Aspects of atmospheric turbulence related to scintillometry
Braam, M.
2014-01-01
Aspects of atmospheric turbulence related to scintillometry Atmospheric turbulence is the main vertical transport mechanism in the atmospheric boundary layer. The surface fluxes related to this turbulent transport are the sensible (
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......, a correct spectral shape, and non-Gaussian statistics, is selected in order to evaluate the model turbulence. An actual turbulence record is analyzed in detail providing both a standard for comparison and input statistics for the generalized spectral analysis, which in turn produces a set of orthonormal....... 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....
Line Transport in Turbulent Atmospheres
Nikoghossian, A. G.
2017-07-01
The spectral line transfer in turbulent atmospheres with a spatially correlated velocity field is examined. Both the finite and semi-infinite media are treated. In finding the observed intensities we first deal with the problem for determining the mean intensity of radiation emerging from the medium for a fixed value of turbulent velocity at its boundary. A new approach proposed for solving this problem is based on the invariant imbedding technique which yields the solution of the proper problems for a family of media of different optical thicknesses and allows tackling different kinds of inhomogeneous problems. The dependence of the line profile, integral intensity, and the line width on the mean correlation length and the average value of the hydrodynamic velocity is studied. It is shown that the transition from a micro-turbulent regime to a macro-turbulence occurs within a comparatively narrow range of variation in the correlation length . Ambartsumian's principle of invariance is used to solve the problem of diffuse reflection of the line radiation from a one-dimensional semi-infinite turbulent atmosphere. In addition to the observed spectral line profile, statistical averages describing the diffusion process in the atmosphere (mean number of scattering events, average time spent by a diffusing photon in the medium) are determined. The dependence of these quantities on the average hydrodynamic velocity and correlation coefficient is studied.
Simulation of atmospheric turbulence measurements : Fractal turbulence (poster)
Oude Nijhuis, A.C.P.; Krasnov, O.A.; Unal, C.M.H.; Russchenberg, H.W.J.; Yarovoy, A.
2014-01-01
A new trend is to observe atmospheric turbulence fields by using scanning Doppler radars and/or lidars. See e.g. Chan (2011) for the retrieval of eddy dissipation rate (EDR) maps at the Hongkong International Airport.
Sonic boom propagation through atmospheric turbulence
Yamashita, Hiroshi; Obayashi, Shigeru; 山下, 博; 大林, 茂
2009-01-01
The effect of the homogeneous atmospheric turbulence on the sonic boom propagation has been investigated. The turbulence field is represented by a finite sum of discrete Fourier modes based on the von Karman and Pao energy spectrum. The sonic boom signature is calculated by the modified Waveform Parameter Method, considering the turbulent velocities. The results show that in 59 % of the cases, the intensity of the sonic boom had decreased, and in other 41 % of the cases had increased the soni...
Robust entangled qutrit states in atmospheric turbulence
CSIR Research Space (South Africa)
Brunner, T
2013-06-01
Full Text Available The entangled quantum state of a photon pair propagating through atmospheric turbulence suffers decay of entanglement due to the scintillation it experiences. Here we investigate the robustness against this decay for different qutrit states. We use...
Laser beam propagation in atmospheric turbulence
Murty, S. S. R.
1979-01-01
The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.
Analyses of Aircraft Responses to Atmospheric Turbulence
Van Staveren, W.H.J.J.
2003-01-01
The response of aircraft to stochastic atmospheric turbulence plays an important role in aircraft-design (load calculations), Flight Control System (FCS) design and flight-simulation (handling qualities research and pilot training). In order to simulate these aircraft responses, an accurate
Turbulent transport in the atmospheric surface layer
Energy Technology Data Exchange (ETDEWEB)
Tagesson, Torbern [Dept. of Physical Geography and Ecosystem Science, Lund Univ., Lund (Sweden)
2012-04-15
In the modelling of transport and accumulation of the radioactive isotope carbon-14 (C-14) in the case of a potential release from a future repository of radioactive waste, it is important to describe the transport of the isotope in the atmosphere. This report aims to describe the turbulent transport within the lower part of the atmosphere; the inertial surface layer and the roughness sublayer. Transport in the inertial surface layer is dependent on several factors, whereof some can be neglected under certain circumstances. Under steady state conditions, fully developed turbulent conditions, in flat and horizontal homogeneous areas, it is possible to apply an eddy diffusivity approach for estimating vertical transport of C. The eddy diffusivity model assumes that there is proportionality between the vertical gradient and the transport of C. The eddy diffusivity is depending on the atmospheric turbulence, which is affected by the interaction between mean wind and friction of the ground surface and of the sensible heat flux in the atmosphere. In this report, it is described how eddy diffusivity of the inertial surface layer can be estimated from 3-d wind measurements and measurements of sensible heat fluxes. It is also described how to estimate the eddy diffusivity in the inertial surface layer from profile measurements of temperature and wind speed. Close to the canopy, wind and C profiles are influenced by effects of the surface roughness; this section of the atmosphere is called the roughness sublayer. Its height is up to {approx}3 times the height of the plant canopy. When the mean wind interacts with the canopy, turbulence is not only produced by shear stress and buoyancy, it is additionally created by wakes, which are formed behind the plants. Turbulence is higher than it would be over a flat surface, and the turbulent transport is hereby more efficient. Above the plant canopy, but still within the roughness sublayer, a function that compensates for the effect
Aircraft Wake Vortex Deformation in Turbulent Atmosphere
Hennemann, Ingo; Holzaepfel, Frank
2007-01-01
Large-scale distortion of aircraft wake vortices appears to play a crucial role for aircraft safety during approach and landing. Vortex distortion is investigated based on large eddy simulations of wake vortex evolution in a turbulent atmosphere. A vortex identification method is developed that can be adapted to the vortex scales of interest. Based on the identified vortex center tracks, a statistics of vortex curvature radii is established. This statistics constitutes the basis for understan...
Turbulence closure model "constants" and the problems of "inactive" atmospheric turbulence
Bottema, M
1997-01-01
Inactive turbulence is associated with waves and large eddies that are relatively ineffective in mixing. Many numerical models evaluate turbulent mixing using turbulent kinetic energy k, which may contain significant amounts of inactive turbulence (e.g., in real or simulated atmospheric boundary
Wind turbine wake in atmospheric turbulence
Energy Technology Data Exchange (ETDEWEB)
Rethore, P.-E.
2009-10-15
This thesis describes the different steps needed to design a steady-state computational fluid dynamics (CFD) wind farm wake model. The ultimate goal of the project was to design a tool that could analyze and extrapolate systematically wind farm measurements to generate wind maps in order to calibrate faster and simpler engineering wind farm wake models. The most attractive solution was the actuator disc method with the steady state k-epsilon turbulence model. The first step to design such a tool is the treatment of the forces. This thesis presents a computationally inexpensive method to apply discrete body forces into the finite-volume flow solver with collocated variable treatment (EllipSys), which avoids the pressure-velocity decoupling issue. The second step is to distribute the body forces in the computational domain accordingly to rotor loading. This thesis presents a generic flexible method that associates any kind of shapes with the computational domain discretization. The special case of the actuator disc performs remarkably well in comparison with Conway's heavily loaded actuator disc analytical solution and a CFD full rotor computation, even with a coarse discretization. The third step is to model the atmospheric turbulence. The standard k-epsilon model is found to be unable to model at the same time the atmospheric turbulence and the actuator disc wake and performs badly in comparison with single wind turbine wake measurements. A comparison with a Large Eddy Simulation (LES) shows that the problem mainly comes from the assumptions of the eddy-viscosity concept, which are deeply invalidated in the wind turbine wake region. Different models that intent to correct the k-epsilon model's issues are investigated, of which none of them is found to be adequate. The mixing of the wake in the atmosphere is a deeply non-local phenomenon that is not handled correctly by an eddy-viscosity model such as k-epsilon. (author)
The determination of turbulent structures in the atmospheric surface layer
Schols, J.L.J.
1984-01-01
The turbulent flow in the atmospheric surface layer (ASL) contains turbulent structures, which are defined as spatially coherent, organized flow motions. 'Organized' means that characteristic patterns, observed at a point in space, occur almost simultaneously in more than one turbulence signal and
A coherent line source in a turbulent atmosphere
Salomons, E.M.
1999-01-01
The sound field of a coherent line source in a nonrefracting, turbulent atmosphere is studied. An expression for the sound pressure level in the frequency domain is developed, based on a discretization of the line source into a set of point sources. Atmospheric turbulence is taken into account by
Dynamic simulation for distortion image with turbulence atmospheric transmission effects
Du, Huijie; Fei, Jindong; Qing, Duzheng; Zhao, Hongming; Yu, Hong; Cheng, Chen
2013-09-01
The imaging through atmospheric turbulence is an inevitable problem encountered by infrared imaging sensors working in the turbulence atmospheric environment. Before light-rays enter the window of the imaging sensors, the atmospheric turbulence will randomly interfere with the transmission of the light waves came from the objects, causing the distribution of image intensity values on the focal plane to diffuse, the peak value to decrease, the image to get blurred, and the pixels to deviate, and making image identification very difficult. Owing to the fact of the long processing time and that the atmospheric turbulent flow field is unknown and hard to be described by mathematical models, dynamic simulation for distortion Image with turbulence atmospheric transmission effects is much more difficult and challenging in the world. This paper discusses the dynamic simulation for distortion Image of turbulence atmospheric transmission effect. First of all, with the data and the optical transmission model of the turbulence atmospheric, the ray-tracing method is applied to obtain the propagation path of optical ray which propagates through the high-speed turbulent flow field, and then to calculate the OPD from the reference wave to the reconverted wave front and obtain the point spread function (PSF). Secondly, infrared characteristics models of typical scene were established according to the theory of infrared physics and heat conduction, and then the dynamic infrared image was generated by OpenGL. The last step is to obtain the distortion Image with turbulence atmospheric transmission effects .With the data of atmospheric transmission computation, infrared simulation image of every frame was processed according to the theory of image processing and the real-time image simulation, and then the dynamic distortion simulation images with effects of blurring, jitter and shifting were obtained. Above-mentioned simulation method can provide the theoretical bases for recovering
Scattering of sonic booms by anisotropic turbulence in the atmosphere
Kelly; Raspet; Bass
2000-06-01
An earlier paper [J. Acoust. Soc. Am. 98, 3412-3417 (1995)] reported on the comparison of rise times and overpressures of sonic booms calculated with a scattering center model of turbulence to measurements of sonic boom propagation through a well-characterized turbulent layer under moderately turbulent conditions. This detailed simulation used spherically symmetric scatterers to calculate the percentage of occurrence histograms of received overpressures and rise times. In this paper the calculation is extended to include distorted ellipsoidal turbules as scatterers and more accurately incorporates the meteorological data into a determination of the number of scatterers per unit volume. The scattering center calculation overpredicts the shifts in rise times for weak turbulence, and still underpredicts the shift under more turbulent conditions. This indicates that a single-scatter center-based model cannot completely describe sonic boom propagation through atmospheric turbulence.
The decay of orbital angular momentum entanglement in atmospheric turbulence
CSIR Research Space (South Africa)
Roux, FS
2013-07-01
Full Text Available Salam International Centre for Theoretical Physics, Trieste, Italy, 8-12 July 2013 The decay of orbital angular momentum entanglement in atmospheric turbulence Roux FS CSIR, National Laser Centre, Pretoria, 0001 Corresponding email: FSroux...
A radiosonde thermal sensor technique for measurement of atmospheric turbulence
Bufton, J. L.
1975-01-01
A new system was developed to measure vertical profiles of microthermal turbulence in the free atmosphere. It combines thermal sensor technology with radiosonde balloon systems. The resultant data set from each thermosonde flight is a profile of the strength and distribution of microthermal fluctuations which act as tracers for turbulence. The optical strength of this turbulence is computed and used to predict optical and laser beam propagation statistics. A description of the flight payload, examples of turbulence profiles, and comparison with simultaneous stellar observations are included.
Hyperspectral Image Turbulence Measurements of the Atmosphere
Lane, Sarah E.; West, Leanne L.; Gimmestad, Gary G.; Kireev, Stanislav; Smith, William L., Sr.; Burdette, Edward M.; Daniels, Taumi; Cornman, Larry
2012-01-01
A Forward Looking Interferometer (FLI) sensor has the potential to be used as a means of detecting aviation hazards in flight. One of these hazards is mountain wave turbulence. The results from a data acquisition activity at the University of Colorado s Mountain Research Station will be presented here. Hyperspectral datacubes from a Telops Hyper-Cam are being studied to determine if evidence of a turbulent event can be identified in the data. These data are then being compared with D&P TurboFT data, which are collected at a much higher time resolution and broader spectrum.
[Turbulent characteristics in forest canopy under atmospheric neutral condition].
Diao, Yi-Wei; Guan, De-Xin; Jin, Chang-Jie; Wang, An-Zhi; Pei, Tie-Fan
2010-02-01
Based on the micrometeorological data of broad-leaved Korean pine forest in Changbai Mountain in 2003, a second-order closure model was employed to calculate and analyze the turbulent characteristics within and above the canopy of the forest. The calculated mean wind profile was coincident with the measured one. The Reynolds stress within the forest was significantly attenuated. The turbulent strength, velocity flux, and skew were the largest at forest-atmosphere interface, as well the wind shear. With the increase of velocity skew, the turbulent intermittence became more significant, and the downward turbulent eddy within the canopy was limited. Most of the turbulent deeply within the forest canopy was produced by the non-local contributions above the canopy.
Weber, Stephan; Kordowski, Klaus
2010-10-01
From September 2006 to September 2007, the intersite variability of turbulence characteristics and turbulent heat fluxes was analysed at two urban stations in Essen, Germany. One site was situated within an urban residential setting while the other was located at the border of an urban park and suburban/urban residential housing. Therefore, the surroundings at both sites contributing to surface-atmosphere exchange differed in terms of surface cover and surface morphology. During the 1-year measurement period, 19% of data were characterised by stable atmospheric stratification. Since observations of urban turbulence characteristics under stable stratification are scarce, so far, this work adds additional input to this discussion. Turbulence characteristics, i.e. normalised standard deviations of wind components, were in agreement to empirical fits from other urban observations under both instable and stable atmospheric stratification. However, differences in magnitude of turbulence characteristics between sites were observable. Comparison of turbulent heat fluxes indicated typical urban features in the site located in the urban setting with increased surface heating and higher surface heat fluxes by about 30%. Also the temporal evolution of heat fluxes on the diurnal course was affected. Differences in momentum flux were of minor magnitude with about 6% variation on average between sites. Findings indicate that multiple urban flux measurements within one city may be characterised by general similarities in terms of turbulent characteristics but are still significantly influenced by differences in the surface cover of the flux footprint.
