Visible imaging of edge turbulence in NSTX
International Nuclear Information System (INIS)
Zweben, S.; Maqueda, R.; Hill, K.; Johnson, D.
2000-01-01
Edge plasma turbulence in tokamaks and stellarators is believed to cause the radical heat and particle flux across the separatrix and into the scrape-off-layers of these devices. This paper describes initial measurements of 2-D space-time structure of the edge density turbulence made using a visible imaging diagnostic in the National Spherical Torus Experiment (NSTX). The structure of the edge turbulence is most clearly visible using a method of gas puff imaging to locally illuminate the edge density turbulence
Visible imaging of edge turbulence in NSTX
International Nuclear Information System (INIS)
S. Zweben; R. Maqueda; K. Hill; D. Johnson; S. Kaye; H. Kugel; F. Levinton; R. Maingi; L. Roquemore; S. Sabbagh; G. Wurden
2000-01-01
Edge plasma turbulence in tokamaks and stellarators is believed to cause the radial heat and particle flux across the separatrix and into the scrape-off-layers of these devices. This paper describes initial measurements of 2-D space-time structure of the edge density turbulence made using a visible imaging diagnostic in the National Spherical Torus Experiment (NSTX). The structure of the edge turbulence is most clearly visible using a method of ''gas puff imaging'' to locally illuminate the edge density turbulence
Visibility of noisy point cloud data
Mehra, Ravish
2010-06-01
We present a robust algorithm for estimating visibility from a given viewpoint for a point set containing concavities, non-uniformly spaced samples, and possibly corrupted with noise. Instead of performing an explicit surface reconstruction for the points set, visibility is computed based on a construction involving convex hull in a dual space, an idea inspired by the work of Katz et al. [26]. We derive theoretical bounds on the behavior of the method in the presence of noise and concavities, and use the derivations to develop a robust visibility estimation algorithm. In addition, computing visibility from a set of adaptively placed viewpoints allows us to generate locally consistent partial reconstructions. Using a graph based approximation algorithm we couple such reconstructions to extract globally consistent reconstructions. We test our method on a variety of 2D and 3D point sets of varying complexity and noise content. © 2010 Elsevier Ltd. All rights reserved.
Visibility of noisy point cloud data
Mehra, Ravish; Tripathi, Pushkar; Sheffer, Alla; Mitra, Niloy J.
2010-01-01
for the points set, visibility is computed based on a construction involving convex hull in a dual space, an idea inspired by the work of Katz et al. [26]. We derive theoretical bounds on the behavior of the method in the presence of noise and concavities
Turbulence evaluation at PSI-2 by fast visible imaging
Energy Technology Data Exchange (ETDEWEB)
Hubeny, Michael; Reinhart, Michael; Huber, Alexander; Unterberg, Bernhard [Institute for Energy and Climate Research - Plasma Physics, Forschungszentrum Juelich GmbH, EURATOM Association (Germany)
2014-07-01
Turbulent transport in the plasma edge poses a critical challenge for fusion reactors due to the high heat and particle fluxes on plasma facing components. Various chemical and physical processes lead to a deterioration of the surface morphology as well as the inner structure of wall materials. These processes depend strongly on the temperature and density of particles in their onset-threshold region. The turbulent, intermittent structures found in the edge of toroidal machines are also present in linear plasma devices, which running steady state, makes them ideal for studying properties of turbulence. A fast CMOS camera with a typical time resolution of several 100.000 fps can resolve short turbulent events (blobs) in the linear plasma device PSI-2. Movies of the plasma were taken perpendicular from a side port and axial through the hollow plasma source. Properties of the intermittent transport are evaluated by conditional averaging and other statistical methods to investigate the dependence of turbulence on discharge parameters and working gases. Intermittent transport events show a strong correlation to the global plasma rotation, thus they might be triggered by an m=1 instability, which appears as a 4 and 8 kHz Fourier component. The profile of the skewness supports the presence of blobs just outside of the density maximum.
On the freestream matching condition for stagnation point turbulent flows
Speziale, C. G.
1989-01-01
The problem of plane stagnation point flow with freestream turbulence is examined from a basic theoretical standpoint. It is argued that the singularity which arises from the standard kappa-epsilon model is not due to a defect in the model but results from the use of an inconsistent freestream boundary condition. The inconsistency lies in the implementation of a production equals dissipation equilibrium hypothesis in conjunction with a freestream mean velocity field that corresponds to homogeneous plane strain - a turbulent flow which does not reach such a simple equilibrium. Consequently, the adjustment that has been made in the constants of the epsilon-transport equation to eliminate this singularity is not self-consistent since it is tantamount to artificially imposing an equilibrium structure on a turbulent flow which is known not to have one.
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...
Time behaviours of visible lines in turbulently heated TRIAM-1 plasma
Energy Technology Data Exchange (ETDEWEB)
Hiraki, N; Nakamura, K; Nakamura, Y; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1981-08-01
Spectroscopic studies were carried out on turbulently heated TRIAM-1 tokamak plasma. The temporal evolutions of the line radiance of visible lines were measured and two types of time behaviours of the line radiance were identified. The observed remarkable reduction of the line radiance of visible lines which have low ionization potential and are localized in the skin-layer due to the application of a pulsed electric-field for turbulent heating is attributed to the strong plasma heating in the peripherical region. Spatial profiles of neutrals and ions which are related to these lines are calculated, and the temporal variations of these profiles caused by the application of the heating pulse are discussed.
Gradients estimation from random points with volumetric tensor in turbulence
Watanabe, Tomoaki; Nagata, Koji
2017-12-01
We present an estimation method of fully-resolved/coarse-grained gradients from randomly distributed points in turbulence. The method is based on a linear approximation of spatial gradients expressed with the volumetric tensor, which is a 3 × 3 matrix determined by a geometric distribution of the points. The coarse grained gradient can be considered as a low pass filtered gradient, whose cutoff is estimated with the eigenvalues of the volumetric tensor. The present method, the volumetric tensor approximation, is tested for velocity and passive scalar gradients in incompressible planar jet and mixing layer. Comparison with a finite difference approximation on a Cartesian grid shows that the volumetric tensor approximation computes the coarse grained gradients fairly well at a moderate computational cost under various conditions of spatial distributions of points. We also show that imposing the solenoidal condition improves the accuracy of the present method for solenoidal vectors, such as a velocity vector in incompressible flows, especially when the number of the points is not large. The volumetric tensor approximation with 4 points poorly estimates the gradient because of anisotropic distribution of the points. Increasing the number of points from 4 significantly improves the accuracy. Although the coarse grained gradient changes with the cutoff length, the volumetric tensor approximation yields the coarse grained gradient whose magnitude is close to the one obtained by the finite difference. We also show that the velocity gradient estimated with the present method well captures the turbulence characteristics such as local flow topology, amplification of enstrophy and strain, and energy transfer across scales.
Visibility Analysis in a Point Cloud Based on the Medial Axis Transform
Peters, R.; Ledoux, H.; Biljecki, F.
2015-01-01
Visibility analysis is an important application of 3D GIS data. Current approaches require 3D city models that are often derived from detailed aerial point clouds. We present an approach to visibility analysis that does not require a city model but works directly on the point cloud. Our approach is
Evolution of branch points for a laser beam propagating through an uplink turbulent atmosphere.
Ge, Xiao-Lu; Liu, Xuan; Guo, Cheng-Shan
2014-03-24
Evolution of branch points in the distorted optical field is studied when a laser beam propagates through turbulent atmosphere along an uplink path. Two categories of propagation events are mainly explored for the same propagation height: fixed wavelength with change of the turbulence strength and fixed turbulence strength with change of the wavelength. It is shown that, when the beam propagates to a certain height, the density of the branch-points reaches its maximum and such a height changes with the turbulence strength but nearly remains constant with different wavelengths. The relationship between the density of branch-points and the Rytov number is also given. A fitted formula describing the relationship between the density of branch-points and propagation height with different turbulence strength and wavelength is found out. Interestingly, this formula is very similar to the formula used for describing the Blackbody radiation in physics. The results obtained may be helpful for atmospheric optics, astronomy and optical communication.
Fast visible imaging and study of edge turbulence in the Aditya tokamak
International Nuclear Information System (INIS)
Banerjee, Santanu; Manchanda, Ranjana; Chowdhuri, Malay Bikas; Ramaiya, Nilam; Parmar, Navin; Ghosh, Joydeep; Tanna, Rakesh L.; Shukla, Braj Kishore; Sharma, Pramod K.
2015-01-01
Fast visible imaging is used on toroidal magnetic confinement devices for a wide variety of purposes. This includes monitoring of the plasma evolution, transient effects in the plasma and the study of edge turbulence. Two fast visible imaging systems are installed on the Aditya tokamak. One of the system is for imaging the plasma evolution with a wide angle lens covering a major portion of the vacuum vessel. The imaging fiber bundle along with the objective lens is installed inside a radial re-entrant viewport, specially designed for the purpose. Another system is intended for tangential imaging of the plasma column. During the termination phase of Aditya plasma, large filaments are seen predominantly across all types of discharges. These filaments are apparent just after the strong interaction of the plasma column with the high field side limiter surface almost at the end of the discharge. Statistical features of these filaments and their role during the termination of plasma is studied. Further, there are many interesting visual impacts of either the experiments carried out or several inherent phenomena in Aditya like the ECRH and LHCD operations, dynamics of the runaway dominated discharges and plasma equilibrium at various discharge scenarios. Such observations and the gained physical insights will be reported. (author)
Numerical schemes for one-point closure turbulence models
International Nuclear Information System (INIS)
Larcher, Aurelien
2010-01-01
First-order Reynolds Averaged Navier-Stokes (RANS) turbulence models are studied in this thesis. These latter consist of the Navier-Stokes equations, supplemented with a system of balance equations describing the evolution of characteristic scalar quantities called 'turbulent scales'. In so doing, the contribution of the turbulent agitation to the momentum can be determined by adding a diffusive coefficient (called 'turbulent viscosity') in the Navier-Stokes equations, such that it is defined as a function of the turbulent scales. The numerical analysis problems, which are studied in this dissertation, are treated in the frame of a fractional step algorithm, consisting of an approximation on regular meshes of the Navier-Stokes equations by the nonconforming Crouzeix-Raviart finite elements, and a set of scalar convection-diffusion balance equations discretized by the standard finite volume method. A monotone numerical scheme based on the standard finite volume method is proposed so as to ensure that the turbulent scales, like the turbulent kinetic energy (k) and its dissipation rate (ε), remain positive in the case of the standard k - ε model, as well as the k - ε RNG and the extended k - ε - ν 2 models. The convergence of the proposed numerical scheme is then studied on a system composed of the incompressible Stokes equations and a steady convection-diffusion equation, which are both coupled by the viscosities and the turbulent production term. This reduced model allows to deal with the main difficulty encountered in the analysis of such problems: the definition of the turbulent production term leads to consider a class of convection-diffusion problems with an irregular right-hand side belonging to L 1 . Finally, to step towards the unsteady problem, the convergence of the finite volume scheme for a model convection-diffusion equation with L 1 data is proved. The a priori estimates on the solution and on its time derivative are obtained in discrete norms, for
International Nuclear Information System (INIS)
Banerjee, Santanu; Manchanda, R.; Chowdhuri, M.B.
2015-01-01
Study of discharge evolution through the different phases of a tokamak plasma shot viz., the discharge initiation, current ramp-up, current flat-top and discharge termination, is essential to address many inherent issues of the operation of a Tokamak. Fast visible imaging of the tokamak plasma can provide valuable insight in this regard. Further, edge turbulence is considered to be one of the quintessential areas of tokamak research as the edge plasma is at the immediate vicinity of the plasma core and plays vital role in the core plasma confinement. The edge plasma also bridges the core and the scrape off layer (SOL) of the tokamak and hence has a bearing on the particle and heat flux escaping the plasma column. Two fast visible imaging systems are installed on the Aditya tokamak. One of the system is for imaging the plasma evolution with a wide angle lens covering a major portion of the vacuum vessel. The imaging fiber bundle along with the objective lens is installed inside a radial re-entrant viewport, specially designed for the purpose. Another system is intended for tangential imaging of the plasma column. Formation of the plasma column and its evolution are studied with the fast visible imaging in Aditya. Features of the ECRH and LHCD operations on Aditya will be discussed. 3D filaments can, be seen at the plasma edge all along the discharge and they get amplified in intensity at the plasma termination phase. Statistical analysis of these filaments, which are essentially plasma blobs will be presented. (author)
Density effects on tokamak edge turbulence and transport with magnetic X-points
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Nevins, W.M.; Rognlien, T.D.; Ryutov, D.D.; Umansky, M.V.; Pearlstein, L.D.; Bulmer, R.H.; Russell, D.A.; Myra, J.R.; D'Ippolito, D.A.; Greenwald, M.; Snyder, P.B.; Mahdavi, M.A.
2005-01-01
Results are presented from the 3D electromagnetic turbulence code BOUT, the 2D transport code UEDGE, and theoretical analysis of boundary turbulence and transport in a real divertor-plasma geometry and its relationship to the density limit. Key results include: (1) a transition of the boundary turbulence from resistive X-point to resistive-ballooning as a critical plasma density is exceeded; (2) formation of an X-point MARFE in 2D UEDGE transport simulations for increasing outboard radial transport as found by BOUT for increasing density; (3) identification of convective transport by localized plasma 'blobs' in the SOL at high density during neutral fueling, and decorrelation of turbulence between the midplane and the divertor leg due to strong X-point magnetic shear; (4) a new divertor-leg instability driven at high plasma beta by a radial tilt of the divertor plate. (author)
Energy Technology Data Exchange (ETDEWEB)
Hiraki, N; Nakamura, K; Toi, K; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1980-07-01
The ion temperature of the turbulently heated TRIAM-1 plasma is obtained from the Doppler-broadening of visible lines. The radial profiles of the volume emission of visible lines are measured beforehand to examine whether the volume emissions are localized at a specified position of the minor cross-section of the plasma or not. The ion temperature of the specified position is determined from these profiles. The time behaviour of thus obtained Doppler ion temperature shows a good agreement with that of the one derived from the Neutral Energy Analyzer.
Turbulence simulations of X point physics on the L-H transitions
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Nevins, W.M.
2001-01-01
We show that the resistive X-point mode is the dominant mode in boundary plasmas in X-point divertor geometry. The poloidal fluctuation phase velocity from the simulation results of the resistive X-point turbulence shows experimentally measured structure across separatrix in many fusion devices. The fluctuation phase velocity is larger than ExB velocity both in L and H mode phases. We also demonstrate that there is a strong poloidal asymmetry of particle flux in the proximity of the separatrix. Turbulence suppression in the L-H transition results when sources of energy and particles drive sufficient gradients as in the experiments. (author)
Strategies to Evaluate the Visibility Along AN Indoor Path in a Point Cloud Representation
Grasso, N.; Verbree, E.; Zlatanova, S.; Piras, M.
2017-09-01
Many research works have been oriented to the formulation of different algorithms for estimating the paths in indoor environments from three-dimensional representations of space. The architectural configuration, the actions that take place within it, and the location of some objects in the space influence the paths along which is it possible to move, as they may cause visibility problems. To overcome the visibility issue, different methods have been proposed which allow to identify the visible areas and from a certain point of view, but often they do not take into account the user's visual perception of the environment and not allow estimating how much may be complicated to follow a certain path. In the field of space syntax and cognitive science, it has been attempted to describe the characteristics of a building or an urban environment by the isovists and visibility graphs methods; some numerical properties of these representations allow to describe the space as for how it is perceived by a user. However, most of these studies are directed to analyze the environment in a two-dimensional space. In this paper we propose a method to evaluate in a quantitative way the complexity of a certain path within an environment represented by a three-dimensional point cloud, by the combination of some of the previously mentioned techniques, considering the space visible from a certain point of view, depending on the moving agent (pedestrian , people in wheelchairs, UAV, UGV, robot).
Numerical Coupling and Simulation of Point-Mass System with the Turbulent Fluid Flow
Gao, Zheng
A computational framework that combines the Eulerian description of the turbulence field with a Lagrangian point-mass ensemble is proposed in this dissertation. Depending on the Reynolds number, the turbulence field is simulated using Direct Numerical Simulation (DNS) or eddy viscosity model. In the meanwhile, the particle system, such as spring-mass system and cloud droplets, are modeled using the ordinary differential system, which is stiff and hence poses a challenge to the stability of the entire system. This computational framework is applied to the numerical study of parachute deceleration and cloud microphysics. These two distinct problems can be uniformly modeled with Partial Differential Equations (PDEs) and Ordinary Differential Equations (ODEs), and numerically solved in the same framework. For the parachute simulation, a novel porosity model is proposed to simulate the porous effects of the parachute canopy. This model is easy to implement with the projection method and is able to reproduce Darcy's law observed in the experiment. Moreover, the impacts of using different versions of k-epsilon turbulence model in the parachute simulation have been investigated and conclude that the standard and Re-Normalisation Group (RNG) model may overestimate the turbulence effects when Reynolds number is small while the Realizable model has a consistent performance with both large and small Reynolds number. For another application, cloud microphysics, the cloud entrainment-mixing problem is studied in the same numerical framework. Three sets of DNS are carried out with both decaying and forced turbulence. The numerical result suggests a new way parameterize the cloud mixing degree using the dynamical measures. The numerical experiments also verify the negative relationship between the droplets number concentration and the vorticity field. The results imply that the gravity has fewer impacts on the forced turbulence than the decaying turbulence. In summary, the
Synthesis of atmospheric turbulence point spread functions by sparse and redundant representations
Hunt, Bobby R.; Iler, Amber L.; Bailey, Christopher A.; Rucci, Michael A.
2018-02-01
Atmospheric turbulence is a fundamental problem in imaging through long slant ranges, horizontal-range paths, or uplooking astronomical cases through the atmosphere. An essential characterization of atmospheric turbulence is the point spread function (PSF). Turbulence images can be simulated to study basic questions, such as image quality and image restoration, by synthesizing PSFs of desired properties. In this paper, we report on a method to synthesize PSFs of atmospheric turbulence. The method uses recent developments in sparse and redundant representations. From a training set of measured atmospheric PSFs, we construct a dictionary of "basis functions" that characterize the atmospheric turbulence PSFs. A PSF can be synthesized from this dictionary by a properly weighted combination of dictionary elements. We disclose an algorithm to synthesize PSFs from the dictionary. The algorithm can synthesize PSFs in three orders of magnitude less computing time than conventional wave optics propagation methods. The resulting PSFs are also shown to be statistically representative of the turbulence conditions that were used to construct the dictionary.
Statistical properties of visible and infrared beams retroreflected through a turbulent atmosphere
International Nuclear Information System (INIS)
Slatkine, M.; Bensimon, D.; Englander, A.; Shtrikman, S.; Treves, D.
1980-01-01
Statistical properties of HeNe and CO 2 laser beams retroreflected through a turbulent atmosphere are investigated experimentally for round paths of 1 km and 12 km. Both heterodyne and direct detection are used
Energy Technology Data Exchange (ETDEWEB)
Hiraki, N; Nakamura, K; Toi, K; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1981-01-01
In the turbulent heating experiment of the high-field tokamak TRIAM-1, the bulk ion heating shown by the neutral energy analyzer measurement is confirmed by the Doppler broadening measurement of visible lines. The increasing rate and decay time of the Doppler ion temperature are almost the same as those derived from the neutral energy analyzer measurement. From both methods of ion temperature measurements, it is shown that the ion temperature has a parabolic profile within 50 ..mu..s after the application of the heating pulse.
Varotsos, G. K.; Nistazakis, H. E.; Petkovic, M. I.; Djordjevic, G. T.; Tombras, G. S.
2017-11-01
Over the last years terrestrial free-space optical (FSO) communication systems have demonstrated an increasing scientific and commercial interest in response to the growing demands for ultra high bandwidth, cost-effective and secure wireless data transmissions. However, due the signal propagation through the atmosphere, the performance of such links depends strongly on the atmospheric conditions such as weather phenomena and turbulence effect. Additionally, their operation is affected significantly by the pointing errors effect which is caused by the misalignment of the optical beam between the transmitter and the receiver. In order to address this significant performance degradation, several statistical models have been proposed, while particular attention has been also given to diversity methods. Here, the turbulence-induced fading of the received optical signal irradiance is studied through the M (alaga) distribution, which is an accurate model suitable for weak to strong turbulence conditions and unifies most of the well-known, previously emerged models. Thus, taking into account the atmospheric turbulence conditions along with the pointing errors effect with nonzero boresight and the modulation technique that is used, we derive mathematical expressions for the estimation of the average bit error rate performance for SIMO FSO links. Finally, proper numerical results are given to verify our derived expressions and Monte Carlo simulations are also provided to further validate the accuracy of the analysis proposed and the obtained mathematical expressions.
A model for the two-point velocity correlation function in turbulent channel flow
International Nuclear Information System (INIS)
Sahay, A.; Sreenivasan, K.R.
1996-01-01
A relatively simple analytical expression is presented to approximate the equal-time, two-point, double-velocity correlation function in turbulent channel flow. To assess the accuracy of the model, we perform the spectral decomposition of the integral operator having the model correlation function as its kernel. Comparisons of the empirical eigenvalues and eigenfunctions with those constructed from direct numerical simulations data show good agreement. copyright 1996 American Institute of Physics
Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes
Chin, C.; Vinuesa, R.; Örlü, R.; Cardesa, J. I.; Noorani, A.; Schlatter, P.; Chong, M. S.
2018-04-01
A study of the back flow events and critical points in the flow through a toroidal pipe at friction Reynolds number Re τ ≈ 650 is performed and compared with the results in a turbulent channel flow at Re τ ≈ 934. The statistics and topological properties of the back flow events are analysed and discussed. Conditionally-averaged flow fields in the vicinity of the back flow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the spanwise wall-shear stress when compared to the channel flow. The comparison between the toroidal pipe and channel flows also shows fewer back flow events and critical points in the torus. This cannot be solely attributed to differences in Reynolds number, but is a clear effect of the secondary flow present in the toroidal pipe. A possible mechanism is the effect of the secondary flow present in the torus, which convects momentum from the inner to the outer bend through the core of the pipe, and back from the outer to the inner bend through the pipe walls. In the region around the critical points, the skin-friction streamlines and vorticity lines exhibit similar flow characteristics with a node and saddle pair for both flows. These results indicate that back flow events and critical points are genuine features of wall-bounded turbulence, and are not artifacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.
The design of visible system for improving the measurement accuracy of imaging points
Shan, Qiu-sha; Li, Gang; Zeng, Luan; Liu, Kai; Yan, Pei-pei; Duan, Jing; Jiang, Kai
2018-02-01
It has a widely applications in robot vision and 3D measurement for binocular stereoscopic measurement technology. And the measure precision is an very important factor, especially in 3D coordination measurement, high measurement accuracy is more stringent to the distortion of the optical system. In order to improving the measurement accuracy of imaging points, to reducing the distortion of the imaging points, the optical system must be satisfied the requirement of extra low distortion value less than 0.1#65285;, a transmission visible optical lens was design, which has characteristic of telecentric beam path in image space, adopted the imaging model of binocular stereo vision, and imaged the drone at the finity distance. The optical system was adopted complex double Gauss structure, and put the pupil stop on the focal plane of the latter groups, maked the system exit pupil on the infinity distance, and realized telecentric beam path in image space. The system mainly optical parameter as follows: the system spectrum rangement is visible light wave band, the optical effective length is f '=30mm, the relative aperture is 1/3, and the fields of view is 21°. The final design results show that the RMS value of the spread spots of the optical lens in the maximum fields of view is 2.3μm, which is less than one pixel(3.45μm) the distortion value is less than 0.1%, the system has the advantage of extra low distortion value and avoids the latter image distortion correction; the proposed modulation transfer function of the optical lens is 0.58(@145 lp/mm), the imaging quality of the system is closed to the diffraction limited; the system has simply structure, and can satisfies the requirements of the optical indexes. Ultimately, based on the imaging model of binocular stereo vision was achieved to measuring the drone at the finity distance.
2017-11-01
authors. Statistical analyses and analysis plots were obtained using IBM SPSS Statistics.* 5.1 Threshold Visible Illuminance by LED Color and...LED Visibility vs. Outdoor Background Illuminance Across all camouflage materials, the outdoor distances of visibility are plotted with SPSS in Fig
Point-of-use water disinfection using ultraviolet and visible light-emitting diodes
Energy Technology Data Exchange (ETDEWEB)
Lui, Gough Yumu, E-mail: gough@student.unsw.edu.au [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); School of Photovoltaics and Renewable Energy Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Roser, David, E-mail: djroser@unsw.edu.au [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Corkish, Richard, E-mail: r.corkish@unsw.edu.au [School of Photovoltaics and Renewable Energy Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Ashbolt, Nicholas J., E-mail: ashbolt@ualberta.ca [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); School of Public Health, South Academic Building, University of Alberta, Edmonton, Alberta T6G 2G7 (Canada); Stuetz, Richard, E-mail: r.stuetz@unsw.edu.au [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia)
2016-05-15
Improvements in point-of-use (POU) drinking water disinfection technologies for remote and regional communities are urgently needed. Conceptually, UV-C light-emitting diodes (LEDs) overcome many drawbacks of low-pressure mercury tube based UV devices, and UV-A or visible light LEDs also show potential. To realistically evaluate the promise of LED disinfection, our study assessed the performance of a model 1.3 L reactor, similar in size to solar disinfection bottles. In all, 12 different commercial or semi-commercial LED arrays (270–740 nm) were compared for their ability to inactivate Escherichia coli K12 ATCC W3110 and Enterococcus faecalis ATCC 19433 over 6 h. Five log{sub 10} and greater reductions were consistently achieved using the 270, 365, 385 and 405 nm arrays. The output of the 310 nm array was insufficient for useful disinfection while 430 and 455 nm performance was marginal (≈ 4.2 and 2.3-log{sub 10}s E. coli and E. faecalis over the 6 h). No significant disinfection was observed with the 525, 590, 623, 660 and 740 nm arrays. Delays in log-phase inactivation of E. coli were observed, particularly with UV-A wavelengths. The radiation doses required for > 3-log{sub 10} reduction of E. coli and E. faecalis differed by 10 fold at 270 nm but only 1.5–2.5 fold at 365–455 nm. Action spectra, consistent with the literature, were observed with both indicators. The design process revealed cost and technical constraints pertaining to LED electrical efficiency, availability and lifetime. We concluded that POU LED disinfection using existing LED technology is already technically possible. UV-C LEDs offer speed and energy demand advantages, while UV-A/violet units are safer. Both approaches still require further costing and engineering development. Our study provides data needed for such work. - Highlights: • Disinfection of E. coli and E. faecalis achieved with 270 and 365–455 nm LEDs • No significant disinfection was found with 310 and > 455 nm LEDs
Point-of-use water disinfection using ultraviolet and visible light-emitting diodes
International Nuclear Information System (INIS)
Lui, Gough Yumu; Roser, David; Corkish, Richard; Ashbolt, Nicholas J.; Stuetz, Richard
2016-01-01
Improvements in point-of-use (POU) drinking water disinfection technologies for remote and regional communities are urgently needed. Conceptually, UV-C light-emitting diodes (LEDs) overcome many drawbacks of low-pressure mercury tube based UV devices, and UV-A or visible light LEDs also show potential. To realistically evaluate the promise of LED disinfection, our study assessed the performance of a model 1.3 L reactor, similar in size to solar disinfection bottles. In all, 12 different commercial or semi-commercial LED arrays (270–740 nm) were compared for their ability to inactivate Escherichia coli K12 ATCC W3110 and Enterococcus faecalis ATCC 19433 over 6 h. Five log_1_0 and greater reductions were consistently achieved using the 270, 365, 385 and 405 nm arrays. The output of the 310 nm array was insufficient for useful disinfection while 430 and 455 nm performance was marginal (≈ 4.2 and 2.3-log_1_0s E. coli and E. faecalis over the 6 h). No significant disinfection was observed with the 525, 590, 623, 660 and 740 nm arrays. Delays in log-phase inactivation of E. coli were observed, particularly with UV-A wavelengths. The radiation doses required for > 3-log_1_0 reduction of E. coli and E. faecalis differed by 10 fold at 270 nm but only 1.5–2.5 fold at 365–455 nm. Action spectra, consistent with the literature, were observed with both indicators. The design process revealed cost and technical constraints pertaining to LED electrical efficiency, availability and lifetime. We concluded that POU LED disinfection using existing LED technology is already technically possible. UV-C LEDs offer speed and energy demand advantages, while UV-A/violet units are safer. Both approaches still require further costing and engineering development. Our study provides data needed for such work. - Highlights: • Disinfection of E. coli and E. faecalis achieved with 270 and 365–455 nm LEDs • No significant disinfection was found with 310 and > 455 nm LEDs. • UV
Dual-Hop FSO Transmission Systems over Gamma-Gamma Turbulence with Pointing Errors
Zedini, Emna
2016-11-18
In this paper, we analyze the end-to-end performance of dual-hop free-space optical (FSO) fixed gain relaying systems under heterodyne detection and intensity modulation with direct detection techniques in the presence of atmospheric turbulence as well as pointing errors. In particular, we derive the cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) in exact closed-form in terms of the bivariate Fox’s H function. Capitalizing on this CDF expression, novel closed-form expressions for the outage probability, the average bit-error rate (BER) for different modulation schemes, and the ergodic capacity of dual-hop FSO transmission systems are presented. Moreover, we present very tight asymptotic results for the outage probability and the average BER at high SNR regime in terms of simple elementary functions and we derive the diversity order of the considered system. By using dual-hop FSO relaying, we demonstrate a better system performance as compared to the single FSO link. Numerical and Monte-Carlo simulation results are provided to verify the accuracy of the newly proposed results, and a perfect agreement is observed.
A star-pointing UV-visible spectrometer for remote-sensing of the stratosphere
Roscoe, Howard K.; Freshwater, Ray A.; Jones, Rod L.; Fish, Debbie J.; Harries, John E.; Wolfenden, Roger; Stone, Phillip
1994-01-01
We have constructed a novel instrument for ground-based remote sensing, by mounting a UV-visible spectrometer on a telescope and observing the absorption by atmospheric constituents of light from stars. Potentially, the instrument can observe stratospheric O3, NO3, NO2, and OClO.
Dual-Hop FSO Transmission Systems over Gamma-Gamma Turbulence with Pointing Errors
Zedini, Emna; Soury, Hamza; Alouini, Mohamed-Slim
2016-01-01
In this paper, we analyze the end-to-end performance of dual-hop free-space optical (FSO) fixed gain relaying systems under heterodyne detection and intensity modulation with direct detection techniques in the presence of atmospheric turbulence
Magnetohydrodynamic turbulence
Biskamp, Dieter
2003-01-01
This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressi
Ahlers, Günter; Calzavarini, E.; Fontenele Araujo Junior, F.; Funfschilling, Denis; Grossmann, Siegfried; Lohse, Detlef; Sugiyama, K.
2008-01-01
As shown in earlier work [Ahlers et al., J. Fluid Mech. 569, 409 (2006)], non-Oberbeck-Boussinesq (NOB) corrections to the center temperature in turbulent Rayleigh-Bénard convection in water and also in glycerol are governed by the temperature dependences of the kinematic viscosity and the thermal
Balaji, K. A.; Prabu, K.
2018-03-01
There is an immense demand for high bandwidth and high data rate systems, which is fulfilled by wireless optical communication or free space optics (FSO). Hence FSO gained a pivotal role in research which has a added advantage of both cost-effective and licence free huge bandwidth. Unfortunately the optical signal in free space suffers from irradiance and phase fluctuations due to atmospheric turbulence and pointing errors which deteriorates the signal and degrades the performance of communication system over longer distance which is undesirable. In this paper, we have considered polarization shift keying (POLSK) system applied with wavelength and time diversity technique over Malaga(M)distribution to mitigate turbulence induced fading. We derived closed form mathematical expressions for estimating the systems outage probability and average bit error rate (BER). Ultimately from the results we can infer that wavelength and time diversity schemes enhances these systems performance.
Kim, Joon Hyun; Kwon, Woo Jin; Shin, Yong-Il
2016-05-01
In a recent experiment, it was found that the dissipative evolution of a corotating vortex pair in a trapped Bose-Einstein condensate is well described by a point vortex model with longitudinal friction on the vortex motion and the thermal friction coefficient was determined as a function of sample temperature. In this poster, we present a numerical study on the relaxation of 2D superfluid turbulence based on the dissipative point vortex model. We consider a homogeneous system in a cylindrical trap having randomly distributed vortices and implement the vortex-antivortex pair annihilation by removing a pair when its separation becomes smaller than a certain threshold value. We characterize the relaxation of the turbulent vortex states with the decay time required for the vortex number to be reduced to a quarter of initial number. We find the vortex decay time is inversely proportional to the thermal friction coefficient. In particular, we observe the decay times obtained from this work show good quantitative agreement with the experimental results in, indicating that in spite of its simplicity, the point vortex model reasonably captures the physics in the relaxation dynamics of the real system.
Alheadary, Wael Ghazy
2016-12-24
In this work, we present a bit error rate (BER) and achievable spectral efficiency (ASE) performance of a freespace optical (FSO) link with pointing errors based on intensity modulation/direct detection (IM/DD) and heterodyne detection over general Malaga turbulence channel. More specifically, we present exact closed-form expressions for adaptive and non-adaptive transmission. The closed form expressions are presented in terms of generalized power series of the Meijer\\'s G-function. Moreover, asymptotic closed form expressions are provided to validate our work. In addition, all the presented analytical results are illustrated using a selected set of numerical results.
Hammergren, Mark; Brucker, Melissa J.; Nault, Kristie A.; Gyuk, Geza; Solontoi, Michael R.
2015-11-01
Near-Earth Objects (NEOs) are interesting to scientists and the general public for diverse reasons: their impacts pose a threat to life and property; they present important albeit biased records of the formation and evolution of the Solar System; and their materials may provide in situ resources for future space exploration and habitation.In January 2015 we began a program of NEO astrometric follow-up and physical characterization using a 17% share of time on the Astrophysical Research Consortium (ARC) 3.5-meter telescope at Apache Point Observatory (APO). Our 500 hours of annual observing time are split into frequent, short astrometric runs (see poster by K. A. Nault et. al), and half-night runs devoted to physical characterization (see poster by M. J. Brucker et. al for preliminary rotational lightcurve results). NEO surface compositions are investigated with 0.36-1.0 μm reflectance spectroscopy using the Dual Imaging Spectrograph (DIS) instrument. As of August 25, 2015, including testing runs during fourth quarter 2014, we have obtained reflectance spectra of 68 unique NEOs, ranging in diameter from approximately 5m to 8km.In addition to investigating the compositions of individual NEOs to inform impact hazard and space resource evaluations, we may examine the distribution of taxonomic types and potential trends with other physical and orbital properties. For example, the Yarkovsky effect, which is dependent on asteroid shape, mass, rotation, and thermal characteristics, is believed to dominate other dynamical effects in driving the delivery of small NEOs from the main asteroid belt. Studies of the taxonomic distribution of a large sample of NEOs of a wide range of sizes will test this hypothesis.We present a preliminary analysis of the reflectance spectra obtained in our survey to date, including taxonomic classifications and potential trends with size.Acknowledgements: Based on observations obtained with the Apache Point Observatory 3.5-meter telescope, which
Yang, X. I. A.; Marusic, I.; Meneveau, C.
2016-06-01
Townsend [Townsend, The Structure of Turbulent Shear Flow (Cambridge University Press, Cambridge, UK, 1976)] hypothesized that the logarithmic region in high-Reynolds-number wall-bounded flows consists of space-filling, self-similar attached eddies. Invoking this hypothesis, we express streamwise velocity fluctuations in the inertial layer in high-Reynolds-number wall-bounded flows as a hierarchical random additive process (HRAP): uz+=∑i=1Nzai . Here u is the streamwise velocity fluctuation, + indicates normalization in wall units, z is the wall normal distance, and ai's are independently, identically distributed random additives, each of which is associated with an attached eddy in the wall-attached hierarchy. The number of random additives is Nz˜ln(δ /z ) where δ is the boundary layer thickness and ln is natural log. Due to its simplified structure, such a process leads to predictions of the scaling behaviors for various turbulence statistics in the logarithmic layer. Besides reproducing known logarithmic scaling of moments, structure functions, and correlation function [" close="]3/2 uz(x ) uz(x +r ) >, new logarithmic laws in two-point statistics such as uz4(x ) > 1 /2, 1/3, etc. can be derived using the HRAP formalism. Supporting empirical evidence for the logarithmic scaling in such statistics is found from the Melbourne High Reynolds Number Boundary Layer Wind Tunnel measurements. We also show that, at high Reynolds numbers, the above mentioned new logarithmic laws can be derived by assuming the arrival of an attached eddy at a generic point in the flow field to be a Poisson process [Woodcock and Marusic, Phys. Fluids 27, 015104 (2015), 10.1063/1.4905301]. Taken together, the results provide new evidence supporting the essential ingredients of the attached eddy hypothesis to describe streamwise velocity fluctuations of large, momentum transporting eddies in wall-bounded turbulence, while observed deviations suggest the need for further extensions of the
Gu, Wenjun; Zhang, Weizhi; Wang, Jin; Amini Kashani, M. R.; Kavehrad, Mohsen
2015-01-01
Over the past decade, location based services (LBS) have found their wide applications in indoor environments, such as large shopping malls, hospitals, warehouses, airports, etc. Current technologies provide wide choices of available solutions, which include Radio-frequency identification (RFID), Ultra wideband (UWB), wireless local area network (WLAN) and Bluetooth. With the rapid development of light-emitting-diodes (LED) technology, visible light communications (VLC) also bring a practical approach to LBS. As visible light has a better immunity against multipath effect than radio waves, higher positioning accuracy is achieved. LEDs are utilized both for illumination and positioning purpose to realize relatively lower infrastructure cost. In this paper, an indoor positioning system using VLC is proposed, with LEDs as transmitters and photo diodes as receivers. The algorithm for estimation is based on received-signalstrength (RSS) information collected from photo diodes and trilateration technique. By appropriately making use of the characteristics of receiver movements and the property of trilateration, estimation on three-dimensional (3-D) coordinates is attained. Filtering technique is applied to enable tracking capability of the algorithm, and a higher accuracy is reached compare to raw estimates. Gaussian mixture Sigma-point particle filter (GM-SPPF) is proposed for this 3-D system, which introduces the notion of Gaussian Mixture Model (GMM). The number of particles in the filter is reduced by approximating the probability distribution with Gaussian components.
Two-point theory of current-driven ion-cyclotron turbulence
International Nuclear Information System (INIS)
Chiueh, T.; Diamond, P.H.
1985-02-01
An analytical theory of current-driven ion-cyclotron turbulenc which treats incoherent phase space density granulations (clumps) is presented. In contrast to previous investigations, attention is focused on the physically relevant regime of weak collective dissipation, where waves and clumps coexist. The threshold current for nonlinear instability is calculated, and is found to deviate from the linear threshold. A necessary condition for the existence of stationary wave-clump turbulence is derived, and shown to be analogous to the test particle model fluctuation-dissipation theorem result. The structure of three dimensional magnetized clumps is characterized. It is proposed that instability is saturated by collective dissipation due to ion-wave scattering. For this wave-clump turbulence regime, it is found that the fluctuation level (e psi/T/sub e/)/sub rms/ less than or equal to 0.1, and that the modification of anomalous resistivity to levels predicted by conventional nonlinear wave theories is moderate. It is also shown that, in marked contrast to the quasilinear prediction, ion heating significantly exceeds electron heating
Yang, Liang
2014-12-01
In this study, we consider a relay-assisted free-space optical communication scheme over strong atmospheric turbulence channels with misalignment-induced pointing errors. The links from the source to the destination are assumed to be all-optical links. Assuming a variable gain relay with amplify-and-forward protocol, the electrical signal at the source is forwarded to the destination with the help of this relay through all-optical links. More specifically, we first present a cumulative density function (CDF) analysis for the end-to-end signal-to-noise ratio. Based on this CDF, the outage probability, bit-error rate, and average capacity of our proposed system are derived. Results show that the system diversity order is related to the minimum value of the channel parameters.
Alheadary, Wael Ghazy
2017-11-16
This work investigates the end-to-end performance of a free space optical amplify-and-forward relaying system using heterodyne detection over Malaga turbulence channels at the presence of pointing error. In order to overcome the analytical difficulties of the proposed composite channel model, we employed the mixture Gamma (MG) distribution. The proposed model shows a high accurate and tractable approximation just by adjusting some parameters. More specifically, we derived new closed-form expression for average bit error rate employing rectangular quadrature amplitude modulation in term of MG distribution and generalized power series of the Meijer\\'s G- function. The closed-form has been validated numerically and asymptotically at high signal to noise ratio.
Alheadary, Wael Ghazy
2017-09-21
This work investigates the end-to-end performance of a free space optical amplify-and-forward (AF) channel-state-information (CSI)-assisted relaying system using heterodyne detection over Malaga turbulence channels at the presence of pointing error employing rectangular quadrature amplitude modulation (R-QAM). More specifically, we present exact closed-form expressions for average bit-error rate for adaptive/non-adaptive modulation, achievable spectral efficiency, and ergodic capacity by utilizing generalized power series of Meijer\\'s G-function. Moreover, asymptotic closed form expressions are provided to validate our work at high power regime. In addition, all the presented analytical results are illustrated using a selected set of numerical results. Moreover, we applied the bisection method to find the optimum beam width for the proposed FSO system.
Lui, Gough Yumu; Roser, David; Corkish, Richard; Ashbolt, Nicholas; Jagals, Paul; Stuetz, Richard
2014-09-15
For many decades, populations in rural and remote developing regions will be unable to access centralised piped potable water supplies, and indeed, decentralised options may be more sustainable. Accordingly, improved household point-of-use (POU) disinfection technologies are urgently needed. Compared to alternatives, ultraviolet (UV) light disinfection is very attractive because of its efficacy against all pathogen groups and minimal operational consumables. Though mercury arc lamp technology is very efficient, it requires frequent lamp replacement, involves a toxic heavy metal, and their quartz envelopes and sleeves are expensive, fragile and require regular cleaning. An emerging alternative is semiconductor-based units where UV light emitting diodes (UV-LEDs) are powered by photovoltaics (PV). Our review charts the development of these two technologies, their current status, and challenges to their integration and POU application. It explores the themes of UV-C-LEDs, non-UV-C LED technology (e.g. UV-A, visible light, Advanced Oxidation), PV power supplies, PV/LED integration and POU suitability. While UV-C LED technology should mature in the next 10 years, research is also needed to address other unresolved barriers to in situ application as well as emerging research opportunities especially UV-A, photocatalyst/photosensitiser use and pulsed emission options. Copyright © 2014 Elsevier B.V. All rights reserved.
Forest - added Turbulence: A parametric study on Turbulence intensity in and around forests
International Nuclear Information System (INIS)
Pedersen, Henrik Sundgaard; Langreder, Wiebke
2007-01-01
The scope of the investigation is to take on-site measured wind data from a number of sites inside and close to forests. From the collected on-site data the ambient turbulence intensity is calculated and analysed depending on the distance to the forest and height above the forest. From this forest turbulence intensity database it is possible to get an overview of the general behaviour of the turbulence above and down stream from the forest. The database currently consists of 65 measurements points from around the globe, and it will be continually updated as relevant sites are made available. Using the database a number of questions can be answered. How does the ambient turbulence intensity decay with height? What does the turbulence profile look like according to wind speed? Is it the general situation that high wind speeds are creating movement in the canopy tops, resulting in higher turbulence? How does the ambient turbulence intensity decay at different height as a function of distance to the forest? From the forest turbulence database it can be seen that in general, the majority of the turbulence intensity created by the forest is visible within a radius of 5 times the forest height in vertical and 500 meters downstream from the forest edge in horizontal direction. Outside these boundaries the ambient turbulence intensity is rapidly approaching normal values
Ansari, Imran Shafique; Yilmaz, Ferkan; Alouini, Mohamed-Slim
2015-01-01
In this work, we present a unified performance analysis of a free-space optical (FSO) link that accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection (IM/DD) as well as heterodyne detection). More specifically, we present unified exact closedform expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system, all in terms of the Meijer’s G function except for the moments that is in terms of simple elementary functions. We then capitalize on these unified results to offer unified exact closed-form expressions for various performance metrics of FSO link transmission systems, such as, the outage probability, the scintillation index (SI), the average error rate for binary and M-ary modulation schemes, and the ergodic capacity (except for IM/DD technique, where we present closed-form lower bound results), all in terms of Meijer’s G functions except for the SI that is in terms of simple elementary functions. Additionally, we derive the asymptotic results for all the expressions derived earlier in terms of Meijer’s G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer’s G function. We also derive new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes in terms of simple elementary functions via utilizing moments. All the presented results are verified via computer-based Monte-Carlo simulations.
Ansari, Imran Shafique
2015-08-12
In this work, we present a unified performance analysis of a free-space optical (FSO) link that accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection (IM/DD) as well as heterodyne detection). More specifically, we present unified exact closedform expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system, all in terms of the Meijer’s G function except for the moments that is in terms of simple elementary functions. We then capitalize on these unified results to offer unified exact closed-form expressions for various performance metrics of FSO link transmission systems, such as, the outage probability, the scintillation index (SI), the average error rate for binary and M-ary modulation schemes, and the ergodic capacity (except for IM/DD technique, where we present closed-form lower bound results), all in terms of Meijer’s G functions except for the SI that is in terms of simple elementary functions. Additionally, we derive the asymptotic results for all the expressions derived earlier in terms of Meijer’s G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer’s G function. We also derive new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes in terms of simple elementary functions via utilizing moments. All the presented results are verified via computer-based Monte-Carlo simulations.
