the
LITOS – a new balloon-borne instrument for fine-scale turbulence soundings in the stratosphere
Directory of Open Access Journals (Sweden)
A. Theuerkauf
2011-01-01
Full Text Available We have developed a new compact balloon payload called LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere for high resolution wind turbulence soundings in the stratosphere up to 35 km altitude. The wind measurements are performed using a constant temperature anemometer (CTA with a vertical resolution of ~2.5 mm, i.e. 2 kHz sampling rate at 5 m/s ascent speed. Thereby, for the first time, it is possible to study the entire turbulence spectrum down to the viscous subrange in the stratosphere. Including telemetry, housekeeping, batteries and recovery unit, the payload weighs less than 5 kg and can be launched from any radiosonde station. Since autumn 2007, LITOS has been successfully launched several times from the Leibniz-Institute of Atmospheric Physics (IAP in Kühlungsborn, Germany (54° N, 12° E. Two additional soundings were carried out in 2008 and 2009 in Kiruna, Sweden (67° N, 21° E as part of the BEXUS program (Balloon-borne EXperiments for University Students. We describe here the basic principle of CTA measurements and prove the validity of this method in the stratosphere. A first case study allows a clear distinction between non-turbulent regions and a turbulent layer with a thickness of some tens of meters. Since our measurements cover the transition between the inertial and viscous subrange, energy dissipation rates can be calculated with high reliability.
Kokmanian, Katherine; Duvvuri, Subrahmanyam; Hultmark, Marcus
2017-11-01
Nano-Scale Thermal Anemometry Probes (NSTAP) have been designed, tested and used in a wide variety of incompressible flows. These sensors are capable of measuring streamwise velocity fluctuations with an order of magnitude better resolution, both temporal and spatial, compared to conventional hot-wires, due to their miniature size and minute thermal mass (the heating element is only 60 microns long, 2 microns wide and 100 nm thick). Here we report recent efforts to redesign the NSTAP to withstand supersonic flow conditions. Work has been performed in Princeton's micro-nano fabrication laboratory in order to modify both the 2D layout and the 3D shapes of these sensors. The supersonic version of the NSTAP is evaluated in collaboration with Bundeswehr University. The ultimate objective of this work is to measure both fluctuating mass flow rate and total temperature in compressible turbulent boundary layers, by combining two supersonic sensors which operate at different overheat ratios. AFOSR FA9550-16-1-0170 (Program manager: Ivett Leyva).
Turbulence scaling study in an MHD wind tunnel on the Swarthmore Spheromak Experiment
Schaffner, D. A.; Brown, M. R.; Wan, A.
2013-12-01
The turbulence of colliding plasmas is explored in an MHD wind tunnel on the SSX in an effort to understand solar wind physics in a laboratory setting. Fully ionized hydrogen plasma is produced by two plasma guns on opposite sides of a 1m by 15cm copper cylinder creating plasma with L/ρi ~ 75-150, β ~ 0.1-0.2 and Lundquist number ~ 1000. Modification of B-field, Ti and β are made through stuffing flux variation of the plasma guns. Presented here are turbulent f-/k-spectra and correlation times and lengths of B-field fluctuations as measured by a 16 channel B-dot radial probe array at the chamber midplane using both FFT and wavelet analysis techniques. Power-law behavior is observed spanning about two decades of frequencies [100kHz-10MHz] and about one decade of wavelength [10cm-1cm]. Power-law fits to spectra show scaling in these regions to be robust to changes in stuffing flux; fits are on the order of f-4 and k-2 for all flux variations. Low frequency fluctuations [law behavior is seen in f-spectra for frequencies around f=fci while changes in k-spectra slopes appear around 1/k ~ 5ρi. Dissipation range fits are made with an exponentially modified power-law model [Terry et al, PoP 2012]. Fluctuation measurements in axial velocity are made using a Mach probe with edge flows reaching M ~ 0.4. Both B-field and velocity fluctuations persist on the same timescale in these experiments, though Mach velocity f-spectra show power-laws slightly shallower than those for B-field. Comparison of spectra from MHD and Hall MHD simulations of SSX performed within the HiFi modeling framework are made to the experimental results.
International Nuclear Information System (INIS)
Lee, Gonghee; Bang, Youngseok; Woo, Swengwoong; Kim, Dohyeong; Kang, Minku
2013-01-01
The types of errors in CFD simulation can be divided into the two main categories: numerical errors and model errors. Turbulence model is one of the important sources for model errors. In this study, in order to assess the prediction performance of Reynolds-averaged Navier-Stokes (RANS)-based two equations turbulence models for the analysis of flow distribution inside a 1/5 scale-down APR+, the simulation was conducted with the commercial CFD software, ANSYS CFX V. 14. In this study, in order to assess the prediction performance of turbulence models for the analysis of flow distribution inside a 1/5 scale-down APR+, the simulation was conducted with the commercial CFD software, ANSYS CFX V. 14. Both standard k-ε model and SST model predicted the similar flow pattern inside reactor. Therefore it was concluded that the prediction performance of both turbulence models was nearly same. Complex thermal-hydraulic characteristics exist inside reactor because the reactor internals consist of fuel assembly, control rod assembly, and the internal structures. Either flow distribution test for the scale-down reactor model or computational fluid dynamics (CFD) simulation have been conducted to understand these complex thermal-hydraulic features inside reactor
Turbulence Profiles and Outer Length Scale Determination in the Atmosphere Using Balloons
National Research Council Canada - National Science Library
Holdaway, Aaron
2000-01-01
Turbulence in the atmosphere drives the formation of temperature inhomogeneities that scatter and diffract propagating electromagnetic waves, adversely affecting laser weapons and high-resolution optical systems...
Kinetic turbulence simulations at extreme scale on leadership-class systems
Energy Technology Data Exchange (ETDEWEB)
Wang, Bei [Princeton Univ., Princeton, NJ (United States); Ethier, Stephane [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Tang, William [Princeton Univ., Princeton, NJ (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Williams, Timothy [Argonne National Lab. (ANL), Argonne, IL (United States); Ibrahim, Khaled Z. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Madduri, Kamesh [The Pennsylvania State Univ., University Park, PA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Williams, Samuel [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Oliker, Leonid [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2013-01-01
Reliable predictive simulation capability addressing confinement properties in magnetically confined fusion plasmas is critically-important for ITER, a 20 billion dollar international burning plasma device under construction in France. The complex study of kinetic turbulence, which can severely limit the energy confinement and impact the economic viability of fusion systems, requires simulations at extreme scale for such an unprecedented device size. Our newly optimized, global, ab initio particle-in-cell code solving the nonlinear equations underlying gyrokinetic theory achieves excellent performance with respect to "time to solution" at the full capacity of the IBM Blue Gene/Q on 786,432 cores of Mira at ALCF and recently of the 1,572,864 cores of Sequoia at LLNL. Recent multithreading and domain decomposition optimizations in the new GTC-P code represent critically important software advances for modern, low memory per core systems by enabling routine simulations at unprecedented size (130 million grid points ITER-scale) and resolution (65 billion particles).
International Nuclear Information System (INIS)
Tokgoz, S; Elsinga, G E; Delfos, R; Westerweel, J
2011-01-01
The effect of flow structures to the torque values of fully turbulent Taylor-Couette flow was experimentally studied using tomographic PIV. The measurements were performed for various relative cylinder rotation speeds and Reynolds numbers, based on a study of Ravelet et al. (2010). We confirmed that the flow structures are strongly influenced by the rotation number. Our analyses using time-averaged mean flow showed the presence of Taylor vortices for the two smallest rotation numbers that were studied. Increasing the rotation number initially resulted in the shape deformation of the Taylor vortices. Further increment towards only outer cylinder rotation, showed transition to the dominance of the small scale vortices and absence of Taylor vortex-like structures. We compared the transition of the flow structures with the curves of dimensionless torque. Sudden changes of the flow structures confirmed the presence of transition points on the torque curve, where the dominance of small and large scale vortical structures on the mean flow interchanges.
Energy Technology Data Exchange (ETDEWEB)
Urbin, Gerald [Institut National Polytechnique, 38 - Grenoble (France)
1998-02-02
This study highlights the potentialities of the numerical technique of large scale simulation in describing and understanding the turbulent flows in a complex geometry. Particularly, it is focussed on flows of free jet, confined jets and multiple jets of high solidity grid. Spatial simulations of the circular zone close to a free jet, of high Reynolds number were performed. In spite of an evident sensitivity to upstream conditions good agreement between our statistical predictions and different experimental measurements was obtained. The multiple coherent vortical structures implied in the transition to turbulence of the jet were found. At the same time, helical or annular axisymmetric vortices were observed. Also, an original vortical arrangement was evidenced, resulting from the alternating inclination and local pairing of these rings. It could been forced through an ad-hoc excitation which modifies subsequently drastically the jet development. When an axisymmetric excitation is imposed after formation of annular structures, pairs of counter-rotative longitudinal vortices occur and generate lateral jets. Their nature and presence in case of a helical excitation are discussed. An efficient method for controlling their number is developed. Then, one is studied the very low frequency periodic phenomenon of backward-facing transition to turbulence which develops in the confined jet and grid multiple jets (a phenomenon generic in numerous flows). It was found to depend not only on the characteristic of the re-circulation (pre-transition) zones but also on the upstream flow (zone of post-transition stagnation, pressure effect). Large scale transversal motions of the fluid have been found beginning from the grid. An interpretation of this phenomenon is suggested 193 refs., 109 figs.
2012-01-01
Tuesday 31 January 2012 at 20.00 Prof. Daniel Treille, CERN, Geneva Physics Auditorium, University of Geneva 24 quai Ernest-Ansermet, Geneva As the universe was expanding in the very first moments of its existence, it underwent a number of changes that determined the structure it has today. Our understanding of these first moments comes from our direct observation of the cosmos via various "messengers" from the past. It also comes from experiments carried out at large particle accelerators which can recreate on a small scale the physics processes taking place as the universe evolved. Going back in time, the facts have been reasonably well established up to about the first picosecond (a thousandth of a millionth of a second) of the universe, which is the point in time when we believe that elementary particles acquired their mass. The Large Hadron Collider (LHC) will help us to find out more about the exact nature of this transition. Beyond that, we have to fall back on extrapolat...
Scale and Scope Economies of Distance Education in Australian Universities
Zhang, Liang-Cheng; Worthington, Andrew C.
2017-01-01
Despite compelling qualitative arguments for scale and scope economies in university-level distance education, as distinct from traditional class-based face-to-face instruction, there is little rigorous quantitative evidence in support. In this paper, we explore the scale and scope economies of distance education using a multiplicatively separable…
Development of Universal Values in School Management Scale (UVISMS)
Sagir, Mahmut
2014-01-01
Current study aims to develop a scale to identify the universal values of school administrators in school management. In order to develop the scale, academic resources were reviewed and a 40-item draft data collection instrument was created by taking the views and suggestions of 5 school administrators, 5 academicians and 5 education inspectors…
Some Aspects of Scaling and Universality in Magnetocaloric Materials
DEFF Research Database (Denmark)
Smith, Anders; Nielsen, Kaspar Kirstein; Bahl, Christian R.H.
2014-01-01
The magnetocaloric effect of a magnetic material is characterized by two quantities, the isothermal entropy change and the adiabatic temperature change, both of which are functions of temperature and applied magnetic field. We discuss the scaling properties of these quantities close to a second...... order phase transition within the context of critical scaling theory. In the critical region the isothermal entropy change will exhibit universal scaling exponents. However, this is only true close to Tc and for small fields; we show that for finite fields the scaling exponents in general become field...... dependent, even at Tc. Furthermore, the scaling exponents at finite fields are not universal: Two models with the same critical exponents can exhibit markedly different scaling behaviour even at relatively low fields. Turning to the adiabatic temperature change, we argue that it is not determined...
Multi-fidelity uncertainty quantification in large-scale predictive simulations of turbulent flow
Geraci, Gianluca; Jofre-Cruanyes, Lluis; Iaccarino, Gianluca
2017-11-01
The performance characterization of complex engineering systems often relies on accurate, but computationally intensive numerical simulations. It is also well recognized that in order to obtain a reliable numerical prediction the propagation of uncertainties needs to be included. Therefore, Uncertainty Quantification (UQ) plays a fundamental role in building confidence in predictive science. Despite the great improvement in recent years, even the more advanced UQ algorithms are still limited to fairly simplified applications and only moderate parameter dimensionality. Moreover, in the case of extremely large dimensionality, sampling methods, i.e. Monte Carlo (MC) based approaches, appear to be the only viable alternative. In this talk we describe and compare a family of approaches which aim to accelerate the convergence of standard MC simulations. These methods are based on hierarchies of generalized numerical resolutions (multi-level) or model fidelities (multi-fidelity), and attempt to leverage the correlation between Low- and High-Fidelity (HF) models to obtain a more accurate statistical estimator without introducing additional HF realizations. The performance of these methods are assessed on an irradiated particle laden turbulent flow (PSAAP II solar energy receiver). This investigation was funded by the United States Department of Energy's (DoE) National Nuclear Security Administration (NNSA) under the Predicitive Science Academic Alliance Program (PSAAP) II at Stanford University.
Bridging the gap between atmospheric physics and chemistry in studies of small-scale turbulence
Vilà-Guerau de Arellano, J.
2003-01-01
The current understanding of the influence of atmospheric turbulence on chemical reactions is briefly reviewed. The fundamentals of this influence and the consequences for the transport and mixing of the reactants are discussed. A classification of the turbulent reacting flows is proposed in terms
Fine Scale Modeling and Forecasts of Upper Atmospheric Turbulence for Operational Use
2014-11-30
performance expectations were assessed to evaluate the suitability of various languages and architectures for software development. Operational...the same plain English Turbulence Report as from the ’Solver Complete’ dialog a. Observe that the instability lines are visually approximate to the...controlling the size, distribution, variability and morphology of high impact stratospheric turbulent layers. Investigated detailed temporal and spatial
Turbulent fluctuations at kinetic scales: from coherent structures to quasi-parallel whistler waves
Alexandrova, Olga; Lacombe, Catherine; Matteini, Lorenzo; Rossi, Claudia; Maksimovic, Milan; Mangeney, Andre; Santolik, Ondrej; Cornilleau-Wehrlin, Nicole; de Conchy, Yvonne
2015-04-01
The nature of the magnetic field fluctuations in the solar wind between the ion and electron scales is still under debate. Using the Cluster/STAFF instrument, we make a survey of the power spectral density and of the polarization of these fluctuations at frequencies f ∈ [1,400] Hz, during five years (2001-2005) when Cluster was in the free solar wind. In most of the analyzed time intervals, the fluctuations have quasi-random polarization and they have a general spectral shape between the ion scales and a fraction of electron scales. The intensity of these spectra is well correlated to the ion thermal pressure. These fluctuations seem to have a negligible frequency in the solar wind frame, and a wavevector anisotropy k⊥ ≫ k||. Such time intervals are dominated by coherent structures, propagating with a finit velocity in the plasma frame, in the plane perpendicular to the mean magnetic field. In the rest ~ 10% of the selected data, we observe narrow-band, right-handed, circularly polarized fluctuations, with wave vectors quasi-parallel to the mean magnetic field, superimposed on the spectrum of the permanent background turbulence. We interpret these coherent fluctuations as whistler mode waves. The life time of such waves varies between a few seconds and several hours. We analyze in details the long-lived whistler waves, i.e. with a life time longer than five minutes. When the electron parallel beta factor βe|| is larger than 3, the whistler waves are seen along the heat flux threshold of the whistler heat flux instability.
Large-scale control strategy for drag reduction in turbulent channel flows
Yao, Jie; Chen, Xi; Thomas, Flint; Hussain, Fazle
2017-06-01
In a recent article, Canton et al. [J. Canton et al., Phys. Rev. Fluids 1, 081501(R) (2016), 10.1103/PhysRevFluids.1.081501] reported significant drag reduction in turbulent channel flow by using large-scale, near-wall streamwise swirls following the control strategy of Schoppa and Hussain [W. Schoppa and F. Hussain, Phys. Fluids 10, 1049 (1998), 10.1063/1.869789] for low Reynolds numbers only, but found no drag reduction at high friction Reynolds numbers (Reτ=550 ). Here we show that the lack of drag reduction at high Re observed by Canton et al. is remedied by the proper choice of the large-scale control flow. In this study, we apply near-wall opposed wall-jet forcing to achieve drag reduction at the same (high) Reynolds number where Canton et al. found no drag reduction. The steady excitation is characterized by three control parameters, namely, the wall-jet-forcing amplitude A+, the spanwise spacing Λ+, and the wall jet height yc+ (+ indicates viscous scaling); the primary difference between Schoppa and Hussain's work (also that of Canton et al.) and this Rapid Communication is the emphasis on the explicit choice of yc+ here. We show as an example that with a choice of A+≈0.015 ,Λ+≈1200 , and yc+≈30 the flow control definitely suppresses the wall shear stress at a series of Reynolds numbers, namely, 19 %,14 % , and 12 % drag reductions at Reτ=180 , 395, and 550, respectively. Further study should explore optimization of these parameter values.
Scaling and Universality at Dynamical Quantum Phase Transitions.
Heyl, Markus
2015-10-02
Dynamical quantum phase transitions (DQPTs) at critical times appear as nonanalyticities during nonequilibrium quantum real-time evolution. Although there is evidence for a close relationship between DQPTs and equilibrium phase transitions, a major challenge is still to connect to fundamental concepts such as scaling and universality. In this work, renormalization group transformations in complex parameter space are formulated for quantum quenches in Ising models showing that the DQPTs are critical points associated with unstable fixed points of equilibrium Ising models. Therefore, these DQPTs obey scaling and universality. On the basis of numerical simulations, signatures of these DQPTs in the dynamical buildup of spin correlations are found with an associated power-law scaling determined solely by the fixed point's universality class. An outlook is given on how to explore this dynamical scaling experimentally in systems of trapped ions.
Basse, N. P.; Zoletnik, S.; Michelsen, P. K.; W7-As Team
2005-01-01
Confinement transitions in the Wendelstein 7-AS stellarator [H. Renner et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)] can be induced by varying either the internal plasma current or the external magnetic field. In this paper we report on experiments where closely matched confinement states (good and bad) were constructed using the latter method. Analysis using the former scheme has been reported upon previously [S. Zoletnik et al., Plasma Phys. Controlled Fusion 44, 1581 (2002)]. The electron temperature, along with the major spectral characteristics of magnetic and small-scale electron density fluctuations, changes dramatically at the transition from good to bad confinement. The fluctuation power is intermittent, and core bursts traveling in the electron diamagnetic drift (DD) direction are correlated between the bottom and top of the plasma, especially during degraded confinement. A corresponding top-bottom correlation for the edge ion DD direction turbulence feature was not found. Strong correlations are observed both between the two density fluctuation signals and between magnetic and density fluctuations in bad compared to good confinement. The correlation time of the bursts is of order 100μs, similar to the lifetime observed during edge localized modes.
International Nuclear Information System (INIS)
Inagaki, Masahide; Abe, Ken-ichi
2017-01-01
Highlights: • An anisotropy-resolving subgrid-scale model, covering a wide range of grid resolutions, is improved. • The new model enhances its applicability to flows in the laminar-turbulent transition region. • A mixed-timescale subgrid-scale model is used as the eddy viscosity model. • The proposed model successfully predicts the channel flows at transitional Reynolds numbers. • The influence of the definition of the grid-filter width is also investigated. - Abstract: Some types of mixed subgrid-scale (SGS) models combining an isotropic eddy-viscosity model and a scale-similarity model can be used to effectively improve the accuracy of large eddy simulation (LES) in predicting wall turbulence. Abe (2013) has recently proposed a stabilized mixed model that maintains its computational stability through a unique procedure that prevents the energy transfer between the grid-scale (GS) and SGS components induced by the scale-similarity term. At the same time, since this model can successfully predict the anisotropy of the SGS stress, the predictive performance, particularly at coarse grid resolutions, is remarkably improved in comparison with other mixed models. However, since the stabilized anisotropy-resolving SGS model includes a transport equation of the SGS turbulence energy, k SGS , containing a production term proportional to the square root of k SGS , its applicability to flows with both laminar and turbulent regions is not so high. This is because such a production term causes k SGS to self-reproduce. Consequently, the laminar–turbulent transition region predicted by this model depends on the inflow or initial condition of k SGS . To resolve these issues, in the present study, the mixed-timescale (MTS) SGS model proposed by Inagaki et al. (2005) is introduced into the stabilized mixed model as the isotropic eddy-viscosity part and the production term in the k SGS transport equation. In the MTS model, the SGS turbulence energy, k es , estimated by
Rosenberg, Duane; Pouquet, Annick; Marino, Raffaele; Mininni, Pablo
2015-04-01
Rotating stratified flows are particularly important in the understanding of the dynamics of our planet and the Sun. Several of the key concepts needed in order to progress in predictions of the weather and in the global evolution of the climate depend crucially on a fundamental understanding of these flows. At different scales, different physical regimes become salient, and yet all scales interact. Fronts and turbulent eddies lead to enhanced dissipation and dispersion of particles and tracers, affecting the global energetic behavior of the atmosphere and climate systems. Rotating stratified turbulence thus plays a crucial role in the dynamics of the atmosphere and oceans, with nonlinear interactions--responsible for the complexity of turbulent flows--having to compete with the waves due to rotation and stratification, of respective frequencies N and f. In this context, we report on results for rotating stratified turbulence in the absence of forcing, with large-scale isotropic initial conditions, using accurate direct numerical simulations computed on cubic grids of up to 40963 points. The Reynolds and Froude numbers are respectively equal to Re=54000 and Fr=0.024, and N/f=4.95, a choice appropriate to model the dynamics of the southern abyssal ocean at mid latitudes. This gives a global buoyancy Reynolds number ReFr^2=32, a value sufficient for some isotropy to be recovered in the small scales beyond the Ozmidov scale, but still moderate enough that the intermediate scales where waves are prevalent are well resolved. We concentrate on the large-scale dynamics, for which we find a spectrum compatible with the Bolgiano-Obukhov prediction, and confirm that the Froude number based on a typical vertical length scale is of order unity, with strong gradients in the vertical. Two characteristic scales emerge from this computation, and are identified from sharp variations in the spectral distribution of either total energy or helicity. A spectral break is also observed
Fu, X.; Li, H.; Guo, F.; Li, X.; Roytershteyn, V.
2017-12-01
The solar wind is a turbulent magnetized plasma extending from the upper atmosphere of the sun to the edge of the heliosphere. It carries charged particles and magnetic fields originated from the Sun, which have great impact on the geomagnetic environment and human activities in space. In such a magnetized plasma, Alfven waves play a crucial role in carrying energy from the surface of the Sun, injecting into the solar wind and establishing power-law spectra through turbulent energy cascades. On the other hand, in compressible plasmas large amplitude Alfven waves are subject to a parametric decay instability (PDI) which converts an Alfven wave to another counter-propagating Alfven wave and an ion acoustic wave (slow mode). The counter-propagating Alfven wave provides an important ingredient for turbulent cascade, and the slow-mode wave provides a channel for solar wind heating in a spatial scale much larger than ion kinetic scales. Growth and saturation of PDI in quiet plasma have been intensively studied using linear theory and nonlinear simulations in the past. Here using 3D hybrid simulations, we show that PDI is still effective in turbulent low-beta plasmas, generating slow modes and causing ion heating. Selected events in WIND data are analyzed to identify slow modes in the solar wind and the role of PDI, and compared with our simulation results. We also investigate the validity of linear Vlasov theory regarding PDI growth and slow mode damping in turbulent plasmas. Since PDI favors low plasma beta, we expect to see more evidence of PDI in the solar wind close to the Sun, especially from the upcoming NASA's Parker Solar Probe mission which will provide unprecedented wave and plasma data as close as 8.5 solar radii from the Sun.
Wang, Wenkang; Pan, Chong; Wang, Jinjun
2018-01-01
The identification and separation of multi-scale coherent structures is a critical task for the study of scale interaction in wall-bounded turbulence. Here, we propose a quasi-bivariate variational mode decomposition (QB-VMD) method to extract structures with various scales from instantaneous two-dimensional (2D) velocity field which has only one primary dimension. This method is developed from the one-dimensional VMD algorithm proposed by Dragomiretskiy and Zosso (IEEE Trans Signal Process 62:531-544, 2014) to cope with a quasi-2D scenario. It poses the feature of length-scale bandwidth constraint along the decomposed dimension, together with the central frequency re-balancing along the non-decomposed dimension. The feasibility of this method is tested on both a synthetic flow field and a turbulent boundary layer at moderate Reynolds number (Re_{τ } = 3458) measured by 2D particle image velocimetry (PIV). Some other popular scale separation tools, including pseudo-bi-dimensional empirical mode decomposition (PB-EMD), bi-dimensional EMD (B-EMD) and proper orthogonal decomposition (POD), are also tested for comparison. Among all these methods, QB-VMD shows advantages in both scale characterization and energy recovery. More importantly, the mode mixing problem, which degrades the performance of EMD-based methods, is avoided or minimized in QB-VMD. Finally, QB-VMD analysis of the wall-parallel plane in the log layer (at y/δ = 0.12) of the studied turbulent boundary layer shows the coexistence of large- or very large-scale motions (LSMs or VLSMs) and inner-scaled structures, which can be fully decomposed in both physical and spectral domains.
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
Universal characterization of wall turbulence for fluids with strong property variations
Patel, A.
2017-01-01
Wall-bounded turbulence involving mixing of scalars, such as temperature or concentration fields, play an important role in many engineering applications. In applications with large temperature or concentration differences, the variation of scalar dependent thermos physical properties can be strong.
Large-scale motions in the universe: a review
International Nuclear Information System (INIS)
Burstein, D.
1990-01-01
The expansion of the universe can be retarded in localised regions within the universe both by the presence of gravity and by non-gravitational motions generated in the post-recombination universe. The motions of galaxies thus generated are called 'peculiar motions', and the amplitudes, size scales and coherence of these peculiar motions are among the most direct records of the structure of the universe. As such, measurements of these properties of the present-day universe provide some of the severest tests of cosmological theories. This is a review of the current evidence for large-scale motions of galaxies out to a distance of ∼5000 km s -1 (in an expanding universe, distance is proportional to radial velocity). 'Large-scale' in this context refers to motions that are correlated over size scales larger than the typical sizes of groups of galaxies, up to and including the size of the volume surveyed. To orient the reader into this relatively new field of study, a short modern history is given together with an explanation of the terminology. Careful consideration is given to the data used to measure the distances, and hence the peculiar motions, of galaxies. The evidence for large-scale motions is presented in a graphical fashion, using only the most reliable data for galaxies spanning a wide range in optical properties and over the complete range of galactic environments. The kinds of systematic errors that can affect this analysis are discussed, and the reliability of these motions is assessed. The predictions of two models of large-scale motion are compared to the observations, and special emphasis is placed on those motions in which our own Galaxy directly partakes. (author)
Development of a Career Resilience Scale for University Students
児玉, 真樹子
2017-01-01
The purpose of this study was to develop a career resilience scale for university students. The data of 114 university students was collected. Career resilience, career decision making anxiety, and the degree of career development were measured. The result of a confirmatory factor analysis indicated a five-factor structure of career resilience with a high Cronbach’s alpha: ability to cope with problems and changes; social skills; interest in novelty; optimism about the future; and willingness...
Scaling and universality of ac conduction in disordered solids
DEFF Research Database (Denmark)
Schrøder, Thomas; Dyre, Jeppe
2000-01-01
Recent scaling results for the ac conductivity of ionic glasses by Roling et al. [Phys. Rev. Lett. 78, 2160 (1997)] and Sidebottom [Phys. Rev. Lett. 82, 3653 (1999)] are discussed. We prove that Sidebottom's version of scaling is completely general. A new approximation to the universal ac conduct...... conductivity arising in the extreme disorder limit of the symmetric hopping model, the "diffusion cluster approximation," is presented and compared to computer simulations and experiments.......Recent scaling results for the ac conductivity of ionic glasses by Roling et al. [Phys. Rev. Lett. 78, 2160 (1997)] and Sidebottom [Phys. Rev. Lett. 82, 3653 (1999)] are discussed. We prove that Sidebottom's version of scaling is completely general. A new approximation to the universal ac...
Limitations of scaling and universality in stock market data
Kertesz, Janos; Eisler, Zoltan
2005-01-01
We present evidence, that if a large enough set of high resolution stock market data is analyzed, certain analogies with physics -- such as scaling and universality -- fail to capture the full complexity of such data. Despite earlier expectations, the mean value per trade, the mean number of trades per minute and the mean trading activity do not show scaling with company capitalization, there is only a non-trivial monotonous dependence. The strength of correlations present in the time series ...
High Reynolds Number Turbulence
National Research Council Canada - National Science Library
Smits, Alexander J
2007-01-01
The objectives of the grant were to provide a systematic study to fill the gap between existing research on low Reynolds number turbulent flows to the kinds of turbulent flows encountered on full-scale vehicles...
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
Fractals and the Large-Scale Structure in the Universe
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 7; Issue 2. Fractals and the Large-Scale Structure in the Universe - Introduction and Basic Concepts. A K Mittal T R Seshadri. General Article Volume 7 Issue 2 February 2002 pp 6-19 ...
Origin of large-scale cell structure in the universe
International Nuclear Information System (INIS)
Zel'dovich, Y.B.
1982-01-01
A qualitative explanation is offered for the characteristic global structure of the universe, wherein ''black'' regions devoid of galaxies are surrounded on all sides by closed, comparatively thin, ''bright'' layers populated by galaxies. The interpretation rests on some very general arguments regarding the growth of large-scale perturbations in a cold gas
Economies of Scale and Scope in Turkish Universities.
Lewis, Darrell R.; Dundar, Halil
1995-01-01
Examines production and cost structures of 28 Turkish universities to estimate their economies of scale and scope. Estimates multiproduct cost functions for teaching and research, examining social, health, and engineering sciences departments across 186 college faculties. Average incremental and marginal costs are highest for graduate instruction…
Fractals and the Large-Scale Structure in the Universe
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 7; Issue 4. Fractals and the Large-Scale Structure in the Universe - Is the Cosmological Principle Valid? A K Mittal T R Seshadri. General Article Volume 7 Issue 4 April 2002 pp 39-47 ...
Fractals and the Large-Scale Structure in the Universe
Indian Academy of Sciences (India)
lien from Harish-Chandra. Research Institute,. Allahabad. Areas of his interest include cosmic microwave background radiation, large scale structures in the Universe and application of fractals in these. A K Mittal and T R Seshadri. During the last decade it has been argued by some investigators that the distribution of galax-.
Isterling, William M; Dally, Bassam B; Alwahabi, Zeyad T; Dubovinsky, Miro; Wright, Daniel
2012-01-01
Narrow laser beams directed from aircraft may at times pass through the exhaust plume of the engines and potentially degrade some of the laser beam characteristics. This paper reports on controlled studies of laser beam deviation arising from propagation through turbulent hot gases, in a well-characterized laboratory burner, with conditions of relevance to aircraft engine exhaust plumes. The impact of the temperature, laser wavelength, and turbulence length scale on the beam deviation has been investigated. It was found that the laser beam displacement increases with the turbulent integral length scale. The effect of temperature on the laser beam angular deviation, σ, using two different laser wavelengths, namely 4.67 μm and 632.8 nm, was recorded. It was found that the beam deviation for both wavelengths may be semiempirically modeled using a single function of the form, σ=a(b+(1/T)(2))(-1), with two parameters only, a and b, where σ is in microradians and T is the temperature in °C. © 2012 Optical Society of America
Three-dimensional spatial structures of solar wind turbulence from 10 000-km to 100-km scales
Directory of Open Access Journals (Sweden)
Y. Narita
2011-10-01
Full Text Available Using the four Cluster spacecraft, we have determined the three-dimensional wave-vector spectra of fluctuating magnetic fields in the solar wind. Three different solar wind intervals of Cluster data are investigated for this purpose, representing three different spatial scales: 10 000 km, 1000 km, and 100 km. The spectra are determined using the wave telescope technique (k-filtering technique without assuming the validity of Taylor's frozen-in-flow hypothesis nor are any assumptions made as to the symmetry properties of the fluctuations. We find that the spectra are anisotropic on all the three scales and the power is extended primarily in the directions perpendicular to the mean magnetic field, as might be expected of two-dimensional turbulence, however, the analyzed fluctuations are not axisymmetric. The lack of axisymmetry invalidates some earlier techniques using single spacecraft observations that were used to estimate the percentage of magnetic energy residing in quasi-two-dimensional power. However, the dominance of two-dimensional turbulence is consistent with the relatively long mean free paths of cosmic rays in observed in the heliosphere. On the other hand, the spectra also exhibit secondary extended structures oblique from the mean magnetic field direction. We discuss possible origins of anisotropy and asymmetry of solar wind turbulence spectra.
Measurement of Turbulent Fluxes of Swirling Flow in a Scaled Up Multi Inlet Vortex Reactor
Olsen, Michael; Hitimana, Emmanual; Hill, James; Fox, Rodney
2017-11-01
The multi-inlet vortex reactor (MIVR) has been developed for use in the FlashNanoprecipitation (FNP) process. The MIVR has four identical square inlets connected to a central cylindrical mixing chamber with one common outlet creating a highly turbulent swirling flow dominated by a strong vortex in the center. Efficient FNP requires rapid mixing within the MIVR. To investigate the mixing, instantaneous velocity and concentration fields were acquired using simultaneous stereoscopic particle image velocimetry and planar laser-induced fluorescence. The simultaneous velocity and concentration data were used to determine turbulent fluxes and spatial cross-correlations of velocity and concentration fluctuations. The measurements were performed for four inlet flow Reynolds numbers (3250, 4875, 6500, and 8125) and at three measurement planes within the reactor. A correlation between turbulent fluxes and vortex strength was found. For all Reynolds numbers, turbulent fluxes are maximum in the vortex dominated central region of the reactor and decay away from the vortex. Increasing Reynolds number increased turbulent fluxes and subsequently enhanced mixing. The mixing performance was confirmed by determining coefficients of concentration variance within the reactor.
Economics of Utility Scale Photovoltaics at Purdue University
Arnett, William
The research for this case study shows that utility scale solar photovoltaics has become a competitive energy investment option, even when a campus operates a power plant at low electricity rates. To evaluate this an economic model called SEEMS (Solar Economic Evaluation Modelling Spreadsheets) was developed to evaluate a number of financial scenarios in Real Time Pricing for universities. The three main financing structures considered are 1) land leasing, 2) university direct purchase, and 3) third party purchase. Unlike other commercially available models SEEMS specifically accounts for real time pricing, where the local utility provides electricity at an hourly rate that changes with the expected demand. In addition, SEEMS also includes a random simulation that allows the model to predict the likelihood of success for a given solar installation strategy. The research showed that there are several options for utility scale solar that are financially attractive. The most practical financing structure is with a third party partnership because of the opportunity to take advantage of tax incentives. Other options could become more attractive if non-financial benefits are considered. The case study for this research, Purdue University, has a unique opportunity to integrate utility-scale solar electricity into its strategic planning. Currently Purdue is updating its master plan which will define how land is developed. Purdue is also developing a sustainability plan that will define long term environmental goals. In addition, the university is developing over 500 acres of land west of campus as part of its Aerospace Innovation District. This research helps make the case for including utility-scale solar electricity as part of the university's strategic planning.
On the Phenomenology of an Accelerated Large-Scale Universe
Directory of Open Access Journals (Sweden)
Martiros Khurshudyan
2016-10-01
Full Text Available In this review paper, several new results towards the explanation of the accelerated expansion of the large-scale universe is discussed. On the other hand, inflation is the early-time accelerated era and the universe is symmetric in the sense of accelerated expansion. The accelerated expansion of is one of the long standing problems in modern cosmology, and physics in general. There are several well defined approaches to solve this problem. One of them is an assumption concerning the existence of dark energy in recent universe. It is believed that dark energy is responsible for antigravity, while dark matter has gravitational nature and is responsible, in general, for structure formation. A different approach is an appropriate modification of general relativity including, for instance, f ( R and f ( T theories of gravity. On the other hand, attempts to build theories of quantum gravity and assumptions about existence of extra dimensions, possible variability of the gravitational constant and the speed of the light (among others, provide interesting modifications of general relativity applicable to problems of modern cosmology, too. In particular, here two groups of cosmological models are discussed. In the first group the problem of the accelerated expansion of large-scale universe is discussed involving a new idea, named the varying ghost dark energy. On the other hand, the second group contains cosmological models addressed to the same problem involving either new parameterizations of the equation of state parameter of dark energy (like varying polytropic gas, or nonlinear interactions between dark energy and dark matter. Moreover, for cosmological models involving varying ghost dark energy, massless particle creation in appropriate radiation dominated universe (when the background dynamics is due to general relativity is demonstrated as well. Exploring the nature of the accelerated expansion of the large-scale universe involving generalized
Legleiter, Carl J.; Phelps, Tracy L.; Wohl, Ellen E.
2007-01-01
Although previous research has documented well-organized interactions between the turbulent flow field and an irregular boundary, the spatial variability of turbulent flow characteristics at the reach-scale remains poorly understood. In this paper, we present detailed field measurements of three-dimensional flow velocities and turbulence intensities in a high-gradient, cobble-bed riffle from three discharges; additional data on sediment grain size and bed topography were used to characterize boundary roughness. An acoustic Doppler velocimeter was used to measure velocities along five cross-sections within a 6 m long reach of the North Fork Cache La Poudre River; vertical profiles were also measured along the channel thalweg. We adopted a spatially explicit stochastic hydraulic approach and focused not on coherent flow structures per se but rather time-averaged, reach-scale variability and spatial pattern. Scaling velocities and turbulence intensities by the reach-averaged friction velocity U* accounted for changes in flow depth and enabled comparisons among the three discharges. We quantified the effects of stage and roughness by assessing differences among probability distributions of hydraulic quantities and by examining geostatistical metrics of spatial variability. We computed semivariograms for streamwise and transverse directions and fit parametric models to summarize the spatial structure of each variable at each discharge. Cross-correlograms were also used to describe the local and lagged effects of boundary roughness on flow characteristics. Although the probability distributions yielded some insight, incorporating spatial information revealed important elements of stage-dependent flow structure. The development of secondary currents and flow convergence at higher stages were clearly documented in maps and semivariograms. In general, the spatial structure of the flow field became smoother and more continuous as stage increased and the effects of boundary
Universal scaling laws in metro area election results.