Turbulence Scales Simulations in Atmospheric Boundary Layer Wind Tunnels
Teleman, Elena-Carmen; Silion, Radu; Axinte, Elena; Pescaru, Radu
2008-01-01
The simulation of the air flow over models in atmospheric boundary layer tunnels is a research domain based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid movements in the proximity of the Earth’s surface. The experiment presented herein is developed in the wind tunnel from the Laboratory of Structural Aerodynamics of the Faculty of Civil Engineering and Building Services in Iassy. Measurements necessary for the determination of the turbulence sca...
Coherence of simulated atmospheric boundary-layer turbulence
Jiadong, Zeng; Zhiguo, Li; Mingshui, Li
2017-12-01
The coherences in a plane perpendicular to incoming flow are measured in wind tunnel simulations of atmospheric turbulent flow. The measured coherences are compared with analytical expressions tailored to field measurements and with theoretical coherence models which assume homogeneous turbulence and the von Kármán’s spectrum. The comparison indicates that the simulated atmospheric boundary layer flow is approximately horizontally homogeneous turbulence. Based on the above assumption and the systematic analysis of lateral coherence, it can be concluded that the lateral coherences of simulated atmospheric boundary turbulence can be determined accurately using the von Kármán spectrum and the turbulence parameters measured by a few measurement points. The measured results also show that the spatial characteristics of vertical coherences are closely related to the dimensionless parameter {{Δ }}z/({\\bar{z}}0.3{L}ux 0.7). The vertical coherence at two heights can be roughly estimated by the ratio to {{Δ }}z/({\\bar{z}}0.3{L}ux 0.7). The relationship between the phase angles of u-, v- and w-components and the vertical separation distance and the height from the ground is further analyzed. Finally, the roles of the type of land surface roughness, the height from the ground, the turbulence intensity and the integral length scale in lateral and vertical coherences are also discussed in this study.
Characteristics of turbulent structures in the unstable atmospheric surface layer
Schols, J. L. J.; Jansen, A. E.; Krom, J. G.
1985-10-01
An atmospheric surface-layer (ASL) experiment conducted at a meteorological site in the Oostelijk-Flevoland polder of the Netherlands is described. Turbulent fluctuations of wind velocity, air temperature and static pressure were measured, using three 10 m towers. Simultaneous turbulent signals at several heights on the towers were used to investigate the properties of the turbulent structures which contribute most significantly to the turbulent vertical transports in the unstable ASL. These turbulent structures produce between 30 and 50% of the mean turbulent vertical transport of horizontal alongwind momentum and they contribute to between 40 and 50% of the mean turbulent vertical heat transport; in both cases this occurs during 15 to 20% of the total observation time. The translation speed of the turbulent structures equals the wind speed averaged over the depth of the ASL, which scales on the surface friction velocity. The inclination angle of the temperature interface at the upstream edge of the turbulent structures to the surface is significantly smaller than that of the internal shear layer, which is associated with the temperature interface. The turbulent structures in the unstable ASL are determined by a large-scale temperature field: Convective motions, which encompass the whole depth of the planetary boundary layer (PBL), penetrate into the ASL. The curvature of the vertical profile of mean horizontal alongwind velocity forces the alignment of the convective cells in the flow direction (Kuettner, 1971), which have an average length of several hundreds of metres and an average width of a few tens of metres. This mechanism leads to the formation of turbulent structures, which extend throughout the depth of the ASL.
Optimization of AMI-MDM-RoFSO under atmospheric turbulence
Chaudhary, Sushank; Amphawan, Angela
2017-11-01
Radio over Free Space (Ro-FSO) is promising candidate for providing ubiquitous digital services especially in rural areas. This work investigates the performance of MDM of two 5Gbps-10GHz data channels over FSO link using LP 01 and LP 02 modes under the effect of atmospheric turbulences. The signal to noise ratio (SNR), total received power, modal decomposition at receiver at the receiver is also reported. The reported result shows the successful transmission of two channels with acceptable SNR over FSO link under atmospheric turbulences.
Atmospheric Turbulence Modeling for Aerospace Vehicles: Fractional Order Fit
Kopasakis, George (Inventor)
2015-01-01
An improved model for simulating atmospheric disturbances is disclosed. A scale Kolmogorov spectral may be scaled to convert the Kolmogorov spectral into a finite energy von Karman spectral and a fractional order pole-zero transfer function (TF) may be derived from the von Karman spectral. Fractional order atmospheric turbulence may be approximated with an integer order pole-zero TF fit, and the approximation may be stored in memory.
Characterising atmospheric optical turbulence using stereo-SCIDAR
Osborn, James; Butterley, Tim; Föhring, Dora; Wilson, Richard
2015-04-01
Stereo-SCIDAR (SCIntillation Detection and Ranging) is a development to the well known SCIDAR method for characterisation of the Earth's atmospheric optical turbulence. Here we present some interesting capabilities, comparisons and results from a recent campaign on the 2.5 m Isaac Newton Telescope on La Palma.
Wind Turbine Wake in Atmospheric Turbulence
DEFF Research Database (Denmark)
Rethore, Pierre-Elouan
This thesis describes the different steps needed to design a steady-state computational fluid dynamics (CFD) wind farm wake model. The ultimate goal of the project was to design a tool that could analyze and extrapolate systematically wind farm measurements to generate wind maps in order...... to calibrate faster and simpler engineering wind farm wake models. The most attractive solution was the actuator disc method with the steady state k-ε turbulence model. The first step to design such a tool is the treatment of the forces. This thesis presents a computationally inexpensive method to apply......) shows that the problem mainly comes from the assumptions of the eddy-viscosity concept, which are deeply invalidated in the wind turbine wake region. Different models that intent to correct the k-ε model's issues are investigated, of which none of them is found to be adequate. The mixing of the wake...
Atmospheric turbulence affects wind turbine nacelle transfer functions
Directory of Open Access Journals (Sweden)
C. M. St. Martin
2017-06-01
Full Text Available Despite their potential as a valuable source of individual turbine power performance and turbine array energy production optimization information, nacelle-mounted anemometers have often been neglected because complex flows around the blades and nacelle interfere with their measurements. This work quantitatively explores the accuracy of and potential corrections to nacelle anemometer measurements to determine the degree to which they may be useful when corrected for these complex flows, particularly for calculating annual energy production (AEP in the absence of other meteorological data. Using upwind meteorological tower measurements along with nacelle-based measurements from a General Electric (GE 1.5sle model, we calculate empirical nacelle transfer functions (NTFs and explore how they are impacted by different atmospheric and turbulence parameters. This work provides guidelines for the use of NTFs for deriving useful wind measurements from nacelle-mounted anemometers. Corrections to the nacelle anemometer wind speed measurements can be made with NTFs and used to calculate an AEP that comes within 1 % of an AEP calculated with upwind measurements. We also calculate unique NTFs for different atmospheric conditions defined by temperature stratification as well as turbulence intensity, turbulence kinetic energy, and wind shear. During periods of low stability as defined by the Bulk Richardson number (RB, the nacelle-mounted anemometer underestimates the upwind wind speed more than during periods of high stability at some wind speed bins below rated speed, leading to a steeper NTF during periods of low stability. Similarly, during periods of high turbulence, the nacelle-mounted anemometer underestimates the upwind wind speed more than during periods of low turbulence at most wind bins between cut-in and rated wind speed. Based on these results, we suggest different NTFs be calculated for different regimes of atmospheric stability and turbulence
Atmospheric Turbulence Modeling for Aero Vehicles: Fractional Order Fits
Kopasakis, George
2015-01-01
Atmospheric turbulence models are necessary for the design of both inlet/engine and flight controls, as well as for studying coupling between the propulsion and the vehicle structural dynamics for supersonic vehicles. Models based on the Kolmogorov spectrum have been previously utilized to model atmospheric turbulence. In this paper, a more accurate model is developed in its representative fractional order form, typical of atmospheric disturbances. This is accomplished by first scaling the Kolmogorov spectral to convert them into finite energy von Karman forms and then by deriving an explicit fractional circuit-filter type analog for this model. This circuit model is utilized to develop a generalized formulation in frequency domain to approximate the fractional order with the products of first order transfer functions, which enables accurate time domain simulations. The objective of this work is as follows. Given the parameters describing the conditions of atmospheric disturbances, and utilizing the derived formulations, directly compute the transfer function poles and zeros describing these disturbances for acoustic velocity, temperature, pressure, and density. Time domain simulations of representative atmospheric turbulence can then be developed by utilizing these computed transfer functions together with the disturbance frequencies of interest.
Scattering of coherent sound waves by atmospheric turbulence
Chow, P. L.; Liu, C. H.; Maestrello, L.
1975-01-01
An analytical study of the propagation of coherent sound waves through an atmosphere containing both mean and fluctuating flow variables is presented. The general flow problem is formulated as a time-dependent wave propagation in a half-space containing the turbulent medium. The coherent acoustic waves are analyzed by a smoothing technique, assuming that mean flow variables vary with the height only. The general equations for the coherent waves are derived, and then applied to two special cases, corresponding to uniform and shear mean flow, respectively. The results show that mean shear and turbulence introduce pronounced effects on the propagation of coherent acoustic disturbances.
Center for Computational Wind Turbine Aerodynamics and Atmospheric Turbulence
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær
2014-01-01
In order to design and operate a wind farm optimally it is necessary to know in detail how the wind behaves and interacts with the turbines in a farm. This not only requires knowledge about meteorology, turbulence and aerodynamics, but it also requires access to powerful computers and efficient...... software. Center for Computational Wind Turbine Aerodynamics and Atmospheric Turbulence was established in 2010 in order to create a world-leading cross-disciplinary flow center that covers all relevant disciplines within wind farm meteorology and aerodynamics....
Laboratory simulation of atmospheric turbulence induced optical wavefront distortion
Taylor, Travis Shane
1999-11-01
Many creative approaches have been taken in the past for simulating the effect that atmospheric turbulence has on optical beams. Most of the experimental architectures have been complicated and consisted of many optical elements as well as moving components. These techniques have shown a modicum of success; however, they are not completely controllable or predictable. A benchtop technique for experimentally producing one important effect that atmospheric turbulence has on optical beams (phase distortion) is presented here. The system is completely controllable and predictable while accurately representing the statistical nature of the problem. Previous experimentation in optical processing through turbulent media has demonstrated that optical wavefront distortions can be produced via spatial light modulating (SLM) devices, and most turbulence models and experimental results indicate that turbulence can be represented as a phase fluctuation. The amplitude distributions in the resulting far field are primarily due to propagation of the phase. Operating a liquid crystal television (LCTV) in the ``phase- mostly'' mode, a phase fluctuation type model for turbulence is utilized in the present investigation, and a real-time experiment for demonstrating the effects was constructed. For an optical system to simulate optical wavefront distortions due to atmospheric turbulence, the following are required: (1)An optical element that modulates the phasefront of an optical beam (2)A model and a technique for generating spatially correlated turbulence simulating distributions (3)Hardware and software for displaying and manipulating the information addressing the optical phase modulation device The LCTV is ideal for this application. When operated in the ``phase-mostly'' mode some LCTVs can modulate the phasefront of an optical beam by as much as 2π and an algorithm for generating spatially correlated phase screens can be constructed via mathematical modeling software such as
Entanglement evolution of twisted photons in strong atmospheric turbulence
Roux, Filippus S.; Wellens, Thomas; Shatokhin, Vyacheslav N.
2015-07-01
Considering the evolution of the quantum state of a pair of entangled photons in a turbulent atmosphere and using the quadratic approximation to the Kolmogorov model of turbulence, we provide an analytical solution for the dynamical equation (an infinitesimal propagation equation) that describes this evolution in the plane-wave basis. As such, this solution fully incorporates the effect of multiple scattering, caused by the medium. After being converted into a discrete orbital angular momentum (OAM) basis, this solution retains the effect of coupling between different OAM modes on the twin-photon state for arbitrary propagation distances and arbitrary turbulence strengths. We define a minimal set of parameters that determines the entanglement evolution in the regime of strong scintillation. Furthermore, we show that in the limit of weak scintillation, our solutions reduce to those obtained from the single-phase-screen model.
Turbulence Scales Simulations in Atmospheric Boundary Layer Wind Tunnels
Directory of Open Access Journals (Sweden)
Elena-Carmen Teleman
2008-01-01
Full Text Available The simulation of the air flow over models in atmospheric boundary layer tunnels is a research domain based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid movements in the proximity of the Earth’s surface. The experiment presented herein is developed in the wind tunnel from the Laboratory of Structural Aerodynamics of the Faculty of Civil Engineering and Building Services in Iassy. Measurements necessary for the determination of the turbulence scales of the wind action in urban environment were conducted. The data obtained were processed and analyzed and interpreted with specific software. The results are used for a synthesis regarding the scales of turbulence of the model of flow and the actual accuracy of measurements. The paper presents some of the important elements of this synthesis.
Higher order correlation beams in atmosphere under strong turbulence conditions.
Avetisyan, H; Monken, C H
2016-02-08
Higher order correlation beams, that is, two-photon beams obtained from the process of spontaneous parametric down-conversion pumped by Hermite-Gauss or Laguerre-Gauss beams of any order, can be used to encode information in many modes, opening the possibility of quantum communication with large alphabets. In this paper we calculate, analytically, the fourth-order correlation function for the Hermite-Gauss and Laguerre-Gauss coherent and partially coherent correlation beams propagating through a strong turbulent medium. We show that fourth-order correlation functions for correlation beams have, under certain conditions, expressions similar to those of intensities of classical beams and are degraded by turbulence in a similar way as the classical beams. Our results can be useful in establishing limits for the use of two-photon beams in quantum communications with larger alphabets under atmospheric turbulence.
Average intensity and spreading of a Lorentz-Gauss beam in turbulent atmosphere.
Zhou, Guoquan; Chu, Xiuxiang
2010-01-18
The propagation of a Lorentz-Gauss beam in turbulent atmosphere is investigated. Based on the extended Huygens-Fresnel integral and the Hermite-Gaussian expansion of a Lorentz function, analytical formulae for the average intensity and the effective beam size of a Lorentz-Gauss beam are derived in turbulent atmosphere. The average intensity distribution and the spreading properties of a Lorentz-Gauss beam in turbulent atmosphere are numerically demonstrated. The influences of the beam parameters and the structure constant of the atmospheric turbulence on the propagation of a Lorentz-Gauss beam in turbulent atmosphere are also discussed in detail.