Ansari, Imran Shafique
2015-03-01
Generalized fading has been an imminent part and parcel of wireless communications. It not only characterizes the wireless channel appropriately but also allows its utilization for further performance analysis of various types of wireless communication systems. Under the umbrella of generalized fading channels, a unified performance analysis of a free-space optical (FSO) link over the Malaga (M) atmospheric turbulence channel that accounts for pointing errors and both types of detection techniques (i.e. indirect modulation/direct detection (IM/DD) as well as heterodyne detection) is presented. Specifically, unified exact closed-form expressions for the probability density function (PDF), the cumulative distribution function (CDF), the moment generating function (MGF), and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system are presented, all in terms of the Meijer\\'s G function except for the moments that is in terms of simple elementary functions. Then capitalizing on these unified results, unified exact closed-form expressions for various performance metrics of FSO link transmission systems are offered, such as, the outage probability (OP), the higher-order amount of fading (AF), the average error rate for binary and M-ary modulation schemes, and the ergodic capacity (except for IM/DD technique, where closed-form lower bound results are presented), all in terms of Meijer\\'s G functions except for the higher-order AF that is in terms of simple elementary functions. Additionally, the asymptotic results are derived for all the expressions derived earlier in terms of the Meijer\\'s G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer\\'s G function. Furthermore, new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes are derived in terms of simple elementary functions via utilizing moments. All the presented results are
International Nuclear Information System (INIS)
Engels, W P; Subhani, S; Zafar, H; Savenije, F
2014-01-01
Extreme wind conditions can cause excessive loading on the turbine. This not only results in higher design loads, but when these conditions occur in practice, will also result in higher maintenance cost. Although there are already effective methods of dealing with gusts, other extreme conditions should also be examined. More specifically, extreme turbulence conditions (e.g. those specified by design load case 1.3 in IEC61400-1 ed. 3) require special attention as they can lead to design-driving extreme loads on blades, tower and other wind turbine components. This paper examines two methods to deal with extreme loads in a case of extreme turbulent wind. One method is derating the turbine, the other method is an individual pitch control (IPC) algorithm. Derating of the turbine can be achieved in two ways, one is changing the rated torque, the other is changing the rated rotor speed. The effect of these methods on fatigue loads and extreme loads is examined. Non-linear aero-elastic simulations using Phatas, show that reducing the rated rotor speed is far more effective at reducing the loads than reducing torque. Then, the IPC algorithm is proposed. This algorithm is a linear quadratic Gaussian (LQG) controller based on a time invariant model, defined in the fixed reference frame that includes the first tower and blade modes. Because this method takes the dynamics of the system into account more than conventional IPC control, it is expected that these loads dealt with more effectively, when they are particularly relevant. It is expected that in extreme turbulent the blade and tower dynamics are indeed more relevant. The effect of this algorithm on fatigue loads and pitch effort is examined and compared with the fatigue loads and pitch effort of reference IPC. Finally, the methods are compared in non-linear aero-elastic simulations with extreme turbulent wind
Energy Technology Data Exchange (ETDEWEB)
Campins-Falco, Pilar; Bosch-Reig, Francisco; Herraez-Hernandez, Rosa; Sevillano-Cabeza, Adela (Universidad de Valencia (Spain). Facultad de Quimica, Departamento de Quimica Analitica)
1992-02-10
This work establishes the fundamentals of the H-point standard additions method for liquid chromatography for the simultaneous analysis of binary mixtures with overlapped chromatographic peaks. The method was compared with the deconvolution method of peak suppression and the second derivative of elution profiles. Different mixtures of diuretics were satisfactorily resolved. (author). 21 refs.; 9 figs.; 2 tabs.
International Nuclear Information System (INIS)
Durani, Smeer; Mathur, Neerja; Chowdary, G.S.
2007-01-01
The cloud point extraction behavior (CPE) of vanadium (V) using 5,7 dibromo 8-hydroxyquinoline (DBHQ) and triton X 100 was investigated. Vanadium (V) was extracted with 4 ml of 0.5 mg/ml DBHQ and 6 ml of 8% (V/V) triton X 100 at the pH 3.7. A few hydrogeochemical samples were analysed for vanadium using the above method. (author)
International Nuclear Information System (INIS)
Lee, L.C.; Shandu, K.T.S.; Nor Syahirah Mohamad Razi; Ab Aziz Ishak; Khairul Osman
2015-01-01
Twelve varieties of blue ball point pens were selected and analyzed using UV-Vis spectrometer and ultra-performance liquid chromatography (UPLC). The aim of the study was to determine discrimination power (DP) of these methods in differentiating pen inks collected from the market in Malaysia. Discrimination analysis of 66 possible pen-pair of blue ball point pens was carried out via one-way ANOVA based on obtained chromatogram and spectra. A total of 18 peaks were determined as coming from inks based on the chromatographic data extracted at three different wavelengths (279, 370 and 400 nm). While for the UV-Vis spectrometer analysis, presence of peaks at 303, 545, 577 and 584 nm wavelengths were recorded. UV-Vis spectral data were mainly produced by the colorant components (for example, dyes) found in inks and UPLC may detect ink components other than dyes, for example, additives. As conclusion, the DP for UV-Vis and UPLC were determined to be 72.12 % and 98.48 %, respectively. This manuscript demonstrates the potential of UPLC for discriminating pen inks based on non-dye components. Additionally, the dye components in inks do not seem to play important role in discrimination of pen inks. (author)
Abu-Almaalie, Zina; Ghassemlooy, Zabih; Bhatnagar, Manav R; Le-Minh, Hoa; Aslam, Nauman; Liaw, Shien-Kuei; Lee, It Ee
2016-11-20
Physical layer network coding (PNC) improves the throughput in wireless networks by enabling two nodes to exchange information using a minimum number of time slots. The PNC technique is proposed for two-way relay channel free space optical (TWR-FSO) communications with the aim of maximizing the utilization of network resources. The multipair TWR-FSO is considered in this paper, where a single antenna on each pair seeks to communicate via a common receiver aperture at the relay. Therefore, chip interleaving is adopted as a technique to separate the different transmitted signals at the relay node to perform PNC mapping. Accordingly, this scheme relies on the iterative multiuser technique for detection of users at the receiver. The bit error rate (BER) performance of the proposed system is examined under the combined influences of atmospheric loss, turbulence-induced channel fading, and pointing errors (PEs). By adopting the joint PNC mapping with interleaving and multiuser detection techniques, the BER results show that the proposed scheme can achieve a significant performance improvement against the degrading effects of turbulences and PEs. It is also demonstrated that a larger number of simultaneous users can be supported with this new scheme in establishing a communication link between multiple pairs of nodes in two time slots, thereby improving the channel capacity.
Stirring turbulence with turbulence
Cekli, H.E.; Joosten, R.; van de Water, W.
2015-01-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the
Nan, Zhufen; Chi, Xuefen
2016-12-20
The IEEE 802.15.7 protocol suggests that it could coordinate the channel access process based on the competitive method of carrier sensing. However, the directionality of light and randomness of diffuse reflection would give rise to a serious imperfect carrier sense (ICS) problem [e.g., hidden node (HN) problem and exposed node (EN) problem], which brings great challenges in realizing the optical carrier sense multiple access (CSMA) mechanism. In this paper, the carrier sense process implemented by diffuse reflection light is modeled as the choice of independent sets. We establish an ICS model with the presence of ENs and HNs for the multi-point to multi-point visible light communication (VLC) uplink communications system. Considering the severe optical ICS problem, an optical hard core point process (OHCPP) is developed, which characterizes the optical CSMA for the indoor VLC uplink communications system. Due to the limited coverage of the transmitted optical signal, in our OHCPP, the ENs within the transmitters' carrier sense region could be retained provided that they could not corrupt the ongoing communications. Moreover, because of the directionality of both light emitting diode (LED) transmitters and receivers, theoretical analysis of the HN problem becomes difficult. In this paper, we derive the closed-form expression for approximating the outage probability and transmission capacity of VLC networks with the presence of HNs and ENs. Simulation results validate the analysis and also show the existence of an optimal physical carrier-sensing threshold that maximizes the transmission capacity for a given emission angle of LED.
Implications of Navier-Stokes turbulence theory for plasma turbulence
International Nuclear Information System (INIS)
Montgomery, David
1977-01-01
A brief discussion of Navier-Stokes turbulence theory is given with particular reference to the two dimensional case. The MHD turbulence is introduced with possible applications of techniques developed in Navier-Stokes theory. Turbulence in Vlasov plasma is also discussed from the point of view of the ''direct interaction approximation'' (DIA). (A.K.)
Kamada, Ray; Decaria, Alex Joseph
1992-01-01
We present DA, a self-affine, multi-fractal which may become the first routine wave/turbulence discriminant for time series data. Using nocturnal atmospheric data, we show the advantages of D A over self-similar fractals and standard turbulence measures such as FFTs, Richardson number, Brunt-Vaisala frequency, buoyancy length scale, variances, turbulent kinetic energy, and phase averaging. DA also shows promise in resolving "wave-break" events. Since it uses local basis functions, DA may be...
Ansari, Imran Shafique
2013-11-13
In this work, we present a unified performance analysis of a free-space optical (FSO) link that accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection as well as heterodyne detection). More specifically, we present unified exact closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system, all in terms of the Meijer\\'s G function except for the moments that is in terms of simple elementary functions. We then capitalize on these unified results to offer unified exact closed-form expressions for various performance metrics of FSO link transmission systems, such as, the outage probability, the higher-order amount of fading (AF), the average error rate for binary and M-ary modulation schemes, and the ergodic capacity, all in terms of Meijer\\'s G functions except for the higher-order AF that is in terms of simple elementary functions. Additionally, we derive the asymptotic results for all the expressions derived earlier in terms of Meijer\\'s G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer\\'s G function. We also derive new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes in terms of simple elementary functions via utilizing moments. All the presented results are verified via computer-based Monte-Carlo simulations.
Stoll, R., II; Christen, A.; Mahaffee, W.; Salesky, S.; Therias, A.; Caitlin, S.
2017-12-01
Pollution in the form of small particles has a strong impact on a wide variety of urban processes that play an important role in the function of urban ecosystems and ultimately human health and well-being. As a result, a substantial body of research exists on the sources, sinks, and transport characteristics of urban particulate matter. Most of the existing experimental work examining point sources employed gases (e.g., SF6) as the working medium. Furthermore, the focus of most studies has been on the dispersion of pollutants far from the source location. Here, our focus is on the turbulent dispersion of heavy particles in the near source region of a suburban neighborhood. To this end, we conducted a series of heavy particle releases in the Sunset neighborhood of Vancouver, Canada during June, 2017. The particles where dispersed from a near ground point source at two different locations. The Sunset neighborhood is composed mostly of single dwelling detached houses and has been used in numerous previous urban studies. One of the release points was just upwind of a 4-way intersection and the other in the middle of a contiguous block of houses. Each location had a significant density of trees. A minimum of four different successful release events were conducted at each site. During each release, fluorescing micro particles (mean diameter approx. 30 micron) were released from ultrasonic atomizer nozzles for a duration of approximately 20 minutes. The particles where sampled at 50 locations (1.5 m height) in the area downwind of the release over distances from 1-15 times the mean canopy height ( 6 m) using rotating impaction traps. In addition to the 50 sampler locations, instantaneous wind velocities were measured with eight sonic anemometers distributed horizontally and vertically throughout the release area. The resulting particle plume distributions indicate a strong impact of local urban form in the near source region and a high degree of sensitivity to the local
International Nuclear Information System (INIS)
Donnelly, R.J.
1988-01-01
Most flows of fluids, in nature and in technology, are turbulent. Since much of the energy expended by machines and devices that involve fluid flows is spent in overcoming drag caused by turbulence, there is a strong motivation to understand the phenomena. Surprisingly, the peculiar, quantum-mechanical form of turbulence that can form in superfluid helium may turn out to be much simpler to understand that the classical turbulence that forms in normal fluids. It now seems that the study of superfluid turbulence may provide simplified model systems for studying some forms of classical turbulence. There are also practical motivations for studying superfluid turbulence. For example, superfuid helium is often used as a coolant in superconducting machinery. Superfluid turbulence is the primary impediment to the transfer of heat by superfluid helium; an understanding of the phenomena may make it possible to design more efficient methods of refrigeration for superconducting devices. 8 figs
Conditional Eddies in Plasma Turbulence
DEFF Research Database (Denmark)
Johnsen, Helene; Pécseli, Hans; Trulsen, J.
1986-01-01
Conditional structures, or eddies, in turbulent flows are discussed with special attention to electrostatic turbulence in plasmas. The potential variation of these eddies is obtained by sampling the fluctuations only when a certain condition is satisfied in a reference point. The resulting...
Kori, Shivpoojan; Parmar, Ankush; Goyal, Jony; Sharma, Shweta
2018-02-01
A procedure for the determination of Eszopiclone (ESZ) from complex matrices i.e. in vitro (spiked matrices), as well as in vivo (mice model) was developed using cloud point extraction coupled with microwave-assisted back-extraction (CPE-MABE). Analytical measurements have been carried using UV-Visible, HPLC and MS techniques. The proposed method has been validated according to ICH guidelines and legitimate reproducible and reliability of protocol is assessed through intraday and inter-day precision UV-Visible techniques, corresponding to assessed linearity range. The coaservate phase in CPE was back extracted under microwaves exposure, with isooctane at pre-concentration factor ~50 when 5mL of sample solution was pre-concentrated to 0.1mL. Under optimized conditions i.e. Aqueous-Triton X-114 4% (w/v), pH4.0, NaCl 4% (w/v) and equilibrium temperature of 45°C for 20min, average extraction recovery has been obtained between 89.8 and 99.2% and 84.0-99.2% from UV-Visible and HPLC analysis, respectively. The method has been successfully applied to the pharmacokinetic estimation (post intraperitoneal administration) of ESZ in mice. MS analysis precisely depicted the presence of active N‑desmethyl zopiclone in impales as well as in mice plasma. Copyright © 2018 Elsevier B.V. All rights reserved.
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.
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
Revisiting visibility in the plane
DEFF Research Database (Denmark)
Wilkinson, Bryan Thomas
Abstract We consider two closely related problems: computing the region visible from a point amid simple polygonal obstacles and computing the lower envelope of a set of disjoint segments. Visibility problems such as these were proposed and promptly solved in the late'80s and early'90s before...
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
Turbulence-Free Double-slit Interferometer
Smith, Thomas A.; Shih, Yanhua
2018-02-01
Optical turbulence can be detrimental for optical observations. For instance, atmospheric turbulence may reduce the visibility or completely blur out the interference produced by an interferometer in open air. However, a simple two-photon interference theory based on Einstein's granularity picture of light makes a turbulence-free interferometer possible; i.e., any refraction index, length, or phase variations along the optical paths of the interferometer do not have any effect on its interference. Applying this mechanism, the reported experiment demonstrates a two-photon double-slit interference that is insensitive to atmospheric turbulence. The turbulence-free mechanism and especially the turbulence-free interferometer would be helpful in optical observations that require high sensitivity and stability such as for gravitational-wave detection.
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
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.
Turbulent Fluid Motion 6: Turbulence, Nonlinear Dynamics, and Deterministic Chaos
Deissler, Robert G.
1996-01-01
Several turbulent and nonturbulent solutions of the Navier-Stokes equations are obtained. The unaveraged equations are used numerically in conjunction with tools and concepts from nonlinear dynamics, including time series, phase portraits, Poincare sections, Liapunov exponents, power spectra, and strange attractors. Initially neighboring solutions for a low-Reynolds-number fully developed turbulence are compared. The turbulence is sustained by a nonrandom time-independent external force. The solutions, on the average, separate exponentially with time, having a positive Liapunov exponent. Thus, the turbulence is characterized as chaotic. In a search for solutions which contrast with the turbulent ones, the Reynolds number (or strength of the forcing) is reduced. Several qualitatively different flows are noted. These are, respectively, fully chaotic, complex periodic, weakly chaotic, simple periodic, and fixed-point. Of these, we classify only the fully chaotic flows as turbulent. Those flows have both a positive Liapunov exponent and Poincare sections without pattern. By contrast, the weakly chaotic flows, although having positive Liapunov exponents, have some pattern in their Poincare sections. The fixed-point and periodic flows are nonturbulent, since turbulence, as generally understood, is both time-dependent and aperiodic.
On the prediction of turbulent secondary flows
Speziale, C. G.; So, R. M. C.; Younis, B. A.
1992-01-01
The prediction of turbulent secondary flows, with Reynolds stress models, in circular pipes and non-circular ducts is reviewed. Turbulence-driven secondary flows in straight non-circular ducts are considered along with turbulent secondary flows in pipes and ducts that arise from curvature or a system rotation. The physical mechanisms that generate these different kinds of secondary flows are outlined and the level of turbulence closure required to properly compute each type is discussed in detail. Illustrative computations of a variety of different secondary flows obtained from two-equation turbulence models and second-order closures are provided to amplify these points.
Computing visibility on terrains in external memory
Haverkort, H.J.; Toma, L.; Zhuang, Yi
2007-01-01
We describe a novel application of the distribution sweeping technique to computing visibility on terrains. Given an arbitrary viewpoint v, the basic problem we address is computing the visibility map or viewshed of v, which is the set of points in the terrain that are visible from v. We give the
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.
Workshop on Engineering Turbulence Modeling
Povinelli, Louis A. (Editor); Liou, W. W. (Editor); Shabbir, A. (Editor); Shih, T.-H. (Editor)
1992-01-01
Discussed here is the future direction of various levels of engineering turbulence modeling related to computational fluid dynamics (CFD) computations for propulsion. For each level of computation, there are a few turbulence models which represent the state-of-the-art for that level. However, it is important to know their capabilities as well as their deficiencies in order to help engineers select and implement the appropriate models in their real world engineering calculations. This will also help turbulence modelers perceive the future directions for improving turbulence models. The focus is on one-point closure models (i.e., from algebraic models to higher order moment closure schemes and partial differential equation methods) which can be applied to CFD computations. However, other schemes helpful in developing one-point closure models, are also discussed.
International Nuclear Information System (INIS)
Drury, L.O.; Stewart, J.M.
1976-01-01
A generalization of a transformation due to Kurskov and Ozernoi is used to rewrite the usual equations governing subsonic turbulence in Robertson-Walker cosmological models as Navier-Stokes equations with a time-dependent viscosity. This paper first rederives some well-known results in a very simple way by means of this transformation. The main result however is that the establishment of a Kolmogorov spectrum at recombination appears to be incompatible with subsonic turbulence. The conditions after recombination are also discussed briefly. (author)
On characterizing terrain visibility graphs
Directory of Open Access Journals (Sweden)
William Evans
2015-06-01
Full Text Available A terrain is an $x$-monotone polygonal line in the $xy$-plane. Two vertices of a terrain are mutually visible if and only if there is no terrain vertex on or above the open line segment connecting them. A graph whose vertices represent terrain vertices and whose edges represent mutually visible pairs of terrain vertices is called a terrain visibility graph. We would like to find properties that are both necessary and sufficient for a graph to be a terrain visibility graph; that is, we would like to characterize terrain visibility graphs.Abello et al. [Discrete and Computational Geometry, 14(3:331--358, 1995] showed that all terrain visibility graphs are “persistent”. They showed that the visibility information of a terrain point set implies some ordering requirements on the slopes of the lines connecting pairs of points in any realization, and as a step towards showing sufficiency, they proved that for any persistent graph $M$ there is a total order on the slopes of the (pseudo lines in a generalized configuration of points whose visibility graph is $M$.We give a much simpler proof of this result by establishing an orientation to every triple of vertices, reflecting some slope ordering requirements that are consistent with $M$ being the visibility graph, and prove that these requirements form a partial order. We give a faster algorithm to construct a total order on the slopes. Our approach attempts to clarify the implications of the graph theoretic properties on the ordering of the slopes, and may be interpreted as defining properties on an underlying oriented matroid that we show is a restricted type of $3$-signotope.
Sutter, Brad; Brown, Adrian J; Stoker, Carol R
2008-10-01
Sampling of subsurface rock may be required to detect evidence of past biological activity on Mars. The Mars Astrobiology Research and Technology Experiment (MARTE) utilized the Río Tinto region, Spain, as a Mars analog site to test dry drilling technologies specific to Mars that retrieve subsurface rock for biological analysis. This work examines the usefulness of visible-near infrared (VNIR) (450-1000 nm) point spectrometry to characterize ferric iron minerals in core material retrieved during a simulated Mars drilling mission. VNIR spectrometry can indicate the presence of aqueously precipitated ferric iron minerals and, thus, determine whether biological analysis of retrieved rock is warranted. Core spectra obtained during the mission with T1 (893-897 nm) and T2 (644-652 nm) features indicate goethite-dominated samples, while relatively lower wavelength T1 (832-880 nm) features indicate hematite. Hematite/goethite molar ratios varied from 0 to 1.4, and within the 880-898 nm range, T1 features were used to estimate hematite/goethite molar ratios. Post-mission X-ray analysis detected phyllosilicates, which indicates that examining beyond the VNIR (e.g., shortwave infrared, 1000-2500 nm) will enhance the detection of other minerals formed by aqueous processes. Despite the limited spectral range of VNIR point spectrometry utilized in the MARTE Mars drilling simulation project, ferric iron minerals could be identified in retrieved core material, and their distribution served to direct core subsampling for biological analysis.
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...
Improved visibility computation on massive grid terrains
Fishman, J.; Haverkort, H.J.; Toma, L.; Wolfson, O.; Agrawal, D.; Lu, C.-T.
2009-01-01
This paper describes the design and engineering of algorithms for computing visibility maps on massive grid terrains. Given a terrain T, specified by the elevations of points in a regular grid, and given a viewpoint v, the visibility map or viewshed of v is the set of grid points of T that are
Turbulent deflagrations, autoignitions, and detonations
Bradley, Derek
2012-09-01
Measurements of turbulent burning velocities in fan-stirred explosion bombs show an initial linear increase with the fan speed and RMS turbulent velocity. The line then bends over to form a plateau of high values around the maximum attainable burning velocity. A further increase in fan speed leads to the eventual complete quenching of the flame due to increasing localised extinctions because of the flame stretch rate. The greater the Markstein number, the more readily does flame quenching occur. Flame propagation along a duct closed at one end, with and without baffles to increase the turbulence, is subjected to a one-dimensional analysis. The flame, initiated at the closed end of the long duct, accelerates by the turbulent feedback mechanism, creating a shock wave ahead of it, until the maximum turbulent burning velocity for the mixture is attained. With the confining walls, the mixture is compressed between the flame and the shock plane up to the point where it might autoignite. This can be followed by a deflagration to detonation transition. The maximum shock intensity occurs with the maximum attainable turbulent burning velocity, and this defines the limit for autoignition of the mixture. For more reactive mixtures, autoignition can occur at turbulent burning velocities that are less than the maximum attainable one. Autoignition can be followed by quasi-detonation or fully developed detonation. The stability of ensuing detonations is discussed, along with the conditions that may lead to their extinction. © 2012 by Pleiades Publishing, Ltd.
Electron acceleration by turbulent plasmoid reconnection
Zhou, X.; Büchner, J.; Widmer, F.; Muñoz, P. A.
2018-04-01
In space and astrophysical plasmas, like in planetary magnetospheres, as that of Mercury, energetic electrons are often found near current sheets, which hint at electron acceleration by magnetic reconnection. Unfortunately, electron acceleration by reconnection is not well understood yet, in particular, acceleration by turbulent plasmoid reconnection. We have investigated electron acceleration by turbulent plasmoid reconnection, described by MHD simulations, via test particle calculations. In order to avoid resolving all relevant turbulence scales down to the dissipation scales, a mean-field turbulence model is used to describe the turbulence of sub-grid scales and their effects via a turbulent electromotive force (EMF). The mean-field model describes the turbulent EMF as a function of the mean values of current density, vorticity, magnetic field as well as of the energy, cross-helicity, and residual helicity of the turbulence. We found that, mainly around X-points of turbulent reconnection, strongly enhanced localized EMFs most efficiently accelerated electrons and caused the formation of power-law spectra. Magnetic-field-aligned EMFs, caused by the turbulence, dominate the electron acceleration process. Scaling the acceleration processes to parameters of the Hermean magnetotail, electron energies up to 60 keV can be reached by turbulent plasmoid reconnection through the thermal plasma.
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...
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...
Nonexistence of two forms of turbulent bremsstrahlung
International Nuclear Information System (INIS)
Kuijpers, J.; Melrose, D.B.
1985-01-01
It is shown that the forms of turbulent bremsstrahlung proposed by Tsytovich, Stenflo, and Wilhelmsson and by Nambu do not exist. The proposed mechanisms involve upconversion of ion sound turbulence into Langmuir turbulence, with the ion sound waves being emitted and absorbed resonantly and the Langmuir waves being emitted and absorbed nonresonantly. It is pointed out that a symmetry implicit in a standard QED treatment implies that there is another contribution to turbulent bremsstrahlung in addition to that calculated by Tsytovich, Stenflo, and Wilhelmsson and that the two contributions cancel exactly, leading to the null result. (Our arguments on this point have proved controversial.) Nambu made an approximation inconsistently, and when this approximation is not made, two terms in his analytic treatment cancel exactly. We argue that turbulent bremsstrahlung is related to a radiative correction in which the resonant emission of ion sound turbulence is modified by the nonresonant emission and absorption of Langmuir waves. Physically we interpret the nonexistence of turbulent bremsstrahlung as being due to each emission of a Langmuir quantum being associated with an absorption of an identical Langmuir quantum so that the Langmuir turbulence is unchanged. Proposed astrophysical applications of turbulent bremsstrahlung need to be reconsidered
Availability and Reliability of FSO Links Estimated from Visibility
Directory of Open Access Journals (Sweden)
M. Tatarko
2012-06-01
Full Text Available This paper is focused on estimation availability and reliability of FSO systems. Shortcut FSO means Free Space Optics. It is a system which allows optical transmission between two steady points. We can say that it is a last mile communication system. It is an optical communication system, but the propagation media is air. This solution of last mile does not require expensive optical fiber and establishing of connection is very simple. But there are some drawbacks which have a bad influence of quality of services and availability of the link. Number of phenomena in the atmosphere such as scattering, absorption and turbulence cause a large variation of receiving optical power and laser beam attenuation. The influence of absorption and turbulence can be significantly reduced by an appropriate design of FSO link. But the visibility has the main influence on quality of the optical transmission channel. Thus, in typical continental area where rain, snow or fog occurs is important to know their values. This article gives a description of device for measuring weather conditions and information about estimation of availability and reliability of FSO links in Slovakia.
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.
Symposium on turbulence, diffusion, and air pollution, 4th, Reno, NV, January 15-18, 1979, preprints
International Nuclear Information System (INIS)
Anon.
1978-01-01
Papers on turbulence, diffusion and air pollution are presented. Major topics include point-source air quality models, point-source air quality studies, geothermal energy and cooling tower studies, wind energy studies, complex terrain diffusion models, complex terrain diffusion studies, the effects of air pollution on visibility, chemical transformations of pollutants, regional air quality studies, urban air quality studies, boundary layer models and experiments, air pollution removal, air quality studies using remote sensing techniques, large-scale and lakeshore air quality studies, the effects of buildings and terrain features on diffusion, and general air quality and diffusion studies
The roles of turbulence on plasma heating
International Nuclear Information System (INIS)
Kawamura, Takaichi; Kawabe, Takaya.
1976-06-01
In this paper, the characteristic features of the turbulent heating are reviewed, which is considered to be one of the strong candidates of the further heating method in fusion reactor systems, referring to the works in the Institute of Plasma Physics, Nagoya University. The roles of turbulence in plasma heating including toroidal plasma heating are discussed from several points of view. The relation between the heating rate of plasma particles and the thermalization (randomization) frequency is theoretically investigated and the role of plasma turbulence in the fast thermalization is shown. The experimental results on fluctuation and heating of electrons and ions in turbulently heated plasmas are presented. The influence of turbulence, which is responsible for the particle heating, on the diffusion across the confinement magnetic field is considered for the application in the toroidal plasmas. It is pointed out that the turbulent fields in the fast turbulent heating give only a minor effect to the loss of particles across the magnetic field. It can be said that the enhanced fluctuation in turbulent plasma gives its field energy to the plasma particles while it can play the role of the fast thermalization of the ordered motion of particles that is produced in the plasma by some acceleration process. (Kato, T.)
Turbulent flux and the diffusion of passive tracers in electrostatic turbulence
DEFF Research Database (Denmark)
Basu, R.; Jessen, T.; Naulin, V.
2003-01-01
The connection between the diffusion of passive tracer particles and the anomalous turbulent flux in electrostatic drift-wave turbulence is investigated by direct numerical solutions of the 2D Hasegawa-Wakatani equations. The probability density functions for the point-wise and flux surface...
Large Eddy Simulations of Severe Convection Induced Turbulence
Ahmad, Nash'at; Proctor, Fred
2011-01-01
Convective storms can pose a serious risk to aviation operations since they are often accompanied by turbulence, heavy rain, hail, icing, lightning, strong winds, and poor visibility. They can cause major delays in air traffic due to the re-routing of flights, and by disrupting operations at the airports in the vicinity of the storm system. In this study, the Terminal Area Simulation System is used to simulate five different convective events ranging from a mesoscale convective complex to isolated storms. The occurrence of convection induced turbulence is analyzed from these simulations. The validation of model results with the radar data and other observations is reported and an aircraft-centric turbulence hazard metric calculated for each case is discussed. The turbulence analysis showed that large pockets of significant turbulence hazard can be found in regions of low radar reflectivity. Moderate and severe turbulence was often found in building cumulus turrets and overshooting tops.
Haze forms when sunlight encounters particle pollution. It reduces visibility in cities and scenic areas. This web area provides regulatory information and progress towards improving visibility through EPA’s regional haze program.
... cryosections are associated with anatomical terminology. AnatLine : A prototype system consisting of an anatomical image database and ... further information is available Publications VHJOE: Visible Human Journal of Endoscopy. NLM's Current Bibliographies in Medicine, Visible ...
DEFF Research Database (Denmark)
Srba, Jiri
2006-01-01
We investigate the possibility of (bi)simulation-like preorder/equivalence checking on the class of visibly pushdown automata and its natural subclasses visibly BPA (Basic Process Algebra) and visibly one-counter automata. We describe generic methods for proving complexity upper and lower bounds...... for a number of studied preorders and equivalences like simulation, completed simulation, ready simulation, 2-nested simulation preorders/equivalences and bisimulation equivalence. Our main results are that all the mentioned equivalences and preorders are EXPTIME-complete on visibly pushdown automata, PSPACE......-complete on visibly one-counter automata and P-complete on visibly BPA. Our PSPACE lower bound for visibly one-counter automata improves also the previously known DP-hardness results for ordinary one-counter automata and one-counter nets. Finally, we study regularity checking problems for visibly pushdown automata...
Advancements in engineering turbulence modeling
Shih, T.-H.
1991-01-01
Some new developments in two-equation models and second order closure models are presented. Two-equation models (k-epsilon models) have been widely used in computational fluid dynamics (CFD) for engineering problems. Most of low-Reynolds number two-equation models contain some wall-distance damping functions to account for the effect of wall on turbulence. However, this often causes the confusion and difficulties in computing flows with complex geometry and also needs an ad hoc treatment near the separation and reattachment points. A set of modified two-equation models is proposed to remove the aforementioned shortcomings. The calculations using various two-equation models are compared with direct numerical simulations of channel flow and flat boundary layers. Development of a second order closure model is also discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All the existing models poorly predict the normal stresses near the wall and fail to predict the 3-D effect of mean flow on the turbulence (e.g. decrease in the shear stress caused by the cross flow in the boundary layer). The newly developed second order near-wall turbulence model is described and is capable of capturing the near-wall behavior of turbulence as well as the effect of 3-D mean flow on the turbulence.
Global variation of meteor trail plasma turbulence
Directory of Open Access Journals (Sweden)
L. P. Dyrud
2011-12-01
Full Text Available We present the first global simulations on the occurrence of meteor trail plasma irregularities. These results seek to answer the following questions: when a meteoroid disintegrates in the atmosphere, will the resulting trail become plasma turbulent? What are the factors influencing the development of turbulence? and how do these trails vary on a global scale? Understanding meteor trail plasma turbulence is important because turbulent meteor trails are visible as non-specular trails to coherent radars. Turbulence also influences the evolution of specular radar meteor trails; this fact is important for the inference of mesospheric temperatures from the trail diffusion rates, and their usage for meteor burst communication. We provide evidence of the significant effect that neutral atmospheric winds and ionospheric plasma density have on the variability of meteor trail evolution and on the observation of non-specular meteor trails. We demonstrate that trails are far less likely to become and remain turbulent in daylight, explaining several observational trends for non-specular and specular meteor trails.
A dynamics investigation into edge plasma turbulence
International Nuclear Information System (INIS)
Thomsen, H.
2002-08-01
The present experimental work investigates plasma turbulence in the edge region of magnetized high-temperature plasmas. A main topic is the turbulent dynamics parallel to the magnetic field, where hitherto only a small data basis existed, especially for very long scale lengths in the order of ten of meters. A second point of special interest is the coupling of the dynamics parallel and perpendicular to the magnetic field. This anisotropic turbulent dynamics is investigated by two different approaches. Firstly, spatially and temporally high-resolution measurements of fluctuating plasma parameters are investigated by means of two-point correlation analysis. Secondly, the propagation of signals externally imposed into the turbulent plasma background is studied. For both approaches, Langmuir probe arrays were utilized for diagnostic purposes. (orig.)
Fractal dimension and turbulence in Giant HII Regions
International Nuclear Information System (INIS)
Caicedo-Ortiz, H E; Santiago-Cortes, E; López-Bonilla, J; er piso, CP 07738, México D.F (Mexico))" data-affiliation=" (ESFM, Instituto Politécnico Nacional, Edif. 9, 1er piso, CP 07738, México D.F (Mexico))" >Castañeda, H O
2015-01-01
We have measured the fractal dimensions of the Giant HII Regions Hubble X and Hubble V in NGC6822 using images obtained with the Hubble's Wide Field Planetary Camera 2 (WFPC2). These measures are associated with the turbulence observed in these regions, which is quantified through the velocity dispersion of emission lines in the visible. Our results suggest low turbulence behaviour
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...
Turbulence modulation induced by bubble swarm in oscillating-grid turbulence
International Nuclear Information System (INIS)
Morikawa, Koichi; Urano, Shigeyuki; Saito, Takayuki
2007-01-01
In the present study, liquid-phase turbulence modulation induced by a bubble swarm ascending in arbitrary turbulence was experimentally investigated. Liquid-phase homogeneous isotropic turbulence was formed using an oscillating grid in a cylindrical acrylic vessel of 149 mm in inner diameter. A bubble swarm consisting of 19 bubbles of 2.8 mm in equivalent diameter was examined; the bubble size and launching time were completely controlled using a bubble launching device through audio speakers. This bubble launching device was able to repeatedly control the bubble swarm arbitrarily and precisely. The bubble swarm was launched at a frequency of 4 Hz. The liquid phase motion was measured via two LDA (Laser Doppler Anemometer) probes. The turbulence intensity, spatial correlation and integral scale were calculated from LDA data obtained by the two spatially-separate-point measurement. When the bubble swarm was added, the turbulence intensity dramatically changed. The original isotropic turbulence was modulated to the anisotropic turbulence by the mutual interference between the bubble swarm and ambient isotropic turbulence. The integral scales were calculated from the spatial correlation function. The effects of the bubble swarm on the integral scales showed the tendencies similar to those on turbulence intensity. (author)
DEFF Research Database (Denmark)
Brand, Arno J.; Peinke, Joachim; Mann, Jakob
2011-01-01
The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed.......The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed....
International Nuclear Information System (INIS)
Goldman, M.V.
1984-01-01
After a brief discussion of beam-excited Langmuir turbulence in the solar wind, we explain the criteria for wave-particle, three-wave and strong turbulence interactions. We then present the results of a numerical integration of the Zakharov equations, which describe the strong turbulence saturation of a weak (low-density) high energy, bump-on-tail beam instability. (author)
Multifractal aspects of the scaling laws in fully developed compressible turbulence
International Nuclear Information System (INIS)
Shivamoggi, B.K.
1995-01-01
In this paper, multifractal aspects of the scalings laws in fully developed compressible turbulence are considered. Compressibility effects on known results of incompressible turbulence are pointed out. copyright 1995 Academic Press, Inc
5th European Turbulence Conference
1995-01-01
Under the auspices of the Euromech Committee, the Fifth European Turbulence Conference was held in Siena on 5-8 July 1994. Following the previous ETC meeting in Lyon (1986), Berlin (1988), Stockholm (1990) and Delft (1992), the Fifth ETC was aimed at providing a review of the fundamental aspects of turbulence from a theoretical, numerical and experimental point of view. In the magnificent town of Siena, more than 250 scientists from all over the world, spent four days discussing new ideas on turbulence. As a research worker in the field of turbulence, I must say that the works presented at the Conference, on which this book is based, covered almost all areas in this field. I also think that this book provides a major opportunity to have a complete overview of the most recent research works. I am extremely grateful to Prof. C. Cercignani, Dr. M. Loffredo, and Prof. R. Piva who, as members of the local organizing committee, share the success of the Conference. I also want to thank Mrs. Liu' Catena, for her inva...
Progress in turbulence research
International Nuclear Information System (INIS)
Bradshaw, P.
1990-01-01
Recent developments in experiments and eddy simulations, as an introduction to a discussion of turbulence modeling for engineers is reviewed. The most important advances in the last decade rely on computers: microcomputers to control laboratory experiments, especially for multidimensional imaging, and supercomputers to simulate turbulence. These basic studies in turbulence research are leading to genuine breakthroughs in prediction methods for engineers and earth scientists. The three main branches of turbulence research: experiments, simulations (numerically-accurate three-dimensional, time-dependent solutions of the Navier-Stokes equations, with any empiricism confined to the smallest eddies), and modeling (empirical closure of time-averaged equations for turbulent flow) are discussed. 33 refs
Visibility and Citation Impact
Ebrahim, Nader Ale; Salehi, Hadi; Embi, Mohamed Amin; Tanha, Farid Habibi; Gholizadeh, Hossein; Motahar, Seyed Mohammad
2014-01-01
The number of publications is the first criteria for assessing a researcher output. However, the main measurement for author productivity is the number of citations, and citations are typically related to the paper's visibility. In this paper, the relationship between article visibility and the number of citations is investigated. A case study of…
Viewer Makes Radioactivity "Visible"
Yin, L. I.
1983-01-01
Battery operated viewer demonstrates feasibility of generating threedimensional visible light simulations of objects that emit X-ray or gamma rays. Ray paths are traced for two pinhold positions to show location of reconstructed image. Images formed by pinholes are converted to intensified visible-light images. Applications range from radioactivity contamination surveys to monitoring radioisotope absorption in tumors.
Homogeneous turbulence dynamics
Sagaut, Pierre
2018-01-01
This book provides state-of-the-art results and theories in homogeneous turbulence, including anisotropy and compressibility effects with extension to quantum turbulence, magneto-hydodynamic turbulence and turbulence in non-newtonian fluids. Each chapter is devoted to a given type of interaction (strain, rotation, shear, etc.), and presents and compares experimental data, numerical results, analysis of the Reynolds stress budget equations and advanced multipoint spectral theories. The role of both linear and non-linear mechanisms is emphasized. The link between the statistical properties and the dynamics of coherent structures is also addressed. Despite its restriction to homogeneous turbulence, the book is of interest to all people working in turbulence, since the basic physical mechanisms which are present in all turbulent flows are explained. The reader will find a unified presentation of the results and a clear presentation of existing controversies. Special attention is given to bridge the results obta...
DEFF Research Database (Denmark)
Gilling, Lasse
of resolved inflow turbulence on airfoil simulations in CFD. The detached-eddy simulation technique is used because it can resolve the inflow turbulence without becoming too computationally expensive due to its limited requirements for mesh resolution in the boundary layer. It cannot resolve the turbulence......Wind turbines operate in inflow turbulence whether it originates from the shear in the atmospheric boundary layer or from the wake of other wind turbines. Consequently, the airfoils of the wings experience turbulence in the inflow. The main topic of this thesis is to investigate the effect...... that is formed in attached boundary layers, but the freestream turbulence can penetrate the boundary layer. The idea is that the resolved turbulence from the freestream should mix high momentum flow into the boundary layer and thereby increase the resistance against separation and increase the maximum lift...
Query Load Balancing For Visible Object Extraction
DEFF Research Database (Denmark)
Bukauskas, Linas; Bøhlen, Michael Hanspeter
2004-01-01
Interactive visual data explorations impose rigid real-time requirements on the extraction of visible objects. Often these requirements are met by deploying powerful hardware that maintains the entire data set in huge main memory structures. In this paper we propose an approach that retrieves...... the visible data on demand and is based on a tight integration of the database and visualization systems. We propose to incrementally adjust the observer path by adding and dropping path points. The result is an optimal path that minimizes the interaction with the database system and retrieves all visible...
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.
Turbulence-chemistry interactions in reacting flows
Energy Technology Data Exchange (ETDEWEB)
Barlow, R.S.; Carter, C.D. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
Interactions between turbulence and chemistry in nonpremixed flames are investigated through multiscalar measurements. Simultaneous point measurements of major species, NO, OH, temperature, and mixture fraction are obtained by combining spontaneous Raman scattering, Rayleigh scattering, and laser-induced fluorescence (LIF). NO and OH fluorescence signals are converted to quantitative concentrations by applying shot-to-shot corrections for local variations of the Boltzmann fraction and collisional quenching rate. These measurements of instantaneous thermochemical states in turbulent flames provide insights into the fundamental nature of turbulence-chemistry interactions. The measurements also constitute a unique data base for evaluation and refinement of turbulent combustion models. Experimental work during the past year has focused on three areas: (1) investigation of the effects of differential molecular diffusion in turbulent combustion: (2) experiments on the effects of Halon CF{sub 3}Br, a fire retardant, on the structure of turbulent flames of CH{sub 4} and CO/H{sub 2}/N{sub 2}; and (3) experiments on NO formation in turbulent hydrogen jet flames.
Analyzing Visibility Configurations.
Dachsbacher, C
2011-04-01
Many algorithms, such as level of detail rendering and occlusion culling methods, make decisions based on the degree of visibility of an object, but do not analyze the distribution, or structure, of the visible and occluded regions across surfaces. We present an efficient method to classify different visibility configurations and show how this can be used on top of existing methods based on visibility determination. We adapt co-occurrence matrices for visibility analysis and generalize them to operate on clusters of triangular surfaces instead of pixels. We employ machine learning techniques to reliably classify the thus extracted feature vectors. Our method allows perceptually motivated level of detail methods for real-time rendering applications by detecting configurations with expected visual masking. We exemplify the versatility of our method with an analysis of area light visibility configurations in ray tracing and an area-to-area visibility analysis suitable for hierarchical radiosity refinement. Initial results demonstrate the robustness, simplicity, and performance of our method in synthetic scenes, as well as real applications.
Statistical Mechanics of Turbulent Flows
International Nuclear Information System (INIS)
Cambon, C
2004-01-01
This is a handbook for a computational approach to reacting flows, including background material on statistical mechanics. In this sense, the title is somewhat misleading with respect to other books dedicated to the statistical theory of turbulence (e.g. Monin and Yaglom). In the present book, emphasis is placed on modelling (engineering closures) for computational fluid dynamics. The probabilistic (pdf) approach is applied to the local scalar field, motivated first by the nonlinearity of chemical source terms which appear in the transport equations of reacting species. The probabilistic and stochastic approaches are also used for the velocity field and particle position; nevertheless they are essentially limited to Lagrangian models for a local vector, with only single-point statistics, as for the scalar. Accordingly, conventional techniques, such as single-point closures for RANS (Reynolds-averaged Navier-Stokes) and subgrid-scale models for LES (large-eddy simulations), are described and in some cases reformulated using underlying Langevin models and filtered pdfs. Even if the theoretical approach to turbulence is not discussed in general, the essentials of probabilistic and stochastic-processes methods are described, with a useful reminder concerning statistics at the molecular level. The book comprises 7 chapters. Chapter 1 briefly states the goals and contents, with a very clear synoptic scheme on page 2. Chapter 2 presents definitions and examples of pdfs and related statistical moments. Chapter 3 deals with stochastic processes, pdf transport equations, from Kramer-Moyal to Fokker-Planck (for Markov processes), and moments equations. Stochastic differential equations are introduced and their relationship to pdfs described. This chapter ends with a discussion of stochastic modelling. The equations of fluid mechanics and thermodynamics are addressed in chapter 4. Classical conservation equations (mass, velocity, internal energy) are derived from their
International Nuclear Information System (INIS)
Hofmann, J.V.
1991-12-01
In this report visible spectroscopy and impurity investigations on ASDEX are reviewed and several sets of visible spectra are presented. As a basis for identification of metallic impurity lines during plasma discharges spectra from a stainless steel - Cu arc have been recorded. In a next step a spectrum overview of ASDEX discharges is shown which reveals the dominating role of lines from light impurities like carbon and oxygen throughout the UV and visible range (2000 A ≤ λ ≤ 8000 A). Metallic impurity lines of neutrals or single ionized atoms are observed near localized surfaces. The dramatic effect of impurity reduction by boronization of the vessel walls is demonstrated in a few examples. In extension to some ivesti-gations already published, further diagnostic applications of visible spectroscopy are presented. Finally, the hardware and software system used on ASDEX are described in detail. (orig.)
Turbulence generation by waves
Energy Technology Data Exchange (ETDEWEB)
Kaftori, D.; Nan, X.S.; Banerjee, S. [Univ. of California, Santa Barbara, CA (United States)
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
Investigation of plasma turbulence in a theta-pinch-discharge
International Nuclear Information System (INIS)
Lins, G.
1980-01-01
This thesis is concerned with investigations of plasma turbulence in a 3 KJ Theta-Pinch during implosion by high-frequency Stark-effect and Thomson scattering. The next points are modifications of electron-distribution function by ionization in low preionizized turbulent plasma and energy losses by particle flow and heat flow at the ends. (HT)
On the Space-Time Structure of Sheared Turbulence
DEFF Research Database (Denmark)
de Mare, Martin Tobias; Mann, Jakob
2016-01-01
We develop a model that predicts all two-point correlations in high Reynolds number turbulent flow, in both space and time. This is accomplished by combining the design philosophies behind two existing models, the Mann spectral velocity tensor, in which isotropic turbulence is distorted according......-assisted feed forward control and wind-turbine wake modelling....
Plasma Turbulence General Topics
Energy Technology Data Exchange (ETDEWEB)
Kadomtsev, B. B. [Nuclear Energy Institute, Academy of Sciences of the USSR, Moscow, USSR (Russian Federation)
1965-06-15
It is known that under experimental conditions plasma often shows chaotic motion. Such motion, when many degrees of freedom are excited to levels considerably above the thermal level, will be called turbulent. The properties of turbulent plasma in many respects differ from the properties of laminar plasma. It can be said that the appearance of various anomalies in plasma behaviour indicates the presence of turbulence in plasma. In order to verify directly the presence of turbulent motion in plasma we must, however, measure the fluctuation of some microscopic parameters in plasma.
Turbulence modeling and surface heat transfer in a stagnation flow region
Wang, C. R.; Yeh, F. C.
1987-01-01
Analysis for the turbulent flow field and the effect of freestream turbulence on the surface heat transfer rate of a stagnation flow is presented. The emphasis is on modeling and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow.
Richardson effects in turbulent buoyant flows
Biggi, Renaud; Blanquart, Guillaume
2010-11-01
Rayleigh Taylor instabilities are found in a wide range of scientific fields from supernova explosions to underwater hot plumes. The turbulent flow is affected by the presence of buoyancy forces and may not follow the Kolmogorov theory anymore. The objective of the present work is to analyze the complex interactions between turbulence and buoyancy. Towards that goal, simulations have been performed with a high order, conservative, low Mach number code [Desjardins et. al. JCP 2010]. The configuration corresponds to a cubic box initially filled with homogeneous isotropic turbulence with heavy fluid on top and light gas at the bottom. The initial turbulent field was forced using linear forcing up to a Reynolds number of Reλ=55 [Meneveau & Rosales, POF 2005]. The Richardson number based on the rms velocity and the integral length scale was varied from 0.1 to 10 to investigate cases with weak and strong buoyancy. Cases with gravity as a stabilizer of turbulence (gravity pointing up) were also considered. The evolution of the turbulent kinetic energy and the total kinetic energy was analyzed and a simple phenomenological model was proposed. Finally, the energy spectra and the isotropy of the flow were also investigated.