Bokányi, Eszter; Szállási, Zoltán; Vattay, Gábor
2018-01-01
We explain the anomaly of election results between large cities and rural areas in terms of urban scaling in the 1948-2016 US elections and in the 2016 EU referendum of the UK. The scaling curves are all universal and depend on a single parameter only, and one of the parties always shows superlinear scaling and drives the process, while the sublinear exponent of the other party is merely the consequence of probability conservation. Based on the recently developed model of urban scaling, we give a microscopic model of voter behavior in which we replace diversity characterizing humans in creative aspects with social diversity and tolerance. The model can also predict new political developments such as the fragmentation of the left and the immigration paradox.
Magnetic turbulence in a table-top laser-plasma relevant to astrophysical scenarios
Chatterjee, Gourab; Schoeffler, Kevin M.; Kumar Singh, Prashant; Adak, Amitava; Lad, Amit D.; Sengupta, Sudip; Kaw, Predhiman; Silva, Luis O.; Das, Amita; Kumar, G. Ravindra
2017-06-01
Turbulent magnetic fields abound in nature, pervading astrophysical, solar, terrestrial and laboratory plasmas. Understanding the ubiquity of magnetic turbulence and its role in the universe is an outstanding scientific challenge. Here, we report on the transition of magnetic turbulence from an initially electron-driven regime to one dominated by ion-magnetization in a laboratory plasma produced by an intense, table-top laser. Our observations at the magnetized ion scale of the saturated turbulent spectrum bear a striking resemblance with spacecraft measurements of the solar wind magnetic-field spectrum, including the emergence of a spectral kink. Despite originating from diverse energy injection sources (namely, electrons in the laboratory experiment and ion free-energy sources in the solar wind), the turbulent spectra exhibit remarkable parallels. This demonstrates the independence of turbulent spectral properties from the driving source of the turbulence and highlights the potential of small-scale, table-top laboratory experiments for investigating turbulence in astrophysical environments.
Plasma Turbulence and Kinetic Instabilities at Ion Scales in the Expanding Solar Wind
Czech Academy of Sciences Publication Activity Database
Hellinger, Petr; Matteini, L.; Landi, S.; Franci, L.; Trávníček, Pavel M.
2015-01-01
Roč. 812, č. 2 (2015), L32/1-L32/6 ISSN 2041-8205 R&D Projects: GA ČR GA15-10057S Grant - others:European Commission(XE) 284515 Institutional support: RVO:67985815 Keywords : instabilities * solar wind * turbulence Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.487, year: 2015
High-resolution Hybrid Simulations of Kinetic Plasma Turbulence at Proton Scales
Czech Academy of Sciences Publication Activity Database
Franci, L.; Landi, S.; Matteini, L.; Verdini, A.; Hellinger, Petr
2015-01-01
Roč. 812, č. 1 (2015), 21/1-21/15 ISSN 0004-637X R&D Projects: GA ČR GA15-10057S Institutional support: RVO:67985815 Keywords : plasmas * solar wind * turbulence Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.909, year: 2015
Plasma turbulence and kinetic instabilities at ion scales in the expanding solar wind
Czech Academy of Sciences Publication Activity Database
Hellinger, Petr; Matteini, L.; Landi, S.; Verdini, A.; Franci, L.; Trávníček, Pavel M.
2015-01-01
Roč. 811, č. 2 (2015), L32/1-L32/6 ISSN 2041-8205 Institutional support: RVO:68378289 Keywords : instabilities * solar wind * turbulence * waves Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.487, year: 2015 http://iopscience.iop.org/article/10.1088/2041-8205/811/2/L32/pdf
International Nuclear Information System (INIS)
Kowal, Grzegorz; Lazarian, A.
2010-01-01
We study compressible magnetohydrodynamic turbulence, which holds the key to many astrophysical processes, including star formation and cosmic-ray propagation. To account for the variations of the magnetic field in the strongly turbulent fluid, we use wavelet decomposition of the turbulent velocity field into Alfven, slow, and fast modes, which presents an extension of the Cho and Lazarian decomposition approach based on Fourier transforms. The wavelets allow us to follow the variations of the local direction of the magnetic field and therefore improve the quality of the decomposition compared to the Fourier transforms, which are done in the mean field reference frame. For each resulting component, we calculate the spectra and two-point statistics such as longitudinal and transverse structure functions as well as higher order intermittency statistics. In addition, we perform a Helmholtz- Hodge decomposition of the velocity field into incompressible and compressible parts and analyze these components. We find that the turbulence intermittency is different for different components, and we show that the intermittency statistics depend on whether the phenomenon was studied in the global reference frame related to the mean magnetic field or in the frame defined by the local magnetic field. The dependencies of the measures we obtained are different for different components of the velocity; for instance, we show that while the Alfven mode intermittency changes marginally with the Mach number, the intermittency of the fast mode is substantially affected by the change.
Magnetic Reconnection as a Driver for a Sub-ion-scale Cascade in Plasma Turbulence
Czech Academy of Sciences Publication Activity Database
Franci, L.; Cerri, S.S.; Califano, F.; Landi, S.; Papini, E.; Verdini, A.; Matteini, L.; Jenko, F.; Hellinger, Petr
2017-01-01
Roč. 850, č. 1 (2017), L16/1-L16/6 ISSN 2041-8205 R&D Projects: GA ČR GA15-10057S Institutional support: RVO:67985815 Keywords : magnetic reconnection * solar wind * turbulence Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.522, year: 2016
Self-sustained large-scale flow in turbulent cryogenic convection
Czech Academy of Sciences Publication Activity Database
Niemela, J. J.; Skrbek, Ladislav; Sreenivasan, K. R.; Donnelly, R. J.
2002-01-01
Roč. 126, 1/2 (2002), s. 297-302 ISSN 0022-2291 Institutional research plan: CEZ:AV0Z1010914 Keywords : thermal convection * turbulence * cryogenic Subject RIV: BK - Fluid Dynamics Impact factor: 1.139, year: 2002
Effect of Fluid Viscoelasticity on Turbulence and Large-Scale Vortices behind Wall-Mounted Plates
Directory of Open Access Journals (Sweden)
Takahiro Tsukahara
2014-03-01
Full Text Available Direct numerical simulations of turbulent viscoelastic fluid flows in a channel with wall-mounted plates were performed to investigate the influence of viscoelasticity on turbulent structures and the mean flow around the plate. The constitutive equation follows the Giesekus model, valid for polymer or surfactant solutions, which are generally capable of reducing the turbulent frictional drag in a smooth channel. We found that turbulent eddies just behind the plates in viscoelastic fluid decreased in number and in magnitude, but their size increased. Three pairs of organized longitudinal vortices were observed downstream of the plates in both Newtonian and viscoelastic fluids: two vortex pairs were behind the plates and the other one with the longest length was in a plate-free area. In the viscoelastic fluid, the latter vortex pair in the plate-free area was maintained and reached the downstream rib, but its swirling strength was weakened and the local skin-friction drag near the vortex was much weaker than those in the Newtonian flow. The mean flow and small spanwise eddies were influenced by the additional fluid force due to the viscoelasticity and, moreover, the spanwise component of the fluid elastic force may also play a role in the suppression of fluid vortical motions behind the plates.
Duality and scale invariant magnetic fields from bouncing universes
DEFF Research Database (Denmark)
Chowdhury, Debika; Sriramkumar, L.; Jain, Rajeev Kumar
2016-01-01
Recently, we numerically showed that, for a nonminimal coupling that is a simple power of the scale factor, scale invariant magnetic fields arise in a class of bouncing universes. In this work, we analytically evaluate the spectrum of magnetic and electric fields generated in a subclass of such m......Recently, we numerically showed that, for a nonminimal coupling that is a simple power of the scale factor, scale invariant magnetic fields arise in a class of bouncing universes. In this work, we analytically evaluate the spectrum of magnetic and electric fields generated in a subclass...... of such models. We illustrate that, for cosmological scales which have wave numbers much smaller than the wave number associated with the bounce, the shape of the spectrum is preserved across the bounce. Using the analytic solutions obtained, we also illustrate that the problem of backreaction is severe...... at the bounce. Finally, we show that the power spectrum of the magnetic field remains invariant under a two-parameter family of transformations of the nonminimal coupling function....
Statistical turbulence theory and turbulence phenomenology
Herring, J. R.
1973-01-01
The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion about randomness. Two concepts are involved: (1) a modeling of the turbulence as nearly multipoint Gaussian, and (2) a simultaneous introduction of a generalized eddy viscosity operator.
Day, M. S.; Bell, J. B.; Cheng, R. K.; Tachibana, S.; Beckner, V. E.; Lijewski, M. J.
2009-07-01
One strategy for reducing US dependence on petroleum is to develop new combustion technologies for burning the fuel-lean mixtures of hydrogen or hydrogen-rich syngas fuels obtained from the gasification of coal and biomass. Fuel-flexible combustion systems based on lean premixed combustion have the potential for dramatically reducing pollutant emissions in transportation systems, heat and stationary power generation. However, lean premixed flames are highly susceptible to fluid-dynamical combustion instabilities making robust and reliable systems difficult to design. Low swirl burners are emerging as an important technology for meeting design requirements in terms of both reliability and emissions for next generation combustion devices. In this paper, we present simulations of a lean, premixed hydrogen flame stabilized on a laboratory-scale low swirl burner. The simulations use detailed chemistry and transport without incorporating explicit models for turbulence or turbulence/chemistry interaction. Here we discuss the overall structure of the flame and compare with experimental data. We also use the simulation data to elucidate the characteristics of the turbulent flame interaction and how this impacts the analysis of experimental measurements.
Samtaney, Ravi
2012-01-01
We present a numerical method based on an Eulerian approach to solve the Vlasov-Poisson system for 4D drift kinetic turbulence. Our numerical approach uses a conservative formulation with high-order (fourth and higher) evaluation of the numerical fluxes coupled with a fourth-order accurate Poisson solver. The fluxes are computed using a low-dissipation high-order upwind differencing method or a tuned high-resolution finite difference method with no numerical dissipation. Numerical results are presented for the case of imposed ion temperature and density gradients. Different forms of controlled regularization to achieve a well-posed system are used to obtain convergent resolved simulations. The regularization of the equations is achieved by means of a simple collisional model, by inclusion of an ad-hoc hyperviscosity or artificial viscosity term or by implicit dissipation in upwind schemes. Comparisons between the various methods and regularizations are presented. We apply a filtering formalism to the Vlasov equation and derive sub-grid-scale (SGS) terms analogous to the Reynolds stress terms in hydrodynamic turbulence. We present a priori quantifications of these SGS terms in resolved simulations of drift-kinetic turbulence by applying a sharp filter. © 2012 IOP Publishing Ltd.
1983-01-01
Influence Scaling of 2D and 3D Shock/Turbulent ioundary Layer Interactions at Compression Corners." AIM Paper 81-334, January 1981. 5. Kubota, H...generating 3D shock wave/boundary layer interactions 2 Unswept sharp fin interaction and coordinate system 3 Cobra probe measurements of Peake (4) at Mach 4...were made by two Druck 50 PSI transducers, each in- stalled in a computer-controlled 48-port Model 48J4 Scani- valve and referenced to vacuum. A 250
Atkinson, Callum; Buchmann, Nicolas; Kuehn, Matthias; Soria, Julio
2011-11-01
Large-scale three-dimensional (3D) structures in a turbulent boundary layer at Reθ = 2000 are examined via the streamwise extrapolation of time-resolved stereo particle image velocimetry (SPIV) measurements in a wall-normal spanwise plane using Taylor's hypothesis. Two overlapping SPIV systems are used to provide a field of view similar to that of direct numerical simulations (DNS) on the order of 50 δ × 1 . 5 δ × 3 . 0 δ in the streamwise, wall-normal and spanwise directions, respectively, with an interrogation window size of 40+ ×20+ ×60+ wall units. Velocity power spectra are compared with DNS to examine the effective resolution of these measurements and two-point correlations are performed to investigate the integral length scales associated with coherent velocity and vorticity fluctuations. Individual coherent structures are detected to provide statistics on the 3D size, spacing, and angular orientation of large-scale structures, as well as their contribution to the total turbulent kinetic energy and Reynolds shear stress. The support of the ARC through Discovery (and LIEF) grants is gratefully acknowledged.
Experimental studies of occupation times in turbulent flows
DEFF Research Database (Denmark)
Mann, J.; Ott, Søren; Pécseli, H.L.
2003-01-01
as the difference between entrance and exit times of surrounding particles convected through the sphere by the turbulent motions. Simple, and seemingly universal, scaling laws are obtained for the probability density of the occupation times in terms of the basic properties for the turbulent flow and the geometry......The motion of passively convected particles in turbulent flows is studied experimentally in approximately homogeneous and isotropic turbulent flows, generated in water by two moving grids. The simultaneous trajectories of many small passively convected, neutrally buoyant, polystyrene particles...
Scale-invariant matter distribution in the universe
International Nuclear Information System (INIS)
Balian, R.; Schaeffer, R.
1989-01-01
We calculate the galaxy counts or the matter content within a randomly placed cell, under the sole hypothesis of scale-invariance of the many-body correlations functions. The various forms taken by the probability for finding N objects in a given volume are obtained as a function of its size. At smallscales ( -1 Mpc), this probability decreases exponentially with N. At larger scales (0.5h -1 Mpc to 10h -1 Mpc) it behaves as a power-law with an upper and possibly a lower exponential cut-off, reminiscent of the current parametrizations of the galaxy and cluster luminosity functions. We show that the large scale void probability, whose logarithm is seen to be a power-law, is a scale-free extrapolation of its small scale behaviour. As long as the correlation functions are power-laws, this void distribution is not compatible with the linear theory, whatever large scale is considered. We relate this large-scale behaviour of the void probability to the power-law observed at the faint end of the luminosity functions. A scaling law is found, the galaxy and cluster distributions being expressed by the same universal function. We show that the counts in cells are approximately gaussian, only at very large scales, above 50h -1 Mpc, provived the density fluctuations are less than 10% of the mean. In the intermediate range of 10h -1 to 50h -1 Mpc, considerable deviations from gaussian statistics are predicted. Counts in cells are seen to provide a cleaner statistical tool than the mass or luminosity functions and are as easy to obtain either from theoretical information on correlation functions or from observations
Quantify the complexity of turbulence
Tao, Xingtian; Wu, Huixuan
2017-11-01
Many researchers have used Reynolds stress, power spectrum and Shannon entropy to characterize a turbulent flow, but few of them have measured the complexity of turbulence. Yet as this study shows, conventional turbulence statistics and Shannon entropy have limits when quantifying the flow complexity. Thus, it is necessary to introduce new complexity measures- such as topology complexity and excess information-to describe turbulence. Our test flow is a classic turbulent cylinder wake at Reynolds number 8100. Along the stream-wise direction, the flow becomes more isotropic and the magnitudes of normal Reynolds stresses decrease monotonically. These seem to indicate the flow dynamics becomes simpler downstream. However, the Shannon entropy keeps increasing along the flow direction and the dynamics seems to be more complex, because the large-scale vortices cascade to small eddies, the flow is less correlated and more unpredictable. In fact, these two contradictory observations partially describe the complexity of a turbulent wake. Our measurements (up to 40 diameters downstream the cylinder) show that the flow's degree-of-complexity actually increases firstly and then becomes a constant (or drops slightly) along the stream-wise direction. University of Kansas General Research Fund.
Cuzzi, J. N.; Hartlep, T.; Estrada, P.
2016-01-01
The initial accretion of primitive bodies from freely-floating nebula particles remains problematic. Traditional growth-by-sticking models in turbulent nebulae encounter a "meter-size barrier" due to both drift and destruction, or even a millimeter-to-centimeter-size "bouncing" barrier. Recent suggestions have been made that some "lucky" particles might be able to outgrow the collision and/or drift barriers, and lead to so-called "streaming instabilities" or SI. However, new full models of growth by sticking in the presence of radial drift show that lucky particles (the largest particles, at the tail of the size distribution, that grow beyond the nominal fragmentation and drift barriers) are far too rare to lead to any collective effects such as streaming or gravitational instabilities. Thus we need to focus on typical radii gamma(sub M) which contain most of the mass. Our models of disks with weak-to-moderate turbulence, which include all the most recent experimental constraints on collisional growth, erosion, bouncing, and fragmentation, as well as radial drift, find that growth stalls quite generally at sizes gamma(sub M) which are too small to settle into layers which are dense enough for any collective effects (streaming or gravitational instabilities) to arise. Even if growth by sticking could somehow breach the nominal barriers (perhaps if the actual sticking or strength is larger than current estimates for pure ice or pure silicate, with specific grain sizes), turbulent nebulae present subsequent formidable obstacles to incremental growth through the 1-10km size range. On the other hand, non-turbulent nebulae alpha is less than 10(Sup -4).
Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region
Directory of Open Access Journals (Sweden)
Šulc Radek
2017-01-01
Full Text Available The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV. The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i distilled water, ii a 28% vol. aqueous solution of glycol, and iii a 43% vol. aqueous solution of glycol, corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the fully-developed turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.388 to 0.540, which corresponds to the high level of turbulence intensity.
Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region
Šulc, Radek; Ditl, Pavel; Fořt, Ivan; Jašíkova, Darina; Kotek, Michal; Kopecký, Václav; Kysela, Bohuš
The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the fully-developed turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.388 to 0.540, which corresponds to the high level of turbulence intensity.
Esters, L. T.; Ward, B.; Sutherland, G.; Ten Doeschate, A.; Landwehr, S.; Bell, T. G.; Christensen, K. H.
2016-02-01
The air-sea exchange of heat, gas and momentum plays an important role for the Earth's weather and global climate. The exchange processes between ocean and atmosphere are influenced by the prevailing surface ocean dynamics. This surface ocean is a highly turbulent region where there is enhanced production of turbulent kinetic energy (TKE). The dissipation rate of TKE (ɛ) in the surface ocean is an important process for governing the depth of both the mixing and mixed layers, which are important length-scales for many aspects of ocean research. However, there exist very limited observations of ɛ under open ocean conditions and consequently our understanding of how to model the dissipation profile is very limited. The approaches to model profiles of ɛ that exist, differ by orders of magnitude depending on their underlying theoretical assumption and included physical processes. Therefore, scaling ɛ is not straight forward and requires open ocean measurements of ɛ to validate the respective scaling laws. This validated scaling of ɛ, is for example required to produce accurate mixed layer depths in global climate models. Errors in the depth of the ocean surface boundary layer can lead to biases in sea surface temperature. Here, we present open ocean measurements of ɛ from the Air-Sea Interaction Profiler (ASIP) collected during several cruises in different ocean basins. ASIP is an autonomous upwardly rising microstructure profiler allowing undisturbed profiling up to the ocean surface. These direct measurements of ɛ under various types of atmospheric and oceanic conditions along with measurements of atmospheric fluxes and wave conditions allow us to make a unique assessment of several scaling approaches based on wind, wave and buoyancy forcing. This will allow us to best assess the most appropriate ɛ-based parameterisation for air-sea exchange.
Origin of the large scale structures of the universe
International Nuclear Information System (INIS)
Oaknin, David H.
2004-01-01
We revise the statistical properties of the primordial cosmological density anisotropies that, at the time of matter-radiation equality, seeded the gravitational development of large scale structures in the otherwise homogeneous and isotropic Friedmann-Robertson-Walker flat universe. Our analysis shows that random fluctuations of the density field at the same instant of equality and with comoving wavelength shorter than the causal horizon at that time can naturally account, when globally constrained to conserve the total mass (energy) of the system, for the observed scale invariance of the anisotropies over cosmologically large comoving volumes. Statistical systems with similar features are generically known as glasslike or latticelike. Obviously, these conclusions conflict with the widely accepted understanding of the primordial structures reported in the literature, which requires an epoch of inflationary cosmology to precede the standard expansion of the universe. The origin of the conflict must be found in the widespread, but unjustified, claim that scale invariant mass (energy) anisotropies at the instant of equality over comoving volumes of cosmological size, larger than the causal horizon at the time, must be generated by fluctuations in the density field with comparably large comoving wavelength
Solar Plasma Radio Emission in the Presence of Imbalanced Turbulence of Kinetic-Scale Alfvén Waves
Lyubchyk, O.; Kontar, E. P.; Voitenko, Y. M.; Bian, N. H.; Melrose, D. B.
2017-09-01
We study the influence of kinetic-scale Alfvénic turbulence on the generation of plasma radio emission in the solar coronal regions where the ratio β of plasma to magnetic pressure is lower than the electron-to-ion mass ratio me/mi. The present study is motivated by the phenomenon of solar type I radio storms that are associated with the strong magnetic field of active regions. The measured brightness temperature of the type I storms can be up to 10^{10} K for continuum emission, and can exceed 10^{11} K for type I bursts. At present, there is no generally accepted theory explaining such high brightness temperatures and some other properties of the type I storms. We propose a model with an imbalanced turbulence of kinetic-scale Alfvén waves that produce an asymmetric quasi-linear plateau on the upper half of the electron velocity distribution. The Landau damping of resonant Langmuir waves is suppressed and their amplitudes grow spontaneously above the thermal level. The estimated saturation level of Langmuir waves is high enough to generate observed type I radio emission at the fundamental plasma frequency. Harmonic emission does not appear in our model because the backward-propagating Langmuir waves undergo strong Landau damping. Our model predicts 100% polarization in the sense of the ordinary (o-) mode of type I emission.
Scaling laws for AC gas breakdown and implications for universality
Loveless, Amanda M.; Garner, Allen L.
2017-10-01
The reduced dependence on secondary electron emission and electrode surface properties makes radiofrequency (RF) and microwave (MW) plasmas advantageous over direct current (DC) plasmas for various applications, such as microthrusters. Theoretical models relating molecular constants to alternating current (AC) breakdown often fail due to incomplete understanding of both the constants and the mechanisms involved. This work derives simple analytic expressions for RF and MW breakdown, demonstrating the transition between these regimes at their high and low frequency limits, respectively. We further show that the limiting expressions for DC, RF, and MW breakdown voltage all have the same universal scaling dependence on pressure and gap distance at high pressure, agreeing with experiment.
Universal scaling for the dilemma strength in evolutionary games
Wang, Zhen; Kokubo, Satoshi; Jusup, Marko; Tanimoto, Jun
2015-09-01
Why would natural selection favor the prevalence of cooperation within the groups of selfish individuals? A fruitful framework to address this question is evolutionary game theory, the essence of which is captured in the so-called social dilemmas. Such dilemmas have sparked the development of a variety of mathematical approaches to assess the conditions under which cooperation evolves. Furthermore, borrowing from statistical physics and network science, the research of the evolutionary game dynamics has been enriched with phenomena such as pattern formation, equilibrium selection, and self-organization. Numerous advances in understanding the evolution of cooperative behavior over the last few decades have recently been distilled into five reciprocity mechanisms: direct reciprocity, indirect reciprocity, kin selection, group selection, and network reciprocity. However, when social viscosity is introduced into a population via any of the reciprocity mechanisms, the existing scaling parameters for the dilemma strength do not yield a unique answer as to how the evolutionary dynamics should unfold. Motivated by this problem, we review the developments that led to the present state of affairs, highlight the accompanying pitfalls, and propose new universal scaling parameters for the dilemma strength. We prove universality by showing that the conditions for an ESS and the expressions for the internal equilibriums in an infinite, well-mixed population subjected to any of the five reciprocity mechanisms depend only on the new scaling parameters. A similar result is shown to hold for the fixation probability of the different strategies in a finite, well-mixed population. Furthermore, by means of numerical simulations, the same scaling parameters are shown to be effective even if the evolution of cooperation is considered on the spatial networks (with the exception of highly heterogeneous setups). We close the discussion by suggesting promising directions for future research
The fusion code XGC: Enabling kinetic study of multi-scale edge turbulent transport in ITER
Energy Technology Data Exchange (ETDEWEB)
D' Azevedo, Eduardo [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Abbott, Stephen [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koskela, Tuomas [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Worley, Patrick [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Ku, Seung-Hoe [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Ethier, Stephane [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Yoon, Eisung [Rensselaer Polytechnic Inst., Troy, NY (United States); Shephard, Mark [Rensselaer Polytechnic Inst., Troy, NY (United States); Hager, Robert [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Lang, Jianying [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Intel Corporation, Santa Clara, CA (United States); Choi, Jong [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Podhorszki, Norbert [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Klasky, Scott [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Parashar, Manish [Rutgers Univ., Piscataway, NJ (United States); Chang, Choong-Seock [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2017-01-01
The XGC fusion gyrokinetic code combines state-of-the-art, portable computational and algorithmic technologies to enable complicated multiscale simulations of turbulence and transport dynamics in ITER edge plasma on the largest US open-science computer, the CRAY XK7 Titan, at its maximal heterogeneous capability, which have not been possible before due to a factor of over 10 shortage in the time-to-solution for less than 5 days of wall-clock time for one physics case. Frontier techniques such as nested OpenMP parallelism, adaptive parallel I/O, staging I/O and data reduction using dynamic and asynchronous applications interactions, dynamic repartitioning.
Multifractal formalism by enforcing the universal behavior of scaling functions
Mukli, Peter; Nagy, Zoltan; Eke, Andras
2015-01-01
Despite its solid foundations, multifractal analysis is still a challenging task. The 'inversed' singularity spectrum is a major pitfall in standard multifractal analyses especially for empirical signals. To resolve this issue, we identified the fan-like convergent geometry of scaling functions yielding a limit value (termed focus) for all moments at the largest scale. Building on this behavior of scaling, we introduce the novel concept of focus-based multifractal formalism. It relies on enforcing this universal behavior when the moment-wise scaling exponents are assessed for the scaling functions. Besides developing focus-based variants of the established multifractal detrended fluctuation analysis and the wavelet leader method, we present a novel analytical tool of multifractal signal summation conversion. All methods are extensively tested on exact multifractal signals synthesized by the generalized binomial multifractal model in terms of precision and incidence of 'inversed' singularity spectra. Our focus-based variants never yielded 'inversed' spectra and their precision was found similar to that of standard methods. Our approach allowed computing a moment-wise and a global error parameter describing the impact of finite size effect and degree of multifractality as compared to that of the fitted exact multifractal model. We demonstrate that the standard approach to multifractal analyses contains a central element that is essentially monofractal due to its regression scheme assessing the scaling exponents for each and every moment, separately. Hence these methods can yield reliable estimates only for ideally behaving multifractal signals. In contrast, our focus-based variants due to their genuine multifractal model fitting always yield reliable estimates accompanied by goodness-of-fit statistics. The presented novel multifractal tools offer means of dealing with the consequences of endogenous impurities of potentially multifractal empirical signals.
Magnetic fields and large scale structure in a hot Universe. IV. The egg-carton Universe
Battaner, E.; Florido, E.
1998-10-01
Considering the possibility of a network of octahedra contacting at their vertexes for the large scale structure of the present Universe, as was discussed in previous papers of this series, we now try to identify real octahedra in the observed distribution of superclusters and voids. This identification is easy and clear. The network seems to have been deformed locally near the great mass associated to the large Piscis-Cetus complex.
Scaling Universality at the Dynamic Vortex Mott Transition.
Energy Technology Data Exchange (ETDEWEB)
Lankhorst, Martijn; Poccia, Nicola; Stehno, Martin; Galda, Alexey; Barman, Himadri; Coneri, Francesco; Hilgenkamp, Hans; Brinkman, Alexander; Gulubov, Alexander A.; Tripathi, Vikram; Baturina, Tatyana; Vinokur, Valerii M.
2018-01-17
The cleanest way to observe a dynamic Mott insulator-to-metal transition (DMT) without the interference from disorder and other effects inherent to electronic and atomic systems, is to employ the vortex Mott states formed by superconducting vortices in a regular array of pinning sites. Here, we report the critical behavior of the vortex system as it crosses the DMT line, driven by either current or temperature. We find universal scaling with respect to both, expressed by the same scaling function and characterized by a single critical exponent coinciding with the exponent for the thermodynamic Mott transition. We develop a theory for the DMT based on the parity reflection-time reversal (PT) symmetry breaking formalism and find that the nonequilibrium-induced Mott transition has the same critical behavior as the thermal Mott transition. Our findings demonstrate the existence of physical systems in which the effect of a nonequilibrium drive is to generate an effective temperature and hence the transition belonging in the thermal universality class.
Statistical Analysis of Large-Scale Structure of Universe
Tugay, A. V.
While galaxy cluster catalogs were compiled many decades ago, other structural elements of cosmic web are detected at definite level only in the newest works. For example, extragalactic filaments were described by velocity field and SDSS galaxy distribution during the last years. Large-scale structure of the Universe could be also mapped in the future using ATHENA observations in X-rays and SKA in radio band. Until detailed observations are not available for the most volume of Universe, some integral statistical parameters can be used for its description. Such methods as galaxy correlation function, power spectrum, statistical moments and peak statistics are commonly used with this aim. The parameters of power spectrum and other statistics are important for constraining the models of dark matter, dark energy, inflation and brane cosmology. In the present work we describe the growth of large-scale density fluctuations in one- and three-dimensional case with Fourier harmonics of hydrodynamical parameters. In result we get power-law relation for the matter power spectrum.
Alignments and small scale statistics in the production region of grid turbulence
Paul, Immanuvel; Papadakis, George; Vassilicos, John Christos; Turbulence, Mixing; Flow Control Group Team
2015-11-01
Direct Numerical Simulation (DNS) of turbulent flow generated by a single square grid is investigated using an unstructured finite volume method. The maximum value of the Taylor length-based Reynolds number throughout the computed flow field is about 40. The main focus of this study is on the production region which lies in the lee of the grid where turbulence builds up. Statistics of vorticity and of eigenvalues (λi, where i =1,2,3) and eigenvectors (ei, where i =1,2,3) of the fluctuating strain rate tensor (Sij) are analyzed. It is observed that the PDFs of all the eigenvalues in the production region are highly non-gaussian. The PDFs of the compressive (λ3) and intermediate (λ2) eigenvalues are strongly skewed to negative and positive values respectively. The energy spectrum of the streamwise fluctuating velocity has a well-defined power law with an exponent around -2 or -5/3 over more than one decade depending on the position in the production region. It is also observed that the most extensive eigenvector (e1) and the intermediate eigenvector (e2) align significantly with vorticity vector in the production region, which in turn increases average enstrophy production.
On the dynamics of large-scale structures in electron temperature gradient turbulence
International Nuclear Information System (INIS)
Holland, C.; Diamond, P.H.
2005-01-01
The electron temperature gradient mode has been proposed to be a source of experimentally relevant electron thermal transport, via a variety of non-linear phenomena such as the generation of streamers. The question of streamer stability and saturation is revisited, with the effects of geometry and perturbation stability highlighted. It is shown that the streamer saturation level is not determined by the balance of Kelvin-Helmholtz rate vs. linear growth rate, but by balancing the non-linear Kelvin-Helmholtz drive against damping mechanisms of the Kelvin-Helmholtz perturbation, suggesting a significantly lower streamer saturation level. In addition, random shear suppression of ETG turbulence by drift-ion temperature gradient (DITG) modes is studied, and it is found that streamers will be sensitive to shearing by short-wavelength DITG modes. An additional interaction mechanism, modulations of the electron temperature gradient induced by the DITG turbulence, is considered and shown to be quite significant. These considerations are used to motivate a discussion of the requirements for a credible theory of streamer transport
Probing cosmology with the homogeneity scale of the Universe through large scale structure surveys
International Nuclear Information System (INIS)
Ntelis, Pierros
2017-01-01
This thesis exposes my contribution to the measurement of homogeneity scale using galaxies, with the cosmological interpretation of results. In physics, any model is characterized by a set of principles. Most models in cosmology are based on the Cosmological Principle, which states that the universe is statistically homogeneous and isotropic on a large scales. Today, this principle is considered to be true since it is respected by those cosmological models that accurately describe the observations. However, while the isotropy of the universe is now confirmed by many experiments, it is not the case for the homogeneity. To study cosmic homogeneity, we propose to not only test a model but to test directly one of the postulates of modern cosmology. Since 1998 the measurements of cosmic distances using type Ia supernovae, we know that the universe is now in a phase of accelerated expansion. This phenomenon can be explained by the addition of an unknown energy component, which is called dark energy. Since dark energy is responsible for the expansion of the universe, we can study this mysterious fluid by measuring the rate of expansion of the universe. The universe has imprinted in its matter distribution a standard ruler, the Baryon Acoustic Oscillation (BAO) scale. By measuring this scale at different times during the evolution of our universe, it is then possible to measure the rate of expansion of the universe and thus characterize this dark energy. Alternatively, we can use the homogeneity scale to study this dark energy. Studying the homogeneity and the BAO scale requires the statistical study of the matter distribution of the universe at large scales, superior to tens of Mega-parsecs. Galaxies and quasars are formed in the vast over densities of matter and they are very luminous: these sources trace the distribution of matter. By measuring the emission spectra of these sources using large spectroscopic surveys, such as BOSS and eBOSS, we can measure their positions
Plaza-Pust, Carolina
2008-01-01
Research over the last decades has shown that language development in its multiple forms is characterized by a succession of stable and unstable states. However, the variation observed is neither expected nor can it be accounted for on the basis of traditional learning concepts conceived of within the Universal Grammar (UG) paradigm. In this…
Universal scaling in disordered systems and nonuniversal exponents
Bardhan, K. K.; Talukdar, D.; Nandi, U. N.; Mukherjee, C. D.
2014-05-01
The effect of an electric field on conduction in a disordered system is an old but largely unsolved problem. Experiments cover a wide variety of systems—amorphous/doped semiconductors, conducting polymers, organic crystals, manganites, composites, metallic alloys, double perovskites—ranging from strongly to weakly localized systems and from strongly to weakly correlated ones. Theories have singularly failed to predict any universal trend resulting in separate theories for separate systems. Here, we discuss a one-parameter scaling that has recently been found to give a systematic account of the field-dependent conductance in two diverse, strongly localized systems of conducting polymers and manganites. Except for a limited number of systems which are described by the hot electron models, the vast majority of different systems in various disorder regimes in two (2D)- and three (2D)-dimensions obey the scaling. The nonlinearity exponent x associated with the scaling was found to be nonuniversal and exhibiting a structure. For 2D weakly localized systems, the nonlinearity exponent x is ≥7 and is roughly inversely proportional to the sheet resistance. The existing theories of weak localization prove to be adequate and a complete scaling function is derived. In a 2D strongly localized system, a temperature-induced scaling-nonscaling transition (SNST) is revealed. For 3D strongly localized systems, the exponent lies between -1 and 1, and surprisingly is quantized (x ≈0.08n). This poses a serious theoretical challenge. Various results are compared with predictions of the existing theories.
Directory of Open Access Journals (Sweden)
David Barton Bray
2012-08-01
Full Text Available Some important elements of common property theory include a focus on individual communities or user groups, local level adjudication of conflicts, local autonomy in rule making, physical harvests, and low levels of articulation with markets. We present a case study of multi-scale collective action around indigenous/community conserved areas (ICCAs in Oaxaca, Mexico that suggests a modification of these components of common property theory. A multi-community ICCA in Oaxaca demonstrates the importance of inter-community collective action as key link in multi-scale governance, that conflicts are often negotiated in multiple arenas, that rules emerge at multiple scales, and that management for conservation and environmental services implies no physical harvests. Realizing economic gains from ICCAs for strict conservation may require something very different than traditional natural resource management. It requires intense engagement with extensive networks of government and civil society actors and new forms of community and inter-community collection action, or multi-scale governance. Multi-scale governance is built on trust and social capital at multiple scales and also constitutes collective action at multiple scales. However, processes of multi-scale governance are also necessarily “turbulent” with actors frequently having conflicting values and goals to be negotiated. We present an analytic history of the process of emergence of community and inter-community collective action around strict conservation and examples of internal and external turbulence. We argue that this case study and other literature requires an extensions of the constitutive elements of common property theory.
Bauer, C.; Feldmann, D.; Wagner, C.