Cui, Linyan
2014-09-01
Current theoretical temporal power spectra models of an optical wave have been developed for terrestrial environments. The interactions between humidity and temperature fluctuations in the marine atmospheric environments make the marine atmospheric turbulence particularly challenging, and the optical waves' propagation through marine turbulence exhibits a different behavior with respect to terrestrial propagation. In this paper, the temporal power spectra of irradiance scintillation under weak marine atmospheric turbulence, which is one of the key temporal statistics to describe the correlation of irradiance fluctuations at different time instances, is investigated in detail both analytically and numerically. Closed-form expressions for the temporal power spectra of irradiance scintillation are derived for infrared plane and spherical waves under weak marine atmospheric turbulence, and they consider physically the influences of finite turbulence inner and outer scales. The final results indicate that the marine atmospheric turbulence brings more effects on the irradiance scintillation than the terrestrial atmospheric 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
LDPC coded OFDM over the atmospheric turbulence channel.
Djordjevic, Ivan B; Vasic, Bane; Neifeld, Mark A
2007-05-14
Low-density parity-check (LDPC) coded optical orthogonal frequency division multiplexing (OFDM) is shown to significantly outperform LDPC coded on-off keying (OOK) over the atmospheric turbulence channel in terms of both coding gain and spectral efficiency. In the regime of strong turbulence at a bit-error rate of 10(-5), the coding gain improvement of the LDPC coded single-side band unclipped-OFDM system with 64 sub-carriers is larger than the coding gain of the LDPC coded OOK system by 20.2 dB for quadrature-phase-shift keying (QPSK) and by 23.4 dB for binary-phase-shift keying (BPSK).
UAV multirotor platform for accurate turbulence measurements in the atmosphere
Carbajo Fuertes, Fernando; Wilhelm, Lionel; Sin, Kevin Edgar; Hofer, Matthias; Porté-Agel, Fernando
2017-04-01
One of the most challenging tasks in atmospheric field studies for wind energy is to obtain accurate turbulence measurements at any location inside the region of interest for a wind farm study. This volume would ideally include from several hundred meters to several kilometers around it and from ground height to the top of the boundary layer. An array of meteorological masts equipped with several sonic anemometers to cover all points of interest would be the best in terms of accuracy and data availability, but it is an obviously unfeasible solution. On the other hand, the evolution of wind LiDAR technology allows to measure at any point in space but unfortunately it involves two important limitations: the first one is the relatively low spatial and temporal resolution when compared to a sonic anemometer and the second one is the fact that the measurements are limited to the velocity component parallel to the laser beam (radial velocity). To overcome the aforementioned drawbacks, a UAV multirotor platform has been developed. It is based on a state-of-the-art octocopter with enough payload to carry laboratory-grade instruments for the measurement of time-resolved atmospheric pressure, three-component velocity vector and temperature; and enough autonomy to fly from 10 to 20 minutes, which is a standard averaging time in most atmospheric measurement applications. The UAV uses a gyroscope, an accelerometer, a GPS and an algorithm has been developed and integrated for the correction of any orientation and movement. This UAV platform opens many possibilities for the study of features that have been almost exclusively studied until now in wind tunnel such as wind turbine blade tip vortex characteristics, near-wake to far-wake transition, momentum entrainment from the higher part of the boundary layer in wind farms, etc. The validation of this new measurement technique has been performed against sonic anemometry in terms of wind speed and temperature time series as well as
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.
Modeling of Atmospheric Turbulence Effect on Terrestrial FSO Link
Directory of Open Access Journals (Sweden)
A. Prokes
2009-04-01
Full Text Available Atmospheric turbulence results in many effects causing fluctuation in the received optical power. Terrestrial laser beam communication is affected above all by scintillations. The paper deals with modeling the influence of scintillation on link performance, using the modified Rytov theory. The probability of correct signal detection in direct detection system in dependence on many parameters such as link distance, power link margin, refractive-index structure parameter, etc. is discussed and different approaches to the evaluation of scintillation effect are compared. The simulations are performed for a horizontal-path propagation of the Gaussian-beam wave.
An instrument to measure turbulent eddy fluxes in the atmosphere of Mars
S. Rafkin; D. Banfield; R. Dissly; J. Silver; A. Stanton; E. Wilkinson; W. Massman; J. Ham
2012-01-01
Turbulent eddies in the planetary boundary layer of the terrestrial planet atmospheres are the primary mechanism by which energy, momentum, gasses, and aerosols are exchanged between the surface and the atmosphere [1]. The importance of eddies has long been recognized by the Earth atmospheric science community, and turbulent theory for Earth has a long history with a...
Kopasakis, George
2014-01-01
The presentation covers a recently developed methodology to model atmospheric turbulence as disturbances for aero vehicle gust loads and for controls development like flutter and inlet shock position. The approach models atmospheric turbulence in their natural fractional order form, which provides for more accuracy compared to traditional methods like the Dryden model, especially for high speed vehicle. The presentation provides a historical background on atmospheric turbulence modeling and the approaches utilized for air vehicles. This is followed by the motivation and the methodology utilized to develop the atmospheric turbulence fractional order modeling approach. Some examples covering the application of this method are also provided, followed by concluding remarks.
Is 2-D turbulence relevant in the atmosphere?
Lovejoy, Shaun; Schertzer, Daniel
2010-05-01
Starting with (Taylor, 1935), the paradigm of isotropic (and scaling!) turbulence was developed initially for laboratory applications, but following (Kolmogorov, 1941), three dimensional isotropic turbulence was progressively applied to the atmosphere. Since the atmosphere is strongly stratified, a single wide scale range model which is both isotropic and scaling is not possible so that theorists had to immediately choose between the two symmetries: isotropy or scale invariance. Following the development of models of two dimensional isotropic turbulence ((Fjortoft, 1953), but especially (Kraichnan, 1967) and (Charney, 1971)), the mainstream choice was to first make the convenient assumption of isotropy and to drop wide range scale invariance. Starting at the end of the 1970's this "isotropy primary" (IP) paradigm has lead to a series of increasingly complex isotropic 2D/isotropic 3D models of atmospheric dynamics which continue to dominate the theoretical landscape. Justifications for IP approaches have focused almost exclusively on the horizontal statistics of the horizontal wind in both numerical models and analyses and from aircraft campaigns, especially the highly cited GASP (Nastrom and Gage, 1983), (Gage and Nastrom, 1986; Nastrom and Gage, 1985) and MOZAIC (Cho and Lindborg, 2001) experiments. Since understanding the anisotropy clearly requires comparisons between horizontal and vertical statistics/structures this focus has been unfortunate. Over the same thirty year period that 2D/3D isotropic models were being elaborated, evidence slowly accumulated in favour of the opposite theoretical choice: to drop the isotropy assumption but to retain wide range scaling. The models in the alternative paradigm are scaling but strongly anisotropic with vertical sections of structures becoming increasingly stratified at larger and larger scales albeit in a power law manner; we collectively refer to these as "SP" for "scaling primary" approaches. Early authors explicitly
Analysis Regarding the Effects of Atmospheric Turbulence on Aircraft Dynamics
Directory of Open Access Journals (Sweden)
Gabriela STROE
2016-06-01
Full Text Available This paper will analyze the Gust Load Alleviation (GLA systems which can be used to reduce the effects of atmospheric turbulences generated by wind gusts on vertical acceleration of aircraft. Their purpose is to reduce airframe loads and to improve passenger comfort. The dynamic model of the aircraft is more realistic than a rigid-body model, since it includes the structural flexibility; due to its complexity, such model can make feedback control design for gust load alleviation more challenging. The gust is generated with the Dryden power spectral density model. This kind of model lends itself well to frequency-domain performance specifications in the form of the weighting functions. Two classical analytical representations for the power spectral density (PSD function of atmospheric turbulence as given by Von Kármán and Dryden, were used. The analysis is performed for a set of specified values for flight velocity and altitude (as test cases, with different gust signals that must be generated with the required intensity, scale lengths and PSD functions.
Turbulent atmospheric flow over a backward-facing step
Kaul, U. K.; Frost, W.
1976-01-01
The phenomenon of atmospheric shear layer separation over a man-made structure such as a building (modeled as a backward-facing step) has been analyzed theoretically by (1) solving the two-dimensional equations of motion in the two variables, stream function and vorticity, and by (2) employing an approximate integral technique. Boundary conditions for the undisturbed flow are that of the turbulent atmospheric shear flow over a rough terrain. In the first approach a two-equation model of turbulence was used. In the second approach an approximate technique was utilized in an attempt to describe the details of the flow in the recirculation zone behind the step. The results predict velocity profiles in sufficient detail that the presence of the corner eddy in the region of negative surface pressure gradient is evident. The magnitude of the reversed flow velocity in the recirculation eddy has been found to agree with that found from experiments. Also, a surface eddy viscosity distribution has been an outgrowth of the method which realistically follows the magnitude of the surface pressure gradient distribution as found experimentally.
Stochastic Models for Laser Propagation in Atmospheric Turbulence.
Leland, Robert Patton
In this dissertation, stochastic models for laser propagation in atmospheric turbulence are considered. A review of the existing literature on laser propagation in the atmosphere and white noise theory is presented, with a view toward relating the white noise integral and Ito integral approaches. The laser beam intensity is considered as the solution to a random Schroedinger equation, or forward scattering equation. This model is formulated in a Hilbert space context as an abstract bilinear system with a multiplicative white noise input, as in the literature. The model is also modeled in the Banach space of Fresnel class functions to allow the plane wave case and the application of path integrals. Approximate solutions to the Schroedinger equation of the Trotter-Kato product form are shown to converge for each white noise sample path. The product forms are shown to be physical random variables, allowing an Ito integral representation. The corresponding Ito integrals are shown to converge in mean square, providing a white noise basis for the Stratonovich correction term associated with this equation. Product form solutions for Ornstein -Uhlenbeck process inputs were shown to converge in mean square as the input bandwidth was expanded. A digital simulation of laser propagation in strong turbulence was used to study properties of the beam. Empirical distributions for the irradiance function were estimated from simulated data, and the log-normal and Rice-Nakagami distributions predicted by the classical perturbation methods were seen to be inadequate. A gamma distribution fit the simulated irradiance distribution well in the vicinity of the boresight. Statistics of the beam were seen to converge rapidly as the bandwidth of an Ornstein-Uhlenbeck process was expanded to its white noise limit. Individual trajectories of the beam were presented to illustrate the distortion and bending of the beam due to turbulence. Feynman path integrals were used to calculate an
Filtering effect of wind flow turbulence on atmospheric pollutant dispersion.
Yassin, Mohamed F
2012-06-01
This paper presents a model for coupling the statistics of wind velocity distribution and atmospheric pollutant dispersion. The effect of wind velocity distribution is modeled as a three-dimensional finite-impulse response (3D-FIR) filter. A phase space representation of the 3D-FIR filter window is discussed. The resulting pollutant dispersion is the multiplication in the phase space of the 3-D Fourier transform of the pollutant concentration and the volume described by the filter window coefficients. The shape of the filter window in the phase space enables representing such effects as vortex shedding thermal currents, etc. The impact of spatial distribution of the sensors on the resulting pollutant spatial distribution and the 3-D FIR filter model employed also discuss. The case of a neutrally buoyant plume emitted from an elevated point source in a turbulent boundary layer considers. The results show that wind turbulence is an important factor in the pollutant dispersion and introduces expected random fluctuations in pollutant distribution and leads to spreading the distribution due to wind mixing.
Temporal averaging of atmospheric turbulence-induced optical scintillation.
Yura, H T; Beck, S M
2015-08-24
Based on the Rytov approximation we have developed for weak scintillation conditions a general expression for the temporal averaged variance of irradiance. The present analysis provides, for what we believe is the first time, a firm theoretical basis for the often-observed reduction of irradiance fluctuations of an optical beam due to atmospheric turbulence. Accurate elementary analytic approximations are presented here for plane, spherical and beam waves for predicting the averaging times required to obtain an arbitrary value of the ratio of the standard deviation to the mean of an optical beam propagating through an arbitrary path in the atmosphere. In particular, a novel application of differential absorption measurement for the purpose of measuring column-integrated concentrations of various so-called greenhouse gas (GHG) atmospheric components is considered where the results of our analysis indicates that relatively short averaging times, on the order of a few seconds, are required to reduce the irradiance fluctuations to a value precise enough for GHG measurements of value to climate related studies.
Non-steady wind turbine response to daytime atmospheric turbulence.
Nandi, Tarak N; Herrig, Andreas; Brasseur, James G
2017-04-13
Relevant to drivetrain bearing fatigue failures, we analyse non-steady wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and the rotating blades of a GE 1.5 MW wind turbine using a unique dataset from a GE field experiment and computer simulation. Time-resolved local velocity data were collected at the leading and trailing edges of an instrumented blade together with generator power, revolutions per minute, pitch and yaw. Wind velocity and temperature were measured upwind on a meteorological tower. The stability state and other atmospheric conditions during the field experiment were replicated with a large-eddy simulation in which was embedded a GE 1.5 MW wind turbine rotor modelled with an advanced actuator line method. Both datasets identify three important response time scales: advective passage of energy-dominant eddies (≈25-50 s), blade rotation (once per revolution (1P), ≈3 s) and sub-1P scale (<1 s) response to internal eddy structure. Large-amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the aerofoil plane, modulated by eddy passage at longer time scales. Generator power responds strongly to large-eddy wind modulations. We show that internal dynamics of the blade boundary layer near the trailing edge is temporally modulated by the non-steady external flow that was measured at the leading edge, as well as blade-generated turbulence motions.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).
Li, Shuhui; Chen, Shi; Gao, Chunqing; Willner, Alan E.; Wang, Jian
2018-02-01
Orbital angular momentum (OAM)-carrying beams have recently generated considerable interest due to their potential use in communication systems to increase transmission capacity and spectral efficiency. For OAM-based free-space optical (FSO) links, a critical challenge is the atmospheric turbulence that will distort the helical wavefronts of OAM beams leading to the decrease of received power, introducing crosstalk between multiple channels, and impairing link performance. In this paper, we review recent advances in turbulence effects compensation techniques for OAM-based FSO communication links. First, basic concepts of atmospheric turbulence and theoretical model are introduced. Second, atmospheric turbulence effects on OAM beams are theoretically and experimentally investigated and discussed. Then, several typical turbulence compensation approaches, including both adaptive optics-based (optical domain) and signal processing-based (electrical domain) techniques, are presented. Finally, key challenges and perspectives of compensation of turbulence-distorted OAM links are discussed.