Turbulence generation through intense kinetic energy sources
Maqui, Agustin F.; Donzis, Diego A.
2016-06-01
Direct numerical simulations (DNS) are used to systematically study the development and establishment of turbulence when the flow is initialized with concentrated regions of intense kinetic energy. This resembles both active and passive grids which have been extensively used to generate and study turbulence in laboratories at different Reynolds numbers and with different characteristics, such as the degree of isotropy and homogeneity. A large DNS database was generated covering a wide range of initial conditions with a focus on perturbations with some directional preference, a condition found in active jet grids and passive grids passed through a contraction as well as a new type of active grid inspired by the experimental use of lasers to photo-excite the molecules that comprise the fluid. The DNS database is used to assert under what conditions the flow becomes turbulent and if so, the time required for this to occur. We identify a natural time scale of the problem which indicates the onset of turbulence and a single Reynolds number based exclusively on initial conditions which controls the evolution of the flow. It is found that a minimum Reynolds number is needed for the flow to evolve towards fully developed turbulence. An extensive analysis of single and two point statistics, velocity as well as spectral dynamics and anisotropy measures is presented to characterize the evolution of the flow towards realistic turbulence.
Predicting visibility of aircraft.
Directory of Open Access Journals (Sweden)
Andrew Watson
Full Text Available Visual detection of aircraft by human observers is an important element of aviation safety. To assess and ensure safety, it would be useful to be able to be able to predict the visibility, to a human observer, of an aircraft of specified size, shape, distance, and coloration. Examples include assuring safe separation among aircraft and between aircraft and unmanned vehicles, design of airport control towers, and efforts to enhance or suppress the visibility of military and rescue vehicles. We have recently developed a simple metric of pattern visibility, the Spatial Standard Observer (SSO. In this report we examine whether the SSO can predict visibility of simulated aircraft images. We constructed a set of aircraft images from three-dimensional computer graphic models, and measured the luminance contrast threshold for each image from three human observers. The data were well predicted by the SSO. Finally, we show how to use the SSO to predict visibility range for aircraft of arbitrary size, shape, distance, and coloration.
Measuring visibility using smartphones
Friesen, Jan; Bialon, Raphael; Claßen, Christoph; Graffi, Kalman
2017-04-01
Spatial information on fog density is an important parameter for ecohydrological studies in cloud forests. The Dhofar cloud forest in Southern Oman exhibits a close interaction between the fog, trees, and rainfall. During the three month monsoon season the trees capture substantial amounts of horizontal precipitation from fog which increases net precipitation below the tree canopy. As fog density measurements are scarce, a smartphone app was designed to measure visibility. Different smartphone units use a variety of different parts. It is therefore important to assess the developed visibility measurement across a suite of different smartphones. In this study we tested five smartphones/ tablets (Google/ LG Nexus 5X, Huawei P8 lite, Huawei Y3, HTC Nexus 9, and Samsung Galaxy S4 mini) against digital camera (Sony DLSR-A900) and visual visibility observations. Visibility was assessed from photos using image entropy, from the number of visible targets, and from WiFi signal strength using RSSI. Results show clear relationships between object distance and fog density, yet a considerable spread across the different smartphone/ tablet units is evident.
PDF Modeling of Turbulent Combustion
National Research Council Canada - National Science Library
Pope, Stephen B
2006-01-01
.... The PDF approach to turbulent combustion has the advantages of fully representing the turbulent fluctuations of species and temperature, and of allowing realistic combustion chemistry to be implemented...
Kinetic features of interchange turbulence
International Nuclear Information System (INIS)
Sarazin, Y; Grandgirard, V; Fleurence, E; Garbet, X; Ghendrih, Ph; Bertrand, P; Depret, G
2005-01-01
Non-linear gyrokinetic simulations of the interchange instability are discussed. The semi-Lagrangian numerical scheme allows one to address two critical points achieved with simulations lasting several confinement times: an accurate statistical analysis of the fluctuations and the back reaction of the turbulence on equilibrium profiles. Zonal flows are found to quench a 2D + 1D interchange turbulence when one of the species has a vanishing response to zonal modes. Conversely, when streamers dominate, the equilibrium profiles are found to be stiff. In the non-linear regime and steady-state turbulence, the distribution function exhibits a significant departure from a Maxwellian distribution. This property is characterized by an expansion on generalized Laguerre functions with a slow decay of the series of moments. This justifies the use of gyrokinetic simulations since a standard fluid approach, based on a limited number of moments, would certainly require a complex closure so as to take into account the impact of these non-vanishing high order moments
International Nuclear Information System (INIS)
Vorotyntsev, M.A.
1991-01-01
Key problems of turbulent mass transfer at a solid wall are reviewed: closure problem for the concentration field, information on wall turbulence, applications of microelectrodes to study the structure of turbulence, correlation properties of current fluctuations. (author). 26 refs
Turbulence modelling; Modelisation de la turbulence isotherme
Energy Technology Data Exchange (ETDEWEB)
Laurence, D. [Electricite de France (EDF), Direction des Etudes et Recherches, 92 - Clamart (France)
1997-12-31
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-{epsilon} two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the `standard` (R{sub ij}-{epsilon}) 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). 37 refs.
Nagendra Prakash, Vivek
2013-01-01
This thesis deals with the broad topic of particles in turbulence, which has applications in a diverse number of fields. A vast majority of fluid flows found in nature and in the industry are turbulent and contain dispersed elements. In this thesis, I have focused on light particles (air bubbles in
Dynamic paradigm of turbulence
International Nuclear Information System (INIS)
Mukhamedov, Alfred M.
2006-01-01
In this paper a dynamic paradigm of turbulence is proposed. The basic idea consists in the novel definition of chaotic structure given with the help of Pfaff system of PDE associated with the turbulent dynamics. A methodological analysis of the new and the former paradigm is produced
Measurements of Turbulent Flame Speed and Integral Length Scales in a Lean Stationary Premixed Flame
Klingmann, Jens; Johansson, Bengt
1998-01-01
Turbulent premixed natural gas - air flame velocities have been measured in a stationary axi-symmetric burner using LDA. The flame was stabilized by letting the flow retard toward a stagnation plate downstream of the burner exit. Turbulence was generated by letting the flow pass through a plate with drilled holes. Three different hole diameters were used, 3, 6 and 10 mm, in order to achieve different turbulent length scales. Turbulent integral length scales were measured using two-point LD...
UVISS preliminary visibility analysis
DEFF Research Database (Denmark)
Betto, Maurizio
1998-01-01
The goal of this work is to obtain a preliminary assessment of the sky visibility for anastronomical telescope located on the express pallet of the International SpaceStation (ISS)} taking into account the major constraints imposed on the instrument by the ISSattitude and structure. Part of the w......The goal of this work is to obtain a preliminary assessment of the sky visibility for anastronomical telescope located on the express pallet of the International SpaceStation (ISS)} taking into account the major constraints imposed on the instrument by the ISSattitude and structure. Part...... of the work is also to setup the kernel of a software tool for the visibility analysis thatshould be easily expandable to consider more complex strucures for future activities.This analysis is part of the UVISS assessment study and it is meant to provide elementsfor the definition and the selection...
Dissipation element analysis of turbulent scalar fields
International Nuclear Information System (INIS)
Wang Lipo; Peters, Norbert
2008-01-01
Dissipation element analysis is a new approach for studying turbulent scalar fields. Gradient trajectories starting from each material point in a scalar field Φ'(x-vector,t) in ascending directions will inevitably reach a maximal and a minimal point. The ensemble of material points sharing the same pair ending points is named a dissipation element. Dissipation elements can be parameterized by the length scale l and the scalar difference Δφ ', which are defined as the straight line connecting the two extremal points and the scalar difference at these points, respectively. The decomposition of a turbulent field into dissipation elements is space-filling. This allows us to reconstruct certain statistical quantities of fine scale turbulence which cannot be obtained otherwise. The marginal probability density function (PDF) of the length scale distribution based on a Poisson random cutting-reconnection process shows satisfactory agreement with the direct numerical simulation (DNS) results. In order to obtain the further information that is needed for the modeling of scalar mixing in turbulence, such as the marginal PDF of the length of elements and all conditional moments as well as their scaling exponents, there is a need to model the joint PDF of l and Δφ ' as well. A compensation-defect model is put forward in this work to show the dependence of Δφ ' on l. The agreement between the model prediction and DNS results is satisfactory, which may provide another explanation of the Kolmogorov scaling and help to improve turbulent mixing models. Furthermore, intermittency and cliff structure can also be related to and explained from the joint PDF.
Making Invisible Forces Visible
DEFF Research Database (Denmark)
Ratner, Helene Gad
2013-01-01
This paper investigates managerial tactics of visualisation when a need to know and manage employees' values and attitudes is expressed. Using the Danish public school as a case study, we explore how school managers use teachers' emotions to render visible presumably invisible information about...... their 'true' attitudes and values. The paper draws on theories of affect as well as actor-network theory to analyse three incidents where managers turn their interpretations of teachers' emotions into such information. These incidents suggest that the efforts to render employees' attitudes and values visible...
Behaviour of turbulence models near a turbulent/non-turbulent interface revisited
International Nuclear Information System (INIS)
Ferrey, P.; Aupoix, B.
2006-01-01
The behaviour of turbulence models near a turbulent/non-turbulent interface is investigated. The analysis holds as well for two-equation as for Reynolds stress turbulence models using Daly and Harlow diffusion model. The behaviour near the interface is shown not to be a power law, as usually considered, but a more complex parametric solution. Why previous works seemed to numerically confirm the power law solution is explained. Constraints for turbulence modelling, i.e., for ensuring that models have a good behaviour near a turbulent/non-turbulent interface so that the solution is not sensitive to small turbulence levels imposed in the irrotational flow, are drawn
Accessibility analysis in manufacturing processes using visibility cones
Institute of Scientific and Technical Information of China (English)
尹周平; 丁汉; 熊有伦
2002-01-01
Accessibility is a kind of important design feature of products,and accessibility analysis has been acknowledged as a powerful tool for solving computational manufacturing problems arising from different manufacturing processes.After exploring the relations among approachability,accessibility and visibility,a general method for accessibility analysis using visibility cones (VC) is proposed.With the definition of VC of a point,three kinds of visibility of a feature,namely complete visibility cone (CVC),partial visibility cone (PVC) and local visibility cone (LVC),are defined.A novel approach to computing VCs is formulated by identifying C-obstacles in the C-space,for which a general and efficient algorithm is proposed and implemented by making use of visibility culling.Lastly,we discuss briefly how to realize accessibility analysis in numerically controlled (NC) machining planning,coordinate measuring machines (CMMs) inspection planning and assembly sequence planning with the proposed methods.
The dynamics of variable-density turbulence
International Nuclear Information System (INIS)
Sandoval, D.L.
1995-11-01
The dynamics of variable-density turbulent fluids are studied by direct numerical simulation. The flow is incompressible so that acoustic waves are decoupled from the problem, and implying that density is not a thermodynamic variable. Changes in density occur due to molecular mixing. The velocity field, is in general, divergent. A pseudo-spectral numerical technique is used to solve the equations of motion. Three-dimensional simulations are performed using a grid size of 128 3 grid points. Two types of problems are studied: (1) the decay of isotropic, variable-density turbulence, and (2) buoyancy-generated turbulence in a fluid with large density fluctuations. In the case of isotropic, variable-density turbulence, the overall statistical decay behavior, for the cases studied, is relatively unaffected by the presence of density variations when the initial density and velocity fields are statistically independent. The results for this case are in quantitative agreement with previous numerical and laboratory results. In this case, the initial density field has a bimodal probability density function (pdf) which evolves in time towards a Gaussian distribution. The pdf of the density field is symmetric about its mean value throughout its evolution. If the initial velocity and density fields are statistically dependent, however, the decay process is significantly affected by the density fluctuations. For the case of buoyancy-generated turbulence, variable-density departures from the Boussinesq approximation are studied. The results of the buoyancy-generated turbulence are compared with variable-density model predictions. Both a one-point (engineering) model and a two-point (spectral) model are tested against the numerical data. Some deficiencies in these variable-density models are discussed and modifications are suggested
Eaton, John; Hwang, Wontae; Cabral, Patrick
2002-11-01
the addition of gravity as a variable parameter may help us to better understand the physics of turbulence attenuation. The experiments are conducted in a turbulence chamber capable of producing stationary or decaying isotropic turbulence with nearly zero mean flow and Taylor microscale Reynolds numbers up to nearly 500. The chamber is a 410 mm cubic box with the corners cut off to make it approximately spherical. Synthetic jet turbulence generators are mounted in each of the eight corners of the box. Each generator consists of a loudspeaker forcing a plenum and producing a pulsed jet through a 20 mm diameter orifice. These synthetic jets are directed into ejector tubes pointing towards the chamber center. The ejector tubes increase the jet mass flow and decrease the velocity. The jets then pass through a turbulence grid. Each of the eight loudspeakers is forced with a random phase and frequency. The resulting turbulence is highly Isotropic and matches typical behavior of grid turbulence. Measurements of both phases are acquired using particle image velocimetry (PIV). The gas is seeded with approximately 1 micron diameter seeding particles while the solid phase is typically 150 micron diameter spherical glass particles. A double-pulsed YAG laser and a Kodak ES-1.0 10-bit PIV camera provide the PIV images. Custom software is used to separate the images into individual images containing either gas-phase tracers or large particles. Modern high-resolution PIV algorithms are then used to calculate the velocity field. A large set of image pairs are acquired for each case, then the results are averaged both spatially and over the ensemble of acquired images. The entire apparatus is mounted in two racks which are carried aboard NASA's KC-135 Flying Microgravity Laboratory. The rack containing the turbulence chamber, the laser head, and the camera floats freely in the airplane cabin (constrained by competent NASA personnel) to minimize g-jitter.
Making Invisible Histories Visible
Hanssen, Ana Maria
2012-01-01
This article features Omaha Public Schools' "Making Invisible Histories Visible" program, or MIHV. Omaha's schools have a low failure rate among 8th graders but a high one among high school freshmen. MIHV was created to help at-risk students "adjust to the increased demands of high school." By working alongside teachers and…
Hikmet, R.A.M.
2007-01-01
Diode lasers can be found in various applications most notably in optical communication and optical storage. Visible lasers were until recently were all based on IR diode lasers. Using GaN, directly blue and violet emitting lasers have also been introduced to the market mainly in the area of optical
Turbulent current drive mechanisms
McDevitt, Christopher J.; Tang, Xian-Zhu; Guo, Zehua
2017-08-01
Mechanisms through which plasma microturbulence can drive a mean electron plasma current are derived. The efficiency through which these turbulent contributions can drive deviations from neoclassical predictions of the electron current profile is computed by employing a linearized Coulomb collision operator. It is found that a non-diffusive contribution to the electron momentum flux as well as an anomalous electron-ion momentum exchange term provide the most efficient means through which turbulence can modify the mean electron current for the cases considered. Such turbulent contributions appear as an effective EMF within Ohm's law and hence provide an ideal means for driving deviations from neoclassical predictions.
Belotserkovskii, OM; Chechetkin, VM
2005-01-01
The authors present the results of numerical experiments carried out to examine the problem of development of turbulence and convection. On the basis of the results, they propose a physical model of the development of turbulence. Numerical algorithms and difference schema for carrying out numerical experiments in hydrodynamics, are proposed. Original algorithms, suitable for calculation of the development of the processes of turbulence and convection in different conditions, even on astrophysical objects, are presented. The results of numerical modelling of several important phenomena having both fundamental and applied importance are described.
Energy Technology Data Exchange (ETDEWEB)
Hoejstrup, J [NEG Micon Project Development A/S, Randers (Denmark); Hansen, K S [Denmarks Technical Univ., Dept. of Energy Engineering, Lyngby (Denmark); Pedersen, B J [VESTAS Wind Systems A/S, Lem (Denmark); Nielsen, M [Risoe National Lab., Wind Energy and Atmospheric Physics, Roskilde (Denmark)
1999-03-01
The pdf`s of atmospheric turbulence have somewhat wider tails than a Gaussian, especially regarding accelerations, whereas velocities are close to Gaussian. This behaviour is being investigated using data from a large WEB-database in order to quantify the amount of non-Gaussianity. Models for non-Gaussian turbulence have been developed, by which artificial turbulence can be generated with specified distributions, spectra and cross-correlations. The artificial time series will then be used in load models and the resulting loads in the Gaussian and the non-Gaussian cases will be compared. (au)
Radio propagation through the turbulent interstellar plasma
International Nuclear Information System (INIS)
Rickett, B.J.
1990-01-01
The current understanding of interstellar scattering is reviewed, and its impact on radio astronomy is examined. The features of interstellar plasma turbulence are also discussed. It is concluded that methods involving the investigation of the flux variability of pulsars and extragalactic sources and the VLBI visibility curves constitute new techniques for probing the ISM. However, scattering causes a seeing limitation in radio observations. It is now clear that variation due to RISS (refractive interstellar scintillations) is likely to be important for several classes of variable sources, especially low-frequency variables and centimeter-wave flickering. 168 refs
Modeling of turbulent chemical reaction
Chen, J.-Y.
1995-01-01
Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.
Aviation turbulence processes, detection, prediction
Lane, Todd
2016-01-01
Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance.
Turbulent buoyant jets and plumes
Rodi, Wolfgang
The Science & Applications of Heat and Mass Transfer: Reports, Reviews, & Computer Programs, Volume 6: Turbulent Buoyant Jets and Plumes focuses on the formation, properties, characteristics, and reactions of turbulent jets and plumes. The selection first offers information on the mechanics of turbulent buoyant jets and plumes and turbulent buoyant jets in shallow fluid layers. Discussions focus on submerged buoyant jets into shallow fluid, horizontal surface or interface jets into shallow layers, fundamental considerations, and turbulent buoyant jets (forced plumes). The manuscript then exami
Heated water jet in coflowing turbulent stream
International Nuclear Information System (INIS)
Shirazi, M.A.; McQuivey, R.S.; Keefer, T.N.
1974-01-01
Effects of ambient turbulence on temperature and salinity distributions of heated water and neutrally buoyant saltwater jets were studied for a wide range of densimetric jet Froude numbers, jet discharge velocities, and ambient turbulence levels in a 4-ft-wide channel. Estimates of vertical and lateral diffusivity coefficients for heat and for salt were obtained from salinity and temperature distributions taken at several stations downstream of the injection point. Readily usable correlations are presented for plume center-line temperature, plume width, and trajectory. The ambient turbulence affects the gross behavior characteristics of the plume. The effects vary with the initial jet Froude number and the jet to ambient velocity ratio. Heat and salinity are transported similarly and the finite source dimensions and the initial jet characteristics alter the numerical value of the diffusivity
Visible imaging of edge fluctuations in TFTR
International Nuclear Information System (INIS)
Zweben, S.J.; Medley, S.S.
1989-03-01
Images of the visible light emission from the inner wall region of TFTR have been made using a rapidly gated, intensified TV camera. Strong ''filamentation'' of the neutral deuterium Dα light is observed when the camera gating time is <100 μsec during neutral-beam-heated discharges. These turbulent filaments vary in position randomly vs. time and have a poloidal wavelength of ∼3-5 cm which is much shorter than their parallel wavelength of ∼100 cm. A second and new type of edge fluctuation phenomenon, which we call a ''merfe,'' is also described. Merfes are a regular poloidal pattern of toroidally symmetric, small-scale marfes which move away from the inner midplane during the current decay after neutral beam injection. Some tentative interpretations of these two phenomena are presented. 27 refs., 8 figs
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-11-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
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.
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-01-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
DEFF Research Database (Denmark)
Uldam, Julie
2018-01-01
of activists remains under-researched. This article examines BP’s surveillance of activists who criticise the company’s corporate social responsibility (CSR) programme as ‘greenwashing’. In this way, it goes beyond corporations’ uses of big data and instead explores how they monitor and discuss strategies......As activists move from alternative media platforms to commercial social media platforms, they face increasing challenges in protecting their online security and privacy. While government surveillance of activists is well-documented in scholarly research and the media, corporate surveillance...... for responding to the activities of individual activists in social media. It shows that while social media afford an unprecedented level of visibility for activists, it comes with the risk of being monitored by corporations. Theoretically, it draws on conceptions of visibility in social sciences and media...
Goodhew, Julie; Pahl, Sabine; Auburn, Tim; Goodhew, Steve
2015-01-01
Householders play a role in energy conservation through the decisions they make about purchases and installations such as insulation, and through their habitual behavior. The present U.K. study investigated the effect of thermal imaging technology on energy conservation, by measuring the behavioral effect after householders viewed images of heat escaping from or cold air entering their homes. In Study 1 (n = 43), householders who received a thermal image reduced their energy use at a 1-year follow-up, whereas householders who received a carbon footprint audit and a non-intervention control demonstrated no change. In Study 2 (n = 87), householders were nearly 5 times more likely to install draught proofing measures after seeing a thermal image. The effect was especially pronounced for actions that addressed an issue visible in the images. Findings indicate that using thermal imaging to make heat loss visible can promote energy conservation. PMID:26635418
Turbulence Generation in Combustion.
1987-07-22
flame length . This work is summarized in this section. I1.1 Model for Turbulent Burning Velocity For a range of turbulence conditions including...Variable density effects have been added in an approximation, and an expression for the length of jet flames has been developed. The flame length expression...of jet mixing and jet flame length data using fractals, College of Engineering, Energy Report E-86-02, Comell University, Ithaca, NY, 1986. Results
Stochastic tools in turbulence
Lumey, John L
2012-01-01
Stochastic Tools in Turbulence discusses the available mathematical tools to describe stochastic vector fields to solve problems related to these fields. The book deals with the needs of turbulence in relation to stochastic vector fields, particularly, on three-dimensional aspects, linear problems, and stochastic model building. The text describes probability distributions and densities, including Lebesgue integration, conditional probabilities, conditional expectations, statistical independence, lack of correlation. The book also explains the significance of the moments, the properties of the
Magnetohydrodynamic turbulence revisited
International Nuclear Information System (INIS)
Goldreich, P.; Sridhar, S.
1997-01-01
In 1965, Kraichnan proposed that MHD turbulence occurs as a result of collisions between oppositely directed Alfvacute en wave packets. Recent work has generated some controversy over the nature of nonlinear couplings between colliding Alfvacute en waves. We find that the resolution to much of the confusion lies in the existence of a new type of turbulence, intermediate turbulence, in which the cascade of energy in the inertial range exhibits properties intermediate between those of weak and strong turbulent cascades. Some properties of intermediate MHD turbulence are the following: (1) in common with weak turbulent cascades, wave packets belonging to the inertial range are long-lived; (2) however, components of the strain tensor are so large that, similar to the situation in strong turbulence, perturbation theory is not applicable; (3) the breakdown of perturbation theory results from the divergence of neighboring field lines due to wave packets whose perturbations in velocity and magnetic fields are localized, but whose perturbations in displacement are not; (4) three-wave interactions dominate individual collisions between wave packets, but interactions of all orders n≥3 make comparable contributions to the intermediate turbulent energy cascade; (5) successive collisions are correlated since wave packets are distorted as they follow diverging field lines; (6) in common with the weak MHD cascade, there is no parallel cascade of energy, and the cascade to small perpendicular scales strengthens as it reaches higher wavenumbers; (7) for an appropriate weak excitation, there is a natural progression from a weak, through an intermediate, to a strong cascade. copyright 1997 The American Astronomical Society
Statistical Study of Turbulence: Spectral Functions and Correlation Coefficients
Frenkiel, Francois N.
1958-01-01
In reading the publications on turbulence of different authors, one often runs the risk of confusing the various correlation coefficients and turbulence spectra. We have made a point of defining, by appropriate concepts, the differences which exist between these functions. Besides, we introduce in the symbols a few new characteristics of turbulence. In the first chapter, we study some relations between the correlation coefficients and the different turbulence spectra. Certain relations are given by means of demonstrations which could be called intuitive rather than mathematical. In this way we demonstrate that the correlation coefficients between the simultaneous turbulent velocities at two points are identical, whether studied in Lagrange's or in Euler's systems. We then consider new spectra of turbulence, obtained by study of the simultaneous velocities along a straight line of given direction. We determine some relations between these spectra and the correlation coefficients. Examining the relation between the spectrum of the turbulence measured at a fixed point and the longitudinal-correlation curve given by G. I. Taylor, we find that this equation is exact only when the coefficient is very small.
Statistical theory of turbulent incompressible multimaterial flow
International Nuclear Information System (INIS)
Kashiwa, B.
1987-10-01
Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of κ-ε modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy κ, and the rate of fluctuational energy dissipation ε, for each material. Hence a set of κ and ε equations must be solved, together with mean mass and momentum conservation equations, for each material. Both κ and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a pipe
Directory of Open Access Journals (Sweden)
Tarnay László
2017-12-01
Full Text Available The paper investigates two possible critical arguments following the pictorial turn. The first is formulated within ocularcentrism, the dominance of sight, and starts with the right to visibility as a general principle that governs today’s digital culture but gets twisted in special cases like the Auschwitz photos of the Shoa, the Abu Ghraib prison videos, or recently the website called Yolocaust. The second is conceived outside the visual culture and is meant to vindicate the other senses vis-à-vis the eyes. However, the argument is truncated here only to highlight the boomerang effect of the other senses: haptic vision. It is the case of visual perception when (a there is a lack of things to see and (b indeterminate synaesthesia: when vision intensifies the other senses in the embodied viewer. The two arguments converge upon a dialectic of the visible and the imaginable, which is formulated here as two paradoxes that the discussed examples transcend. By enforcing visibility at all costs where there is hardly anything recognizable to see, they lead to two diverging results. On the one hand, the meaning of “image” is extended toward the unimaginable, the traumatic experience, on the other hand, it is extended toward the invisible, the encounter with the radical Other.
International Nuclear Information System (INIS)
Krupnick, A.; DeWitt, D.
1994-01-01
The benefits of visibility improvement (or the damages with additional degradation) refer to increases (or decreases) in utility obtained in three different dimensions. The first of these is associated with the nature of the visibility change. Visual range may be improved so that features of an area become more distinct or the sky becomes clearer. Alternatively, normal features of an area may be marred, say by the site of a power plant or its plume (called plume blight). The second dimension is the location of the change: in an urban area, in a rural setting, or in a recreational area or area of particular beauty, such as the Grand Canyon. The third dimension is the type of value: use or non-use. Thus, a person who visits the Grand Canyon (or may visit it in the future) may hold use values for improving his view of the Canyon or its surroundings and may also old non-use values for improved visibility (whether for altruistic or other reasons) irrespective of present or planned visits. In all, therefore, there are 12 possible combinations of the elements in these three dimension, each of which is logically distinct from the others and which demands attention in the literature to derive willingness to pay (WTP)
Energy Technology Data Exchange (ETDEWEB)
Krupnick, A; DeWitt, D
1994-07-01
The benefits of visibility improvement (or the damages with additional degradation) refer to increases (or decreases) in utility obtained in three different dimensions. The first of these is associated with the nature of the visibility change. Visual range may be improved so that features of an area become more distinct or the sky becomes clearer. Alternatively, normal features of an area may be marred, say by the site of a power plant or its plume (called plume blight). The second dimension is the location of the change: in an urban area, in a rural setting, or in a recreational area or area of particular beauty, such as the Grand Canyon. The third dimension is the type of value: use or non-use. Thus, a person who visits the Grand Canyon (or may visit it in the future) may hold use values for improving his view of the Canyon or its surroundings and may also old non-use values for improved visibility (whether for altruistic or other reasons) irrespective of present or planned visits. In all, therefore, there are 12 possible combinations of the elements in these three dimension, each of which is logically distinct from the others and which demands attention in the literature to derive willingness to pay (WTP)
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.
Wang, Chi R.; Yeh, Frederick C.
1987-01-01
A theoretical analysis and numerical calculations for the turbulent flow field and for the effect of free-stream turbulence on the surface heat transfer rate of a stagnation flow are presented. The emphasis is on the modeling of turbulence and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow. The free stream is steady and incompressible with a Reynolds number of the order of 10 to the 5th power and turbulence intensity of less than 5 percent. For this analysis, the flow field is divided into three regions: (1) a uniform free-stream region where the turbulence is homogeneous and isotropic; (2) an external viscid flow region where the turbulence is distorted by the variation of the mean flow velocity; and, (3) an anisotropic turbulent boundary layer region over the cylinder surface. The turbulence modeling techniques used are the kappa-epsilon two-equation model in the external flow region and the time-averaged turbulence transport equation in the boundary layer region. The turbulence double correlations, the mean velocity, and the mean temperature within the boundary layer are solved numerically from the transport equations. The surface heat transfer rate is calculated as functions of the free-stream turbulence longitudinal microlength scale, the turbulence intensity, and the Reynolds number.
Gyrokinetic simulations of ETG Turbulence*
Nevins, William
2005-10-01
Recent gyrokinetic simulations of electron temperature gradient (ETG) turbulence [1,2] produced different results despite similar plasma parameters. Ref.[1] differs from Ref.[2] in that [1] eliminates magnetically trapped particles ( r/R=0 ), while [2] retains magnetically trapped particles ( r/R 0.18 ). Differences between [1] and [2] have been attributed to insufficient phase-space resolution and novel physics associated with toroidicity and/or global simulations[2]. We have reproduced the results reported in [2] using a flux-tube, particle-in-cell (PIC) code, PG3EQ[3], thereby eliminating global effects as the cause of the discrepancy. We observe late-time decay of ETG turbulence and the steady-state heat transport in agreement with [2], and show this results from discrete particle noise. Discrete particle noise is a numerical artifact, so both the PG3EQ simulations reported here and those reported in Ref.[2] have little to say about steady-state ETG turbulence and the associated anomalous electron heat transport. Our attempts to benchmark PIC and continuum[4] codes at the plasma parameters used in Ref.[2] produced very large, intermittent transport. We will present an alternate benchmark point for ETG turbulence, where several codes reproduce the same transport levels. Parameter scans about this new benchmark point will be used to investigate the parameter dependence of ETG transport and to elucidate saturation mechanisms proposed in Refs.[1,2] and elsewhere[5-7].*In collaboration with A. Dimits (LLNL), J. Candy, C. Estrada-Mila (GA), W. Dorland (U of MD), F. Jenko, T. Dannert (Max-Planck Institut), and G. Hammett (PPPL). Work at LLNL performed for US DOE under Contract W7405-ENG-48.[1] F. Jenko and W. Dorland, PRL 89, 225001 (2002).[2] Z. Lin et al, 2004 Sherwood Mtg.; 2004 TTF Mtg.; Fusion Energy 2004 (IAEA, Vienna, 2005); Bull. Am. Phys. Soc. (November, 2004); 2005 TTF Mtg.; 2005 Sherwood Mtg.; Z. Lin, et al, Phys. Plasmas 12, 056125 (2005). [3] A.M. Dimits
Robust optical wireless links over turbulent media using diversity solutions
Moradi, Hassan
Free-space optic (FSO) technology, i.e., optical wireless communication (OWC), is widely recognized as superior to radio frequency (RF) in many aspects. Visible and invisible optical wireless links solve first/last mile connectivity problems and provide secure, jam-free communication. FSO is license-free and delivers high-speed data rates in the order of Gigabits. Its advantages have fostered significant research efforts aimed at utilizing optical wireless communication, e.g. visible light communication (VLC), for high-speed, secure, indoor communication under the IEEE 802.15.7 standard. However, conventional optical wireless links demand precise optical alignment and suffer from atmospheric turbulence. When compared with RF, they suffer a low degree of reliability and lack robustness. Pointing errors cause optical transceiver misalignment, adversely affecting system reliability. Furthermore, atmospheric turbulence causes irradiance fluctuations and beam broadening of transmitted light. Innovative solutions to overcome limitations on the exploitation of high-speed optical wireless links are greatly needed. Spatial diversity is known to improve RF wireless communication systems. Similar diversity approaches can be adapted for FSO systems to improve its reliability and robustness; however, careful diversity design is needed since FSO apertures typically remain unbalanced as a result of FSO system sensitivity to misalignment. Conventional diversity combining schemes require persistent aperture monitoring and repetitive switching, thus increasing FSO implementation complexities. Furthermore, current RF diversity combining schemes may not be optimized to address the issue of unbalanced FSO receiving apertures. This dissertation investigates two efficient diversity combining schemes for multi-receiving FSO systems: switched diversity combining and generalized selection combining. Both can be exploited to reduce complexity and improve combining efficiency. Unlike maximum
Definition of Turbulent Boundary-Layer with Entropy Concept
Directory of Open Access Journals (Sweden)
Zhao Rui
2016-01-01
Full Text Available The relationship between the entropy increment and the viscosity dissipation in turbulent boundary-layer is systematically investigated. Through theoretical analysis and direct numerical simulation (DNS, an entropy function fs is proposed to distinguish the turbulent boundary-layer from the external flow. This approach is proved to be reliable after comparing its performance in the following complex flows, namely, low-speed airfoil flows with different wall temperature, supersonic cavity-ramp flow dominated by the combination of free-shear layer, larger recirculation and shocks, and the hypersonic flow past an aeroplane configuration. Moreover, fs is deduced from the point of energy, independent of any particular turbulent quantities. That is, this entropy concept could be utilized by other engineering applications related with turbulent boundary-layer, such as turbulence modelling transition prediction and engineering thermal protection.
Inverse scattering problem in turbulent magnetic fluctuations
Directory of Open Access Journals (Sweden)
R. A. Treumann
2016-08-01
Full Text Available We apply a particular form of the inverse scattering theory to turbulent magnetic fluctuations in a plasma. In the present note we develop the theory, formulate the magnetic fluctuation problem in terms of its electrodynamic turbulent response function, and reduce it to the solution of a special form of the famous Gelfand–Levitan–Marchenko equation of quantum mechanical scattering theory. The last of these applies to transmission and reflection in an active medium. The theory of turbulent magnetic fluctuations does not refer to such quantities. It requires a somewhat different formulation. We reduce the theory to the measurement of the low-frequency electromagnetic fluctuation spectrum, which is not the turbulent spectral energy density. The inverse theory in this form enables obtaining information about the turbulent response function of the medium. The dynamic causes of the electromagnetic fluctuations are implicit to it. Thus, it is of vital interest in low-frequency magnetic turbulence. The theory is developed until presentation of the equations in applicable form to observations of turbulent electromagnetic fluctuations as input from measurements. Solution of the final integral equation should be done by standard numerical methods based on iteration. We point to the possibility of treating power law fluctuation spectra as an example. Formulation of the problem to include observations of spectral power densities in turbulence is not attempted. This leads to severe mathematical problems and requires a reformulation of inverse scattering theory. One particular aspect of the present inverse theory of turbulent fluctuations is that its structure naturally leads to spatial information which is obtained from the temporal information that is inherent to the observation of time series. The Taylor assumption is not needed here. This is a consequence of Maxwell's equations, which couple space and time evolution. The inversion procedure takes
On court interpreters' visibility
DEFF Research Database (Denmark)
Dubslaff, Friedel; Martinsen, Bodil
of the service they receive. Ultimately, the findings will be used for training purposes. Future - and, for that matter, already practising - interpreters as well as the professional users of interpreters ought to take the reality of the interpreters' work in practice into account when assessing the quality...... on the interpreter's interpersonal role and, in particular, on signs of the interpreter's visibility, i.e. active co-participation. At first sight, the interpreting assignment in question seems to be a short and simple routine task which would not require the interpreter to deviate from the traditional picture...
Making Invisible Forces Visible
DEFF Research Database (Denmark)
Ratner, Helene Gad
2013-01-01
their 'true' attitudes and values. The paper draws on theories of affect as well as actor-network theory to analyse three incidents where managers turn their interpretations of teachers' emotions into such information. These incidents suggest that the efforts to render employees' attitudes and values visible...... install a normative emotional scale where an ideal employee displays emotional investment and self-control. This has implications, not only for employees who are expected to exhibit the 'right' emotions, but also for management, which comes to depend on transient emotions and co-presence in situations...
Tearing instabilities in turbulence
International Nuclear Information System (INIS)
Ishizawa, A.; Nakajima, N.
2009-01-01
Full text: Effects of micro-turbulence on tearing instabilities are investigated by numerically solving a reduced set of two-fluid equations. Micro-turbulence excites both large-scale and small-scale Fourier modes through energy transfer due to nonlinear mode coupling. The energy transfer to large scale mode does not directly excite tearing instability but it gives an initiation of tearing instability. When tearing instability starts to grow, the excited small scale mode plays an important role. The mixing of magnetic flux by micro-turbulence is the dominant factor of non-ideal MHD effect at the resonant surface and it gives rise to magnetic reconnection which causes tearing instability. Tearing instabilities were investigated against static equilibrium or flowing equilibrium so far. On the other hand, the recent progress of computer power allows us to investigate interactions between turbulence and coherent modes such as tearing instabilities in magnetically confined plasmas by means of direct numerical simulations. In order to investigate effects of turbulence on tearing instabilities we consider a situation that tearing mode is destabilized in a quasi-equilibrium including micro-turbulence. We choose an initial equilibrium that is unstable against kinetic ballooning modes and tearing instabilities. Tearing instabilities are current driven modes and thus they are unstable for large scale Fourier modes. On the other hand kinetic ballooning modes are unstable for poloidal Fourier modes that are characterized by ion Larmor radius. The energy of kinetic ballooning modes spreads over wave number space through nonlinear Fourier mode coupling. We present that micro-turbulence affects tearing instabilities in two different ways by three-dimensional numerical simulation of a reduced set of two-fluid equations. One is caused by energy transfer to large scale modes, the other is caused by energy transfer to small scale modes. The former is the excitation of initial
Flapping model of scalar mixing in turbulence
International Nuclear Information System (INIS)
Kerstein, A.R.
1991-01-01
Motivated by the fluctuating plume model of turbulent mixing downstream of a point source, a flapping model is formulated for application to other configurations. For the scalar mixing layer, simple expressions for single-point scalar fluctuation statistics are obtained that agree with measurements. For a spatially homogeneous scalar mixing field, the family of probability density functions previously derived using mapping closure is reproduced. It is inferred that single-point scalar statistics may depend primarily on large-scale flapping motions in many cases of interest, and thus that multipoint statistics may be the principal indicators of finer-scale mixing effects
Turbulence introduction to theory and applications of turbulent flows
Westerweel, Jerry; Nieuwstadt, Frans T M
2016-01-01
This book provides a general introduction to the topic of turbulent flows. Apart from classical topics in turbulence, attention is also paid to modern topics. After studying this work, the reader will have the basic knowledge to follow current topics on turbulence in scientific literature. The theory is illustrated with a number of examples of applications, such as closure models, numerical simulations and turbulent diffusion, and experimental findings. The work also contains a number of illustrative exercises.
Flux surface shaping effects on tokamak edge turbulence and flows
International Nuclear Information System (INIS)
Kendl, A.; Scott, B.D.
2004-01-01
The influence of shaping of magnetic flux surfaces in tokamaks on gyro-fluid edge turbulence is studied numerically. Magnetic field shaping in tokamaks is mainly due to elongation, triangularity, shift and the presence of a divertor X-point. A series of tokamak configurations with varying elongation 1 ≤ κ ≥ 2 and triangularity 0 ≤ δ ≤ 0.4, and an actual ASDEX Upgrade divertor configuration are obtained with the equilibrium code HELENA and implemented into the gyro-fluid turbulence code GEM. The study finds minimal impact on the zonal flow physics itself, but strong impact on the turbulence and transport. (authors)
Turbulence studies in tokamak boundary plasmas with realistic divertor geometry
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Porter, G.D.; Rognlien, T.; Ryutov, D.D.; Myra, J.R.; D'Ippolito, D.A.; Moyer, R.; Groebner, R.J.
2001-01-01
Results are presented from the 3D nonlocal electromagnetic turbulence code BOUT and the linearized shooting code BAL for studies of turbulence in tokamak boundary plasmas and its relationship to the L-H transition, in a realistic divertor plasma geometry. The key results include: (1) the identification of the dominant resistive X-point mode in divertor geometry and (2) turbulence suppression in the L-H transition by shear in the ExB drift speed, ion diamagnetism and nite polarization. Based on the simulation results, a parameterization of the transport is given that includes the dependence on the relevant physical parameters. (author)
Turbulence studies in tokamak boundary plasmas with realistic divertor geometry
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Por, G.D. ter; Rognlien, T.D.; Ryutov, D.D.; Myra, J.R.; D'Ippolito, D.A.; Moyer, R.; Groebner, R.J.
1999-01-01
Results are presented from the 3D nonlocal electromagnetic turbulence code BOUT and the linearized shooting code BAL for studies of turbulence in tokamak boundary plasmas and its relationship to the L-H transition, in a realistic divertor plasma geometry. The key results include: (1) the identification of the dominant resistive X-point mode in divertor geometry and (2) turbulence suppression in the L-H transition by shear in the E x B drift speed, ion diamagnetism and finite polarization. Based on the simulation results, a parameterization of the transport is given that includes the dependence on the relevant physical parameters. (author)
Flux surface shaping effects on tokamak edge turbulence and flows
Energy Technology Data Exchange (ETDEWEB)
Kendl, A. [Innsbruck Univ., Institut fuer Theoretische Physik, Association EURATOM (Austria); Scott, B.D. [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Garching bei Muenchen (Germany)
2004-07-01
The influence of shaping of magnetic flux surfaces in tokamaks on gyro-fluid edge turbulence is studied numerically. Magnetic field shaping in tokamaks is mainly due to elongation, triangularity, shift and the presence of a divertor X-point. A series of tokamak configurations with varying elongation 1 {<=} {kappa} {>=} 2 and triangularity 0 {<=} {delta} {<=} 0.4, and an actual ASDEX Upgrade divertor configuration are obtained with the equilibrium code HELENA and implemented into the gyro-fluid turbulence code GEM. The study finds minimal impact on the zonal flow physics itself, but strong impact on the turbulence and transport. (authors)
A mathematical model of turbulence for turbulent boundary layers
International Nuclear Information System (INIS)
Pereira Filho, H.D.V.
1977-01-01
Equations to the so called Reynolds stress-tensor (kinetic turbulent energy) and dissipation rate are developed and a turbulence flux approximation used. Our ideia here is to use those equations in order to develop an economical and fast numeircal procedure for computation of turbulent boundary layer. (author) [pt
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids.
Energy Technology Data Exchange (ETDEWEB)
Caldas, Ibere L.; Heller, M.V.A.P.; Brasilio, Z.A. [Sao Paulo Univ., SP, RJ (Brazil). Inst. de Fisica
1997-12-31
Full text. In this work we summarize the results from experiments on electrostatic and magnetic fluctuations in tokamak plasmas. Spectral analyses show that these fluctuations are turbulent, having a broad spectrum of wavectors and a broad spectrum of frequencies at each wavector. The electrostatic turbulence induces unexpected anomalous particle transport that deteriorates the plasma confinement. The relationship of these fluctuations to the current state of plasma theory is still unclear. Furthermore, we describe also attempts to control this plasma turbulence with external magnetic perturbations that create chaotic magnetic configurations. Accordingly, the magnetic field lines may become chaotic and then induce a Lagrangian diffusion. Moreover, to discuss nonlinear coupling and intermittency, we present results obtained by using numerical techniques as bi spectral and wavelet analyses. (author)
Energy Technology Data Exchange (ETDEWEB)
Mann, Jakob [Risoe National Lab., Wind Energy and Atmosheric Physics Dept., Roskilde (Denmark)
1999-03-01
The purpose of this work is to develop a model of the spectral velocity-tensor in neutral flow over complex terrain. The resulting equations are implemented in a computer code using the mean flow generated by a linear mean flow model as input. It estimates turbulence structure over hills (except on the lee side if recirculation is present) in the so-called outer layer and also models the changes in turbulence statistics in the vicinity roughness changes. The generated turbulence fields are suitable as input for dynamic load calculations on wind turbines and other tall structures and is under implementation in the collection of programs called WA{sup s}P Engineering. (au) EFP-97; EU-JOULE-3. 15 refs.
On Electron-Scale Whistler Turbulence in the Solar Wind
Narita, Y.; Nakamura, R.; Baumjohann, W.; Glassmeier, K.-H.; Motschmann, U.; Giles, B.; Magnes, W.; Fischer, D.; Torbert, R. B.; Russell, C. T.
2016-01-01
For the first time, the dispersion relation for turbulence magnetic field fluctuations in the solar wind is determined directly on small scales of the order of the electron inertial length, using four-point magnetometer observations from the Magnetospheric Multiscale mission. The data are analyzed using the high-resolution adaptive wave telescope technique. Small-scale solar wind turbulence is primarily composed of highly obliquely propagating waves, with dispersion consistent with that of the whistler mode.
Multispectral Image Feature Points
Directory of Open Access Journals (Sweden)
Cristhian Aguilera
2012-09-01
Full Text Available This paper presents a novel feature point descriptor for the multispectral image case: Far-Infrared and Visible Spectrum images. It allows matching interest points on images of the same scene but acquired in different spectral bands. Initially, points of interest are detected on both images through a SIFT-like based scale space representation. Then, these points are characterized using an Edge Oriented Histogram (EOH descriptor. Finally, points of interest from multispectral images are matched by finding nearest couples using the information from the descriptor. The provided experimental results and comparisons with similar methods show both the validity of the proposed approach as well as the improvements it offers with respect to the current state-of-the-art.
Turbulence Intensity Scaling: A Fugue
Basse, Nils T.
2018-01-01
We study streamwise turbulence intensity definitions using smooth- and rough-wall pipe flow measurements made in the Princeton Superpipe. Scaling of turbulence intensity with the bulk (and friction) Reynolds number is provided for the definitions. The turbulence intensity is proportional to the square root of the friction factor with the same proportionality constant for smooth- and rough-wall pipe flow. Turbulence intensity definitions providing the best description of the measurements are i...