2017-12-01
Direct numerical simulations of turbulent pipe flow in a flow domain of length L = 42R, friction Reynolds number in the range of 180 ≤ Reτ ≤ 1500, and two different wall-normal grid refinements were carried out and investigated in terms of high-order turbulence statistics. The phenomenology of large local wall-normal velocity fluctuations (velocity spikes) was discussed by means of time series and instantaneous flow-field realisations. Due to their rare appearance both in space and time, statistical high-order moments take a long time to converge. A convergence study was performed and for fully converged statistics the sensitivity of the grid resolution on the wall-normal kurtosis component value at the wall as well as the scaling behaviour of high-order statistics was investigated. The streamwise Reynolds stress as well as the streamwise skewness and the wall-normal flatness exhibited logarithmic Reynolds number dependencies in the vicinity of the wall and scaling laws were derived accordingly. In the bulk flow region, a sudden increase in magnitude in both the streamwise Reynolds stress and skewness was determined for the largest Reynolds number Reτ = 1500, while the profiles collapsed well in wall units for Reτ ≤ 720. Both Reynolds number dependencies in the near-wall and the bulk region could be related to large-scale outer-flow motions penetrating the buffer layer. While wavelengths related to larger-scale motions (λz ≈ 3R) were computed for Reynolds numbers up to Reτ = 720 by means of two-dimensional two-point velocity correlations, even larger wavelengths related to very-large-scale motions appeared for Reτ = 1500. They are probably the reason for the sudden increase in magnitude of streamwise Reynolds stress and skewness, respectively. With the aid of instantaneous flow-field realisations and conditional averaged statistics, the Reynolds dependency of the wall-normal flatness value at the wall was related to the scaling failure of the
The Student Perception of University Support and Structure Scale: Development and Validation
Wintre, Maxine G.; Gates, Shawn K. E.; Pancer, W. Mark; Pratt, Michael S.; Polivy, Janet; Birnie-Lefcovitch, S.; Adams, Gerald
2009-01-01
A new scale, the Student Perception of University Support and Structure Scale (SPUSS), was developed for research on the transition to university. The scale was based on concepts derived from Baumrind's (1971) theory of parenting styles. Data were obtained from two separate cohorts of freshmen (n=759 and 397) attending six Canadian universities of…
International Nuclear Information System (INIS)
Li Ya-Qing; Wu Zhen-Sen; Zhang Yuan-Yuan; Wang Ming-Jun
2014-01-01
Based on the modified Rytov theory and the international telecommunication union-radio (ITU-R) slant atmospheric structure constant model, the uniform scintillation index of partially coherent Gaussian—Schell model (GSM) beam propagation in the slant path is derived from weak- to strong-turbulence regions considering inner- and outer-scale effects. The effects of wavelength of beams and inner- and outer-scale of turbulence on scintillation are analyzed numerically. Comparison between the scintillation of GSM beams under the von Karman spectrum and that of beams under the modified Hill spectrum is made. The results obtained show that the scintillation index obtained under the von Karman spectrum is smaller than that under the modified Hill spectrum. This study can find theory bases for the experiments of the partially coherent GSM beam propagation through atmospheric turbulence. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Experiments in turbulent pipe flow
Energy Technology Data Exchange (ETDEWEB)
Torbergsen, Lars Even
1998-12-31
This thesis reports experimental results for the mean velocity and turbulence statistics in two straight pipe sections for bulk Reynolds numbers in the range 22000 to 75000. The flow was found consistent with a fully developed state. Detailed turbulence spectra were obtained for low and moderate turbulent Reynolds number. For the pipe centre line location at R{sub {lambda}} = 112, a narrow range in the streamwise power spectrum applied to the -5/3 inertial subrange. However this range was influenced both by turbulence production and viscous dissipation, and therefore did not reflect a true inertial range. The result indicates how the intermediate range between the production and dissipative scales can be misinterpreted as an inertial range for low and moderate R{sub {lambda}}. To examine the universal behaviour of the inertial range, the inertial scaling of the streamwise power spectrum is compared to the inertial scaling of the second order longitudinal velocity structure function, which relate directly by a Fourier transform. Increasing agreement between the Kolmogorov constant C{sub K} and the second order structure function scaling constant C{sub 2} was observed with increasing R{sub {lambda}}. The result indicates that a true inertial range requires several decades of separation between the energy containing and dissipative scales. A method for examining spectral anisotropy is reported and applied to turbulence spectra in fully developed pipe flow. It is found that the spectral redistribution from the streamwise to the two lateral spectra goes primarily to the circumferential component. Experimental results are reported for an axisymmetric contraction of a fully developed pipe flow. 67 refs., 75 figs., 9 tabs.
Bardoczi, L.
2016-10-01
We present the first localized measurements of ITG scale temperature and density fluctuations and TEM scale density fluctuations modified by an m=2, n=1 magnetic island. These islands are formed by a Neoclassical Tearing Mode (NTM) deep in the core plasma at the q=2 surface. NTMs are important as they often degrade confinement and lead to disruption. This is the first experimental confirmation of a long-standing theory prediction of decreased local small-scale turbulence levels across large-scale magnetic islands. Our measurements capture a mean reduction of turbulence inside (and enhancement just outside) the island region during island evolution. Additionally, in the island saturated state, the fluctuations at the O-point are observed to be reduced compared to the X-point. These measurements allow the determination of the turbulence length scale at the island separatrix that is predicted to affect NTM stability. A novel, non-perturbative measurement technique finds reduced cross-field electron thermal diffusivity (by 1-2 orders of magnitude) at the O-point, consistent with the local turbulence reduction. Initial comparisons to the GENE non-linear gyrokinetic code are promising with GENE predicting the observed turbulence reduction inside the island and increase just outside the island and replicating the observed scaling with island size. These results allow the validation of gyrokinetic simulations modeling the interaction of multi-scale phenomena as well as have potential implications for improved NTM control. Supported by USDOE under DE-FG02-08ER54984, DE-FG02-08ER54999 and DE-FC02-04ER54698.
Li, Guang-Xing
2018-03-01
Astrophysical systems, such as clumps that form star clusters share a density profile that is close to ρ ˜ r-2. We prove analytically this density profile is the result of the scale-free nature of the gravitational collapse. Therefore, it should emerge in many different situations as long as gravity is dominating the evolution for a period that is comparable or longer than the free-fall time, and this does not necessarily imply an isothermal model, as many have previously believed. To describe the collapse process, we construct a model called the turbulence-regulated gravitational collapse model, where turbulence is sustained by accretion and dissipates in roughly a crossing time. We demonstrate that a ρ ˜ r-2 profile emerges due to the scale-free nature the system. In this particular case, the rate of gravitational collapse is regulated by the rate at which turbulence dissipates the kinetic energy such that the infall speed can be 20-50% of the free-fall speed(which also depends on the interpretation of the crossing time based on simulations of driven turbulence). These predictions are consistent with existing observations, which suggests that these clumps are in the stage of turbulence-regulated gravitational collapse. Our analysis provides a unified description of gravitational collapse in different environments.
Energy Technology Data Exchange (ETDEWEB)
Chasapis, Alexandros; Matthaeus, W. H.; Parashar, T. N.; Maruca, B. A. [University of Delaware, Newark, DE (United States); Fuselier, S. A.; Burch, J. L. [Southwest Research Institute, San Antonio, TX (United States); Phan, T. D. [Space Sciences Laboratory, University of California, Berkeley, CA (United States); Moore, T. E.; Pollock, C. J.; Gershman, D. J. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Torbert, R. B. [University of New Hampshire, Durham, NH (United States); Russell, C. T.; Strangeway, R. J., E-mail: chasapis@udel.edu [University of California, Los Angeles, CA (United States)
2017-07-20
Using data from the Magnetospheric Multiscale (MMS) and Cluster missions obtained in the solar wind, we examine second-order and fourth-order structure functions at varying spatial lags normalized to ion inertial scales. The analysis includes direct two-spacecraft results and single-spacecraft results employing the familiar Taylor frozen-in flow approximation. Several familiar statistical results, including the spectral distribution of energy, and the sale-dependent kurtosis, are extended down to unprecedented spatial scales of ∼6 km, approaching electron scales. The Taylor approximation is also confirmed at those small scales, although small deviations are present in the kinetic range. The kurtosis is seen to attain very high values at sub-proton scales, supporting the previously reported suggestion that monofractal behavior may be due to high-frequency plasma waves at kinetic scales.
A Study on Time-Scales Ratio and Turbulent Prandtl Number in Ducts of Industrial Applications
DEFF Research Database (Denmark)
Rokni, Masoud
2006-01-01
is solved using a two-equation heat ﬂux model. The computed results compare satisfactory with the available experimental data. The time-scale ratio R is deﬁned as the ratio between the dynamic time-scale (k/ε) and the scalar time-scale(0.5θθ/εθ). Based on existing DNS data and calculations in this work...... of heat exchangers for various applications area....
Effect of helicity on the correlation time of large scales in turbulent flows
Cameron, Alexandre; Alexakis, Alexandros; Brachet, Marc-Étienne
2017-11-01
Solutions of the forced Navier-Stokes equation have been conjectured to thermalize at scales larger than the forcing scale, similar to an absolute equilibrium obtained for the spectrally truncated Euler equation. Using direct numeric simulations of Taylor-Green flows and general-periodic helical flows, we present results on the probability density function, energy spectrum, autocorrelation function, and correlation time that compare the two systems. In the case of highly helical flows, we derive an analytic expression describing the correlation time for the absolute equilibrium of helical flows that is different from the E-1 /2k-1 scaling law of weakly helical flows. This model predicts a new helicity-based scaling law for the correlation time as τ (k ) ˜H-1 /2k-1 /2 . This scaling law is verified in simulations of the truncated Euler equation. In simulations of the Navier-Stokes equations the large-scale modes of forced Taylor-Green symmetric flows (with zero total helicity and large separation of scales) follow the same properties as absolute equilibrium including a τ (k ) ˜E-1 /2k-1 scaling for the correlation time. General-periodic helical flows also show similarities between the two systems; however, the largest scales of the forced flows deviate from the absolute equilibrium solutions.
Energy Technology Data Exchange (ETDEWEB)
Talbot, L.; Cheng, R.K. [Lawrence Berkeley Laboratory, CA (United States)
1993-12-01
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
Czech Academy of Sciences Publication Activity Database
Nakayama, H.; Jurčáková, Klára; Nagai, H.
2013-01-01
Roč. 50, č. 5 (2013), s. 503-519 ISSN 0022-3131 Institutional support: RVO:61388998 Keywords : local-scale high-resolution dispersion model * nuclear emergency response system * large-eddy simulation * spatially developing turbulent boundary layer flow Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.452, year: 2013
Chhiber, Rohit; Usmanov, Arcadi V.; DeForest, Craig E.; Matthaeus, William H.; Parashar, Tulasi N.; Goldstein, Melvyn L.
2018-04-01
Recent analysis of Solar-Terrestrial Relations Observatory (STEREO) imaging observations have described the early stages of the development of turbulence in the young solar wind in solar minimum conditions. Here we extend this analysis to a global magnetohydrodynamic (MHD) simulation of the corona and solar wind based on inner boundary conditions, either dipole or magnetogram type, that emulate solar minimum. The simulations have been calibrated using Ulysses and 1 au observations, and allow, within a well-understood context, a precise determination of the location of the Alfvén critical surfaces and the first plasma beta equals unity surfaces. The compatibility of the the STEREO observations and the simulations is revealed by direct comparisons. Computation of the radial evolution of second-order magnetic field structure functions in the simulations indicates a shift toward more isotropic conditions at scales of a few Gm, as seen in the STEREO observations in the range 40–60 R ⊙. We affirm that the isotropization occurs in the vicinity of the first beta unity surface. The interpretation based on early stages of in situ solar wind turbulence evolution is further elaborated, emphasizing the relationship of the observed length scales to the much smaller scales that eventually become the familiar turbulence inertial range cascade. We argue that the observed dynamics is the very early manifestation of large-scale in situ nonlinear couplings that drive turbulence and heating in the solar wind.
Scaling of mean inertia and theoretical basis for a log law in turbulent boundary layers
Philip, Jimmy; Morrill-Winter, Caleb; Klewicki, Joseph
2017-11-01
Log law in the mean streamwise velocity (U) for pipes/channels is well accepted based on the derivation from the mean momentum balance (MMB) equation and support from experimental data. For flat plate turbulent boundary layers (TBLs), however, there is only empirical evidence and a theoretical underpinning of the kind available for pipes/channels in lacking. The main difficultly is the mean inertia (MI) term in the MMB equation, which, unlike in pipes/channels, is not a constant in TBLs. We present results from our paper (JFM `` 2017, Vol 813, pp 594-617), where the MI term for TBL is transformed so as to render it invariant in the outer region, corroborated with high Re (δ+) data from Melbourne Wind Tunnel and New Hampshire Flow Physics Facility. The transformation is possible because the MI term in the TBL has a `shape' which becomes invariant with increasing δ+ and a `magnitude' which is proportional to 1 /δ+ . The transformed equation is then employed to derive a log law for U with κ an order one (von-Karman) constant. We also show that the log law begins at y+ =C1√{δ+} , and the peak location of the Reynolds shear stress, ym+ =C2√{δ+} , where, C1 3.6 and C2 2.17 are from high Re data. Australian Research Council and the US National Science Foundation.
Coronae as Consequence of Large Scale Magnetic Fields in Turbulent Accretion Disks
DEFF Research Database (Denmark)
G. Blackman, Eric; Pessah, Martin Elias
2009-01-01
emission. Our results suggest that a significant fraction of the magnetic energy in accretion disks resides in large scale fields, which in turn provides circumstantial evidence for significant non-local transport phenomena and the need for large scale magnetic field generation. For the example of Seyfert...
Interdisciplinary aspects of turbulence
Kupka, Friedrich
2008-01-01
What do combustion engines, fusion reactors, weather forecast, ocean flows, our sun, and stellar explosions in outer space have in common? Of course, the physics and the length and time scales are vastly different in all cases, but it is also well known that in all of them, on some relevant length scales, the material flows that govern the dynamical and/or secular evolution of the systems are chaotic and often unpredictable: they are said to be turbulent. The interdisciplinary aspects of turbulence are brought together in this volume containing chapters written by experts from very different fields, including geophysics, astrophysics, and engineering. It covers several subjects on which considerable progress was made during the last decades, from questions concerning the very nature of turbulence to some practical applications. These subjects include: a basic introduction into turbulence, statistical mechanics and nonlinear dynamics, turbulent convection in stars, atmospheric turbulence in the context of nume...
International Nuclear Information System (INIS)
Nagaosa, Ryuichi; Handler, Robert A
2011-01-01
The purpose of this study is to model scalar transfer mechanisms in a fully developed turbulence for accurate predictions of the turbulent scalar flux across a shear-free gas-liquid interface. The concept of the surface-renewal approximation (Dankwerts, 1951) is introduced in this study to establish the predictive models for the interfacial scalar flux. Turbulent flow realizations obtained by a direct numerical simulation technique are employed to prepare details of three-dimensional information on turbulence in the region very close to the interface. Two characteristic time scales at the interface have been examined for exact prediction of the scalar transfer flux. One is the time scale which is reciprocal of the root-mean-square surface divergence, T γ = (γγ) −1/2 , where γ is the surface divergence. The other time scale to be examined is T S = Λ/V, where Λ is the zero-correlation length of the surface divergence as the interfacial length scale, and V is the root-mean-square velocity fluctuation in the streamwise direction as the interfacial velocity scale. The results of this study suggests that T γ is slightly unsatisfactory to correlate the turbulent scalar flux at the gas-liquid interface based on the surface-renewal approximation. It is also found that the proportionality constant appear to be 0.19, which is different with that observed in the laboratory experiments, 0.34 (Komori, Murakami, and Ueda, 1989). It is concluded that the time scale, T γ , is considered a different kind of the time scale observed in the laboratory experiments. On the other hand, the present in-silico experiments indicate that T s predicts the turbulent scalar flux based on the surface-renewal approximation in a satisfactory manner. It is also elucidated that the proportionality constant for T s is approximately 0.36, which is very close to that found by the laboratory experiments. This fact shows that the time scale T s appears to be essentially the same as the time scale
Towards a universal scaling for broadband turbulent noise in internal flow devices
Jong, A.T. de; Golliard, J.
2013-01-01
An investigation is performed on the scalability of broadband noise sources from separated flows in internal pipe systems. Broadband sources from for example wellhead chokes, bends and valves can potentially excite subsea manifolds through fluid acoustic coupling and fluid structural coupling. The
Scaled electron experiments at the University of Maryland
International Nuclear Information System (INIS)
Haber, I.; Bai, G.; Bernal, S.; Beaudoin, B.; Feldman, D.; Fiorito, R.B.; Godlove, T.F.; Kishek, R.A.; O'Shea, P.G.; Quinn, B.; Papadopoulos, C.; Reiser, M.; Rodgers, J.; Stratakis, D.; Sutter, D.; Thangaraj, J.C.T.; Tian, K.; Walter, M.; Wu, C.
2007-01-01
The University of Maryland Electron Ring (UMER) and the Long Solenoid Experiment (LSE) are two electron machines that were designed explicitly to study the physics of space-charge-dominated beams. The operating parameters of these machines can be varied by choice of apertures and gun operating conditions to access a wide range of parameters that reproduce, on a scaled basis, the full nonlinear time-dependent physics that is expected in much costlier ion systems. Early operation of these machines has demonstrated the importance of the details of beam initial conditions in determining the downstream evolution. These machines have also been a convenient tested for benchmarking simulation codes such as WARP, and for development of several novel diagnostic techniques. We present our recent experience with multi-turn operation as well as recent longitudinal and transverse physics experiments and comparisons to simulation results. Development of novel diagnostic techniques such as time-dependent imaging using optical transition radiation and tomographic beam reconstruction are also described
Anomalous scaling of low-order structure functions of turbulent velocity
International Nuclear Information System (INIS)
Chen, S.Y.; Dhruva, B.; Kurien, S.; Sreenivasan, K.R.; Taylor, M.A.
2006-12-01
It is now believed that the scaling exponents of moments of velocity increments are anomalous, or that the departures from Kolmogorov's (1941) self-similar scaling increase nonlinearly with the increasing order of the moment. This appears to be true whether one considers velocity increments themselves or their absolute values. However, moments of order lower than 2 of the absolute values of velocity increments have not been investigated thoroughly for anomaly. Here, we discuss the importance of the scaling of non-integer moments of order between +2 and -1, and obtain them from direct numerical simulations at moderate Taylor microscale Reynolds numbers R λ ≤ 450, and experimental data at high Reynolds numbers (R λ ∼ 10 000). The relative difference between the measured exponents and Kolmogorov's prediction increases as the moment order decreases towards -1, thus showing that the anomaly is manifested in low-order moments as well. (author)
Mantica, Paola
2016-10-01
Heat transport experiments in JET, based on ICRH heat flux scans and temperature modulation, have confirmed the importance of two transport mechanisms that are often neglected in modeling experimental results, but are crucial to reach agreement between theory and experiment and may be significant in ITER. The first mechanism is the stabilizing effect of the total pressure gradient (including fast ions) on ITG driven ion heat transport. Such stabilization is found in non-linear gyro-kinetic electro-magnetic simulations using GENE and GYRO, and is the explanation for the observed loss of ion stiffness in the core of high NBI-power JET plasmas. The effect was recently observed also in JET plasmas with dominant ICRH heating and small rotation, due to ICRH fast ions, which is promising for ITER. Such mechanism dominates over ExB flow shear in the core and needs to be included in quasi-linear models to increase their ability to capture the relevant physics. The second mechanism is the capability of small- scale ETG instabilities to carry a significant fraction of electron heat. A decrease in Te peaking is observed when decreasing Zeff Te/Ti, which cannot be ascribed to TEMs but is in line with ETGs. Non-linear GENE single-scale simulations of ETGs and ITG/TEMs show that the ITG/TEM electron heat flux is not enough to match experiment. TEM stiffness is also much lower than measured. In the ETG single scale simulations the external flow shear is used to saturate the ETG streamers. Multi-scale simulations are ongoing, in which the ion zonal flows are the main saturating mechanism for ETGs. These costly simulations should provide the final answer on the importance of ETG-driven electron heat flux in JET. with JET contributors [F.Romanelli, Proc.25thIAEA FEC]. Supported by EUROfusion Grant 633053.
COHERENT EVENTS AND SPECTRAL SHAPE AT ION KINETIC SCALES IN THE FAST SOLAR WIND TURBULENCE
International Nuclear Information System (INIS)
Lion, Sonny; Alexandrova, Olga; Zaslavsky, Arnaud
2016-01-01
In this paper we investigate spectral and phase coherence properties of magnetic fluctuations in the vicinity of the spectral transition from large, magnetohydrodynamic to sub-ion scales using in situ measurements of the Wind spacecraft in a fast stream. For the time interval investigated by Leamon et al. (1998) the phase coherence analysis shows the presence of sporadic quasi-parallel Alfvén ion cyclotron (AIC) waves as well as coherent structures in the form of large-amplitude, quasi-perpendicular Alfvén vortex-like structures and current sheets. These waves and structures importantly contribute to the observed power spectrum of magnetic fluctuations around ion scales; AIC waves contribute to the spectrum in a narrow frequency range whereas the coherent structures contribute to the spectrum over a wide frequency band from the inertial range to the sub-ion frequency range. We conclude that a particular combination of waves and coherent structures determines the spectral shape of the magnetic field spectrum around ion scales. This phenomenon provides a possible explanation for a high variability of the magnetic power spectra around ion scales observed in the solar wind.
Validating the Orientations to Happiness Scale in a Chinese Sample of University Students
Chen, Guo-Hai
2010-01-01
This paper examined the reliability and validity of the Orientation to Happiness Scale with a sample of Chinese correspondents. Chinese translation of the Orientation to Happiness Scale, Satisfaction with Life Scale, Temporal Satisfaction with Life Scale, and General Life Satisfaction Scale, were administered to 671 Chinese university students…
Scaling of the velocity profile in strongly drag reduced turbulent flows over an oscillating wall
International Nuclear Information System (INIS)
Skote, Martin
2014-01-01
Highlights: • Scaling analysis is used to derive a log-law for drag reduced flow. • The slope of the log layer is directly linked to the drag reduction. • The result is only valid for wall manipulated flows – not fluid altering methods. • Extensive comparison with data found in the literature is made. - Abstract: Scaling analysis of the velocity profiles in strongly drag reduced flows reveals that the slope of the logarithmic part depends on the amount of drag reduction (DR). Unlike DR due to polymeric fluids, the slope changes gradually and can be predicted by the analysis. Furthermore, the intercept of the profiles is found to vary linearly with the DR. Two velocity scales are utilized: the reference (undisturbed) and the actual friction velocity. The theory is based on the assumption that the near-wall linear region is only governed by the actual friction velocity, while the outer part is governed by the reference friction velocity. As a result, logarithmic part is influenced by both velocity scales and the slope of the velocity profile is directly linked to the DR. The theoretically obtained results are verified by data from six previously performed direct numerical simulations (DNSs) of boundary layers over spatial and temporal wall oscillations, with a wide range of resulting DR. The theory is further supported by data from numerous investigations (DNSs as well as experiments) of wall-bounded flows forced by various forms of oscillating wall-motion. The assumption that the outer part is unaffected by the actual friction velocity limits the validity of the proposed log-law to flows not fully adapted to the imposed wall forcing, hence the theory provides a measure of the level of adjustment. In addition, a fundamental difference in the applicability of the theory to spatially developing boundary flow and infinite channel flow is discussed
Exploring the large-scale structure of Taylor–Couette turbulence through Large-Eddy Simulations
Ostilla-Mónico, Rodolfo; Zhu, Xiaojue; Verzicco, Roberto
2018-04-01
Large eddy simulations (LES) of Taylor-Couette (TC) flow, the flow between two co-axial and independently rotating cylinders are performed in an attempt to explore the large-scale axially-pinned structures seen in experiments and simulations. Both static and dynamic LES models are used. The Reynolds number is kept fixed at Re = 3.4 · 104, and the radius ratio η = ri /ro is set to η = 0.909, limiting the effects of curvature and resulting in frictional Reynolds numbers of around Re τ ≈ 500. Four rotation ratios from Rot = ‑0.0909 to Rot = 0.3 are simulated. First, the LES of TC is benchmarked for different rotation ratios. Both the Smagorinsky model with a constant of cs = 0.1 and the dynamic model are found to produce reasonable results for no mean rotation and cyclonic rotation, but deviations increase for increasing rotation. This is attributed to the increasing anisotropic character of the fluctuations. Second, “over-damped” LES, i.e. LES with a large Smagorinsky constant is performed and is shown to reproduce some features of the large-scale structures, even when the near-wall region is not adequately modeled. This shows the potential for using over-damped LES for fast explorations of the parameter space where large-scale structures are found.
Scaling forecast models for wind turbulence and wind turbine power intermittency
Duran Medina, Olmo; Schmitt, Francois G.; Calif, Rudy
2017-04-01
The intermittency of the wind turbine power remains an important issue for the massive development of this renewable energy. The energy peaks injected in the electric grid produce difficulties in the energy distribution management. Hence, a correct forecast of the wind power in the short and middle term is needed due to the high unpredictability of the intermittency phenomenon. We consider a statistical approach through the analysis and characterization of stochastic fluctuations. The theoretical framework is the multifractal modelisation of wind velocity fluctuations. Here, we consider three wind turbine data where two possess a direct drive technology. Those turbines are producing energy in real exploitation conditions and allow to test our forecast models of power production at a different time horizons. Two forecast models were developed based on two physical principles observed in the wind and the power time series: the scaling properties on the one hand and the intermittency in the wind power increments on the other. The first tool is related to the intermittency through a multifractal lognormal fit of the power fluctuations. The second tool is based on an analogy of the power scaling properties with a fractional brownian motion. Indeed, an inner long-term memory is found in both time series. Both models show encouraging results since a correct tendency of the signal is respected over different time scales. Those tools are first steps to a search of efficient forecasting approaches for grid adaptation facing the wind energy fluctuations.
PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and Beyond
Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
2008-10-01
mixing dynamics are interplayed with fundamental properties of the Euler and compressible Navier-Stokes equations, with the problem sensitivity to the initial conditions and to the boundary conditions at the discontinuities, and with its stochastic description. The state-of-the-art numerical simulations of the multi-phase non-equilibrium dynamics suggest new methods for capturing discontinuities and singularities and shock-interface interaction, for predictive modeling of the multi-scale dynamics in fluids and plasmas, for error estimate and uncertainty quantification as well as for novel data assimilation techniques. The First International Conference `Turbulent Mixing and Beyond' (TMB-2007), was held on 18-26 August 2007 at the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy. This was a highly informative and exciting meeting, by all the standards a major success. The Conference brought together 120 participants (307 authors) from five continents, ranging from students to members of National Academies of Sciences and Engineering and including researchers from the Universities, National Laboratories, Leading Scientific Institutions and Industry. TMB-2007 covered 16 different topics, maintaining the scope and the interdisciplinary character of the meeting, and kept the focus on a fundamental fluid dynamic problem of unsteady turbulent processes and the Conference Objectives. The success of the TMB-07 was a result of the successful work of all the participants, who were serious and professional people, caring for the quality of their research and sharing their scientific vision. The level of presentations was high, and the presentations included 87 oral contributions, 32 invited lectures and 5 tutorials and over 30 poster contributions. The round table discussions held at TMB-2007 investigated the organization of a Collaborative Computing Environment for the Turbulent Mixing and Beyond Community. The abstracts of the 150 accepted Conference
Leung, Marco Y. T.; Zhou, Wen; Shun, Chi-Ming; Chan, Pak-Wai
2018-04-01
This study identifies the atmospheric circulation features that are favorable for the occurrence of low-level turbulence at Hong Kong International Airport [below 1600 feet (around 500 m)]. By using LIDAR data at the airport, turbulence and nonturbulence cases are selected. It is found that the occurrence of turbulence is significantly related to the strength of the southerly wind at 850 hPa over the South China coast. On the other hand, the east-west wind at this height demonstrates a weak relation to the occurrence. This suggests that turbulence is generated by flow passing Lantau Island from the south. The southerly wind also transports moisture from the South China Sea to Hong Kong, reducing local stability. This is favorable for the development of strong turbulence. It is also noted that the strong southerly wind during the occurrence of low-level turbulence is contributed by an anomalous zonal gradient of geopotential in the lower troposphere over the South China Sea. This gradient is caused by the combination of variations at different timescales. These are the passage of synoptic extratropical cyclones and anticyclones and the intraseasonal variation in the western North Pacific subtropical high. The seasonal variation in geopotential east of the Tibetan Plateau leads to a seasonal change in meridional wind, by which the frequency of low-level turbulence is maximized in spring and minimized in autumn.
Universal scaling of grain size distributions during dislocation creep
Aupart, Claire; Dunkel, Kristina G.; Angheluta, Luiza; Austrheim, Håkon; Ildefonse, Benoît; Malthe-Sørenssen, Anders; Jamtveit, Bjørn
2017-04-01
Grain size distributions are major sources of information about the mechanisms involved in ductile deformation processes and are often used as paleopiezometers (stress gauges). Several factors have been claimed to influence the stress vs grain size relation, including the water content (Jung & Karato 2001), the temperature (De Bresser et al., 2001), the crystal orientation (Linckens et al., 2016), the presence of second phase particles (Doherty et al. 1997; Cross et al., 2015), and heterogeneous stress distributions (Platt & Behr 2011). However, most of the studies of paleopiezometers have been done in the laboratory under conditions different from those in natural systems. It is therefore essential to complement these studies with observations of naturally deformed rocks. We have measured olivine grain sizes in ultramafic rocks from the Leka ophiolite in Norway and from Alpine Corsica using electron backscatter diffraction (EBSD) data, and calculated the corresponding probability density functions. We compared our results with samples from other studies and localities that have formed under a wide range of stress and strain rate conditions. All distributions collapse onto one universal curve in a log-log diagram where grain sizes are normalized by the mean grain size of each sample. The curve is composed of two straight segments with distinct slopes for grains above and below the mean grain size. These observations indicate that a surprisingly simple and universal power-law scaling describes the grain size distribution in ultramafic rocks during dislocation creep irrespective of stress levels and strain rates. Cross, Andrew J., Susan Ellis, and David J. Prior. 2015. « A Phenomenological Numerical Approach for Investigating Grain Size Evolution in Ductiley Deforming Rocks ». Journal of Structural Geology 76 (juillet): 22-34. doi:10.1016/j.jsg.2015.04.001. De Bresser, J. H. P., J. H. Ter Heege, and C. J. Spiers. 2001. « Grain Size Reduction by Dynamic
An idealised study of the effects of small scales on chemistry in a two-dimensional turbulent flow.
Chaalal, F. Ait; Bartello, P.; Bourqui, M.
2009-04-01
The non-linear nature of stratospheric chemical reactions makes them sensitive to mixing and diffusion. Most stratospheric Climate-Chemistry Models neglect the effects of sub-grid flow structures on chemistry. Several previous studies have pointed out that such unresolved small scales could significantly affect the chemistry. However this problem has not been thoroughly studied from a theoretical point of view. To fulfill this gap, we investigate the interactions between advection, diffusion and chemistry for a simple bimolecular reaction between two initially unmixed reactants, within the framework of two-dimensional isotropic and homogenous turbulence. This is a highly simplified representation of quasi-isentropic mixing in the stratosphere. Our goal here is to describe and understand how the production rate of the product species is affected by the size of the smallest scales of the tracer field, as determined by the tracer diffusion coefficient Î°. The spatial average of the prognostic equation for the product's concentration involves the covariance of the reactants. The time evolution of this covariance depends in turn on a dissipative term, and on second and third order chemical terms. The set of equations is not closed and any finite resolution model would need a parameterization of the dissipation and a closure hypothesis on the chemical terms. To study these terms, we perform ensembles of direct numerical simulations using a pseudo-spectral two-dimensional periodic model. The ensembles span different initial conditions of the flow and different tracer diffusion coefficients Î°. Our results show a strong dependence of the total production on the diffusion coefficient. This production scales like Î°p(t) , where p(t) is a positive decreasing function of time. This scaling is very similar to the one found by Tan et al. (1998) for atmospheric flows on the deactivation of chlorine by nitrogen oxide at the southern edge of the winter time polar vortex
Numerical Simulation of a Laboratory-Scale Turbulent SlotFlame
Energy Technology Data Exchange (ETDEWEB)
Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Lijewski,Michael J.; Driscoll, James F.; Filatyev, Sergei A.
2006-04-20
We present three-dimensional, time-dependent simulations ofthe flowfield of a laboratory-scale slot burner. The simulations areperformed using an adaptive time-dependent low Mach number combustionalgorithm based on a second-order projection formulation that conservesboth species mass and total enthalpy. The methodology incorporatesdetailed chemical kinetics and a mixture model for differential speciesdiffusion. Methane chemistry and transport are modeled using the DRM-19mechanism along with its associated thermodynamics and transportdatabases. Adaptive mesh refinementdynamically resolves the flame andturbulent structures. Detailedcomparisons with experimental measurementsshow that the computational results provide a good prediction of theflame height, the shape of the time-averaged parabolic flame surfacearea, and the global consumption speed (the volume per second ofreactants consumed divided by the area of the time-averaged flame). Thethickness of the computed flamebrush increases in the streamwisedirection, and the flamesurface density profiles display the same generalshapes as the experiment. The structure of the simulated flame alsomatches the experiment; reaction layers are thin (typically thinner than1 mm) and the wavelengths of large wrinkles are 5--10 mm. Wrinklesamplify to become long fingers of reactants which burn through at a neckregion, forming isolated pockets of reactants. Thus both the simulatedflame and the experiment are in the "corrugated flameletregime."
Directory of Open Access Journals (Sweden)
Vesselin Krassimirov Krastev
2017-12-01
Full Text Available The unsteady and random character of turbulent flow motion is a key aspect of the multidimensional modeling of internal combustion engines (ICEs. A typical example can be found in the prediction of the cycle-to-cycle variability (CCV in modern, highly downsized gasoline direct injection (GDI engines, which strongly depends on the accurate simulation of turbulent in-cylinder flow structures. The current standard for turbulence modeling in ICEs is still represented by the unsteady form of Reynold-averaged Navier Stokes equations (URANS, which allows the simulation of full engine cycles at relatively low computational costs. URANS-based methods, however, are only able to return a statistical description of turbulence, as the effects of all scales of motion are entirely modeled. Therefore, during the last decade, scale-resolving methods such as large eddy simulation (LES or hybrid URANS/LES approaches are gaining increasing attention among the engine-modeling community. In the present paper, we propose a scale-resolving capable modification of the popular RNG k– ε URANS model. The modification is based on a detached-eddy simulation (DES framework and allows one to explicitly set the behavior (URANS, DES or LES of the model in different zones of the computational domain. The resulting zonal formulation has been tested on two reference test cases, comparing the numerical predictions with the available experimental data sets and with previous computational studies. Overall, the scale-resolved part of the computed flow has been found to be consistent with the expected flow physics, thus confirming the validity of the proposed simulation methodology.
Weber, Maria Ann
2014-12-01
The Sun exhibits cyclic properties of its large-scale magnetic field on the order of sigma22 years, with a ˜11 year frequency of sunspot occurrence. These sunspots, or active regions, are the centers of magnetically driven phenomena such as flares and coronal mass ejections. Volatile solar magnetic events directed toward the Earth pose a threat to human activities and our increasingly technological society. As such, the origin and nature of solar magnetic flux emergence is a topic of global concern. Sunspots are observable manifestations of solar magnetic fields, thus providing a photospheric link to the deep-seated dynamo mechanism. However, the manner by which bundles of magnetic field, or flux tubes, traverse the convection zone to eventual emergence at the solar surface is not well understood. To provide a connection between dynamo-generated magnetic fields and sunspots, I have performed simulations of magnetic flux emergence through the bulk of a turbulent, solar convective envelope by employing a thin flux tube model subject to interaction with flows taken from a hydrodynamic convection simulation computed through the Anelastic Spherical Harmonic (ASH) code. The convective velocity field interacts with the flux tube through the drag force it experiences as it traverses through the convecting medium. Through performing these simulations, much insight has been gained about the influence of turbulent solar-like convection on the flux emergence process and resulting active region properties. I find that the dynamic evolution of flux tubes change from convection dominated to magnetic buoyancy dominated as the initial field strength of the flux tubes increases from 15 kG to 100 kG. Additionally, active-region-scale flux tubes of 40 kG and greater exhibit properties similar to those of active regions on the Sun, such as: tilt angles, rotation rates, and morphological asymmetries. The joint effect of the Coriolis force and helical motions present in convective
Ruiz Ruiz, Juan; Guttenfelder, Walter; Loureiro, Nuno; Ren, Yang; White, Anne; MIT/PPPL Collaboration
2017-10-01
Turbulent fluctuations on the electron gyro-radius length scale are thought to cause anomalous transport of electron energy in spherical tokamaks such as NSTX and MAST in some parametric regimes. In NSTX, electron-scale turbulence is studied through a combination of experimental measurements from a high-k scattering system and gyrokinetic simulations. Until now most comparisons between experiment and simulation of electron scale turbulence have been qualitative, with recent work expanding to more quantitative comparisons via synthetic diagnostic development. In this new work, we propose two alternate, complementary ways to perform a synthetic diagnostic using the gyrokinetic code GYRO. The first approach builds on previous work and is based on the traditional selection of wavenumbers using a wavenumber filter, for which a new wavenumber mapping was implemented for general axisymmetric geometry. A second alternate approach selects wavenumbers in real-space to compute the power spectra. These approaches are complementary, and recent results from both synthetic diagnostic approaches applied to NSTX plasmas will be presented. Work supported by U.S. DOE contracts DE-AC02-09CH11466 and DE-AC02-05CH11231.
Czech Academy of Sciences Publication Activity Database
Musilová, Věra; Králík, Tomáš; La Mantia, M.; Macek, Michal; Urban, Pavel; Skrbek, L.
2017-01-01
Roč. 832, OCT 26 (2017), s. 721-744 ISSN 0022-1120 R&D Projects: GA ČR(CZ) GA17-03572S; GA MŠk(CZ) LO1212 Institutional support: RVO:68081731 Keywords : Benard convection * turbulent convection * turbulent flows Subject RIV: BK - Fluid Dynamics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.821, year: 2016
Rates of Return on University Education With Economies of Scale.
Bottomley, Anthony; Dunworth, John
The authors of the present document had as their purpose to determine somewhat the worth of a college education. In order to do this, they show (1) how much a university education costs; (2) what the rates of return on this cost are and who the beneficiary of these returns is; (3) how costs might be reduced with expanded enrollment; and (4) how…
Development of a Fabric Lustre Scale | Gundola | University of ...
African Journals Online (AJOL)
University of Mauritius Research Journal. Journal Home · ABOUT THIS JOURNAL · Advanced Search · Current Issue · Archives · Journal Home > Vol 13 (2007) >. Log in or Register to get access to full text downloads. Username, Password, Remember me, or Register · Download this PDF file. The PDF file you selected ...