Development of an embedded atmospheric turbulence mitigation engine
Paolini, Aaron; Bonnett, James; Kozacik, Stephen; Kelmelis, Eric
2017-05-01
Methods to reconstruct pictures from imagery degraded by atmospheric turbulence have been under development for decades. The techniques were initially developed for observing astronomical phenomena from the Earth's surface, but have more recently been modified for ground and air surveillance scenarios. Such applications can impose significant constraints on deployment options because they both increase the computational complexity of the algorithms themselves and often dictate a requirement for low size, weight, and power (SWaP) form factors. Consequently, embedded implementations must be developed that can perform the necessary computations on low-SWaP platforms. Fortunately, there is an emerging class of embedded processors driven by the mobile and ubiquitous computing industries. We have leveraged these processors to develop embedded versions of the core atmospheric correction engine found in our ATCOM software. In this paper, we will present our experience adapting our algorithms for embedded systems on a chip (SoCs), namely the NVIDIA Tegra that couples general-purpose ARM cores with their graphics processing unit (GPU) technology and the Xilinx Zynq which pairs similar ARM cores with their field-programmable gate array (FPGA) fabric.
The collapse of turbulence in the atmospheric boundary layer
Energy Technology Data Exchange (ETDEWEB)
Van de Wiel, B J H; Clercx, H J H [Department of Physics, Eindhoven University of Technology (Netherlands); Moene, A F [Department of Meteorology and Air Quality, Wageningen University and Research Centre (Netherlands); Jonker, H J J, E-mail: b.j.h.v.d.wiel@tue.nl [Department of Multi-scale Pysics, Delft University of Technology (Netherlands)
2011-12-22
A well-known phenomenon in the atmospheric boundary layer is the fact that winds may become very weak in the evening after a clear sunny day. In these quiet conditions usually hardly any turbulence is present. Consequently this type of boundary layer is referred to as the quasi-laminar boundary layer. In spite of its relevance, the appearance of laminar boundary layers is poorly understood and forms a long standing problem in meteorological research. Here we investigate an analogue problem in the form of a stably stratified channel flow. The flow is studied with a simplified atmospheric model as well as with Direct Numerical Simulations. Both models show remarkably similar behaviour with respect to the mean variables such as temperature and wind speed. The similarity between both models opens new way for understanding and predicting the laminarization process. Mathematical analysis on the simplified model shows that relaminarization can be understood from the existence of a definite limit in the maximum sustainable heat flux under stably stratified conditions. This fascinating aspect will be elaborated in future work.
Stability of sonic boom metrics regarding signature distortions from atmospheric turbulence.
Doebler, William J; Sparrow, Victor W
2017-06-01
The degree of insensitivity to atmospheric turbulence was evaluated for five metrics (A-, B-, E-weighted sound exposure level, Stevens Mark VII Perceived Level, and NASA's Indoor Sonic Boom Annoyance Predictor) that correlate to human annoyance from sonic booms. Eight N-wave shaped sonic booms from NASA's FaINT experiment and five simulated "low-boom" sonic booms were turbulized by Locey's ten atmospheric filter functions. The B-weighted sound exposure level value changed the least due to the turbulence filters for twelve of thirteen booms. This makes it the most turbulence stable metric which may be useful for quiet supersonic aircraft certification.
Osborn, J.; Butterley, T.; Townson, M. J.; Reeves, A. P.; Morris, T. J.; Wilson, R. W.
2017-02-01
As telescopes become larger, into the era of ˜40 m Extremely Large Telescopes, the high-resolution vertical profile of the optical turbulence strength is critical for the validation, optimization and operation of optical systems. The velocity of atmospheric optical turbulence is an important parameter for several applications including astronomical adaptive optics systems. Here, we compare the vertical profile of the velocity of the atmospheric wind above La Palma by means of a comparison of Stereo-SCIntillation Detection And Ranging (Stereo-SCIDAR) with the Global Forecast System models and nearby balloon-borne radiosondes. We use these data to validate the automated optical turbulence velocity identification from the Stereo-SCIDAR instrument mounted on the 2.5 m Isaac Newton Telescope, La Palma. By comparing these data we infer that the turbulence velocity and the wind velocity are consistent and that the automated turbulence velocity identification of the Stereo-SCIDAR is precise. The turbulence velocities can be used to increase the sensitivity of the turbulence strength profiles, as weaker turbulence that may be misinterpreted as noise can be detected with a velocity vector. The turbulence velocities can also be used to increase the altitude resolution of a detected layer, as the altitude of the velocity vectors can be identified to a greater precision than the native resolution of the system. We also show examples of complex velocity structure within a turbulent layer caused by wind shear at the interface of atmospheric zones.
Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review
Directory of Open Access Journals (Sweden)
R. Wilson
2004-11-01
Full Text Available The actual impact on vertical transport of small-scale turbulence in the free atmosphere is still a debated issue. Numerous estimates of an eddy diffusivity exist, clearly showing a lack of consensus. MST radars were, and continue to be, very useful for studying atmospheric turbulence, as radar measurements allow one to estimate the dissipation rates of energy (kinetic and potential associated with turbulent events. The two commonly used methods for estimating the dissipation rates, from the backscattered power and from the Doppler width, are discussed. The inference methods of a local diffusivity (local meaning here "within" the turbulent patch by using the dissipation rates are reviewed, with some of the uncertainty causes being stressed. Climatological results of turbulence diffusivity inferred from radar measurements are reviewed and compared.
As revealed by high resolution MST radar measurements, atmospheric turbulence is intermittent in space and time. Recent theoretical works suggest that the effective diffusivity of such a patchy turbulence is related to statistical parameters describing the morphology of turbulent events: filling factor, lifetime and height of the patches. It thus appears that a statistical description of the turbulent patches' characteristics is required in order to evaluate and parameterize the actual impact of small-scale turbulence on transport of energy and materials. Clearly, MST radars could be an essential tool in that matter.
Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review
Directory of Open Access Journals (Sweden)
R. Wilson
2004-11-01
Full Text Available The actual impact on vertical transport of small-scale turbulence in the free atmosphere is still a debated issue. Numerous estimates of an eddy diffusivity exist, clearly showing a lack of consensus. MST radars were, and continue to be, very useful for studying atmospheric turbulence, as radar measurements allow one to estimate the dissipation rates of energy (kinetic and potential associated with turbulent events. The two commonly used methods for estimating the dissipation rates, from the backscattered power and from the Doppler width, are discussed. The inference methods of a local diffusivity (local meaning here "within" the turbulent patch by using the dissipation rates are reviewed, with some of the uncertainty causes being stressed. Climatological results of turbulence diffusivity inferred from radar measurements are reviewed and compared. As revealed by high resolution MST radar measurements, atmospheric turbulence is intermittent in space and time. Recent theoretical works suggest that the effective diffusivity of such a patchy turbulence is related to statistical parameters describing the morphology of turbulent events: filling factor, lifetime and height of the patches. It thus appears that a statistical description of the turbulent patches' characteristics is required in order to evaluate and parameterize the actual impact of small-scale turbulence on transport of energy and materials. Clearly, MST radars could be an essential tool in that matter.
Zhai, Xiaochun; Wu, Songhua; Liu, Bingyi
2017-06-12
Four field experiments based on Pulsed Coherent Doppler Lidar with different surface roughness have been carried out in 2013-2015 to study the turbulent wind field in the vicinity of operating wind turbine in the onshore and offshore wind parks. The turbulence characteristics in ambient atmosphere and wake area was analyzed using transverse structure function based on Plane Position Indicator scanning mode. An automatic wake processing procedure was developed to determine the wake velocity deficit by considering the effect of ambient velocity disturbance and wake meandering with the mean wind direction. It is found that the turbine wake obviously enhances the atmospheric turbulence mixing, and the difference in the correlation of turbulence parameters under different surface roughness is significant. The dependence of wake parameters including the wake velocity deficit and wake length on wind velocity and turbulence intensity are analyzed and compared with other studies, which validates the empirical model and simulation of a turbine wake for various atmosphere conditions.
Synthetic atmospheric turbulence and wind shear in large eddy simulations of wind turbine wakes
DEFF Research Database (Denmark)
Keck, Rolf-Erik; Mikkelsen, Robert Flemming; Troldborg, Niels
2014-01-01
A method of generating a synthetic ambient wind field in neutral atmosphere is described and verified for modelling the effect of wind shear and turbulence on a wind turbine wake using the flow solver EllipSys3D. The method uses distributed volume forces to represent turbulent fluctuations......, superimposed on top of a mean deterministic shear layer consistent with that used in the IEC standard for wind turbine load calculations. First, the method is evaluated by running a series of large-eddy simulations in an empty domain, where the imposed turbulence and wind shear is allowed to reach a fully...... developed stage in the domain. The performance of the method is verified by comparing the turbulence intensity and spectral distribution of the turbulent energy to the spectral distribution of turbulence generated by the IEC suggested Mann model. Second, the synthetic turbulence and wind shear is used...
Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study
Directory of Open Access Journals (Sweden)
Yu-Ting Wu
2012-12-01
Full Text Available A numerical study of atmospheric turbulence effects on wind-turbine wakes is presented. Large-eddy simulations of neutrally-stratified atmospheric boundary layer flows through stand-alone wind turbines were performed over homogeneous flat surfaces with four different aerodynamic roughness lengths. Emphasis is placed on the structure and characteristics of turbine wakes in the cases where the incident flows to the turbine have the same mean velocity at the hub height but different mean wind shears and turbulence intensity levels. The simulation results show that the different turbulence intensity levels of the incoming flow lead to considerable influence on the spatial distribution of the mean velocity deficit, turbulence intensity, and turbulent shear stress in the wake region. In particular, when the turbulence intensity level of the incoming flow is higher, the turbine-induced wake (velocity deficit recovers faster, and the locations of the maximum turbulence intensity and turbulent stress are closer to the turbine. A detailed analysis of the turbulence kinetic energy budget in the wakes reveals also an important effect of the incoming flow turbulence level on the magnitude and spatial distribution of the shear production and transport terms.
Effects of atmospheric turbulence on the return photon flux of sodium laser guide star
Liu, Xiangyuan; Qian, Xianmei; Fan, Chuanyu; Du, Chengtao; Lu, Chengling; Zhang, Lei; Yang, Huan
2016-03-01
The circular-polarized laser can excite Sodium Laser Guide Star (SLGS) to obtain a large number of the return photons. Re-pumping technology can further enhance the return photon flux of SLGS. But laser propagating in the atmosphere suffers the atmospheric turbulence which causes the stochastic distributions of laser intensity in mesosphere. This leads to the fluctuations of return photon flux as the strength of atmospheric turbulence. We study effects of atmospheric turbulence on the return photon flux of SLGS under the Hufnagle-vally5/7(HV5/7), Greenwood and Mod-HV models by numerical simulation. Results show that both the return photon flux and fluctuations under the strong atmospheric turbulence are more than those under the weak one. Comparing re-pumping with no re-pumping, increment of the return photon flux under the three atmospheric turbulence models increase with the decreasing strength of atmospheric turbulence. But the fluctuations of the return photon flux greatly decrease for re-pumping.
Wave equations and computational models for sonic boom propagation through a turbulent atmosphere
Pierce, Allan D.
1992-01-01
The improved simulation of sonic boom propagation through the real atmosphere requires greater understanding of how the transient acoustic pulses popularly termed sonic booms are affected by atmospheric turbulence. A nonlinear partial differential equation that can be used to simulate the effects of smaller-scale atmospheric turbulence on sonic boom waveforms is described. The equation is first order in the time derivative and involves an extension of geometrical acoustics to include diffraction phenomena. Various terms in the equation are explained in physical terms. Such terms include those representing convection at the wave speed, diffraction, molecular relaxation, classical dissipation, and nonlinear steepening. The atmospheric turbulence enters through an effective sound speed, which varies with all three spatial coordinates, and which is the sum of the local sound speed and the component of the turbulent flow velocity projected along a central ray that connects the aircraft trajectory with the listener.
A Fast-Response Atmospheric Turbulence (FRAT) Probe with Gas-Sampling Ducts Project
National Aeronautics and Space Administration — The objective of this proposal is to design, construct and test a high-frequency-response air-data probe, the Fast Response Atmospheric Turbulence probe (FRAT probe)...
Atmospheric turbulence temperature on the laser wavefront properties
Contreras López, J. C.; Ballesteros Díaz, A.; Tíjaro Rojas, O. J.; Torres Moreno, Y.
2017-06-01
Temperature is a physical magnitude that if is higher, the refractive index presents more important random fluctuations, which produce a greater distortion in the wavefront and thus a displacement in its centroid. To observe the effect produced by the turbulent medium strongly influenced by temperature on propagation laser beam, we experimented with two variable and controllable temperature systems designed as optical turbulence generators (OTG): a Turbulator and a Parallelepiped glass container. The experimental setup use three CMOS cameras and four temperature sensors spatially distributed to acquire synchronously information of the laser beam wavefront and turbulence temperature, respectively. The acquired information was analyzed with MATLAB® software tool, that it allows to compute the position, in terms of the evolution time, of the laser beam center of mass and their deviations produced by different turbulent conditions generated inside the two manufactured systems. The results were reflected in the statistical analysis of the centroid shifting.
Why turbulence dominates the atmosphere and hydrosphere? (Alfred Wegener Medal Lecture)
Zilitinkevich, Sergej
2015-04-01
It is widely recognised that in very stable stratifications, at Richardson numbers (Ri) exceeding the critical value Ric ~ 0.25, turbulence inevitably decays and the flow becomes laminar. This is so, indeed, in the low-Reynolds-number (Re) flows, e.g., in some laboratory experiments; but this is by no means always the case. Air flows in the free atmosphere and water currents in deep ocean are almost always turbulent in spite of the strongly supercritical stratifications, with typical values of Ri varying in the interval 10 Ric the familiar 'strong-mixing turbulence' regime, typical of boundary-layer flows and characterised by the practically invariable turbulent Prandtl number PrT ~ 1 (the so-called 'Reynolds analogy'), gives way to a previously unknown 'wave-like turbulence' regime, wherein PrT sharply increases with increasing Ri (rather than to the laminar regime as is often the case in lab experiments). It is precisely the wave-like turbulence that dominates the free flows in the atmosphere and ocean. Modellers have long been aware that the turbulent heat transfer in the free atmosphere/ocean is much weaker than the momentum transfer. Our theory gives authentic formulation for this heuristic rule and provides physically grounded method for modelling geophysical turbulence up to very stable startifications.