Turbulent Flame Propagation Characteristics of High Hydrogen Content Fuels
Energy Technology Data Exchange (ETDEWEB)
Seitzman, Jerry [Georgia Inst. of Technology, Atlanta, GA (United States); Lieuwen, Timothy [Georgia Inst. of Technology, Atlanta, GA (United States)
2014-09-30
This final report describes the results of an effort to better understand turbulent flame propagation, especially at conditions relevant to gas turbines employing fuels with syngas or hydrogen mixtures. Turbulent flame speeds were measured for a variety of hydrogen/carbon monoxide (H2/CO) and hydrogen/methane (H2/CH4) fuel mixtures with air as the oxidizer. The measurements include global consumption speeds (ST,GC) acquired in a turbulent jet flame at pressures of 1-10 atm and local displacement speeds (ST,LD) acquired in a low-swirl burner at atmospheric pressure. The results verify the importance of fuel composition in determining turbulent flame speeds. For example, different fuel-air mixtures having the same unstretched laminar flame speed (SL,0) but different fuel compositions resulted in significantly different ST,GC for the same turbulence levels (u'). This demonstrates the weakness of turbulent flame speed correlations based simply on u'/SL,0. The results were analyzed using a steady-steady leading points concept to explain the sensitivity of turbulent burning rates to fuel (and oxidizer) composition. Leading point theories suggest that the premixed turbulent flame speed is controlled by the flame front characteristics at the flame brush leading edge, or, in other words, by the flamelets that advance farthest into the unburned mixture (the so-called leading points). For negative Markstein length mixtures, this is assumed to be close to the maximum stretched laminar flame speed (SL,max) for the given fuel-oxidizer mixture. For the ST,GC measurements, the data at a given pressure were well-correlated with an SL,max scaling. However the variation with pressure was not captured, which may be due to non-quasi-steady effects that are not included in the current model. For the ST,LD data, the leading points model again faithfully captured the variation of turbulent flame speed over a wide range of fuel-compositions and turbulence intensities. These
DEFF Research Database (Denmark)
Torkilsheyggi, Arnvør Martinsdóttir á; Hertzum, Morten
2015-01-01
Studies have shown that whiteboards support much cooper-ative work by for example strengthening awareness, im-proving communication, and reducing mental workload. In line with these predominantly positive findings, an emer-gency department (ED) turned to its whiteboard to improve the coordination...... of its work with blood tests. We investi-gate this use of the whiteboard through observations and informal interviews in the ED and analyze the ability of the whiteboard to support coordination and awareness in the work with blood tests. Our findings show limitations in the ability of the whiteboard...... to support awareness in a setting where the users are (locally) mobile, specifically in regard to information that requires continuous monitoring. We do however also find that the whiteboard safeguarded the work with blood tests against some risks by making blood-test information socially visible....
Turbulent wakes of fractal objects
Staicu, A.D.; Mazzi, B.; Vassilicos, J.C.; Water, van de W.
2003-01-01
Turbulence of a windtunnel flow is stirred using objects that have a fractal structure. The strong turbulent wakes resulting from three such objects which have different fractal dimensions are probed using multiprobe hot-wire anemometry in various configurations. Statistical turbulent quantities are
Plasma turbulence calculations on supercomputers
International Nuclear Information System (INIS)
Carreras, B.A.; Charlton, L.A.; Dominguez, N.; Drake, J.B.; Garcia, L.; Leboeuf, J.N.; Lee, D.K.; Lynch, V.E.; Sidikman, K.
1991-01-01
Although the single-particle picture of magnetic confinement is helpful in understanding some basic physics of plasma confinement, it does not give a full description. Collective effects dominate plasma behavior. Any analysis of plasma confinement requires a self-consistent treatment of the particles and fields. The general picture is further complicated because the plasma, in general, is turbulent. The study of fluid turbulence is a rather complex field by itself. In addition to the difficulties of classical fluid turbulence, plasma turbulence studies face the problems caused by the induced magnetic turbulence, which couples field by itself. In addition to the difficulties of classical fluid turbulence, plasma turbulence studies face the problems caused by the induced magnetic turbulence, which couples back to the fluid. Since the fluid is not a perfect conductor, this turbulence can lead to changes in the topology of the magnetic field structure, causing the magnetic field lines to wander radially. Because the plasma fluid flows along field lines, they carry the particles with them, and this enhances the losses caused by collisions. The changes in topology are critical for the plasma confinement. The study of plasma turbulence and the concomitant transport is a challenging problem. Because of the importance of solving the plasma turbulence problem for controlled thermonuclear research, the high complexity of the problem, and the necessity of attacking the problem with supercomputers, the study of plasma turbulence in magnetic confinement devices is a Grand Challenge problem
Gyrokinetic statistical absolute equilibrium and turbulence
International Nuclear Information System (INIS)
Zhu Jianzhou; Hammett, Gregory W.
2010-01-01
A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence [T.-D. Lee, Q. Appl. Math. 10, 69 (1952)] is taken to study gyrokinetic plasma turbulence: a finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N+1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperature states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney-Hasegawa-Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.
Gyrokinetic Statistical Absolute Equilibrium and Turbulence
International Nuclear Information System (INIS)
Zhu, Jian-Zhou; Hammett, Gregory W.
2011-01-01
A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence (T.-D. Lee, 'On some statistical properties of hydrodynamical and magnetohydrodynamical fields,' Q. Appl. Math. 10, 69 (1952)) is taken to study gyrokinetic plasma turbulence: A finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N + 1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperature states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney-Hasegawa-Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.
2012-01-01
Dagobert, and C. Franchis . Atmospheric tur- bulence restoration by diffeomorphic image registration and blind deconvolution. In ACIVS, 2008. 1 [4] S...20] V. Tatarskii. Wave Propagation in a Turbulent Medium. McGraw-Hill Books, 1961. 2 [21] Y. Tian and S. Narasimhan. A globally optimal data-driven
van der Veen, Roeland
2016-01-01
In this thesis, several questions related to drop impact and Taylor-Couette turbulence are answered. The deformation of a drop just before impact can cause a bubble to be entrapped. For many applications, such as inkjet printing, it is crucial to control the size of this entrapped bubble. To study
Turbulence and Flying Machines
Indian Academy of Sciences (India)
other to make the aircraft roll. For example, a downward dis- placement of the left aileron causes the airplane to roll to the right. In Figure 4 the elevators have been deflected downwards, giving rise to a 'nose-down' moment about the pitch axis. Delaying Turbulence. In the last few decades, flying machines have proliferated ...
Turbulence and particle acceleration
International Nuclear Information System (INIS)
Scott, J.S.
1975-01-01
A model for the production of high energy particles in the supernova remnant Cas A is considered. The ordered expansion of the fast moving knots produce turbulent cells in the ambient interstellar medium. The turbulent cells act as magnetic scattering centers and charged particles are accelerated to large energies by the second order Fermi mechanism. Model predictions are shown to be consistent with the observed shape and time dependence of the radio spectrum, and with the scale size of magnetic field irregularities. Assuming a galactic supernova rate at 1/50 yr -1 , this mechanism is capable of producing the observed galactic cosmic ray flux and spectrum below 10 16 eV/nucleon. Several observed features of galactic cosmic rays are shown to be consistent with model predictions. A model for the objects known as radio tall galaxies is also presented. Independent blobs of magnetized plasma emerging from an active radio galaxy into an intracluster medium become turbulent due to Rayleigh--Taylor and Kelvin--Helmholz instabilities. The turbulence produces both in situ betatron and 2nd order Fermi accelerations. Predictions of the dependence of spectral index and flux on distance along the tail match observations well. Fitting provides values of physical parameters in the blobs. The relevance of this method of particle acceleration for the problem of the origin of x-ray emission in clusters of galaxies is discussed
Nature of interstellar turbulence
International Nuclear Information System (INIS)
Altunin, V.
1981-01-01
A significant role in producing the pattern of interstellar scintillation observed in discrete radio sources may be played by the magnetoacoustic turbulence that will be generated as shock waves are propagated at velocity V/sub sh/roughly-equal 20--100 km/sec through the interstellar medium, as well as by irregularities in stellar wind emanating from type OB stars
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...
Analysis of turbulent boundary layers
Cebeci, Tuncer
1974-01-01
Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculati
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
1993-04-14
flame length L simultaneously with h, and measuring the visible radiation I simultaneously with h. L(t) was found to be nearly uncorrelated with h(t...variation of 7i/2 /76 with ýh. These experiments included measuring the flame length L simultaneously with h, and measuring the visible radiation I...Measurements of Liftoff Height and Flame Length ... 66 4.5 Simultaneous Measurements of Liftoff Height and Radiation ....... 71 4.6 D scussion
Turbulence measurements in fusion plasmas
International Nuclear Information System (INIS)
Conway, G D
2008-01-01
Turbulence measurements in magnetically confined toroidal plasmas have a long history and relevance due to the detrimental role of turbulence induced transport on particle, energy, impurity and momentum confinement. The turbulence-the microscopic random fluctuations in particle density, temperature, potential and magnetic field-is generally driven by radial gradients in the plasma density and temperature. The correlation between the turbulence properties and global confinement, via enhanced diffusion, convection and direct conduction, is now well documented. Theory, together with recent measurements, also indicates that non-linear interactions within the turbulence generate large scale zonal flows and geodesic oscillations, which can feed back onto the turbulence and equilibrium profiles creating a complex interdependence. An overview of the current status and understanding of plasma turbulence measurements in the closed flux surface region of magnetic confinement fusion devices is presented, highlighting some recent developments and outstanding problems.
Destabilizing turbulence in pipe flow
Kühnen, Jakob; Song, Baofang; Scarselli, Davide; Budanur, Nazmi Burak; Riedl, Michael; Willis, Ashley P.; Avila, Marc; Hof, Björn
2018-04-01
Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities1-3, so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism4,5 measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.
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.
Scale-similar clustering of heavy particles in the inertial range of turbulence
Ariki, Taketo; Yoshida, Kyo; Matsuda, Keigo; Yoshimatsu, Katsunori
2018-03-01
Heavy particle clustering in turbulence is discussed from both phenomenological and analytical points of view, where the -4 /3 power law of the pair-correlation function is obtained in the inertial range. A closure theory explains the power law in terms of the balance between turbulence mixing and preferential-concentration mechanism. The obtained -4 /3 power law is supported by a direct numerical simulation of particle-laden turbulence.
Compressibility and rotation effects on transport suppression in magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
Yoshizawa, A.
1996-01-01
Compressibility and rotation effects on turbulent transports in magnetohydrodynamic (MHD) flows under arbitrary mean field are investigated using a Markovianized two-scale statistical approach. Some new aspects of MHD turbulence are pointed out in close relation to plasma compressibility. Special attention is paid to the turbulent electromotive force, which plays a central role in the generation of magnetic and velocity fluctuations. In addition to plasma rotation, the interaction between compressibility and magnetic fields is shown to bring a few factors suppressing MHD fluctuations and, eventually, density and temperature transports, even in the presence of steep mean density and temperature gradients. This finding is discussed in the context of the turbulence-suppression mechanism in the tokamak close-quote s high-confinement modes. copyright 1996 American Institute of Physics
Advances in engineering turbulence modeling. [computational fluid dynamics
Shih, T.-H.
1992-01-01
Some new developments in two equation models and second order closure models are presented. In this paper, modified two equation models are proposed to remove shortcomings such as computing flows over complex geometries and the ad hoc treatment near the separation and reattachment points. The calculations using various two equation models are compared with direct numerical solutions of channel flows and flat plate boundary layers. Development of second order closure models will also be discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All existing models poorly predict the normal stresses near the wall and fail to predict the three dimensional effect of mean flow on the turbulence. The newly developed second order near-wall turbulence model to be described in this paper is capable of capturing the near-wall behavior of turbulence as well as the effect of three dimension mean flow on the turbulence.
Turbulent transport and shear at the E x B velocity in wall plasma of the TF-2 tokamak
International Nuclear Information System (INIS)
Budaev, V.P.
1999-01-01
Turbulence of near-the-wall plasma and potentialities of affecting the turbulence and periphery transport of the TF-2 tokamak by inducing radial electric fields and ergodization of periphery magnetic structure have been investigated, the results are presented. Essential role of the E x B velocity shear in suppression of the turbulence and turbulent transport in periphery has been pointed out. Decrease in transport losses stemming from effect of radial electric fields is brought about suppression of turbulence amplitude, decrease in correlations and decrease in the width of the wave numbers spectrum. Profiles of plasma density, electron temperature, turbulence level, electric fields over entire periphery of discharge change as a result. Ergodization of magnetic structure also results in the change of properties of periphery turbulence and turbulent transport [ru
Anaïs Schaeffer
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. The last day of data collection, tired but satisfied after seven intense days of measurements. Around the cryostat, from left to right: Philippe-E. Roche, Éléonore Rusaouen (CNRS), Olivier Pirotte, Jean-Marc Quetsch (CERN), Nicolas Friedlin (CERN), Vladislav Benda (CERN). Not in the photo: Laurent Le Mao (CERN), Jean-Marc Debernard (CERN), Jean-Paul Lamboy (CERN), Nicolas Guillotin (CERN), Benoit Chabaud (Grenoble Uni), and Gregory Garde (CNRS). CERN has a unique cryogenic facility in hall SM18, consisting of 21 liquid-helium-cooled test stations. While this equipment was, of course, designed for testing parts of CERN's acce...
Efficient Geometric Sound Propagation Using Visibility Culling
Chandak, Anish
2011-07-01
Simulating propagation of sound can improve the sense of realism in interactive applications such as video games and can lead to better designs in engineering applications such as architectural acoustics. In this thesis, we present geometric sound propagation techniques which are faster than prior methods and map well to upcoming parallel multi-core CPUs. We model specular reflections by using the image-source method and model finite-edge diffraction by using the well-known Biot-Tolstoy-Medwin (BTM) model. We accelerate the computation of specular reflections by applying novel visibility algorithms, FastV and AD-Frustum, which compute visibility from a point. We accelerate finite-edge diffraction modeling by applying a novel visibility algorithm which computes visibility from a region. Our visibility algorithms are based on frustum tracing and exploit recent advances in fast ray-hierarchy intersections, data-parallel computations, and scalable, multi-core algorithms. The AD-Frustum algorithm adapts its computation to the scene complexity and allows small errors in computing specular reflection paths for higher computational efficiency. FastV and our visibility algorithm from a region are general, object-space, conservative visibility algorithms that together significantly reduce the number of image sources compared to other techniques while preserving the same accuracy. Our geometric propagation algorithms are an order of magnitude faster than prior approaches for modeling specular reflections and two to ten times faster for modeling finite-edge diffraction. Our algorithms are interactive, scale almost linearly on multi-core CPUs, and can handle large, complex, and dynamic scenes. We also compare the accuracy of our sound propagation algorithms with other methods. Once sound propagation is performed, it is desirable to listen to the propagated sound in interactive and engineering applications. We can generate smooth, artifact-free output audio signals by applying
EFFECT OF ION ∇ B DRIFT DIRECTION ON TURBULENCE FLOW AND FLOW SHEAR
International Nuclear Information System (INIS)
FENZI, C; McKEE, G.R; BURRELL, K.H; CARLSTROM, T.N; FONCK, R.J; GROEBNER, R.J
2003-01-01
The divertor magnetic geometry has a significant effect on the poloidal flow and resulting flow shear of turbulence in the outer region of L-mode tokamak plasmas, as determined via two-dimensional measurements of density fluctuations with Beam Emission Spectroscopy on DIII-D. Plasmas with similar parameters, except that in one case the ion (del)B drift points towards the divertor X-point (lower single-null, LSN), and in the other case, the ion (del)B drift points away from the divertor X-point (upper single-null, USN), are compared. Inside of r/a=0.9, the turbulence characteristics (amplitude, flow direction, correlation lengths) are similar in both cases, while near r/a=0.92, a dramatic reversal of the poloidal flow of turbulence relative to the core flow direction is observed in plasmas with the ion (del)B drift pointing towards the divertor X-point. No such flow reversal is observed in plasmas with the ion (del)B drift pointing away from the divertor X-point. This poloidal flow reversal results in a significantly larger local shear in the poloidal turbulence flow velocity in plasmas with the ion (del)B drift pointing towards the divertor X-point. Additionally, these plasmas locally exhibit significant dispersion, with two distinct and counter-propagating turbulence modes. Likewise, the radial correlation length of the turbulence is reduced in these plasmas, consistent with biorthogonal decomposition measurements of dominant turbulence structures. The naturally occurring turbulence flow shear in these LSN plasmas may facilitate the LH transition that occurs at an input power of roughly one-half to one-third that of corresponding plasmas with the ion (del)B drift pointing away from the X-point
Nonlinear simulation of electromagnetic current diffusive interchange mode turbulence
International Nuclear Information System (INIS)
Yagi, M.; Itoh, S.I.; Fukuyama, A.
1998-01-01
The anomalous transport in toroidal plasmas has been investigated extensively. It is pointed out that the nonlinear instability is important in driving the microturbulence[1], i.e., the self-sustained plasma turbulence. This concept is explained as follows; when the electron motion along the magnetic field line is resisted by the background turbulence, it gives rise to the effective resistivity and enhances the level of the turbulence. The nonlinear simulation of the electrostatic current diffusive interchange mode (CDIM) in the two dimensional sheared slab geometry has been performed as an example. The occurrence of the nonlinear instability and the self-sustainment of the plasma turbulence were confirmed by this simulation[2]. On the other hand, the electromagnetic turbulence is sustained in the high pressure limit. The possibility of the self-organization with more variety has been pointed out[3]. It is important to study the electromagnetic turbulence based on the nonlinear simulation. In this paper, the model equation for the electrostatic CDIM turbulence[2] is extended for both electrostatic and electromagnetic turbulence. (1) Not only E x B convective nonlinearity but also the electromagnetic nonlinearity which is related to the parallel flow are incorporated into the model equation. (2) The electron and ion pressure evolution equations are solved separately, making it possible to distinguish the electron and ion thermal diffusivities. The two dimensional nonlinear simulation of the electromagnetic CDIM is performed based on the extended fluid model. This paper is organized as follows. The model equation is explained in section II. The result of simulation is shown in section III. The conclusion and discussion are given in section IV. (author)
BOOK REVIEW: Statistical Mechanics of Turbulent Flows
Cambon, C.
2004-10-01
This is a handbook for a computational approach to reacting flows, including background material on statistical mechanics. In this sense, the title is somewhat misleading with respect to other books dedicated to the statistical theory of turbulence (e.g. Monin and Yaglom). In the present book, emphasis is placed on modelling (engineering closures) for computational fluid dynamics. The probabilistic (pdf) approach is applied to the local scalar field, motivated first by the nonlinearity of chemical source terms which appear in the transport equations of reacting species. The probabilistic and stochastic approaches are also used for the velocity field and particle position; nevertheless they are essentially limited to Lagrangian models for a local vector, with only single-point statistics, as for the scalar. Accordingly, conventional techniques, such as single-point closures for RANS (Reynolds-averaged Navier-Stokes) and subgrid-scale models for LES (large-eddy simulations), are described and in some cases reformulated using underlying Langevin models and filtered pdfs. Even if the theoretical approach to turbulence is not discussed in general, the essentials of probabilistic and stochastic-processes methods are described, with a useful reminder concerning statistics at the molecular level. The book comprises 7 chapters. Chapter 1 briefly states the goals and contents, with a very clear synoptic scheme on page 2. Chapter 2 presents definitions and examples of pdfs and related statistical moments. Chapter 3 deals with stochastic processes, pdf transport equations, from Kramer-Moyal to Fokker-Planck (for Markov processes), and moments equations. Stochastic differential equations are introduced and their relationship to pdfs described. This chapter ends with a discussion of stochastic modelling. The equations of fluid mechanics and thermodynamics are addressed in chapter 4. Classical conservation equations (mass, velocity, internal energy) are derived from their
Mean-Lagrangian formalism and covariance of fluid turbulence.
Ariki, Taketo
2017-05-01
Mean-field-based Lagrangian framework is developed for the fluid turbulence theory, which enables physically objective discussions, especially, of the history effect. Mean flow serves as a purely geometrical object of Lie group theory, providing useful operations to measure the objective rate and history integration of the general tensor field. The proposed framework is applied, on the one hand, to one-point closure model, yielding an objective expression of the turbulence viscoelastic effect. Application to two-point closure, on the other hand, is also discussed, where natural extension of known Lagrangian correlation is discovered on the basis of an extended covariance group.
Unidentified point sources in the IRAS minisurvey
Houck, J. R.; Soifer, B. T.; Neugebauer, G.; Beichman, C. A.; Aumann, H. H.; Clegg, P. E.; Gillett, F. C.; Habing, H. J.; Hauser, M. G.; Low, F. J.
1984-01-01
Nine bright, point-like 60 micron sources have been selected from the sample of 8709 sources in the IRAS minisurvey. These sources have no counterparts in a variety of catalogs of nonstellar objects. Four objects have no visible counterparts, while five have faint stellar objects visible in the error ellipse. These sources do not resemble objects previously known to be bright infrared sources.
Suppression of turbulent resistivity in turbulent Couette flow
Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe
2015-07-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
Energy Technology Data Exchange (ETDEWEB)
Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-07-15
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
International Nuclear Information System (INIS)
Si, Jiahe; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.
2015-01-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations
Turbulence and fossil turbulence lead to life in the universe
International Nuclear Information System (INIS)
Gibson, Carl H
2013-01-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than all the other forces that tend to damp the eddies out. Fossil turbulence is a perturbation produced by turbulence that persists after the fluid ceases to be turbulent at the scale of the perturbation. Because vorticity is produced at small scales, turbulence must cascade from small scales to large, providing a consistent physical basis for Kolmogorovian universal similarity laws. Oceanic and astrophysical mixing and diffusion are dominated by fossil turbulence and fossil turbulent waves. Observations from space telescopes show turbulence and vorticity existed in the beginning of the universe and that their fossils persist. Fossils of big bang turbulence include spin and the dark matter of galaxies: clumps of ∼10 12 frozen hydrogen planets that make globular star clusters as seen by infrared and microwave space telescopes. When the planets were hot gas, they hosted the formation of life in a cosmic soup of hot-water oceans as they merged to form the first stars and chemicals. Because spontaneous life formation according to the standard cosmological model is virtually impossible, the existence of life falsifies the standard cosmological model. (paper)
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...
4th European Turbulence Conference
1993-01-01
The European Turbulence Conferences have been organized under the auspices of the European Mechanics Committee (Euromech) to provide a forum for discussion and exchange of recent and new results in the field of turbulence. The first conference was organized in Lyon in 1986 with 152 participants. The second and third conferences were held in Berlin (1988) and Stockholm (1990) with 165 and 172 participants respectively. The fourth was organized in Delft from 30 June to 3 July 1992 by the J.M. Burgers Centre. There were 214 participants from 22 countries. This steadily growing number of participants demonstrates both the success and need for this type of conference. The main topics of the Fourth European Turbulence Conference were: Dynamical Systems and Transition; Statistical Physics and Turbulence; Experiments and Novel Experimental Techniques; Particles and Bubbles in Turbulence; Simulation Methods; Coherent Structures; Turbulence Modelling and Compressibility Effects. In addition a special session was held o...
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Russo, E.; Kuerten, J.G.M.; Geld, van der C.W.M.; Geurts, B.J.
2011-01-01
In this paper a point particle model for two-way coupling in water droplet-laden incompressible turbulent flow of air is proposed. The model is based on conservation laws and semi-empirical correlations. It has been implemented and tested in a DNS code based for turbulent channel flow with an
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Russo, E; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Geurts, Bernardus J.
In this paper a point particle model for two-way coupling in water droplet-laden incompressible turbulent flow of air is proposed. The model is based on conservation laws and semi-empirical correlations. It has been implemented and tested in a DNS code based for turbulent channel flow with an
Water circulation in non-isothermal droplet-laden turbulent channel flow
Russo, E; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Geurts, Bernardus J.; Simos, T.; Psihoyios, G.; Tsitouras, Ch.
2013-01-01
We propose a point-particle model for two-way coupling of water droplets dispersed in turbulent flow of a carrier gas consisting of air and water vapor. An incompressible flow formulation is applied for direct numerical simulation (DNS) of turbulent channel flow with a warm and a cold wall. Compared
Understanding the sub-critical transition to turbulence in wall flows
Indian Academy of Sciences (India)
In contrast with free shear flows presenting velocity profiles with injection points which cascade to turbulence in a relatively mild way, wall bounded flows are deprived of (inertial) instability modes at low Reynolds numbers and become turbulent in a much wilder way, most often marked by the coexistence of laminar and ...
Characterizing the Motion of Solar Magnetic Bright Points at High Resolution
Van Kooten, Samuel J.; Cranmer, Steven R.
2017-11-01
Magnetic bright points in the solar photosphere, visible in both continuum and G-band images, indicate footpoints of kilogauss magnetic flux tubes extending to the corona. The power spectrum of bright-point motion is thus also the power spectrum of Alfvén wave excitation, transporting energy up flux tubes into the corona. This spectrum is a key input in coronal and heliospheric models. We produce a power spectrum of bright-point motion using radiative magnetohydrodynamic simulations, exploiting spatial resolution higher than can be obtained in present-day observations, while using automated tracking to produce large data quantities. We find slightly higher amounts of power at all frequencies compared to observation-based spectra, while confirming the spectrum shape of recent observations. This also provides a prediction for observations of bright points with DKIST, which will achieve similar resolution and high sensitivity. We also find a granule size distribution in support of an observed two-population distribution, and we present results from tracking passive tracers, which show a similar power spectrum to that of bright points. Finally, we introduce a simplified, laminar model of granulation, with which we explore the roles of turbulence and of the properties of the granulation pattern in determining bright-point motion.
Efficient visibility-driven medical image visualisation via adaptive binned visibility histogram.
Jung, Younhyun; Kim, Jinman; Kumar, Ashnil; Feng, David Dagan; Fulham, Michael
2016-07-01
'Visibility' is a fundamental optical property that represents the observable, by users, proportion of the voxels in a volume during interactive volume rendering. The manipulation of this 'visibility' improves the volume rendering processes; for instance by ensuring the visibility of regions of interest (ROIs) or by guiding the identification of an optimal rendering view-point. The construction of visibility histograms (VHs), which represent the distribution of all the visibility of all voxels in the rendered volume, enables users to explore the volume with real-time feedback about occlusion patterns among spatially related structures during volume rendering manipulations. Volume rendered medical images have been a primary beneficiary of VH given the need to ensure that specific ROIs are visible relative to the surrounding structures, e.g. the visualisation of tumours that may otherwise be occluded by neighbouring structures. VH construction and its subsequent manipulations, however, are computationally expensive due to the histogram binning of the visibilities. This limits the real-time application of VH to medical images that have large intensity ranges and volume dimensions and require a large number of histogram bins. In this study, we introduce an efficient adaptive binned visibility histogram (AB-VH) in which a smaller number of histogram bins are used to represent the visibility distribution of the full VH. We adaptively bin medical images by using a cluster analysis algorithm that groups the voxels according to their intensity similarities into a smaller subset of bins while preserving the distribution of the intensity range of the original images. We increase efficiency by exploiting the parallel computation and multiple render targets (MRT) extension of the modern graphical processing units (GPUs) and this enables efficient computation of the histogram. We show the application of our method to single-modality computed tomography (CT), magnetic resonance
2016-06-23
AFRL-AFOSR-VA-TR-2016-0277 Experimental Investigation of Turbulence-Chemistry Interaction in High- Reynolds -Number Turbulent Partially Premixed...4. TITLE AND SUBTITLE [U] Experimental investigation of turbulence-chemistry interaction in high- Reynolds -number 5a. CONTRACT NUMBER turbulent...for public release Final Report: Experimental investigation of turbulence-chemistry interaction in high- Reynolds -number turbulent partially premixed
Wave turbulence in magnetized plasmas
Directory of Open Access Journals (Sweden)
S. Galtier
2009-02-01
Full Text Available The paper reviews the recent progress on wave turbulence for magnetized plasmas (MHD, Hall MHD and electron MHD in the incompressible and compressible cases. The emphasis is made on homogeneous and anisotropic turbulence which usually provides the best theoretical framework to investigate space and laboratory plasmas. The solar wind and the coronal heating problems are presented as two examples of application of anisotropic wave turbulence. The most important results of wave turbulence are reported and discussed in the context of natural and simulated magnetized plasmas. Important issues and possible spurious interpretations are also discussed.
Renormalized plasma turbulence theory: A quasiparticle picture
International Nuclear Information System (INIS)
DuBois, D.F.
1981-01-01
A general renormalized statistical theory of Vlasov turbulence is given which proceeds directly from the Vlasov equation and does not assume prior knowledge of sophisticated field-theoretic techniques. Quasiparticles are the linear excitations of the turbulent system away from its instantaneous mean (ensemble-averaged) state or background; the properties of this background state ''dress'' or renormalize the quasiparticle responses. It is shown that all two-point responses (including the dielectric) and all two-point correlation functions can be completely described by the mean distribution function and three fundamental quantities. Two of these are the quasiparticle responses: the propagator and the potential source: which measure, respectively, the separate responses of the mean distribution function and the mean electrostatic potential to functional changes in an external phase-space source added to Vlasov's equation. The third quantity is the two-point correlation function of the incoherent part of the phase-space density which acts as a self-consistent source of quasiparticle and potential fluctuations. This theory explicitly takes into account the self-consistent nature of the electrostatic-field fluctuations which introduces new effects not found in the usual ''test-particle'' theories. Explicit equations for the fundamental quantities are derived in the direct interaction approximation. Special attention is paid to the two-point correlations and the relation to theories of phase-space granulation
Full Text Available ... en español Blog About OnSafety CPSC Stands for Safety The Tipping Point Home > 60 Seconds of Safety (Videos) > The Tipping Point The Tipping Point by ... danger death electrical fall furniture head injury product safety television tipover tv Watch the video in Adobe ...
An Examination of Aviation Accidents Associated with Turbulence, Wind Shear and Thunderstorm
Evans, Joni K.
2013-01-01
The focal point of the study reported here was the definition and examination of turbulence, wind shear and thunderstorm in relation to aviation accidents. NASA project management desired this information regarding distinct subgroups of atmospheric hazards, in order to better focus their research portfolio. A seven category expansion of Kaplan's turbulence categories was developed, which included wake turbulence, mountain wave turbulence, clear air turbulence, cloud turbulence, convective turbulence, thunderstorm without mention of turbulence, and low altitude wind shear, microburst or turbulence (with no mention of thunderstorms).More than 800 accidents from flights based in the United States during 1987-2008 were selected from a National Transportation Safety Board (NTSB) database. Accidents were selected for inclusion in this study if turbulence, thunderstorm, wind shear or microburst was considered either a cause or a factor in the accident report, and each accident was assigned to only one hazard category. This report summarizes the differences between the categories in terms of factors such as flight operations category, aircraft engine type, the accident's geographic location and time of year, degree of injury to aircraft occupants, aircraft damage, age and certification of the pilot and the phase of flight at the time of the accident.
Turbulent kinetic energy balance measurements in the wake of a low-pressure turbine blade
International Nuclear Information System (INIS)
Sideridis, A.; Yakinthos, K.; Goulas, A.
2011-01-01
The turbulent kinetic energy budget in the wake generated by a high lift, low-pressure two-dimensional blade cascade of the T106 profile was investigated experimentally using hot-wire anemometry. The purpose of this study is to examine the transport mechanism of the turbulent kinetic energy and provide validation data for turbulence modeling. Point measurements were conducted on a high spatial resolution, two-dimensional grid that allowed precise derivative calculations. Positioning of the probe was achieved using a high accuracy traversing mechanism. The turbulent kinetic energy (TKE) convection, production, viscous diffusion and turbulent diffusion were all obtained directly from experimental measurements. Dissipation and pressure diffusion were calculated indirectly using techniques presented and validated by previous investigators. Results for all terms of the turbulent kinetic energy budget are presented and discussed in detail in the present work.
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.
Incremental Visualizer for Visible Objects
DEFF Research Database (Denmark)
Bukauskas, Linas; Bøhlen, Michael Hanspeter
This paper discusses the integration of database back-end and visualizer front-end into a one tightly coupled system. The main aim which we achieve is to reduce the data pipeline from database to visualization by using incremental data extraction of visible objects in a fly-through scenarios. We...... also argue that passing only relevant data from the database will substantially reduce the overall load of the visualization system. We propose the system Incremental Visualizer for Visible Objects (IVVO) which considers visible objects and enables incremental visualization along the observer movement...... path. IVVO is the novel solution which allows data to be visualized and loaded on the fly from the database and which regards visibilities of objects. We run a set of experiments to convince that IVVO is feasible in terms of I/O operations and CPU load. We consider the example of data which uses...
Visible neutrino decay at DUNE
Energy Technology Data Exchange (ETDEWEB)
Coloma, Pilar [Fermilab; Peres, Orlando G. [ICTP, Trieste
2017-05-09
If the heaviest neutrino mass eigenstate is unstable, its decay modes could include lighter neutrino eigenstates. In this case part of the decay products could be visible, as they would interact at neutrino detectors via mixing. At neutrino oscillation experiments, a characteristic signature of such \\emph{visible neutrino decay} would be an apparent excess of events at low energies. We focus on a simple phenomenological model in which the heaviest neutrino decays as $\
Sooting turbulent jet flame: characterization and quantitative soot measurements
Köhler, M.; Geigle, K. P.; Meier, W.; Crosland, B. M.; Thomson, K. A.; Smallwood, G. J.
2011-08-01
Computational fluid dynamics (CFD) modelers require high-quality experimental data sets for validation of their numerical tools. Preferred features for numerical simulations of a sooting, turbulent test case flame are simplicity (no pilot flame), well-defined boundary conditions, and sufficient soot production. This paper proposes a non-premixed C2H4/air turbulent jet flame to fill this role and presents an extensive database for soot model validation. The sooting turbulent jet flame has a total visible flame length of approximately 400 mm and a fuel-jet Reynolds number of 10,000. The flame has a measured lift-off height of 26 mm which acts as a sensitive marker for CFD model validation, while this novel compiled experimental database of soot properties, temperature and velocity maps are useful for the validation of kinetic soot models and numerical flame simulations. Due to the relatively simple burner design which produces a flame with sufficient soot concentration while meeting modelers' needs with respect to boundary conditions and flame specifications as well as the present lack of a sooting "standard flame", this flame is suggested as a new reference turbulent sooting flame. The flame characterization presented here involved a variety of optical diagnostics including quantitative 2D laser-induced incandescence (2D-LII), shifted-vibrational coherent anti-Stokes Raman spectroscopy (SV-CARS), and particle image velocimetry (PIV). Producing an accurate and comprehensive characterization of a transient sooting flame was challenging and required optimization of these diagnostics. In this respect, we present the first simultaneous, instantaneous PIV, and LII measurements in a heavily sooting flame environment. Simultaneous soot and flow field measurements can provide new insights into the interaction between a turbulent vortex and flame chemistry, especially since soot structures in turbulent flames are known to be small and often treated in a statistical manner.
Turbulent Premixed Flame Propagation in Microgravity
Menon, S.; Disseau, M.; Chakravarthy, V. K.; Jagoda, J.
1997-01-01
A facility in which turbulent Couette flow could be generated in a microgravity environment was designed and built. To fit into the NASA Lewis drop tower the device had to be very compact. This means that edge effects and flow re-circulation were expected to affect the flow. The flow was thoroughly investigated using LDV and was found to be largely two dimensional away from the edges with constant turbulence intensities in the core. Slight flow asymmetries are introduced by the non symmetric re-circulation of the fluid outside the test region. Belt flutter problems were remedied by adding a pair of guide plates to the belt. In general, the flow field was found to be quite similar to previously investigated Couette flows. However, turbulence levels and associated shear stresses were higher. This is probably due to the confined re-circulation zone reintroducing turbulence into the test section. An estimate of the length scales in the flow showed that the measurements were able to resolve nearly all the length scales of interest. Using a new LES method for subgrid combustion it has been demonstrated that the new procedure is computational feasible even on workstation type environment. It is found that this model is capable of capturing the propagation of the premixed names by resolving the flame in the LES grid within 2-3 grid points. In contrast, conventional LES results in numerical smearing of the flame and completely inaccurate estimate of the turbulent propagation speed. Preliminary study suggests that there is observable effect of buoyancy in the 1g environment suggesting the need for microgravity experiments of the upcoming experimental combustion studies. With the cold flow properties characterized, an identical hot flow facility is under construction. It is assumed that the turbulence properties ahead of the flame in this new device will closely match the results obtained here. This is required since the hot facility will not enable LDV measurements. The
Particle Acceleration and Heating by Turbulent Reconnection
Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios
2016-08-01
Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (I.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method to estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker-Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.
PARTICLE ACCELERATION AND HEATING BY TURBULENT RECONNECTION
International Nuclear Information System (INIS)
Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios
2016-01-01
Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (i.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method to estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker–Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.
PARTICLE ACCELERATION AND HEATING BY TURBULENT RECONNECTION
Energy Technology Data Exchange (ETDEWEB)
Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis, Vassilis [Department of Physics, Aristotle University of Thessaloniki, GR-52124 Thessaloniki (Greece); Anastasiadis, Anastasios [Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR-15236 Penteli (Greece)
2016-08-10
Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (i.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method to estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker–Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.
Phase space diffusion in turbulent plasmas
International Nuclear Information System (INIS)
Pecseli, H.L.
1990-01-01
Turbulent diffusion of charged test particles in electrostatic plasma turbulence is reviewed. Two different types of test particles can be distinguished. First passice particles which are subject to the fluctuating electric fields without themselves contributing to the local space charge. The second type are particles introduced at a prescribed phase space position at a certain time and which then self-consistently participate in the phase space dynamics of the turbulent. The latter ''active'' type of particles can be subjected to an effective frictional force due to radiation of plasma waves. In terms of these test particle types, two basically different problems can be formulated. One deals with the diffusion of a particle with respect to its point of release in phase space. Alternatively the relative diffusion between many, or just two, particles can be analyzed. Analytical expressions for the mean square particle displacements in phase space are discussed. More generally equations for the full probability densities are derived and these are solved analytically in special limits. (orig.)
Turbulent cascades in foreign exchange markets
Ghashghaie, S.; Breymann, W.; Peinke, J.; Talkner, P.; Dodge, Y.
1996-06-01
THE availability of high-frequency data for financial markets has made it possible to study market dynamics on timescales of less than a day1. For foreign exchange (FX) rates Müller et al.2 have shown that there is a net flow of information from long to short timescales: the behaviour of long-term traders (who watch the markets only from time to time) influences the behaviour of short-term traders (who watch the markets continuously). Motivated by this hierarchical feature, we have studied FX market dynamics in more detail, and report here an analogy between these dynamics and hydrodynamic turbulence3-8. Specifically, the relationship between the probability density of FX price changes (δx) and the time delay (δt) (Fig. la) is much the same as the relationship between the probability density of the velocity differences (δv) of two points in a turbulent flow and their spatial separation δr (Fig. 1b). Guided by this similarity we claim that there is an information cascade in FX market dynamics that corresponds to the energy cascade in hydrodynamic turbulence. On the basis of this analogy we can now rationalize the statistics of FX price differences at different time delays, which is important for, for example, option pricing. The analogy also provides a conceptual framework for understanding the short-term dynamics of speculative markets.
Large Eddy Simulation of turbulence
International Nuclear Information System (INIS)
Poullet, P.; Sancandi, M.
1994-12-01
Results of Large Eddy Simulation of 3D isotropic homogeneous turbulent flows are presented. A computer code developed on Connexion Machine (CM5) has allowed to compare two turbulent viscosity models (Smagorinsky and structure function). The numerical scheme influence on the energy density spectrum is also studied [fr
Advances in compressible turbulent mixing
International Nuclear Information System (INIS)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately
Interstellar turbulence and shock waves
International Nuclear Information System (INIS)
Bykov, A.M.
1982-01-01
Random deflections of shock fronts propagated through the turbulent interstellar medium can produce the strong electro-density fluctuations on scales l> or approx. =10 13 cm inferred from pulsar radio scintillations. The development of turbulence in the hot-phase ISM is discussed
Memory effects in turbulent diffusion
International Nuclear Information System (INIS)
Zagorodny, A.G.; Weiland, J.; Wilhelmsson, H.
1993-01-01
A non-Markovian approach is proposed for the derivation of the diffusion coefficient of saturated turbulence. A memory term accounting for nonlocal coherence effects is introduced in a new attempt to describe the transition between weak and strong turbulence. The result compares favourably with recent experiments as well as mode coupling simulations of fusion plasmas. (14 refs.)
Advances in compressible turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E. [eds.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately.
STRUCTURES OF TURBULENT VORTICES AND THEIR INFLUENCE ON FLOW PROPERTIES
Directory of Open Access Journals (Sweden)
Alfonsas Rimkus
2015-03-01
Full Text Available In spite of the many investigations that have been conducted on turbulent flows, the generation and development of turbulent vortices has not been investigated sufficiently yet. This prevents to understand well the processes involved in the flow. That is unfavorable for the further investigations. The developing vortex structures are interacting, and this needs to be estimated. Physical summing of velocities, formed by all structures, can be unfavorable for investigations, therefore they must be separated; otherwise bias errors can occur. The difficulty for investigations is that the widely employed Particle Image Velocity (PIV method, when a detailed picture of velocity field picture is necessary, can provide photos covering only a short interval of flow, which can’t include the largest flow structures, i.e. macro whirlpools. Consequently, action of these structures could not be investigated. Therefore, in this study it is tried to obtain the necessary data about the flow structure by analyzing the instantaneous velocity measurements by 3D means, which lasts for several minutes, therefore the existence and interaction of these structures become visible in measurement data. The investigations conducted in this way have been already discussed in the article, published earlier. Mostly the generation and development of bottom vortices was analyzed. In this article, the analysis of these turbulent velocity measurements is continued and the additional data about the structure of turbulent vortices is obtained.
Nondissipative gravitational turbulence
International Nuclear Information System (INIS)
Gurevich, A.V.; Zybin, K.P.
1988-01-01
The nonlinear stage of development of the Jeans instability in a cold nondissipative gravitating gas is considered. It is shown that for a time exceeding the Jeans time a nondissipative gravitational singularity (NGS) is formed in the vicinity of a local density maximum. The NGS is a stationary dynamic structure, the basis of which is the singularity. The density of the gas at the center of the NGS (for r → 0) tends to infinity, and the field potential and the mean velocity of the trapped gas, possess a power singularity. The turbulent state arises as the result of development of the instability in the case of an irregular initial density distribution. It is an hierarchic structure consisting of nested moving NGS of various sizes, the NGS of smaller dimensions being trapped in the field of a NGS of larger dimensions. The scaling relations for each given NGS in this case hold for both the gas density and density of smaller size trapped NGS. A brief comparison with the observational data shows that the real hierarchic structure of the Universe ranging from scales pertaining to spherical stellar clusters up to those of rich galaxy clusters is apparently a developed gravitational turbulence
Vortex dynamics and Lagrangian statistics in a model for active turbulence.
James, Martin; Wilczek, Michael
2018-02-14
Cellular suspensions such as dense bacterial flows exhibit a turbulence-like phase under certain conditions. We study this phenomenon of "active turbulence" statistically by using numerical tools. Following Wensink et al. (Proc. Natl. Acad. Sci. U.S.A. 109, 14308 (2012)), we model active turbulence by means of a generalized Navier-Stokes equation. Two-point velocity statistics of active turbulence, both in the Eulerian and the Lagrangian frame, is explored. We characterize the scale-dependent features of two-point statistics in this system. Furthermore, we extend this statistical study with measurements of vortex dynamics in this system. Our observations suggest that the large-scale statistics of active turbulence is close to Gaussian with sub-Gaussian tails.
Coherent structures in wall-bounded turbulence
Jiménez, Javier
2018-05-01
This article discusses the description of wall-bounded turbulence as a deterministic high-dimensional dynamical system of interacting coherent structures, defined as eddies with enough internal dynamics to behave relatively autonomously from any remaining incoherent part of the flow. The guiding principle is that randomness is not a property, but a methodological choice of what to ignore in the flow, and that a complete understanding of turbulence, including the possibility of control, requires that it be kept to a minimum. After briefly reviewing the underlying low-order statistics of flows at moderate Reynolds numbers, the article examines what two-point statistics imply for the decomposition of the flow into individual eddies. Intense eddies are examined next, including their temporal evolution, and shown to satisfy many of the properties required for coherence. In particular, it is shown that coherent structures larger than the Corrsin scale are a natural consequence of the shear. In wall-bounded turbulence, they can be classified into coherent dispersive waves and transient bursts. The former are found in the viscous layer near the wall and as very-large structures spanning the boundary layer thickness. Although they are shear-driven, these waves have enough internal structure to maintain a uniform advection velocity. Conversely, bursts exist at all scales, are characteristic of the logarithmic layer, and interact almost linearly with the shear. While the waves require a wall to determine their length scale, the bursts are essentially independent from it. The article concludes with a brief review of our present theoretical understanding of turbulent structures, and with a list of open problems and future perspectives.
Water droplet condensation and evaporation in turbulent channel flow
Russo, E; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Geurts, Bernardus J.
We propose a point-particle model for two-way coupling of water droplets dispersed in the turbulent flow of a carrier gas consisting of air and water vapour. We adopt an Euler–Lagrangian formulation based on conservation laws for the mass, momentum and energy of the continuous phase and on empirical
Physical mechanisms in shock-induced turbulent separated flow
Dolling, D. S.
1987-12-01
It has been demonstrated that the flow downstream of the moving shock is separated and that the foot of the shock is effectively the instantaneous separation point. The shock induced turbulent separation is an intermittant process and the separation line indicated by surface tracer methods, such as kerosene-lampblack, is a downstream boundary of a region of intermittent separation.
Phase space diffusion in turbulent plasmas
DEFF Research Database (Denmark)
Pécseli, Hans
1990-01-01
. The second type are particles introduced at a prescribed phase space position at a certain time and which then self-consistently participate in the phase space dynamics of the turbulence. The latter "active" type of particles can be subject to an effective frictional force due to radiation of plasma waves....... In terms of these test particle types, two basically different problems can be formulated. One deals with the diffusion of a particle with respect to its point of release in phase space. Alternatively the relative diffusion between many, or just two, particles can be analyzed. Analytical expressions...
Numerical study of turbulent diffusion
International Nuclear Information System (INIS)
McCoy, M.G.
1975-01-01
The problem of the numerical simulation of turbulent diffusion is studied. The two-dimensional velocity fields are assumed to be incompressible, homogeneous and stationary, and they are represented as stochastic processes. A technique is offered which creates velocity fields accurately representing the input statistics once a two point correlation function or an energy spectrum is given. Various complicated energy spectra may be represented utilizing this model. The program is then used to extract information concerning Gaussian diffusion processes. Various theories of other workers are tested including Taylor's classical representation of dispersion for times long compared with the Lagrangian correlation time. Also, a study is made of the relation between the Lagrangian and the Eulerian correlation function and a hypothesis is advanced and successfully tested. Questions concerning the relation between small eddies and the energy spectrum are considered. A criterion is advanced and successfully tested to decide whether small scale flow can be detected within the large eddies for any given spectrum. A method is developed to determine whether this small scale motion is in any sense periodic. Finally, the relation between two particle dispersion and the energy spectrum is studied anew and various theories are tested
Turbulent premixed flames on fractal-grid-generated turbulence
Energy Technology Data Exchange (ETDEWEB)
Soulopoulos, N; Kerl, J; Sponfeldner, T; Beyrau, F; Hardalupas, Y; Taylor, A M K P [Mechanical Engineering Department, Imperial College London, London SW7 2AZ (United Kingdom); Vassilicos, J C, E-mail: ns6@ic.ac.uk [Department of Aeronautics, Imperial College London, London SW7 2AZ (United Kingdom)
2013-12-15
A space-filling, low blockage fractal grid is used as a novel turbulence generator in a premixed turbulent flame stabilized by a rod. The study compares the flame behaviour with a fractal grid to the behaviour when a standard square mesh grid with the same effective mesh size and solidity as the fractal grid is used. The isothermal gas flow turbulence characteristics, including mean flow velocity and rms of velocity fluctuations and Taylor length, were evaluated from hot-wire measurements. The behaviour of the flames was assessed with direct chemiluminescence emission from the flame and high-speed OH-laser-induced fluorescence. The characteristics of the two flames are considered in terms of turbulent flame thickness, local flame curvature and turbulent flame speed. It is found that, for the same flow rate and stoichiometry and at the same distance downstream of the location of the grid, fractal-grid-generated turbulence leads to a more turbulent flame with enhanced burning rate and increased flame surface area. (paper)
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 5; Issue 5. Fixed Points - From Russia with Love - A Primer of Fixed Point Theory. A K Vijaykumar. Book Review Volume 5 Issue 5 May 2000 pp 101-102. Fulltext. Click here to view fulltext PDF. Permanent link:
Full Text Available ... OnSafety CPSC Stands for Safety The Tipping Point Home > 60 Seconds of Safety (Videos) > The Tipping Point ... 24 hours a day. For young children whose home is a playground, it’s the best way to ...