University's Multi-Scale Initiatives for Redefining City Development
Ratajczyk, Natalia; Wagner, Iwona; Wolanska-Kaminska, Agnieszka; Jurczak, Tomasz; Zalewski, Maciej
2017-01-01
Purpose: The purpose of this paper is to present the varied roles played by the University of Lódz (UL) in maintaining and restoring the natural capital of a city as a driver for sustainable city development. The higher education institution can be perceived as visionary, originator and executor of natural capital projects.…
Ferreira, Ana Veríssimo; Neto, Félix
2002-12-01
To facilitate use of the adult form of the Francis Scale of Attitude Towards Christianity in cross-cultural studies, the psychometric characteristics of the translated scale were examined among 323 university students in Portugal (130 men and 193 women). Their ages ranged from 18 to 31 years. Analysis supported the unidimensionality, internal consistency, and construct validity of this scale in this sample of Portuguese university students.
Energy Technology Data Exchange (ETDEWEB)
Labit, B
2002-10-01
In a fusion machine, understanding plasma turbulence, which causes a degradation of the measured energy confinement time, would constitute a major progress in this field. In tokamaks, the measured ion and electron thermal conductivities are of comparable magnitude. The possible sources of turbulence are the temperature and density gradients occurring in a fusion plasma. Whereas the heat losses in the ion channel are reasonably well understood, the origin of the electron losses is more uncertain. In addition to the radial velocity associated to the fluctuations of the electric field, electrons are more affected than ions by the magnetic field fluctuations. In experiments, the confinement time can be conveniently expressed in terms of dimensionless parameters. Although still somewhat too imprecise, these scaling laws exhibit strong dependencies on the normalized pressure {beta} or the normalized Larmor radius, {rho}{sub *}. The present thesis assesses whether a tridimensional, electromagnetic, nonlinear fluid model of plasma turbulence driven by a specific instability can reproduce the dependence of the experimental electron heat losses on the dimensionless parameters {beta} and {rho}{sub *}. The investigated interchange instability is the Electron Temperature Gradient driven one (ETG). The model is built by using the set of Braginskii equations. The developed simulation code is global in the sense that a fixed heat flux is imposed at the inner boundary, leaving the gradients free to evolve. From the nonlinear simulations, we have put in light three characteristics for the ETG turbulence: the turbulent transport is essentially electrostatic; the potential and pressure fluctuations form radially elongated cells called streamers; the transport level is very low compared to the experimental values. The thermal transport dependence study has shown a very small role of the normalized pressure, which is in contradiction with the Ohkama's formula. On the other hand
Energy Technology Data Exchange (ETDEWEB)
Klein, Kristopher G.; Howes, Gregory G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); TenBarge, Jason M. [IREAP, University of Maryland, College Park, MD 20742 (United States); Podesta, John J., E-mail: kristopher-klein@uiowa.edu [Center for Space Plasma Physics, Space Science Institute, Boulder, CO 80301 (United States)
2014-04-20
Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.
Large-scale structure in the universe: Theory vs observations
International Nuclear Information System (INIS)
Kashlinsky, A.; Jones, B.J.T.
1990-01-01
A variety of observations constrain models of the origin of large scale cosmic structures. We review here the elements of current theories and comment in detail on which of the current observational data provide the principal constraints. We point out that enough observational data have accumulated to constrain (and perhaps determine) the power spectrum of primordial density fluctuations over a very large range of scales. We discuss the theories in the light of observational data and focus on the potential of future observations in providing even (and ever) tighter constraints. (orig.)
Fractals and the Large-Scale Structure in the Universe -R-ES ...
Indian Academy of Sciences (India)
in the Universe. The latter structures are broadly re- ferred to as large-scale structures and understanding the physics operating at these scales is an important chal- lenge to present day cosmology. The standard model of cosmology rests on the assump- tion that although there are structures at various scales,. A K Mittal is ...
Energy scale of inflation from the recurrence time of the universe
Ropotenko, K.
2015-01-01
It is shown that the de Sitter equilibrium cosmology predicts the energy scale of inflation that significantly exceeds the Planck scale. An alternative calculation of the probability for a fluctuation into an inflationary universe is proposed which gives a more realistic energy scale of inflation. An interpretation of the cosmological constant problem in the de Sitter equilibrium cosmology is briefly discussed.
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
International Nuclear Information System (INIS)
Iovane, G.; Giordano, P.
2005-01-01
In this work we introduce the hypersingular integral equations and analyze a realistic model of gravitational waveguides on a cantorian space-time. A waveguiding effect is considered with respect to the large scale structure of the Universe, where the structure formation appears as if it were a classically self-similar random process at all astrophysical scales. The result is that it seems we live in an El Naschie's o (∞) Cantorian space-time, where gravitational lensing and waveguiding effects can explain the appearing Universe. In particular, we consider filamentary and planar large scale structures as possible refraction channels for electromagnetic radiation coming from cosmological structures. From this vision the Universe appears like a large self-similar adaptive mirrors set, thanks to three numerical simulations. Consequently, an infinite Universe is just an optical illusion that is produced by mirroring effects connected with the large scale structure of a finite and not a large Universe
Fractals and the Large-Scale Structure in the Universe
Indian Academy of Sciences (India)
lieved to have been formed due to a number of physical processes in addition to gravity. Structures of galactic ... So we now repeat this exercise using a scale of smaller length. Naive logic would suggest that as we .... dimensional smooth curve and do this exercise, the ex- ponent D will turn out to be 1. Similarly if we do this ...
Coherence in Turbulence: New Perspective
Levich, Eugene
2009-07-01
It is claimed that turbulence in fluids is inherently coherent phenomenon. The coherence shows up clearly as strongly correlated helicity fluctuations of opposite sign. The helicity fluctuations have cellular structure forming clusters that are actually observed as vorticity bands and coherent structures in laboratory turbulence, direct numerical simulations and most obviously in atmospheric turbulence. The clusters are named BCC - Beltrami Cellular Clusters - because of the observed nearly total alignment of the velocity and vorticity fields in each particular cell, and hence nearly maximal possible helicity in each cell; although when averaged over all the cells the residual mean helicity in general is small and does not play active dynamical role. The Beltrami like fluctuations are short-lived and stabilize only in small and generally contiguous sub-domains that are tending to a (multi)fractal in the asymptotic limit of large Reynolds numbers, Re → ∞. For the model of homogeneous isotropic turbulence the theory predicts the leading fractal dimension of BCC to be: DF = 2.5. This particular BCC is responsible for generating the Kolmogorov -5/3 power law energy spectrum. The most obvious role that BCC play dynamically is that the nonlinear interactions in them are relatively reduced, due to strong spatial alignment between the velocity field v(r, t) and the vorticity field ω(r, t) = curlv(r, t), while the physical quantities typically best characterizing turbulence intermittency, such as entrophy, vorticity stretching and generation, and energy dissipation are maximized in and near them. The theory quantitatively relates the reduction of nonlinear inter-actions to the BCC fractal dimension DF and subsequent turbulence intermittency. It is further asserted that BCC is a fundamental feature of all turbulent flows, e.g., wall bounded turbulent flows, atmospheric and oceanic flows, and their leading fractal dimension remains invariant and universal in these flows
Akashi, Megumi; Tasaka, Yuji; Yanagisawa, Takatoshi; Murai, Yuichi; Vogt, Tobias; Eckert, Sven
2017-11-01
We report laboratory experiments of Rayleigh-Bénard convection with a liquid metal, Prandtl number Pr = 0.03, in a rectangular cell at a moderate aspect ratio of 5. The Rayleigh number, Ra, was varied in a range from 7.9-103 to 3.5-105 in which the regime of thermal turbulence regime is to be expected. Multiple horizontal velocity profiles were measured in the fluid layer by ultrasonic velocity profiling. The reconstruction of the flow pattern elucidated the occurrence of large scale structures with periodic oscillations. An increasing Ra number causes a transition from a quasi-two-dimensional roll-like structure to a three-dimensional cell-like structure. The transition of the flow structure passes several unstable intermediate regimes accompanied by a stepwise increase of the horizontal scale. For explaining the increase in the horizontal scale, we suggest a model relying on observed Ra dependences of the oscillation frequency and the typical flow velocity of the large scales. Moreover, we have found that the morphology of the roll-like structure can be understood by evaluating the effective viscosity and diffusivity on the basis of turbulent fluctuations.
Stochastic differential equations and turbulent dispersion
Durbin, P. A.
1983-01-01
Aspects of the theory of continuous stochastic processes that seem to contribute to an understanding of turbulent dispersion are introduced and the theory and philosophy of modelling turbulent transport is emphasized. Examples of eddy diffusion examined include shear dispersion, the surface layer, and channel flow. Modeling dispersion with finite-time scale is considered including the Langevin model for homogeneous turbulence, dispersion in nonhomogeneous turbulence, and the asymptotic behavior of the Langevin model for nonhomogeneous turbulence.
Directory of Open Access Journals (Sweden)
Manić Nebojša G.
2017-01-01
Full Text Available Due to the rapid progress in computer hardware and software, CFD became a powerful and effective tool for implementation turbulence modeling in defined combustion mathematical models in the complex boiler geometries. In this paper the commercial CFD package, ANSYS FLUENT was used to model fluid flow through the boiler, in order to define velocity field and predict pressure drop. Mathematical modeling was carried out with application of Standard, RNG, and Realizable k-ε turbulence model using the constants presented in literature. Three boilers geometry were examined with application of three different turbulence models with variants, which means consideration of 7 turbulence model arrangements in FLUENT. The obtained model results are presented and compared with data collected from experimental tests. All experimental tests were performed according to procedures defined in the standard SRPS EN 303-5 and obtained results are presented in this paper for all three examined geometries. This approach was used for improving construction of boiler fired by solid fuel with heat output up to 35 kW and for selection of the most convenient construction.
International Nuclear Information System (INIS)
Childress, S.
1995-01-01
The authors formulate and study an elementary one-dimensional model mimicking some of the features of fluid turbulence. The underlying vorticity field corresponds to a parallel flow. Structure on all scales down to the numerical resolution is generated by the action of baker's maps acting on the vorticity of the flow. These transformations conserve kinetic energy locally in the Euler model, while viscous diffusion of vorticity occurs in the Navier-Stokes case. The authors apply the model to the study of homogeneous fully, developed turbulence, and to turbulent channel flow
The structure of turbulence in a rapid tidal flow.
Milne, I A; Sharma, R N; Flay, R G J
2017-08-01
The structure of turbulence in a rapid tidal flow is characterized through new observations of fundamental statistical properties at a site in the UK which has a simple geometry and sedate surface wave action. The mean flow at the Sound of Islay exceeded 2.5 m s -1 and the turbulent boundary layer occupied the majority of the water column, with an approximately logarithmic mean velocity profile identifiable close to the seabed. The anisotropic ratios, spectral scales and higher-order statistics of the turbulence generally agree well with values reported for two-dimensional open channels in the laboratory and other tidal channels, therefore providing further support for the application of universal models. The results of the study can assist in developing numerical models of turbulence in rapid tidal flows such as those proposed for tidal energy generation.
Towards a Gravity Dual for the Large Scale Structure of the Universe
DEFF Research Database (Denmark)
Kehagias, A.; Riotto, Antonio; Sloth, M. S.
2016-01-01
The dynamics of the large-scale structure of the universe enjoys at all scales, even in the highly non-linear regime, a Lifshitz symmetry during the matter-dominated period. In this paper we propose a general class of six-dimensional spacetimes which could be a gravity dual to the four-dimensiona......The dynamics of the large-scale structure of the universe enjoys at all scales, even in the highly non-linear regime, a Lifshitz symmetry during the matter-dominated period. In this paper we propose a general class of six-dimensional spacetimes which could be a gravity dual to the four...
Universal scaling of the distribution of land in urban areas
Riascos, A. P.
2017-09-01
In this work, we explore the spatial structure of built zones and green areas in diverse western cities by analyzing the probability distribution of areas and a coefficient that characterize their respective shapes. From the analysis of diverse datasets describing land lots in urban areas, we found that the distribution of built-up areas and natural zones in cities obey inverse power laws with a similar scaling for the cities explored. On the other hand, by studying the distribution of shapes of lots in urban regions, we are able to detect global differences in the spatial structure of the distribution of land. Our findings introduce information about spatial patterns that emerge in the structure of urban settlements; this knowledge is useful for the understanding of urban growth, to improve existing models of cities, in the context of sustainability, in studies about human mobility in urban areas, among other applications.
Nakayama, H.; Takemi, T.; Nagai, H.
2015-06-01
A significant amount of radioactive material was accidentally discharged into the atmosphere from the Fukushima Dai-ichi Nuclear Power Plant from 12 March 2011, which produced high contaminated areas over a wide region in Japan. In conducting regional-scale atmospheric dispersion simulations, the computer-based nuclear emergency response system WSPEEDI-II developed by Japan Atomic Energy Agency was used. Because this system is driven by a meso-scale meteorological (MM) model, it is difficult to reproduce small-scale wind fluctuations due to the effects of local terrain variability and buildings within a nuclear facility that are not explicitly represented in MM models. In this study, we propose a computational approach to couple an LES-based CFD model with a MM model for detailed simulations of turbulent winds with buoyancy effects under real meteorological conditions using turbulent inflow technique. Compared to the simple measurement data, especially, the 10 min averaged wind directions of the LES differ by more than 30 degrees during some period of time. However, distribution patterns of wind speeds, directions, and potential temperature are similar to the MM data. This implies that our coupling technique has potential performance to provide detailed data on contaminated area in the nuclear accidents.
Turbulence Visualization at the Terascale on Desktop PCs
Treib, M.
2012-12-01
Despite the ongoing efforts in turbulence research, the universal properties of the turbulence small-scale structure and the relationships between small-and large-scale turbulent motions are not yet fully understood. The visually guided exploration of turbulence features, including the interactive selection and simultaneous visualization of multiple features, can further progress our understanding of turbulence. Accomplishing this task for flow fields in which the full turbulence spectrum is well resolved is challenging on desktop computers. This is due to the extreme resolution of such fields, requiring memory and bandwidth capacities going beyond what is currently available. To overcome these limitations, we present a GPU system for feature-based turbulence visualization that works on a compressed flow field representation. We use a wavelet-based compression scheme including run-length and entropy encoding, which can be decoded on the GPU and embedded into brick-based volume ray-casting. This enables a drastic reduction of the data to be streamed from disk to GPU memory. Our system derives turbulence properties directly from the velocity gradient tensor, and it either renders these properties in turn or generates and renders scalar feature volumes. The quality and efficiency of the system is demonstrated in the visualization of two unsteady turbulence simulations, each comprising a spatio-temporal resolution of 10244. On a desktop computer, the system can visualize each time step in 5 seconds, and it achieves about three times this rate for the visualization of a scalar feature volume. © 1995-2012 IEEE.
An Examination and Validation of an Adapted Youth Experience Scale for University Sport
Rathwell, Scott; Young, Bradley W.
2016-01-01
Limited tools assess positive development through university sport. Such a tool was validated in this investigation using two independent samples of Canadian university athletes. In Study 1, 605 athletes completed 99 survey items drawn from the Youth Experience Scale (YES 2.0), and separate a priori measurement models were evaluated (i.e., 99…
Psychology in an Interdisciplinary Setting: A Large-Scale Project to Improve University Teaching
Koch, Franziska D.; Vogt, Joachim
2015-01-01
At a German university of technology, a large-scale project was funded as a part of the "Quality Pact for Teaching", a programme launched by the German Federal Ministry of Education and Research to improve the quality of university teaching and study conditions. The project aims at intensifying interdisciplinary networking in teaching,…
Directory of Open Access Journals (Sweden)
H. Z. Baumert
2009-03-01
Full Text Available This paper extends a turbulence closure-like model for stably stratified flows into a new dynamic domain in which turbulence is generated by internal gravity waves rather than mean shear. The model turbulent kinetic energy (TKE, K balance, its first equation, incorporates a term for the energy transfer from internal waves to turbulence. This energy source is in addition to the traditional shear production. The second variable of the new two-equation model is the turbulent enstrophy (Ω. Compared to the traditional shear-only case, the Ω-equation is modified to account for the effect of the waves on the turbulence time and space scales. This modification is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean shear when turbulence is produced exclusively by internal waves. This paper is part 1 of a continuing theoretical development. It accounts for mean shear- and internal wave-driven mixing only in the two limits of mean shear and no waves and waves but no mean shear, respectively.
The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000b. At small energy density E of the internal wave field, the turbulent dissipation rate (ε scales like ε~E^{2}. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E^{1}. This is observed, for example, in the highly energetic tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.
A New Universal Gas Breakdown Theory for Classical Length Scales
Loveless, Amanda Mae
While Paschen's law is commonly used to predict breakdown voltage, it fails at microscale gaps when field emission becomes important. Accurate breakdown voltage predictions at microscale are even more important as electronic device dimensions decrease. Developing analytic models to accurately predict breakdown at microscale is vital for understanding the underlying physics occurring within the system and to either prevent or produce a discharge, depending on the application. We first take a pre-existing breakdown model coupling field emission and Townsend breakdown and perform a matched asymptotic analysis to obtain analytic equations for breakdown voltage in argon at atmospheric pressure. Next, we extend this model to generalize for gas and further explore the independent contributions of field emission and Townsend discharge. Finally, we present analytic expressions for breakdown voltage valid for any gas at any pressure, and discuss the modified Paschen minimum at microscale. The presented models agree well with numerical simulations and experimental data when using the field enhancement factor as a fitting parameter. The work presented in this thesis is a first step in unifying gas breakdown across length scales and breakdown mechanisms. Future work will aim to incorporate other breakdown mechanisms, such as quantum effects and space charge, to provide a more complete unified model for gas breakdown.
ISM and dynamical scaling relations in the local Universe
Cortese, L.
2016-06-01
In the last decade we have seen a tremendous progress in our understanding of the life cycle of galaxies. Particularly powerful has been the synergy between representative surveys of cold gas, dust and metals and improved theoretical models able to follow the evolution of the different phases of the ISM in a self-consistent way. At the same time, the advent of optical integral field spectroscopic surveys is finally allowing us to quantify how the kinematical properties of gas and stars vary across the Hubble sequence. In this talk, I will review recent observational work aimed at providing a local benchmark for the study of the star formation cycle in galaxies and dynamical scaling relations in galaxies. By combining observations obtained as part the Herschel Reference Survey, the GALEX Arecibo SDSS survey, the ALFALFA survey and the SAMI Galaxy Survey, I will discuss what nearby galaxies can teach us about the interplay between kinematics, star formation, chemical enrichment and environmental effects in our neighbourhoods.
THE EMOTIONAL EXPRESSIVITY SCALE VALIDATION IN ARGENTINE UNIVERSITY STUDENTS
Directory of Open Access Journals (Sweden)
Sebastián Eduardo Piemontesi
2012-06-01
Full Text Available Emotional Expressivity, defined as the ability to express emotional states in ob-servable behaviors, is essential for individuals healthy functioning, and was po -sitively associated with wellbeing, self-esteem, life satisfaction and negatively related with diseases such as schizophrenia, depression, personality disorders and post traumatic stress disorder. To answer the need for an instrument which can evaluate this construct in a valid and reliable manner, this study explored the psychometric properties of the Emotional Expressivity Scale adapted into Spa-nish. For this reason, an exploratory factor analysis replicating the one-dimension solution was performed, a coefficient alpha of .94 was obtained, gender differen -ces with higher scores in women, and test-retest coefficients for a 4-week interval with values of .88 in women and .86 in men. Additionally, confirmatory factor analyzes were performed separately for each gender obtaining appropriate va-lues for all fit indices, but not in men. Finally the results, scope and limitations of this paper are discussed.
Validation of the Temporal Satisfaction with Life Scale in a Sample of Chinese University Students
Ye, Shengquan
2007-01-01
The study aims at validating the Temporal Satisfaction With Life Scale (TSWLS; Pavot et al., 1998, "The Temporal Satisfaction With Life Scale", Journal of Personality Assessment 70, pp. 340-354) in a non-western context. Data from 646 Chinese university students (330 females and 316 males) supported the three-factor structure of the…
Bruno, Roberto
2016-01-01
This book provides an overview of solar wind turbulence from both the theoretical and observational perspective. It argues that the interplanetary medium offers the best opportunity to directly study turbulent fluctuations in collisionless plasmas. In fact, during expansion, the solar wind evolves towards a state characterized by large-amplitude fluctuations in all observed parameters, which resembles, at least at large scales, the well-known hydrodynamic turbulence. This text starts with historical references to past observations and experiments on turbulent flows. It then introduces the Navier-Stokes equations for a magnetized plasma whose low-frequency turbulence evolution is described within the framework of the MHD approximation. It also considers the scaling of plasma and magnetic field fluctuations and the study of nonlinear energy cascades within the same framework. It reports observations of turbulence in the ecliptic and at high latitude, treating Alfvénic and compressive fluctuations separately in...
Generalized similarity in magnetohydrodynamic turbulence as seen in the solar corona and solar wind
Chapman, S. C.; Leonardis, E.; Nicol, R. M.; Foullon, C.
2010-12-01
A key property of turbulence is that it can be characterized and quantified in a robust and reproducible way in terms of the ensemble averaged statistical properties of fluctuations. Importantly, fluctuations associated with a turbulent field show similarity or scaling in their statistics and we test for this in observations of magnetohydrodynamic turbulence in the solar corona and solar wind with both power spectra and Generalized Structure Functions. Realizations of turbulence that are finite sized are known to exhibit a generalized or extended self-similarity (ESS). ESS was recently demonstrated in magnetic field timeseries of Ulysses single point in-situ observations of fluctuations of quiet solar wind for which a single robust scaling function was found [1-2]. Flows in solar coronal prominences can be highly variable, with dynamics suggestive of turbulence. The Hinode SOT instrument provides observations (images) at simultaneous high spatial and temporal resolution which span several decades in both spatial and temporal scales. We focus on specific Calcium II H-line observations of solar quiescent prominences with dynamic, highly variable small-scale flows. We analyze these images from the perspective of a finite sized turbulent flow. We discuss this evidence of ESS in the SOT images and in Ulysses solar wind observations- is there a single universal scaling of the largest eddies in the finite range magnetohydrodynamic turbulent flow? [1] S. C. Chapman, R. M. Nicol, Generalized Similarity in Finite Range Solar Wind Magnetohydrodynamic Turbulence, Phys. Rev. Lett., 103, 241101 (2009) [2] S. C. Chapman, R. M. Nicol, E. Leonardis, K. Kiyani, V. Carbone, Observation of universality in the generalized similarity of evolving solar wind turbulence as seen by ULYSSES, Ap. J. Letters, 695, L185, (2009)
PREFACE Turbulent Mixing and Beyond
Abarzhi, Snezhana I.; Gauthier, Serge; Niemela, Joseph J.
2010-12-01
, maintaining the scope and the interdisciplinary character of the meeting while keeping the focus on a fundamental scientific problem of non-equilibrium processes and on the Conference objectives. The abstracts of the 194 accepted presentations of more than 400 authors were published in the Book of Abstracts of the Second International Conference and Advanced School 'Turbulent Mixing and Beyond', 27 July-7 August 2009 , Copyright © 2009, the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy (ISBN 92095003-41-1). This Topical Issue consists of 70 articles accepted for publication in the Conference Proceedings and represents a substantial part of the Conference contributions. The articles are in a broad variety of TMB-2009 themes and are sorted alphabetically by the last name of the first author within each of the following topics: Canonical turbulence and turbulent mixing: invariant, scaling, spectral properties, scalar transports, convection; Wall-bounded flows: structure and fundamentals, non-canonical turbulent boundary layers, including unsteady and transitional flows, supersonic and hypersonic flows, shock-boundary layer interactions; Non-equilibrium processes: unsteady, multiphase and shock-driven turbulent flows, anisotropic non-local dynamics, connection of continuous description at macro-scales to kinetic processes at atomistic scales; Interfacial dynamics: instabilities of Rayleigh-Taylor, Kelvin-Helmholtz, Richtmyer-Meshkov, Landau-Darrieus, Saffman-Taylor High energy density physics: inertial confinement and heavy-ion fusion, Z-pinches, light-matter and laser-plasma interactions, non-equilibrium heat transfer; Material science: material transformation under high strain rates, equation of state, impact dynamics, mixing at nano- and micro-scales; Astrophysics: supernovae, interstellar medium, star formation, stellar interiors, early Universe, cosmic-microwave background, accretion disks; Magneto-hydrodynamics: magnetic fusion and magnetically
Transitional-turbulent spots and turbulent-turbulent spots in boundary layers.
Wu, Xiaohua; Moin, Parviz; Wallace, James M; Skarda, Jinhie; Lozano-Durán, Adrián; Hickey, Jean-Pierre
2017-07-03
Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a [Formula: see text] vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitional-turbulent spot. Streak waviness and breakdown are, therefore, not the mechanisms for the inception of transitional-turbulent spots found here. Rather, they only facilitate the growth and spreading of existing transitional-turbulent spots. The second observation is the discovery, in the inner layer of the developed turbulent boundary layer, of what we call turbulent-turbulent spots. These turbulent-turbulent spots are dense concentrations of small-scale vortices with high swirling strength originating from hairpin packets. Although structurally quite similar to the transitional-turbulent spots, these turbulent-turbulent spots are generated locally in the fully turbulent environment, and they are persistent with a systematic variation of detection threshold level. They exert indentation, segmentation, and termination on the viscous sublayer streaks, and they coincide with local concentrations of high levels of Reynolds shear stress, enstrophy, and temperature fluctuations. The sublayer streaks seem to be passive and are often simply the rims of the indentation pockets arising from the turbulent-turbulent spots.
Transitional-turbulent spots and turbulent-turbulent spots in boundary layers
Wu, Xiaohua; Moin, Parviz; Wallace, James M.; Skarda, Jinhie; Lozano-Durán, Adrián; Hickey, Jean-Pierre
2017-07-01
Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a ΛΛ vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitional-turbulent spot. Streak waviness and breakdown are, therefore, not the mechanisms for the inception of transitional-turbulent spots found here. Rather, they only facilitate the growth and spreading of existing transitional-turbulent spots. The second observation is the discovery, in the inner layer of the developed turbulent boundary layer, of what we call turbulent-turbulent spots. These turbulent-turbulent spots are dense concentrations of small-scale vortices with high swirling strength originating from hairpin packets. Although structurally quite similar to the transitional-turbulent spots, these turbulent-turbulent spots are generated locally in the fully turbulent environment, and they are persistent with a systematic variation of detection threshold level. They exert indentation, segmentation, and termination on the viscous sublayer streaks, and they coincide with local concentrations of high levels of Reynolds shear stress, enstrophy, and temperature fluctuations. The sublayer streaks seem to be passive and are often simply the rims of the indentation pockets arising from the turbulent-turbulent spots.
International Nuclear Information System (INIS)
Javadi, Ardalan; Nilsson, Håkan
2014-01-01
The strongly swirling turbulent flow through an abrupt expansion is investigated using highly resolved LES and SAS, to shed more light on the stagnation region and the helical vortex breakdown. The vortex breakdown in an abrupt expansion resembles the so-called vortex rope occurring in hydro power draft tubes. It is known that the large-scale helical vortex structures can be captured by regular RANS turbulence models. However, the spurious suppression of the small-scale structures should be avoided using less diffusive methods. The present work compares LES and SAS results with the experimental measurement of Dellenback et al. (1988). The computations are conducted using a general non-orthogonal finite-volume method with a fully collocated storage available in the OpenFOAM-2.1.x CFD code. The dynamics of the flow is studied at two Reynolds numbers, Re=6.0×10 4 and Re=10 5 , at the almost constant high swirl numbers of Sr=1.16 and Sr=1.23, respectively. The time-averaged velocity and pressure fields and the root mean square of the velocity fluctuations, are captured and investigated qualitatively. The flow with the lower Reynolds number gives a much weaker outburst although the frequency of the structures seems to be constant for the plateau swirl number
Inflow Turbulence Generation Methods
Wu, Xiaohua
2017-01-01
Research activities on inflow turbulence generation methods have been vigorous over the past quarter century, accompanying advances in eddy-resolving computations of spatially developing turbulent flows with direct numerical simulation, large-eddy simulation (LES), and hybrid Reynolds-averaged Navier-Stokes-LES. The weak recycling method, rooted in scaling arguments on the canonical incompressible boundary layer, has been applied to supersonic boundary layer, rough surface boundary layer, and microscale urban canopy LES coupled with mesoscale numerical weather forecasting. Synthetic methods, originating from analytical approximation to homogeneous isotropic turbulence, have branched out into several robust methods, including the synthetic random Fourier method, synthetic digital filtering method, synthetic coherent eddy method, and synthetic volume forcing method. This article reviews major progress in inflow turbulence generation methods with an emphasis on fundamental ideas, key milestones, representative applications, and critical issues. Directions for future research in the field are also highlighted.
Energy Technology Data Exchange (ETDEWEB)
S. Dartevelle
2005-09-05
The objective of this manuscript is to fully derive a geophysical multiphase model able to ''accommodate'' different multiphase turbulence approaches; viz., the Reynolds Averaged Navier-Stokes (RANS), the Large Eddy Simulation (LES), or hybrid RANSLES. This manuscript is the first part of a larger geophysical multiphase project--lead by LANL--that aims to develop comprehensive modeling tools for large-scale, atmospheric, transient-buoyancy dusty jets and plume (e.g., plinian clouds, nuclear ''mushrooms'', ''supercell'' forest fire plumes) and for boundary-dominated geophysical multiphase gravity currents (e.g., dusty surges, diluted pyroclastic flows, dusty gravity currents in street canyons). LES is a partially deterministic approach constructed on either a spatial- or a temporal-separation between the large and small scales of the flow, whereas RANS is an entirely probabilistic approach constructed on a statistical separation between an ensemble-averaged mean and higher-order statistical moments (the so-called ''fluctuating parts''). Within this specific multiphase context, both turbulence approaches are built up upon the same phasic binary-valued ''function of presence''. This function of presence formally describes the occurrence--or not--of any phase at a given position and time and, therefore, allows to derive the same basic multiphase Navier-Stokes model for either the RANS or the LES frameworks. The only differences between these turbulence frameworks are the closures for the various ''turbulence'' terms involving the unknown variables from the fluctuating (RANS) or from the subgrid (LES) parts. Even though the hydrodynamic and thermodynamic models for RANS and LES have the same set of Partial Differential Equations, the physical interpretations of these PDEs cannot be the same, i.e., RANS models an averaged field, while LES simulates a
Tang, S.; Xie, S.; Tang, Q.; Zhang, Y.
2017-12-01
Two types of instruments, the eddy correlation flux measurement system (ECOR) and the energy balance Bowen ratio system (EBBR), are used at the Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site to measure surface latent and sensible fluxes. ECOR and EBBR typically sample different land surface types, and the domain-mean surface fluxes derived from ECOR and EBBR are not always consistent. The uncertainties of the surface fluxes will have impacts on the derived large-scale forcing data and further affect the simulations of single-column models (SCM), cloud-resolving models (CRM) and large-eddy simulation models (LES), especially for the shallow-cumulus clouds which are mainly driven by surface forcing. This study aims to quantify the uncertainties of the large-scale forcing caused by surface turbulence flux measurements and investigate the impacts on cloud simulations using long-term observations from the ARM SGP site.
Poludnenko, Alexei
2016-11-01
Turbulent reacting flows are pervasive both in our daily lives on Earth and in the Universe. They power modern society being at the heart of many energy generation and propulsion systems, such as gas turbines, internal combustion and jet engines. On astronomical scales, thermonuclear turbulent flames are the driver of some of the most powerful explosions in the Universe, knows as Type Ia supernovae. Despite this ubiquity in Nature, turbulent reacting flows still pose a number of fundamental questions often exhibiting surprising and unexpected behavior. In this talk, we will discuss several such phenomena observed in direct numerical simulations of high-speed, premixed, turbulent flames. We show that turbulent flames in certain regimes are intrinsically unstable even in the absence of the surrounding combustor walls or obstacles, which can support the thermoacoustic feedback. Such instability can fundamentally change the structure and dynamics of the turbulent cascade, resulting in a significant (and anisotropic) redistribution of kinetic energy from small to large scales. In particular, three effects are observed. 1) The turbulent burning velocity can develop pulsations with significant peak-to-peak amplitudes. 2) Unstable burning can result in pressure build-up and the formation of pressure waves or shocks when the flame speed approaches or exceeds the speed of a Chapman-Jouguet deflagration. 3) Coupling of pressure and density gradients across the flame can lead to the anisotropic generation of turbulence inside the flame volume and flame acceleration. We extend our earlier analysis, which relied on a simplified single-step reaction model, by demonstrating existence of these effects in realistic chemical flames (hydrogen and methane) and in thermonuclear flames in degenerate, relativistic plasmas found in stellar interiors. Finally, we discuss the implications of these results for subgrid-scale LES combustion models. This work was supported by the Air Force
Developing an Assessment Method of Active Aging: University of Jyvaskyla Active Aging Scale.
Rantanen, Taina; Portegijs, Erja; Kokko, Katja; Rantakokko, Merja; Törmäkangas, Timo; Saajanaho, Milla
2018-01-01
To develop an assessment method of active aging for research on older people. A multiphase process that included drafting by an expert panel, a pilot study for item analysis and scale validity, a feedback study with focus groups and questionnaire respondents, and a test-retest study. Altogether 235 people aged 60 to 94 years provided responses and/or feedback. We developed a 17-item University of Jyvaskyla Active Aging Scale with four aspects in each item (goals, ability, opportunity, and activity; range 0-272). The psychometric and item properties are good and the scale assesses a unidimensional latent construct of active aging. Our scale assesses older people's striving for well-being through activities pertaining to their goals, abilities, and opportunities. The University of Jyvaskyla Active Aging Scale provides a quantifiable measure of active aging that may be used in postal questionnaires or interviews in research and practice.
Coughtrie, AR; Borman, DJ; Sleigh, PA
2013-01-01
Flow in a gas-lift digester with a central draft-tube was investigated using computational fluid dynamics (CFD) and different turbulence closure models. The k-ω Shear-Stress-Transport (SST), Renormalization-Group (RNG) k-∊, Linear Reynolds-Stress-Model (RSM) and Transition-SST models were tested for a gas-lift loop reactor under Newtonian flow conditions validated against published experimental work. The results identify that flow predictions within the reactor (where flow is transitional) ar...
Satellite sensing of submerged fossil turbulence and zombie turbulence
Gibson, Carl H.
2004-11-01
Surface brightness anomalies from a submerged municipal wastewater outfall trapped by buoyancy in an area 0.1 km^2 are surprisingly detected from space satellites in areas > 200 km^2. How is this possible? Microstructure measurements near the outfall diffuser reveal enhanced turbulence and temperature dissipation rates above the 50 m trapping depth. Near-vertical radiation of internal waves by fossil and zombie turbulence microstructure patches produce wind ripple smoothing with 30-50 m internal wave patterns in surface Fourier brightness anomalies near the outfall. Detections at 10-14 km distances are at 100-220 m bottom boundary layer (BBL) fossil turbulence scales. Advected outfall fossils form zombie turbulence patches in internal wave patterns as they extract energy, vorticity, turbulence and ambient vertical internal wavelength information as their density gradients are tilted by the waves. As the zombies fossilize, patterned energy radiates near-vertically to produce the detected Fourier anomalies. Zombie turbulence patches beam extracted energy in a preferred direction with a special frequency, like energized metastable molecules in a chemical maser. Thus, kilowatts to produce the submerged field of advected fossil outfall turbulence patches are amplified by beamed zombie turbulence maser action (BZTMA) into megawatts of turbulence dissipation to affect sea surface brightness on wide surface areas using gigawatts of BBL fossil turbulence wave energy available.
Directory of Open Access Journals (Sweden)
Berta Schnettler
2017-07-01
Full Text Available The Multidimensional Students’ Life Satisfaction Scale is an instrument to assess life satisfaction in children and adolescents in five life domains. However, research on multidimensional life satisfaction in older students, such as those attending university, is still scarce. This paper undertook to evaluate the psychometric properties of the Multidimensional Students’ Life Satisfaction Scale in a sample of university students from five state universities in Chile. The Multidimensional Students’ Life Satisfaction Scale and Satisfaction with Life Scale were applied to 369 participants. Confirmatory factor analysis was used to evaluate the expected correlated five-factor model of the long version (40 items and the abbreviated version (30 items of the Multidimensional Students’ Life Satisfaction Scale. The goodness-of-fit values obtained from confirmatory factor analysis revealed that the data fit better to the 30-items and five-factor structure than to the 40-item structure. The convergent, concurrent and discriminant validity of the 30-item version was demonstrated. The 30-item version of the Multidimensional Students’ Life Satisfaction Scale may be a promising alternative to measure satisfaction in different life domains in university students, and a valuable tool for differential assessments that guide research and intervention on this population.
van Loon, Johannes P A M; Van Dierendonck, Machteld C
2015-01-01
Although recognition of equine pain has been studied extensively over the past decades there is still need for improvement in objective identification of pain in horses with acute colic. This study describes scale construction and clinical applicability of the Equine Utrecht University Scale for
Turbulent energy dissipation rate in a tilting flume with a highly rough bed
Coscarella, F.; Servidio, S.; Ferraro, D.; Carbone, V.; Gaudio, R.
2017-08-01
Turbulent flows on highly rough beds, such as those occurring in natural watercourses, represent a longstanding and fascinating problem of hydraulics, motivating in the past few decades huge research on new models of turbulence. In this work, laboratory experiments are presented on a stream flowing on a heterogeneous pebble bed with varying slope. The analysis of the flow speed puts in evidence a clear inertial range, where the Kolmogorov 4/5-law for the streamwise velocity spatial increments holds. The law is used for a systematic estimation of the turbulent kinetic energy dissipation rate 𝜖 , here measured for three different bed slopes and hence for three different shear Reynolds numbers. The experiments presented here suggest that small scale turbulence has properties similar to the classical picture of homogeneous universal turbulence invoked by the Kolmogorov theory.