Numerical study of the Bessel beams carrying optical vortices propagating in turbulent atmosphere
Zhang, Yalin; Ma, Donglin; Yuan, Xiuhua; Zhou, Zeyu
2017-02-01
In this paper, the aperture averaged scintillations of the Bessel beams carrying optical vortices propagating in turbulent atmosphere are evaluated. The multistep form of the propagation algorithm and a numerical phase screen simulation method are applied to the calculations of the aperture averaged scintillation. The results show that the Bessel beam with more topological charges delivers the smaller scintillation. The relation between the aperture averaged scintillation and the size of the beams is investigated. The effect of inner and outer scales of turbulence on the scintillations of the Bessel beams is also studied. These results may be useful in long-distance optical communications in free space or in turbulent atmosphere.
Influence of non-Kolmogorov atmospheric turbulence on the beam quality of vortex beams.
Li, Jinhong; Wang, Weiwei; Duan, Meiling; Wei, Jinlin
2016-09-05
Based on the extended Huygens-Fresnel principle and the definition of second-order moments of the Wigner distribution function (WDF), the analytical expressions for the propagation factors (M2-factors) and Strehl ratio SR of the Gaussian Schell-model (GSM) vortex beams and GSM non-vortex beams propagation through non-Kolmogorov atmospheric turbulence are derived, and used to study the influence of non-Kolmogorov atmospheric turbulence on beam quality of the GSM vortex beams. It is shown that the smaller the generalized structure constant and the outer scale of turbulence are, and the bigger the inner scale of turbulence is, the smaller the normalized propagation factor is, the bigger the Strehl ratio is, and the better the beam quality of GSM vortex beams in atmospheric turbulence is. The variation of beam quality with the generalized exponent α is nonmonotonic, when α = 3.11, the beam quality of the GSM vortex beams is the poorest through non-Kolmogorov atmospheric turbulence. GSM vortex beams is less affected by turbulence than GSM non-vortex beams under certain condition, and will be useful in long-distance free-space optical communications.
Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Ren, Bin; Li, Yanfang
2015-02-23
The on-axis two-frequency mutual coherence function (MCF) for beam waves propagating along a horizontal path in strong anisotropic atmospheric turbulence is theoretically formulated by making use of the extended Huygens-Fresnel principle. Based on this formulation, a new closed-form expression for the mean square temporal width of Gaussian-beam-wave pulses passing horizontally through strong anisotropic atmospheric turbulence is developed. With the help of this expression, the increments of mean square temporal pulse width due to strong anisotropic atmospheric turbulence under various conditions are further calculated. Results show that the increment of mean square temporal pulse width due to strong anisotropic atmospheric turbulence is basically proportional to the effective anisotropic factor in most situations of interest, with the possible exception of cases in which both the Fresnel ratio and spectral index become relatively small; increasing the effective anisotropic factor can reduce the number of the said exceptions; the turbulence-induced increment of mean square temporal pulse width enlarges as the spectral index increases with a fixed value of the nondimensional turbulence-strength parameter. It is also illustrated that a significant enlargement in the turbulence-induced increment of mean square temporal pulse width occurs by changing the Fresnel ratio from a large to a tiny value if both the effective anisotropic factor and spectral index are relatively small.
Tíjaro Rojas, Omar J.; Torres Moreno, Yezid; Rhodes, William T.
2017-06-01
Different theories including Kolmogorov have been valid to explain and model physic phenomenal like vertical atmospheric turbulence. In horizontal path, we still have many questions, due to weather problems and consequences that it generates. To emulate some conditions of environment, we built an Optical Turbulence Generator (OTG) having spatial, humidity and temperature, measurements that were captured in the same time from optical synchronization. This development was made using digital modules as ADC (Analog to Digital Converters) and communications protocol as SPI. We all made from microcontrollers. On the other hand, to measure optical signal, we used a photomultiplier tube (PMT) where captured the intensity of fringes that shifted with a known frequency. Outcomes show temporal shift and phase drive from dependent samples (in time domain) that correspond with frozen turbulence given by Taylor theory. Parameters studied were C2n, scintillation and inner scale in temporal patterns and analysis of their relationship with the physical associated variables. These patterns were taken from Young Interferometer in laboratory room scale. In the future, we hope with these studies, we will can implement an experiment to characterize atmospheric turbulence in a long distance, placed in the equatorial weather zone.
Liu, Huilong; Lü, Yanfei; Zhang, Jing; Xia, Jing; Pu, Xiaoyun; Dong, Yuan; Li, Shutao; Fu, Xihong; Zhang, Angfeng; Wang, Changjia; Tan, Yong; Zhang, Xihe
2015-01-01
This paper studies the propagation properties of controllable hollow flat-topped beams (CHFBs) in turbulent atmosphere based on ABCD matrix, sets up a propagation model and obtains an analytical expression for the propagation. With the help of numerical simulation, the propagation properties of CHFBs in different parameters are studied. Results indicate that in turbulent atmosphere, with the increase of propagation distance, the darkness of CHFBs gradually annihilate, and eventually evolve into Gaussian beams. Compared with the propagation properties in free space, the turbulent atmosphere enhances the diffraction effect of CHFBs and reduces the propagation distance for CHFBs to evolve into Gaussian beams. In strong turbulence atmospheric propagation, Airy disk phenomenon will disappear. The study on the propagation properties of CHFBs in turbulence atmosphere by using ABCD matrix is simple and convenient. This method can also be applied to study the propagation properties of other hollow laser beams in turbulent atmosphere.
Diffusion of Sound Waves in a Turbulent Atmosphere
Lyon, Richard H.
1960-01-01
The directional and frequency diffusion of a plane monochromatic 2 sound wave in statistically homogeneous, isotropic, and stationary turbulence is analyzed theoretically. The treatment is based on the diffusion equation for the energy density of sound waves, using the scattering cross section derived by Kraichnan for the type of turbulence assumed here. A form for the frequency-wave number spectrum of the turbulence is adopted which contains the pertinent parameters of the flow and is adapted to ease of calculation. A new approach to the evaluation of the characteristic period of the flow is suggested. This spectrum is then related to the scattering cross section. Finally, a diffusion equation is derived as a small-angle scattering approximation to the rigorous transport equation. The rate of spread of the incident wave in frequency and direction is calculated, as well as the power spectrum and autocorrelation for the wave.
Modelling atmospheric turbulence effects on ground-based telescope systems
Energy Technology Data Exchange (ETDEWEB)
Bradford, L.W.; Flatte, S.M. [California Univ., Santa Cruz, CA (United States). Dept. of Physics; Max, C.E. [Lawrence Livermore National Lab., CA (United States)
1993-09-30
Questions still exist concerning the appropriate model for turbulence- induced phase fluctuations seen in ground-based telescopes. Bester et al. used a particular observable (slope of the Allan variance) with an infrared interferometer in an attempt to distinguish models. The authors have calculated that observable for Kolmogorov and {open_quotes}random walk{close_quotes} models with a variety of outer scales and altitude-dependent turbulence and wind velocity. The authors have found that clear distinction between models requires good data on the vertical distribution of wind and turbulence. Furthermore, measurements at time separations of order 60 s are necessary to distinguish the {open_quotes}random walk{close_quotes} model from the Kolmogorov model.
Infulence of atmospheric stability on the spatial structure of turbulence
DEFF Research Database (Denmark)
Chougule, Abhijit S.
This thesis consists of three chapters. In the first chapter, the cross-spectral phases between velocity components at two heights are analyzed from observations at the Høvsøre test site under diabatic conditions. These phases represent the degree to which turbulence sensed at one height leads (or...... lags) in time the turbulence sensed at the other height. The phase angle of the cross-wind component is observed to be significantly greater than the phase for the along-wind component, which in turn is greater than the phase for the vertical component. The cross-wind and along-wind phases increase...
Analysis of atmospheric flow over a surface protrusion using the turbulence kinetic energy equation
Frost, W.; Harper, W. L.; Fichtl, G. H.
1975-01-01
Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer/Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to determine the dissipative effects of turbulent shear on the mean flow. Mean-flow results are compared with those given in a previous paper where the same problem was attacked using a Prandtl mixing-length hypothesis. Iso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow. They highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient.
Effects of incident angles on reflective ghost imaging through atmospheric turbulence
Tang, Lingli; Bai, Yanfeng; Duan, Chao; Nan, Suqin; Shen, Qian; Fu, Xiquan
2018-01-01
The influence of the incident angle on the imaging quality of reflective ghost imaging is investigated through atmospheric turbulence. It is shown that under mediate turbulence, small angles have almost no effect on the imaging quality, while the result for direct imaging gets slightly worse. An increase of the incident angle leads to the degradation of the imaging quality of direct imaging and ghost imaging, while the imaging quality of the latter is better under the same angle and turbulent intensity. For large angles, the image from direct imaging cannot be distinguished under mediate turbulence, but ghost imaging can obtain a relatively good ghost image. Moreover, the relationship between the fidelity and the incident angle under different turbulent intensities is presented.
Sensible Heat Flux Related to Variations in Atmospheric Turbulence Kinetic Energy on a Sandy Beach
2017-06-01
FLUX RELATED TO VARIATIONS IN ATMOSPHERIC TURBULENCE KINETIC ENERGY ON A SANDY BEACH by Jessica S. Koscinski June 2017 Thesis Advisor...KINETIC ENERGY ON A SANDY BEACH 5. FUNDING NUMBERS 6. AUTHOR(S) Jessica S. Koscinski 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Naval...Sensible heat flux, turbulence kinetic energy , surf zone 15. NUMBER OF PAGES 57 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT
Yi, Xiang; Liu, Zengji; Yue, Peng
2012-12-15
A computationally efficient expression is presented for evaluating the average bit error rate (BER) of an intensity-modulation and direct-detection free-space optical system with on-off keying signaling technique operating in turbulent atmosphere described by the exponentiated Weibull distribution. The presented numerical results show the effects of aperture averaging on the average BER under weak and moderate turbulence conditions, and are confirmed by Monte Carlo simulations.
Experimental Characterisation and Modelling of Atmospheric Fog and Turbulence in FSO
Ijaz, Muhammad
2013-01-01
Free space optical (FSO) communication uses visible or infrared (IR) wavelengths to broadcast high-speed data wirelessly through the atmospheric channel. The performance of FSO communications is mainly dependent on the unpredictable atmospheric channel such as fog, smoke and temperature dependent turbulence. However, as the real outdoor atmosphere (ROA) is time varying and heterogeneous in nature as well as depending on the magnitude and intensity of different weather conditions, carrying out...
Han, Guowen; Zheng, X. J.; Bo, Tianli
2017-11-01
In our study, turbulent transport of momentum and heat is investigated in the neutral and unstable atmospheric surface layer (ASL) over the edge of a desert. Our results reveal that with the increase of wind speed the transport efficiencies for momentum and heat increased, furthermore, transport efficiency of momentum increases faster than that of heat. In addition, the method of quadrant analysis and turbulent events were used to analyze the moment flux and heat flux. Experimental results show that the influence of wind speed on moment flux and heat flux can be quite different, which maybe has a great impact on the turbulent transport of momentum and heat in ASL.
Page 1 Laser beam propagation in atmospheric turbulence 195 ...
Indian Academy of Sciences (India)
Tatarski VI 1971 Wave propagation in turbulent medium (Springfield, Virginia: National Technical. Information Service) -. Valley S L 1965 Handbook of geophysics and space environment (New York: McGraw Hill). Weaver E A, Bilbro J W, Dunkin J A & Jeffries H B 1976 Conf. Proc. of NASA Aviation Safety and Operational ...
Propagation of Porro "petal" beams through a turbulent atmosphere
CSIR Research Space (South Africa)
Burger, L
2009-07-01
Full Text Available Laboratory experiment using a turbulence phase screen Page 18 Join the Mathematical Optics research team! Opportunities: MSc and PhD studentships, Post docs and Sabbaticals Contact: Dr Andrew Forbes or Dr Stef Roux www.csir.co.za/lasers/index_mathematical_optics.html ...
Laser beam propagation through an atmospheric transitional and turbulent boundary layer
Katz, Richard A.; Manzur, Tariq
2015-05-01
This study investigates laser beam propagation through an atmospheric boundary layer near the ocean surface. Objectives of this research are to ascertain feasibility limits for achieving maximum energy efficiency at extended ranges in the face of atmospheric and other distortions as the laser beam penetrates through transitional (anisotropic) and turbulent (isotropic) boundary layer regimes. Various aspects of turbulence modeling of laser beam propagation near the ocean surface are discussed including: Kolmogorov's model of atmospheric turbulence, parameterized structure functions (e.g., velocity and temperature gradients, gradients in refractive index) and other important factors affecting near surface propagation such as humidity, aerosols, and wave slap. Various preliminary modeled propagation results are shown, and a new methodology is proposed for improving existing model estimates with new time domain measurement procedures.
Influence of vortex dynamics and atmospheric turbulence on the early evolution of a contrail
Directory of Open Access Journals (Sweden)
R. Paugam
2010-04-01
Full Text Available This study describes three-dimensional numerical simulations of the evolution of an aircraft contrail during the first 30 min following the emission of exhausts. The wake is modeled as a vortex pair descending in a stratified atmosphere where turbulent fluctuations are sustained in the late dissipation regime. The focus of the study is laid on the interactions between vortex dynamics, atmospheric turbulence and contrail microphysics, and their role in determining the growth and the distribution of ice crystals. The atmospheric turbulence is synthesized using a methodology developed to force anisotropic turbulent fluctuations. The results show the feasibility of three-dimensional simulations of the early development of a contrail in supersaturated conditions before its transition into a contrail-cirrus. %(when radiative heating and sedimentation are no more negligible. It is shown that in case of strongly supersaturated and shear-free atmosphere the optical depth is maintained as the contrail spreads by turbulent diffusion in the late dissipation regime.
Lachinova, Svetlana L.; Vorontsov, Mikhail A.; Filimonov, Grigory A.; LeMaster, Daniel A.; Trippel, Matthew E.