Full Text Available ... 60 Seconds of Safety (Videos) > The Tipping Point The Tipping Point by CPSC Blogger September 22, 2009 appliance child Childproofing CPSC danger death electrical fall furniture head injury product safety television tipover tv Watch the video in Adobe Flash ...
International Nuclear Information System (INIS)
Hanssen, A.; Mjolhus, E.
1993-01-01
In ionospheric radio modification experiments, manifestations of excited Langmuir turbulence are observed by means of VHF or UHF radars. Such experiments are performed in Arecibo, Puerto Rico, and at Tromso, Northern Norway. A weak turbulence theory involving parametric cascade of Langmuir waves, has earlier dominated the theoretical understanding of these experiments. This has recently been challenged, both from a theoretical and an experimental point of view, and a theory of strong Langmuir turbulence, involving a large number of nucleation collapse burnout cycles has been advocated. A version of the Zakharov model including damping and parametric driving, contains both of these scenarios, the crucial parameter being ΔΩ = ω-ω pe where ω is the applied frequency and ω pe the plasma frequency. This model allows the construction of a weak turbulence wave kinetic equation. In the present work spectra obtained from full wave solutions of the one dimensional Zakharov model are compared with saturation spectra of the wave kinetic model. The results can be described as follows: (i) for large values of ΔΩ, cascades are formed, and the number of cascades increases with the strength of the driver E 0 ; (ii) the number of cascades found in the full wave solution is smaller than that obtained from the wave kinetic equation; (iii) when E 0 becomes sufficiently large, the narrowly peaked cascade structure of the full wave spectrum breaks down, and a broad spectrum comes instead; (iv) this breakdown comes far before the cascade sequence has reached the Langmuir condensate; thus the Langmuir condensate plays no role in this process. At smaller values of ΔΩ, the turbulence is characterized by caviton nucleation resulting in broad wave number spectra. Also a coexistence range is found at intermediate values of ΔΩ, in which a few cascade lines ride upon a broad cavitation type spectrum
Influence of pinches on magnetic reconnection in turbulent space plasmas
Olshevsky, Vyacheslav; Lapenta, Giovanni; Markidis, Stefano; Divin, Andrey
A generally accepted scenario of magnetic reconnection in space plasmas is the breakage of magnetic field lines in X-points. In laboratory, reconnection is widely studied in pinches, current channels embedded into twisted magnetic fields. No model of magnetic reconnection in space plasmas considers both null-points and pinches as peers. We have performed a particle-in-cell simulation of magnetic reconnection in a three-dimensional configuration where null-points are present nitially, and Z-pinches are formed during the simulation. The X-points are relatively stable, and no substantial energy dissipation is associated with them. On contrary, turbulent magnetic reconnection in the pinches causes the magnetic energy to decay at a rate of approximately 1.5 percent per ion gyro period. Current channels and twisted magnetic fields are ubiquitous in turbulent space plasmas, so pinches can be responsible for the observed high magnetic reconnection rates.
Visibility in a pure model of golden spiral phyllotaxis.
Herrmann, Burghard
2018-07-01
This paper considers the geometry of plants with golden spiral phyllotaxis, i.e. growing leaf by leaf on a spiral with golden divergence angle, via the simplest mathematical model, a cylinder with regular arrangement of points on its surface. As is well-known, Fibonacci numbers appear by means of the order of parastichies. This fact is shown to be a straightforward application of logical consequences to a particular model with respect to pure visibility. This notion is very similar to that of contact parastichies. The 3-D cylindrical model of golden spiral phyllotaxis abstracts from the form of leaves and identifies them with points. Pure visibility is specified in the 2-D representation so that common sense parastichies can be scrutinized. The main Theorem states that the orders of the purely most visible parastichies are Fibonacci numbers. Copyright © 2018 Elsevier Inc. All rights reserved.
Turbulent/non-turbulent interfaces detected in DNS of incompressible turbulent boundary layers
Watanabe, T.; Zhang, X.; Nagata, K.
2018-03-01
The turbulent/non-turbulent interface (TNTI) detected in direct numerical simulations is studied for incompressible, temporally developing turbulent boundary layers at momentum thickness Reynolds number Reθ ≈ 2000. The outer edge of the TNTI layer is detected as an isosurface of the vorticity magnitude with the threshold determined with the dependence of the turbulent volume on a threshold level. The spanwise vorticity magnitude and passive scalar are shown to be good markers of turbulent fluids, where the conditional statistics on a distance from the outer edge of the TNTI layer are almost identical to the ones obtained with the vorticity magnitude. Significant differences are observed for the conditional statistics between the TNTI detected by the kinetic energy and vorticity magnitude. A widely used grid setting determined solely from the wall unit results in an insufficient resolution in a streamwise direction in the outer region, whose influence is found for the geometry of the TNTI and vorticity jump across the TNTI layer. The present results suggest that the grid spacing should be similar for the streamwise and spanwise directions. Comparison of the TNTI layer among different flows requires appropriate normalization of the conditional statistics. Reference quantities of the turbulence near the TNTI layer are obtained with the average of turbulent fluids in the intermittent region. The conditional statistics normalized by the reference turbulence characteristics show good quantitative agreement for the turbulent boundary layer and planar jet when they are plotted against the distance from the outer edge of the TNTI layer divided by the Kolmogorov scale defined for turbulent fluids in the intermittent region.
Comparison of turbulence mitigation algorithms
Kozacik, Stephen T.; Paolini, Aaron; Sherman, Ariel; Bonnett, James; Kelmelis, Eric
2017-07-01
When capturing imagery over long distances, atmospheric turbulence often degrades the data, especially when observation paths are close to the ground or in hot environments. These issues manifest as time-varying scintillation and warping effects that decrease the effective resolution of the sensor and reduce actionable intelligence. In recent years, several image processing approaches to turbulence mitigation have shown promise. Each of these algorithms has different computational requirements, usability demands, and degrees of independence from camera sensors. They also produce different degrees of enhancement when applied to turbulent imagery. Additionally, some of these algorithms are applicable to real-time operational scenarios while others may only be suitable for postprocessing workflows. EM Photonics has been developing image-processing-based turbulence mitigation technology since 2005. We will compare techniques from the literature with our commercially available, real-time, GPU-accelerated turbulence mitigation software. These comparisons will be made using real (not synthetic), experimentally obtained data for a variety of conditions, including varying optical hardware, imaging range, subjects, and turbulence conditions. Comparison metrics will include image quality, video latency, computational complexity, and potential for real-time operation. Additionally, we will present a technique for quantitatively comparing turbulence mitigation algorithms using real images of radial resolution targets.
International Nuclear Information System (INIS)
Kahn, F.D.
1983-01-01
A relativistic plasma flow can explain many of the observations on the one-sided jets, which are associated with radio sources that show superluminal motions in their cores. The pressure from the ambient medium will communicate across the jet in a relatively short distance, typically 30 kpc. The friction between the jet and the external medium then makes the flow go turbulent. As a result the jet dissipates energy and will be brought to rest within a few hundred kpc, if it does not strike an obstacle before. The mean flow in the jet is strongly sheared and stretches the lines of force of any magnetic field frozen into the plasma. The dominant field direction, as seen from the rest frame of the plasma, is therefore parallel to the length of the jet. Polarization measurements have shown that this is in fact the case. (author)
International Nuclear Information System (INIS)
Pomeau, Y.
1981-07-01
In this work it is reviewed a few known types of transition to turbulence, as the cascade of period doubling and the intermittent transition. This happens in dynamical systems with a few degrees of freedom, as modelled by the iteration of non linear maps. Then it is presented specific transitions for systems with many degrees of freedom. It is condidered first the occurence of a low frequency broadband noise in large cells at the onset of Rayleigh-Benard convection; then the transition by intermittent bursts in parallel flows. In this last case, one is concerned with localized and finite amplitude perturbations. Simple geometric arguments show that these fluctuations, when they are isolated and with a well definite relative speed, exist for a single value of the Reynolds number only [fr
Approximate deconvolution models of turbulence analysis, phenomenology and numerical analysis
Layton, William J
2012-01-01
This volume presents a mathematical development of a recent approach to the modeling and simulation of turbulent flows based on methods for the approximate solution of inverse problems. The resulting Approximate Deconvolution Models or ADMs have some advantages over more commonly used turbulence models – as well as some disadvantages. Our goal in this book is to provide a clear and complete mathematical development of ADMs, while pointing out the difficulties that remain. In order to do so, we present the analytical theory of ADMs, along with its connections, motivations and complements in the phenomenology of and algorithms for ADMs.
Saturation of the turbulent dynamo.
Schober, J; Schleicher, D R G; Federrath, C; Bovino, S; Klessen, R S
2015-08-01
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence.
Statistical properties of turbulence: An overview
Indian Academy of Sciences (India)
the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer ... However, it is not easy to state what would consti- tute a solution of the turbulence ...... flow with Lagrangian tracers and use a cubic spline interpolation method to calculate their ...
Scale separation closure and Alfven wave turbulence
International Nuclear Information System (INIS)
Chen, C.Y.; Mahajan, S.M.
1985-04-01
Based on the concept of scale separation between coherent response function and incoherent source for renormalized turbulence theories, a closure scheme is proposed. A model problem dealing with shear-Alfven wave turbulence is numerically solved; the solution explicitly shows expected turbulence features such as frequency shift from linear modes, band-broadening, and a power law dependence for the turbulence spectrum
Strong Turbulence in Low-beta Plasmas
DEFF Research Database (Denmark)
Tchen, C. M.; Pécseli, Hans; Larsen, Søren Ejling
1980-01-01
An investigation of the spectral structure of turbulence in a plasma confined by a strong homogeneous magnetic field was made by means of a fluid description. The turbulent spectrum is divided into subranges. Mean gradients of velocity and density excite turbulent motions, and govern the production......-cathode reflex arc, Stellarator, Zeta discharge, ionospheric plasmas, and auroral plasma turbulence....
Goldsmith, Shelly
1999-01-01
Dew Point was a solo exhibition originating at PriceWaterhouseCoopers Headquarters Gallery, London, UK and toured to the Centre de Documentacio i Museu Textil, Terrassa, Spain and Gallery Aoyama, Tokyo, Japan.
Full Text Available ... Point by CPSC Blogger September 22, 2009 appliance child Childproofing CPSC danger death electrical fall furniture head injury product safety television tipover tv Watch the video in Adobe Flash ...
... Point by CPSC Blogger September 22, 2009 appliance child Childproofing CPSC danger death electrical fall furniture head injury product safety television tipover tv Watch the video in Adobe Flash ...
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Effects of premixed flames on turbulence and turbulent scalar transport
Energy Technology Data Exchange (ETDEWEB)
Lipatnikov, A.N.; Chomiak, J. [Department of Applied Mechanics, Chalmers University of Technology, 412 75 Goeteborg (Sweden)
2010-02-15
Experimental data and results of direct numerical simulations are reviewed in order to show that premixed combustion can change the basic characteristics of a fluctuating velocity field (the so-called flame-generated turbulence) and the direction of scalar fluxes (the so-called countergradient or pressure-driven transport) in a turbulent flow. Various approaches to modeling these phenomena are discussed and the lack of a well-elaborated and widely validated predictive approach is emphasized. Relevant basic issues (the transition from gradient to countergradient scalar transport, the role played by flame-generated turbulence in the combustion rate, the characterization of turbulence in premixed flames, etc.) are critically considered and certain widely accepted concepts are disputed. Despite the substantial progress made in understanding the discussed effects over the past decades, these basic issues strongly need further research. (author)
Effect of turbulent collisions on diffusion in stationary plasma turbulence
International Nuclear Information System (INIS)
Xia, H.; Ishihara, O.
1990-01-01
Recently the velocity diffusion process was studied by the generalized Langevin equation derived by the projection operator method. The further study shows that the retarded frictional function plays an important role in suppressing particle diffusion in the velocity space in stronger turbulence as much as the resonance broadening effect. The retarded frictional effect, produced by the effective collisions due to the plasma turbulence is assumed to be a Gaussian, but non-Markovian and non-wide-sense stationary process. The relations between the proposed formulation and the extended resonance broadening theory is discussed. The authors also carry out test particle numerical experiment for Langmuir turbulence to test the theories. In a stronger turbulence a deviation of the diffusion rate from the one predicted by both the quasilinear and the extended resonance theories has been observed and is explained qualitatively by the present formulation
Wind energy impact of turbulence
Hölling, Michae; Ivanell, Stefan
2014-01-01
This book presents the results of the seminar ""Wind Energy and the Impact of Turbulence on the Conversion Process"" which was supported from three societies, namely the EUROMech, EAWE and ERCOFATC and took place in Oldenburg, Germany in spring 2012.The seminar was one of the first scientific meetings devoted to the common topic of wind energy and basic turbulence. The established community of researchers working on the challenging puzzle of turbulence for decades met the quite young community of researchers, who face the upcoming challenges in the fast growing field of wind energy application
Outer scale of atmospheric turbulence
Lukin, Vladimir P.
2005-10-01
In the early 70's, the scientists in Italy (A.Consortini, M.Bertolotti, L.Ronchi), USA (R.Buser, Ochs, S.Clifford) and USSR (V.Pokasov, V.Lukin) almost simultaneously discovered the phenomenon of deviation from the power law and the effect of saturation for the structure phase function. During a period of 35 years we have performed successively the investigations of the effect of low-frequency spectral range of atmospheric turbulence on the optical characteristics. The influence of the turbulence models as well as a outer scale of turbulence on the characteristics of telescopes and systems of laser beam formations has been determined too.
Quantum Turbulence ---Another da Vinci Code---
Tsubota, M.
Quantum turbulence comprises a tangle of quantized vorticeswhich are stable topological defects created by Bose-Einstein condensation, being realized in superfluid helium and atomic Bose-Einstein condensates. In recent years there has been a growing interest in quantum turbulence. One of the important motivations is to understand the relation between quantum and classical turbulence. Quantum turbulence is expected to be much simpler than usual classical turbulence and give a prototype of turbulence. This article reviews shortly the recent research developments on quantum turbulence.
Understanding and Approaching Muslim Visibilities
DEFF Research Database (Denmark)
Schmidt, Garbi
2011-01-01
Within Western nation-states such as Denmark, Islamic identities are often seen as inherently and divergently visible, an aspect that some argue is detrimental to the secular nation-state. From a research perspective, one way to nuance this position is by focusing on groups of 'invisible' Muslims...
Early Learning Theories Made Visible
Beloglovsky, Miriam; Daly, Lisa
2015-01-01
Go beyond reading about early learning theories and see what they look like in action in modern programs and teacher practices. With classroom vignettes and colorful photographs, this book makes the works of Jean Piaget, Erik Erikson, Lev Vygotsky, Abraham Maslow, John Dewey, Howard Gardner, and Louise Derman-Sparks visible, accessible, and easier…
Non-Euclidean visibility problems
Indian Academy of Sciences (India)
FERNANDO CHAMIZO. Departamento de Matemáticas, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain. MS received 14 November 2005. Abstract. We consider the analog of visibility problems in hyperbolic plane (repre- sented by Poincaré half-plane model H), replacing the standard lattice Z ...
Are naked singularities really visible
Energy Technology Data Exchange (ETDEWEB)
Calvani, M [Padua Univ. (Italy). Ist. di Astronomia; De Felice, F [Alberta Univ., Edmonton (Canada); Nobili, L [Padua Univ. (Italy). Ist. di Fisica
1978-12-09
The question whether a Kerr naked singularity is actually visible from infinity is investigated; it is shown that in fact any signal which could be emitted from the singularity is infinitely red-shifted. This implies that naked singularities would be indistinguishable from a black hole.
Visible Machine Learning for Biomedicine.
Yu, Michael K; Ma, Jianzhu; Fisher, Jasmin; Kreisberg, Jason F; Raphael, Benjamin J; Ideker, Trey
2018-06-14
A major ambition of artificial intelligence lies in translating patient data to successful therapies. Machine learning models face particular challenges in biomedicine, however, including handling of extreme data heterogeneity and lack of mechanistic insight into predictions. Here, we argue for "visible" approaches that guide model structure with experimental biology. Copyright © 2018. Published by Elsevier Inc.
The large Reynolds number - Asymptotic theory of turbulent boundary layers.
Mellor, G. L.
1972-01-01
A self-consistent, asymptotic expansion of the one-point, mean turbulent equations of motion is obtained. Results such as the velocity defect law and the law of the wall evolve in a relatively rigorous manner, and a systematic ordering of the mean velocity boundary layer equations and their interaction with the main stream flow are obtained. The analysis is extended to the turbulent energy equation and to a treatment of the small scale equilibrium range of Kolmogoroff; in velocity correlation space the two-thirds power law is obtained. Thus, the two well-known 'laws' of turbulent flow are imbedded in an analysis which provides a great deal of other information.
Experiments in polydisperse two-phase turbulent flows
International Nuclear Information System (INIS)
Bachalo, W.D.; Houser, M.J.
1985-01-01
Aspects of turbulent two-phase flow measurements obtained with a laser Doppler velocimeter that was modified to also obtain particle size were investigated. Simultaneous measurements of the particle size and velocity allowed the determination of the lag characteristics of particles over a range of sizes. Relatively large particles were found to respond well to the turbulent fluctuations in low speed flows. Measurements of sprays were obtained at various points throughout the spray plume. Velocity measurements for each drop size class were obtained and revealed the relative velocity relaxation with downstream distance. The evolution of the rms velocities for each size class was also examined. Difficulties associated with seeding polydispersions to obtain gas phase turbulence data were discussed. Several approaches for mitigating the errors due to seed particle concentration bias were reviewed
Turbulence optimisation in stellarator experiments
Energy Technology Data Exchange (ETDEWEB)
Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)
2015-05-01
Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.
Optimizing Stellarators for Turbulent Transport
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2010-01-01
Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.
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)
Modeling Compressed Turbulence with BHR
Israel, Daniel
2011-11-01
Turbulence undergoing compression or expansion occurs in systems ranging from internal combustion engines to supernovae. One common feature in many of these systems is the presence of multiple reacting species. Direct numerical simulation data is available for the single-fluid, low turbulent Mach number case. Wu, et al. (1985) compared their DNS results to several Reynolds-averaged Navier-Stokes models. They also proposed a three-equation k - ɛ - τ model, in conjunction with a Reynolds-stress model. Subsequent researchers have proposed alternative corrections to the standard k - ɛ formulation. Here we investigate three variants of the BHR model (Besnard, 1992). BHR is a model for multi-species variable-density turbulence. The three variants are the linear eddy-viscosity, algebraic-stress, and full Reynolds-stress formulations. We then examine the predictions of the model for the fluctuating density field for the case of variable-density turbulence.
Premixed autoignition in compressible turbulence
Konduri, Aditya; Kolla, Hemanth; Krisman, Alexander; Chen, Jacqueline
2016-11-01
Prediction of chemical ignition delay in an autoignition process is critical in combustion systems like compression ignition engines and gas turbines. Often, ignition delay times measured in simple homogeneous experiments or homogeneous calculations are not representative of actual autoignition processes in complex turbulent flows. This is due the presence of turbulent mixing which results in fluctuations in thermodynamic properties as well as chemical composition. In the present study the effect of fluctuations of thermodynamic variables on the ignition delay is quantified with direct numerical simulations of compressible isotropic turbulence. A premixed syngas-air mixture is used to remove the effects of inhomogeneity in the chemical composition. Preliminary results show a significant spatial variation in the ignition delay time. We analyze the topology of autoignition kernels and identify the influence of extreme events resulting from compressibility and intermittency. The dependence of ignition delay time on Reynolds and turbulent Mach numbers is also quantified. Supported by Basic Energy Sciences, Dept of Energy, United States.
Toy models of developed turbulence
Directory of Open Access Journals (Sweden)
M.Hnatich
2005-01-01
Full Text Available We have investigated the advection of a passive scalar quantity by incompressible helical turbulent flow within the framework of extended Kraichnan model. Turbulent fluctuations of velocity field are assumed to have the Gaussian statistics with zero mean and defined noise with finite time-correlation. Actual calculations have been done up to two-loop approximation within the framework of field-theoretic renormalization group approach. It turned out that space parity violation (helicity of turbulent environment does not affect anomalous scaling which is a peculiar attribute of the corresponding model without helicity. However, stability of asymptotic regimes, where anomalous scaling takes place, strongly depends on the amount of helicity. Moreover, helicity gives rise to the turbulent diffusivity, which has been calculated in one-loop approximation.
Stochastic Subspace Modelling of Turbulence
DEFF Research Database (Denmark)
Sichani, Mahdi Teimouri; Pedersen, B. J.; Nielsen, Søren R.K.
2009-01-01
positive definite cross-spectral density matrix a frequency response matrix is constructed which determines the turbulence vector as a linear filtration of Gaussian white noise. Finally, an accurate state space modelling method is proposed which allows selection of an appropriate model order......, and estimation of a state space model for the vector turbulence process incorporating its phase spectrum in one stage, and its results are compared with a conventional ARMA modelling method.......Turbulence of the incoming wind field is of paramount importance to the dynamic response of civil engineering structures. Hence reliable stochastic models of the turbulence should be available from which time series can be generated for dynamic response and structural safety analysis. In the paper...
[Qualitative Determination of Organic Vapour Using Violet and Visible Spectrum].
Jiang, Bo; Hu, Wen-zhong; Liu, Chang-jian; Zheng, Wei; Qi, Xiao-hui; Jiang, Ai-li; Wang, Yan-ying
2015-12-01
Vapours of organic matters were determined qualitatively employed with ultraviolet-visible absorption spectroscopy. Vapours of organic matters were detected using ultraviolet-visible spectrophotometer employing polyethylene film as medium, the ultraviolet and visible absorption spectra of vegetable oil vapours of soybean oil, sunflower seed oil, peanut oil, rapeseed oil, sesame oil, cotton seed oil, tung tree seed oil, and organic compound vapours of acetone, ethyl acetate, 95% ethanol, glacial acetic acid were obtained. Experimental results showed that spectra of the vegetable oil vapour and the organic compound vapour could be obtained commendably, since ultra violet and visible spectrum of polyethylene film could be deducted by spectrograph zero setting. Different kinds of vegetable oils could been distinguished commendably in the spectra since the λ(max), λ(min), number of absorption peak, position, inflection point in the ultra violet and visible spectra obtained from the vapours of the vegetable oils were all inconsistent, and the vapours of organic compounds were also determined perfectly. The method had a good reproducibility, the ultraviolet and visible absorption spectra of the vapours of sunflower seed oil in 10 times determination were absolutely the same. The experimental result indicated that polyethylene film as a kind of medium could be used for qualitative analysis of ultraviolet and visible absorption spectroscopy. The method for determination of the vapours of the vegetable oils and organic compounds had the peculiarities of fast speed analysis, well reproducibility, accuracy and reliability and low cost, and so on. Ultraviolet and visible absorption spectrum of organic vapour could provide feature information of material vapour and structural information of organic compound, and provide a novel test method for identifying vapour of compound and organic matter.
Turbulence in unmagnetized Vlasov plasmas
International Nuclear Information System (INIS)
Kuo, S.P.
1985-01-01
The classical technique of transformation and characteristics is employed to analyze the problem of strong turbulence in unmagnetized plasmas. The effect of resonance broadening and perturbation expansion are treated simultaneously, without time secularities. The renormalization procedure of Dupree and Tetreault is used in the transformed Vlasov equation to analyze the turbulence and to derive explicitly a diffusion equation. Analyses are extended to inhomogeneous plasmas and the relationship between the transformation and ponderomotive force is obtained. (author)
Turbulent effective absorptivity and refractivity
International Nuclear Information System (INIS)
Rax, J.M.
1984-09-01
The problem of wave propagation in a turbulent magnetized plasma is investigated. Considering small scale, low frequency density fluctuations we solve the Maxwell equations and show that the eikonal approximation remains valid with an effective refractivity and an effective absorptivity taking into account the energy diffusion due to the turbulent motion. Then the result is applied to the problem of lower hybrid waves scattering by drift waves density fluctuations in tokamaks
Asymptotic expansion and statistical description of turbulent systems
International Nuclear Information System (INIS)
Hagan, W.K. III.
1986-01-01
A new approach to studying turbulent systems is presented in which an asymptotic expansion of the general dynamical equations is performed prior to the application of statistical methods for describing the evolution of the system. This approach has been applied to two specific systems: anomalous drift wave turbulence in plasmas and homogeneous, isotropic turbulence in fluids. For the plasma case, the time and length scales of the turbulent state result in the asymptotic expansion of the Vlasov/Poisson equations taking the form of nonlinear gyrokinetic theory. Questions regarding this theory and modern Hamiltonian perturbation methods are discussed and resolved. A new alternative Hamiltonian method is described. The Eulerian Direct Interaction Approximation (EDIA) is slightly reformulated and applied to the equations of nonlinear gyrokinetic theory. Using a similarity transformation technique, expressions for the thermal diffusivity are derived from the EDIA equations for various geometries, including a tokamak. In particular, the unique result for generalized geometry may be of use in evaluating fusion reactor designs and theories of anomalous thermal transport in tokamaks. Finally, a new and useful property of the EDIA is pointed out. For the fluid case, an asymptotic expansion is applied to the Navier-Stokes equation and the results lead to the speculation that such an approach may resolve the problem of predicting the Kolmogorov inertial range energy spectrum for homogeneous, isotropic turbulence. 45 refs., 3 figs
Turbulence and energy confinement in TORE SUPRA ohmic discharges
International Nuclear Information System (INIS)
Garbet, X.; Payan, J.; Laviron, C.; Devynck, P.; Saha, S.K.; Capes, H.; Chen, X.P.; Coulon, J.P.; Gil, C.; Harris, G.; Hutter, T.; Pecquet, A.L.
1992-06-01
Results on confinement and turbulence from a set of ohmic discharges in Tore Supra are discussed. The attention is focused on the saturation of the energy confinement time and it is emphasized that this saturation could be explained by a saturation of the electron heat diffusivity. Ion behaviour is indeed governed by dilution and equipartition effects. Although the ion heat transport is never neoclassical, there is no enhanced degradation at the saturation. This behaviour is confirmed by turbulence measurements given by CO 2 laser coherent scattering. The density fluctuations level follows the electron heat diffusivity variations with the average density. Waves propagating in the ion diamagnetic direction are always present in turbulence frequency spectra. Thus, the saturation cannot be explained by the onset of an ion turbulence. The existence of an ion turbulence at the edge at all densities cannot be excluded. However, this ion feature in scattering spectra could be explained by a Doppler shift associated to an inversion point of the radial electric field at the edge
Description of group-theoretical model of developed turbulence
International Nuclear Information System (INIS)
Saveliev, V L; Gorokhovski, M A
2008-01-01
We propose to associate the phenomenon of stationary turbulence with the special self-similar solutions of the Euler equations. These solutions represent the linear superposition of eigenfields of spatial symmetry subgroup generators and imply their dependence on time through the parameter of the symmetry transformation only. From this model, it follows that for developed turbulent process, changing the scale of averaging (filtering) of the velocity field is equivalent to composition of scaling, translation and rotation transformations. We call this property a renormalization-group invariance of filtered turbulent fields. The renormalization group invariance provides an opportunity to transform the averaged Navier-Stokes equation over a small scale (inner threshold of the turbulence) to larger scales by simple scaling. From the methodological point of view, it is significant to note that the turbulent viscosity term appeared not as a result of averaging of the nonlinear term in the Navier-Stokes equation, but from the molecular viscosity term with the help of renormalization group transformation.
Turbulence generation through intense localized sources of energy
Maqui, Agustin; Donzis, Diego
2015-11-01
Mechanisms to generate turbulence in controlled conditions have been studied for nearly a century. Most common methods include passive and active grids with a focus on incompressible turbulence. However, little attention has been given to compressible flows, and even less to hypersonic flows, where phenomena such as thermal non-equilibrium can be present. Using intense energy from lasers, extreme molecule velocities can be generated from photo-dissociation. This creates strong localized changes in both the hydrodynamics and thermodynamics of the flow, which may perturb the flow in a way similar to an active grid to generate turbulence in hypersonic flows. A large database of direct numerical simulations (DNS) are used to study the feasibility of such an approach. An extensive analysis of single and two point statistics, as well as spectral dynamics is used to characterize the evolution of the flow towards realistic turbulence. Local measures of enstrophy and dissipation are studied to diagnose the main mechanisms for energy exchange. As commonly done in compressible flows, dilatational and solenoidal components are separated to understand the effect of acoustics on the development of turbulence. Further results for cases that assimilate laboratory conditions will be discussed. The authors gratefully acknowledge the support of AFOSR.
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.
Measurement of Spatial Coherence of Light Propagating in a Turbulent Atmosphere
Directory of Open Access Journals (Sweden)
P. Barcik
2013-04-01
Full Text Available A lot of issues have to be taken into account when designing a reliable free space optical communication link. Among these are e.g.,beam wander, fluctuation of optical intensity and loss of spatial coherence that are caused by atmospheric turbulence. This paper presents experimental measurements of spatial coherence of a laser beam. The experimental setup is based on Young's double pinhole experiment. Fringe patterns under atmospheric turbulence for four different pinhole separations are presented. From these fringe patterns, visibility is determined and the coherence radius is estimated.
Systems and Methods for Automated Water Detection Using Visible Sensors
Rankin, Arturo L. (Inventor); Matthies, Larry H. (Inventor); Bellutta, Paolo (Inventor)
2016-01-01
Systems and methods are disclosed that include automated machine vision that can utilize images of scenes captured by a 3D imaging system configured to image light within the visible light spectrum to detect water. One embodiment includes autonomously detecting water bodies within a scene including capturing at least one 3D image of a scene using a sensor system configured to detect visible light and to measure distance from points within the scene to the sensor system, and detecting water within the scene using a processor configured to detect regions within each of the at least one 3D images that possess at least one characteristic indicative of the presence of water.
Observation of a visible charmed particle decay in neutrino interactions
International Nuclear Information System (INIS)
Cnops, A.M.; Connolly, P.L.; Kahn, S.A.
1979-01-01
In a sample of 250 semileptonic charmed particle decays (ν/sub μ/ + Neon → μ - + e + + ... events), one clear event is found where the e + does not come directly from the ν interaction vertex but from a decay point 1.1 cm downstream of the vertex. This event is interpreted as a visible charmed particle decay: into an e + and a positive and a negative charged track. The observation of a visible charm decay in the sample is consistent with what is expected if the charm lifetime were of the order 5 x 10 -13 sec. 5 references
Recent developments in plasma turbulence and turbulent transport
Energy Technology Data Exchange (ETDEWEB)
Terry, P.W. [Univ. of Wisconsin, Madison, WI (United States)
1997-09-22
This report contains viewgraphs of recent developments in plasma turbulence and turbulent transport. Localized nonlinear structures occur under a variety of circumstances in turbulent, magnetically confined plasmas, arising in both kinetic and fluid descriptions, i.e., in either wave-particle or three-wave coupling interactions. These structures are non wavelike. They cannot be incorporated in the collective wave response, but interact with collective modes through their shielding by the plasma dielectric. These structures are predicted to modify turbulence-driven transport in a way that in consistent with, or in some cases are confirmed by recent experimental observations. In kinetic theory, non wavelike structures are localized perturbations of phase space density. There are two types of structures. Holes are self-trapped, while clumps have a self-potential that is too weak to resist deformation and mixing by ambient potential fluctuations. Clumps remain correlated in turbulence if their spatial extent is smaller than the correlation length of the scattering fields. In magnetic turbulence, clumps travel along stochastic magnetic fields, shielded by the plasma dielectric. A drag on the clump macro-particle is exerted by the shielding, inducing emission into the collective response. The emission in turn damps back on the particle distribution via Landau dampling. The exchange of energy between clumps and particles, as mediated by the collective mode, imposes constraints on transport. For a turbulent spectrum whose mean wavenumber along the equilibrium magnetic field is nonzero, the electron thermal flux is proportional to the ion thermal velocity. Conventional predictions (which account only for collective modes) are larger by the square root of the ion to electron mass ratio. Recent measurements are consistent with the small flux. In fluid plasma,s localized coherent structures can occur as intense vortices.
International Nuclear Information System (INIS)
Boudjemadi, R.
1996-03-01
The main objectives of this thesis are the direct numerical simulation of natural convection in a vertical differentially heated slot and the improvements of second-order turbulence modelling. A three-dimensional direct numerical simulation code has been developed in order to gain a better understanding of turbulence properties in natural convection flows. This code has been validated in several physical configurations: non-stratified natural convection flows (conduction solution), stratified natural convection flows (double boundary layer solution), transitional and turbulent Poiseuille flows. For the conduction solution, the turbulent regime was reached at a Rayleigh number of 1*10 5 and 5.4*10 5 . A detailed analysis of these results has revealed the principal qualities of the available models but has also pointed our their shortcomings. This data base has been used in order to improve the triple correlations transport models and to select the turbulent time scales suitable for such flows. (author). 122 refs., figs., tabs., 4 appends
Measurement of turbulent kinetic energy spectrum - Part 2: Convection record measurements
DEFF Research Database (Denmark)
Velte, Clara Marika; Buchhave, Preben; Hodzic, Azur
2017-01-01
A novel exact temporal to spatial mapping for point measurements in turbulence has been applied to various flow conditions existing in a round turbulent jet. The conditions range between equilibrium and non-equilibrium as well as mid to high turbulence intensities. The exact mapping applies to all...... flows, including high intensity non-equilibrium flows, since it is based on the instantaneous velocity magnitude, thereby incorporating all relevant aspects of the flow dynamics. Devel-opment of the jet turbulence along the stream, from non-equilibrium to equilibrium, is observed. In the developed...... region of the jet, Taylor’s hypothesis is tested and the spectra using the novel exact mapping is validated with excellent agreement against directly measured spatial spectra in a mapped similarity space using PIV. The method is observed to produce the expected results even at turbulence intensi...
Influence of coma aberration on aperture averaged scintillations in oceanic turbulence
Luo, Yujuan; Ji, Xiaoling; Yu, Hong
2018-01-01
The influence of coma aberration on aperture averaged scintillations in oceanic turbulence is studied in detail by using the numerical simulation method. In general, in weak oceanic turbulence, the aperture averaged scintillation can be effectively suppressed by means of the coma aberration, and the aperture averaged scintillation decreases as the coma aberration coefficient increases. However, in moderate and strong oceanic turbulence the influence of coma aberration on aperture averaged scintillations can be ignored. In addition, the aperture averaged scintillation dominated by salinity-induced turbulence is larger than that dominated by temperature-induced turbulence. In particular, it is shown that for coma-aberrated Gaussian beams, the behavior of aperture averaged scintillation index is quite different from the behavior of point scintillation index, and the aperture averaged scintillation index is more suitable for characterizing scintillations in practice.
Energy Technology Data Exchange (ETDEWEB)
Shojaeefard, M.H.; Pirnia, A.; Fallahian, M.A. [Iran University of Science and Technology, School of Mechanical Engineering, Tehran (Iran, Islamic Republic of); Tahani, M. [Iran University of Science and Technology, School of Mechanical Engineering, Tehran (Iran, Islamic Republic of); University of Tehran, Faculty of New Science and Technology, Tehran (Iran, Islamic Republic of)
2012-06-15
In this study the effects of induced jet at trailing edge of a two dimensional airfoil on its boundary layer shape, separation over surface and turbulent parameters behind trailing edge are numerically investigated and compared against a previous experimental data. After proving independency of results from mesh size and obtaining the required mesh size, different turbulent models are examined and RNG k-epsilon model is chosen because of good agreement with experimental data in velocity and turbulent intensity variations. A comparison between ordinary and jet induced cases, regarding numerical data, is made. The results showed that because of low number of measurement points in experimental study, turbulent intensity extremes are not captured. While in numerical study, these values and their positions are well calculated and exact variation of turbulent intensity is acquired. Also a study in effect of jet at high angles of attack is done and the results showed the ability of jet in controlling separation and reducing wake region. (orig.)
A self-consistent turbulence generated scenario for L-H transition
International Nuclear Information System (INIS)
Zhang, Y.Z.; Mahajan, S.M.
1992-10-01
The turbulence-induced ion banana polarization current associated with steep ion temperature gradients is explored as a possible mechanism for generating poloidal momentum at the tokamak edge. In the light of a recently developed two-dimensional turbulence theory, one can obtain a simple closed expression relating this current (determined by turbulence levels) to the derivatives of the poloidal rotation speed. A self-consistent system, then, emerges, if we balance the turbulence-induced poloidal momentum with that dissipated by viscosity. Under suitable conditions this system may show a bifurcation controlled by a parameter dependent on temperature gradients. Both the bifurcation point, and the shear layer width are predicted for a prescribed flow in terms of a scale characterizing the nonlinearity of viscosity. The crucial relevance of the flow parity with the turbulence scenario is analyzed
Experimental study of wind-turbine airfoil aerodynamics in high turbulence
Energy Technology Data Exchange (ETDEWEB)
Devinant, Ph.; Laverne, T.; Hureau, J. [Laboratoire de Mecanique et d' Energetique Ecole Superieure de l' Energie et des Materiaux Universite d' Orleans, rue Leonard de Vinci F-45072 , Cedex 2 Orleans (France)
2002-06-01
Wind turbines very often have to operate in high turbulence related, for example, with lower layers atmospheric turbulence or wakes of other wind turbines. Most available data on airfoil aerodynamics concerns mainly aeronautical applications, which are characterized by a low level of turbulence (generally less than 1%) and low angles of attack. This paper presents wind tunnel test data for the aerodynamic properties-lift, drag, pitching moment, pressure distributions-of an airfoil used on a wind turbine when subjected to incident flow turbulence levels of 0.5-16% and placed at angles of attack up to 90. The results show that the aerodynamic behavior of the airfoil can be strongly affected by the turbulence level both qualitatively and quantitatively. This effect is especially evidenced in the angle of attack range corresponding to airfoil stall, as the boundary layer separation point advances along the leeward surface of the airfoil.
Bominaar, Jeroen; Pashtrapanska, Mira; Elenbaas, Thijs; Dam, Nico; ter Meulen, Hans; van de Water, Willem
2008-04-01
We describe a scheme of molecular tagging velocimetry in air in which nitric oxide (NO) molecules are created out of O2 and N2 molecules in the focus of a strong laser beam. The NO molecules are visualized a while later by laser-induced fluorescence. The precision of the molecular tagging velocimetry of gas flows is affected by the gradual blurring of the written patterns through molecular diffusion. In the case of turbulent flows, molecular diffusion poses a fundamental limit on the resolution of the smallest scales in the flow. We study the diffusion of written patterns in detail for our tagging scheme which, at short (micros) delay times is slightly anomalous due to local heating by absorption of laser radiation. We show that our experiments agree with a simple convection-diffusion model that allows us to estimate the temperature rise upon writing. Molecular tagging can be a highly nonlinear process, which affects the art of writing. We find that our tagging scheme is (only) quadratic in the intensity of the writing laser.
Common origin of visible and dark universe
International Nuclear Information System (INIS)
Gu Peihong; Sarkar, Utpal
2010-01-01
Dark matter, baryonic matter, and dark energy have different properties but contribute comparable energy density to the present Universe. We point out that they may have a common origin. As the dark energy has a scale far lower than all known scales in particle physics but very close to neutrino masses, while the excess matter over antimatter in the baryonic sector is probably related to the neutrino-mass generation, we unify the origin of the dark and visible universe in a variant of the seesaw model. In our model (i) the dark matter relic density is a dark matter asymmetry emerged simultaneously with the baryon asymmetry from leptogenesis; (ii) the dark energy is due to a pseudo-Nambu-Goldstone-Boson associated with the neutrino-mass generation.
Ultraviolet, Visible, and Fluorescence Spectroscopy
Penner, Michael H.
Spectroscopy in the ultraviolet-visible (UV-Vis) range is one of the most commonly encountered laboratory techniques in food analysis. Diverse examples, such as the quantification of macrocomponents (total carbohydrate by the phenol-sulfuric acid method), quantification of microcomponents, (thiamin by the thiochrome fluorometric procedure), estimates of rancidity (lipid oxidation status by the thiobarbituric acid test), and surveillance testing (enzyme-linked immunoassays), are presented in this text. In each of these cases, the analytical signal for which the assay is based is either the emission or absorption of radiation in the UV-Vis range. This signal may be inherent in the analyte, such as the absorbance of radiation in the visible range by pigments, or a result of a chemical reaction involving the analyte, such as the colorimetric copper-based Lowry method for the analysis of soluble protein.
Chemical lasers in the visible
International Nuclear Information System (INIS)
Jones, C.R.; Broida, H.P.
1974-01-01
Since the beginning of the laser era in 1960, a continuing search for chemical lasers has been carried out. This quest has been influenced by the knowledge that many chemical reactions produce visible chemiluminescence and, therefore, partition some of the reaction products into emitting, electronically excited states. Such luminescence has been observed not only from low-pressure, gas-phase reactions, notably those of alkali metals and halogens, but also from a limited number of liquid-phase reactions. (U.S.)
Computing Visible-Surface Representations,
1985-03-01
Terzopoulos N00014-75-C-0643 9. PERFORMING ORGANIZATION NAME AMC ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK Artificial Inteligence Laboratory AREA A...Massachusetts Institute of lechnolog,. Support lbr the laboratory’s Artificial Intelligence research is provided in part by the Advanced Rtccarcl Proj...dynamically maintaining visible surface representations. Whether the intention is to model human vision or to design competent artificial vision systems
Adaptive LES Methodology for Turbulent Flow Simulations
Energy Technology Data Exchange (ETDEWEB)
Oleg V. Vasilyev
2008-06-12
turbulence have recently been completed at the Japanese Earth Simulator (Yokokawa et al. 2002, Kaneda et al. 2003) using a resolution of 40963 (approximately 10{sup 11}) grid points with a Taylor-scale Reynolds number of 1217 (Re {approx} 10{sup 6}). Impressive as these calculations are, performed on one of the world's fastest super computers, more brute computational power would be needed to simulate the flow over the fuselage of a commercial aircraft at cruising speed. Such a calculation would require on the order of 10{sup 16} grid points and would have a Reynolds number in the range of 108. Such a calculation would take several thousand years to simulate one minute of flight time on today's fastest super computers (Moin & Kim 1997). Even using state-of-the-art zonal approaches, which allow DNS calculations that resolve the necessary range of scales within predefined 'zones' in the flow domain, this calculation would take far too long for the result to be of engineering interest when it is finally obtained. Since computing power, memory, and time are all scarce resources, the problem of simulating turbulent flows has become one of how to abstract or simplify the complexity of the physics represented in the full Navier-Stokes (NS) equations in such a way that the 'important' physics of the problem is captured at a lower cost. To do this, a portion of the modes of the turbulent flow field needs to be approximated by a low order model that is cheaper than the full NS calculation. This model can then be used along with a numerical simulation of the 'important' modes of the problem that cannot be well represented by the model. The decision of what part of the physics to model and what kind of model to use has to be based on what physical properties are considered 'important' for the problem. It should be noted that 'nothing is free', so any use of a low order model will by definition lose some information about the
High visibility temporal ghost imaging with classical light
Liu, Jianbin; Wang, Jingjing; Chen, Hui; Zheng, Huaibin; Liu, Yanyan; Zhou, Yu; Li, Fu-li; Xu, Zhuo
2018-03-01
High visibility temporal ghost imaging with classical light is possible when superbunching pseudothermal light is employed. In the numerical simulation, the visibility of temporal ghost imaging with pseudothermal light, equaling (4 . 7 ± 0 . 2)%, can be increased to (75 ± 8)% in the same scheme with superbunching pseudothermal light. The reasons for that the retrieved images are different for superbunching pseudothermal light with different values of degree of second-order coherence are discussed in detail. It is concluded that high visibility and high quality temporal ghost image can be obtained by collecting sufficient number of data points. The results are helpful to understand the difference between ghost imaging with classical light and entangled photon pairs. The superbunching pseudothermal light can be employed to improve the image quality in ghost imaging applications.
Direct numerical simulation and statistical analysis of turbulent convection in lead-bismuth
Energy Technology Data Exchange (ETDEWEB)
Otic, I.; Grotzbach, G. [Forschungszentrum Karlsruhe GmbH, Institut fuer Kern-und Energietechnik (Germany)
2003-07-01
Improved turbulent heat flux models are required to develop and analyze the reactor concept of an lead-bismuth cooled Accelerator-Driven-System. Because of specific properties of many liquid metals we have still no sensors for accurate measurements of the high frequency velocity fluctuations. So, the development of the turbulent heat transfer models which are required in our CFD (computational fluid dynamics) tools needs also data from direct numerical simulations of turbulent flows. We use new simulation results for the model problem of Rayleigh-Benard convection to show some peculiarities of the turbulent natural convection in lead-bismuth (Pr = 0.025). Simulations for this flow at sufficiently large turbulence levels became only recently feasible because this flow requires the resolution of very small velocity scales with the need for recording long-wave structures for the slow changes in the convective temperature field. The results are analyzed regarding the principle convection and heat transfer features. They are also used to perform statistical analysis to show that the currently available modeling is indeed not adequate for these fluids. Basing on the knowledge of the details of the statistical features of turbulence in this convection type and using the two-point correlation technique, a proposal for an improved statistical turbulence model is developed which is expected to account better for the peculiarities of the heat transfer in the turbulent convection in low Prandtl number fluids. (authors)
Edge turbulence imaging in the Alcator C-Mod tokamak
International Nuclear Information System (INIS)
Zweben, S.J.; Stotler, D.P.; Terry, J.L.; La Bombard, B.; Greenwald, M.; Muterspaugh, M.; Pitcher, C.S.; Hallatschek, K.; Maqueda, R.J.; Rogers, B.; Lowrance, J.L.; Mastrocola, V.J.; Renda, G.F.
2002-01-01
The two-dimensional (2D) radial vs poloidal structure of edge turbulence in the Alcator C-Mod tokamak [I. H. Hutchinson, R. Boivin, P. T. Bonoli et al., Nucl. Fusion 41, 1391 (2001)] was measured using fast cameras and compared with three-dimensional numerical simulations of edge plasma turbulence. The main diagnostic is gas puff imaging, in which the visible D α emission from a localized D 2 gas puff is viewed along a local magnetic field line. The observed D α fluctuations have a typical radial and poloidal scale of ≅1 cm, and often have strong local maxima ('blobs') in the scrape-off layer. The motion of this 2D structure motion has also been measured using an ultrafast framing camera with 12 frames taken at 250 000 frames/s. Numerical simulations produce turbulent structures with roughly similar spatial and temporal scales and transport levels as that observed in the experiment; however, some differences are also noted, perhaps requiring diagnostic improvement and/or additional physics in the numerical model
[Street Outreach Offices: visibility, invisibility, and enhanced visibility].