Quantum quenches in free field theory: universal scaling at any rate
International Nuclear Information System (INIS)
Das, Sumit R.; Galante, Damián A.; Myers, Robert C.
2016-01-01
Quantum quenches display universal scaling in several regimes. For quenches which start from a gapped phase and cross a critical point, with a rate slow compared to the initial gap, many systems obey Kibble-Zurek scaling. More recently, a different scaling behaviour has been shown to occur when the quench rate is fast compared to all other physical scales, but still slow compared to the UV cutoff. We investigate the passage from fast to slow quenches in scalar and fermionic free field theories with time dependent masses for which the dynamics can be solved exactly for all quench rates. We find that renormalized one point functions smoothly cross over between the regimes.
Quantum quenches in free field theory: universal scaling at any rate
Energy Technology Data Exchange (ETDEWEB)
Das, Sumit R. [Department of Physics and Astronomy, University of Kentucky,Lexington, KY 40506 (United States); Galante, Damián A. [Department of Applied Mathematics, University of Western Ontario,London, ON N6A 5B7 (Canada); Perimeter Institute for Theoretical Physics,Waterloo, ON N2L 2Y5 (Canada); Myers, Robert C. [Perimeter Institute for Theoretical Physics,Waterloo, ON N2L 2Y5 (Canada)
2016-05-27
Quantum quenches display universal scaling in several regimes. For quenches which start from a gapped phase and cross a critical point, with a rate slow compared to the initial gap, many systems obey Kibble-Zurek scaling. More recently, a different scaling behaviour has been shown to occur when the quench rate is fast compared to all other physical scales, but still slow compared to the UV cutoff. We investigate the passage from fast to slow quenches in scalar and fermionic free field theories with time dependent masses for which the dynamics can be solved exactly for all quench rates. We find that renormalized one point functions smoothly cross over between the regimes.
Coughtrie, A R; Borman, D J; Sleigh, P A
2013-06-01
Flow in a gas-lift digester with a central draft-tube was investigated using computational fluid dynamics (CFD) and different turbulence closure models. The k-ω Shear-Stress-Transport (SST), Renormalization-Group (RNG) k-∊, Linear Reynolds-Stress-Model (RSM) and Transition-SST models were tested for a gas-lift loop reactor under Newtonian flow conditions validated against published experimental work. The results identify that flow predictions within the reactor (where flow is transitional) are particularly sensitive to the turbulence model implemented; the Transition-SST model was found to be the most robust for capturing mixing behaviour and predicting separation reliably. Therefore, Transition-SST is recommended over k-∊ models for use in comparable mixing problems. A comparison of results obtained using multiphase Euler-Lagrange and singlephase approaches are presented. The results support the validity of the singlephase modelling assumptions in obtaining reliable predictions of the reactor flow. Solver independence of results was verified by comparing two independent finite-volume solvers (Fluent-13.0sp2 and OpenFOAM-2.0.1). Copyright © 2013 Elsevier Ltd. All rights reserved.
Turbulent dispersion of many particles
Pratt, J.; Busse, A.; Muller, W. C.
2017-12-01
We demonstrate the utility of the convex hull to analyze dispersion of groups of many Lagrangian tracer particles in turbulence. We examine dispersion in turbulent flows driven by convection, relevant to geophysical flows and the spread of contaminants in the atmosphere, and in turbulent flows affected by magnetic fields, relevant to stellar winds and stellar interiors. Convex hull analysis can provide new information about local dispersion, in the form of the surface area and volume for a cluster of particles. We use dispersive information to examine the local anisotropy that occurs in these turbulent settings, and to understand fundamental characteristics of heat transfer and the small-scale dynamo.
Universal Scaling and Critical Exponents of the Anisotropic Quantum Rabi Model
Liu, Maoxin; Chesi, Stefano; Ying, Zu-Jian; Chen, Xiaosong; Luo, Hong-Gang; Lin, Hai-Qing
2017-12-01
We investigate the quantum phase transition of the anisotropic quantum Rabi model, in which the rotating and counterrotating terms are allowed to have different coupling strengths. The model interpolates between two known limits with distinct universal properties. Through a combination of analytic and numerical approaches, we extract the phase diagram, scaling functions, and critical exponents, which determine the universality class at finite anisotropy (identical to the isotropic limit). We also reveal other interesting features, including a superradiance-induced freezing of the effective mass and discontinuous scaling functions in the Jaynes-Cummings limit. Our findings are extended to the few-body quantum phase transitions with N >1 spins, where we expose the same effective parameters, scaling properties, and phase diagram. Thus, a stronger form of universality is established, valid from N =1 up to the thermodynamic limit.
Validation of the JDS satisfaction scales applied to educational university environments
Directory of Open Access Journals (Sweden)
Martha Giraldo-O'Meara
2014-01-01
Full Text Available Purpose: The aim of this study is to review and summarize the main satisfaction scales used in publications about human Resource Management and educational research, in order to adapt the satisfaction scales of the Job Diagnostic Survey (JDS to higher education and validate it with a sample of university students and to assess the concept of satisfaction in two different ways: as a single-item measure, with a global indicator and as a multi-item measure, analyzed as a global model and composed by several scales. Design/methodology/approach: Confirmatory factor analysis with maximum likelihood, using structural equations model, was employed to assess the model fit in 152 business management undergraduates. Findings and Originality/value: The satisfaction model measured as multi-item scale present an acceptable fit. Even though, some of the satisfaction scales did not present a satisfactory fit, they can be used and interpreted independently with carefulness. Nevertheless, the satisfaction single-item scale presents a better fit and has been validated as a simpler and less costly measure of satisfaction. Originality/value: In the current process of change that is taking place in universities according to the plan developed by the European Space of higher Education, validated instruments as the satisfaction scale of JDS, adapted to teaching, may facilitate this process through the diagnosis, and follow-up of changes in satisfaction levels in university classrooms.
Turbulence via information field dynamics
Ensslin, Torsten A.
2015-08-01
Turbulent flows exhibit-scale free regimes, for which information on the statistical properties of the dynamics exists for many length-scales. The simulation of turbulent systems can benefit from the inclusion of such information on sub-grid process. How can statistical information about the flow on small scales be optimally be incorporated into simulation schemes? Information field dynamics (IFD) is a novel information theoretical framework to design schemes that exploit such statistical knowledge on sub-grid flow fluctuations. In this talk, I will introduce the basic idea of IFD, present its first toy applications, and discuss the next steps towards its usage in complex turbulence simulations.
EuHIT, Collaboration
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed.
Lundquist, J. K.; Handschy, M.
2013-12-01
During the year 2012, the cumulative wind power capacity installed in the United States could provide roughly 4.4% of electricity demand. Although the wind resource can provide many times over the entire US electrical needs, and costs for onshore wind deployment are continually dropping, the variability of the wind represents one of the greatest remaining barriers to wide-scale wind deployment. This study focuses on the nature of this variability. We quantify the axiom 'geographic diversity reduces variability' (of wind generation) by relating resource variability characteristics to the well-understood physical phenomena of turbulence in the Earth's atmosphere. Many existing studies focus on datasets of a few years' duration in a particular geographic area; such results are difficult to generalize. Our approach builds on the fundamental nonlinear characteristics of turbulence in the atmosphere to characterize wind speed and power generation correlations between wind plants from local to continental scales. The resulting general principles enable estimation of the benefits of geographic aggregation absent detailed site-specific historical data, thereby enabling more efficient transmission grid models, expediting transmission plans, and providing a framework for evaluating the requirements and benefits of electric storage at higher wind penetrations. To validate these general principles, we compare them to observed inter-station correlations in a number of wind-speed data sets, including a 40-year Canadian dataset that spans the continent of North America, as well as shorter-duration datasets in smaller regions within the United States. This presentation will present general rules for the dependence of correlation between wind turbines on separation and time scale. We suggest these general rules could help shift renewable integration planning from simulation towards optimization.
MULTIFLUID MAGNETOHYDRODYNAMIC TURBULENT DECAY
International Nuclear Information System (INIS)
Downes, T. P.; O'Sullivan, S.
2011-01-01
It is generally believed that turbulence has a significant impact on the dynamics and evolution of molecular clouds and the star formation that occurs within them. Non-ideal magnetohydrodynamic (MHD) effects are known to influence the nature of this turbulence. We present the results of a suite of 512 3 resolution simulations of the decay of initially super-Alfvenic and supersonic fully multifluid MHD turbulence. We find that ambipolar diffusion increases the rate of decay of the turbulence while the Hall effect has virtually no impact. The decay of the kinetic energy can be fitted as a power law in time and the exponent is found to be -1.34 for fully multifluid MHD turbulence. The power spectra of density, velocity, and magnetic field are all steepened significantly by the inclusion of non-ideal terms. The dominant reason for this steepening is ambipolar diffusion with the Hall effect again playing a minimal role except at short length scales where it creates extra structure in the magnetic field. Interestingly we find that, at least at these resolutions, the majority of the physics of multifluid turbulence can be captured by simply introducing fixed (in time and space) resistive terms into the induction equation without the need for a full multifluid MHD treatment. The velocity dispersion is also examined and, in common with previously published results, it is found not to be power law in nature.
Pan, Wen-hao; Liu, Shi-he; Huang, Li
2018-02-01
This study developed a three-layer velocity model for turbulent flow over large-scale roughness. Through theoretical analysis, this model coupled both surface and subsurface flow. Flume experiments with flat cobble bed were conducted to examine the theoretical model. Results show that both the turbulent flow field and the total flow characteristics are quite different from that in the low gradient flow over microscale roughness. The velocity profile in a shallow stream converges to the logarithmic law away from the bed, while inflecting over the roughness layer to the non-zero subsurface flow. The velocity fluctuations close to a cobble bed are different from that of a sand bed, and it indicates no sufficiently large peak velocity. The total flow energy loss deviates significantly from the 1/7 power law equation when the relative flow depth is shallow. Both the coupled model and experiments indicate non-negligible subsurface flow that accounts for a considerable proportion of the total flow. By including the subsurface flow, the coupled model is able to predict a wider range of velocity profiles and total flow energy loss coefficients when compared with existing equations.
DEFF Research Database (Denmark)
Schnettler, Berta; Miranda, Horacio; Miranda-Zapata, Edgardo
2017-01-01
This study examined longitudinal measurement invariance in the Satisfaction with Food-related Life (SWFL) scale using follow-up data from university students. We examined this measure of the SWFL in different groups of students, separated by various characteristics. Through non...... in this research. It is also possible to suggest that satisfaction with food-related life is associated with sex and age....... students of both sexes, and among those older and younger than 22 years. Generally, these findings suggest that the SWFL scale has satisfactory psychometric properties for longitudinal measurement invariance in university students with similar characteristics as the students that participated...
Primordial Non-Gaussianity in the Large-Scale Structure of the Universe
Directory of Open Access Journals (Sweden)
Vincent Desjacques
2010-01-01
generated the cosmological fluctuations observed today. Any detection of significant non-Gaussianity would thus have profound implications for our understanding of cosmic structure formation. The large-scale mass distribution in the Universe is a sensitive probe of the nature of initial conditions. Recent theoretical progress together with rapid developments in observational techniques will enable us to critically confront predictions of inflationary scenarios and set constraints as competitive as those from the Cosmic Microwave Background. In this paper, we review past and current efforts in the search for primordial non-Gaussianity in the large-scale structure of the Universe.
Structure and modeling of turbulence
International Nuclear Information System (INIS)
Novikov, E.A.
1995-01-01
The open-quotes vortex stringsclose quotes scale l s ∼ LRe -3/10 (L-external scale, Re - Reynolds number) is suggested as a grid scale for the large-eddy simulation. Various aspects of the structure of turbulence and subgrid modeling are described in terms of conditional averaging, Markov processes with dependent increments and infinitely divisible distributions. The major request from the energy, naval, aerospace and environmental engineering communities to the theory of turbulence is to reduce the enormous number of degrees of freedom in turbulent flows to a level manageable by computer simulations. The vast majority of these degrees of freedom is in the small-scale motion. The study of the structure of turbulence provides a basis for subgrid-scale (SGS) models, which are necessary for the large-eddy simulations (LES)
Baya Toda, Hubert; Cabrit, Olivier; Truffin, Karine; Bruneaux, Gilles; Nicoud, Franck
2014-07-01
Large-Eddy Simulation (LES) in complex geometries and industrial applications like piston engines, gas turbines, or aircraft engines requires the use of advanced subgrid-scale (SGS) models able to take into account the main flow features and the turbulence anisotropy. Keeping this goal in mind, this paper reports a LES-dedicated experiment of a pulsatile hot-jet impinging a flat-plate in the presence of a cold turbulent cross-flow. Unlike commonly used academic test cases, this configuration involves different flow features encountered in complex configurations: shear/rotating regions, stagnation point, wall-turbulence, and the propagation of a vortex ring along the wall. This experiment was also designed with the aim to use quantitative and nonintrusive optical diagnostics such as Particle Image Velocimetry, and to easily perform a LES involving a relatively simple geometry and well-controlled boundary conditions. Hence, two eddy-viscosity-based SGS models are investigated: the dynamic Smagorinsky model [M. Germano, U. Piomelli, P. Moin, and W. Cabot, "A dynamic subgrid-scale eddy viscosity model," Phys. Fluids A 3(7), 1760-1765 (1991)] and the σ-model [F. Nicoud, H. B. Toda, O. Cabrit, S. Bose, and J. Lee, "Using singular values to build a subgrid-scale model for large eddy simulations," Phys. Fluids 23(8), 085106 (2011)]. Both models give similar results during the first phase of the experiment. However, it was found that the dynamic Smagorinsky model could not accurately predict the vortex-ring propagation, while the σ-model provides a better agreement with the experimental measurements. Setting aside the implementation of the dynamic procedure (implemented here in its simplest form, i.e., without averaging over homogeneous directions and with clipping of negative values to ensure numerical stability), it is suggested that the mitigated predictions of the dynamic Smagorinsky model are due to the dynamic constant, which strongly depends on the mesh resolution
International Nuclear Information System (INIS)
Qian Mengcen; Jiang Zhiqiang; Zhou Weixing
2010-01-01
The investigations of financial markets from a complex network perspective have unveiled many phenomenological properties, in which the majority of these studies map the financial markets into one complex network. In this work, we investigate 30 world stock market indices through their visibility graphs by adopting the visibility algorithm to convert each single stock index into one visibility graph. A universal allometric scaling law is uncovered in the minimal spanning trees, whose scaling exponent is independent of the stock market and the length of the stock index. In contrast, the maximal spanning trees and the random spanning trees do not exhibit universal allometric scaling behaviors. There are marked discrepancies in the allometric scaling behaviors between the stock indices and the Brownian motions. Using surrogate time series, we find that these discrepancies are caused by the fat-tailedness of the return distribution and the nonlinear long-term correlation.
Directory of Open Access Journals (Sweden)
Mohammad Ali Zaki
2006-10-01
Full Text Available The advent of the third millennium witnessed the culmination of two decades of interest expressed by social researchers about the importance, status and utilization of ICT, particularly the Net, concerning scientific production in the areas of theory-formation and research. Part of this scientific output dealt with measurement of internet attitude. The present paper attempts to test, measure and validate internet attitude scales. It offers the findings of a survey conducted among 200 students, both male and female, at Isfahan University and Isfahan University of Medical Science. Standard Dinev and Koufteros questionnaire was used. It measures two kinds of attitude towards internet use and self-efficacy. Using factor analysis, the present paper investigated the reliability of two sets of questionnaires. Both possessed appropriate internal consistency. Construct Validity was confirmed using factor analysis. The statements incorporated within the research instrument could be distinguished and therefore offers a suitable tool for evaluating internet attitude.
Statistics and Dynamics in the Large-scale Structure of the Universe
International Nuclear Information System (INIS)
Matsubara, Takahiko
2006-01-01
In cosmology, observations and theories are related to each other by statistics in most cases. Especially, statistical methods play central roles in analyzing fluctuations in the universe, which are seeds of the present structure of the universe. The confrontation of the statistics and dynamics is one of the key methods to unveil the structure and evolution of the universe. I will review some of the major statistical methods in cosmology, in connection with linear and nonlinear dynamics of the large-scale structure of the universe. The present status of analyses of the observational data such as the Sloan Digital Sky Survey, and the future prospects to constrain the nature of exotic components of the universe such as the dark energy will be presented
Computational Cosmology: From the Early Universe to the Large Scale Structure.
Anninos, Peter
2001-01-01
In order to account for the observable Universe, any comprehensive theory or model of cosmology must draw from many disciplines of physics, including gauge theories of strong and weak interactions, the hydrodynamics and microphysics of baryonic matter, electromagnetic fields, and spacetime curvature, for example. Although it is difficult to incorporate all these physical elements into a single complete model of our Universe, advances in computing methods and technologies have contributed significantly towards our understanding of cosmological models, the Universe, and astrophysical processes within them. A sample of numerical calculations (and numerical methods applied to specific issues in cosmology are reviewed in this article: from the Big Bang singularity dynamics to the fundamental interactions of gravitational waves; from the quark-hadron phase transition to the large scale structure of the Universe. The emphasis, although not exclusively, is on those calculations designed to test different models of cosmology against the observed Universe.
Computational Cosmology: from the Early Universe to the Large Scale Structure
Directory of Open Access Journals (Sweden)
Peter Anninos
1998-09-01
Full Text Available In order to account for the observable Universe, any comprehensive theory or model of cosmology must draw from many disciplines of physics, including gauge theories of strong and weak interactions, the hydrodynamics and microphysics of baryonic matter, electromagnetic fields, and spacetime curvature, for example. Although it is difficult to incorporate all these physical elements into a single complete model of our Universe, advances in computing methods and technologies have contributed significantly towards our understanding of cosmological models, the Universe, and astrophysical processes within them. A sample of numerical calculations addressing specific issues in cosmology are reviewed in this article: from the Big Bang singularity dynamics to the fundamental interactions of gravitational waves; from the quark--hadron phase transition to the large scale structure of the Universe. The emphasis, although not exclusively, is on thosecalculations designed to test different models of cosmology against the observed Universe.
Computational Cosmology: from the Early Universe to the Large Scale Structure
Directory of Open Access Journals (Sweden)
Anninos Peter
2001-01-01
Full Text Available In order to account for the observable Universe, any comprehensive theory or model of cosmology must draw from many disciplines of physics, including gauge theories of strong and weak interactions, the hydrodynamics and microphysics of baryonic matter, electromagnetic fields, and spacetime curvature, for example. Although it is difficult to incorporate all these physical elements into a single complete model of our Universe, advances in computing methods and technologies have contributed significantly towards our understanding of cosmological models, the Universe, and astrophysical processes within them. A sample of numerical calculations (and numerical methods applied to specific issues in cosmology are reviewed in this article: from the Big Bang singularity dynamics to the fundamental interactions of gravitational waves; from the quark-hadron phase transition to the large scale structure of the Universe. The emphasis, although not exclusively, is on those calculations designed to test different models of cosmology against the observed Universe.
Calderer, Antoni; Guo, Xin; Shen, Lian; Sotiropoulos, Fotis
2018-02-01
We develop a numerical method for simulating coupled interactions of complex floating structures with large-scale ocean waves and atmospheric turbulence. We employ an efficient large-scale model to develop offshore wind and wave environmental conditions, which are then incorporated into a high resolution two-phase flow solver with fluid-structure interaction (FSI). The large-scale wind-wave interaction model is based on a two-fluid dynamically-coupled approach that employs a high-order spectral method for simulating the water motion and a viscous solver with undulatory boundaries for the air motion. The two-phase flow FSI solver is based on the level set method and is capable of simulating the coupled dynamic interaction of arbitrarily complex bodies with airflow and waves. The large-scale wave field solver is coupled with the near-field FSI solver with a one-way coupling approach by feeding into the latter waves via a pressure-forcing method combined with the level set method. We validate the model for both simple wave trains and three-dimensional directional waves and compare the results with experimental and theoretical solutions. Finally, we demonstrate the capabilities of the new computational framework by carrying out large-eddy simulation of a floating offshore wind turbine interacting with realistic ocean wind and waves.
Ida, Masato; Taniguchi, Nobuyuki
2003-09-01
This paper introduces a candidate for the origin of the numerical instabilities in large eddy simulation repeatedly observed in academic and practical industrial flow computations. Without resorting to any subgrid-scale modeling, but based on a simple assumption regarding the streamwise component of flow velocity, it is shown theoretically that in a channel-flow computation, the application of the Gaussian filtering to the incompressible Navier-Stokes equations yields a numerically unstable term, a cross-derivative term, which is similar to one appearing in the Gaussian filtered Vlasov equation derived by Klimas [J. Comput. Phys. 68, 202 (1987)] and also to one derived recently by Kobayashi and Shimomura [Phys. Fluids 15, L29 (2003)] from the tensor-diffusivity subgrid-scale term in a dynamic mixed model. The present result predicts that not only the numerical methods and the subgrid-scale models employed but also only the applied filtering process can be a seed of this numerical instability. An investigation concerning the relationship between the turbulent energy scattering and the unstable term shows that the instability of the term does not necessarily represent the backscatter of kinetic energy which has been considered a possible origin of numerical instabilities in large eddy simulation. The present findings raise the question whether a numerically stable subgrid-scale model can be ideally accurate.
Woodham, Lloyd D.; Wicks, Robert T.; Verscharen, Daniel; Owen, Christopher J.
2018-03-01
We use magnetic field and ion moment data from the MFI and SWE instruments on board the Wind spacecraft to study the nature of solar wind turbulence at ion-kinetic scales. We analyze the spectral properties of magnetic field fluctuations between 0.1 and 5.4 Hz during 2012 using an automated routine, computing high-resolution 92 s power and magnetic helicity spectra. To ensure the spectral features are physical, we make the first in-flight measurement of the MFI “noise-floor” using tail-lobe crossings of the Earth’s magnetosphere during early 2004. We utilize Taylor’s hypothesis to Doppler-shift into the spacecraft frequency frame, finding that the spectral break observed at these frequencies is best associated with the proton cyclotron resonance scale, 1/k c , rather than the proton inertial length, d i , or proton gyroscale, ρ i . This agreement is strongest when we consider periods where β i,\\perp ∼ 1, and is consistent with a spectral break at d i for β i,\\perp ≪1 and at ρ i for β i,\\perp ≫1. We also find that the coherent magnetic helicity signature observed at these frequencies is bounded at low frequencies by 1/k c , and its absolute value reaches a maximum at ρ i . These results hold in both slow and fast wind streams, but with a better correlation in the more Alfvénic fast wind where the helicity signature is strongest. We conclude that these findings are consistent with proton cyclotron resonance as an important mechanism for dissipation of turbulent energy in the solar wind, occurring at least half the time in our selected interval. However, we do not rule out additional mechanisms.
Hierarchical formation of large scale structures of the Universe: observations and models
International Nuclear Information System (INIS)
Maurogordato, Sophie
2003-01-01
In this report for an Accreditation to Supervise Research (HDR), the author proposes an overview of her research works in cosmology. These works notably addressed the large scale distribution of the Universe (with constraints on the scenario of formation, and on the bias relationship, and the structuring of clusters), the analysis of galaxy clusters during coalescence, mass distribution within relaxed clusters [fr
Factor Analytic Study of Lecturer's Teaching Assessment Scale in Obafemi Awolowo University, Nigeria
Jegede, Olu Philip; Faleye, Bamidele Abiodun; Adeyemo, Emily Oluseyi
2015-01-01
This study presents a validation report of the Lecturer's Teaching Assessment Scale (LTAS) developed for the assessment of lecturer's teaching effectiveness in Obafemi Awolowo University, Ile-Ife, Nigeria. It also examined the factor structure of the LTAS, its construct validity, and internal consistency reliability coefficients. The study adopted…
Economies of Scale and Scope in Turkish Universities. ASHE Annual Meeting Paper.
Lewis, Darrell R.; Dundar, Halil
This study examined the collegiate production and cost structures of the 28 universities in Turkey in order to estimate their degrees of economies of scale and scope. Multi-product cost functions were estimated for the collegiate production of teaching and research in order to determine the most efficient level and product-mix for differing types…
Phase transitions as the origin of large scale structure in the universe
Turok, Neil
1989-01-01
A review of the formation of large scale structure through gravitational growth of primordial perturbations is given. This is followed by a discussion of how symmetry breaking phase transitions in the early universe might have produced the required perturbations, in particular through the formation and evolution of a network of cosmic strings.
Fractals and the Large-Scale Structure in the Universe -R-ES ...
Indian Academy of Sciences (India)
In Part 1 of this article, we had introduced the reader to some basic concepts of fractals and some operational algorithms to characterize them. We had also pointed out and clarified some com- mon misconceptions about fractals. In this part we apply the fractal concepts to large-scale struc- tures in the Universe. In particular ...
LARGE-SCALE STRUCTURE OF THE UNIVERSE AS A COSMIC STANDARD RULER
International Nuclear Information System (INIS)
Park, Changbom; Kim, Young-Rae
2010-01-01
We propose to use the large-scale structure (LSS) of the universe as a cosmic standard ruler. This is possible because the pattern of large-scale distribution of matter is scale-dependent and does not change in comoving space during the linear-regime evolution of structure. By examining the pattern of LSS in several redshift intervals it is possible to reconstruct the expansion history of the universe, and thus to measure the cosmological parameters governing the expansion of the universe. The features of the large-scale matter distribution that can be used as standard rulers include the topology of LSS and the overall shapes of the power spectrum and correlation function. The genus, being an intrinsic topology measure, is insensitive to systematic effects such as the nonlinear gravitational evolution, galaxy biasing, and redshift-space distortion, and thus is an ideal cosmic ruler when galaxies in redshift space are used to trace the initial matter distribution. The genus remains unchanged as far as the rank order of density is conserved, which is true for linear and weakly nonlinear gravitational evolution, monotonic galaxy biasing, and mild redshift-space distortions. The expansion history of the universe can be constrained by comparing the theoretically predicted genus corresponding to an adopted set of cosmological parameters with the observed genus measured by using the redshift-comoving distance relation of the same cosmological model.
Hendy, Helen M.; Can, S. Hakan; Joseph, Lauren J.; Scherer, Cory R.
2013-01-01
The University Students Leaving Relationships scale was developed to identify student concerns when contemplating dissolution of romantic relationships. Participants included 1,106 students who rated the importance of issues when deciding to leave relationships. Factor analysis produced three dimensions: Missing the Relationship, Social…
On the universality of MOG weak field approximation at galaxy cluster scale
Directory of Open Access Journals (Sweden)
Ivan De Martino
2017-07-01
Full Text Available In its weak field limit, Scalar-tensor-vector gravity theory introduces a Yukawa-correction to the gravitational potential. Such a correction depends on the two parameters, α which accounts for the modification of the gravitational constant, and μ⁎−1 which represents the scale length on which the scalar field propagates. These parameters were found to be universal when the modified gravitational potential was used to fit the galaxy rotation curves and the mass profiles of galaxy clusters, both without Dark Matter. We test the universality of these parameters using the temperature anisotropies due to the thermal Sunyaev–Zeldovich effect. In our model the intra-cluster gas is in hydrostatic equilibrium within the modified gravitational potential well and it is described by a polytropic equation of state. We predict the thermal Sunyaev–Zeldovich temperature anisotropies produced by Coma cluster, and we compare them with those obtained using the Planck 2013 Nominal maps. In our analysis, we find α and the scale length, respectively, to be consistent and to depart from their universal values. Our analysis points out that the assumption of the universality of the Yukawa-correction to the gravitational potential is ruled out at more than 3.5σ at galaxy clusters scale, while demonstrating that such a theory of gravity is capable to fit the cluster profile if the scale dependence of the gravitational potential is restored.
Towards a Gravity Dual for the Large Scale Structure of the Universe
Kehagias, A.
2016-01-01
The dynamics of the large-scale structure of the universe enjoys at all scales, even in the highly non-linear regime, a Lifshitz symmetry during the matter-dominated period. In this paper we propose a general class of six-dimensional spacetimes which could be a gravity dual to the four-dimensional large-scale structure of the universe. In this set-up, the Lifshitz symmetry manifests itself as an isometry in the bulk and our universe is a four-dimensional brane moving in such six-dimensional bulk. After finding the correspondence between the bulk and the brane dynamical Lifshitz exponents, we find the intriguing result that the preferred value of the dynamical Lifshitz exponent of our observed universe, at both linear and non-linear scales, corresponds to a fixed point of the RGE flow of the dynamical Lifshitz exponent in the dual system where the symmetry is enhanced to the Schrodinger group containing a non-relativistic conformal symmetry. We also investigate the RGE flow between fixed points of the Lifshitz...
Stochastic modelling of turbulence
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
previously been shown to be closely connected to the energy dissipation. The incorporation of the small scale dynamics into the spatial model opens the door to a fully fledged stochastic model of turbulence. Concerning the interaction of wind and wind turbine, a new method is proposed to extract wind turbine...
Lu, Wei; Bian, Qian; Wang, Wenzheng; Wu, Xiaoling; Wang, Zhen; Zhao, Min
2017-01-01
Chinese university students often suffer from acute stress, which can affect their mental health. We measured and evaluated perceived stress in this population using the Simplified Chinese version of the 10-item Perceived Stress Scale (SCPSS-10). The SCPSS-10, Patient Health Questionnaire (PHQ), and Generalized Anxiety Disorder 7-item scale (GAD-7) were conducted in 1096 university students. Two weeks later, 129 participants were re-tested using the SCPSS-10. Exploratory factor analysis yielded two factors with Eigen values of 4.76 and 1.48, accounting for 62.41% of the variance. Confirmatory factor analysis demonstrated good fit of this two-factor model. The internal consistency reliability, as measured by Cronbach's α, was 0.85. The test-retest reliability coefficient was 0.7. The SCPSS-10 exhibited high correlation with the PHQ-9 and GAD-7, indicating an acceptable concurrent validity. The SCPSS-10 exhibited satisfactory psychometric properties in Chinese university students.
Universal scaling of the stress-strain curve in amorphous solids.
Lin, Jie; Zheng, Wen
2017-09-01
The yielding transition of amorphous solids is a phase transition with a special type of universality. Critical exponents and scaling relations have been defined and proposed near the yield stress. We show here that, even in the initial stage of shear far below the yield stress, the stress-strain curve of amorphous solids also shows critical scaling with universal exponents. The key point is to remove the elastic part of the strain, and the shear stress exhibits a sublinear scaling with the plastic strain. We show how this critical scaling is related to the finite size effect of the minimum strain to trigger the first plastic avalanche after a quench. We point out that this sublinear scaling between the stress and the plastic strain implies the divergence of a high-order shear modulus. A scaling relation is derived between two exponents characterizing the stress-strain curve and the density distribution of the local stabilities, respectively. We test the critical scaling of the stress-strain curve using both mesoscopic and atomistic simulations and get satisfying agreement in two and three dimensions.
Rank-Ordered Multifractal Analysis (ROMA of probability distributions in fluid turbulence
Directory of Open Access Journals (Sweden)
C. C. Wu
2011-04-01
Full Text Available Rank-Ordered Multifractal Analysis (ROMA was introduced by Chang and Wu (2008 to describe the multifractal characteristic of intermittent events. The procedure provides a natural connection between the rank-ordered spectrum and the idea of one-parameter scaling for monofractals. This technique has successfully been applied to MHD turbulence simulations and turbulence data observed in various space plasmas. In this paper, the technique is applied to the probability distributions in the inertial range of the turbulent fluid flow, as given in the vast Johns Hopkins University (JHU turbulence database. In addition, a new way of finding the continuous ROMA spectrum and the scaled probability distribution function (PDF simultaneously is introduced.
Validity and reliability of the Multidimensional Body Image Scale in Malaysian university students.
Gan, W Y; Mohd, Nasir M T; Siti, Aishah H; Zalilah, M S
2012-12-01
This study aimed to evaluate the validity and reliability of the Multidimensional Body Image Scale (MBIS), a seven-factor, 62-item scale developed for Malaysian female adolescents. This scale was evaluated among male and female Malaysian university students. A total of 671 university students (52.2% women and 47.8% men) completed a self-administered questionnaire on MBIS, Eating Attitude Test-26, and Rosenberg Self-Esteem Scale. Their height and weight were measured. Results in confirmatory factor analysis showed that the 62-item MBIS reported poor fit to the data, xhi2/df = 4.126, p validity, it showed positive correlations with disordered eating and body weight status, but negative correlation with self-esteem. Also, this scale discriminated well between participants with and without disordered eating. The MBIS-46 demonstrated good reliability and validity for the evaluation of body image among university students. Further studies need to be conducted to confirm the validation results of the 46-item MBIS.
van Milligen, B. Ph.; Sánchez, R.; Carreras, B. A.; Lynch, V. E.; LaBombard, B.; Pedrosa, M. A.; Hidalgo, C.; Gonçalves, B.; Balbín, R.
2005-05-01
Plasma density fluctuations and electrostatic turbulent fluxes measured at the scrape-off layer of the Alcator C-Mod tokamak [B. LaBombard, R. L. Boivin, M. Greenwald, J. Hughes, B. Lipschultz, D. Mossessian, C. S. Pitcher, J. L. Terry, and S. J. Zweben, Phys. Plasmas 8, 2107 (2001)], the Wendelstein 7-Advanced Stellarator [H. Renner, E. Anabitarte, E. Ascasibar et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)], and the TJ-II stellarator [C. Alejaldre, J. Alonso, J. Botija et al., Fusion Technol. 17, 131 (1990)] are shown to obey a non-Gaussian but apparently universal (i.e., not dependent on device and discharge parameters) probability density distribution (pdf). The fact that a specific shape acts as an attractor for the pdf seems to suggest that emergent behavior and self-regulation are relevant concepts for these fluctuations. This shape is closely similar to the so-called Bramwell, Holdsworth, and Pinton distribution, which does not have any free parameters.
Transport of Charged Particles in Turbulent Magnetic Fields
Parashar, T.; Subedi, P.; Sonsrettee, W.; Blasi, P.; Ruffolo, D. J.; Matthaeus, W. H.; Montgomery, D.; Chuychai, P.; Dmitruk, P.; Wan, M.; Chhiber, R.
2017-12-01
Magnetic fields permeate the Universe. They are found in planets, stars, galaxies, and the intergalactic medium. The magnetic field found in these astrophysical systems are usually chaotic, disordered, and turbulent. The investigation of the transport of cosmic rays in magnetic turbulence is a subject of considerable interest. One of the important aspects of cosmic ray transport is to understand their diffusive behavior and to calculate the diffusion coefficient in the presence of these turbulent fields. Research has most frequently concentrated on determining the diffusion coefficient in the presence of a mean magnetic field. Here, we will particularly focus on calculating diffusion coefficients of charged particles and magnetic field lines in a fully three-dimensional isotropic turbulent magnetic field with no mean field, which may be pertinent to many astrophysical situations. For charged particles in isotropic turbulence we identify different ranges of particle energy depending upon the ratio of the Larmor radius of the charged particle to the characteristic outer length scale of the turbulence. Different theoretical models are proposed to calculate the diffusion coefficient, each applicable to a distinct range of particle energies. The theoretical ideas are tested against results of detailed numerical experiments using Monte-Carlo simulations of particle propagation in stochastic magnetic fields. We also discuss two different methods of generating random magnetic field to study charged particle propagation using numerical simulation. One method is the usual way of generating random fields with a specified power law in wavenumber space, using Gaussian random variables. Turbulence, however, is non-Gaussian, with variability that comes in bursts called intermittency. We therefore devise a way to generate synthetic intermittent fields which have many properties of realistic turbulence. Possible applications of such synthetically generated intermittent fields are
CERN. Geneva. Audiovisual Unit
2005-01-01
Understanding turbulence is vital in astrophysics, geophysics and many engineering applications, with thermal convection playing a central role. I shall describe progress that has recently been made in understanding this ubiquitous phenomenon by making controlled experiments using low-temperature helium, and a brief account of the frontier topic of superfluid turbulence will also be given. CERN might be able to play a unique role in experiments to probe these two problems.
Observing a scale anomaly and a universal quantum phase transition in graphene.
Ovdat, O; Mao, Jinhai; Jiang, Yuhang; Andrei, E Y; Akkermans, E
2017-09-11
One of the most interesting predictions resulting from quantum physics, is the violation of classical symmetries, collectively referred to as anomalies. A remarkable class of anomalies occurs when the continuous scale symmetry of a scale-free quantum system is broken into a discrete scale symmetry for a critical value of a control parameter. This is an example of a (zero temperature) quantum phase transition. Such an anomaly takes place for the quantum inverse square potential known to describe 'Efimov physics'. Broken continuous scale symmetry into discrete scale symmetry also appears for a charged and massless Dirac fermion in an attractive 1/r Coulomb potential. The purpose of this article is to demonstrate the universality of this quantum phase transition and to present convincing experimental evidence of its existence for a charged and massless fermion in an attractive Coulomb potential as realized in graphene.When the continuous scale symmetry of a quantum system is broken, anomalies occur which may lead to quantum phase transitions. Here, the authors provide evidence for such a quantum phase transition in the attractive Coulomb potential of vacancies in graphene, and further envision its universality for diverse physical systems.
Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry
Energy Technology Data Exchange (ETDEWEB)
Hong G. Im; Arnaud Trouve; Christopher J. Rutland; Jacqueline H. Chen
2009-02-02
The TSTC project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of our approach is direct numerical simulation (DNS) featuring highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. The code named S3D, developed and shared with Chen and coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for spray dynamics, combustion, and pollutant formation processes in turbulent combustion. Major accomplishments include improved characteristic boundary conditions, fundamental studies of auto-ignition in turbulent stratified reactant mixtures, flame-wall interaction, and turbulent flame extinction by water spray. The overarching scientific issue in our recent investigations is to characterize criticality phenomena (ignition/extinction) in turbulent combustion, thereby developing unified criteria to identify ignition and extinction conditions. The computational development under TSTC has enabled the recent large-scale 3D turbulent combustion simulations conducted at Sandia National Laboratories.
Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry
Energy Technology Data Exchange (ETDEWEB)
Im, Hong G [University of Michigan; Trouve, Arnaud [University of Maryland; Rutland, Christopher J [University of Wisconsin; Chen, Jacqueline H [Sandia National Laboratories
2012-08-13
The TSTC project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of our approach is direct numerical simulation (DNS) featuring highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. The code named S3D, developed and shared with Chen and coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for spray dynamics, combustion, and pollutant formation processes in turbulent combustion. Major accomplishments include improved characteristic boundary conditions, fundamental studies of auto-ignition in turbulent stratified reactant mixtures, flame-wall interaction, and turbulent flame extinction by water spray. The overarching scientific issue in our recent investigations is to characterize criticality phenomena (ignition/extinction) in turbulent combustion, thereby developing unified criteria to identify ignition and extinction conditions. The computational development under TSTC has enabled the recent large-scale 3D turbulent combustion simulations conducted at Sandia National Laboratories.
Lu, Feiyu; Yuan, Naiming; Fu, Zuntao; Mao, Jiangyu
2012-10-01
Volatility series (defined as the magnitude of the increments between successive elements) of five different meteorological variables over China are analyzed by means of detrended fluctuation analysis (DFA for short). Universal scaling behaviors are found in all volatility records, whose scaling exponents take similar distributions with similar mean values and standard deviations. To reconfirm the relation between long-range correlations in volatility and nonlinearity in original series, DFA is also applied to the magnitude records (defined as the absolute values of the original records). The results clearly indicate that the nonlinearity of the original series is more pronounced in the magnitude series.
Validation of the JDS satisfaction scales applied to educational university environments
Giraldo-O'Meara, Martha; Marin-Garcia, Juan A.; Martinez-Gomez, Monica
2014-01-01
Purpose: The aim of this study is to review and summarize the main satisfaction scales used in publications about human Resource Management and educational research, in order to adapt the satisfaction scales of the Job Diagnostic Survey (JDS) to higher education and validate it with a sample of university students and to assess the concept of satisfaction in two different ways: as a single-item measure, with a global indicator and as a multi-item measure, analyzed as a global model and compos...
Peet, Yulia; Sakievich, Philip; Adrian, Ronald
2017-11-01
At high Rayleigh numbers in moderate aspect-ratio cylindrical domains turbulent Rayleigh-Béenard convection (RBC) exhibits coherent large-scale motions that organize themselves into a collection of three-dimensional ``roll cells''. The current study presents a relatively long, on the order of 3000 free fall time units (or 100 eddy turnovers), Direct Numerical Simulation of the RBC in a cylindrical domain with a 6.3 aspect ratio and the Rayleigh number of 9.6x107. The study shows that the spatial organization of the roll cells in the investigated domain can be well described by the azimuthal Fourier modes. A hub-and-spoke mode-3 pattern first emerges and dominates the flow for the first 20 eddy turnovers, which then transitions into a mode-2 pattern that persists for the remainder of the simulations. A spatial inhomogeneity of the observed mode-3 and mode-2 structures is investigated. A conclusion follows that the cylindrical geometry constraint applies a ``squeezing'' effect to the large-scale structures, which forces them to align with a strong azimuthal periodicity. NSF CBET 1335731, NSF CBET 1707075.
Oceanic turbulence - Big bangs or continuous creation?
Caldwell, D. R.
1983-01-01
A hypothesis concerning the turbulence characteristics of 'microstructure' patches in the ocean is proposed in which a turbulence field is driven at the same time and scale at which it is observed. The driving energy is converted into turbulence kinetic energy in such a way that the observed overturning thickness scale is linearly related to the length scale. This hypothesis is contrasted with that of Gibson (1982), in which the 'patches' are produced by rare, powerful turbulence generators that have 'fossilized' prior to their observation. Careful attention is given to the sampling process and its assumptions.
Fundamental Physics and Model Assumptions in Turbulent Combustion Models for Aerospace Propulsion
2014-06-01
University, 2012. 9U.Piomelli, W. H. Cabot , P. Moin, and S. Lee, Subgridscale backscatter in turbulent and transitional flows. Physics of Fluids A, 3:1766...primitive equations. I. The basic experiment. Mon Weather Rev, 91:99-164, 1963. 15M. Germano, U. Piomelli, P. Moin, and W. Cabot . A dynamic subgrid-scale
Large scale geometry and evolution of a universe with radiation pressure and cosmological constant
Coquereaux, Robert; Coquereaux, Robert; Grossmann, Alex
2000-01-01
In view of new experimental results that strongly suggest a non-zero cosmological constant, it becomes interesting to revisit the Friedmann-Lemaitre model of evolution of a universe with cosmological constant and radiation pressure. In this paper, we discuss the explicit solutions for that model, and perform numerical explorations for reasonable values of cosmological parameters. We also analyse the behaviour of redshifts in such models and the description of ``very large scale geometrical features'' when analysed by distant observers.
Universal scaling laws of top jet drop size and speed in bubble bursting
Ganan-Calvo, Alfonso
2017-11-01
The collapse of a bubble of radius Ro at the surface of a liquid generating a liquid jet and a subsequent first drop of radius R follows a universal flow pattern that can be universally scaled using the difference between the parent bubble radius and a critical radius R* =Oh*-2μ2 /(ρσ) below which no droplet is ejected for a given Newtonian liquid. Here, Oh* = 0.037 is the critical Ohnesorge number, where Oh = μ /(ρσRo) 1 / 2 ; ρ, σ and μ are the liquid density, surface tension and viscosity. Based on a flow singularity occurring for Ro =R* , a scaling analysis of the complex flow structure at the onset of jet ejection for Ro >R* leads to the diameter of the first emitted droplet and the initial ejection velocity: D =kd(Ro -R*) 5 / 4R* - 1 / 4 and V =kv σμ-1(Ro -R*) 3 / 4R* - 3 / 4 , respectively. A remarkable collapse of data taken from available literature since 1954 to 2017 furnishes the universal constants kd = 0.1 and kv = 1.6 , for negligible gravity effects.The role of gravity is subdominant and can be reflected by the exponential dependence of the scaling laws obtained on the Bond number. This work was supported by the Ministerio de Economy Competitividad, Plan Estatal 2013-2016 Retos, project DPI2016-78887-C3-1-R.
Generating scale-invariant tensor perturbations in the non-inflationary universe
Directory of Open Access Journals (Sweden)
Mingzhe Li
2014-09-01
Full Text Available It is believed that the recent detection of large tensor perturbations strongly favors the inflation scenario in the early universe. This common sense depends on the assumption that Einstein's general relativity is valid at the early universe. In this paper we show that nearly scale-invariant primordial tensor perturbations can be generated during a contracting phase before the radiation dominated epoch if the theory of gravity is modified by the scalar–tensor theory at that time. The scale-invariance protects the tensor perturbations from suppressing at large scales and they may have significant amplitudes to fit BICEP2's result. We construct a model to achieve this purpose and show that the universe can bounce to the hot big bang after long time contraction, and at almost the same time the theory of gravity approaches to general relativity through stabilizing the scalar field. Theoretically, such models are dual to inflation models if we change to the frame in which the theory of gravity is general relativity. Dual models are related by the conformal transformations. With this study we reinforce the point that only the conformal invariant quantities such as the scalar and tensor perturbations are physical. How did the background evolve before the radiation time depends on the frame and has no physical meaning. It is impossible to distinguish different pictures by later time cosmological probes.
International Nuclear Information System (INIS)
Guo Fan; Giacalone, Joe
2010-01-01
We study the physics of electron acceleration at collisionless shocks that move through a plasma containing large-scale magnetic fluctuations. We numerically integrate the trajectories of a large number of electrons, which are treated as test particles moving in the time-dependent electric and magnetic fields determined from two-dimensional hybrid simulations (kinetic ions and fluid electron). The large-scale magnetic fluctuations effect the electrons in a number of ways and lead to efficient and rapid energization at the shock front. Since the electrons mainly follow along magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons to cross the shock front several times, leading to efficient acceleration. Ripples in the shock front occurring at various scales will also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. The current study is also helpful in understanding the injection problem for electron acceleration by collisionless shocks. It is also shown that the spatial distribution of energetic electrons is similar to in situ observations. The process may be important to our understanding of energetic electrons in planetary bow shocks and interplanetary shocks, and explaining herringbone structures seen in some type II solar radio bursts.
Turbulence in Natural Environments
Banerjee, Tirtha
Problems in the area of land/biosphere-atmosphere interaction, hydrology, climate modeling etc. can be systematically organized as a study of turbulent flow in presence of boundary conditions in an increasing order of complexity. The present work is an attempt to study a few subsets of this general problem of turbulence in natural environments- in the context of neutral and thermally stratified atmospheric surface layer, the presence of a heterogeneous vegetation canopy and the interaction between air flow and a static water body in presence of flexible protruding vegetation. The main issue addressed in the context of turbulence in the atmospheric surface layer is whether it is possible to describe the macro-states of turbulence such as mean velocity and turbulent velocity variance in terms of the micro-states of the turbulent flow, i.e., a distribution of turbulent kinetic energy across a multitude of scales. This has been achieved by a `spectral budget approach' which is extended for thermal stratification scenarios as well, in the process unifying the seemingly different and unrelated theories of turbulence such as Kolmogorov's hypothesis, Heisenberg's eddy viscosity, Monin Obukhov Similarity Theory (MOST) etc. under a common framework. In the case of a more complex scenario such as presence of a vegetation canopy with edges and gaps, the question that is addressed is in what detail the turbulence is needed to be resolved in order to capture the bulk flow features such as recirculation patterns. This issue is addressed by a simple numerical framework and it has been found out that an explicit prescription of turbulence is not necessary in presence of heterogeneities such as edges and gaps where the interplay between advection, pressure gradients and drag forces are sufficient to capture the first order dynamics. This result can be very important for eddy-covariance flux calibration strategies in non-ideal environments and the developed numerical model can be
Kegel, Karen; DeBlaere, Cirleen
2014-07-01
Despite apparent relevance to Asian international students, universal-diverse orientation (UDO) has not been psychometrically validated with this population. The current study investigated the most researched UDO measure, the Miville-Guzman Universality-Diversity Scale, Short Form (M-GUDS-S; Fuertes, Miville, Mohr, Sedlacek, & Gretchen, 2000), with 333 Asian international college students. The M-GUDS-S evidenced good reliability and convergent validity, and analyses confirmed a three-factor structure, supporting expanded use of the scale.
International Nuclear Information System (INIS)
Laurence, D.
1997-01-01
This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-ε two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the 'standard' (R ij -ε) Reynolds tensions transport model and introduces more recent models called 'feasible'. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author)
Moore, Eric J.; Smith, Frances G.; Hollingshead, Aleksandra; Wojcik, Brian
2018-01-01
There is increasing pressure on universities in the United States to meet the needs of diverse learners. This fact increases the urgency for implementation and scaling up of Universal Design for Learning (UDL) in higher education. This qualitative study draws two major insights from interviews with six faculty members from universities and…
Energy Technology Data Exchange (ETDEWEB)
Hassan, Yassin A., E-mail: y-hassan@tamu.edu
2016-04-01
Highlights: • Near wall full-field velocity components under subcooled boiling were measured. • Simultaneous shadowgraphy, infrared thermometry wall temperature and particle-tracking velocimetry techniques were combined. • Near wall velocity modifications under subcooling boiling were observed. - Abstract: Multi-phase flows are one of the challenges on which the CFD simulation community has been working extensively with a relatively low success. The phenomena associated behind the momentum and heat transfer mechanisms associated to multi-phase flows are highly complex requiring resolving simultaneously for multiple scales on time and space. Part of the reasons behind the low predictive capability of CFD when studying multi-phase flows, is the scarcity of CFD-grade experimental data for validation. The complexity of the phenomena and its sensitivity to small sources of perturbations makes its measurements a difficult task. Non-intrusive and innovative measuring techniques are required to accurately measure multi-phase flow parameters while at the same time satisfying the high resolution required to validate CFD simulations. In this context, this work explores the feasible implementation of innovative measuring techniques that can provide whole-field and multi-scale measurements of two-phase flow turbulence, heat transfer, and boiling parameters. To this end, three visualization techniques are simultaneously implemented to study subcooled boiling flow through a vertical rectangular channel with a single heated wall. These techniques are listed next and are used as follow: (1) High-speed infrared thermometry (IR-T) is used to study the impact of the boiling level on the heat transfer coefficients at the heated wall, (2) Particle Tracking Velocimetry (PTV) is used to analyze the influence that boiling parameters have on the liquid phase turbulence statistics, (3) High-speed shadowgraphy with LED illumination is used to obtain the gas phase dynamics. To account
PERCEPTIONS OF ENTREPRENEURSHIP IN A UNIVERSITY AGRIBUSINESS PROGRAM: DEVELOPING A SCALE
Directory of Open Access Journals (Sweden)
Joey E. Mehlhorn
2017-07-01
Full Text Available This paper develops a scale to measure student perceptions of entrepreneurship in an agribusiness undergraduate program. The study builds on Morris, Webb, Fu and Singhal (2013 and Kriewall and Mekemson (2010 conceptualization of entrepreneurial competencies to develop a brief nine-item scale for agribusiness students. It contributes to the integration of entrepreneurship into the agribusiness curriculum by first explaining the challenges that may be best addressed through building competencies in innovation and entrepreneurship in undergraduate agribusiness education. In this scale development study, undergraduate agribusiness students from a U.S. Land Grant University considered oral communication, motivation and the ability to recognize opportunities to be the most significant capabilities for entrepreneurship.
Implementation of the Alarm Distress Baby Scale as a universal screening instrument in primary care:
DEFF Research Database (Denmark)
Smith-Nielsen, Johanne; Lønfeldt, Nicole Nadine; Guedeney, Antoine
2018-01-01
the health visitors started the training on how to use the Alarm Distress Baby Scale to one year after they began using the instrument in practice. To monitor screening prevalence rates and adherence to guidelines, we used three data extractions (6, 9, and 12 months post-implementation) from the electronic...... to screening guidelines, resulting in low screening prevalence rates. OBJECTIVES: To examine feasibility and acceptability of implementing universal screening for infant socioemotional problems with the Alarm Distress Baby Scale in primary care. The following questions were addressed: Is it possible to obtain...... a positive contribution to their work. The majority (81%) also reported that it posed a challenge in their daily work at least to some degree. The health visitors' attitudes (positive and negative) toward the Alarm Distress Baby Scale, measured 7 months post-implementation, significantly predicted screening...
Implementation of the Alarm Distress Baby Scale as a universal screening instrument in primary care:
DEFF Research Database (Denmark)
Smith-Nielsen, Johanne; Lønfeldt, Nicole; Guedeney, Antoine
2018-01-01
the health visitors started the training on how to use the Alarm Distress Baby Scale to one year after they began using the instrument in practice. To monitor screening prevalence rates and adherence to guidelines, we used three data extractions (6, 9, and 12 months post-implementation) from the electronic...... to screening guidelines, resulting in low screening prevalence rates. Objectives: To examine feasibility and acceptability of implementing universal screening for infant socioemotional problems with the Alarm Distress Baby Scale in primary care. The following questions were addressed: Is it possible to obtain...... a positive contribution to their work. The majority (81%) also reported that it posed a challenge in their daily work at least to some degree. The health visitors’ attitudes (positive and negative) toward the Alarm Distress Baby Scale, measured 7 months post-implementation, significantly predicted screening...
Velocity Statistics Distinguish Quantum Turbulence from Classical Turbulence
International Nuclear Information System (INIS)
Paoletti, M. S.; Fisher, Michael E.; Sreenivasan, K. R.; Lathrop, D. P.
2008-01-01
By analyzing trajectories of solid hydrogen tracers, we find that the distributions of velocity in decaying quantum turbulence in superfluid 4 He are strongly non-Gaussian with 1/v 3 power-law tails. These features differ from the near-Gaussian statistics of homogenous and isotropic turbulence of classical fluids. We examine the dynamics of many events of reconnection between quantized vortices and show by simple scaling arguments that they produce the observed power-law tails
PROTOSTELLAR OUTFLOW EVOLUTION IN TURBULENT ENVIRONMENTS
International Nuclear Information System (INIS)
Cunningham, Andrew J.; Frank, Adam; Carroll, Jonathan; Blackman, Eric G.; Quillen, Alice C.
2009-01-01
The link between turbulence in star-forming environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows, we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star-forming environments. In the last section, we contrast our work and its conclusions with previous studies which claim that jets cannot be the source of turbulence.
Helbig, M.; Wischnewski, K.; Kljun, N.; Chasmer, L.; Quinton, W. L.; Detto, M.; Sonnentag, O.
2015-12-01
Boreal forests in the sporadic permafrost zone have been shown to decline at the expense of wetlands following permafrost disappearance. These land cover changes cause shifts in ecosystem properties and affect biosphere-atmosphere interactions. The goal of our study is to examine the effects of permafrost disappearance on landscape-scale sensible (H) and latent heat fluxes (LE) and related potential feedbacks on regional air temperatures (Ta) We use a combination of nested eddy covariance flux towers, flux footprint and planetary boundary layer (PBL) dynamic modelling, and MOderate-resolution Imaging Spectroradiometer (MODIS) remote sensing products to resolve spatio-temporal dynamics in H and LE at the landscape scale at Scotty Creek, NWT (61º18' N; 121º18' W) and in radiometric land surface temperatures (LST) at the regional scale across the southern Taiga Plains in the sporadic permafrost zone of northwestern Canada. The heterogeneous landscape comprises boreal forests with permafrost and permafrost-free wetlands. Our results show that H above the heterogeneous landscape was about twice as high as above a nearby treeless, permafrost-free bog. In contrast, landscape-scale LE was only about 50 % of LE over the bog. These differences were primarily driven by higher heat transfer efficiency of the aerodynamically rougher forest and lower albedo of the forest compared to the bog (about 10 % lower during summer and about 40 % lower during late winter). Aerodynamic LST increased with the fraction of forest in the flux footprints. This effect was strongest (r2 = 0.55, slope = 0.06 K per % forest) at the end of winter when contrasts in albedo are largest. Bulk surface conductance increased with the fraction of wetlands in the footprints. On a regional scale, radiometric MODIS LST increased with tree cover during the snow cover period (0.06 K per % tree cover), but decreased during the summer (-0.04 K per % tree cover). Modelling results showed that a shift from the
Investigation of the Validity of the Universal Scaling Law on Linear Chains of Silver Nanoparticles
Directory of Open Access Journals (Sweden)
Mohammed Alsawafta
2015-01-01
Full Text Available Due to the wide range of variation in the plasmonic characteristics of the metallic nanoparticles arranged in linear arrays, the optical spectra of these arrays provide a powerful platform for spectroscopic studies and biosensing applications. Due to the coupling effect between the interacting nanoparticles, the excited resonance mode is shifted with the interparticle separation. The change in the resonance energy of the coupled mode is expressed by the fractional plasmon shift which would normally follow a universal scaling behavior. Such a universal law has been successfully applied on a system of dimers under parallel polarization. It has been found that the plasmon shift decays exponentially over interparticle spacing. The decay length is independent of both the nanoparticle and dielectric properties of the surrounding medium. In this paper, the discrete dipole approximation (DDA is used to examine the validity of extending the universal scaling law to linear chains of several interacting nanoparticles embedded in various host media for both parallel and perpendicular polarizations. Our calculations reveal that the decay length of both the coupled longitudinal mode (LM and transverse modes (TM is strongly dependent on the refractive index of the surrounding medium nm. The decay constant of the LM is linearly proportional to nm while the corresponding constant of the TM decays exponentially with nm. Upon changing the nanoparticle size, the change in the peak position of the LM decreases exponentially with the interparticle separation and hence, it obeys the universal law. The sensitivity of coupled LM to the nanoparticle size is more pronounced at both smaller nanoparticle sizes and separations. The sensitivity of the coupled TM to the nanoparticle size on the other hand changes linearly with the separation and therefore, the universal law does not apply in the case of the excited TM.
Revisiting the universal scaling hypothesis: do all plants respond similarly to aridification?
Caddy-Retalic, S.; McInerney, F. A.; Lowe, A. J.; Prentice, I. C.; Wardle, G. M.
2016-12-01
Our limited understanding of how plants respond to aridification is a major barrier to predicting the future composition and distribution of global flora. Measurement of stable carbon isotope ratios in leaves is an established methodology for detecting water stress. Measuring carbon isotope ratios on aridity gradients has the potential to be used to determine the relative sensitivity of many co-occurring species. By comparing the slopes of the relationship between isotope ratios and mean annual precipitation (MAP) between species and to a common slope for all plants in a region, we can test for consistency in aridity sensitivity between different species, growth forms, local environment and continents. We present data from 1329 individual plants of 204 C3 species collected on two bioclimatic gradients: one in China (145-710mm MAP) and one in South Australia (160-980mm MAP). In examining differences between plants of different types and origins, we test the universal scaling hypothesis postulated by Prentice et al. (2010), which suggests that C3 plants have similar patterns of stomatal adjustment, irrespective of phylogeny and traits, including life form. If universal scaling were supported, plant attributes could be disregarded for the purposes of modeling community and regional ecophysiology. We find that less than a third of tested species conform to the universal scaling model, and postulate a new model of four response modes: regional scaling, biotic homeostasis, insensitive response and contrary response. We discuss potential mechanisms for each response mode and their ecological ramifications. Finally, we consider the broader utility for these data, including environmental monitoring and combining isotope data with species distributions to improve predictive vegetation mapping under future climate change scenarios.
Wang, X.; Tu, C. Y.; He, J.; Wang, L.
2017-12-01
The spectrum break at the ion scale of the solar wind magnetic fluctuations are considered to give important clue on the turbulence dissipation mechanism. Among several possible mechanisms, the most notable ones are the two mechanisms that related respectively with proton thermal gyro-radius and proton inertial length. However, no definite conclusion has been given for which one is more reasonable because the two parameters have similar values in the normal plasma beta range. Here we do a statistical study for the first time to see if the two mechanism predictions have different dependence on the solar wind velocity and on the plasma beta in the normal plasma beta range in the solar wind at 1 AU. From magnetic measurements by Wind, Ulysses and Messenger, we select 60 data sets with duration longer than 8 hours. We found that the ratio between the proton inertial scale and the spectrum break scale do not change considerably with both varying the solar wind speed from 300km/s to 800km/s and varying the plasma beta from 0.2 to 1.4. The average value of the ratio times 2pi is 0.46 ± 0.08. However, the ratio between the proton gyro-radius and the break scale changes clearly. This new result shows that the proton inertial scale could be a single factor that determines the break length scale and hence gives a strong evidence to support the dissipation mechanism related to it in the normal plasma beta range. The value of the constant ratio may relate with the dissipation mechanism, but it needs further theoretical study to give detailed explanation.
The Universal Patient Centredness Questionnaire: scaling approaches to reduce positive skew
Directory of Open Access Journals (Sweden)
Bjertnaes O
2016-11-01
Full Text Available Oyvind Bjertnaes, Hilde Hestad Iversen, Andrew M Garratt Unit for Patient-Reported Quality, Norwegian Institute of Public Health, Oslo, Norway Purpose: Surveys of patients’ experiences typically show results that are indicative of positive experiences. Unbalanced response scales have reduced positive skew for responses to items within the Universal Patient Centeredness Questionnaire (UPC-Q. The objective of this study was to compare the unbalanced response scale with another unbalanced approach to scaling to assess whether the positive skew might be further reduced. Patients and methods: The UPC-Q was included in a patient experience survey conducted at the ward level at six hospitals in Norway in 2015. The postal survey included two reminders to nonrespondents. For patients in the first month of inclusion, UPC-Q items had standard scaling: poor, fairly good, good, very good, and excellent. For patients in the second month, the scaling was more positive: poor, good, very good, exceptionally good, and excellent. The effect of scaling on UPC-Q scores was tested with independent samples t-tests and multilevel linear regression analysis, the latter controlling for the hierarchical structure of data and known predictors of patient-reported experiences. Results: The response rate was 54.6% (n=4,970. Significantly lower scores were found for all items of the more positively worded scale: UPC-Q total score difference was 7.9 (P<0.001, on a scale from 0 to 100 where 100 is the best possible score. Differences between the four items of the UPC-Q ranged from 7.1 (P<0.001 to 10.4 (P<0.001. Multivariate multilevel regression analysis confirmed the difference between the response groups, after controlling for other background variables; UPC-Q total score difference estimate was 8.3 (P<0.001. Conclusion: The more positively worded scaling significantly lowered the mean scores, potentially increasing the sensitivity of the UPC-Q to identify differences over
Aerotaxis in Bacterial Turbulence
Fernandez, Vicente; Bisson, Antoine; Bitton, Cindy; Waisbord, Nicolas; Smriga, Steven; Rusconi, Roberto; Stocker, Roman
2012-11-01
Concentrated suspensions of motile bacteria exhibit correlated dynamics on spatial scales much larger than an individual bacterium. The resulting flows, visually similar to turbulence, can increase mixing and decrease viscosity. However, it remains unclear to what degree the collective dynamics depend on the motile behavior of bacteria at the individual level. Using a new microfluidic device to create controlled horizontal oxygen gradients, we studied the two dimensional behavior of dense suspensions of Bacillus subtilis. This system makes it possible to assess the interplay between the coherent large-scale motions of the suspension, oxygen transport, and the directional response of cells to oxygen gradients (aerotaxis). At the same time, this device has enabled us to examine the onset of bacterial turbulence and its influence on the propagation of the diffusing oxygen front, as the bacteria begin in a dormant state and transition to swimming when exposed to oxygen.
DEFF Research Database (Denmark)
Nielsen, Mogens Peter; Shui, Wan; Johansson, Jens
2011-01-01
term with stresses depending linearly on the strain rates. This term takes into account the transfer of linear momentum from one part of the fluid to another. Besides there is another term, which takes into account the transfer of angular momentum. Thus the model implies a new definition of turbulence...
Schnettler, Berta; Miranda, Horacio; Miranda-Zapata, Edgardo; Salinas-Oñate, Natalia; Grunert, Klaus G; Lobos, Germán; Sepúlveda, José; Orellana, Ligia; Hueche, Clementina; Bonilla, Héctor
2017-06-01
This study examined longitudinal measurement invariance in the Satisfaction with Food-related Life (SWFL) scale using follow-up data from university students. We examined this measure of the SWFL in different groups of students, separated by various characteristics. Through non-probabilistic longitudinal sampling, 114 university students (65.8% female, mean age: 22.5) completed the SWFL questionnaire three times, over intervals of approximately one year. Confirmatory factor analysis was used to examine longitudinal measurement invariance. Two types of analysis were conducted: first, a longitudinal invariance by time, and second, a multigroup longitudinal invariance by sex, age, socio-economic status and place of residence during the study period. Results showed that the 3-item version of the SWFL exhibited strong longitudinal invariance (equal factor loadings and equal indicator intercepts). Longitudinal multigroup invariance analysis also showed that the 3-item version of the SWFL displays strong invariance by socio-economic status and place of residence during the study period over time. Nevertheless, it was only possible to demonstrate equivalence of the longitudinal factor structure among students of both sexes, and among those older and younger than 22 years. Generally, these findings suggest that the SWFL scale has satisfactory psychometric properties for longitudinal measurement invariance in university students with similar characteristics as the students that participated in this research. It is also possible to suggest that satisfaction with food-related life is associated with sex and age. Copyright © 2017 Elsevier Ltd. All rights reserved.
Universal scaling and nonlinearity of aggregate price impact in financial markets
Patzelt, Felix; Bouchaud, Jean-Philippe
2018-01-01
How and why stock prices move is a centuries-old question still not answered conclusively. More recently, attention shifted to higher frequencies, where trades are processed piecewise across different time scales. Here we reveal that price impact has a universal nonlinear shape for trades aggregated on any intraday scale. Its shape varies little across instruments, but drastically different master curves are obtained for order-volume and -sign impact. The scaling is largely determined by the relevant Hurst exponents. We further show that extreme order-flow imbalance is not associated with large returns. To the contrary, it is observed when the price is pinned to a particular level. Prices move only when there is sufficient balance in the local order flow. In fact, the probability that a trade changes the midprice falls to zero with increasing (absolute) order-sign bias along an arc-shaped curve for all intraday scales. Our findings challenge the widespread assumption of linear aggregate impact. They imply that market dynamics on all intraday time scales are shaped by correlations and bilateral adaptation in the flows of liquidity provision and taking.
Bieda, Angela; Hirschfeld, Gerrit; Schönfeld, Pia; Brailovskaia, Julia; Zhang, Xiao Chi; Margraf, Jürgen
2017-04-01
Research into positive aspects of the psyche is growing as psychologists learn more about the protective role of positive processes in the development and course of mental disorders, and about their substantial role in promoting mental health. With increasing globalization, there is strong interest in studies examining positive constructs across cultures. To obtain valid cross-cultural comparisons, measurement invariance for the scales assessing positive constructs has to be established. The current study aims to assess the cross-cultural measurement invariance of questionnaires for 6 positive constructs: Social Support (Fydrich, Sommer, Tydecks, & Brähler, 2009), Happiness (Subjective Happiness Scale; Lyubomirsky & Lepper, 1999), Life Satisfaction (Diener, Emmons, Larsen, & Griffin, 1985), Positive Mental Health Scale (Lukat, Margraf, Lutz, van der Veld, & Becker, 2016), Optimism (revised Life Orientation Test [LOT-R]; Scheier, Carver, & Bridges, 1994) and Resilience (Schumacher, Leppert, Gunzelmann, Strauss, & Brähler, 2004). Participants included German (n = 4,453), Russian (n = 3,806), and Chinese (n = 12,524) university students. Confirmatory factor analyses and measurement invariance testing demonstrated at least partial strong measurement invariance for all scales except the LOT-R and Subjective Happiness Scale. The latent mean comparisons of the constructs indicated differences between national groups. Potential methodological and cultural explanations for the intergroup differences are discussed. (PsycINFO Database Record (c) 2017 APA, all rights reserved).
Multiscale coherent structures in tokamak plasma turbulence
International Nuclear Information System (INIS)
Xu, G. S.; Wan, B. N.; Zhang, W.; Yang, Q. W.; Wang, L.; Wen, Y. Z.
2006-01-01
A 12-tip poloidal probe array is used on the HT-7 superconducting tokamak [Li, Wan, and Mao, Plasma Phys. Controlled Fusion 42, 135 (2000)] to measure plasma turbulence in the edge region. Some statistical analysis techniques are used to characterize the turbulence structures. It is found that the plasma turbulence is composed of multiscale coherent structures, i.e., turbulent eddies and there is self-similarity in a relative short scale range. The presence of the self-similarity is found due to the structural similarity of these eddies between different scales. These turbulent eddies constitute the basic convection cells, so the self-similar range is just the dominant scale range relevant to transport. The experimental results also indicate that the plasma turbulence is dominated by low-frequency and long-wavelength fluctuation components and its dispersion relation shows typical electron-drift-wave characteristics. Some large-scale coherent structures intermittently burst out and exhibit a very long poloidal extent, even longer than 6 cm. It is found that these large-scale coherent structures are mainly contributed by the low-frequency and long-wavelength fluctuating components and their presence is responsible for the observations of long-range correlations, i.e., the correlation in the scale range much longer than the turbulence decorrelation scale. These experimental observations suggest that the coexistence of multiscale coherent structures results in the self-similar turbulent state
Le Doussal, Pierre; Wiese, Kay Jörg
2003-10-01
Recently we constructed a renormalizable field theory up to two loops for the quasistatic depinning of elastic manifolds in a disordered environment. Here we explore further properties of the theory. We show how higher correlation functions of the displacement field can be computed. Drastic simplifications occur, unveiling much simpler diagrammatic rules than anticipated. This is applied to the universal scaled width distribution. The expansion in d=4-epsilon predicts that the scaled distribution coincides to the lowest orders with the one for a Gaussian theory with propagator G(q)=1/q(d+2 zeta), zeta being the roughness exponent. The deviations from this Gaussian result are small and involve higher correlation functions, which are computed here for different boundary conditions. Other universal quantities are defined and evaluated: We perform a general analysis of the stability of the fixed point. We find that the correction-to-scaling exponent is omega=-epsilon and not -epsilon/3 as used in the analysis of some simulations. A more detailed study of the upper critical dimension is given, where the roughness of interfaces grows as a power of a logarithm instead of a pure power.
Dissipative structures in magnetorotational turbulence
Ross, Johnathan; Latter, Henrik N.
2018-03-01
Via the process of accretion, magnetorotational turbulence removes energy from a disk's orbital motion and transforms it into heat. Turbulent heating is far from uniform and is usually concentrated in small regions of intense dissipation, characterised by abrupt magnetic reconnection and higher temperatures. These regions are of interest because they might generate non-thermal emission, in the form of flares and energetic particles, or thermally process solids in protoplanetary disks. Moreover, the nature of the dissipation bears on the fundamental dynamics of the magnetorotational instability (MRI) itself: local simulations indicate that the large-scale properties of the turbulence (e.g. saturation levels, the stress-pressure relationship) depend on the short dissipative scales. In this paper we undertake a numerical study of how the MRI dissipates and the small-scale dissipative structures it employs to do so. We use the Godunov code RAMSES and unstratified compressible shearing boxes. Our simulations reveal that dissipation is concentrated in ribbons of strong magnetic reconnection that are significantly elongated in azimuth, up to a scale height. Dissipative structures are hence meso-scale objects, and potentially provide a route by which large scales and small scales interact. We go on to show how these ribbons evolve over time — forming, merging, breaking apart, and disappearing. Finally, we reveal important couplings between the large-scale density waves generated by the MRI and the small-scale structures, which may illuminate the stress-pressure relationship in MRI turbulence.
Some Consequences of the Expansion of the Universe on Small Scales
Harutyunian, H. A.
2017-12-01
The possibility of detecting the accelerated expansion of the universe at all its points is examined. Observational data indicative of Hubble expansion on small scales are adduced for this purpose. The validity of current opinion on the equilibrium of systems of cosmic objects is also discussed. It is noted that this opinion is a simple consequence of the unproved Kant-Laplace hypothesis on the formation of cosmic objects and systems of them. It is proposed that a system attached to the cosmological horizon be used as a reference system. It is noted that all points on this sphere are an initial point from which expansion of the observed universe of the given observer began. The numerical value of the acceleration obtained in this way is almost the same as the anomalous acceleration found by space probes.
Energy Technology Data Exchange (ETDEWEB)
Randall, David A. [Colorado State Univ., Fort Collins, CO (United States). Dept. of Atmospheric Science
2015-11-01
We proposed to implement, test, and evaluate recently developed turbulence parameterizations, using a wide variety of methods and modeling frameworks together with observations including ARM data. We have successfully tested three different turbulence parameterizations in versions of the Community Atmosphere Model: CLUBB, SHOC, and IPHOC. All three produce significant improvements in the simulated climate. CLUBB will be used in CAM6, and also in ACME. SHOC is being tested in the NCEP forecast model. In addition, we have achieved a better understanding of the strengths and limitations of the PDF-based parameterizations of turbulence and convection.
Impact of terrain heterogeneity on near-surface turbulence structure
Fesquet, Clément; Drobinski, Philippe; Barthlott, Christian; Dubos, Thomas
2009-10-01
This study investigates the impact of terrain heterogeneity on local turbulence measurements using 18 months of turbulence data taken on a 30 m tower at the SIRTA mixed land-use observatory under varying stability conditions and fetch configurations. These measurements show that turbulence variables such as the turbulent kinetic energy or momentum fluxes are strongly dependent on the upstream complexity of the terrain (presence of trees or buildings, open field). However, using a detection technique based on wavelet transforms which permits the isolation of the large-scale coherent structures from small-scale background fluctuations, the study shows that, for all stability conditions, whatever the upstream complexity of the terrain, the coherent structures display universal properties which are independent of the terrain nature: the frequency of occurrence, time duration of the coherent structures, the time separation between coherent structures and the relative contribution of the coherent structures to the total fluxes (momentum and heat) appear to be independent of the upstream roughness. This is an important result since coherent structures are known to transport a large portion of the total energy. This study extends to all stability conditions a numerical study by Fesquet et al. [Fesquet, C., Dupont, S., Drobinski, P., Barthlott, C., Dubos, T., 2008. Impact of terrain heterogeneities on coherent structures properties: experimental and numerical approaches. In: 18th Symposium on Boundary Layers and Turbulence. No. 11B.1. Stockholm, Sweden., Fesquet, C., Dupont, S., Drobinski, P., Dubos, T., Barthlott, C., in press. Impact of terrain heterogeneity on coherent structure properties: numerical approach. Bound.-Layer Meteorol.] conducted in neutral conditions which shows that a reason for such behavior is that the production of local active turbulence in an internal boundary layer associated with coherent structure originating from the outer layer and impinging
DEFF Research Database (Denmark)
Nielsen, T Rune; Andersen, Birgitte Bo; Gottrup, Hanne
2013-01-01
Background/Aims: The Rowland Universal Dementia Assessment Scale (RUDAS) is a brief cognitive screening test that was developed to detect dementia in multicultural populations. The RUDAS has not previously been validated in multicultural populations outside of Australia. The aim of this study...... was to evaluate the diagnostic accuracy of the RUDAS in a multicultural sample of patients referred to Danish memory clinics. Methods: Data were collected from 137 consecutive patients (34 with an immigrant background) in three Danish memory clinics. All patients were given the RUDAS as a supplement...