2017-07-01
Computational efficiency and accuracy of wave-optics-based Monte-Carlo and brightness function numerical simulation techniques for incoherent imaging of extended objects through atmospheric turbulence are evaluated. Simulation results are compared with theoretical estimates based on known analytical solutions for the modulation transfer function of an imaging system and the long-exposure image of a Gaussian-shaped incoherent light source. It is shown that the accuracy of both techniques is comparable over the wide range of path lengths and atmospheric turbulence conditions, whereas the brightness function technique is advantageous in terms of the computational speed.
BER of subcarrier MPSK and MDPSK systems in atmospheric turbulence
Song, Xuegui
2015-01-01
Bit-error rate (BER) performance of subcarrier $M$-ary phase-shift keying (MPSK) and $M$-ary differential PSK (MDPSK) is analyzed for optical wireless communications over Gamma-Gamma and lognormal turbulence channels. We study the relation between the exact BER and the approximate BER, which is obtained by dividing the symbol-error rate by the number of bits per symbol, for subcarrier MPSK and MDPSK modulations. The asymptotic BER performance gap between the exact and the approximate BERs is quantified analytically through our asymptotic analyses. The accuracy of the approximate BER of both MPSK and MDPSK depends on the channel conditions. Under weak turbulence conditions, the approximate BER expression can be used to predict the system performance with high accuracy, while under strong turbulence conditions the approximate BER becomes inaccurate and can only serve as a loose lower bound of the exact BER. The asymptotic BER performance loss of MDPSK with respect to MPSK is also quantified analytically.
Off-Axis Gaussian Beams with Random Displacement in Atmospheric Turbulence
Directory of Open Access Journals (Sweden)
Yahya Baykal
2006-10-01
Full Text Available Our recent work in which we study the propagation of the general Hermite-sinusoidal-Gaussian laser beams in wireless broadband access telecommunication systems is elaborated in this paper to cover the special case of an off-axis Gaussian beam. We mainly investigate the propagation characteristics in atmospheric turbulence of an off-axis Gaussian beam possessing Gaussian distributed random displacement parameters. Our interest is to search for different types of laser beams that will improve the performance of a wireless broadband access system when atmospheric turbulence is considered. Our formulation is based on the basic solution of the second order mutual coherence function evaluated at the receiver plane. For fixed turbulence strength, the coherence length calculated at the receiver plane is found to decrease as the variance of the random displacement is increased. It is shown that as the turbulence becomes stronger, coherence lengths due to off-axis Gaussian beams tend to approach the same value, irrespective of the variance of the random displacement. As expected, the beam spreading is found to be pronounced for larger variance of displacement parameter. Average intensity profiles when atmospheric turbulence is present are plotted for different values of the variance of the random displacement parameter of the off-axis Gaussian beam.
Imaging through atmospheric turbulence for laser based C-RAM systems: an analytical approach
Buske, Ivo; Riede, Wolfgang; Zoz, Jürgen
2013-10-01
High Energy Laser weapons (HEL) have unique attributes which distinguish them from limitations of kinetic energy weapons. HEL weapons engagement process typical starts with identifying the target and selecting the aim point on the target through a high magnification telescope. One scenario for such a HEL system is the countermeasure against rockets, artillery or mortar (RAM) objects to protect ships, camps or other infrastructure from terrorist attacks. For target identification and especially to resolve the aim point it is significant to ensure high resolution imaging of RAM objects. During the whole ballistic flight phase the knowledge about the expectable imaging quality is important to estimate and evaluate the countermeasure system performance. Hereby image quality is mainly influenced by unavoidable atmospheric turbulence. Analytical calculations have been taken to analyze and evaluate image quality parameters during an approaching RAM object. In general, Kolmogorov turbulence theory was implemented to determine atmospheric coherence length and isoplanatic angle. The image acquisition is distinguishing between long and short exposure times to characterize tip/tilt image shift and the impact of high order turbulence fluctuations. Two different observer positions are considered to show the influence of the selected sensor site. Furthermore two different turbulence strengths are investigated to point out the effect of climate or weather condition. It is well known that atmospheric turbulence degenerates image sharpness and creates blurred images. Investigations are done to estimate the effectiveness of simple tip/tilt systems or low order adaptive optics for laser based C-RAM systems.
Study of the Temperature Turbulences Effect upon Optical Beam in Atmospheric Optical Communication
Directory of Open Access Journals (Sweden)
F. Dvorak
2011-09-01
Full Text Available The paper deals with the study of the effect of temperature turbulences upon the optical beam. The polarization parameters of optical radiation sources and different optical beam states of polarization have been investigated. The obtained polarization parameters are projected on the Poincare sphere by means of Stokes vectors. The optical power distribution curves of optical beams are processed into diagrams. The horizontal and vertical components of linearly and circularly polarized optical beams have been studied. The turbulence flux has vertical direction and the optical beam is propagating through an atmosphere environment with three different states of turbulence. The evaluation of the obtained data was done by means of variance and correlation functions computing. Different rates of effect of temperature turbulences upon horizontal and vertical components were found. To reduce the rate of effect the advantage of an optical beam with circular polarization has been proposed.
Overestimation of closed-chamber soil CO2 effluxes at low atmospheric turbulence
DEFF Research Database (Denmark)
Brændholt, Andreas; Larsen, Klaus Steenberg; Ibrom, Andreas
2017-01-01
Soil respiration (R-s) is an important component of ecosystem carbon balance, and accurate quantification of the diurnal and seasonal variation of R-s is crucial for a correct interpretation of the response of R-s to biotic and abiotic factors, as well as for estimating annual soil CO2 efflux rates......, such that the highest effluxes were now observed during daytime, and also led to a substantial decrease in the estimated annual soil CO2 efflux.By installing fans to produce continuous turbulent mixing of air around the soil chambers, we tested the hypothesis that overestimation of soil CO2 effluxes during low u(*) can...... atmospheric turbulence conditions. Other possible effects from using fans during soil CO2 efflux measurements are discussed. In conclusion, periods with low atmospheric turbulence may provide a significant source of error in R-s rates estimated by the use of closed-chamber tech-niques and erroneous data must...
Li, Nan; Chu, Xiuxiang; Zhang, Pengfei; Feng, Xiaoxing; Fan, ChengYu; Qiao, Chunhong
2018-01-01
A method which can be used to compensate for a distorted orbital angular momentum and wavefront of a beam in atmospheric turbulence, simultaneously, has been proposed. To confirm the validity of the method, an experimental setup for up-link propagation of a vortex beam in a turbulent atmosphere has been simulated. Simulation results show that both of the distorted orbital angular momentum and the distorted wavefront of a beam due to turbulence can be compensated by an adaptive optics system with the help of a cooperative beacon at satellite. However, when the number of the lenslet of wavefront sensor (WFS) and the actuators of the deform mirror (DM) is small, satisfactory results cannot be obtained.
Measurements of indoor/outdoor atmospheric turbulence through optical triangulation method
de Oliveira, Gúbio; Silva, Vinicius N. H.; Barbero, Andrés P. L.; Ribeiro, Ricardo M.; Coelho, Thiago V. N.; Bessa dos Santos, A.
2017-05-01
Atmospheric turbulence degrades the performance of wireless optical communication links. This phenomenon distorts the light wave-front, and changes the spatial optical power distribution, spread and wander of the beam on the receiver plane. In this paper we present measurements of indoor and outdoor atmospheric turbulence taken using a simple and low-cost device based on an optical triangulation method. The device tracks a Gaussian beam due to the beam wander effect and measures the effective Gaussian width due to beam spread in order to calculate the refractive index structure constant in real time. Thus, the device operation principle, the outdoor/indoor turbulence profile during the day, the hotspot dispersion and the beam width variation are shown.
500 Gb/s free-space optical transmission over strong atmospheric turbulence channels.
Qu, Zhen; Djordjevic, Ivan B
2016-07-15
We experimentally demonstrate a high-spectral-efficiency, large-capacity, featured free-space-optical (FSO) transmission system by using low-density, parity-check (LDPC) coded quadrature phase shift keying (QPSK) combined with orbital angular momentum (OAM) multiplexing. The strong atmospheric turbulence channel is emulated by two spatial light modulators on which four randomly generated azimuthal phase patterns yielding the Andrews spectrum are recorded. The validity of such an approach is verified by reproducing the intensity distribution and irradiance correlation function (ICF) from the full-scale simulator. Excellent agreement of experimental, numerical, and analytical results is found. To reduce the phase distortion induced by the turbulence emulator, the inexpensive wavefront sensorless adaptive optics (AO) is used. To deal with remaining channel impairments, a large-girth LDPC code is used. To further improve the aggregate data rate, the OAM multiplexing is combined with WDM, and 500 Gb/s optical transmission over the strong atmospheric turbulence channels is demonstrated.
DEFF Research Database (Denmark)
Keck, Rolf-Erik; Veldkamp, Dick; Wedel-Heinen, Jens Jakob
evolution 4. atmospheric stability effects on wake deficit evolution and meandering The conducted research is to a large extent based on detailed wake investigations and reference data generated through computational fluid dynamics simulations, where the wind turbine rotor has been represented...... as a standalone flow-solver for the velocity and turbulence distribution, and power production in a wind farm. The performance of the standalone implementation is validated against field data, higher-order computational fluid dynamics models, as well as the most common engineering wake models in the wind industry....... 2. The EllipSys3D actuator line model, including the synthetic methods used to model atmospheric boundary layer shear and turbulence, is verified for modelling the evolution of wind turbine wake turbulence by comparison to field data and wind tunnel experiments. 3. A two-dimensional eddy viscosity...
Zhou, Guoquan; Cai, Yangjian; Chu, Xiuxiang
2012-04-23
The propagation of a partially coherent hollow vortex Gaussian beam through a paraxial ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity and the degree of the polarization of a partially coherent hollow vortex Gaussian beam through a paraxial ABCD optical system are derived in turbulent atmosphere, respectively. The average intensity distribution and the degree of the polarization of a partially coherent hollow vortex Gaussian beam in turbulent atmosphere are numerically demonstrated. The influences of the beam parameters, the topological charge, the transverse coherent lengths, and the structure constant of the atmospheric turbulence on the propagation of a partially coherent hollow vortex Gaussian beam in turbulent atmosphere are also examined in detail. This research is beneficial to the practical applications in free-space optical communications and the remote sensing of the dark hollow beams. © 2012 Optical Society of America
2012-06-01
The optical setup shown in Figure 2 is a Mach - Zehnder interferometer set up to characterize the LC SLM7. A linearly polarized beam at 45º enters a...combination with software that generates atmospheric turbulence gives the flexibility to simulate different atmospheric conditions and path lengths in the...closed-loop adaptive optics with a point-diffraction interferometer in strong scintillation with optical vortices”, Optics Express 15-21, 13745-13756
Toward defeating diffraction and randomness for laser beam propagation in turbulent atmosphere
Lushnikov, Pavel M.; Vladimirova, Natalia
2017-01-01
A large distance propagation in turbulent atmosphere results in disintegration of laser beam into speckles. We find that the most intense speckle approximately preserves both the Gaussian shape and the diameter of the initial collimated beam while loosing energy during propagation. One per 1000 of atmospheric realizations produces at 7km distance an intense speckle above 20\\% of the initial power. Such optimal realizations create effective extended lenses focusing the intense speckle beyond t...
2016-12-29
we consider the capabilities of a millimeter-wave radar to make atmospheric air flow measurements relevant to naval operations . The measurements could...Conclusions 14 References 14 1iii Millimeter Wave Radar for Atmospheric Turbulence Characterization and Wind Profiling for Improved Naval Operations Ben Rock... operations . We begin with a discussion of previous efforts to mitigate the aforementioned difficulties, and argue that millimeter wave radar techniques can be
Mei, Haiping; Rao, Ruizhong
2006-02-01
Optical turbulence degrades the quality of laser beam propagation and the quality of the image of optical system, limiting the spatial resolution that can be obtained. A novel single-air-gap fiber optical interferometric system useful for non-contact measurement of the fine structure of optical turbulence is presented. The main idea of this system is based on the application of a specially constructed optical fiber Mach-Zehnder interferometer to measure the phase fluctuations effected by the random fluctuations of refractive index in the turbulent atmosphere. The light source is a long coherence length infrared laser operating at the wavelength of 1.31μm and the optical path exposed to the atmosphere can be adjusted to a most suitable value according to the operational environment. Theoretical estimation illustrates that the system can measure the minimal atmospheric refractive index fluctuation up to 10 -10 during a 2cm propagation path. It is easy to have a calibration of the system and the result shows that the voltage refractive index sensitivity is about 2.1x10 -6 V -1. The system is integrated and well fixed in a burly airproof box with only the sensing arm exposed to the air. It follows that the system is suitable for the measurement of atmospheric turbulence over land and ocean surfaces.
An improved k-ε model applied to a wind turbine wake in atmospheric turbulence
DEFF Research Database (Denmark)
Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan
2015-01-01
An improved k-ε turbulence model is developed and applied to a single wind turbine wake in a neutral atmospheric boundary layer using a Reynolds averaged Navier–Stokes solver. The proposed model includes a flow-dependent Cμ that is sensitive to high velocity gradients, e.g., at the edge of a wind...
Atmospheric turbulence effects on the performance of the laser wireless power transfer system
Kapranov, V. V.; Matsak, I. S.; Tugaenko, V. Yu.; Blank, A. V.; Suhareva, N. A.
2017-02-01
Application of adaptive correction is necessary to control wandering of the laser beam in wireless power transfer (WPT) system. In this paper we describe experimental results of using different adaptive correction techniques for both weak and strong turbulence conditions. All experiments were performed over a 1.5 km near-horizontal atmospheric path. Some criteria for choosing parameters of adaptive correction are given.
Sonic Booms in Atmospheric Turbulence (SonicBAT) Ground Measurements in a Hot Desert Climate
Haering, Edward A., Jr.
2017-01-01
The Sonic Booms in Atmospheric Turbulence (SonicBAT) Project flew a series of 20 F-18 flights with 69 supersonic passes at Edwards Air Force Base in July 2016 to quantify the effect of atmospheric turbulence on sonic booms. Most of the passes were at a pressure altitude of 32,000 feet and a Mach number of 1.4, yielding a nominal sonic boom overpressure of 1.6 pounds per square foot. Atmospheric sensors such as GPS sondeballoons, Sonic Detection and Ranging (SODAR) acoustic sounders, and ultrasonic anemometers were used to characterize the turbulence state of the atmosphere for each flight. Spiked signatures in excess of 7 pounds per square foot were measured at some locations, as well as rounded sonic-boom signatures with levels much lower than the nominal. This presentation will quantify the range of overpressure and Perceived Level of the sonic boom as a function of turbulence parameters, and also present the spatial variation of these quantities over the array. Comparison with historical data will also be shown.