Hallais, Janaína Alves da Silveira; Barros, Nelson Filice de
2015-07-01
This article discusses care for street people from a socio-anthropological perspective, using participant observation conducted with a team from a street outreach project. Based on observations, street people are historically viewed as marginal and rarely obtain access to health services, thus making them invisible to the Brazilian Unified National Health System. Brazil's National Policy for the Homeless provides for their access to health care, but such care is not always guaranteed in practice, because health services and professionals have little experience in dealing with homeless persons. The study concludes that enhanced visibility is needed to ensure care for people living on the street, establishing a therapeutic bond that deconstructs stigmatizing practice.
Modeling of Turbulent Swirling Flows
Shih, Tsan-Hsing; Zhu, Jiang; Liou, William; Chen, Kuo-Huey; Liu, Nan-Suey; Lumley, John L.
1997-01-01
Aircraft engine combustors generally involve turbulent swirling flows in order to enhance fuel-air mixing and flame stabilization. It has long been recognized that eddy viscosity turbulence models are unable to appropriately model swirling flows. Therefore, it has been suggested that, for the modeling of these flows, a second order closure scheme should be considered because of its ability in the modeling of rotational and curvature effects. However, this scheme will require solution of many complicated second moment transport equations (six Reynolds stresses plus other scalar fluxes and variances), which is a difficult task for any CFD implementations. Also, this scheme will require a large amount of computer resources for a general combustor swirling flow. This report is devoted to the development of a cubic Reynolds stress-strain model for turbulent swirling flows, and was inspired by the work of Launder's group at UMIST. Using this type of model, one only needs to solve two turbulence equations, one for the turbulent kinetic energy k and the other for the dissipation rate epsilon. The cubic model developed in this report is based on a general Reynolds stress-strain relationship. Two flows have been chosen for model evaluation. One is a fully developed rotating pipe flow, and the other is a more complex flow with swirl and recirculation.
TRIAM-1 turbulent heating experiment
Energy Technology Data Exchange (ETDEWEB)
Nakamura, Yukio; Hiraki, Naoji; Nakamura, Kazuo; Kikuchi, Mitsuru; Nagao, Akihiro [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1983-02-01
The experimental studies on the containment of high temperature plasma and turbulent heating using the tokamak device with strong magnetic field (TRIAM-1) started in 1977 have achieved much results up to fiscal 1979, and the anticipated objectives were almost attained. The results of these studies were summarized in the ''Report of the results of strong magnetic field tokamak TRIAM-1 experiment''. In this report, the results obtained by the second stage project of the TRIAM-1 project are summarized. The second stage was the two-year project for fiscal 1980 and 81. In the second stage project, by the complete preparation of measuring instrument and the improvement of the experimental setup, the carefully planned experiment on turbulent heating was performed, in particular, the clarification of the mechanism of turbulent heating was the central theme. As the important results obtained, the detection of ion sound waves at the time of turbulent heating, the formation of high energy ions by wave-particle interaction and the clarification of the process of their energy relaxation, and the verification of the effectiveness of double pulse turbulent heating are enumerated.
TRIAM-1 turbulent heating experiment
International Nuclear Information System (INIS)
Nakamura, Yukio; Hiraki, Naoji; Nakamura, Kazuo; Kikuchi, Mitsuru; Nagao, Akihiro
1983-01-01
The experimental studies on the containment of high temperature plasma and turbulent heating using the tokamak device with strong magnetic field (TRIAM-1) started in 1977 have achieved much results up to fiscal 1979, and the anticipated objectives were almost attained. The results of these studies were summarized in the ''Report of the results of strong magnetic field tokamak TRIAM-1 experiment''. In this report, the results obtained by the second stage project of the TRIAM-1 project are summarized. The second stage was the two-year project for fiscal 1980 and 81. In the second stage project, by the complete preparation of measuring instrument and the improvement of the experimental setup, the carefully planned experiment on turbulent heating was performed, in particular, the clarification of the mechanism of turbulent heating was the central theme. As the important results obtained, the detection of ion sound waves at the time of turbulent heating, the formation of high energy ions by waveparticle interaction and the clarification of the process of their energy relaxation, and the verification of the effectiveness of double pulse turbulent heating are enumerated. (Kako, I.)
PDF turbulence modeling and DNS
Hsu, A. T.
1992-01-01
The problem of time discontinuity (or jump condition) in the coalescence/dispersion (C/D) mixing model is addressed in probability density function (pdf). A C/D mixing model continuous in time is introduced. With the continuous mixing model, the process of chemical reaction can be fully coupled with mixing. In the case of homogeneous turbulence decay, the new model predicts a pdf very close to a Gaussian distribution, with finite higher moments also close to that of a Gaussian distribution. Results from the continuous mixing model are compared with both experimental data and numerical results from conventional C/D models. The effect of Coriolis forces on compressible homogeneous turbulence is studied using direct numerical simulation (DNS). The numerical method used in this study is an eight order compact difference scheme. Contrary to the conclusions reached by previous DNS studies on incompressible isotropic turbulence, the present results show that the Coriolis force increases the dissipation rate of turbulent kinetic energy, and that anisotropy develops as the Coriolis force increases. The Taylor-Proudman theory does apply since the derivatives in the direction of the rotation axis vanishes rapidly. A closer analysis reveals that the dissipation rate of the incompressible component of the turbulent kinetic energy indeed decreases with a higher rotation rate, consistent with incompressible flow simulations (Bardina), while the dissipation rate of the compressible part increases; the net gain is positive. Inertial waves are observed in the simulation results.
Two-dimensional turbulent convection
Mazzino, Andrea
2017-11-01
We present an overview of the most relevant, and sometimes contrasting, theoretical approaches to Rayleigh-Taylor and mean-gradient-forced Rayleigh-Bénard two-dimensional turbulence together with numerical and experimental evidences for their support. The main aim of this overview is to emphasize that, despite the different character of these two systems, especially in relation to their steadiness/unsteadiness, turbulent fluctuations are well described by the same scaling relationships originated from the Bolgiano balance. The latter states that inertial terms and buoyancy terms balance at small scales giving rise to an inverse kinetic energy cascade. The main difference with respect to the inverse energy cascade in hydrodynamic turbulence [R. H. Kraichnan, "Inertial ranges in two-dimensional turbulence," Phys. Fluids 10, 1417 (1967)] is that the rate of cascade of kinetic energy here is not constant along the inertial range of scales. Thanks to the absence of physical boundaries, the two systems here investigated turned out to be a natural physical realization of the Kraichnan scaling regime hitherto associated with the elusive "ultimate state of thermal convection" [R. H. Kraichnan, "Turbulent thermal convection at arbitrary Prandtl number," Phys. Fluids 5, 1374-1389 (1962)].
TEM turbulence optimisation in stellarators
Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.
2016-01-01
With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.
Directory of Open Access Journals (Sweden)
Ben Magolan
2017-09-01
Full Text Available Direct Numerical Simulation (DNS serves as an irreplaceable tool to probe the complexities of multiphase flow and identify turbulent mechanisms that elude conventional experimental measurement techniques. The insights unlocked via its careful analysis can be used to guide the formulation and development of turbulence models used in multiphase computational fluid dynamics simulations of nuclear reactor applications. Here, we perform statistical analyses of DNS bubbly flow data generated by Bolotnov (Reτ = 400 and Lu–Tryggvason (Reτ = 150, examining single-point statistics of mean and turbulent liquid properties, turbulent kinetic energy budgets, and two-point correlations in space and time. Deformability of the bubble interface is shown to have a dramatic impact on the liquid turbulent stresses and energy budgets. A reduction in temporal and spatial correlations for the streamwise turbulent stress (uu is also observed at wall-normal distances of y+ = 15, y/δ = 0.5, and y/δ = 1.0. These observations motivate the need for adaptation of length and time scales for bubble-induced turbulence models and serve as guidelines for future analyses of DNS bubbly flow data.
Beyond Language Equivalence on Visibly Pushdown Automata
DEFF Research Database (Denmark)
Srba, Jiri
2009-01-01
We study (bi)simulation-like preorder/equivalence checking on the class of visibly pushdown automata and its natural subclasses visibly BPA (Basic Process Algebra) and visibly one-counter automata. We describe generic methods for proving complexity upper and lower bounds for a number of studied...... preorders and equivalences like simulation, completed simulation, ready simulation, 2-nested simulation preorders/equivalences and bisimulation equivalence. Our main results are that all the mentioned equivalences and preorders are EXPTIME-complete on visibly pushdown automata, PSPACE-complete on visibly...... one-counter automata and P-complete on visibly BPA. Our PSPACE lower bound for visibly one-counter automata improves also the previously known DP-hardness results for ordinary one-counter automata and one-counter nets. Finally, we study regularity checking problems for visibly pushdown automata...
Lagrangian statistics in compressible isotropic homogeneous turbulence
Yang, Yantao; Wang, Jianchun; Shi, Yipeng; Chen, Shiyi
2011-11-01
In this work we conducted the Direct Numerical Simulation (DNS) of a forced compressible isotropic homogeneous turbulence and investigated the flow statistics from the Lagrangian point of view, namely the statistics is computed following the passive tracers trajectories. The numerical method combined the Eulerian field solver which was developed by Wang et al. (2010, J. Comp. Phys., 229, 5257-5279), and a Lagrangian module for tracking the tracers and recording the data. The Lagrangian probability density functions (p.d.f.'s) have then been calculated for both kinetic and thermodynamic quantities. In order to isolate the shearing part from the compressing part of the flow, we employed the Helmholtz decomposition to decompose the flow field (mainly the velocity field) into the solenoidal and compressive parts. The solenoidal part was compared with the incompressible case, while the compressibility effect showed up in the compressive part. The Lagrangian structure functions and cross-correlation between various quantities will also be discussed. This work was supported in part by the China's Turbulence Program under Grant No.2009CB724101.
Efficient visibility encoding for dynamic illumination in direct volume rendering.
Kronander, Joel; Jönsson, Daniel; Löw, Joakim; Ljung, Patric; Ynnerman, Anders; Unger, Jonas
2012-03-01
We present an algorithm that enables real-time dynamic shading in direct volume rendering using general lighting, including directional lights, point lights, and environment maps. Real-time performance is achieved by encoding local and global volumetric visibility using spherical harmonic (SH) basis functions stored in an efficient multiresolution grid over the extent of the volume. Our method enables high-frequency shadows in the spatial domain, but is limited to a low-frequency approximation of visibility and illumination in the angular domain. In a first pass, level of detail (LOD) selection in the grid is based on the current transfer function setting. This enables rapid online computation and SH projection of the local spherical distribution of visibility information. Using a piecewise integration of the SH coefficients over the local regions, the global visibility within the volume is then computed. By representing the light sources using their SH projections, the integral over lighting, visibility, and isotropic phase functions can be efficiently computed during rendering. The utility of our method is demonstrated in several examples showing the generality and interactive performance of the approach.
Turbulent structure and emissions of strongly-pulsed jet diffusion flames
Fregeau, Mathieu
-pulsed flames was not strongly impacted by buoyancy. This lack of sensitivity to buoyancy was consistent with offsetting changes in flame puff celerity and time to burnout for the microgravity versus normal-gravity cases. The emissions of CO and NO were examined in the vicinity of the visible flame tip and at the combustor exit for strongly-pulsed flames. The highest exhaust-point emission indices of CO for compact, isolated puffs were as much as a factor of six higher than those of elongated flames with longer injection times. The amount of CO decreased substantially with a decreased amount of flame puff interaction. The higher CO levels for pulsed flames with the shortest injection times were consistent with quenching due to the very rapid mixing and dilution with excess air for the most compact flame puffs. The injection time for which steady-flame emission levels were attained was comparable to the injection time for which the visible flame length approached the flame length of steady flames. The CO emissions, for a given fuelling rate, were strongly dependent on both the injection time and jet-off time for a jet-on fraction less than approximately 50%. The NO levels were generally proportional to the fuelling rate. This work indicates that there are specific combinations of injection time and jet-off time that considerably change the fuel/air mixing, resulting in emissions comparable to those of the steady flame while the flame length is significantly shorter. This points the potential utility of the strongly-pulsed injection technique in the development of compact, low emissions combustors involving turbulent diffusion flames. (Abstract shortened by UMI.)
Multi-fragment visibility determination in the context of order-independent transparency rendering
Marilena Maule
2015-01-01
Multi-fragment effects, in the computer-generated imagery context, are effects that determine pixel color based on information computed from more than one fragment. In such effects, the contribution of each fragment is extracted from its visibility with respect to a point of view. Seen through a pixel’s point of view, the visibility of one fragment depends on its spatial relationship with other fragments. This relationship can be reduced to the problem of sorting multiple fragments. Therefore...
Aspects of frequency redistribution for non-coherent scattering in a turbulent medium
International Nuclear Information System (INIS)
Magnan, C.
1975-01-01
The scattering of line phonons in a turbulent medium is re-examined. The fact is taken into account that a photon absorbed in a turbulent element having some velocity will be re-emitted by the same element and keeps in that way a certain 'memory' of its absorption. Adding the contributions of all turbulent elements at a given point new redistribution functions are constructed, describing this correlation. They give the probability that a photon with frequency x in the direction n is absorbed and re-emitted at frequency x' in the direction n'. A preliminary discussion of the problem is given in an astrophysical context. (author)
Les Houches 2000 Summer School: Session 74: New Trends in Turbulence
Yaglom, A; David, F; New Trends in Turbulence
2001-01-01
This book is written for researchers as well as engineers in an industrial environment. Following a longstanding tradition of the Les Houches Summer Schools, all chapters are pedagogically presented and accessible for graduate students. The book treats 2D and 3D turbulence from the experimental, theoretical and computational points of view. The reader will find, for example, comprehensive accounts of fully developed turbulence experiments, simulating deterministically coherent vortices formation, and statistical prediction of industrial flows, and a very complete review of 2D turbulence. Fundamental concepts like topological fluid dynamics in MHD flows or finite-time singularities of the Burgers, Euler and Navier--Stokes equations complete the volume.
An Optimal Parametrization of Turbulent Scales
Thalabard, S.
2015-12-01
To numerically capture the large-scale dynamics of atmospheric flows, geophysicists need to rely on reasonable parametrizations of the energy transfers to and from the non-resolved small scale eddies, mediated through turbulence. The task is notoriously not trivial, and is typically solved by ingenious but ad-hoc elaborations on the concept of eddy viscosities. The difficulty is tied into the intrinsic Non-Gaussianity of turbulence, a feature that may explain why standard Quasi-Normal cumulant discard statistical closure strategies can fail dramatically, an example being the development of negative energy spectra in Millionshtchikov's 1941 Quasi-Normal (QN) theory. While Orszag's 1977 Eddy Damped Quasi Normal Markovian closure (EDQNM) provides an ingenious patch to the issue, the reason why the QN theory fails so badly is not so clear. Are closures necessarily either trivial or ad-hoc, when proxies for true ensemble averages are taken to be Gaussian ? The purpose of the talk is to answer negatively, using the lights of a new ``optimal closure framework'' recently exposed by [Turkington,2013]. For turbulence problems, the optimal closure allows a consistent use of a Gaussian Ansatz (and corresponding vanishing third cumulant) that also retains an intrinsic damping. The key to this apparent paradox lies in a clear distinction between the true ensemble averages and their proxies, most easily grasped provided one uses the Liouville equation as a starting point, rather than the cumulant hierarchy. Schematically said, closure is achieved by minimizing a lack-of-fit residual, which retains the intrinsic features of the true dynamics. The optimal closure is not restricted to the Gaussian modeling. Yet, for the sake of clarity, I will discuss the optimal closure on a problem where it can be entirely implemented, and compared to DNS : the relaxation of an arbitrarily far from equilibrium energy shell towards the Gibbs equilibrium for truncated Euler dynamics. Predictive
Turbulent exchange processes of the planetary boundary layer - TUAREG
International Nuclear Information System (INIS)
Beier, N.; Weber, M.
1992-11-01
A mobile groundstation with associated sovftware has been developed to measure fluxes of properties and constituents, and the vertical distribution of chemically reactive trace gases. The significance and accuracy of the derived fluxes have been investigated. Within the validity of the meteorological assumptions used, the error is less than 10%. The turbulent vertical transport has been investigated over homogeneous areas in mixed heterogeneous terrain during four field experiments. The following results were obtained: characteristics of the structure of the turbulence - diurnal variations of the fluxes of momentum and energy - the vertical distribution of NO, NO 2 and O 3 -diurnal variations of their flux and deposition velocity - balance of ozone and exchange processes in the convective PBL. Correlation and profile measurements at a fixed point in mixed heterogeneous terrain are representative of the surface type, if the upwind dimension of the homogeneous areas is at least 500 m. If this is not the case, anisotropic and organized turbulence develops. Then the formally calculated fluxes arise, in part, due to random numbers and cannot be attributed to a local site. A definitive conclusion would require measurements of the three dimensional structure of turbulence. There are no counter-gradient fluxes in the nondivergent PBL. They arise from the use of inadequate integration intervals in correlation and profile calculations. In contrast, they do occur in regions of divergence. Since the similarity theory is not valid in this case, fluxes can be neither measured nor calculated. Airborne measurements were carried out by the ''Institut fuer Physik der Atmosphaere'', DLR. The following results are attached: the mean structure of the PBL - the turbulent fluxes of meteorological variables - the horizontal variability of the fluxes near the ground - the turbulent flux of ozone and the ozone balance. Comparisons with model calculations show good agreement. (orig./KW). 116
Turbulence models in supersonic flows
International Nuclear Information System (INIS)
Shirani, E.; Ahmadikia, H.; Talebi, S.
2001-05-01
The aim of this paper is to evaluate five different turbulence models when used in rather complicated two-dimensional and axisymmetric supersonic flows. They are Baldwin-Lomax, k-l, k-ε, k-ω and k-ζ turbulence models. The compressibility effects, axisymmetric correction terms and some modifications for transition region are used and tested in the models. Two computer codes based on the control volume approach and two flux-splitting methods. Roe and Van Leer, are developed. The codes are used to simulate supersonic mixing layers, flow behind axisymmetric body, under expanded jet, and flow over hollow cylinder flare. The results are compared with experimental data and behavior of the turbulence models is examined. It is shown that both k-l and k-ζ models produce very good results. It is also shown that the compressibility correction in the model is required to obtain more accurate results. (author)
Atmospheric turbulence and diffusion research
International Nuclear Information System (INIS)
Hosker, R.P. Jr.
1993-01-01
The Atmospheric Turbulence and Diffusion Division (well known in the atmospheric dispersion community as the Atmospheric Turbulence and Diffusion Laboratory, ATDL) is one of several field facilities of NOAAs Air Resources Laboratory, headquartered in Silver Spring, Maryland. The laboratory conducts research on matters of atmospheric diffusion and turbulent exchange, concerning air quality. ATDD focuses attention on the physics of the lower atmosphere, with special emphasis on the processes contributing to atmospheric transport, dispersion, deposition, and air-surface exchange, and on the development of predictive capabilities using the results of this research. Research is directed toward issues of national and global importance related to the missions of DOE, to DOE's Oak Ridge Field Office, and to NOAA. The program is divided into four major projects: plume transport and diffusion in the planetary boundary layer, complex topography, canopy micrometeorology, and air-surface exchange
ANISOTROPIC INTERMITTENCY OF MAGNETOHYDRODYNAMIC TURBULENCE
International Nuclear Information System (INIS)
Osman, K. T.; Kiyani, K. H.; Chapman, S. C.; Hnat, B.
2014-01-01
A higher-order multiscale analysis of spatial anisotropy in inertial range magnetohydrodynamic turbulence is presented using measurements from the STEREO spacecraft in fast ambient solar wind. We show for the first time that, when measuring parallel to the local magnetic field direction, the full statistical signature of the magnetic and Elsässer field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multiexponent statistics observed when the local magnetic field is perpendicular to the flow direction. These observations are interpreted as evidence for the weakness, or absence, of a parallel magnetofluid turbulence energy cascade. As such, these results present strong observational constraints on the statistical nature of intermittency in turbulent plasmas
Resonant quasiparticles in plasma turbulence
International Nuclear Information System (INIS)
Mendonca, J.T.; Bingham, R.; Shukla, P.K.
2003-01-01
A general view is proposed on wave propagation in fluids and plasmas where the resonant interaction of monochromatic waves with quasiparticles is considered. A kinetic equation for quasiparticles is used to describe the broadband turbulence interacting with monochromatic waves. Resonant interactions occur when the phase velocity of the long wavelength monochromatic wave is nearly equal to the group velocity of short wavelength wave packets, or quasiparticles, associated with the turbulent spectrum. It is shown that quasiparticle Landau damping can take place, as well as quasiparticle beam instabilities, thus establishing a direct link between short and large wavelength perturbations of the medium. This link is distinct from the usual picture of direct and inverse energy cascades, and it can be used as a different paradigm for the fluid and plasma turbulence theories
Turbulent breakage of ductile aggregates.
Marchioli, Cristian; Soldati, Alfredo
2015-05-01
In this paper we study breakage rate statistics of small colloidal aggregates in nonhomogeneous anisotropic turbulence. We use pseudospectral direct numerical simulation of turbulent channel flow and Lagrangian tracking to follow the motion of the aggregates, modeled as sub-Kolmogorov massless particles. We focus specifically on the effects produced by ductile rupture: This rupture is initially activated when fluctuating hydrodynamic stresses exceed a critical value, σ>σ(cr), and is brought to completion when the energy absorbed by the aggregate meets the critical breakage value. We show that ductile rupture breakage rates are significantly reduced with respect to the case of instantaneous brittle rupture (i.e., breakage occurs as soon as σ>σ(cr)). These discrepancies are due to the different energy values at play as well as to the statistical features of energy distribution in the anisotropic turbulence case examined.
Directory of Open Access Journals (Sweden)
P R Renosh
Full Text Available Satellite remote sensing observations allow the ocean surface to be sampled synoptically over large spatio-temporal scales. The images provided from visible and thermal infrared satellite observations are widely used in physical, biological, and ecological oceanography. The present work proposes a method to understand the multi-scaling properties of satellite products such as the Chlorophyll-a (Chl-a, and the Sea Surface Temperature (SST, rarely studied. The specific objectives of this study are to show how the small scale heterogeneities of satellite images can be characterised using tools borrowed from the fields of turbulence. For that purpose, we show how the structure function, which is classically used in the frame of scaling time series analysis, can be used also in 2D. The main advantage of this method is that it can be applied to process images which have missing data. Based on both simulated and real images, we demonstrate that coarse-graining (CG of a gradient modulus transform of the original image does not provide correct scaling exponents. We show, using a fractional Brownian simulation in 2D, that the structure function (SF can be used with randomly sampled couple of points, and verify that 1 million of couple of points provides enough statistics.
Orbital-angular-momentum entanglement in turbulence
CSIR Research Space (South Africa)
Hamadou Ibrahim, A
2013-06-01
Full Text Available The turbulence-induced decay of orbital-angular-momentum (OAM) entanglement between two photons is investigated numerically and experimentally. To compare our resultswith previouswork,we simulate the turbulent atmosphere with a single phase screen...
Particle Settling in Low Energy Turbulence
Allen, Rachel; MacVean, Lissa; Tse, Ian; Mazzaro, Laura; Stacey, Mark; Variano, Evan
2014-11-01
Particle settling velocities can be altered by turbulence. In turbulence, dense particles may get trapped in convergent flow regions, and falling particles may be swept towards the downward side of turbulent eddies, resulting in enhanced settling velocities. The degree of velocity enhancement may depend on the Stokes number, the Rouse number, and the turbulent Reynolds number. In a homogeneous, isotropic turbulence tank, we tested the effects of particle size and type, suspended sediment concentration, and level of turbulence on the settling velocities of particles typically found in muddy estuaries. Two Acoustic Doppler Velocimeters (ADVs), separated vertically, measured turbulent velocities and suspended sediment concentrations, which yield condition dependent settling velocities, via ∂/á C ñ ∂ t = -∂/∂ z (ws á C ñ + á w ' C ' ñ) . These results are pertinent to fine sediment transport in estuaries, where high concentrations of suspended material are transported and impacted by low energy turbulence.
PDF methods for turbulent reactive flows
Hsu, Andrew T.
1995-01-01
Viewgraphs are presented on computation of turbulent combustion, governing equations, closure problem, PDF modeling of turbulent reactive flows, validation cases, current projects, and collaboration with industry and technology transfer.
Visibility of sutures of the orbit and periorbital region using multidetector computed tomography
Energy Technology Data Exchange (ETDEWEB)
Gufler, Hubert; Preis, Markus; Koesling, Sabrina [Dept. of Diagnostic Radiology, Martin-Luther-University Halle-Wittenberg, Halle (Germany)
2014-12-15
Knowledge of cranial suture morphology is crucial in emergency medicine, forensic medicine, and maxillofacial reconstructive surgery. This study assessed the visibility of sutures of the orbit and periorbital region on multidetector computed tomography. Multidetector computed tomography scans of 200 patients (127 males, 73 females; mean age 51.3 years; range, 6-92 years) were evaluated retrospectively. The slice thicknesses varied from 0.5 to 1 mm, and the tube current from 25 to 370 mAs, depending on the CT indication. The visibility of sutures was estimated according to a 4-point scale from 'not visible to well visible' The chi-squared test was used to test the association of the visibility of sutures with the slice thickness, tube current, and age of patients. Statistical significance was assumed at p < 0.05. Overall, best visibility was found for the sutura frontozygomatica (98%), sutura frontonasalis (88.5%), and sutura sphenozygomatica (71.5%), followed by the sutura zygomaticomaxillaris (65.8%), sutura temporozygomatica (41.8%), sutura frontomaxillaris (44.5%), and sutura sphenofrontalis (31%). Poor visibility was found for the sutura frontolacrimalis (16.8%) and sutura frontoethmoidalis (1.3%). The sutura ethmoidomaxillaris, sutura lacrimomaxillaris, and sutura ethmoidolacrimalis were not visible. Although the sutures of the superior, lateral, and inferior orbit are well visible, those of the medial orbit are poorly visible on CT scans.
Visible Nulling Coronagraph Progress Report
Lyon, R. G.; Clampin, M.; Woodruff, R. A.; Vasudevan, G.; Thompson, P.; Petrone, P.; Madison, T.; Rizzo, M.; Melnick, G.; Tolls, V.
2010-10-01
We report on recent laboratory results with the NASA Goddard Space Flight Center Visible Nulling Coronagraph (VNC) testbed. We have achieved focal plane contrasts of 108 and approaching 109 at inner working angles of 2 λ/D and 4 λ/D, respectively. Results were obtained with a broadband source and 40 nm filter centered on 630 nm. A null control breadboard (NCB) was also developed to assess and quantify MEMS based deformable mirror technology (DM), and to develop and assess closed-loop null control algorithms. We have demonstrated closed-loop performance at 27 Hz.
Frontogenesis and turbulent mixing
Zhang, S.; Chen, F.; Shang, Q.
2017-12-01
ageostrophic secondary circulation together with the cross-frontal ageostrophic speed. The mixed characteristic is weak in summer, but the large turbulent dissipation and mixing rate measured in the frontal region, which show that the front promoted exchange of material and energy in the upper ocean.
Molecular mixing in turbulent flow
International Nuclear Information System (INIS)
Kerstein, A.R.
1993-01-01
The evolution of a diffusive scalar field subject to turbulent stirring is investigated by comparing two new modeling approaches, the linear-eddy model and the clipped-laminar-profile representation, to results previously obtained by direct numerical simulation (DNS) and by mapping-closure analysis. The comparisons indicate that scalar field evolution is sensitive to the bandwidth of the stirring process, and they suggest that the good agreement between DNS and mapping closure reflects the narrowband character of both. The new models predict qualitatively new behaviors in the wideband stirring regime corresponding to high-Reynolds-number turbulence
Plasma turbulence effects on aurorae
International Nuclear Information System (INIS)
Mishin, E.V.; Telegin, V.A.
1989-01-01
Analysis of modern state of microprocesses physics in plasma of aurorare, initiated by energetic electron flow intrusion, is presented. It is shown that there is a number of phenomena, which cannot be explained under non-collision (collective) mechanisms of interaction are applied. Effects of plasma turbulence in the area of auroral arcs are considered. Introduction of a new structural element to auroral arc - plasma-turbulence (PT) layer is substantiated. Numerical simulation of electron kinetics, changes in neutral composition, as well as generation of IR- and UV-radiation in PT layer has been realized
Ion-acoustic plasma turbulence
International Nuclear Information System (INIS)
Bychenkov, V.Y.; Silin, V.P.
1982-01-01
A theory is developed of the nonlinear state that is established in a plasma as a result of development of ion-acoustic instability. Account is taken simultaneously of the linear induced scattering of the waves by the ions and of the quasilinear relaxation of the electrons by the ion-acoustic pulsations. The distribution of the ion-acoustic turbulence in frequency and in angle is obtained. An Ohm's law is established and expressions are obtained for the electronic heat flux and for the relaxation time of the electron temperature in a turbulent plasma. Anomalously large absorption and scattering of the electromagnetic waves by the ion-acoustic pulsations is predicted
The roles of turbulence on plasma heating
International Nuclear Information System (INIS)
Kawamura, Takaichi; Kawabe, Takaya
1976-01-01
The relation between the heating rate of plasma particles and the thermalization frequency is established, and the important role of plasma turbulence in the fast thermalization process is underlined. This relation can be applied not only in the case of high current turbulent heating but also when turbulent phenomena occur with other heating means. The experimental results on ion and electron heating during the Mach II experiment are presented. The role of turbulence on particle losses accross the magnetic field is analyzed
Allen, Rachel M.; Simeonov, Julian A.; Calantoni, Joseph; Stacey, Mark T.; Variano, Evan A.
2018-05-01
Turbulence measurements were collected in the bottom boundary layer of the California inner shelf near Point Sal, CA, for 2 months during summer 2015. The water column at Point Sal is stratified by temperature, and internal bores propagate through the region regularly. We collected velocity, temperature, and turbulence data on the inner shelf at a 30-m deep site. We estimated the turbulent shear production ( P), turbulent dissipation rate ( ɛ), and vertical diffusive transport ( T), to investigate the near-bed local turbulent kinetic energy (TKE) budget. We observed that the local TKE budget showed an approximate balance ( P ≈ ɛ) during the observational period, and that buoyancy generally did not affect the TKE balance. On a finer resolution timescale, we explored the balance between dissipation and models for production and observed that internal waves did not affect the balance in TKE at this depth.
Exploiting similarity in turbulent shear flows for turbulence modeling
Robinson, David F.; Harris, Julius E.; Hassan, H. A.
1992-01-01
It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.
Exploiting similarity in turbulent shear flows for turbulence modeling
Robinson, David F.; Harris, Julius E.; Hassan, H. A.
1992-12-01
It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.
Intermittency exponent of the turbulent energy cascade
International Nuclear Information System (INIS)
Cleve, J.; Greiner, M.; Pearson, B.R.; Sreenivasan, K.R.
2006-12-01
We consider the turbulent energy dissipation from one-dimensional records in experiments using air and gaseous helium at cryogenic temperatures, and obtain the intermittency exponent via the two-point correlation function of the energy dissipation. The air data are obtained in a number of flows in a wind tunnel and the atmospheric boundary layer at a height of about 35 m above the ground. The helium data correspond to the centerline of a jet exhausting into a container. The air data on the intermittency exponent are consistent with each other and with a trend that increases with the Taylor microscale Reynolds number, R λ , of up to about 1000 and saturates thereafter. On the other hand, the helium data cluster around a constant value at nearly all R λ , this being about half of the asymptotic value for the air data. Some possible explanation is offered for this anomaly. (author)
Constructive modelling of structural turbulence: computational experiment
Energy Technology Data Exchange (ETDEWEB)
Belotserkovskii, O M; Oparin, A M; Troshkin, O V [Institute for Computer Aided Design, Russian Academy of Sciences, Vtoraya Brestskaya st., 19/18, Moscow, 123056 (Russian Federation); Chechetkin, V M [Keldysh Institute for Applied Mathematics, Russian Academy of Sciences, Miusskaya sq., 4, Moscow, 125047 (Russian Federation)], E-mail: o.bel@icad.org.ru, E-mail: a.oparin@icad.org.ru, E-mail: troshkin@icad.org.ru, E-mail: chech@gin@keldysh.ru
2008-12-15
Constructively, the analysis of the phenomenon of turbulence must and can be performed through direct numerical simulations of mechanics supposed to be inherent to secondary flows. This one reveals itself through such instances as large vortices, structural instabilities, vortex cascades and principal modes discussed in this paper. Like fragments of a puzzle, they speak of a motion ordered with its own nuts and bolts, however chaotic it appears at first sight. This opens an opportunity for a multi-oriented approach of which a prime ideology seems to be a rational combination of grid, spectral and statistical methods. An attempt is made to bring together the above instances and produce an alternative point of view on the phenomenon in question when based on the main laws of conservation.
Halloran, Siobhan; Ristenpart, William
2013-11-01
Virologists and other researchers who test pathogens for airborne disease transmissibility often place a test animal downstream from an inoculated animal and later determine whether the test animal became infected. Despite the crucial role of the airflow in pathogen transmission between the animals, to date the infectious disease community has paid little attention to the effect of airspeed or turbulent intensity on the probability of transmission. Here we present measurements of the turbulent dispersivity under conditions relevant to experimental tests of airborne disease transmissibility between laboratory animals. We used time lapse photography to visualize the downstream transport and turbulent dispersion of smoke particulates released from a point source downstream of an axial fan, thus mimicking the release and transport of expiratory aerosols exhaled by an inoculated animal. We show that for fan-generated turbulence the plume width is invariant with the mean airspeed and, close to the point source, increases linearly with downstream position. Importantly, the turbulent dispersivity is insensitive to the presence of meshes placed downstream from the point source, indicating that the fan length scale dictates the turbulent intensity and corresponding dispersivity.
Plasma Soliton Turbulence and Statistical Mechanics
International Nuclear Information System (INIS)
Treumann, R.A.; Pottelette, R.
1999-01-01
Collisionless kinetic plasma turbulence is described approximately in terms of a superposition of non-interacting solitary waves. We discuss the relevance of such a description under astrophysical conditions. Several types of solitary waves may be of interest in this relation as generators of turbulence and turbulent transport. A consistent theory of turbulence can be given only in a few particular cases when the description can be reduced to the Korteweg-de Vries equation or some other simple equation like the Kadomtsev-Petviashvili equation. It turns out that the soliton turbulence is usually energetically harder than the ordinary weakly turbulent plasma description. This implies that interaction of particles with such kinds of turbulence can lead to stronger acceleration than in ordinary turbulence. However, the description in our model is only classical and non-relativistic. Transport in solitary turbulence is most important for drift wave turbulence. Such waves form solitary drift wave vortices which may provide cross-field transport. A more general discussion is given on transport. In a model of Levy flight trapping of particles in solitons (or solitary turbulence) one finds that the residence time of particles in the region of turbulence may be described by a generalized Lorentzian probability distribution. It is shown that under collisionless equilibrium conditions far away from thermal equilibrium such distributions are natural equilibrium distributions. A consistent thermodynamic description of such media can be given in terms of a generalized Lorentzian statistical mechanics and thermodynamics. (author)
Wall roughness induces asymptotic ultimate turbulence
Zhu, Xiaojue; Verschoof, Ruben Adriaan; Bakhuis, Dennis; Huisman, Sander Gerard; Verzicco, Roberto; Sun, Chao; Lohse, Detlef
2018-01-01
Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by
Analysis of chaos in plasma turbulence
DEFF Research Database (Denmark)
Pedersen, T.S.; Michelsen, Poul; Juul Rasmussen, J.
1996-01-01
-stationary turbulent state is reached in a finite time, independent of the initial conditions. Different regimes of the turbulent state can be obtained by varying the coupling parameter C, related to the parallel electron dynamics. The turbulence is described by using particle tracking and tools from chaos analysis...
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.
Global Turbulence Decision Support for Aviation
Williams, J.; Sharman, R.; Kessinger, C.; Feltz, W.; Wimmers, A.
2009-09-01
Turbulence is widely recognized as the leading cause of injuries to flight attendants and passengers on commercial air carriers, yet legacy decision support products such as SIGMETs and SIGWX charts provide relatively low spatial- and temporal-resolution assessments and forecasts of turbulence, with limited usefulness for strategic planning and tactical turbulence avoidance. A new effort is underway to develop an automated, rapid-update, gridded global turbulence diagnosis and forecast system that addresses upper-level clear-air turbulence, mountain-wave turbulence, and convectively-induced turbulence. This NASA-funded effort, modeled on the U.S. Federal Aviation Administration's Graphical Turbulence Guidance (GTG) and GTG Nowcast systems, employs NCEP Global Forecast System (GFS) model output and data from NASA and operational satellites to produce quantitative turbulence nowcasts and forecasts. A convective nowcast element based on GFS forecasts and satellite data provides a basis for diagnosing convective turbulence. An operational prototype "Global GTG” system has been running in real-time at the U.S. National Center for Atmospheric Research since the spring of 2009. Initial verification based on data from TRMM, Cloudsat and MODIS (for the convection nowcasting) and AIREPs and AMDAR data (for turbulence) are presented. This product aims to provide the "single authoritative source” for global turbulence information for the U.S. Next Generation Air Transportation System.
The PDF method for turbulent combustion
Pope, S. B.
1991-01-01
Probability Density Function (PDF) methods provide a means of calculating the properties of turbulent reacting flows. They have been successfully applied to many turbulent flames, including some with finite rate kinetic effects. Here the methods are reviewed with an emphasis on computational issues and their application to turbulent combustion.
2D turbulence structure observed by a fast framing camera system in linear magnetized device PANTA
International Nuclear Information System (INIS)
Ohdachi, Satoshi; Inagaki, S.; Kobayashi, T.; Goto, M.
2015-01-01
Mesoscale structure, such as the zonal flow and the streamer plays important role in the drift-wave turbulence. The interaction of the mesoscale structure and the turbulence is not only interesting phenomena but also a key to understand the turbulence driven transport in the magnetically confined plasmas. In the cylindrical magnetized device, PANTA, the interaction of the streamer and the drift wave has been found by the bi-spectrum analysis of the turbulence. In order to study the mesoscale physics directly, the 2D turbulence is studied by a fast-framing visible camera system view from a window located at the end plate of the device. The parameters of the plasma is the following; Te∼3eV, n ∼ 1x10 19 m -3 , Ti∼0.3eV, B=900G, Neutral pressure P n =0.8 mTorr, a∼ 6cm, L=4m, Helicon source (7MHz, 3kW). Fluctuating component of the visible image is decomposed by the Fourier-Bessel expansion method. Several rotating mode is observed simultaneously. From the images, m = 1 (f∼0.7 kHz) and m = 2, 3 (f∼-3.4 kHz) components which rotate in the opposite direction can be easily distinguished. Though the modes rotate constantly in most time, there appear periods where the radially complicated node structure is formed (for example, m=3 component, t = 142.5∼6 in the figure) and coherent mode structures are disturbed. Then, a new rotating period is started again with different phase of the initial rotation until the next event happens. The typical time interval of the event is 0.5 to 1.0 times of the one rotation of the slow m = 1 mode. The wave-wave interaction might be interrupted occasionally. Detailed analysis of the turbulence using imaging technique will be discussed. (author)
The spatio-temporal structure of electrostatic turbulence in the WEGA stellarator
International Nuclear Information System (INIS)
Marsen, Stefan
2008-03-01
The main object of this work is to provide a detailed characterisation of electrostatic turbulence in WEGA and to identify the underlying instability mechanism driving turbulence. The spatio-temporal structure of turbulence is studied using multiple Langmuir probes providing a sufficiently high spatial and temporal resolution. Turbulence in WEGA is dominated by drift wave dynamics. The phase shift between density and potential fluctuations is close to zero, fluctuations are mainly driven by the density gradient, and the phase velocity of turbulent structures points in the direction of the electron diamagnetic drift. The structure of turbulence is studied mainly in the plasma edge region inside the last closed flux surface. WEGA can be operated in two regimes differing in the magnetic field strength by almost one order of magnitude (57 mT and 500 mT, respectively). At 57 mT large structures with a poloidal extent comparable to the machine dimensions are observed, whereas at 500 mT turbulent structures are much smaller. The poloidal structure size scales nearly linearly with the inverse magnetic field strength. This scaling may be argued to be related to the drift wave dispersion scale, ρ s =√(m i k B T e )/(qB). However, the structure size remains unchanged when the ion mass is changed by using different discharge gases. Inside the last closed flux surface the poloidal E x B drift in WEGA is negligible. The three-dimensional structure is studied in detail using probes which are toroidally separated but aligned along connecting magnetic field lines. A small but finite parallel wavenumber is found. The ratio between the average parallel and perpendicular wavenumber is in the order of anti κ parallel / anti κ θ ∼ 10 -2 . The parallel phase velocity of turbulent structures is in-between the ion sound velocity and the Alfven velocity. In the parallel dynamics a fundamental difference between the two operational regimes at different magnetic field strength is
Turbulence, Magnetic Reconnection in Turbulent Fluids and Energetic Particle Acceleration
Lazarian, A.; Vlahos, L.; Kowal, G.; Yan, H.; Beresnyak, A.; de Gouveia Dal Pino, E. M.
2012-11-01
Turbulence is ubiquitous in astrophysics. It radically changes many astrophysical phenomena, in particular, the propagation and acceleration of cosmic rays. We present the modern understanding of compressible magnetohydrodynamic (MHD) turbulence, in particular its decomposition into Alfvén, slow and fast modes, discuss the density structure of turbulent subsonic and supersonic media, as well as other relevant regimes of astrophysical turbulence. All this information is essential for understanding the energetic particle acceleration that we discuss further in the review. For instance, we show how fast and slow modes accelerate energetic particles through the second order Fermi acceleration, while density fluctuations generate magnetic fields in pre-shock regions enabling the first order Fermi acceleration of high energy cosmic rays. Very importantly, however, the first order Fermi cosmic ray acceleration is also possible in sites of magnetic reconnection. In the presence of turbulence this reconnection gets fast and we present numerical evidence supporting the predictions of the Lazarian and Vishniac (Astrophys. J. 517:700-718, 1999) model of fast reconnection. The efficiency of this process suggests that magnetic reconnection can release substantial amounts of energy in short periods of time. As the particle tracing numerical simulations show that the particles can be efficiently accelerated during the reconnection, we argue that the process of magnetic reconnection may be much more important for particle acceleration than it is currently accepted. In particular, we discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers as well as the origin cosmic ray excess in the direction of Heliotail.
Modelling of turbulence and combustion for simulation of gas explosions in complex geometries
Energy Technology Data Exchange (ETDEWEB)
Arntzen, Bjoern Johan
1998-12-31
This thesis analyses and presents new models for turbulent reactive flows for CFD (Computational Fluid Dynamics) simulation of gas explosions in complex geometries like offshore modules. The course of a gas explosion in a complex geometry is largely determined by the development of turbulence and the accompanying increased combustion rate. To be able to model the process it is necessary to use a CFD code as a starting point, provided with a suitable turbulence and combustion model. The modelling and calculations are done in a three-dimensional finite volume CFD code, where complex geometries are represented by a porosity concept, which gives porosity on the grid cell faces, depending on what is inside the cell. The turbulent flow field is modelled with a k-{epsilon} turbulence model. Subgrid models are used for production of turbulence from geometry not fully resolved on the grid. Results from laser doppler anemometry measurements around obstructions in steady and transient flows have been analysed and the turbulence models have been improved to handle transient, subgrid and reactive flows. The combustion is modelled with a burning velocity model and a flame model which incorporates the burning velocity into the code. Two different flame models have been developed: SIF (Simple Interface Flame model), which treats the flame as an interface between reactants and products, and the {beta}-model where the reaction zone is resolved with about three grid cells. The flame normally starts with a quasi laminar burning velocity, due to flame instabilities, modelled as a function of flame radius and laminar burning velocity. As the flow field becomes turbulent, the flame uses a turbulent burning velocity model based on experimental data and dependent on turbulence parameters and laminar burning velocity. The laminar burning velocity is modelled as a function of gas mixture, equivalence ratio, pressure and temperature in reactant. Simulations agree well with experiments. 139
Statistical descriptions of polydisperse turbulent two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Minier, Jean-Pierre, E-mail: jean-pierre.minier@edf.fr
2016-12-15
results for dynamical systems influenced by colored or white noises are established which point to the necessity of developing statistical models for particles in random media from a new standpoint that breaks away from descriptions based only on particle kinetic variables. This is needed to obtain well-posed formulations of particle dispersion by non fully-resolved turbulent flows and suggests also to revisit classical ideas of particle–particle interactions in the presence of a turbulent flow which correlates the dynamics of colliding discrete elements.
Electrohydrodynamic (EHD) vortices in helical turbulence
International Nuclear Information System (INIS)
Kikuchi, H.
1996-01-01
The study of large-scale coherent hydrodynamic (HD) vortex generation has been extended to electrified charged dusty vortices to be termed as electrohydrodynamic (EHD) vortices, incorporating helical turbulence in electric and magnetic fields into that in fluid velocity, which are all created by an external DC electric field on the background. A new equation of EHD vortices is introduced on the basis of a set of EHD or electromagnetohydrodynamic (EMHD) equations, including equations of state and a full set of Maxwell's equations by using functional techniques for estimating equations for an ensemble average, turbulent background, and additional random field. In fact, EHD vortices for a charged dusty fluid can be more explosive with larger instabilities than HD vortices. In addition, it is inferred that an external DC electric field could provide the origin of additional self-organization to a coalescence of fluid vortex and electric field lines as a manifestation of a new frozen-in field concept for electric fields when the electric Reynolds number is sufficiently high. This is discussed on the basis of a set of general transport equations for fluid vorticity, magnetic and electric fields that are rederived concisely. In particular, a novel concept of electric field line merging-reconnection is developed in close relation to fluid vortex line merging, indicating a coalescence of fluid vortex breakdown or merging point and electric field line reconnection point, X-type or O-type with possible application to tornadic thunderstorms. In fact, a thundercloud charge distribution so as to provide a coalescence of fluid vortex and electric field lines is quite possible without theoretical inconsistency, and is thought most likely to occur from observations available so far. (orig.)
On the asymptotic ergodic capacity of FSO links with generalized pointing error model
Al-Quwaiee, Hessa
2015-09-11
Free-space optical (FSO) communication systems are negatively affected by two physical phenomenon, namely, scintillation due to atmospheric turbulence and pointing errors. To quantize the effect of these two factors on FSO system performance, we need an effective mathematical model for them. Scintillations are typically modeled by the log-normal and Gamma-Gamma distributions for weak and strong turbulence conditions, respectively. In this paper, we propose and study a generalized pointing error model based on the Beckmann distribution. We then derive the asymptotic ergodic capacity of FSO systems under the joint impact of turbulence and generalized pointing error impairments. © 2015 IEEE.