Magnetosheath electrostatic turbulence
International Nuclear Information System (INIS)
Rodriguez, P.
1979-01-01
By using measurements with the University of Iowa plasma wave experiment on the Imp 6 satellite a study has been conducted of the spectrum of electrostatic plasma waves in the terrestrial magnetosheath. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz to 70 kHz) rms field intensities typically 0.01--1.0 mV m -1 . Peak intensities of about 1.0 mV m -1 near the electron plasma frequency (30--60 kHz) have been detected occasionally. Two or three components can usually be identified in the spectrum of magnetosheath electrostatic turbulence: a high-frequency (> or =30kHz) component peaking at the electron plasma frequency f/sub p/e, a low-frequency component with a broad intensity maximum below the nominal ion plasma frequency f/sub p/i (approx. f/sub p/e/43), and a less well defined intermediate component in the range f/sub p/i < f< f/sub p/e. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low-frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath. Electrostatic waves below 1 kHz are polarized along the magnetic field direction, a result consistent with the polarization of electrostatic waves at the shock. The high- and intermediate-frequency components are features of the magnetosheath spectrum which are not characteristic of the shock spectrum but are often detected in the upstream solar wind. The intensity distribution of electrostatic turbulence at the magnetosheath plasma frequency has no apparent correlation with the shock, indicating that electron plasma oscillations are a general feature of the magnetosheath. The plasma wave noise shows a tendency to decrease toward the dawn and dusk regions, consistent with a general decrease in turbulence away from the subsolar magnetosheath
Scaling Universality between Band Gap and Exciton Binding Energy of Two-Dimensional Semiconductors
Jiang, Zeyu; Liu, Zhirong; Li, Yuanchang; Duan, Wenhui
2017-06-01
Using first-principles G W Bethe-Salpeter equation calculations and the k .p theory, we unambiguously show that for two-dimensional (2D) semiconductors, there exists a robust linear scaling law between the quasiparticle band gap (Eg) and the exciton binding energy (Eb), namely, Eb≈Eg/4 , regardless of their lattice configuration, bonding characteristic, as well as the topological property. Such a parameter-free universality is never observed in their three-dimensional counterparts. By deriving a simple expression for the 2D polarizability merely with respect to Eg, and adopting the screened hydrogen model for Eb, the linear scaling law can be deduced analytically. This work provides an opportunity to better understand the fantastic consequence of the 2D nature for materials, and thus offers valuable guidance for their property modulation and performance control.
Magnetic turbulence and anomalous transport
International Nuclear Information System (INIS)
Garbet, X.; Mourgues, F.; Samain, A.
1990-01-01
The self consistency conditions for magnetic turbulence are reviewed. The main features of magnetic topology involving stochastic flux lines are summarized. Two driving sources are considered: thermal effects which require large scale residual islands and electron diamagnetism which involves fluctuation scales smaller than the ion Larmor radius and a β p threshold of order one. Stability criteria and transport coefficients are given
Turbulent jet in confined counterflow
Indian Academy of Sciences (India)
Abstract. The mean flowfield of a turbulent jet issuing into a confined, uniform counterflow was investigated computationally. Based on dimensional analysis, the jet penetration length was shown to scale with jet-to-counterflow momentum flux ratio. This scaling and the computational results reproduce the well-known correct ...
Turbulent jet in confined counterflow
Indian Academy of Sciences (India)
The mean flowfield of a turbulent jet issuing into a confined, uniform counterflow was investigated computationally. Based on dimensional analysis, the jet penetration length was shown to scale with jet-to-counterflow momentum flux ratio. This scaling and the computational results reproduce the well-known correct limit of ...
Turbulent dispersion from line sources in grid turbulence
Viswanathan, Sharadha; Pope, Stephen B.
2008-10-01
Probability density function (PDF) calculations are reported for the dispersion from line sources in decaying grid turbulence. The calculations are performed using a modified form of the interaction by exchange with the conditional mean (IECM) mixing model. These flows pose a significant challenge to statistical models because the scalar length scale (of the initial plume) is much smaller than the turbulence integral scale. Consequently, this necessitates incorporating the effects of molecular diffusion in order to model laboratory experiments. Previously, Sawford [Flow Turb. Combust. 72, 133 (2004)] performed PDF calculations in conjunction with the IECM mixing model, modeling the effects of molecular diffusion as a random walk in physical space and using a mixing time scale empirically fit to the experimental data of Warhaft [J. Fluid Mech. 144, 363 (1984)]. The resulting transport equation for the scalar variance contains a spurious production term. In the present work, the effects of molecular diffusion are instead modeled by adding a conditional mean scalar drift term, thus avoiding the spurious production of scalar variance. A laminar wake model is used to obtain an analytic expression for the mixing time scale at small times, and this is used as part of a general specification of the mixing time scale. Based on this modeling, PDF calculations are performed, and comparison is made primarily with the experimental data of Warhaft on single and multiple line sources and with the previous calculations of Sawford. A heated mandoline is also considered with comparison to the experimental data of Warhaft and Lumley [J. Fluid Mech. 88, 659 (1978)]. This establishes the validity of the proposed model and the significant effect of molecular diffusion on the decay of scalar fluctuations. The following are the significant predictions of the model. For the line source, the effect of the source size is limited to early times and can be completely accounted for by simple
Aperture averaging in strong oceanic turbulence
Gökçe, Muhsin Caner; Baykal, Yahya
2018-04-01
Receiver aperture averaging technique is employed in underwater wireless optical communication (UWOC) systems to mitigate the effects of oceanic turbulence, thus to improve the system performance. The irradiance flux variance is a measure of the intensity fluctuations on a lens of the receiver aperture. Using the modified Rytov theory which uses the small-scale and large-scale spatial filters, and our previously presented expression that shows the atmospheric structure constant in terms of oceanic turbulence parameters, we evaluate the irradiance flux variance and the aperture averaging factor of a spherical wave in strong oceanic turbulence. Irradiance flux variance variations are examined versus the oceanic turbulence parameters and the receiver aperture diameter are examined in strong oceanic turbulence. Also, the effect of the receiver aperture diameter on the aperture averaging factor is presented in strong oceanic turbulence.
Effects of baryons on the statistical properties of large scale structure of the Universe
International Nuclear Information System (INIS)
Guillet, T.
2010-01-01
Observations of weak gravitational lensing will provide strong constraints on the cosmic expansion history and the growth rate of large scale structure, yielding clues to the properties and nature of dark energy. Their interpretation is impacted by baryonic physics, which are expected to modify the total matter distribution at small scales. My work has focused on determining and modeling the impact of baryons on the statistics of the large scale matter distribution in the Universe. Using numerical simulations, I have extracted the effect of baryons on the power spectrum, variance and skewness of the total density field as predicted by these simulations. I have shown that a model based on the halo model construction, featuring a concentrated central component to account for cool condensed baryons, is able to reproduce accurately, and down to very small scales, the measured amplifications of both the variance and skewness of the density field. Because of well-known issues with baryons in current cosmological simulations, I have extended the central component model to rely on as many observation-based ingredients as possible. As an application, I have studied the effect of baryons on the predictions of the upcoming Euclid weak lensing survey. During the course of this work, I have also worked at developing and extending the RAMSES code, in particular by developing a parallel self-gravity solver, which offers significant performance gains, in particular for the simulation of some astrophysical setups such as isolated galaxy or cluster simulations. (author) [fr
Synchronization of two coupled turbulent fires
Takagi, Kazushi; Gotoda, Hiroshi; Miyano, Takaya; Murayama, Shogo; Tokuda, Isao T.
2018-04-01
We numerically study the scale-free nature of a buoyancy-induced turbulent fire and synchronization of two coupled turbulent fires. A scale-free structure is detected in weighted networks between vortices, while its lifetime obeys a clear power law, indicating intermittent appearances, disappearances, and reappearances of the scale-free property. A significant decrease in the distance between the two fire sources gives rise to a synchronized state in the near field dominated by the unstable motion of large-scale of transverse vortex rings. The synchronized state vanishes in the far field forming well-developed turbulent plumes, regardless of the distance between the two fire sources.
Lecture archiving on a larger scale at the University of Michigan and CERN
International Nuclear Information System (INIS)
Herr, Jeremy; Lougheed, Robert; Neal, Homer A
2010-01-01
The ATLAS Collaboratory Project at the University of Michigan has been a leader in the area of collaborative tools since 1999. Its activities include the development of standards, software and hardware tools for lecture archiving, and making recommendations for videoconferencing and remote teaching facilities. Starting in 2006 our group became involved in classroom recordings, and in early 2008 we spawned CARMA, a University-wide recording service. This service uses a new portable recording system that we developed. Capture, archiving and dissemination of rich multimedia content from lectures, tutorials and classes are increasingly widespread activities among universities and research institutes. A growing array of related commercial and open source technologies is becoming available, with several new products introduced in the last couple years. As the result of a new close partnership between U-M and CERN IT, a market survey of these products was conducted and a summary of the results are presented here. It is informing an ambitious effort in 2009 to equip many CERN rooms with automated lecture archiving systems, on a much larger scale than before. This new technology is being integrated with CERN's existing webcast, CDS, and Indico applications.
Lecture archiving on a larger scale at the University of Michigan and CERN
Energy Technology Data Exchange (ETDEWEB)
Herr, Jeremy; Lougheed, Robert; Neal, Homer A, E-mail: herrj@umich.ed [University of Michigan, 450 Church St., Ann Arbor, MI 48109 (United States)
2010-04-01
The ATLAS Collaboratory Project at the University of Michigan has been a leader in the area of collaborative tools since 1999. Its activities include the development of standards, software and hardware tools for lecture archiving, and making recommendations for videoconferencing and remote teaching facilities. Starting in 2006 our group became involved in classroom recordings, and in early 2008 we spawned CARMA, a University-wide recording service. This service uses a new portable recording system that we developed. Capture, archiving and dissemination of rich multimedia content from lectures, tutorials and classes are increasingly widespread activities among universities and research institutes. A growing array of related commercial and open source technologies is becoming available, with several new products introduced in the last couple years. As the result of a new close partnership between U-M and CERN IT, a market survey of these products was conducted and a summary of the results are presented here. It is informing an ambitious effort in 2009 to equip many CERN rooms with automated lecture archiving systems, on a much larger scale than before. This new technology is being integrated with CERN's existing webcast, CDS, and Indico applications.
Dissipation range turbulent cascades in plasmas
International Nuclear Information System (INIS)
Terry, P. W.; Almagri, A. F.; Forest, C. B.; Nornberg, M. D.; Rahbarnia, K.; Sarff, J. S.; Fiksel, G.; Hatch, D. R.; Jenko, F.; Prager, S. C.; Ren, Y.
2012-01-01
Dissipation range cascades in plasma turbulence are described and spectra are formulated from the scaled attenuation in wavenumber space of the spectral energy transfer rate. This yields spectra characterized by the product of a power law and exponential fall-off, applicable to all scales. Spectral indices of the power law and exponential fall-off depend on the scaling of the dissipation, the strength of the nonlinearity, and nonlocal effects when dissipation rates of multiple fluctuation fields are different. The theory is used to derive spectra for MHD turbulence with magnetic Prandtl number greater than unity, extending previous work. The theory is also applied to generic plasma turbulence by considering the spectrum from damping with arbitrary wavenumber scaling. The latter is relevant to ion temperature gradient turbulence modeled by gyrokinetics. The spectrum in this case has an exponential component that becomes weaker at small scale, giving a power law asymptotically. Results from the theory are compared to three very different types of turbulence. These include the magnetic plasma turbulence of the Madison Symmetric Torus, the MHD turbulence of liquid metal in the Madison Dynamo Experiment, and gyrokinetic simulation of ion temperature gradient turbulence.
Turbulent/non-turbulent interfaces in jets and wakes
Zecchetto, Marco; Silva, Carlos; Lasef Team
2017-11-01
The characteristics of the turbulent/non-turbulent interface (TNTI) at the edges of jets and wakes at high Reynolds numbers are compared by using new direct numerical simulations (DNS) of temporally evolving planar jets (PJET) and wakes (PWAKE). The new simulations attain a Reynolds number based on the Taylor micro-scale of Reλ 350 which are the highest Reynolds number used so far in numerical investigations of TNTI. The similarities and differences between the TNTIs from PJET and PWAKE are assessed in relation to i) their structure and scaling, ii) the vorticity dynamics and, iii) and entrainment velocity. Portuguese Foundation for Science and Technology (FST); PRACE.
Campo-Arias, Adalberto; Herazo, Edwin; Oviedo, Heidi Celina
The process of evaluating measurement scales is an ongoing procedure that requires revisions and adaptations according to the characteristics of the participants. The Homophobia Scale of seven items (EHF-7) has showed acceptable performance in medical students attending to two universities in Colombia. However, performance of some items was poor and could be removed, with an improvement in the psychometric findings of items retained. To review the psychometric functioning and refine the content of EHF-7 among medical students from two Colombian universities. A group of 667 students from the first to tenth semester participated in the research. Theirs ages were between 18 and 34 (mean, 20.9±2.7) years-old, and 60.6% were females. Cronbach alpha (α) and omega of McDonald (Ω) were calculated as indicators of reliability and to refine the scale, an exploratory (EFA) and confirmatory factor analysis (CFA) was performed. EHF-7 showed α=.793 and Ω=.796 and a main factor that explained 45.2% of the total variance. EFA and CFA suggested the suppression of three items. The four-item version (EHF-4) reached an α=.770 and Ω=.775, with a single factor that accounted for 59.7% of the total variance. CFA showed better indexes (χ 2 =3.622; df=1; P=.057; Root-mean-square error of approximation (RMSEA)=.063, 90% CI, .000-.130; Comparative Fit Indices (CFI)=.998; Tucker-Lewis Index (TLI)=.991). EHF-4 shows high internal consistency and a single dimension that explains more than 50% of the total variance. Further studies are needed to confirm these observations, that can be taken as preliminary. Copyright © 2016 Asociación Colombiana de Psiquiatría. Publicado por Elsevier España. All rights reserved.
Ugulu, Ilker
2013-01-01
This study focuses on the confirmatory factor analysis for testing validity and reliability of Traditional Knowledge Attitude Scale (TKAS) to measure university students' attitudes. The items in the TKAS were developed initially from the responses to two open-ended items by 30 university students and literature review on traditional knowledge.…
Fokker-Planck description of the inverse cascade in two-dimensional turbulence
Kamps, Oliver; Vosskuhle, Michel
2012-11-01
In many approaches the mathematical description of fully developed turbulence relies on the statistical properties of the longitudinal velocity increments ξ (r) = U (x + r) - U (x) . In the increment statistics is described as a Markov process in scale, leading to a Fokker-Planck description of the probability density functions (PDFs) for the velocity increments. The universality of this approach was tested for different kinds of three-dimensional flows like inhomogeneous turbulence, fractal grid generated turbulence and for the transition of a flow from a vortex street to fully developed turbulence in a cylinder wake the flow. In this talk we want to extend the test for the universality of the Markov description by analyzing data from numerical simulations of the inverse energy cascade in two-dimensional turbulence. The central question is whether the velocity field of the inverse cascade can be modeled as Markov process in scale similar to the three-dimensional case. By estimating the coefficients of the Fokker-Planck equation we are able to discuss the role of intermittency and differences to three-dimensional flows.
Nonomura, Yoshihiko; Tomita, Yusuke
2015-03-01
Recently we have found that the nonequilibrium relaxation from the perfectly-ordered state of the 2D and 3D Ising models in cluster algorithms shows nontrivial stretched-exponential decay at the transition temperature. Similar nontrivial nonequilibrium critical relaxation is also observed in the 2D XY, 3D XY and 3D Heisenberg models; simple exponential decay in these cases. In order to confirm these behaviors and evaluate the scaling form precisely and robustly, we have proposed a universal scaling procedure to connect nonequilibrium and equilibrium behaviors continuously. For example, when the critical relaxation of the average magnetization of a system with linear size L is observed in local-update algorithms, this quantity decays in a power law in the early-stage relaxation with ~t - β / (zν) and converges to the critical magnetization mc (L) ~L - β / ν in equilibrium. Then, when L β / ν is plotted versus tL-z , data for various system sizes are scaled on a single curve in the whole parameter region. This procedure also holds for the cases with cluster algorithms.
Turbulent characteristics of a solar quiescent prominence observed by the SOT on board Hinode
Leonardis, E.; Chapman, S. C.; Foullon, C.
2011-12-01
Most of the solar quiescent prominences (QPs) observed by the Solar Optical Telescope (SOT) on board Hinode exhibit highly variable dynamics suggestive of turbulence [1]. Unlike in-situ spacecraft measurements, these QPs offer an opportunity to test statistical measures of turbulence in both space and time. We focus on one of these QPs by analysing images in the Calcium II H-line that cover a sufficient range of scales spatially ( ˜ 0.1-100 arc seconds) and temporally ( ˜ 16.8 s- 4.5 hrs) to allow the application of statistical methods generally used to quantify finite range fluid turbulence. We present such techniques applied for the first time to the spatial intensity field of the QP's flow. Fully evolved inertial range turbulence in an infinite medium has the statistical property of multifractal scale invariance, which implies power law power spectra and scaling of the higher order moments (structure functions) in the non-Gaussian statistics of the fluctuating quantities that characterize the system. Fluctuations δ I(r,L)=I(r+L)-I(r) on lengthscale L along a given direction in observed spatial field I, have indeed moments that scale as ˜ Lζ (p). A generalized scale invariance, or Eextended Self-Similarity (ESS), is instead recovered for turbulent systems of finite size - i.e. in the quiet solar wind [2]- for which the dependence on a single robust scaling function G(L) has been observed such that ˜ G(L)ζ (p). We find that the QP intensity measurements are well described by non-Gaussian statistics and show power law power spectra. We also find ESS and the generalized scaling for the intesity fluctuations δ I(r,L). Finally, we use ESS to obtain ratios of the scaling exponents ζ (p), which are consistent with a multifractal field. The statistical properties found for the intensity fluctuations in the QP are therefore in agreement with those ones expected for finite sized turbulent systems supporting the idea of the turbulent nature of the prominence flow
Numerical Simulation of a Convective Turbulence Encounter
Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.
2002-01-01
A numerical simulation of a convective turbulence event is investigated and compared with observational data. The numerical results show severe turbulence of similar scale and intensity to that encountered during the test flight. This turbulence is associated with buoyant plumes that penetrate the upper-level thunderstorm outflow. The simulated radar reflectivity compares well with that obtained from the aircraft's onboard radar. Resolved scales of motion as small as 50 m are needed in order to accurately diagnose aircraft normal load accelerations. Given this requirement, realistic turbulence fields may be created by merging subgrid-scales of turbulence to a convective-cloud simulation. A hazard algorithm for use with model data sets is demonstrated. The algorithm diagnoses the RMS normal loads from second moments of the vertical velocity field and is independent of aircraft motion.
Graphical Turbulence Guidance - Composite
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Inner-outer predictive wall model for wall-bounded turbulence in hypersonic flow
Martin, M. Pino; Helm, Clara M.
2017-11-01
The inner-outer predictive wall model of Mathis et al. is modified for hypersonic turbulent boundary layers. The model is based on a modulation of the energized motions in the inner layer by large scale momentum fluctuations in the logarithmic layer. Using direct numerical simulation (DNS) data of turbulent boundary layers with free stream Mach number 3 to 10, it is shown that the variation of the fluid properties in the compressible flows leads to large Reynolds number (Re) effects in the outer layer and facilitate the modulation observed in high Re incompressible flows. The modulation effect by the large scale increases with increasing free-stream Mach number. The model is extended to include spanwise and wall-normal velocity fluctuations and is generalized through Morkovin scaling. Temperature fluctuations are modeled using an appropriate Reynolds Analogy. Density fluctuations are calculated using an equation of state and a scaling with Mach number. DNS data are used to obtain the universal signal and parameters. The model is tested by using the universal signal to reproduce the flow conditions of Mach 3 and Mach 7 turbulent boundary layer DNS data and comparing turbulence statistics between the modeled flow and the DNS data. This work is supported by the Air Force Office of Scientific Research under Grant FA9550-17-1-0104.
Gloria, Alberta M.; Castellanos, Jeanett; Herrera, Nancy
2016-01-01
Following the calls for increased research on the educational experiences of Chicana/o community college students, and the development of culturally applicable measures for communities of color, this study examined the utility and the applicability of the Cultural Congruity Scale (CCS) and University Environment Scale (UES) for use with Chicana/o…
Leonardis, E.; Chapman, S. C.; Foullon, C.
2010-12-01
The Hinode SOT instrument provides observations (images) of the solar corona at simultaneous high spatial and temporal resolution which span several decades in both spatial and temporal scales. We focus on specific Calcium II H-line observations of solar quiescent prominences with small-scale flows which exhibit a high degree of variability. We analyze these images from the perspective of a finite sized turbulent flow. A key property of turbulence is that it can be characterized and quantified in a robust and reproducible way in terms of the ensemble averaged statistical properties of fluctuations. Importantly, fluctuations associated with a turbulent field show similarity or scaling in their statistics and we test for this with both power spectra and Generalized Structure Functions. Realizations of turbulence that are finite sized are known to exhibit a generalized or extended self-similarity (ESS). ESS was recently demonstrated in Ulysses in-situ observations of magnetic field fluctuations of the solar wind emanating from the polar regions for which a single robust scaling function was found, suggesting a single universal character of the largest eddies in the finite range magnetohydrodynamic turbulent flow [1-2]. We find evidence of ESS in the SOT images and examine the details of this generalized scaling. [1] S. C. Chapman, R. M. Nicol, Generalized Similarity in Finite Range Solar Wind Magnetohydrodynamic Turbulence, Phys. Rev. Lett., 103, 241101 (2009) [2] S. C. Chapman, R. M. Nicol, E. Leonardis, K. Kiyani, V. Carbone, Observation of universality in the generalized similarity of evolving solar wind turbulence as seen by ULYSSES, Ap. J. Letters, 695, L185, (2009)
Turbulence spreading, anomalous transport, and pinch effect
DEFF Research Database (Denmark)
Naulin, V.; Nielsen, A.H.; Juul Rasmussen, J.
2005-01-01
, and front propagation are observed. The model accounts for the interaction between the microscale of the turbulence and the meso-, respectively, system scale on which profile modifications occur. Comparison with direct numerical simulations of two-dimensional interchange turbulence shows qualitatively good...
Evolution of passive scalar statistics in a spatially developing turbulence
Paul, I.; Papadakis, G.; Vassilicos, J. C.
2018-02-01
We investigate the evolution of passive scalar statistics in a spatially developing turbulence using direct numerical simulation. Turbulence is generated by a square grid element, which is heated continuously, and the passive scalar is temperature. The square element is the fundamental building block for both regular and fractal grids. We trace the dominant mechanisms responsible for the dynamical evolution of scalar-variance and its dissipation along the bar and grid-element centerlines. The scalar-variance is generated predominantly by the action of the mean scalar gradient behind the bar and is transported laterally by turbulent fluctuations to the grid-element centerline. The scalar-variance dissipation (proportional to the scalar-gradient variance) is produced primarily by the compression of the fluctuating scalar-gradient vector by the turbulent strain rate, while the contribution of mean velocity and scalar fields is negligible. Close to the grid element the scalar spectrum exhibits a well-defined -5 /3 power-law, even though the basic premises of the Kolmogorov-Obukhov-Corrsin theory are not satisfied (the fluctuating scalar field is highly intermittent, inhomogeneous, and anisotropic, and the local Corrsin-microscale-Péclet number is small). At this location, the PDF of scalar gradient production is only slightly skewed towards positive, and the fluctuating scalar-gradient vector aligns only with the compressive strain-rate eigenvector. The scalar-gradient vector is stretched or compressed stronger than the vorticity vector by turbulent strain rate throughout the grid-element centerline. However, the alignment of the former changes much earlier in space than that of the latter, resulting in scalar-variance dissipation to decay earlier along the grid-element centerline compared to the turbulent kinetic energy dissipation. The universal alignment behavior of the scalar-gradient vector is found far downstream, although the local Reynolds and Péclet numbers
Nicol, R.; Leonardis, E.; Chapman, S. C.; Foullon, C.
2011-12-01
Fluctuations associated with fully developed magnetohydrodynamic (MHD) turbulent flows in an infinite medium are characterized by non-Gaussian statistics which are scale invariant; this implies power law power spectra and multiscaling for the Generalized Structure Functions (GSFs). Given an observable f(r,t) and assuming statistical stationary, the p'th order moment of the GSF of the fluctuating differences scales as Lzeta(p), where L is the observation scale and ζ (p) are the scaling exponents. For turbulence in a system that is of finite size, or that is not fully developed, the statistical property of scale invariance is replaced by a generalized scale invariance, or extended self- similarity (ESS), for which the various moments of the GSF have a power-law dependence on an initially unknown functions, G, such that Nicol, Generalized Similarity in Finite Range Solar Wind Magnetohydrodynamic Turbulence, Phys. Rev. Lett. 103, 241101 (2009); S. C. Chapman, R. M. Nicol, E. Leonardis, K. Kiyani, V. Carbone, Observation of universality in the generalized similarity of evolving solar wind turbulence as seen by ULYSSES, Ap. J. Letters, 695, L185, (2009)
An university-scale pulsed-power system using a bipolar Marx generator
Chang, Po-Yu; Yang, Sheng-Hua; Huang, Mei-Feng; Isaps, Natl Cheng Kung Univ Team
2017-10-01
A bipolar Marx generator is being built for x-ray sources or laboratory astrophysics and space research for university-scale laboratory. The system consists of ten stages. In each stage, two 1 μF capacitors connected in series are charged to +/- 30 kV storing 9 kJ of total energy. It delivers a current of 200 kA to the load with a 200 ns rise time during the discharge. It will be used for following three purposes: (1) gas-puff z pinches generating soft x-ray for bio-medical research in the future; (2) generating plasma jets to study interactions between plasma flows and unmagnetized/magnetized obstacles analogous to the interactions between solar winds and planetary magnetic fields or unmagnetized planets; and (3) studying the pinch in a dense plasma focus device. The results of current measurements and circuit characteristics are shown.
Probing the two-scale-factor universality hypothesis by exact rotation symmetry-breaking mechanism
Energy Technology Data Exchange (ETDEWEB)
Neto, J.F.S.; Lima, K.A.L.; Carvalho, P.R.S. [Universidade Federal do Piaui, Departamento de Fisica, Teresina, PI (Brazil); Sena-Junior, M.I. [Universidade de Pernambuco, Escola Politecnica de Pernambuco, Recife, PE (Brazil); Universidade Federal de Alagoas, Instituto de Fisica, Maceio, AL (Brazil)
2017-12-15
We probe the two-scale-factor universality hypothesis by evaluating, firstly explicitly and analytically at the one-loop order, the loop quantum corrections to the amplitude ratios for O(N)λφ{sup 4} scalar field theories with rotation symmetry breaking in three distinct and independent methods in which the rotation symmetry-breaking mechanism is treated exactly. We show that the rotation symmetry-breaking amplitude ratios turn out to be identical in the three methods and equal to their respective rotation symmetry-breaking ones, although the amplitudes themselves, in general, depend on the method employed and on the rotation symmetry-breaking parameter. At the end, we show that all these results can be generalized, through an inductive process based on a general theorem emerging from the exact calculation, to any loop level and physically interpreted based on symmetry ideas. (orig.)
Stochastic inflation lattice simulations: Ultra-large scale structure of the universe
International Nuclear Information System (INIS)
Salopek, D.S.
1990-11-01
Non-Gaussian fluctuations for structure formation may arise in inflation from the nonlinear interaction of long wavelength gravitational and scalar fields. Long wavelength fields have spatial gradients α -1 triangledown small compared to the Hubble radius, and they are described in terms of classical random fields that are fed by short wavelength quantum noise. Lattice Langevin calculations are given for a ''toy model'' with a scalar field interacting with an exponential potential where one can obtain exact analytic solutions of the Fokker-Planck equation. For single scalar field models that are consistent with current microwave background fluctuations, the fluctuations are Gaussian. However, for scales much larger than our observable Universe, one expects large metric fluctuations that are non-Guassian. This example illuminates non-Gaussian models involving multiple scalar fields which are consistent with current microwave background limits. 21 refs., 3 figs
Exploration of potential of Smart Grids at the scale of the University campus in Provence
International Nuclear Information System (INIS)
2014-09-01
This study notably aimed at determining how strategies provided by smart grid technologies operate in an existing area where electric equipment and infrastructures are already largely developed, which perspectives of evolution these technologies offer for the power demand curve of the electric power distribution network, and how to assess benefits associated with the implementation of these technologies at the scale of an existing area. After a presentation of various concepts, the report presents a simplified model of the electric power consumption structure for the studied area (a university campus). The next part proposes an assessment of potentials related to smart grid technologies by using six scenarios and by modelling their effect. The different possible strategies are then analysed
Dynamics and universal scaling law in geometrically-controlled sessile drop evaporation
Sáenz, P. J.; Wray, A. W.; Che, Z.; Matar, O. K.; Valluri, P.; Kim, J.; Sefiane, K.
2017-01-01
The evaporation of a liquid drop on a solid substrate is a remarkably common phenomenon. Yet, the complexity of the underlying mechanisms has constrained previous studies to spherically symmetric configurations. Here we investigate well-defined, non-spherical evaporating drops of pure liquids and binary mixtures. We deduce a universal scaling law for the evaporation rate valid for any shape and demonstrate that more curved regions lead to preferential localized depositions in particle-laden drops. Furthermore, geometry induces well-defined flow structures within the drop that change according to the driving mechanism. In the case of binary mixtures, geometry dictates the spatial segregation of the more volatile component as it is depleted. Our results suggest that the drop geometry can be exploited to prescribe the particle deposition and evaporative dynamics of pure drops and the mixing characteristics of multicomponent drops, which may be of interest to a wide range of industrial and scientific applications. PMID:28294114
Extensive strain along gradient trajectories in the turbulent kinetic energy field
Gampert, Markus; Goebbert, Jens Henrik; Schaefer, Philip; Gauding, Michael; Peters, Norbert; Aldudak, Fettah; Oberlack, Martin
2011-04-01
Based on direct numerical simulations of forced turbulence, shear turbulence, decaying turbulence, a turbulent channel flow as well as a Kolmogorov flow with Taylor-based Reynolds numbers Reλ between 69 and 295, the normalized probability density function of the length distribution \\skew3\\tilde{P}(\\tilde{l}) of dissipation elements, the conditional mean scalar difference langΔkmidlrang at the extreme points as well as the scaling of the two-point velocity difference along gradient trajectories langΔunrang are studied. Using the field of the instantaneous turbulent kinetic energy k as a scalar, we find good agreement between the model equation for \\skew3\\tilde{P}(\\tilde{l}) as proposed by Wang and Peters (2008 J. Fluid Mech. 608 113-38) and the results obtained in the different direct numerical simulation cases. This confirms the independence of the model solution from both the Reynolds number and the type of turbulent flow, so that it can be considered universally valid. In addition, we show a 2/3 scaling for the mean conditional scalar difference. In the second part of the paper, we examine the scaling of the conditional two-point velocity difference along gradient trajectories. In particular, we compare the linear s/τ scaling, where τ denotes an integral time scale and s the separation arclength along a gradient trajectory in the inertial range as derived by Wang (2009 Phys. Rev. E 79 046325) with the s·a∞ scaling, where a∞ denotes the asymptotic value of the conditional mean strain rate of large dissipation elements.
Mixing and diffusion in intermittent overturning turbulence
Redondo, Jose M.; Mahjoub, Otman B.; Gonzalez-Nieto, Pilar L.; Lawry, Andrew
2014-05-01
The improvements in experimental methods and high resolution image analysis are nowadays able to detect subtle changes in the structure of the turbulence over a wide range of temporal and spatial scales [1], we compare the scaling shown by different mixing fronts driven by buoyancy that form a Rayleigh-Taylor mixing front. We use PIV and density front tracking in several experimental configurations akin to geophysical overturning [2-7]. We parametrize the role of unstable stratification by means of the Atwood number and compare both the scaling and the multifractal and the maximum local fractal structure functions of the different markers used to visualize the front. Both reactive and passive scalar tracers are used to investigate the mixing structure and the intermittency of the flow. Different initial conditions are compared and the mixing efficiency of the overal turbulent process evaluated [6-7]. An interesting approach, relating the Multi-Fractal dimension spectra, the intermittency and the spectral exponent is to find relationships that may be used to parameterise the sub-grid turbulence in terms of generalized diffusivities [4 ] that take into account the topology and the self-similarity of the Mixing RT and RM flows. As an example, a relationship between the diffusivity, the exponent β, the intermittency μ, and D(i), may be found for the volume fraction or the concentration, at the same time other locally measured parameters such as the enstrophy or the gradient alignment as well as their multi-fractal structures may turn out to be physically relevant indicators of the local turbulence and the mixing. Several methods of deriving local eddy diffusivity and local entrainment should give more realistic estimates of the spatial/temporal non-homogeneities (and intermittencies in the Kolmogorov 62 sense obtained as spatial correlations of the turbulent dissipation, or from structure functions) and these values may be used to parameterise turbulence at a variety
Universal scaling relations for the energies of many-electron Hooke atoms
Odriazola, A.; Solanpää, J.; Kylänpää, I.; González, A.; Räsänen, E.
2017-04-01
A three-dimensional harmonic oscillator consisting of N ≥2 Coulomb-interacting charged particles, often called a (many-electron) Hooke atom, is a popular model in computational physics for, e.g., semiconductor quantum dots and ultracold ions. Starting from Thomas-Fermi theory, we show that the ground-state energy of such a system satisfies a nontrivial relation: Eg s=ω N4 /3fg s(β N1 /2) , where ω is the oscillator strength, β is the ratio between Coulomb and oscillator characteristic energies, and fg s is a universal function. We perform extensive numerical calculations to verify the applicability of the relation. In addition, we show that the chemical potentials and addition energies also satisfy approximate scaling relations. In all cases, analytic expressions for the universal functions are provided. The results have predictive power in estimating the key ground-state properties of the system in the large-N limit, and can be used in the development of approximative methods in electronic structure theory.
Turbulence modification and multiphase turbulence transport modeling
International Nuclear Information System (INIS)
Besnard, D.C.; Kataoka, I.; Serizawa, A.
1991-01-01
It is shown here that in the derivation of turbulence transport models for multiphase flows, terms naturally appear that can be interpreted as related to turbulence modification of one field by the other. We obtain two such terms, one suggesting turbulence enhancement due to instabilities in two-phase flow, the second one showing turbulence damping due to the presence of the other field, both in gas-particle and gas-liquid cases
Galaxies distribution in the universe: large-scale statistics and structures
International Nuclear Information System (INIS)
Maurogordato, Sophie
1988-01-01
This research thesis addresses the distribution of galaxies in the Universe, and more particularly large scale statistics and structures. Based on an assessment of the main used statistical techniques, the author outlines the need to develop additional tools to correlation functions in order to characterise the distribution. She introduces a new indicator: the probability of a volume randomly tested in the distribution to be void. This allows a characterisation of void properties at the work scales (until 10h -1 Mpc) in the Harvard Smithsonian Center for Astrophysics Redshift Survey, or CfA catalog. A systematic analysis of statistical properties of different sub-samples has then been performed with respect to the size and location, luminosity class, and morphological type. This analysis is then extended to different scenarios of structure formation. A program of radial speed measurements based on observations allows the determination of possible relationships between apparent structures. The author also presents results of the search for south extensions of Perseus supernova [fr
New class of turbulence in active fluids
Bratanov, Vasil; Frey, Erwin
2015-01-01
Turbulence is a fundamental and ubiquitous phenomenon in nature, occurring from astrophysical to biophysical scales. At the same time, it is widely recognized as one of the key unsolved problems in modern physics, representing a paradigmatic example of nonlinear dynamics far from thermodynamic equilibrium. Whereas in the past, most theoretical work in this area has been devoted to Navier–Stokes flows, there is now a growing awareness of the need to extend the research focus to systems with more general patterns of energy injection and dissipation. These include various types of complex fluids and plasmas, as well as active systems consisting of self-propelled particles, like dense bacterial suspensions. Recently, a continuum model has been proposed for such “living fluids” that is based on the Navier–Stokes equations, but extends them to include some of the most general terms admitted by the symmetry of the problem [Wensink HH, et al. (2012) Proc Natl Acad Sci USA 109:14308–14313]. This introduces a cubic nonlinearity, related to the Toner–Tu theory of flocking, which can interact with the quadratic Navier–Stokes nonlinearity. We show that as a result of the subtle interaction between these two terms, the energy spectra at large spatial scales exhibit power laws that are not universal, but depend on both finite-size effects and physical parameters. Our combined numerical and analytical analysis reveals the origin of this effect and even provides a way to understand it quantitatively. Turbulence in active fluids, characterized by this kind of nonlinear self-organization, defines a new class of turbulent flows. PMID:26598708
Investigation of universal plasma instabilities. Final report
International Nuclear Information System (INIS)
Lashinsky, H.
1977-01-01
This project was undertaken in order to carry out a comprehensive experimental investigation of universal plasma instabilities under a variety of conditions and a wide range of experimental parameters to scale the results appropriately to make comparisons with plasmas of thermonuclear interest. Of particular importance are the roles played by collisions and resonance particles (Landau damping and excitation) and the various stages in the development of the instabilities i.e., the linear onset of the instability, the quasilinear stage, and the transition to turbulence. General nonlinear effects such as mode locking and mode competition, and the relation of these phenomena to plasma turbulence, are also of great interest and were studied experimentally. The ultimate aim was to measure certain plasma transport coefficients in the plasma under stable and turbulent conditions with the particular view of evaluating the effect of the universal plasma instabilities of plasma confinement in a magnetic field
Electromotive force in strongly compressible magnetohydrodynamic turbulence
Yokoi, N.