ACTIVE TURBULENCE AND SCALAR TRANSPORT NEAR THE FOREST-ATMOSPHERE INTERFACE
Turbulent velocity, temperature, water vapor concentration, and other scalars were measured at the canopy-atmosphere interface of a 13–14-m-tall uniform pine forest and a 33-m-tall nonuniform hardwood forest. These measurements were used to investigate whether the mixing la...
Simulating atmospheric turbulence using a phase-only spatial light modulator
CSIR Research Space (South Africa)
Burger, L
2008-04-01
Full Text Available transmission windows. The authors demonstrate the simulation of atmospheric turbulence in the laboratory using a phase-only spatial light modulator, and illustrate the advantages of this approach, as well as some of the limitations, when using spatial light...
Directory of Open Access Journals (Sweden)
C. M. St. Martin
2016-11-01
Full Text Available Using detailed upwind and nacelle-based measurements from a General Electric (GE 1.5sle model with a 77 m rotor diameter, we calculate power curves and annual energy production (AEP and explore their sensitivity to different atmospheric parameters to provide guidelines for the use of stability and turbulence filters in segregating power curves. The wind measurements upwind of the turbine include anemometers mounted on a 135 m meteorological tower as well as profiles from a lidar. We calculate power curves for different regimes based on turbulence parameters such as turbulence intensity (TI as well as atmospheric stability parameters such as the bulk Richardson number (RB. We also calculate AEP with and without these atmospheric filters and highlight differences between the results of these calculations. The power curves for different TI regimes reveal that increased TI undermines power production at wind speeds near rated, but TI increases power production at lower wind speeds at this site, the US Department of Energy (DOE National Wind Technology Center (NWTC. Similarly, power curves for different RB regimes reveal that periods of stable conditions produce more power at wind speeds near rated and periods of unstable conditions produce more power at lower wind speeds. AEP results suggest that calculations without filtering for these atmospheric regimes may overestimate the AEP. Because of statistically significant differences between power curves and AEP calculated with these turbulence and stability filters for this turbine at this site, we suggest implementing an additional step in analyzing power performance data to incorporate effects of atmospheric stability and turbulence across the rotor disk.
Simple method to measure effects of horizontal atmospherical turbulence at ground level
Tíjaro Rojas, Omar J.; Galeano Traslaviña, Yuber A.; Torres Moreno, Yezid
2016-09-01
The Kolmogorov's theory has been used to explain physical phenomena like the vertical turbulence in atmosphere, others recent works have made new advances and have improved K41 theory. In addition, this theory has been applied to studying different issues associated to measure atmospheric effects, and have special interest to find answers in optics to questions as e.g. at ground level, Could it find edges of two or more close objects, from a distant observer? (Classic resolution problem). Although this subject is still open, we did a model using the statistics of the centroid and the diameter of the laser beam propagated under horizontal turbulence at ground level until the object plane. The goal is to measure efficiently the turbulence effects in the long horizontal path propagation of electromagnetic wave. Natural movement of laser beam within the cavity needs be subtracted from the total transversal displacement in order to obtain a best approach. This simple proposed method is used to find the actual statistics of the centroid and beam diameter on the object plane where the turbulence introduces an additional transversal shift. And it has been tested for different values of horizontal distances under non-controlled environment in a synchronized acquisition scheme. Finally, we show test results in open very strong turbulence with high controlled temperature. This paper presents the implemented tests mainly into laboratory and discuss issues to resolve.
Black carbon solar absorption suppresses turbulence in the atmospheric boundary layer.
Wilcox, Eric M; Thomas, Rick M; Praveen, Puppala S; Pistone, Kristina; Bender, Frida A-M; Ramanathan, Veerabhadran
2016-10-18
The introduction of cloud condensation nuclei and radiative heating by sunlight-absorbing aerosols can modify the thickness and coverage of low clouds, yielding significant radiative forcing of climate. The magnitude and sign of changes in cloud coverage and depth in response to changing aerosols are impacted by turbulent dynamics of the cloudy atmosphere, but integrated measurements of aerosol solar absorption and turbulent fluxes have not been reported thus far. Here we report such integrated measurements made from unmanned aerial vehicles (UAVs) during the CARDEX (Cloud Aerosol Radiative Forcing and Dynamics Experiment) investigation conducted over the northern Indian Ocean. The UAV and surface data reveal a reduction in turbulent kinetic energy in the surface mixed layer at the base of the atmosphere concurrent with an increase in absorbing black carbon aerosols. Polluted conditions coincide with a warmer and shallower surface mixed layer because of aerosol radiative heating and reduced turbulence. The polluted surface mixed layer was also observed to be more humid with higher relative humidity. Greater humidity enhances cloud development, as evidenced by polluted clouds that penetrate higher above the top of the surface mixed layer. Reduced entrainment of dry air into the surface layer from above the inversion capping the surface mixed layer, due to weaker turbulence, may contribute to higher relative humidity in the surface layer during polluted conditions. Measurements of turbulence are important for studies of aerosol effects on clouds. Moreover, reduced turbulence can exacerbate both the human health impacts of high concentrations of fine particles and conditions favorable for low-visibility fog events.
Liu, Yang; Zhang, Guo-an
2014-09-01
In order to mitigate atmospheric turbulence, the free space optical (FSO) system model with spatial diversity is analyzed based on intensity detection pulse position modulation (PPM) in the weak turbulence atmosphere. The slot error rate (SER) calculating formula of the system without diversity is derived under pulse position modulation firstly. Then as a benchmark, independent of identical distribution, the average slot error rates of the three linear combining technologies, which are the maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SelC), are compared. Simulation results show that the performance of system is the best improved by MRC, followed by EGC, and is poor by SelC, but SelC is simpler and more convenient. Spatial diversity is efficient to improve the performance and has strong ability on resistance to atmospheric channel decline. The above scheme is more suitable for optical wireless communication systems.
Puryear, Andrew L.; Shapiro, Jeffrey H.; Parenti, Ronald R.
2012-10-01
Free-space optical communication provides rapidly deployable, dynamic communication links that are capable of very high data rates compared with those of radio-frequency systems. As such, free-space optical communication is ideal for mobile platforms, for platforms that require the additional security afforded by the narrow divergence of a laser beam, and for systems that must be deployed in a relatively short time frame. In clear-weather conditions the data rate and utility of free-space optical communication links are primarily limited by fading caused by micro-scale atmospheric temperature variations that create parts-per-million refractive-index fluctuations known as atmospheric turbulence. Typical communication techniques to overcome turbulence-induced fading, such as interleavers with sophisticated codes, lose viability as the data rate is driven higher or the delay requirement is driven lower. This paper, along with its companion [J. H. Shapiro and A. Puryear, "Reciprocity-Enhanced Optical Communication through Atmospheric Turbulence-Part I: Reciprocity Proofs and Far-Field Power Transfer"], present communication systems and techniques that exploit atmospheric reciprocity to overcome turbulence which are viable for high data rate and low delay requirement systems. Part I proves that reciprocity is exhibited under rather general conditions, and derives the optimal power-transfer phase compensation for far-field operation. The Part II paper presents capacity-achieving architectures that exploit reciprocity to overcome the complexity and delay issues that limit state-of-the art free-space optical communications. Further, this paper uses theoretical turbulence models to determine the performance—delay, throughput, and complexity—of the proposed architectures.
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...
Marlton, Graeme; Harrison, Giles; Nicoll, Keri; Williams, Paul
2017-04-01
This work describes the instrument development, characterisation and data analysis from 51 radiosondes specially equipped with accelerometers to measure atmospheric turbulence. Turbulence is hazardous to aircraft as it cannot be observed in advance. It is estimated that turbulence costs the airline industry millions of US dollars a year through damage to aircraft and injuries to passengers and crew. To avoid turbulence pilots and passengers rely on Clear Air Turbulence forecasts, which have limited skill. One limitation in this area is lack of quantitative unbiased observations. The main source of turbulence observations is from commercial airline pilot reports, which are subjective, biased by the size of aircraft and pilot experience. This work seeks to improve understanding of turbulence through a standardised method of turbulence observations amenable throughout the troposphere. A sensing package has been developed to measure the acceleration of the radiosonde as it swings in response to turbulent agitation of its carrier balloon. The accelerometer radiosonde has been compared against multiple turbulence remote sensing methods to characterise its measurements including calibration with Doppler lidar eddy dissipation rate in the boundary layer. A further relationship has been found by comparison with the spectral width of a Mesospheric, Stratospheric and Tropospheric (MST) radar. From the full dataset of accelerometer sonde ascents a standard deviation of 5 m s-2 is defined as a threshold for significant turbulence. The dataset spans turbulence generated in meteorological phenomena such as jet streams, clouds and in the presence of convection. The analysis revealed that 77% of observed turbulence could be explained by the aforementioned phenomena. In jet streams, turbulence generation was often caused by horizontal processes such as deformation. In convection, turbulence is found to form when CAPE >150 J kg-1. Deeper clouds were found to be more turbulent due to
Smoothed Spectra, Ogives, and Error Estimates for Atmospheric Turbulence Data
Dias, Nelson Luís
2017-09-01
A systematic evaluation is conducted of the smoothed spectrum, which is a spectral estimate obtained by averaging over a window of contiguous frequencies. The technique is extended to the ogive, as well as to the cross-spectrum. It is shown that, combined with existing variance estimates for the periodogram, the variance—and therefore the random error—associated with these estimates can be calculated in a straightforward way. The smoothed spectra and ogives are biased estimates; with simple power-law analytical models, correction procedures are devised, as well as a global constraint that enforces Parseval's identity. Several new results are thus obtained: (1) The analytical variance estimates compare well with the sample variance calculated for the Bartlett spectrum and the variance of the inertial subrange of the cospectrum is shown to be relatively much larger than that of the spectrum. (2) Ogives and spectra estimates with reduced bias are calculated. (3) The bias of the smoothed spectrum and ogive is shown to be negligible at the higher frequencies. (4) The ogives and spectra thus calculated have better frequency resolution than the Bartlett spectrum, with (5) gradually increasing variance and relative error towards the low frequencies. (6) Power-law identification and extraction of the rate of dissipation of turbulence kinetic energy are possible directly from the ogive. (7) The smoothed cross-spectrum is a valid inner product and therefore an acceptable candidate for coherence and spectral correlation coefficient estimation by means of the Cauchy-Schwarz inequality. The quadrature, phase function, coherence function and spectral correlation function obtained from the smoothed spectral estimates compare well with the classical ones derived from the Bartlett spectrum.
Optical seeing-mechanism of formation of thin turbulent laminae in the atmosphere.
Coulman, C E; Vernin, J; Fuchs, A
1995-08-20
Data from balloon soundings taken at sites in the Canary Islands, France, and Chile are used to show that hydrodynamic instability, perhaps engendered by the propagation of buoyancy (gravity) or other waves, leads to the formation of thin, turbulent laminae, or "seeing layers." These seeing layers occur almost invariably in pairs and exhibit large values for the temperature-structure coefficient C(T)(2) because they form where the gradient of temperature is particularly steep. The refractive-index-structure coefficient is correspondingly large, and so these layers adversely affect the quality of optical propagation. The mechanism proposed here is already known to create clear air turbulence in the stratosphere, and we show how it is consistent with the formation of thin turbulent seeing layers in the troposphere and the stratosphere at night, when the atmosphere is generally stably stratified.
Woo, R.; Ishimaru, A.
1973-01-01
The purpose of this paper is to analyze the effects of small-scale turbulence on radio waves propagating through a planetary atmosphere. The analysis provides a technique for inferring the turbulence characteristics of a planetary atmosphere from the radio signals received from a spacecraft as it is occulted by the planet. The planetary turbulence is assumed to be localized and smoothly varying, with the structure constant varying exponentially with altitude. Rytov's method is used to derive the variance of log-amplitude and phase fluctuations of a wave propagating through the atmosphere.
Overestimation of closed-chamber soil CO2 effluxes at low atmospheric turbulence
Brændholt, Andreas; Steenberg Larsen, Klaus; Ibrom, Andreas; Pilegaard, Kim
2017-03-01
Soil respiration (Rs) is an important component of ecosystem carbon balance, and accurate quantification of the diurnal and seasonal variation of Rs is crucial for a correct interpretation of the response of Rs to biotic and abiotic factors, as well as for estimating annual soil CO2 efflux rates. In this study, we measured Rs hourly for 1 year by automated closed chambers in a temperate Danish beech forest. The data showed a clear diurnal pattern of Rs across all seasons with higher rates during night-time than during daytime. However, further analysis showed a clear negative relationship between flux rates and friction velocity (u∗) above the canopy, suggesting that Rs was overestimated at low atmospheric turbulence throughout the year due to non-steady-state conditions during measurements. Filtering out data at low u∗ values removed or even inverted the observed diurnal pattern, such that the highest effluxes were now observed during daytime, and also led to a substantial decrease in the estimated annual soil CO2 efflux. By installing fans to produce continuous turbulent mixing of air around the soil chambers, we tested the hypothesis that overestimation of soil CO2 effluxes during low u∗ can be eliminated if proper mixing of air is ensured, and indeed the use of fans removed the overestimation of Rs rates during low u∗. Artificial turbulent air mixing may thus provide a method to overcome the problems of using closed-chamber gas-exchange measurement techniques during naturally occurring low atmospheric turbulence conditions. Other possible effects from using fans during soil CO2 efflux measurements are discussed. In conclusion, periods with low atmospheric turbulence may provide a significant source of error in Rs rates estimated by the use of closed-chamber techniques and erroneous data must be filtered out to obtain unbiased diurnal patterns, accurate relationships to biotic and abiotic factors, and before estimating Rs fluxes over longer timescales.
Chen, Chunyi; Yang, Huamin
2017-05-29
Expressions for the correlation coefficient between light-flux fluctuations of two waves counter-propagating along a common path in weak turbulence are developed. Only the aperture and inner-scale Fresnel parameters are needed for evaluation of the correlation coefficient if the turbulence spectrum has no path dependence, and of the path weighting functions for the cross-covariance and variances of normalized light-flux fluctuations if the turbulence spectrum is dependent on path locations. Under the condition that atmospheric turbulence is statistically homogeneous over a path, although good correlation between light-flux fluctuations of two counter-propagating spherical waves may be achieved for a relatively small aperture Fresnel parameter or relatively large inner-scale Fresnel parameter, the correlation coefficient between light-flux fluctuations of two counter-propagating plane waves is always lower than 1 obviously. When the aperture Fresnel parameter becomes larger than the inner-scale Fresnel parameter, the inner scale of turbulence tends to play an unimportant role in determining the correlation coefficient.