The effects of local blowing perturbations on thermal turbulent structures
Liu, Can; Araya, Guillermo; Leonardi, Stefano; Castillo, Luciano
2013-11-01
Blowing is an active flow control technique with several industrial applications, particularly in film cooling of turbine blades. In the past, the effects of localized blowing have been mostly analyzed on the velocity field and its influence of the flow parameters and turbulence structures (Krogstad and Kourakine, 2000). However, little literature can be found on the effects of blowing on the coherent thermal structures. In the present study, an incompressible turbulent channel flow with given steady blowing at the wall is simulated via DNS by means of five spanwise holes. The Reynolds number based on the friction velocity and half channel height is approximately Re = 394 and the molecular Prandtl number is Pr = 0.71. Temperature is considered a passive scalar with isothermal conditions at the wall. Different blowing amplitudes and perturbing angles (with respect to the streamwise direction) are applied to find out their effects on the turbulent thermal structures by means of a two-point correlation analysis. In addition, local reduction and increase of drag are connected to vorticity. The corresponding influence of perturbing amplitudes and angles on the energy budget of thermal fluctuations and turbulent Prandtl numbers are also shown and discussed.
Finite-Reynolds-number effects in turbulence using logarithmic expansions
International Nuclear Information System (INIS)
Sreenivasan, K.R.; Bershadskii, A.
2006-12-01
Experimental or numerical data in turbulence are invariably obtained at finite Reynolds numbers whereas theories of turbulence correspond to infinitely large Reynolds numbers. A proper merger of the two approaches is possible only if corrections for finite Reynolds numbers can be quantified. This paper heuristically considers examples in two classes of finite-Reynolds-number effects. Expansions in terms of logarithms of appropriate variables are shown to yield results in agreement with experimental and numerical data in the following instances: the third-order structure function in isotropic turbulence, the mixed-order structure function for the passive scalar and the Reynolds shear stress around its maximum point. Results suggestive of expansions in terms of the inverse logarithm of the Reynolds number, also motivated by experimental data, concern the tendency for turbulent structures to cluster along a line of observation and (more speculatively) for the longitudinal velocity derivative to become singular at some finite Reynolds number. We suggest an elementary hydrodynamical process that may provide a physical basis for the expansions considered here, but note that the formal justification remains tantalizingly unclear. (author)
Stochastic acceleration by hydromagnetic turbulence
International Nuclear Information System (INIS)
Kulsrud, R.M.
1979-03-01
A general theory for particle acceleration by weak hydromagnetic turbulence with a given spectrum of waves is described. Various limiting cases, corresponding to Fermi acceleration and magnetic pumping, are discussed and two numerical examples illustrating them are given. An attempt is made to show that the expression for the rate of Fermi acceleration is valid for finite amplitudes
Topology optimization of turbulent flows
DEFF Research Database (Denmark)
Dilgen, Cetin B.; Dilgen, Sumer B.; Fuhrman, David R.
2018-01-01
The aim of this work is to present a fast and viable approach for taking into account turbulence in topology optimization of complex fluid flow systems, without resorting to any simplifying assumptions in the derivation of discrete adjoints. Topology optimization is an iterative gradient...
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.
Turbulent magnetohydrodynamics in liquid metals
International Nuclear Information System (INIS)
Berhanu, Michael
2008-01-01
In electrically conducting fluids, the electromagnetic field is coupled with the fluid motion by induction effects. We studied different magnetohydrodynamic phenomena, using two experiments involving turbulent flows of liquid metal. The first mid-sized uses gallium. The second, using sodium, is conducted within the VKS (Von Karman Sodium) collaboration. It has led to the observation of the dynamo effect, namely converting a part of the kinetic energy of the fluid into magnetic energy. We have shown that, depending on forcing conditions, a statistically stationary dynamo, or dynamical regimes of magnetic field can be generated. In particular, polarity reversals similar to those of Earth's magnetic field were observed. Meanwhile, experiment with Gallium has been developed to study the effects of electromagnetic induction by turbulent flows in a more homogeneous and isotropic configuration than in the VKS experiment. Using data from these two experiments, we studied the advection of magnetic field by a turbulent flow and the induced fluctuations. The development of probes measuring electrical potential difference allowed us to further highlight the magnetic braking of a turbulent flow of Gallium by Lorentz force. This mechanism is involved in the saturation of the dynamo instability. (author) [fr
Nonuniform quantum turbulence in superfluids
Nemirovskii, Sergey K.
2018-04-01
The problem of quantum turbulence in a channel with an inhomogeneous counterflow of superfluid turbulent helium is studied. The counterflow velocity Vns x(y ) along the channel is supposed to have a parabolic profile in the transverse direction y . Such statement corresponds to the recent numerical simulation by Khomenko et al. [Phys. Rev. B 91, 180504 (2015), 10.1103/PhysRevB.91.180504]. The authors reported about a sophisticated behavior of the vortex-line density (VLD) L (r ,t ) , different from L ∝Vns x(y) 2 , which follows from the straightforward application of the conventional Vinen theory. It is clear that Vinen theory should be refined by taking into account transverse effects, and the way it ought to be done is the subject of active discussion in the literature. In this work, we discuss several possible mechanisms of the transverse flux of VLD L (r ,t ) which should be incorporated in the standard Vinen equation to describe adequately the inhomogeneous quantum turbulence. It is shown that the most effective among these mechanisms is the one that is related to the phase-slippage phenomenon. The use of this flux in the modernized Vinen equation corrects the situation with an unusual distribution of the vortex-line density, and satisfactorily describes the behavior L (r ,t ) both in stationary and nonstationary situations. The general problem of the phenomenological Vinen theory in the case of nonuniform and nonstationary quantum turbulence is thoroughly discussed.
Turbulent transport in magnetized plasmas
Horton, Wendell
2012-01-01
This book explains how magnetized plasmas self-organize in states of electromagnetic turbulence that transports particles and energy out of the core plasma faster than anticipated by the fusion scientists designing magnetic confinement systems in the 20th century. It describes theory, experiments and simulations in a unified and up-to-date presentation of the issues of achieving nuclear fusion power.
Magnetohydrodynamics turbulence: An astronomical perspective
Indian Academy of Sciences (India)
MHD turbulence in the solar wind are described in §6, and a theory of ..... on plasmas are very difficult to perform, and so experimental verification was not forth- .... checks of self-consistency regarding the assumed weakness of the cascade.
Turbulent jet in confined counterflow
Indian Academy of Sciences (India)
framework for presenting the results of the flowfield and jet penetration length. ... A turbulent jet is a basic free shear flow and has received research attention (see, .... MBE76 identify this to be a transitional zone and for. √ .... higher return flow and also higher velocity from counterflow due to a narrower gap thus leading.
Statistical description of turbulent dispersion
Brouwers, J.J.H.
2012-01-01
We derive a comprehensive statistical model for dispersion of passive or almost passive admixture particles such as fine particulate matter, aerosols, smoke and fumes, in turbulent flow. The model rests on the Markov limit for particle velocity. It is in accordance with the asymptotic structure of
Magnetic fluctuations in turbulent flow
International Nuclear Information System (INIS)
Ruzmaikin, A.A.
1990-01-01
For dynamo excitation of the magnetic fluctuations in infinite fluid only a sufficient large magnetic Reynolds number is needed. In a infinite region an additional condition appears. Due to the diffusion of the magnetic field through the boundaries a size of the region must be large enough compare with a correlation length of the turbulence. Author)
Turbulent flows over sparse canopies
Sharma, Akshath; García-Mayoral, Ricardo
2018-04-01
Turbulent flows over sparse and dense canopies exerting a similar drag force on the flow are investigated using Direct Numerical Simulations. The dense canopies are modelled using a homogeneous drag force, while for the sparse canopy, the geometry of the canopy elements is represented. It is found that on using the friction velocity based on the local shear at each height, the streamwise velocity fluctuations and the Reynolds stress within the sparse canopy are similar to those from a comparable smooth-wall case. In addition, when scaled with the local friction velocity, the intensity of the off-wall peak in the streamwise vorticity for sparse canopies also recovers a value similar to a smooth-wall. This indicates that the sparse canopy does not significantly disturb the near-wall turbulence cycle, but causes its rescaling to an intensity consistent with a lower friction velocity within the canopy. In comparison, the dense canopy is found to have a higher damping effect on the turbulent fluctuations. For the case of the sparse canopy, a peak in the spectral energy density of the wall-normal velocity, and Reynolds stress is observed, which may indicate the formation of Kelvin-Helmholtz-like instabilities. It is also found that a sparse canopy is better modelled by a homogeneous drag applied on the mean flow alone, and not the turbulent fluctuations.
Wind effect in turbulence parametrization
Colombini, M.; Stocchino, A.
2005-09-01
The action of wind blowing over a closed basin ultimately results in a steady shear-induced circulation pattern and in a leeward rising of the free surface—and a corresponding windward lowering—known as wind set-up. If the horizontal dimensions of the basin are large with respect to the average flow depth, the occurrence of local quasi-equilibrium conditions can be expected, i.e. the flow can be assumed to be locally driven only by the wind stress and by the opposing free surface gradient due to set-up. This wind-induced flow configuration shows a strong similarity with turbulent Couette-Poiseuille flow, the one dimensional flow between parallel plates generated by the simultaneous action of a constant pressure gradient and of the shear induced by the relative motion of the plates. A two-equation turbulence closure is then employed to perform a numerical study of turbulent Couette-Poiseuille flows for different values of the ratio of the shear stresses at the two walls. The resulting eddy viscosity vertical distributions are analyzed in order to devise analytical profiles of eddy viscosity that account for the effect of wind. The results of this study, beside allowing for a physical insight on the turbulence process of this class of flows, will allow for a more accurate description of the wind effect to be included in the formulation of quasi-3D and 3D models of lagoon hydrodynamics.
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 ...
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
Group-kinetic theory and modeling of atmospheric turbulence
Tchen, C. M.
1989-01-01
A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.
An introduction to turbulence and its measurement
Bradshaw, P
1971-01-01
An Introduction to Turbulence and Its Measurement is an introductory text on turbulence and its measurement. It combines the physics of turbulence with measurement techniques and covers topics ranging from measurable quantities and their physical significance to the analysis of fluctuating signals, temperature and concentration measurements, and the hot-wire anemometer. Examples of turbulent flows are presented. This book is comprised of eight chapters and begins with an overview of the physics of turbulence, paying particular attention to Newton's second law of motion, the Newtonian viscous f
Turbulence and Interfacial Mixing
Energy Technology Data Exchange (ETDEWEB)
Glimm, James; Li, Xiaolin
2005-03-15
The authors study mix from analytical and numerical points of view. These investigations are linked. The analytical studies (in addition to laboratory experiments) provide bench marks for the direct simulation of mix. However, direct simulation is too detailed to be useful and to expensive to be practical. They also consider averaged equations. Here the major issue is the validation of the closure assumptions. They appeal to the direct simulation methods for this step. They have collaborated with several NNSA teams; moreover, Stony Brook alumni (former students, faculty and research collaborators) presently hold staff positions in NNSA laboratories.
Topics in strong Langmuir turbulence
International Nuclear Information System (INIS)
Skoric, M.M.
1981-01-01
This thesis discusses certain aspects of the turbulence of a fully ionised non-isothermal plasma dominated by the Langmuir mode. Some of the basic properties of strongly turbulent plasmas are reviewed. In particular, interest is focused on the state of Langmuir turbulence, that is the turbulence of a simple externally unmagnetized plasma. The problem of the existence and dynamics of Langmuir collapse is discussed, often met as a non-linear stage of the modulational instability in the framework of the Zakharov equations (i.e. simple time-averaged dynamical equations). Possible macroscopic consequences of such dynamical turbulent models are investigated. In order to study highly non-linear collapse dynamics in its advanced stage, a set of generalized Zakharov equations are derived. Going beyond the original approximation, the author includes the effects of higher electron non-linearities and a breakdown of slow-timescale quasi-neutrality. He investigates how these corrections may influence the collapse stabilisation. Recently, it has been realised that the modulational instability in a Langmuir plasma will be accompanied by the collisionless-generation of a slow-timescale magnetic field. Accordingly, a novel physical situation has emerged which is investigated in detail. The stability of monochromatic Langmuir waves in a self-magnetized Langmuir plasma, is discussed, and the existence of a novel magneto-modulational instability shown. The wave collapse dynamics is investigated and a physical interpretation of the basic results is given. A problem of the transient analysis of an interaction of time-dependent electromagnetic pulses with linear cold plasma media is investigated. (Auth.)
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.
Visible light broadband perfect absorbers
Energy Technology Data Exchange (ETDEWEB)
Jia, X. L.; Meng, Q. X.; Yuan, C. X.; Zhou, Z. X.; Wang, X. O., E-mail: wxo@hit.edu.cn [School of Science, Harbin Institute of Technology, Harbin 150001 (China)
2016-03-15
The visible light broadband perfect absorbers based on the silver (Ag) nano elliptical disks and holes array are studied using finite difference time domain simulations. The semiconducting indium silicon dioxide thin film is introduced as the space layer in this sandwiched structure. Utilizing the asymmetrical geometry of the structures, polarization sensitivity for transverse electric wave (TE)/transverse magnetic wave (TM) and left circular polarization wave (LCP)/right circular polarization wave (RCP) of the broadband absorption are gained. The absorbers with Ag nano disks and holes array show several peaks absorbance of 100% by numerical simulation. These simple and flexible perfect absorbers are particularly desirable for various potential applications including the solar energy absorber.
Visible nulling coronagraph testbed results
Lyon, Richard G.; Clampin, Mark; Woodruff, Robert A.; Vasudevan, Gopal; Thompson, Patrick; Petrone, Peter; Madison, Timothy; Rizzo, Maxime; Melnick, Gary; Tolls, Volker
2009-08-01
We report on our recent laboratory results with the NASA/Goddard Space Flight Center (GSFC) Visible Nulling Coronagraph (VNC) testbed. We have experimentally achieved focal plane contrasts of 1 x 108 and approaching 109 at inner working angles of 2 * wavelength/D and 4 * wavelength/D respectively where D is the aperture diameter. The result was obtained using a broadband source with a narrowband spectral filter of width 10 nm centered on 630 nm. To date this is the deepest nulling result with a visible nulling coronagraph yet obtained. Developed also is a Null Control Breadboard (NCB) to assess and quantify MEMS based segmented deformable mirror technology and develop and assess closed-loop null sensing and control algorithm performance from both the pupil and focal planes. We have demonstrated closed-loop control at 27 Hz in the laboratory environment. Efforts are underway to first bring the contrast to > 109 necessary for the direct detection and characterization of jovian (Jupiter-like) and then to > 1010 necessary for terrestrial (Earth-like) exosolar planets. Short term advancements are expected to both broaden the spectral passband from 10 nm to 100 nm and to increase both the long-term stability to > 2 hours and the extent of the null out to a ~ 10 * wavelength / D via the use of MEMS based segmented deformable mirror technology, a coherent fiber bundle, achromatic phase shifters, all in a vacuum chamber at the GSFC VNC facility. Additionally an extreme stability textbook sized compact VNC is under development.
ADIABATIC HEATING OF CONTRACTING TURBULENT FLUIDS
International Nuclear Information System (INIS)
Robertson, Brant; Goldreich, Peter
2012-01-01
Turbulence influences the behavior of many astrophysical systems, frequently by providing non-thermal pressure support through random bulk motions. Although turbulence is commonly studied in systems with constant volume and mean density, turbulent astrophysical gases often expand or contract under the influence of pressure or gravity. Here, we examine the behavior of turbulence in contracting volumes using idealized models of compressed gases. Employing numerical simulations and an analytical model, we identify a simple mechanism by which the turbulent motions of contracting gases 'adiabatically heat', experiencing an increase in their random bulk velocities until the largest eddies in the gas circulate over a Hubble time of the contraction. Adiabatic heating provides a mechanism for sustaining turbulence in gases where no large-scale driving exists. We describe this mechanism in detail and discuss some potential applications to turbulence in astrophysical settings.
Contribution to the study of turbulence spectra
Dumas, R.
1979-01-01
An apparatus suitable for turbulence measurement between ranges of 1 to 5000 cps and from 6 to 16,000 cps was developed and is described. Turbulence spectra downstream of the grills were examined with reference to their general characteristics, their LF qualities, and the effects of periodic turbulence. Medium and HF are discussed. Turbulence spectra in the boundary layers are similarly examined, with reference to their fluctuations at right angles to the wall, and to lateral fluctuations. Turbulence spectra in a boundary layer with suction to the wall is discussed. Induced turbulence, and turbulence spectra at high Reynolds numbers. Calculations are presented relating to the effect of filtering on the value of the correlations in time and space.
International Nuclear Information System (INIS)
Hosokawa, Shigeo; Tomiyama, Akio
1999-01-01
One of the key issues in two-phase turbulence modeling is the turbulence modification due to the momentum exchange between the dispersed and continuous phases. As for the gas-liquid two-phase flows in vertical pipes, Serizawa and Kataoka carried out detailed measurement of turbulence intensity and detected the turbulence modification. Gore and Crowe pointed out that the modification is well correlated with the ratio of a particle diameter to a turbulence length scale (d/l t ). However the modification may depend on not only the length scales but also the eddy viscosities of shear-induced and particle-induced turbulence. Hosokawa et al. proposed the ratio φ of the eddy viscosity induced by a dispersed phase to the shear-induced eddy viscosity and confirmed that measured turbulence modification was well correlated with φ for a gas-solid two-phase flow. In this study, we examine whether or not φ is also applicable to gas-liquid and solid-liquid two-phase dispersed upflows in vertical pipes. Using the eddy viscosity ratio instead of d/l t , we could obtain much better correlation. The critical point at which no modification occurred was close to φ = 1, irrespective of a type of a two-phase dispersed flow. Consequently, we could confirm that the eddy viscosity ratio is a more appropriate parameter for correlating the turbulent modification than the conventional critical parameter d/l t . (author)
Energy Technology Data Exchange (ETDEWEB)
Merci, Bart [Department of Flow, Heat and Combustion Mechanics, Ghent University-UGent, Ghent (Belgium); Roekaerts, Dirk [Department of Multi-Scale Physics, Delft University of Technology, Delft (Netherlands); Naud, Bertrand [CIEMAT, Madrid (Spain); Pope, Stephen B. [Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY (United States)
2006-07-15
Numerical simulation results are presented for turbulent jet diffusion flames with various levels of turbulence-chemistry interaction, stabilized behind a bluff body (Sydney Flames HM1-3). Interaction between turbulence and combustion is modeled with the transported joint-scalar PDF approach. The mass density function transport equation is solved in a Lagrangian manner. A second-moment-closure turbulence model is applied to obtain accurate mean flow and turbulent mixing fields. The behavior of two micromixing models is discussed: the Euclidean minimum spanning tree model and the modified Curl coalescence dispersion model. The impact of the micromixing model choice on the results in physical space is small, although some influence becomes visible as the amount of local extinction increases. Scatter plots and profiles of conditional means and variances of thermochemical quantities, conditioned on the mixture fraction, are discussed both within and downstream of the recirculation region. A distinction is made between local extinction and incomplete combustion, based on the CO species mass fraction. The differences in qualitative behavior between the micromixing models are explained and quantitative comparison to experimental data is made. (author)
Statistical Mechanics of Turbulent Dynamos
Shebalin, John V.
2014-01-01
Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much
PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and Beyond
Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
2008-10-01
The goals of the International Conference `Turbulent Mixing and Beyond' are to expose the generic problem of Turbulence and Turbulent Mixing in Unsteady Flows to a wide scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the non-canonical turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together scientists from the areas which include, but are not limited to, high energy density physics, plasmas, fluid dynamics, turbulence, combustion, material science, geophysics, astrophysics, optics and telecommunications, applied mathematics, probability and statistics, and to have their attention focused on the long-standing formidable task. The Turbulent Mixing and Turbulence in Unsteady Flows, including multiphase flows, plays a key role in a wide variety of phenomena, ranging from astrophysical to nano-scales, under either high or low energy density conditions. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, properties of materials under high strain rates, strong shocks, explosions, blast waves, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, oceanography, atmospheric flows, unsteady boundary layers, hypersonic and supersonic flows, are a few examples to list. A grip on unsteady turbulent processes is crucial for cutting-edge technology such as laser-micromachining and free-space optical telecommunications, and for industrial applications in aeronautics. Unsteady Turbulent Processes are anisotropic, non-local and multi-scale, and their fundamental scaling, spectral and invariant properties depart from the classical Kolmogorov scenario. The singular aspects and similarity of the
The critical point of quantum chromodynamics through lattice and ...
Indian Academy of Sciences (India)
The Padé approximants are the rational functions. PL. M (z) = .... Deviations from a smooth behaviour near the critical point are visible in these extrap- ... see that there is evidence, albeit statistically not very significant, that the kurtosis changes.
Comparison of turbulent particle dispersion models in turbulent shear flows
Directory of Open Access Journals (Sweden)
S. Laín
2007-09-01
Full Text Available This work compares the performance of two Lagrangian turbulent particle dispersion models: the standard model (e.g., that presented in Sommerfeld et al. (1993, in which the fluctuating fluid velocity experienced by the particle is composed of two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, and the model proposed by Minier and Peirano (2001, which is based on the PDF approach and performs closure at the level of acceleration of the fluid experienced by the particle. Formulation of a Langevin equation model for the increments of fluid velocity seen by the particle allows capturing some underlying physics of particle dispersion in general turbulent flows while keeping the mathematical manipulation of the stochastic model simple, thereby avoiding some pitfalls and simplifying the derivation of macroscopic relations. The performance of both dispersion models is tested in the configurations of grid-generated turbulence (Wells and Stock (1983 experiments, simple shear flow (Hyland et al., 1999 and confined axisymmetric jet flow laden with solids (Hishida and Maeda (1987 experiments.
Kinetic energy budgets near the turbulent/nonturbulent interface in jets
Taveira, Rodrigo R.; da Silva, Carlos B.
2013-01-01
The dynamics of the kinetic energy near the turbulent/nonturbulent (T/NT) interface separating the turbulent from the irrotational flow regions is analysed using three direct numerical simulations of turbulent planar jets, with Reynolds numbers based on the Taylor micro-scale across the jet shear layer in the range Reλ ≈ 120-160. Important levels of kinetic energy are already present in the irrotational region near the T/NT interface. The mean pressure and kinetic energy are well described by the Bernoulli equation in this region and agree with recent results obtained from rapid distortion theory in the turbulent region [M. A. C. Teixeira and C. B. da Silva, "Turbulence dynamics near a turbulent/non-turbulent interface," J. Fluid Mech. 695, 257-287 (2012)], 10.1017/jfm.2012.17 while the normal Reynolds stresses agree with the theoretical predictions from Phillips ["The irrotational motion outside a free turbulent boundary," Proc. Cambridge Philos. Soc. 51, 220 (1955)], 10.1017/S0305004100030073. The use of conditional statistics in relation to the distance from the T/NT interface allow a detailed study of the build up of kinetic energy across the T/NT interface, pointing to a very different picture than using classical statistics. Conditional kinetic energy budgets show that apart from the viscous dissipation of kinetic energy, the maximum of all the mechanisms governing the kinetic energy are concentrated in a very narrow region distancing about one to two Taylor micro-scales from the T/NT interface. The (total and fluctuating) kinetic energy starts increasing in the irrotational region by pressure-velocity interactions - a mechanism that can act at distance, and continue to grow by advection (for the total kinetic energy) and turbulent diffusion (for the turbulent kinetic energy) inside the turbulent region. These mechanisms tend to occur preferentially around the core of the large-scale vortices existing near T/NT interface. The production of turbulent
European developments in single phase turbulence for innovative reactors
Energy Technology Data Exchange (ETDEWEB)
Roelofs, F., E-mail: roelofs@nrg.eu [NRG, Petten (Netherlands); Rohde, M. [DUT, Delft (Netherlands); and others
2011-07-01
Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in specific behavior of flow and heat transfer, which requires specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. In Europe, such cross-cutting thermal-hydraulics topics are the motivation for the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which is sponsored by the European Commission from 2010 to 2014. This paper describes the ongoing developments in an important part of this project devoted to single phase turbulence issues. To this respect, the two main issues have been identified: Non-unity Prandtl number turbulence. In case of liquid metals, molten salts or supercritical fluids, the commonly applied constant turbulent Prandtl number concept is not applicable and robust engineering turbulence models are needed. This paper will report on the progress achieved with respect to the development and validation of turbulence models available in commonly used engineering tools. The paper also reports about the supporting experiments and direct numerical simulations; and, Temperature fluctuations possibly leading to thermal fatigue in innovative reactors. The status is described of a fundamental experiment dealing with the mixing of different density gases in a rectangular channel, an experiment in a more complex geometry of a small mixing plenum using a supercritical fluid, and direct numerical simulations of conjugate heat transfer on temperature fluctuations in liquid metal. (author)
Turbulent mixing and fluid transport within Florida Bay seagrass meadows
Hansen, Jennifer C. R.; Reidenbach, Matthew A.
2017-10-01
Seagrasses serve an important function in the ecology of Florida Bay, providing critical nursery habitat and a food source for a variety of organisms. They also create significant benthic structure that induces drag, altering local hydrodynamics that can influence mixing and nutrient dynamics. Thalassia testudinum seagrass meadows were investigated to determine how shoot density and morphometrics alter local wave conditions, the generation of turbulence, and fluid exchange above and within the canopy. Sparsely vegetated and densely vegetated meadows were monitored, with shoot densities of 259 ± 26 and 484 ± 78 shoots m-2, respectively. The temporal and spatial structure of velocity and turbulence were measured using acoustic Doppler velocimeters and an in situ particle image velocimetry (PIV) system positioned both above and within the seagrass canopy. The retention of fluid within the canopy was determined by examining e-folding times calculated from the concentration curves of dye plumes released within the seagrass canopy. Results show that a shear layer with an inflection point develops at the top of the seagrass canopy, which generates instabilities that impart turbulence into the seagrass meadow. Compared to the overlying water column, turbulence was enhanced within the sparse canopy due to flow interaction with the seagrass blades, but reduced within the dense canopy. Wave generated oscillatory motion penetrated deeper into the canopy than unidirectional currents, enhancing fluid exchange. Both shoot density and the relative magnitude of wave- versus current-driven flow conditions were found to be important controls on turbulent exchange of water masses across the canopy-water interface.
European developments in single phase turbulence for innovative reactors
International Nuclear Information System (INIS)
Roelofs, F.; Rohde, M.
2011-01-01
Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in specific behavior of flow and heat transfer, which requires specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. In Europe, such cross-cutting thermal-hydraulics topics are the motivation for the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which is sponsored by the European Commission from 2010 to 2014. This paper describes the ongoing developments in an important part of this project devoted to single phase turbulence issues. To this respect, the two main issues have been identified: Non-unity Prandtl number turbulence. In case of liquid metals, molten salts or supercritical fluids, the commonly applied constant turbulent Prandtl number concept is not applicable and robust engineering turbulence models are needed. This paper will report on the progress achieved with respect to the development and validation of turbulence models available in commonly used engineering tools. The paper also reports about the supporting experiments and direct numerical simulations; and, Temperature fluctuations possibly leading to thermal fatigue in innovative reactors. The status is described of a fundamental experiment dealing with the mixing of different density gases in a rectangular channel, an experiment in a more complex geometry of a small mixing plenum using a supercritical fluid, and direct numerical simulations of conjugate heat transfer on temperature fluctuations in liquid metal. (author)
Bao, Jian; Lau, Calvin; Kuley, Animesh; Lin, Zhihong; Fulton, Daniel; Tajima, Toshiki; Tri Alpha Energy, Inc. Team
2017-10-01
Collisional and turbulent transport in a field reversed configuration (FRC) is studied in global particle simulation by using GTC (gyrokinetic toroidal code). The global FRC geometry is incorporated in GTC by using a field-aligned mesh in cylindrical coordinates, which enables global simulation coupling core and scrape-off layer (SOL) across the separatrix. Furthermore, fully kinetic ions are implemented in GTC to treat magnetic-null point in FRC core. Both global simulation coupling core and SOL regions and independent SOL region simulation have been carried out to study turbulence. In this work, the ``logical sheath boundary condition'' is implemented to study parallel transport in the SOL. This method helps to relax time and spatial steps without resolving electron plasma frequency and Debye length, which enables turbulent transports simulation with sheath effects. We will study collisional and turbulent SOL parallel transport with mirror geometry and sheath boundary condition in C2-W divertor.
Direct numerical simulation of the passive scalar field in a two-dimensional turbulent channel flow
International Nuclear Information System (INIS)
Kasagi, N.; Tomita, Y.; Kuroda, A.
1991-01-01
This paper reports on a direct numerical simulation (DNS) of the fully developed thermal field in a two-dimensional turbulent channel flow of air that was carried out. The iso-flux condition is imposed on the walls so that the local mean temperature linearly increases in the streamwise direction. The computation was executed on 1,589,248 grid points by using a spectral method. The statistics obtained include rms velocity and temperature fluctuations, Reynolds stresses, turbulent heat fluxes and other higher order correlations. They are compared mainly with the DNS data obtained by Kim and Moin (1987) and Kim (1987) in a higher Reynolds number flow with isothermal walls. Agreement between these two results is generally good. Each term in the budget equations of temperature variance, its dissipation rate and turbulent heat fluxes is also calculated in order to establish a data base of convective heat transfer for thermal turbulence modeling
MHD from a Microscopic Concept and Onset of Turbulence in Hartmann Flow
International Nuclear Information System (INIS)
Jirkovsky, L.; Bo-ot, L. Ma.; Chiang, C. M.
2010-01-01
We derive higher order magneto-hydrodynamic (MHD) equations from a microscopic picture using projection and perturbation formalism. In an application to Hartmann flow we find velocity profiles flattening towards the center at the onset of turbulence in hydrodynamic limit. Comparison with the system under the effect of a uniform magnetic field yields difference in the onset of turbulence consistent with observations, showing that the presence of magnetic field inhibits onset of instability or turbulence. The laminar-turbulent transition is demonstrated in a phase transition plot of the development in time of the relative average velocities vs. Reynolds number showing a sharp increase of the relative average velocity at the transition point as determined by the critical Reynolds number. (physics of gases, plasmas, and electric discharges)
The essence of turbulence as a physical phenomenon with emphasis on issues of paradigmatic nature
Tsinober, Arkady
2014-01-01
This book critically reexamines what turbulence really is, from a fundamental point of view and based on observations from nature, laboratories, and direct numerical simulations. It includes critical assessments and a comparative analysis of the key developments, their evolution and failures, along with key misconceptions and outdated paradigms. The main emphasis is on conceptual and problematic aspects, physical phenomena, observations, misconceptions and unresolved issues rather than on conventional formalistic aspects, models, etc. Apart from the obvious fundamental importance of turbulent flows, this emphasis stems from the basic premise that without corresponding progress in fundamental aspects there is little chance for progress in applications such as drag reduction, mixing, control and modeling of turbulence. More generally, there is also a desperate need to grasp the physical fundamentals of the technological processes in which turbulence plays a central role.
Directory of Open Access Journals (Sweden)
Kangkang Yu
Full Text Available This study is to distinguish the objective and subjective measures of atmospheric visibility, and investigate the relationship between the two measures as well as the effect on the people's behavioral intentions on air pollution in China. A mixed method was adopted in this study combining both lab experiments to measure objective atmospheric visibility and a questionnaire survey to measure subjective atmospheric visibility. The regression results show that: (a The people's perception of atmospheric visibility is based on objective information about the ambient air (Relative Humidity, PM2.5, Atmospheric Visibility and there are some turning points that could enable people to distinguish good and poor air quality; (b The people's perception of visibility has a significant effect on either their willingness-to-accept (WTA the visibility or on their willingness-to-pay (WTP for improving the air quality;
Energy Awareness Displays - Making the Invisible Visible
Börner, Dirk
2011-01-01
Börner, D. (2011). Energy Awareness Displays - Making the Invisible Visible. Presentation given at the Startbijeenkomst SURFnet Innovatieregeling Duurzaamheid & ICT. May, 13, 2011, Utrecht, The Netherlands.
Flow Visualization in Supersonic Turbulent Boundary Layers.
Smith, Michael Wayne
This thesis is a collection of novel flow visualizations of two different flat-plate, zero pressure gradient, supersonic, turbulent boundary layers (M = 2.8, Re _theta ~ 82,000, and M = 2.5, Re_ theta ~ 25,000, respectively). The physics of supersonic shear flows has recently drawn increasing attention with the renewed interest in flight at super and hypersonic speeds. This work was driven by the belief that the study of organized, Reynolds -stress producing turbulence structures will lead to improved techniques for the modelling and control of high-speed boundary layers. Although flow-visualization is often thought of as a tool for providing qualitative information about complex flow fields, in this thesis an emphasis is placed on deriving quantitative results from image data whenever possible. Three visualization techniques were applied--'selective cut-off' schlieren, droplet seeding, and Rayleigh scattering. Two experiments employed 'selective cut-off' schlieren. In the first, high-speed movies (40,000 fps) were made of strong density gradient fronts leaning downstream at between 30^circ and 60^ circ and travelling at about 0.9U _infty. In the second experiment, the same fronts were detected with hot-wires and imaged in real time, thus allowing the examination of the density gradient fronts and their associated single-point mass -flux signals. Two experiments employed droplet seeding. In both experiments, the boundary layer was seeded by injecting a stream of acetone through a single point in the wall. The acetone is atomized by the high shear at the wall into a 'fog' of tiny (~3.5mu m) droplets. In the first droplet experiment, the fog was illuminated with copper-vapor laser sheets of various orientations. The copper vapor laser pulses 'froze' the fog motion, revealing a variety of organized turbulence structures, some with characteristic downstream inclinations, others with large-scale roll-up on the scale of delta. In the second droplet experiment, high
Onsager and the theory of hydrodynamic turbulence
International Nuclear Information System (INIS)
Eyink, Gregory L.; Sreenivasan, Katepalli R.
2006-12-01
Lars Onsager, a giant of twentieth-century science and the 1968 Nobel Laureate in Chemistry, made deep contributions to several areas of physics and chemistry. Perhaps less well known is his ground-breaking work and lifelong interest in the subject of hydrodynamic turbulence. He wrote two papers on the subject in the 1940s, one of them just a short abstract. Unbeknownst to Onsager, one of his major results was derived a few years earlier by A. N. Kolmogorov, but Onsager's work contains many gems and shows characteristic originality and deep understanding. His only full-length article on the subject in 1949 introduced two novel ideas - negative-temperature equilibria for two-dimensional ideal fluids and an energy-dissipation anomaly for singular Euler solutions - that stimulated much later work. However, a study of Onsager's letters to his peers around that time, as well as his private papers of that period and the early 1970s, shows that he had much more to say about the problem than he published. Remarkably, his private notes of the 1940s contain the essential elements of at least four major results that appeared decades later in the literature: (1) a mean-field Poisson-Boltzmann equation and other thermodynamic relations for point vortices; (2) a relation similar to Kolmogorov's 4/5 law connecting singularities and dissipation; (3) the modern physical picture of spatial intermittency of velocity increments, explaining anomalous scaling of the spectrum; and (4) a spectral turbulence closure quite similar to the modern eddy-damped quasinormal Markovian equations. This paper is a summary of Onsager's published and unpublished contributions to hydrodynamic turbulence and an account of their place in the field as the subject has evolved through the years. A discussion is also given of the historical context of the work, especially of Onsager's interactions with his contemporaries who were acknowledged experts in the subject at the time. Finally, a brief speculation is
Structure functions and intermittency in ionospheric plasma turbulence
Directory of Open Access Journals (Sweden)
L. Dyrud
2008-11-01
Full Text Available Low frequency electrostatic turbulence in the ionospheric E-region is studied by means of numerical and experimental methods. We use the structure functions of the electrostatic potential as a diagnostics of the fluctuations. We demonstrate the inherently intermittent nature of the low level turbulence in the collisional ionospheric plasma by using results for the space-time varying electrostatic potential from two dimensional numerical simulations. An instrumented rocket can not directly detect the one-point potential variation, and most measurements rely on records of potential differences between two probes. With reference to the space observations we demonstrate that the results obtained by potential difference measurements can differ significantly from the one-point results. It was found, in particular, that the intermittency signatures become much weaker, when the proper rocket-probe configuration is implemented. We analyze also signals from an actual ionospheric rocket experiment, and find a reasonably good agreement with the appropriate simulation results, demonstrating again that rocket data, obtained as those analyzed here, are unlikely to give an adequate representation of intermittent features of the low frequency ionospheric plasma turbulence for the given conditions.
Tracking coherent structures in massively-separated and turbulent flows
Rockwood, Matthew; Huang, Yangzi; Green, Melissa
2018-01-01
Coherent vortex structures are tracked in simulations of massively-separated and turbulent flows. Topological Lagrangian saddle points are found using intersections of the positive and negative finite-time Lyapunov exponent ridges, and these points are then followed in order to track individual coherent structure motion both in a complex interacting three-dimensional flow (turbulent channel) and during vortex formation (two-dimensional bluff body shedding). For a simulation of wall-bounded turbulence in a channel flow, tracking Lagrangian saddles shows that the average structure convection speed exhibits a similar trend as a previously published result based on velocity and pressure correlations, giving validity to the method. When this tracking method is applied in a study of a circular cylinder in cross-flow it shows that Lagrangian saddles rapidly accelerate away from the cylinder surface as the vortex sheds. This saddle behavior is compared with the time-resolved static pressure distribution on the circular cylinder, yielding locations on a cylinder surface where common sensors could detect this phenomenon, which is not available from force measurements or vortex circulation calculations. The current method of tracking coherent structures yields insight into the behavior of the coherent structures in both of the diverse flows presented, highlighting the breadth of its potential application.
Catadioptric lenses in Visible Light Communications
Garcia-Marquez, J.; Valencia, J. C.; Perez, H.; Topsu, S.
2015-04-01
Since few years ago, visible light communications (VLC) have experience an accelerated interest from a research point of view. The beginning of this decade has seen many improvements in VLC at an electronic level. High rates of transmission at low bit error ratios (BER) have been reported. A few numbers of start-ups have initiated activities to offer a variety of applications ranging from indoor geo-localization to internet, but in spite of these advancements, some other problems arise. Long-range transmissions mean a high BER which reduce the number of applications. In this sense, new redesigned optical collectors or in some cases, optical reflectors must be considered to ensure a low BER at higher distance transmissions. Here we also expose a preliminary design of a catadioptric and monolithical lens for a LI-FI receiver with two rotationally symmetrical main piecewise surfaces za and zb. These surfaces are represented in a system of cylindrical coordinates with an anterior surface za with a central and refractive sector surrounded by a peripheral reflective sector and a back piecewise surface zb with a central refractive sector and a reflective sector, both characterized as ideal for capturing light within large acceptance angles.
Energy Technology Data Exchange (ETDEWEB)
Wu Hong [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China); Wang Jiao, E-mail: wangjiao@sjp.buaa.edu.cn [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China); Tao Zhi [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China)
2011-12-15
Highlights: Black-Right-Pointing-Pointer A double MRT-LBM is used to study heat transfer in turbulent channel flow. Black-Right-Pointing-Pointer Turbulent Pr is modeled by dynamic subgrid scale model. Black-Right-Pointing-Pointer Temperature gradients are calculated by the non-equilibrium temperature distribution moments. - Abstract: In this paper, a large eddy simulation based on the lattice Boltzmann framework is carried out to simulate the heat transfer in a turbulent channel flow, in which the temperature can be regarded as a passive scalar. A double multiple relaxation time (DMRT) thermal lattice Boltzmann model is employed. While applying DMRT, a multiple relaxation time D3Q19 model is used to simulate the flow field, and a multiple relaxation time D3Q7 model is used to simulate the temperature field. The dynamic subgrid stress model, in which the turbulent eddy viscosity and the turbulent Prandtl number are dynamically computed, is integrated to describe the subgrid effect. Not only the strain rate but also the temperature gradient is calculated locally by the non-equilibrium moments. The Reynolds number based on the shear velocity and channel half height is 180. The molecular Prandtl numbers are set to be 0.025 and 0.71. Statistical quantities, such as the average velocity, average temperature, Reynolds stress, root mean square (RMS) velocity fluctuations, RMS temperature and turbulent heat flux are obtained and compared with the available data. The results demonstrate great reliability of DMRT-LES in studying turbulence.
Hierarchy compensation of non-homogeneous intermittent atmospheric turbulence
Redondo, Jose M.; Mahjoub, Otman B.; Cantalapiedra, Inma R.
2010-05-01
In this work a study both the internal turbulence energy cascade intermittency evaluated from wind speed series in the atmospheric boundary layer, as well as the role of external or forcing intermittency based on the flatness (Vindel et al 2008)is carried out. The degree of intermittency in the stratified ABL flow (Cuxart et al. 2000) can be studied as the deviation, from the linear form, of the absolute scaling exponents of the structure functions as well as generalizing for non-isotropic and non-homogeneous turbulence, even in non-inertial ranges (in the Kolmogorov-Kraichnan sense) where the scaling exponents are not constant. The degree of intermittency, evaluated in the non-local quasi-inertial range, is explained from the variation with scale of the energy transfer as well as the dissipation. The scale to scale transfer and the structure function scaling exponents are calculated and from these the intermittency parametres. The turbulent diffusivity could also be estimated and compared with Richardson's law. Some two point correlations and time lag calculations are used to investigate the time and spatial integral length scales obtained from both Lagrangian and Eulerian correlations and functions, and we compare these results with both theoretical and laboratory data. We develop a theoretical description of how to measure the different levels of intermittency following (Mahjoub et al. 1998, 2000) and the role of locality in higher order exponents of structure function analysis. Vindel J.M., Yague C. and Redondo J.M. (2008) Structure function analysis and intermittency in the ABL. Nonlin. Processes Geophys., 15, 915-929. Cuxart J, Yague C, Morales G, Terradellas E, Orbe J, Calvo J, Fernández A, Soler M R, Infante C, Buenestado P, Espinalt A, Joergensen H E, Rees J M, Vilá J, Redondo J M, Cantalapiedra R and Conangla L (2000): Stable atmospheric boundary-layer experiment in Spain (Sables 98): a report, Boundary-Layer Meteorology 96, 337-370 Mahjoub O
Turbulent equipartitions in two dimensional drift convection
International Nuclear Information System (INIS)
Isichenko, M.B.; Yankov, V.V.
1995-01-01
Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly non-equilibrium systems such as turbulent plasmas. In turbulent systems, energy is no longer a good invariant, but one can utilize the conservation of other quantities, such as adiabatic invariants, frozen-in magnetic flux, entropy, or combination thereof, in order to derive new, turbulent quasi-equilibria. These TEP equilibria assume various forms, but in general they sustain spatially inhomogeneous distributions of the usual thermodynamic quantities such as density or temperature. This mechanism explains the effects of particle and energy pinch in tokamaks. The analysis of the relaxed states caused by turbulent mixing is based on the existence of Lagrangian invariants (quantities constant along fluid-particle or other orbits). A turbulent equipartition corresponds to the spatially uniform distribution of relevant Lagrangian invariants. The existence of such turbulent equilibria is demonstrated in the simple model of two dimensional electrostatically turbulent plasma in an inhomogeneous magnetic field. The turbulence is prescribed, and the turbulent transport is assumed to be much stronger than the classical collisional transport. The simplicity of the model makes it possible to derive the equations describing the relaxation to the TEP state in several limits
Entrainment by turbulent plumes
Parker, David; Burridge, Henry; Partridge, Jamie; Linden, Paul
2017-11-01
Plumes are of relevance to nature and real consequence to industry. While the Morton, Taylor & Turner (1956) plume model is able to estimate the mean physical flux parameters, the process of entrainment is only parametrised in a time-averaged sense and a deeper understanding is key to understanding how they evolve. Various flow configurations, resulting in different entrainment values, are considered; we perform simultaneous PIV and plume-edge detection on saline plumes in water resulting from a point source, a line source and a line source where a vertical wall is placed immediately adjacent. Of particular interest is the effect the large scale eddies, forming at the edge of the plume and engulfing ambient fluid, have on the entrainment process. By using velocity statistics in a coordinate system based on the instantaneous scalar edge of the plume the significance of this large scale engulfment is quantified. It is found that significant mass is transported outside the plumes, in particular in regions where large scale structures are absent creating regions of relatively high-momentum ambient fluid. This suggests that the large scale processes, whereby ambient fluid is engulfed into the plume, contribute significantly to the entrainment.
On the Asymptotic Capacity of Dual-Aperture FSO Systems with a Generalized Pointing Error Model
Al-Quwaiee, Hessa; Yang, Hong-Chuan; Alouini, Mohamed-Slim
2016-01-01
Free-space optical (FSO) communication systems are negatively affected by two physical phenomenon, namely, scintillation due to atmospheric turbulence and pointing errors. To quantify the effect of these two factors on FSO system performance, we
On the asymptotic ergodic capacity of FSO links with generalized pointing error model
Al-Quwaiee, Hessa; Yang, Hong-Chuan; Alouini, Mohamed-Slim
2015-01-01
Free-space optical (FSO) communication systems are negatively affected by two physical phenomenon, namely, scintillation due to atmospheric turbulence and pointing errors. To quantize the effect of these two factors on FSO system performance, we
Cape Point GAW Station Rn-222 detector: factors affecting sensitivity and accuracy
CSIR Research Space (South Africa)
Brunke, EG
2002-05-01
Full Text Available Specific factors of a baseline Rn-222 detector installed at Cape Point, South Africa, were studied with the aim of improving its performance. Direct sunlight caused air turbulence within the instrument, resulting in 13.6% variability...
Relation of astrophysical turbulence and magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Lazarian, A. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706 (United States); Eyink, Gregory L. [Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Vishniac, E. T. [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)
2012-01-15
Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al.[Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.
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
Model for Simulation Atmospheric Turbulence
DEFF Research Database (Denmark)
Lundtang Petersen, Erik
1976-01-01
A method that produces realistic simulations of atmospheric turbulence is developed and analyzed. The procedure makes use of a generalized spectral analysis, often called a proper orthogonal decomposition or the Karhunen-Loève expansion. A set of criteria, emphasizing a realistic appearance...... eigenfunctions and estimates of the distributions of the corresponding expansion coefficients. The simulation method utilizes the eigenfunction expansion procedure to produce preliminary time histories of the three velocity components simultaneously. As a final step, a spectral shaping procedure is then applied....... The method is unique in modeling the three velocity components simultaneously, and it is found that important cross-statistical features are reasonably well-behaved. It is concluded that the model provides a practical, operational simulator of atmospheric turbulence....
Langmuir turbulence in space plasmas
Energy Technology Data Exchange (ETDEWEB)
Goldman, M.V. [Colorado Univ., Boulder, CO (United States); Newman, D.L. [Colorado Univ., Boulder, CO (United States); Wang, J.G. [Colorado Univ., Boulder, CO (United States); Muschietti, L. [California Univ., Berkeley (United States). Space Sciences Lab.