2017-12-01
Variable density fluid turbulence is ubiquitous in geo-fluids, not to mention in astrophysics. Depending on the source of density variation, variable density fluid turbulence may be divided into two categories: the weak compressible (entropy mode) turbulence for slow flow and the strong compressible (acoustic mode) turbulence for fast flow. In the strong compressible turbulence, the pressure fluctuation induces a strong density fluctuation ρ ', which is represented by the density variance ( denotes the ensemble average). The turbulent effect on the large-scale magnetic-field B induction is represented by the turbulent electromotive force (EMF) (u': velocity fluctuation, b': magnetic-field fluctuation). In the usual treatment in the dynamo theory, the expression for the EMF has been obtained in the framework of incompressible or weak compressible turbulence, where only the variation of the mean density , if any, is taken into account. We see from the equation of the density fluctuation ρ', the density variance is generated by the large mean density variation ∂ coupled with the turbulent mass flux . This means that in the region where the mean density steeply changes, the density variance effect becomes relevant for the magnetic field evolution. This situation is typically the case for phenomena associated with shocks and compositional discontinuities. With the aid of the analytical theory of inhomogeneous compressible magnetohydrodynamic (MHD) turbulence, the expression for the turbulent electromotive force is investigated. It is shown that, among others, an obliqueness (misalignment) between the mean density gradient ∂ and the mean magnetic field B may contribute to the EMF as ≈χ B×∂ with the turbulent transport coefficient χ proportional to the density variance (χ ). This density variance effect is expected to strongly affect the EMF near the interface, and changes the transport properties of turbulence. In the case of an interface under the MHD slow
A near-wall turbulence model and its application to fully developed turbulent channel and pipe flows
Kim, S.-W.
1988-01-01
A near wall turbulence model and its incorporation into a multiple-time-scale turbulence model are presented. In the method, the conservation of mass, momentum, and the turbulent kinetic energy equations are integrated up to the wall; and the energy transfer rate and the dissipation rate inside the near wall layer are obtained from algebraic equations. The algebraic equations for the energy transfer rate and the dissipation rate inside the near wall layer were obtained from a k-equation turbulence model and the near wall analysis. A fully developed turbulent channel flow and fully developed turbulent pipe flows were solved using a finite element method to test the predictive capability of the turbulence model. The computational results compared favorably with experimental data. It is also shown that the present turbulence model could resolve the over shoot phenomena of the turbulent kinetic energy and the dissipation rate in the region very close to the wall.
International Nuclear Information System (INIS)
Ishii, M.; Revankar, S.T.; Leonardi, T.; Dowlati, R.; Bertodano, M.L.; Babelli, I.; Wang, W.; Pokharna, H.; Ransom, V.H.; Viskanta, R.
1998-01-01
The three-level scaling approach was developed for the scientific design of an integral test facility and then it was applied to the design of the scaled facility known as the Purdue University Multi-Dimensional Integral Test Assembly (PUMA). The NRC technical program group for severe accident scaling developed the conceptual framework for this scaling methodology. The present scaling method consists of the integral system scaling, whose components comprise the first two levels, and the phenomenological scaling constitutes the third level of scaling. More specifically, the scaling is considered as follows: (1) the integral response function scaling, (2) control volume and boundary flow scaling, and (3) local phenomena scaling. The first two levels are termed the top-down approach while the third level is the bottom-up approach. This scheme provides a scaling methodology that is practical and yields technically justifiable results. It ensures that both the steady state and dynamic conditions are simulated within each component, and also scales the inter-component mass and energy flows as well as the mass and energy inventories within each component. (orig.)
Modelling and simulation of turbulence and heat transfer in wall-bounded flows
Popovac, M.
2006-01-01
At present it is widely accepted that there is no universal turbulence model, i.e. no turbulence model can give acceptably good predictions for all turbulent flows that are found in nature or engineering. Every turbulence model is based on certain assumptions, and hence it is aimed at certain type
Toward large eddy simulation of turbulent flow over an airfoil
Choi, Haecheon
1993-01-01
The flow field over an airfoil contains several distinct flow characteristics, e.g. laminar, transitional, turbulent boundary layer flow, flow separation, unstable free shear layers, and a wake. This diversity of flow regimes taxes the presently available Reynolds averaged turbulence models. Such models are generally tuned to predict a particular flow regime, and adjustments are necessary for the prediction of a different flow regime. Similar difficulties are likely to emerge when the large eddy simulation technique is applied with the widely used Smagorinsky model. This model has not been successful in correctly representing different turbulent flow fields with a single universal constant and has an incorrect near-wall behavior. Germano et al. (1991) and Ghosal, Lund & Moin have developed a new subgrid-scale model, the dynamic model, which is very promising in alleviating many of the persistent inadequacies of the Smagorinsky model: the model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model has been remarkably successful in prediction of several turbulent and transitional flows. We plan to simulate turbulent flow over a '2D' airfoil using the large eddy simulation technique. Our primary objective is to assess the performance of the newly developed dynamic subgrid-scale model for computation of complex flows about aircraft components and to compare the results with those obtained using the Reynolds average approach and experiments. The present computation represents the first application of large eddy simulation to a flow of aeronautical interest and a key demonstration of the capabilities of the large eddy simulation technique.
Czech Academy of Sciences Publication Activity Database
Franci, L.; Landi, S.; Matteini, L.; Verdini, A.; Hellinger, Petr
2016-01-01
Roč. 833, č. 1 (2016), 91/1-91/7 ISSN 0004-637X R&D Projects: GA ČR GA15-10057S Institutional support: RVO:67985815 Keywords : plasmas * solar wind * turbulence Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.533, year: 2016
Magnetohydrodynamics turbulence: An astronomical perspective
Indian Academy of Sciences (India)
Since the discovery of pulsars in 1967, many years of work on interstellar scintillation suggested that small-scale interstellar turbulence must have a hydromagnetic origin; but the IK spectrum was too ﬂat and the ideas on anisotropic spectra too qualitative to explain the observations. In response, new theories of balanced ...
Characterization of local turbulence in magnetic confinement devices
International Nuclear Information System (INIS)
Rajkovic, Milan; Skoric, Milos; Solna, Knut; Antar, Ghassan
2007-07-01
A multifractal analysis based on evaluation and interpretation of Large Deviation spectra is applied to plasma edge turbulence data from different devices (MAST and Tore Supra). It is demonstrated that in spite of some universal features there are unique characteristics for each device as well as for different confinement regimes. In the second part of the exposition the issue of estimating the variable power law behavior of spectral densities is addressed. The analysis of this issue is performed using fractional Brownian motion (fBm) as the underlying stochastic model whose parameters are estimated locally in time by wavelet scale spectra. In such a manner information about the inertial range as well as variability of the fBm parameters is obtained giving more information important for understanding edge turbulence and intermittency. (author)
Probing the Large-Scale Structure of the Universe Through Luminous Red Galaxies
Prakash, Abhishek
The study of Baryon Acoustic Oscillations (BAO) has become a key tool for exploring the nature of Dark Energy. BAO refers to periodic fluctuations in the density of baryonic matter in the universe that were caused by acoustic oscillations created by radiation pressure differences. Luminous Red Galaxies (LRGs) have played a vital role in the detection of BAO. These are the most massive galaxies in the z˜1 universe, showing a characteristic 4000A break in their spectral energy distributions (SEDs). This thesis establishes a new algorithm for selecting high redshift LRGs for spectroscopic surveys like SDSS-IV/eBOSS and DESI, which aim to precisely measure the BAO signal at high redshifts. We further adapt these methods for assembling the next generation eBOSS LRG sample and explain these methods in detail. These methods have been used by other international teams to assemble high redshift LRG sample for various investigations. Large-scale clustering measurements are prone to systematic uncertainties associated with imaging surveys. This thesis establishes modern statistical techniques to overcome these challenges. A multivariate regression analysis, primarily applied on the eBOSS LRG and quasar samples, is presented for a better understanding of the systematic uncertainties and their effects on the clustering measurements. Another key aspect of this work is the development of a machine learning algorithm for estimating photometric redshifts. Applying this machinery yields accurate estimates of the distances of galaxies using their photometric properties alone, i.e., their colors and magnitudes. This work culminates with new clustering measurements that use these photometric redshifts in an attempt to detect BAO in the eBOSS LRG sample. We also presented initial results from an ongoing effort to measure the clustering of LRGs around quasars using the first two years of spectroscopic data from eBOSS.
New perspectives on superparameterization for geophysical turbulence
International Nuclear Information System (INIS)
Majda, Andrew J.; Grooms, Ian
2014-01-01
This is a research expository paper regarding superparameterization, a class of multi-scale numerical methods designed to cope with the intermittent multi-scale effects of inhomogeneous geophysical turbulence where energy often inverse-cascades from the unresolved scales to the large scales through the effects of waves, jets, vortices, and latent heat release from moist processes. Original as well as sparse space–time superparameterization algorithms are discussed for the important case of moist atmospheric convection including the role of multi-scale asymptotic methods in providing self-consistent constraints on superparameterization algorithms and related deterministic and stochastic multi-cloud parameterizations. Test models for the statistical numerical analysis of superparameterization algorithms are discussed both to elucidate the performance of the basic algorithms and to test their potential role in efficient multi-scale data assimilation. The very recent development of grid-free seamless stochastic superparameterization methods for geophysical turbulence appropriate for “eddy-permitting” mesoscale ocean turbulence is presented here including a general formulation and illustrative applications to two-layer quasigeostrophic turbulence, and another difficult test case involving one-dimensional models of dispersive wave turbulence. This last test case has randomly generated solitons as coherent structures which collapse and radiate wave energy back to the larger scales, resulting in strong direct and inverse turbulent energy cascades
Wavenumber spectrum of whistler turbulence: Particle-in-cell simulation
International Nuclear Information System (INIS)
Saito, S.; Gary, S. Peter; Narita, Y.
2010-01-01
The forward cascade of decaying whistler turbulence is studied in low beta plasma to understand essential properties of the energy spectrum at electron scales, by using a two-dimensional electromagnetic particle-in-cell (PIC) simulation. This simulation demonstrates turbulence in which the energy cascade rate is greater than the dissipation rate at the electron inertial length. The PIC simulation shows that the magnetic energy spectrum of forward-cascaded whistler turbulence at electron inertial scales is anisotropic and develops a very steep power-law spectrum which is consistent with recent solar wind observations. A comparison of the simulated spectrum with that predicted by a phenomenological turbulence scaling model suggests that the energy cascade at the electron inertial scale depends on both magnetic fluctuations and electron velocity fluctuations, as well as on the whistler dispersion relation. Thus, not only kinetic Alfven turbulence but also whistler turbulence may explain recent solar wind observations of very steep magnetic spectra at short scales.
Doudna, Kelly
2015-01-01
The Universe explores the science of what we see in the night sky. Kids will learn about the life cycle of a star, find out how our universe was created, explore nebulae, galaxies, black holes, giant stars and more. Engaging photos, exciting graphics, and a fun quiz at the end of each book will keep them learning. Aligned to Common Core Standards and correlated to state standards. Super Sandcastle is an imprint of Abdo Publishing, a division of ABDO.
Turbulence transport with nonlocal interactions
Energy Technology Data Exchange (ETDEWEB)
Linn, R.R.; Clark, T.T.; Harlow, F.H.; Turner, L.
1998-03-01
This preliminary report describes a variety of issues in turbulence transport analysis with particular emphasis on closure procedures that are nonlocal in wave-number and/or physical space. Anomalous behavior of the transport equations for large scale parts of the turbulence spectrum are resolved by including the physical space nonlocal interactions. Direct and reverse cascade processes in wave-number space are given a much richer potential for realistic description by the nonlocal formulations. The discussion also describes issues, many still not resolved, regarding new classes of self-similar form functions.
Scalplo - A universal program for plotting flux output from scale modules
International Nuclear Information System (INIS)
Hersman, A.; Leege, P.F.A. de; Hoogenboom, J.E.
1994-01-01
SCALPLO is a universal Fortran-77 program to plot the output obtained from core calculation programs or shielding programs. It can plot flux distributions for one or more energy groups and power distributions, but also flux spectra as a function of energy at a specific position. The flux or power distributions can be plotted for one dimensional geometry or as a cut through two or three dimensional geometries. It can also plot distributions for a two dimensional geometry or a plane cut through a three dimensional geometry. It has options to zoom in on the geometry. The flux or power distribution data as well as the geometry description will be read from separate files in the so called CCCC format. To facilitate the output from relevant data from the flux calculation program, a set of subroutines are added to the package which can be linked with the flux calculation program in order to produce the required output by including only a few simple calls to these subroutines. The graphical part of the SCALPLO program is based on DISSPLA, the graphical package used in several modules of the SCALE system. (authors). 5 refs., 4 figs
Revisiting the Scale Length-μ0 Plane and the Freeman Law in the Local Universe
Fathi, Kambiz
2010-10-01
We have used Virtual Observatory technology to analyze the disk scale length rd and central surface brightness μ0 for a sample of 29,955 bright disk galaxies from the Sloan Digital Sky Survey. We use the results in the r band and revisit the relation between these parameters and the galaxy morphology, and find the average value langμ0rang = 20.2 ± 0.7 mag arcsec-2. We confirm that late-type spirals populate the lower left corner of the rd -μ0 plane and that the early and intermediate spirals are mixed in this diagram, with disky ellipticals at the top left corner. We further investigate the Freeman Law and confirm that it indeed defines an upper limit for μ0 in bright disk galaxies with r mag = 6) have fainter central surface brightness. Our results are based on a volume-corrected sample of galaxies in the local universe (z numerical simulations of galaxy formation and evolution.
Assessment of nurse's knowledge about Glasgow coma scale at a university hospital.
Santos, Wesley Cajaíba; Vancini-Campanharo, Cássia Regina; Lopes, Maria Carolina Barbosa Teixeira; Okuno, Meiry Fernanda Pinto; Batista, Ruth Ester Assayag
2016-01-01
To assess knowledge of nurses of emergency services and intensive care units about Glasgow Coma Scale. This cross-sectional analytical study included 127 nurses of critical units of an university hospital. We used structured interview with 12 questions to evaluate their knowledge about the scale. Association of Knowledge with professionals' sociodemographic variables were verified by the Fisher-test, χ2 and likelihood ratio. Most of participants were women mean aged 31.1 years, they had graduated more than 5 years previously, and had 1 to 3 years of work experience. In the assessment of best score possible for Glasgow scale (question 3) nurses who had graduate more than 5 years ago presented a lower percentage success rate (p=0.0476). However, in the question 7, which evaluated what interval of the scale indicated moderate severity of brain trauma injury, those with more years of experience had higher percentage of correct answers (p=0.0251). In addition, nurses from emergency service had more correct answers than nurses from intensive care unit (p=0.0143) in the same question. Nurses graduated for more than 5 years ago had a lower percentage of correct answers in question 7 (p=0.0161). Nurses with more work experience had a better score (p=0.0119) to identify how assessment of motor response should be started. Number of year since graduation, experience, and work at critical care units interfered in nurses' knowledge about the scale, which indicates the need of training. Avaliar o conhecimento de enfermeiros de unidades críticas, serviços de emergência e unidades de terapia intensiva em relação à escala de coma de Glasgow. Estudo transversal e analítico com 127 enfermeiros de unidades críticas de um hospital universitário. Utilizou-se entrevista estruturada com 12 questões que avaliaram conhecimento sobre a escala. Associação do conhecimento com variáveis sociodemográficas dos profissionais foi verificada pelo teste de Fisher, teste χ2 e razão de
Clumps in drift wave turbulence
DEFF Research Database (Denmark)
Pecseli, H. L.; Mikkelsen, Torben
1986-01-01
In a statistical analysis pair correlation of particles is eventually destroyed by small scale fluctuations giving rise to relative particle diffusion. However, in any one given realization of the statistical ensemble particles may remain correlated in certain regions of space. A perfectly frozen......, two-dimensional random flow serves as a particularly simple illustration. For this case particles can be trapped for all times in a local vortex (macro-clump). A small test-cloud of particles (micro-clump) chosen arbitrarily in a realization will on the other hand expand on average. A formulation...... is proposed in terms of conditional eddies, in order to discriminate turbulent flows where macro-clumps may be observed. The analysis is illustrated by results from experimental investigations of strongly turbulent, resistive drift-wave fluctuations. The related problem for electrostatic turbulence...
Horiuti, Kiyosi; Sayama, Shotaro
2017-11-01
We consider turbulent flows diluted with the polymers. The polymer chains are modeled as elastic dumbbells and represented by Brownian dynamics. The motion of solvent fluid is pursued by DNS. Affinity in the motion of the bead-spring configuration with the fluid surrounding the dumbbells is commonly assumed, but it results in emergence of Elasto-inertial turbulence (EIT) regime. When the polymers are highly stretched, molecular motions may not precisely correspond to the macroscopic deformation (de Gennes 1986). We develop a new dumbbell model in which the affine constraint is removed and non-affinity is introduced by allowing slippage of the dumbbells against the solvent. This is done by adopting the lower-convective derivative in addition to the upper-convective derivative in the governing equation for the motion of the dumbbells. We conduct its assessment in the forced homogeneous isotropic turbulence. It is shown that the dumbbells obtained from the case with complete affinity are rotated and converted to the alignment of the dumbbells in the complete non-affine case, and vice versa. This alteration of configurations is repeated quasi-periodically with the intervals comparable to the relaxation time. The largest stretching of the dumbbells and elastic energy production are achieved in the complete non-affine dumbbells. Occurrence of EIT is eliminated and de Gennes hypothesis is justified.
THE SIGNATURE OF INITIAL CONDITIONS ON MAGNETOHYDRODYNAMIC TURBULENCE
Energy Technology Data Exchange (ETDEWEB)
Dallas, V.; Alexakis, A., E-mail: vdallas@lps.ens.fr, E-mail: alexakis@lps.ens.fr [Laboratoire de Physique Statistique, École Normale Supérieure, Université Pierre et Marié Curie, Université Paris Diderot, CNRS, 24 rue Lhomond, F-75005 Paris (France)
2014-06-20
We demonstrate that the initial correlation between velocity and current density fluctuations can lead to the formation of enormous current sheets in freely evolving magnetohydrodynamic (MHD) turbulence. These coherent structures are observed at the peak of the energy dissipation rate and are the carriers of long-range correlations despite all of the nonlinear interactions during the formation of turbulence. The size of these structures spans our computational domain, dominating the scaling of the energy spectrum, which follows a E∝k {sup –2} power law. As the Reynolds number increases, the curling of the current sheets due to Kelvin-Helmholtz-type instabilities and reconnection modifies the scaling of the energy spectrum from k {sup –2} toward k {sup –5/3}. This transition occurs due to the decorrelation of the velocity and the current density which is proportional to Re{sub λ}{sup −3/2}. Finite Reynolds number behavior is observed without reaching a finite asymptote for the energy dissipation rate even for a simulation of Re{sub λ} ≅ 440 with 2048{sup 3} grid points. This behavior demonstrates that even state-of-the-art numerical simulations of the highest Reynolds numbers can be influenced by the choice of initial conditions and consequently they are inadequate to deduce unequivocally the fate of universality in MHD turbulence. Implications for astrophysical observations are discussed.
Cascade of circulations in fluid turbulence.
Eyink, Gregory L
2006-12-01
Kelvin's theorem on conservation of circulations is an essential ingredient of Taylor's theory of turbulent energy dissipation by the process of vortex-line stretching. In previous work, we have proposed a nonlinear mechanism for the breakdown of Kelvin's theorem in ideal turbulence at infinite Reynolds number. We develop here a detailed physical theory of this cascade of circulations. Our analysis is based upon an effective equation for large-scale coarse-grained velocity, which contains a turbulent-induced vortex force that can violate Kelvin's theorem. We show that singularities of sufficient strength, which are observed to exist in turbulent flow, can lead to nonvanishing dissipation of circulation for an arbitrarily small coarse-graining length in the effective equations. This result is an analog for circulation of Onsager's theorem on energy dissipation for singular Euler solutions. The physical mechanism of the breakdown of Kelvin's theorem is diffusion of lines of large-scale vorticity out of the advected loop. This phenomenon can be viewed as a classical analog of the Josephson-Anderson phase-slip phenomenon in superfluids due to quantized vortex lines. We show that the circulation cascade is local in scale and use this locality to develop concrete expressions for the turbulent vortex force by a multiscale gradient expansion. We discuss implications for Taylor's theory of turbulent dissipation and we point out some related cascade phenomena, in particular for magnetic flux in magnetohydrodynamic turbulence.
Durak, Mithat; Senol-Durak, Emre; Gencoz, Tulin
2010-01-01
This study aims to extensively examine the psychometric properties of adapted version of the Satisfaction with Life Scale (SWLS) in different Turkish samples. In order to test the psychometric properties of the SWLS three separate and independent samples are utilized in this study, namely university students (n = 547), correctional officers (n =…
Arslan, Fethi
2016-01-01
The purpose of this study is to investigate the differences in anger traits of university students and teacher candidates studying in various social and cultural regions, of Batman and Denizli, Turkey. Modelling anger and anger expression style scale according to some variables such as age, gender, education level, number of siblings, parents'…
Wasser, L. A.; Gram, W.; Lunch, C. K.; Petroy, S. B.; Elmendorf, S.
2013-12-01
'Big Data' are becoming increasingly common in many fields. The National Ecological Observatory Network (NEON) will be collecting data over the 30 years, using consistent, standardized methods across the United States. Similar efforts are underway in other parts of the globe (e.g. Australia's Terrestrial Ecosystem Research Network, TERN). These freely available new data provide an opportunity for increased understanding of continental- and global scale processes such as changes in vegetation structure and condition, biodiversity and landuse. However, while 'big data' are becoming more accessible and available, integrating big data into the university courses is challenging. New and potentially unfamiliar data types and associated processing methods, required to work with a growing diversity of available data, may warrant time and resources that present a barrier to classroom integration. Analysis of these big datasets may further present a challenge given large file sizes, and uncertainty regarding best methods to properly statistically summarize and analyze results. Finally, teaching resources, in the form of demonstrative illustrations, and other supporting media that might help teach key data concepts, take time to find and more time to develop. Available resources are often spread widely across multi-online spaces. This presentation will overview the development of NEON's collaborative University-focused online education portal. Portal content will include 1) interactive, online multi-media content that explains key concepts related to NEON's data products including collection methods, key metadata to consider and consideration of potential error and uncertainty surrounding data analysis; and 2) packaged 'lab' activities that include supporting data to be used in an ecology, biology or earth science classroom. To facilitate broad use in classrooms, lab activities will take advantage of freely and commonly available processing tools, techniques and scripts. All
Necci, Marco; Piovesan, Damiano; Tosatto, Silvio C E
2016-12-01
Intrinsic disorder (ID) in proteins has been extensively described for the last decade; a large-scale classification of ID in proteins is mostly missing. Here, we provide an extensive analysis of ID in the protein universe on the UniProt database derived from sequence-based predictions in MobiDB. Almost half the sequences contain an ID region of at least five residues. About 9% of proteins have a long ID region of over 20 residues which are more abundant in Eukaryotic organisms and most frequently cover less than 20% of the sequence. A small subset of about 67,000 (out of over 80 million) proteins is fully disordered and mostly found in Viruses. Most proteins have only one ID, with short ID evenly distributed along the sequence and long ID overrepresented in the center. The charged residue composition of Das and Pappu was used to classify ID proteins by structural propensities and corresponding functional enrichment. Swollen Coils seem to be used mainly as structural components and in biosynthesis in both Prokaryotes and Eukaryotes. In Bacteria, they are confined in the nucleoid and in Viruses provide DNA binding function. Coils & Hairpins seem to be specialized in ribosome binding and methylation activities. Globules & Tadpoles bind antigens in Eukaryotes but are involved in killing other organisms and cytolysis in Bacteria. The Undefined class is used by Bacteria to bind toxic substances and mediate transport and movement between and within organisms in Viruses. Fully disordered proteins behave similarly, but are enriched for glycine residues and extracellular structures. © 2016 The Protein Society.
Swami, Viren; Hwang, Choon-Sup; Jung, Jaehee
2012-02-01
Research on the acceptance of cosmetic surgery has focused on relatively affluent Western samples, to the exclusion of non-Western samples and any potential cross-cultural differences. While rates of cosmetic surgery in South Korea have risen sharply in the past decade, mirroring rates in other East Asian nations, little is known about attitudes toward cosmetic surgery in the Korean population. To examine the factor structure and correlates of a Korean adaptation of the previously-published Acceptance of Cosmetic Surgery Scale (ACSS). South Korean university students (N = 267) completed the ACSS, as well as included Korean translations of measures for actual vs. ideal body weight discrepancy, body appreciation, sociocultural attitudes toward appearance, and demographics. The Korean ACSS reduced to a two-factor solution, mirroring results among other non-Western samples, although a one-factor solution was deemed more plausible. Compared to men, women had significantly higher total scores, suggesting that they were more accepting of cosmetic surgery. A multiple regression showed that, after controlling for the effects of participant sex, the only significant predictor of acceptance of cosmetic surgery was general body appreciation, suggesting that some may view cosmetic surgery as a means of enhancing their body image. The results reveal important global information for plastic surgeons-not only on the treatment of non-Western patients but on the South Korean market, in which the cosmetic surgery industry remains unregulated. Given the popularity and acceptance of cosmetic surgery in South Korea, there is an urgent need for regulatory intervention to ensure patient safety and satisfaction.
Flux driven turbulence in tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Ghendrih, P.; Ottaviani, M.; Sarazin, Y.; Beyer, P.; Benkadda, S.; Waltz, R.E.
1999-01-01
This work deals with tokamak plasma turbulence in the case where fluxes are fixed and profiles are allowed to fluctuate. These systems are intermittent. In particular, radially propagating fronts, are usually observed over a broad range of time and spatial scales. The existence of these fronts provide a way to understand the fast transport events sometimes observed in tokamaks. It is also shown that the confinement scaling law can still be of the gyroBohm type in spite of these large scale transport events. Some departure from the gyroBohm prediction is observed at low flux, i.e. when the gradients are close to the instability threshold. Finally, it is found that the diffusivity is not the same for a turbulence calculated at fixed flux than at fixed temperature gradient, with the same time averaged profile. (author)
Improved Nonequilibrium Algebraic Model Of Turbulence
Johnson, D. A.; Coakley, T. J.
1993-01-01
Blend of previous models predicts pressure distributions more accurately. Improved algebraic model represents some of time-averaged effects of turbulence in transonic flow of air over airfoil. Based partly on comparisons among various eddy-viscosity formulations for turbulence and partly on premise that law of wall more universally valid in immediate region of surface in presence of adverse gradient of pressure than mixing-length theory and original Johnson and King model.
Radio-isotope production scale-up at the University of Wisconsin
Energy Technology Data Exchange (ETDEWEB)
Nickles, Robert Jerome [Univ of Wisconsin
2014-06-19
small scale metallurgy with greater control. This alloy feedstock was then used to electroplate cyclotron targets with elevated melting temperatures capable of withstanding higher beam currents. 6. Finished the beam-line developments needed for the irradiation of low-melting target materials (Se and Ga) now being used for the production of Br-76, and radioactive germanium (68, 69, 71Ge). Our planned development of I-124 production has been deferred, given the wide access from commercial suppliers. The passing of these milestones has been the subject of the previous quarterly reports. These signature accomplishments were made possible by the DOE support, and have strengthened the infrastructure at the University of Wisconsin, provided the training ground for a very talented graduate research assistant (Mr. Valdovinos) and more than doubled our out-shipments of Cu-64 and Zr-89.
Turbulence in the Heliospheric Jets
Drake, J. F.; Swisdak, M.; Opher, M.; Hassam, A.; Ohia, O.
2016-12-01
The conventional picture of the heliosphere is that of a comet-shaped structure with an extended tail produced by the relative motion of the sun through the local interstellar medium (LISM). Recent MHD simulations of the global heliosphere have revealed, however, that the heliosphere drives magnetized jets to the North and South similar to those driven by the Crab Nebula and other astrophysical objects. These simulations reveal that the jets become turbulent with scale lengths as large as 100AU [1,2]. An important question is what drives this large-scale turbulence, what are the implications for mixing of interstellar and heliospheric plasma and does this turbulence drive energetic particles? An analytic model of the heliospheric jets in the simple limit in which the interstellar flow and magnetic field are neglected yields an equilibrium state that can be analyzed to explore potential instabilities [3]. Calculations suggest that because the axial magnetic field within the jets is small, the dominant instability is the sausage mode, driven by the azimuthal solar magnetic field. Other drive mechanisms, including Kelvin Helmholtz, are also being explored. 3D MHD and Hall MHD simulations are being carried out to explore the development of this turbulence, its impact on the mixing of interstellar and heliosheath plasma and the production of energetic particles. [1] Opher et al ApJ Lett. 800, L28, 2015[2] Pogorelov et al ApJ Lett. 812,L6, 2015[3] Drake et al ApJ Lett. 808, L44, 2015
Umegaki, Yusuke; Todo, Naoya
2017-03-01
We used an item response theory (IRT) model to simultaneously compare the psychometric properties of 3 commonly used self-report depression scales translated into Japanese-the Zung Self-Rating Depression Scale (SDS), the Center for Epidemiologic Studies Depression Scale (CES-D), and the Patient Health Questionnaire Depression Scale (PHQ-9)-in a Japanese university student sample. Although the 3 scales were likely to measure the same underlying construct-that is, depression-the choices of the negatively worded items in the SDS and CES-D did not function well. The CES-D provided more information than the other scales at the range of depression severity approximately from the mean through 2 standard deviations above the mean, while the PHQ-9 provided more information for the other degrees of depression. The PHQ-9 performed better as a whole, as it provided more information than the other scales on the broadest range of depression severity, and it did not contain items with inefficient choices. The CES-D may also be a good choice when sampling students with elevated levels of depressive symptoms. Finally, we linked the 3 instruments on a common scale using parameters derived from IRT analysis, and we provided a crosswalk table to enable the conversion of each scale score. (PsycINFO Database Record (c) 2017 APA, all rights reserved).
Tharayil, Davis Porinchu
2012-01-01
As the existing scales to measure loneliness are almost all Western and there is no single scale developed cross-culturally for this purpose, this study is designed to develop a reliable and valid scale to measure the experience of loneliness of individuals from individualistic or collectivistic cultures. There are three samples for this study…
Toward the Theory of Turbulence in Magnetized Plasmas
International Nuclear Information System (INIS)
Boldyrev, Stanislav
2013-01-01
The goal of the project was to develop a theory of turbulence in magnetized plasmas at large scales, that is, scales larger than the characteristic plasma microscales (ion gyroscale, ion inertial scale, etc.). Collisions of counter-propagating Alfven packets govern the turbulent cascade of energy toward small scales. It has been established that such an energy cascade is intrinsically anisotropic, in that it predominantly supplies energy to the modes with mostly field-perpendicular wave numbers. The resulting energy spectrum of MHD turbulence, and the structure of the fluctuations were studied both analytically and numerically. A new parallel numerical code was developed for simulating reduced MHD equations driven by an external force. The numerical setting was proposed, where the spectral properties of the force could be varied in order to simulate either strong or weak turbulent regimes. It has been found both analytically and numerically that weak MHD turbulence spontaneously generates a 'condensate', that is, concentration of magnetic and kinetic energy at small kllel)). A related topic that was addressed in the project is turbulent dynamo action, that is, generation of magnetic field in a turbulent flow. We were specifically concentrated on the generation of large-scale magnetic field compared to the scales of the turbulent velocity field. We investigate magnetic field amplification in a turbulent velocity field with nonzero helicity, in the framework of the kinematic Kazantsev-Kraichnan model
National Research Council Canada - National Science Library
Drikakis, D; Geurts, Bernard
2002-01-01
... discretization 3 A test-case: turbulent channel flow 4 Conclusions 75 75 82 93 98 4 Analysis and control of errors in the numerical simulation of turbulence Sandip Ghosal 1 Introduction 2 Source...
Varni, James W; Limbers, Christine A
2008-02-01
The PedsQL (Pediatric Quality of Life Inventory) is a modular instrument designed to measure health-related quality of life (HRQOL) and disease-specific symptoms in children and adolescents ages 2-18. The PedsQL Multidimensional Fatigue Scale was designed as a generic symptom-specific instrument to measure fatigue in pediatric patients ages 2-18. Since a sizeable number of pediatric patients prefer to remain with their pediatric providers after age 18, the objective of the present study was to determine the feasibility, reliability, and validity of the PedsQL Multidimensional Fatigue Scale in young adults. The 18-item PedsQL Multidimensional Fatigue Scale (General Fatigue, Sleep/Rest Fatigue, and Cognitive Fatigue domains), the PedsQL 4.0 Generic Core Scales Young Adult Version, and the SF-8 Health Survey were completed by 423 university students ages 18-25. The PedsQL Multidimensional Fatigue Scale evidenced minimal missing responses, achieved excellent reliability for the Total Scale Score (alpha = 0.90), distinguished between healthy young adults and young adults with chronic health conditions, was significantly correlated with the relevant PedsQL 4.0 Generic Core Scales and the SF-8 standardized scores, and demonstrated a factor-derived structure largely consistent with the a priori conceptual model. The results demonstrate the measurement properties of the PedsQL Multidimensional Fatigue Scale in a convenience sample of young adult university students. The findings suggest that the PedsQL Multidimensional Fatigue Scale may be utilized in the evaluation of fatigue for a broad age range.
Jaafar, Fauziah Md.; Hashim, Rosna Awang; Ariffin, Tengku Faekah Tengku
2012-01-01
Purpose: In western countries, a model to explain student engagement in college or university has long been established. However, there is a lack of research to develop and validate a model which may help to better understand student engagement in the local university context. There is currently no established instrument to measure student…
Turbulent mixing of a critical fluid: The non-perturbative renormalization
Directory of Open Access Journals (Sweden)
M. Hnatič
2018-01-01
Full Text Available Non-perturbative Renormalization Group (NPRG technique is applied to a stochastical model of a non-conserved scalar order parameter near its critical point, subject to turbulent advection. The compressible advecting flow is modeled by a random Gaussian velocity field with zero mean and correlation function 〈υjυi〉∼(Pji⊥+αPji∥/kd+ζ. Depending on the relations between the parameters ζ, α and the space dimensionality d, the model reveals several types of scaling regimes. Some of them are well known (model A of equilibrium critical dynamics and linear passive scalar field advected by a random turbulent flow, but there is a new nonequilibrium regime (universality class associated with new nontrivial fixed points of the renormalization group equations. We have obtained the phase diagram (d, ζ of possible scaling regimes in the system. The physical point d=3, ζ=4/3 corresponding to three-dimensional fully developed Kolmogorov's turbulence, where critical fluctuations are irrelevant, is stable for α≲2.26. Otherwise, in the case of “strong compressibility” α≳2.26, the critical fluctuations of the order parameter become relevant for three-dimensional turbulence. Estimations of critical exponents for each scaling regime are presented.
Energy Technology Data Exchange (ETDEWEB)
Vega, H.J. de [Sorbonne Universites, Universite Pierre et Marie Curie UPMC Paris VI, LPTHE CNRS UMR 7589, Paris Cedex 05 (France); Sanchez, N.G. [Observatoire de Paris PSL Research University, Sorbonne Universites UPMC Paris VI, Observatoire de Paris, LERMA CNRS UMR 8112, Paris (France)
2017-02-15
The Thomas-Fermi approach to galaxy structure determines self-consistently and non-linearly the gravitational potential of the fermionic warm dark matter (WDM) particles given their quantum distribution function f(E). This semiclassical framework accounts for the quantum nature and high number of DM particles, properly describing gravitational bounded and quantum macroscopic systems as neutron stars, white dwarfs and WDM galaxies. We express the main galaxy magnitudes as the halo radius r{sub h}, mass M{sub h}, velocity dispersion and phase space density in terms of the surface density which is important to confront to observations. From these expressions we derive the general equation of state for galaxies, i.e., the relation between pressure and density, and provide its analytic expression. Two regimes clearly show up: (1) Large diluted galaxies for M{sub h} >or similar 2.3 x 10{sup 6} M {sub CircleDot} and effective temperatures T{sub 0} > 0.017 K described by the classical self-gravitating WDM Boltzman gas with a space-dependent perfect gas equation of state, and (2) Compact dwarf galaxies for 1.6 x 10{sup 6} M {sub CircleDot} >or similar M{sub h} >or similar M{sub h,min} ≅ 3.10 x 10{sup 4} (2 keV/m){sup (16)/(5)} M {sub CircleDot}, T{sub 0} < 0.011 K described by the quantum fermionic WDM regime with a steeper equation of state close to the degenerate state. In particular, the T{sub 0} = 0 degenerate or extreme quantum limit yields the most compact and smallest galaxy. In the diluted regime, the halo radius r{sub h}, the squared velocity v{sup 2}(r{sub h}) and the temperature T{sub 0} turn to exhibit square-root of M{sub h} scaling laws. The normalized density profiles ρ(r)/ρ(0) and the normalized velocity profiles v{sup 2}(r)/v{sup 2}(0) are universal functions of r/r{sub h} reflecting the WDM perfect gas behavior in this regime. These theoretical results contrasted to robust and independent sets of galaxy data remarkably reproduce the observations. For
2009-01-01
The Universe, is one book in the Britannica Illustrated Science Library Series that is correlated to the science curriculum in grades 5-8. The Britannica Illustrated Science Library is a visually compelling set that covers earth science, life science, and physical science in 16 volumes. Created for ages 10 and up, each volume provides an overview on a subject and thoroughly explains it through detailed and powerful graphics-more than 1,000 per volume-that turn complex subjects into information that students can grasp. Each volume contains a glossary with full definitions for vocabulary help and an index.