1996-11-01
Recent developments in theoretical and numerical modeling of Langmuir turbulence in space and laboratory plasmas are addressed. Kinetic effects, which have been missing from (fluid) traditional Zakharov equation models are explored using Vlasov code simulations. These studies are motivated by beam-driven Langmuir waves and particle distributions measured in earth`s foreshock region, and by beam-driven Langmuir waves and beams that underlie type III solar radio emission in the solar wind. The nonlinear physical processes studied in these 1-D Vlasov simulations include both wave-wave interactions and acceleration of particles by waves-leading to electron-beam flattening. We study bump-on-tail instabilities as boundary value problems, and determine the interplay in space and time between beam plateau formation, stimulated wave-wave backscatter cascades, and strong turbulence wave-packet collapse. (orig.).
Transition and turbulence (hydrodynamic visualizations)
Werle, Henri
The very extensive Reynolds number domain (10 to the 4th power less than or equal to Re sub L greater than or equal to 10 to the 6th power) of the TH2 water tunnel at Chatillon, allowed for laminar-turbulent transition phenomena to be studied systematically by visualizations and with methods previously developed in the TH1 water tunnel. These tests concern a wide variety of models including, Flate plate type models (smooth or grooved, with curved afterbody or right base), cylindrical pod type models (smooth or grooved, with curved afterbody or plane base), and models of different shapes (recall). The purpose of these tests is to provide a visualization of these transition and turbulence phenomena in order to better understand the phenomena.
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)
John Leask Lumley: Whither Turbulence?
Leibovich, Sidney; Warhaft, Zellman
2018-01-01
John Lumley's contributions to the theory, modeling, and experiments on turbulent flows played a seminal role in the advancement of our understanding of this subject in the second half of the twentieth century. We discuss John's career and his personal style, including his love and deep knowledge of vintage wine and vintage cars. His intellectual contributions range from abstract theory to applied engineering. Here we discuss some of his major advances, focusing on second-order modeling, proper orthogonal decomposition, path-breaking experiments, research on geophysical turbulence, and important contributions to the understanding of drag reduction. John Lumley was also an influential teacher whose books and films have molded generations of students. These and other aspects of his professional career are described.
Statistical theory of plasmas turbulence
International Nuclear Information System (INIS)
Kim, Eun-jin; Anderson, Johan
2009-01-01
We present a statistical theory of intermittency in plasma turbulence based on short-lived coherent structures (instantons). In general, the probability density functions (PDFs) of the flux R are shown to have an exponential scaling P(R) ∝ exp (-cR s ) in the tails. In ion-temperature-gradient turbulence, the exponent takes the value s=3/2 for momentum flux and s=3 for zonal flow formation. The value of s follows from the order of the highest nonlinear interaction term and the moments for which the PDFs are computed. The constant c depends on the spatial profile of the coherent structure and other physical parameters in the model. Our theory provides a powerful mechanism for ubiquitous exponential scalings of PDFs, often observed in various tokamaks. Implications of the results, in particular, on structure formation are further discussed. (author)
Heat flux driven ion turbulence
International Nuclear Information System (INIS)
Garbet, X.
1998-01-01
This work is an analysis of an ion turbulence in a tokamak in the case where the thermal flux is fixed and the temperature profile is allowed to fluctuate. The system exhibits some features of Self-Organized Critical systems. In particular, avalanches are observed. Also the frequency spectrum of the thermal flux exhibits a structure similar to the one of a sand pile automaton, including a 1/f behavior. However, the time average temperature profile is found to be supercritical, i.e. the temperature gradient stays above the critical value. Moreover, the heat diffusivity is lower for a turbulence calculated at fixed flux than a fixed temperature gradient, with the same time average temperature. This behavior is attributed to a stabilizing effect of avalanches. (author)
Multifractal Modeling of Turbulent Mixing
Samiee, Mehdi; Zayernouri, Mohsen; Meerschaert, Mark M.
2017-11-01
Stochastic processes in random media are emerging as interesting tools for modeling anomalous transport phenomena. Applications include intermittent passive scalar transport with background noise in turbulent flows, which are observed in atmospheric boundary layers, turbulent mixing in reactive flows, and long-range dependent flow fields in disordered/fractal environments. In this work, we propose a nonlocal scalar transport equation involving the fractional Laplacian, where the corresponding fractional index is linked to the multifractal structure of the nonlinear passive scalar power spectrum. This work was supported by the AFOSR Young Investigator Program (YIP) award (FA9550-17-1-0150) and partially by MURI/ARO (W911NF-15-1-0562).
Quantitative imaging of turbulent and reacting flows
Energy Technology Data Exchange (ETDEWEB)
Paul, P.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
Quantitative digital imaging, using planar laser light scattering techniques is being developed for the analysis of turbulent and reacting flows. Quantitative image data, implying both a direct relation to flowfield variables as well as sufficient signal and spatial dynamic range, can be readily processed to yield two-dimensional distributions of flowfield scalars and in turn two-dimensional images of gradients and turbulence scales. Much of the development of imaging techniques to date has concentrated on understanding the requisite molecular spectroscopy and collision dynamics to be able to determine how flowfield variable information is encoded into the measured signal. From this standpoint the image is seen as a collection of single point measurements. The present effort aims at realizing necessary improvements in signal and spatial dynamic range, signal-to-noise ratio and spatial resolution in the imaging system as well as developing excitation/detection strategies which provide for a quantitative measure of particular flowfield scalars. The standard camera used for the study is an intensified CCD array operated in a conventional video format. The design of the system was based on detailed modeling of signal and image transfer properties of fast UV imaging lenses, image intensifiers and CCD detector arrays. While this system is suitable for direct scalar imaging, derived quantities (e.g. temperature or velocity images) require an exceptionally wide dynamic range imaging detector. To apply these diagnostics to reacting flows also requires a very fast shuttered camera. The authors have developed and successfully tested a new type of gated low-light level detector. This system relies on fast switching of proximity focused image-diode which is direct fiber-optic coupled to a cooled CCD array. Tests on this new detector show significant improvements in detection limit, dynamic range and spatial resolution as compared to microchannel plate intensified arrays.
Microstructures (clumps) in turbulent plasmas
International Nuclear Information System (INIS)
Balescu, R.; Misguich, J.H.
1977-01-01
A general analysis of binary correlations in a turbulent plasma leads to a functional relation relating correlations to the one-particle distribution function. Such a relation allows to understand the mechanism of generation of the microstructures or clumps introduced by Dupree. The expressions introduced by this author appear as a lowest approximation of the general equation. The features and interpretation of these microstructures are briefly discussed [fr
Geometry Dependence of Stellarator Turbulence
International Nuclear Information System (INIS)
Mynick, H.E.; Xanthopoulos, P.; Boozer, A.H.
2009-01-01
Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes
Shell Models of Superfluid Turbulence
International Nuclear Information System (INIS)
Wacks, Daniel H; Barenghi, Carlo F
2011-01-01
Superfluid helium consists of two inter-penetrating fluids, a viscous normal fluid and an inviscid superfluid, coupled by a mutual friction. We develop a two-fluid shell model to study superfluid turbulence and investigate the energy spectra and the balance of fluxes between the two fluids in a steady state. At sufficiently low temperatures a 'bottle-neck' develops at high wavenumbers suggesting the need for a further dissipative effect, such as the Kelvin wave cascade.
Turbulent diffusion of small particles
International Nuclear Information System (INIS)
Margolin, L.G.
1977-11-01
The diffusion of small, spherical, rigid particles suspended in an incompressible turbulent fluid, but not interacting with each other, was studied. As a stochastic process, the turbulent fluid velocity field is assumed to be homogeneous, isotropic and stationary. Assuming the Stokes regime, a particle of equation of motion is used which includes only the effects of Stokes drag and a virtual mass force and an exact solution is found for the particle velocity correlation function, for all times and initial conditions, in terms of a fluid velocity correlation function measured along the motion of the particle. This shows that for times larger than a certain time scale, the particle velocity correlation becomes stationary. The effect of small shears in the fluid velocity was considered, under the additional restrictions of a certain high frequency regime for the turbulence. The shears convected past the particle much faster than the growth of the boundary layer. New force terms due to the presence of such shears are calculated and incorporated into the equation of motion. A perturbation solution to this equation is constructed, and the resultant particle velocity correlation function and diffusion coefficient are calculated. To lowest order, the particle diffusivity is found to be unaltered by the presence of small mean flow shears. The last model treated is one in which particles traverse a turbulent fluid with a large mean velocity. Among other restrictions, linearized form drag is assumed. The diffusion coefficient for such particles was calculated, and found to be much smaller than the passive scalar diffusion coefficient. This agrees within 5 percent with the experimental results of Snyder and Lumley
Conditional Eddies in Plasma Turbulence
DEFF Research Database (Denmark)
Johnsen, H.; Pécseli, H.L.; Trulsen, J.
1987-01-01
Low‐frequency electrostatic turbulence generated by the ion–ion beam instability was investigated experimentally in a double‐plasma device. Real time signals were recorded and examined by a conditional statistical analysis. Conditionally averaged potential distributions reveal the formation...... and propagation of structures with a relatively long lifetime. Various methods for making a conditional analysis are discussed and compared. The results are discussed with reference to ion phase space vortices and clump formation in collisionless plasmas....
Plankton Dynamics and Mesoscale Turbulence
2010-06-29
transformation of inorganic materials and light into living matter by photosynthesis) is operated mainly by small, unicellular algae that float freely in the...Aquatic ecosystems are characterized by the essential role played by fluid dynamics. The small organisms which compose the plankton are advected by the...surrounding flow and must cope with environmental currents, turbulence, and waves. And those organisms which anchor themselves to the rocks and to the
Information Theory and Plasma Turbulence
International Nuclear Information System (INIS)
Dendy, R. O.
2009-01-01
Information theory, applied directly to measured signals, yields new perspectives on, and quantitative knowledge of, the physics of strongly nonlinear and turbulent phenomena in plasmas. It represents a new and productive element of the topical research programmes that use modern techniques to characterise strongly nonlinear signals from plasmas, and that address global plasma behaviour from a complex systems perspective. We here review some pioneering studies of mutual information in solar wind and magnetospheric plasmas, using techniques tested on standard complex systems.
Visibility of wavelet quantization noise
Watson, A. B.; Yang, G. Y.; Solomon, J. A.; Villasenor, J.
1997-01-01
The discrete wavelet transform (DWT) decomposes an image into bands that vary in spatial frequency and orientation. It is widely used for image compression. Measures of the visibility of DWT quantization errors are required to achieve optimal compression. Uniform quantization of a single band of coefficients results in an artifact that we call DWT uniform quantization noise; it is the sum of a lattice of random amplitude basis functions of the corresponding DWT synthesis filter. We measured visual detection thresholds for samples of DWT uniform quantization noise in Y, Cb, and Cr color channels. The spatial frequency of a wavelet is r 2-lambda, where r is display visual resolution in pixels/degree, and lambda is the wavelet level. Thresholds increase rapidly with wavelet spatial frequency. Thresholds also increase from Y to Cr to Cb, and with orientation from lowpass to horizontal/vertical to diagonal. We construct a mathematical model for DWT noise detection thresholds that is a function of level, orientation, and display visual resolution. This allows calculation of a "perceptually lossless" quantization matrix for which all errors are in theory below the visual threshold. The model may also be used as the basis for adaptive quantization schemes.
Turbulent Liquid Metal Dynamo Experiments
International Nuclear Information System (INIS)
Forest, Cary
2007-01-01
The self-generation of magnetic fields in planets and stars--the dynamo effect--is a long-standing problem of magnetohydrodynamics and plasma physics. Until recently, research on the self-excitation process has been primarily theoretical. In this talk, I will begin with a tutorial on how magnetic fields are generated in planets and stars, describing the 'Standard Model' of self-excitation known as the alpha-omega dynamo. In this model, axisymmetric differential rotation can produce the majority of the magnetic field, but some non-axisymmetric, turbulence driven currents are also necessary. Understanding the conversion of turbulent kinetic energy in the fluid motion into electrical currents and thus magnetic fields, is a major challenge for both experiments and theory at this time. I will then report on recent results from a 1 meter diameter, spherical, liquid sodium dynamo experiment at the University of Wisconsin, in which the first clear evidence for these turbulence driven currents has been observed.
Conformal invariance in hydrodynamic turbulence
International Nuclear Information System (INIS)
Falkovich, Gregory
2007-01-01
This short survey is written by a physicist. It contains neither theorems nor precise definitions. Its main content is a description of the results of numerical solution of the equations of fluid mechanics in the regime of developed turbulence. Due to limitations of computers, the results are not very precise. Despite being neither exact nor rigorous, the findings may nevertheless be of interest for mathematicians. The main result is that the isolines of some scalar fields (vorticity, temperature) in two-dimensional turbulence belong to the class of conformally invariant curves called SLE (Scramm-Loewner evolution) curves. First, this enables one to predict and find a plethora of quantitative relations going far beyond what was known previously about turbulence. Second, it suggests relations between phenomena that seemed unrelated, like the Euler equation and critical percolation. Third, it shows that one is able to get exact analytic results in statistical hydrodynamics. In short, physicists have found something unexpected and hope that mathematicians can help to explain it.
Application of some turbulence models
International Nuclear Information System (INIS)
Ushijima, Sho; Kato, Masanobu; Fujimoto, Ken; Moriya, Shoichi
1985-01-01
In order to predict numerically the thermal stratification and the thermal striping phenomena in pool-type FBRs, it is necessary to simulate adequately various turbulence properties of flows with good turbulence models. This report presents numerical simulations of two dimensional isothermal steady flows in a rectangular plenum using three types of turbulence models. Three models are general k-ε model and two Reynolds stress models. The agreements of these results are examined and the properties of these models are compared. The main results are summarized as follows. (1) Concerning the mean velocity distributions, although a little differences exist, all results of three models agree with experimental values. (2) It can be found that non-isotropy of normal Reynolds stresses (u' 2 , v' 2 ) distributions is qwite well simulated by two Reynolds stress models, but not adequately by k-ε model, shear Reynolds stress (-u', v') distribations of three models have little differences and agree good with experiments. (3) Balances of the various terms of Reynolds stress equations are examined. Comparing the results obtained by analyses and those of previous experiments, both distributions show qualitative agreements. (author)
Turbulence modelling for incompressible flows
International Nuclear Information System (INIS)
Rodi, W.
1985-12-01
EUROMECH colloquium 180 was held at Karlsruhe from 4-6 July, 1984, with the aim of bringing together specialists working in the area of turbulence modelling and of reviewing the state-of-the-art in this field. 44 scientists from 12 countries participated and 28 papers were presented. The meeting started with a review of the performance of two-equation turbulence models employing transport equations for both the velocity and the length scale of turbulence. These models are now generally well established, but it was found that their application to certain flow situations remains problematic. The modelling assumptions involved in Reynolds stress-equation models were reviewed next, and new assumptions were proposed. It was generally agreed that, as computing power increases, these more complex models will become more popular also for practical applications. The increase in computing power also allows more and more to resolve the viscous sublayer with low Reynolds numbers models, and the capabilities and problems of these models were discussed. In this connection, special aspects of boundary layer calculations were also discussed, namely those associated with 3D boundary layers, converging and diverging flow and slightly detached boundary layers. The complex physical phenomena prevalent in situations under the influence of buoyancy and rotation were reviewed, and several papers were presented on models for simulating these effects. (orig./HP) [de
International Nuclear Information System (INIS)
Imaizumi, Ryota; Morikawa, Koichi; Higuchi, Masamori; Saito, Takayuki
2009-01-01
In this study, the interaction between a bubble swarm and homogeneous isotropic turbulence was experimentally investigated. The objective is to clarify the turbulence modulation induced by interaction between the bubble swarm and the homogeneous isotropic turbulence without mean flow. In order to generate simultaneously ideally homogeneous isotropic turbulence and a sufficiently controlled bubble swarm, we employed both oscillating grid and bubble generators equipped with audio speakers. First, the homogeneous isotropic turbulence was formed by operating the oscillating grid cylindrical acrylic pipe (height: 600 mm, inner diameter: 149 mm) filled with ion-exchanged and degassed water. Second, we stopped the oscillating-grid in arbitrary time after the homogeneous isotropic turbulence was achieved. A few moments later, the controlled bubble swarm (number of bubbles: 3, average equivalent diameter of bubble: 3 mm, bubble Reynolds number: 859, Weber number: 3.48) was launched into the decaying turbulence described above, using the bubble generators. The bubble formation, bubble size and bubble-launch timing are controlled arbitrarily and precisely by this device. In this study, we conducted the following experiments: 1) measurement of the motion of bubbles in rest water and oscillating grid turbulence via high-speed visualization, 2) measurement of the liquid phase motion around the bubbles in rest water via PIV system with LIF method, 3) measurement of the liquid phase motion around the bubbles in oscillating-grid turbulence via PIV system with LIF method. In the vitalization of the liquid-phase motion of both experiments, two high speed video cameras were employed in order to simultaneously film large- and small-scale interrogation areas. The liquid-phase ambient turbulence hastened the change of the bubble motion from zigzag mode to spiral mode. The interaction between the bubble swarm and liquid-phase turbulence increased decay-rate of the turbulence. (author)
Numerical and experimental study of two turbulent opposed plane jets
Energy Technology Data Exchange (ETDEWEB)
Besbes, Sonia; Mhiri, Hatem [Laboratoire de Mecanique des Fluides et Thermique, Ecole Nationale d' Ingenieurs de Monastir, Route de Ouardanine, Monastir (Tunisia); Le Palec, Georges; Bournot, Philippe [Institut de Mecanique de Marseille, UNIMECA, Technopole de Chateau-Gombert, 60 rue Joliot-Curie, 13453 Marseille (France)
2003-09-01
The turbulent interaction between two opposed plane jets separated by a distance H is experimentally studied by using a PIV (Particle Image Velocimetry) method and numerically investigated by means of a finite volume code. Two turbulence models have been tested: the standard k-{epsilon} model and a second-order model. The validation of the numerical study was performed by comparing the results with experimental data obtained for the case of two interacting opposed jets at ambient temperature (isothermal case). The effect of the angle of inclination of the jets is studied. Conclusions of the validation are then used to study the interaction between two jets, one being maintained at ambient temperature whereas the other is heated. Results show that the stagnation point moves towards the heated jet. It is shown that the heating induces a stabilizing effect on the flow. (orig.)
Finite-temperature effects in helical quantum turbulence
Clark Di Leoni, Patricio; Mininni, Pablo D.; Brachet, Marc E.
2018-04-01
We perform a study of the evolution of helical quantum turbulence at different temperatures by solving numerically the Gross-Pitaevskii and the stochastic Ginzburg-Landau equations, using up to 40963 grid points with a pseudospectral method. We show that for temperatures close to the critical one, the fluid described by these equations can act as a classical viscous flow, with the decay of the incompressible kinetic energy and the helicity becoming exponential. The transition from this behavior to the one observed at zero temperature is smooth as a function of temperature. Moreover, the presence of strong thermal effects can inhibit the development of a proper turbulent cascade. We provide Ansätze for the effective viscosity and friction as a function of the temperature.
Electrostatic turbulence in the Tokamak TBR-1
International Nuclear Information System (INIS)
Castro, R.M. de.
1991-01-01
Characteristics of turbulence at plasma edge of tokamak TBR - 1 are determined from measurements of potentials and density fluctuations, done with a square array of four single Langmuir probes. Two adjacent probes are used to measure the floating potential of the plasma in either poloidal or toroidal directions, the remaining two probes are used to measure saturation current also in poloidal and toroidal directions. Using multiple shot data from the four probe array the radial fluctuation density (n ∼ ) and floating potential (φ ∼ ) profiles are estimated. Analysing the fluctuations spectra the wavenumber-frequency spectrum S(k,ω) from two points measurements is determined. An extension of the cross-correlation concept to a three points correlations leads to the estimation of the fluctuation induced particle flux, from which the particle diffusion coefficient and the convected heat flux can be estimated. All this measurements were performed with and without a resonant magnetic field to verify the eventual influence of this field on the data already mentioned. It was verified that the particle flux is outward and due to electrostatic fluctuations with frequencies lower than 150 khz. (author)
International Nuclear Information System (INIS)
Mitani, Akira; Tsubota, Makoto
2006-01-01
The energy spectrum of decaying quantum turbulence at T=0 obeys Kolmogorov's law. In addition to this, recent studies revealed that the vortex-length distribution (VLD), meaning the size distribution of the vortices, in decaying Kolmogorov quantum turbulence also obeys a power law. This power-law VLD suggests that the decaying turbulence has scale-free structure in real space. Unfortunately, however, there has been no practical study that answers the following important question: why can quantum turbulence acquire a scale-free VLD? We propose here a model to study the origin of the power law of the VLD from a generic point of view. The nature of quantized vortices allows one to describe the decay of quantum turbulence with a simple model that is similar to the Barabasi-Albert model, which explains the scale-invariance structure of large networks. We show here that such a model can reproduce the power law of the VLD well
Stochastic catastrophe theory and instabilities in plasma turbulence
International Nuclear Information System (INIS)
Rajkovic, Milan; Skoric, Milos
2009-01-01
Full text: A Langevin equation (LE) describing evolution of turbulence amplitude in plasma is analyzed from the aspect of stochastic catastrophe theory (SCT) so that turbulent plasma is considered as a stochastic gradient system. According to SCT the dynamics of the system is completely determined by the stochastic potential function and the maximum likelihood estimates of stable and unstable equilibria are associated with the modes and anti-modes, respectively, of the system's stationary probability density function. First order phase transitions occur at degenerate equilibrium points and the potential function at these points may be represented in a generic way. Since the diffusion function of plasma LE is not constant the probability density function (pdf) is not a reliable estimator of the number of stable states. We show that the generalized pdf represented as the product of the stationary pdf and the diffusion function is a reliable estimator of the stable states and that it can be evaluated from the zero mean crossing analysis of plasma turbulence signal. Stochastic bifurcations, and particularly the sudden (catastrophic) ones, are recognized from the pdf's obtained by the zero crossing analysis and we illustrate the applications of SCT in plasma turbulence on data obtained from the MAST (Mega Ampere Spherical Tokamak) for low (L), high (H) and unstable dithering (L/H) confinement regimes. The relationship of the transformation invariant zero-crossing function and SCT is shown to provide important information about the nature of edge localized modes (ELMs) and L-H transition. Finally we show that ELMs occur as a result of catastrophic (hard) bifurcations ruling out the self-organized criticality scenario for their origin. (author)
Compressibility, turbulence and high speed flow
Gatski, Thomas B
2009-01-01
This book introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. For the computation of turbulent compressible flows, current methods of averaging and filtering are presented so that the reader is exposed to a consistent development of applicable equation sets for both the mean or resolved fields as well as the transport equations for the turbulent stress field. For the measurement of turbulent compressible flows, current techniques ranging from hot-wire anemometry to PIV are evaluated and limitations assessed. Characterizing dynamic features of free shear flows, including jets, mixing layers and wakes, and wall-bounded flows, including shock-turbulence and shock boundary-layer interactions, obtained from computations, experiments and simulations are discussed. Key features: * Describes prediction methodologies in...
Sudden viscous dissipation in compressing plasma turbulence
Davidovits, Seth; Fisch, Nathaniel
2015-11-01
Compression of a turbulent plasma or fluid can cause amplification of the turbulent kinetic energy, if the compression is fast compared to the turnover and viscous dissipation times of the turbulent eddies. The consideration of compressing turbulent flows in inviscid fluids has been motivated by the suggestion that amplification of turbulent kinetic energy occurred on experiments at the Weizmann Institute of Science Z-Pinch. We demonstrate a sudden viscous dissipation mechanism whereby this amplified turbulent kinetic energy is rapidly converted into thermal energy, which further increases the temperature, feeding back to further enhance the dissipation. Application of this mechanism in compression experiments may be advantageous, if the plasma can be kept comparatively cold during much of the compression, reducing radiation and conduction losses, until the plasma suddenly becomes hot. This work was supported by DOE through contract 67350-9960 (Prime # DOE DE-NA0001836) and by the DTRA.
Compressibility, turbulence and high speed flow
Gatski, Thomas B
2013-01-01
Compressibility, Turbulence and High Speed Flow introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range, through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. The book provides the reader with the necessary background and current trends in the theoretical and experimental aspects of compressible turbulent flows and compressible turbulence. Detailed derivations of the pertinent equations describing the motion of such turbulent flows is provided and an extensive discussion of the various approaches used in predicting both free shear and wall bounded flows is presented. Experimental measurement techniques common to the compressible flow regime are introduced with particular emphasis on the unique challenges presented by high speed flows. Both experimental and numerical simulation work is supplied throughout to provide the reader with an overall perspective of current tre...
Current-driven turbulence in plasmas
International Nuclear Information System (INIS)
Kluiver, H. de.
1977-10-01
Research on plasma heating in linear and toroidal systems using current-driven turbulence is reviewed. The motivation for this research is presented. Relations between parameters describing the turbulent plasma state and macroscopic observables are given. Several linear and toroidal devices used in current-driven turbulence studies are described, followed by a discussion of special diagnostic methods used. Experimental results on the measurement of electron and ion heating, anomalous plasma conductivity and associated turbulent fluctuation spectra are reviewed. Theories on current-driven turbulence are discussed and compared with experiments. It is demonstrated from the experimental results that current-driven turbulence occurs not only for extreme values of the electric field but also for an experimentally much more accessible and wide range of parameters. This forms a basis for a discussion on possible future applications in fusion-oriented plasma research
Mathematical and physical theory of turbulence
Cannon, John
2006-01-01
Although the current dynamical system approach offers several important insights into the turbulence problem, issues still remain that present challenges to conventional methodologies and concepts. These challenges call for the advancement and application of new physical concepts, mathematical modeling, and analysis techniques. Bringing together experts from physics, applied mathematics, and engineering, Mathematical and Physical Theory of Turbulence discusses recent progress and some of the major unresolved issues in two- and three-dimensional turbulence as well as scalar compressible turbulence. Containing introductory overviews as well as more specialized sections, this book examines a variety of turbulence-related topics. The authors concentrate on theory, experiments, computational, and mathematical aspects of Navier-Stokes turbulence; geophysical flows; modeling; laboratory experiments; and compressible/magnetohydrodynamic effects. The topics discussed in these areas include finite-time singularities a...
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.
National Research Council Canada - National Science Library
Lowe, Kevin T; Simpson, Roger L
2006-01-01
An advanced laser-Doppler velocimeter (LDV), deemed the 'comprehensive LDV', is designed to acquire fully-resolved turbulence structural measurements in high Reynolds number two- and three-dimensional turbulent boundary layers...
Rechargeable solid state neutron detector and visible radiation indicator
Stowe, Ashley C.; Wiggins, Brenden; Burger, Arnold
2017-05-23
A radiation detection device, including: a support structure; and a chalcopyrite crystal coupled to the support structure; wherein, when the chalcopyrite crystal is exposed to radiation, a visible spectrum of the chalcopyrite crystal changes from an initial color to a modified color. The visible spectrum of the chalcopyrite crystal is changed back from the modified color to the initial color by annealing the chalcopyrite crystal at an elevated temperature below a melting point of the chalcopyrite crystal over time. The chalcopyrite crystal is optionally a .sup.6LiInSe.sub.2 crystal. The radiation is comprised of neutrons that decrease the .sup.6Li concentration of the chalcopyrite crystal via a .sup.6Li(n,.alpha.) reaction. The initial color is yellow and the modified color is one of orange and red. The annealing temperature is between about 450 degrees C. and about 650 degrees C. and the annealing time is between about 12 hrs and about 36 hrs.
Rendering Visible: Painting and Sexuate Subjectivity
Daley, Linda
2015-01-01
In this essay, I examine Luce Irigaray's aesthetic of sexual difference, which she develops by extrapolating from Paul Klee's idea that the role of painting is to render the non-visible rather than represent the visible. This idea is the premise of her analyses of phenomenology and psychoanalysis and their respective contributions to understanding…
40 CFR 52.2179 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.2179 Section 52.2179 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) South Dakota § 52.2179 Visibility protection...
40 CFR 52.1606 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1606 Section 52.1606 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) New Jersey § 52.1606 Visibility protection...
40 CFR 52.1236 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1236 Section 52.1236 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Minnesota § 52.1236 Visibility protection. (a...
40 CFR 52.1488 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1488 Section 52.1488 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Nevada § 52.1488 Visibility protection. (a...
40 CFR 52.2383 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.2383 Section 52.2383 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Vermont § 52.2383 Visibility protection. (a...
40 CFR 52.2498 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.2498 Section 52.2498 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Washington § 52.2498 Visibility protection...
40 CFR 52.2304 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.2304 Section 52.2304 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Texas § 52.2304 Visibility protection. (a...
40 CFR 52.1387 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1387 Section 52.1387 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Montana § 52.1387 Visibility protection. (a...
40 CFR 52.1831 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1831 Section 52.1831 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) North Dakota § 52.1831 Visibility protection...
40 CFR 52.2533 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.2533 Section 52.2533 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) West Virginia § 52.2533 Visibility protection...
40 CFR 52.1183 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1183 Section 52.1183 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Michigan § 52.1183 Visibility protection. (a...
40 CFR 52.1531 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1531 Section 52.1531 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) New Hampshire § 52.1531 Visibility protection...
40 CFR 52.2452 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.2452 Section 52.2452 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Virginia § 52.2452 Visibility protection. (a...
40 CFR 52.1033 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1033 Section 52.1033 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Maine § 52.1033 Visibility protection. (a...
40 CFR 52.1339 - Visibility protection.
2010-07-01
... 40 Protection of Environment 4 2010-07-01 2010-07-01 false Visibility protection. 52.1339 Section 52.1339 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS (CONTINUED) Missouri § 52.1339 Visibility protection. (a...
On the theory of turbulent flame velocity
Bychkov, Vitaly; Akkerman, Vyacheslav; Petchenko, Arkady
2012-01-01
The renormalization ideas of self-similar dynamics of a strongly turbulent flame front are applied to the case of a flame with realistically large thermal expansion of the burning matter. In that case a flame front is corrugated both by external turbulence and the intrinsic flame instability. The analytical formulas for the velocity of flame propagation are obtained. It is demonstrated that the flame instability is of principal importance when the integral turbulent length scale is much large...
Visibility, Power and Citizen Intervention: The Five Eyes and New Zealand’s Southern Cross Cable
DEFF Research Database (Denmark)
McCrow-Young, Ally
2017-01-01
government, as part of the Five Eyes intelligence community, had been collecting data on the population by tapping the Southern Cross Cable. ‘If you live in New Zealand,’ Snowden wrote, ‘you are being watched.’ This article examines the relationship between power and visibility; specifically how creative...... citizen engagement can serve to reveal structures of power surrounding global politics and surveillance. Visibility is a central concept, extending beyond issues of local visibility at the micro level, into the networked, global environment through online media. The significance of the cable landing point...
International Nuclear Information System (INIS)
Birkenmeier, Gregor
2012-01-01
For more than 60 years, fusion scientists try to confine a plasma by means of external magnetic fields in order to achieve appropriately high densities and temperatures for the ignition of nuclear fusion. Despite of great progress in the design of confinement concepts, which are considered for the confinement of burning plasmas in the near future, theoretical plasma physics promises further confinement improvements using novel magnetic field geometries. Therefor, the key is the minimization of turbulent transport by choosing appropiate magnetic field geometries, which necessitates a fundamental understanding of the influence of magnetic field geometry on plasma turbulence. There are several theoretical works on turbulent plasma dynamics in three-dimensional geometries, but only a few experimental studies for validation of the theoretical results exist. Hence, the present work aims at providing experimental data for comparison with theory and to gain insights into the interplay between drift-wave turbulence and magnetic field geometry. By means of two multi-probe arrays, local density and potential fluctuations are measured in low-temperature plasmas at 128 positions on a single flux surface of the stellarator TJ-K with high temporal resolution. Using methods of statistical timeseries analysis structure sizes and dynamic properties of the drift-wave turbulence in TJ-K are determined. Thereby, it is shown that the size of turbulent structures perpendicular to the magnetic field is reduced in regions of high absolute local magnetic shear. In addition, a poloidal displacement with respect to the magnetic field lines and a complex propagation pattern of parallelly extended turbulent structures is found. Also, poloidal profiles of turbulent transport are calculated from the probe data. The maximum transport is found to be poloidally localized in a region of negative normal curvature (unfavourable curvature). In addition, the results point to an influence of geodesic
Development of remote vibration measurement technique through turbulent media
Energy Technology Data Exchange (ETDEWEB)
Baik, Sung Hoon; Chung, Chin Man; Kim, Min Suk; Park, Seung Kyu; Chung, Heung Jone
2002-12-01
The effect of wavefront distortion of laser beam of a LDV(Laser Doppler Vibrometer) in the turbulence media was investigated for application of adaptive optics to LDV. The high-speed tip/tilt adaptive optics system and closed-loop steering algorithm were developed for real-time correction of the direction fluctuation of the laser beam of LDV. The measuring performance of the LDV was improved when the steering system was applied to LDV at the vibration frequency range of 10 Hz - 30 Hz. The high-speed Shack-Hartmann wavefront sensor(400 Hz) was developed to measure the performance of the LDV due to wavefront distortion. The wavefront distortion due to the turbulence media induced low visibility and degraded the performance of the vibrometer. From the experiments, when the wavefront distortion is above 2 wavelengths in the cross section of the laser beam(dia. 20 mm), the vibration signal from laser vibrometer was severely degraded. When the wavefront distortion is smaller than one wave, the vibration signal was good. From the this research, high-speed closed-loop tip/tilt control technique of the laser beam was developed and applied to the laser metrology area. In the future, the adaptive optics system for wavefront correction will be applied to other research area.
Maqui, Agustin Francisco
Turbulence in high-speed flows is an important problem in aerospace applications, yet extremely difficult from a theoretical, computational and experimental perspective. A main reason for the lack of complete understanding is the difficulty of generating turbulence in the lab at a range of speeds which can also include hypersonic effects such as thermal non-equilibrium. This work studies the feasibility of a new approach to generate turbulence based on laser-induced photo-excitation/dissociation of seeded molecules. A large database of incompressible and compressible direct numerical simulations (DNS) has been generated to systematically study the development and evolution of the flow towards realistic turbulence. Governing parameters and the conditions necessary for the establishment of turbulence, as well as the length and time scales associated with such process, are identified. For both the compressible and incompressible experiments a minimum Reynolds number is found to be needed for the flow to evolve towards fully developed turbulence. Additionally, for incompressible cases a minimum time scale is required, while for compressible cases a minimum distance from the grid and limit on the maximum temperature introduced are required. Through an extensive analysis of single and two point statistics, as well as spectral dynamics, the primary mechanisms leading to turbulence are shown. As commonly done in compressible turbulence, dilatational and solenoidal components are separated to understand the effect of acoustics on the development of turbulence. Finally, a large database of forced isotropic turbulence has been generated to study the effect of internal degrees of freedom on the evolution of turbulence.
Evaluation of Driver Visibility from Mobile LIDAR Data and Weather Conditions
González-Jorge, H.; Díaz-Vilariño, L.; Lorenzo, H.; Arias, P.
2016-06-01
Visibility of drivers is crucial to ensure road safety. Visibility is influenced by two main factors, the geometry of the road and the weather present therein. The present work depicts an approach for automatic visibility evaluation using mobile LiDAR data and climate information provided from weather stations located in the neighbourhood of the road. The methodology is based on a ray-tracing algorithm to detect occlusions from point clouds with the purpose of identifying the visibility area from each driver position. The resulting data are normalized with the climate information to provide a polyline with an accurate area of visibility. Visibility ranges from 25 m (heavy fog) to more than 10,000 m (clean atmosphere). Values over 250 m are not taken into account for road safety purposes, since this value corresponds to the maximum braking distance of a vehicle. Two case studies are evaluated an urban road in the city of Vigo (Spain) and an inter-urban road between the city of Ourense and the village of Castro Caldelas (Spain). In both cases, data from the Galician Weather Agency (Meteogalicia) are used. The algorithm shows promising results allowing the detection of particularly dangerous areas from the viewpoint of driver visibility. The mountain road between Ourense and Castro Caldelas, with great presence of slopes and sharp curves, shows special interest for this type of application. In this case, poor visibility can especially contribute to the run over of pedestrians or cyclists traveling on the road shoulders.
EVALUATION OF DRIVER VISIBILITY FROM MOBILE LIDAR DATA AND WEATHER CONDITIONS
Directory of Open Access Journals (Sweden)
H. González-Jorge
2016-06-01
Full Text Available Visibility of drivers is crucial to ensure road safety. Visibility is influenced by two main factors, the geometry of the road and the weather present therein. The present work depicts an approach for automatic visibility evaluation using mobile LiDAR data and climate information provided from weather stations located in the neighbourhood of the road. The methodology is based on a ray-tracing algorithm to detect occlusions from point clouds with the purpose of identifying the visibility area from each driver position. The resulting data are normalized with the climate information to provide a polyline with an accurate area of visibility. Visibility ranges from 25 m (heavy fog to more than 10,000 m (clean atmosphere. Values over 250 m are not taken into account for road safety purposes, since this value corresponds to the maximum braking distance of a vehicle. Two case studies are evaluated an urban road in the city of Vigo (Spain and an inter-urban road between the city of Ourense and the village of Castro Caldelas (Spain. In both cases, data from the Galician Weather Agency (Meteogalicia are used. The algorithm shows promising results allowing the detection of particularly dangerous areas from the viewpoint of driver visibility. The mountain road between Ourense and Castro Caldelas, with great presence of slopes and sharp curves, shows special interest for this type of application. In this case, poor visibility can especially contribute to the run over of pedestrians or cyclists traveling on the road shoulders.
The visibility of mandibular canal on orthoradial and oblique CBCT slices at molar implant sites
International Nuclear Information System (INIS)
Alkhader, Mustafa; Jarab, Fadi; Shaweesh, Ashraf; Hudieb, Malik
2016-01-01
The aim of the present study was to compare visibility of the mandibular canal on cone beam computed tomography (CBCT)-based orthoradial and oblique slices at molar implant sites. CBCT images for 132 mandibular molar implant sites were selected for the study. After generating orthoradial and oblique slices, two observers evaluated the visibility of the mandibular canal using three-point scoring scale (1-3, good to excellent). Wilcoxon signed-rank test compared the visibility scores of the two slices. Both orthoradial and oblique slices obtained from CBCT had only very good to excellent mandibular canal visibility scores. At 114 mandibular molar implant sites, the visibility score was equal on both orthoradial and oblique slices. Although the visibility score was higher on orthoradial slices for 12 implant sites, the visibility score was higher for six implant sites on oblique slices and the difference was not significant. Therefore, the visibility of the mandibular canal was excellent and comparable on most of orthoradial and oblique slices obtained from CBCT images
Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows
Energy Technology Data Exchange (ETDEWEB)
Magnussen, B F [The Norwegian Univ. of Science and Technology, Trondheim (Norway)
1998-12-31
The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.
Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows
Energy Technology Data Exchange (ETDEWEB)
Magnussen, B.F. [The Norwegian Univ. of Science and Technology, Trondheim (Norway)
1997-12-31
The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.
Measurement of beam driven hydrodynamic turbulence
International Nuclear Information System (INIS)
Norem, J.; Black, E.; Bandura, L.; Errede, D.; Cummings, M. A. C.
2003-01-01
Cooling intense muon beams in liquid hydrogen absorbers introduces kW of heating to the cold fluid, which will drive turbulent flow. The amount of turbulence may be sufficient to help cool the liquid, but calculations are difficult. We have used a 20 MeV electron beam in a water tank to look at the scale of the beam driven convection and turbulence. The density and flow measurements are made with schlieren and Ronchi systems. We describe the optical systems and the turbulence measured. These data are being used to calibrate hydrodynamic calculations of convection driven and forced flow cooling in muon cooling absorbers
Predator-prey encounters in turbulent waters
DEFF Research Database (Denmark)
Mann, J.; Ott, Søren; Pécseli, H.L.
2002-01-01
With reference to studies of predator-prey encounters in turbulent waters, we demonstrate the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows. A laboratory experiment is carried out, where an approximately homogeneous and isot......With reference to studies of predator-prey encounters in turbulent waters, we demonstrate the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows. A laboratory experiment is carried out, where an approximately homogeneous...
De-trending of turbulence measurements
DEFF Research Database (Denmark)
Hansen, Kurt Schaldemose; Larsen, Gunner Chr.
2006-01-01
contribution to the wind speed turbulence intensity for a number of representative locations. A linear de-trending process has been implemented during indexing of the time-series. The observed de-trended turbulence intensities are reduced 3 – 15 % compared to the raw turbulence intensity. This reduction...... depends primarily on site characteristics and local mean wind speed variations. Reduced turbulence intensity will result in lower design fatigue loads. This aspect of de-trending is discussed by use of a simple heuristic load model. Finally an empirical model for de-trending wind resource data...
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.
Anisotropy of turbulence in wind turbine wakes
Energy Technology Data Exchange (ETDEWEB)
Gomez-Elvira, Rafael [Comision Nacional de Energia (Spain); Crespo, Antonio; Migoya, Emilio; Manuel, Fernando [Departamento de Ingenieria Energetica y Fluidomecanica, Escuela Tecnica Superior de Ingenieros Industriales, Universidad Politecnica de Madrid, Jose Gutierrez Abascal, 2. 28006 Madrid (Spain); Hernandez, Julio [Departamento de Mecanica, ETSII, Universidad Nacional de Educacion a Distancia, Ciudad Universitaria, 28040 Madrid (Spain)
2005-10-01
This work is mainly dedicated to the study of non-isotropic characteristics of turbulence in wind turbine wakes, specifically the shear layer of the near wake. A calculation method based on an explicit algebraic model for the components of the turbulent stress tensor is proposed, and the results are found to be in acceptable agreement with experimental results. Analytical expressions for the estimation of an upper limit of the global turbulence kinetic energy, k, and the individual contributions of each diagonal term in the turbulent stress tensor are proposed. Their predictions are compared with experimental results.
DNS of turbulent channel flow with conjugate heat transfer at Prandtl number 0.01
Energy Technology Data Exchange (ETDEWEB)
Tiselj, Iztok, E-mail: iztok.tiselj@ijs.si [' Jozef Stefan' Institute, Jamova 39, SI-1000 Ljubljana (Slovenia); Cizelj, Leon, E-mail: leon.cizelj@ijs.si [' Jozef Stefan' Institute, Jamova 39, SI-1000 Ljubljana (Slovenia)
2012-12-15
Highlights: Black-Right-Pointing-Pointer DNS database for turbulent channel flow at Prandtl number 0.01 and various Re{sub {tau}}. Black-Right-Pointing-Pointer Two ideal boundary condition analyzed: non-fluctuating and fluctuating temperature. Black-Right-Pointing-Pointer DNS database with conjugate heat transfer for liquid sodium-steel contact. Black-Right-Pointing-Pointer Penetration of the turbulent temperature fluctuations into the solid wall analyzed. - Abstract: Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in a turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed with passive scalar approximation at Prandtl number 0.01, which roughly corresponds to the Prandtl number of liquid sodium. DNSs were performed at friction Reynolds numbers 180, 395 and 590. The obtained statistical quantities like mean temperatures, profiles of the root-mean-square (RMS) temperature fluctuations for various thermal properties of wall and fluid, and various wall thicknesses were obtained from a pseudo-spectral channel-flow code. Even for the highest implemented Reynolds number the temperature profile in the fluid does not exhibit log-law region and the near-wall RMS temperature fluctuations show Reynolds number dependence. Conjugate heat transfer simulations of liquid sodium-steel system point to a relatively intensive penetration of turbulent temperature fluctuations into the heated wall. Database containing the results is available in a digital form.
Network coding multiuser scheme for indoor visible light communications
Zhang, Jiankun; Dang, Anhong
2017-12-01
Visible light communication (VLC) is a unique alternative for indoor data transfer and developing beyond point-to-point. However, for realizing high-capacity networks, VLC is facing challenges including the constrained bandwidth of the optical access point and random occlusion. A network coding scheme for VLC (NC-VLC) is proposed, with increased throughput and system robustness. Based on the Lambertian illumination model, theoretical decoding failure probability of the multiuser NC-VLC system is derived, and the impact of the system parameters on the performance is analyzed. Experiments demonstrate the proposed scheme successfully in the indoor multiuser scenario. These results indicate that the NC-VLC system shows a good performance under the link loss and random occlusion.
Turbulent Statistics From Time-Resolved PIV Measurements of a Jet Using Empirical Mode Decomposition
Dahl, Milo D.
2013-01-01
Empirical mode decomposition is an adaptive signal processing method that when applied to a broadband signal, such as that generated by turbulence, acts as a set of band-pass filters. This process was applied to data from time-resolved, particle image velocimetry measurements of subsonic jets prior to computing the second-order, two-point, space-time correlations from which turbulent phase velocities and length and time scales could be determined. The application of this method to large sets of simultaneous time histories is new. In this initial study, the results are relevant to acoustic analogy source models for jet noise prediction. The high frequency portion of the results could provide the turbulent values for subgrid scale models for noise that is missed in large-eddy simulations. The results are also used to infer that the cross-correlations between different components of the decomposed signals at two points in space, neglected in this initial study, are important.
Gyrokinetic simulation of microtearing turbulence
International Nuclear Information System (INIS)
Doerk, Hauke
2013-01-01
In modern fusion experiments, plasma turbulence is responsible for the radial heat transport and thus determines the plasma confinement within the magnetic field of tokamak devices. Deeper theoretical understanding is needed to explain today's and future fusion experiments. The goal of fusion research is to establish nuclear fusion as a safe and sustainable energy source. In future fusion power plants, and also in large fusion experiments like the presently constructed ITER, plasma heating predominantly affects the electron species. The reason is of fundamental nature: the collisional cross section of fast ions that are produced by the heating systems is larger for thermal electrons than for thermal ions. It is thus essential to correctly predict electron thermal transport, but the overall picture still continues to evolve. Besides microinstabilities on the electron gyroradius scales, also a stochastized magnetic field can contribute to enhanced electron transport. Already since the 1970's, the so-called microtearing instability is discussed as a source of stochastic fields. This microinstability deserves its name for breaking up the magnetic field structure by forming small-scale magnetic islands. The linear microtearing instability and its nonlinear, turbulent behavior is investigated in this thesis by means of numerical simulations with the gyrokinetic turbulence code Gene. The underlying gyrokinetic equations are not only appropriate to predict turbulent transport, but also describe neoclassical transport that is drift-kinetic in nature. Besides revealing interesting physics on long time scales, solving the neoclassical equation serves as an excellent test for the numerical implementation of the collision operator in Gene. Focusing on the local limit, it is found that a modification of this implementation that considers certain symmetries is necessary to obtain a satisfactory agreement with the well-established drift-kinetic neoclassical code Neo. Also the
Laser pointing in the vicinity of jet engine plumes
Schleijpen, H.M.A.
2010-01-01
Target tracking and laser-based pointing from airborne platforms can be degraded significantly by the propagation environment around an airborne platform including zones of severe turbulence generated by rotor downwash and engine exhausts. This is the topic of the EDA study group ERG 108.019 on