Wang, Yukun; Xu, Huanyu; Li, Dayu; Wang, Rui; Jin, Chengbin; Yin, Xianghui; Gao, Shijie; Mu, Quanquan; Xuan, Li; Cao, Zhaoliang
2018-01-18
The performance of free-space optics communication (FSOC) is greatly degraded by atmospheric turbulence. Adaptive optics (AO) is an effective method for attenuating the influence. In this paper, the influence of the spatial and temporal characteristics of turbulence on the performance of AO in a FSOC system is investigated. Based on the Greenwood frequency (GF) and the ratio of receiver aperture diameter to atmospheric coherent length (D/r 0 ), the relationship between FSOC performance (CE) and AO parameters (corrected Zernike modes number and bandwidth) is derived for the first time. Then, simulations and experiments are conducted to analyze the influence of AO parameters on FSOC performance under different GF and D/r 0 . The simulation and experimental results show that, for common turbulence conditions, the number of corrected Zernike modes can be fixed at 35 and the bandwidth of the AO system should be larger than the GF. Measurements of the bit error rate (BER) for moderate turbulence conditions (D/r 0 = 10, f G = 60 Hz) show that when the bandwidth is two times that of GF, the average BER is decreased by two orders of magnitude compared with f G /f 3dB = 1. These results and conclusions can provide important guidance in the design of an AO system for FSOC.
Wilson
2000-11-01
A three-dimensional model for turbulent velocity fluctuations in the atmospheric boundary layer is developed and used to calculate scattering of sound. The model, which is based on von Karman's spectrum, incorporates separate contributions from shear- and buoyancy-forced turbulence. New equations are derived from the model that predict the strength and diffraction parameters for scattering of sound as a function of height from the ground and atmospheric conditions. The need is demonstrated for retaining two distinct scattering length scales, one associated with scattering strength and the other with diffraction. These length scales are height dependent and vary substantially with the relative proportions of shear and buoyancy forcing. The turbulence model predicts that for forward-scattered waves the phase variance is much larger than the log-amplitude variance, a behavior borne out by experimental data. A new method for synthesizing random fields, based on empirical orthogonal functions, is developed to accommodate the height dependence of the turbulence model. The method is applied to numerical calculations of scattering into an acoustic shadow zone, yielding good agreement with previous measurements.
Characterization of atmospheric turbulence during the NATO RTG-40 land field trials
Tofsted, David; O'Brien, Sean; Yarbrough, Jimmy; Quintis, David; Bustillos, Manuel
2007-04-01
The NATO RTG-40 Active Imaging Land Field Trials were conducted at the High Energy Laser System Test Facility at White Sands Missile Range, NM, during November of 2005. This experiment intercompared six active imager systems operating in the visible, near-infrared, and short-wave infrared sensing bands. To characterize the atmospheric turbulence structure present during the optical measurements eight scintillometers were arranged along or near the atmospheric path to characterize the vertical and temporal structure of scintillation, and inner and outer scales of turbulence. A met mast, two 32-m met towers, and an 8-m tower complemented the scintillometer data. This report focuses on analysis of data from four 3-D sonic anemometers positioned at midrange on the 8-m tower and on four of the scintillometers arranged along the 2-km propagation path. First and second order statistics from the sonic sensors are illustrated, along with an analysis of the turbulence spectrum measured by the sonic temperature sensors. The analysis of this data should support both estimating turbulence strength using sonic anemometers as well as outer scale. The data acquired throughout the 10-day measurement period and have proved useful in characterization of the overall weather conditions present during testing and in prediction of various surface layer characteristics.
Liu, Dachang; Wang, Zixiong; Liu, Jianguo; Tan, Jun; Yu, Lijuan; Mei, Haiping; Zhou, Yusong; Zhu, Ninghua
2017-10-01
The performance of a free-space optical communication system is highly affected by the atmospheric turbulence in terms of scintillation. An optical communication system based on intensity-modulation direct-detection was built with 1-km transmission distance to evaluate the bit error rate (BER) performance over real atmospheric turbulence. 2.5-, 5-, and 10-Gbps data rate transmissions were carried out, where error-free transmission could be achieved during over 37% of the 2.5-Gbps transmissions and over 43% of the 5-Gbps transmissions. In the rest of the transmissions, BER deteriorated as the refractive-index structure constant increased, while the two measured items have almost the same trend.
Yang, Liang
2014-04-01
Free-space optical (FSO) communication has become a cost-effective method to provide high data rates. However, the turbulence-induced fading limits its application to short-range applications. To address this, we propose a multiuser diversity (MD) FSO scheme in which the Nth best user is selected and the channel fluctuations can be effectively exploited to produce a selection diversity gain. More specifically, we first present the statistics analysis for the considered system over both weak and strong atmospheric turbulence channels. Based on these statistics, the outage probability, bit-error rate performance, average capacity, diversity order, and coverage are analyzed. Results show that the diversity order for the gamma-gamma fading is N min{α, β}/2, where N is the number of users, and α and β are the channel fading parameters related to the effective atmospheric conditions of the link.
Avila, R.; Aviles, J. L.; Wilson, R. W.; Chun, M.; Butterley, T.; Carrasco, E.
2008-01-01
We report the development and first results of an instrument called Low Layer Scidar (LOLAS) which is aimed at the measurement of optical-turbulence profiles in the atmospheric boundary layer with high altitude-resolution. The method is based on the Generalized Scidar (GS) concept, but unlike the GS instruments which need a 1- m or larger telescope, LOLAS is implemented on a dedicated 40-cm telescope, making it an independent instrument. The system is designed for widely separated double-star...
1992-12-01
traveling from space to Earth are distorted when they pass through the Earth’s atmosphere. This distortion gives rise to the well known twinkling...same point in space at all times. Such an approach requires knowledge of the quantity being measured, therefore the variance of the intersection will...IEEE, 66:651-697 (June 1978). 9. Kolmogoroff , A. N. "The Local Structure of Turbulence in Incompressible Viscous Fluids for Very Large Reynolds
Interferometry through the turbulent atmosphere at an optical path difference of 354 m.
Herrick, R B; Meyer-Arendt, J R
1966-06-01
A modified Michelson interferometer with a stable He-Ne laser source has been used to study fluctuations in the mean refractive index over a long path through the turbulent atmosphere. Distinct interference fringes were obtained at mirror separations up to 177 m, corresponding to an optical path difference of 354 m. The spatial stability of the interference fringes was found to decrease with increasing optical path length, indicating an increasing contribution from the atmosphere. Details of the interferometer and the experimental procedure are given as well as a discussion of the fluctuations in the mean refractive index.
DEFF Research Database (Denmark)
Ostashev, Vladimir E.; Wilson, D. K.; Finn, Anthony
2016-01-01
The acoustic spectrum emitted by unmanned aerial vehicles (UAVs) and other aircraft can be distorted by propagation through atmospheric turbulence. Since most UAVs are propeller-based, they generate a series of acoustic tones and harmonics. In this paper, spectral broadening of these tones due......, spectral broadening is calculated and analyzed for typical meteorological regimes of the atmospheric boundary layer and different flight trajectories of UAVs. Experimental results are presented and compared with theoretical predictions. Spectral broadening might also provide a means for remotely sensing...
Harger, R. O.
1974-01-01
Abstracts are reported relating to the techniques used in the research concerning optical transmission of information. Communication through the turbulent atmosphere, quantum mechanics, and quantum communication theory are discussed along with the results.
Gudadze, N.; Chau, J. L.; Stober, G.; Latteck, R.
2016-12-01
Mesosphere-lower-thermosphere (MLT) polar dynamics are interesting and important subject for study in atmospheric physic. It is considered that mesopause region is where the main part of the Atmospheric gravity waves breaks and/or dissipates. However this region is difficult to observe. Continuous Observations of the polar summer mesosphere with the Middle Atmosphere Alomar Radar System (MAARSY) and its predecessor the ALOMAR-Wind-Radar (ALWIN) (before 2010), have been used to investigate dynamical structures of well-known phenomenon - Polar Mesosphere Summer Echoes (PMSE) which is an important tracer in the summer polar mesopause region. Signal to Noise Ratio (SNR) and Doppler radial velocity from the PMSE are used to investigate the wave-like motions with periods larger than 5 minutes. Such oscillations are studied in terms of atmospheric gravity waves (AGWs). Processes also connected with AGWs as PMSE layering, are studied in connection with the background conditions of the neutral atmosphere as well. Background winds are obtained from collocated meteor radar (MR). We used local enhancement method for the processing of altitude-time SNR images to detect layers in the PMSEs and characterised them. Our preliminary results indicate that PMSE strength and behaviour is correlated with the meridional wind. Furthermore we found that the spectral width (SW), which is a proxy of turbulence, is most of the time weakly dependent on SNR strength. However, there are some events where SW is highly dependent on SNR intensity indicating that they could be associated to turbulent-dominated events.
Characteristics of ground-based adaptive telescope determined by atmospheric turbulence
Lukin, Vladimir P.
1996-08-01
Numerical simulation on a computer is one of the main methods used for studying the possibilities of adaptive correction of turbulent distortions of imaging forming in the atmosphere. The problem of compensation for atmospheric distortions of a wave front has been studied sufficiently long. The first papers on this subject were published in the mid-1960's. At that time, however, the engineering base gives no way for designing the efficient devices for compensating for atmospheric distortions. In recent years much progress has been reached in developing wave front distortion meters and correctors and then fitting the optical facilities operating under atmospheric distortions with these devices. In this connection an increased interest of researchers is observed to the theoretical works concerning with selection of an optical design and configuration of the wave front corrections.
Directory of Open Access Journals (Sweden)
J. Picot
2015-07-01
Full Text Available In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES coupled to a Lagrangian particle tracking method to treat the ice phase. In this paper, fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere and lower stratosphere. The initial flow field is composed of the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail descent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex breakup dominates over background turbulence until the end of the vortex regime and controls the mixing with ambient air. This results in mean microphysical characteristics such as ice mass and optical depth that are slightly affected by the intensity of atmospheric turbulence. However, the background humidity and temperature have a first-order effect on the survival of ice crystals and particle size distribution, which is in line with recent studies.
An observational investigation of transitory turbulence in the atmospheric boundary layer
Jensen, Derek D.
Within the atmospheric boundary layer (ABL), atmospheric fluid flow is in a constant state of transition in both time and space. Under calm conditions through the mid-daytime hours and over quasi-uniform terrain, the temporal and spatial evolution of the atmosphere is gradual. The structure and governing equations are well understood, allowing for numerical models to accurately forecast the evolution of the ABL. Under nocturnal conditions, the atmospheric processes are more complicated, yet numerical models still perform reasonably well. When changes in the state of the atmosphere occur abruptly, whether in time or space, the fidelity of most numerical weather models diminishes appreciably. This occurs because many of the simplifying assumptions intrinsic in most numerical models are no longer valid. The objective of this dissertation is to use observational data collected within such transitions to gain more insight into the mechanisms responsible for the evolution of the rapidly evolving ABL. First, near-surface turbulence data are used to study countergradient heat fluxes that occur through the evening transition. The countergradient heat flux may be produced by the sign change of the sensible heat flux preceding the sign change of the local temperature gradient and vice versa. The phenomenon is studied by considering the budget equations of both temperature and sensible heat flux. The behaviour of the countergradient heat flux is governed by the surface and subsurface characteristics. The duration of the countergradient flux may be prognosed by considering a ratio of terms in the heat flux budget equation evaluated during the mid- to late afternoon. Next, data collected over an arid shallow slope (2-4°) are used to study the structure and onset of katabatic flow through the evening transition. The katabatic onset, jet velocity and jet height all show a large degree of interdiurnal variability. The slope-aligned budgets of momentum and potential temperature are
Wang, Qiang
2015-07-22
The blow-out limits of nonpremixed turbulent jet flames in cross flows were studied, especially concerning the effect of ambient pressure, by conducting experiments at atmospheric and sub-atmospheric pressures. The combined effects of air flow and pressure were investigated by a series of experiments conducted in an especially built wind tunnel in Lhasa, a city on the Tibetan plateau where the altitude is 3650 m and the atmospheric pressure condition is naturally low (64 kPa). These results were compared with results obtained from a wind tunnel at standard atmospheric pressure (100 kPa) in Hefei city (altitude 50 m). The size of the fuel nozzles used in the experiments ranged from 3 to 8 mm in diameter and propane was used as the fuel. It was found that the blow-out limit of the air speed of the cross flow first increased (“cross flow dominant” regime) and then decreased (“fuel jet dominant” regime) as the fuel jet velocity increased in both pressures; however, the blow-out limit of the air speed of the cross flow was much lower at sub-atmospheric pressure than that at standard atmospheric pressure whereas the domain of the blow-out limit curve (in a plot of the air speed of the cross flow versus the fuel jet velocity) shrank as the pressure decreased. A theoretical model was developed to characterize the blow-out limit of nonpremixed jet flames in a cross flow based on a Damköhler number, defined as the ratio between the mixing time and the characteristic reaction time. A satisfactory correlation was obtained at relative strong cross flow conditions (“cross flow dominant” regime) that included the effects of the air speed of the cross flow, fuel jet velocity, nozzle diameter and pressure.
Large- and small-scale turbulent spectra in MHD and atmospheric flows
Directory of Open Access Journals (Sweden)
O. G. Chkhetiani
2006-01-01
Full Text Available In the present review we discuss certain studies of large- and small-scale turbulent spectra in MHD and atmospheric flows performed by S. S. Moiseev and his co-authors during the last years of his life and continued by his co-authors after he passed away. It is shown that many ideas developed in these works have not lost their novelty and urgency until now, and can form the basis of future studies in this field.
Flat-topped Gaussian laser beam scintillation in weakly turbulent marine atmospheric medium
Gerçekcioğlu, Hamza; Abbas, Ahmed A.; Göktaş, H. Haldun
2017-09-01
In a weakly marine turbulent medium, formulation of the on-axis scintillation index of a flat topped Gaussian beam is derived by using the Rytov method and the intensity has log-normal distribution expressed. The scintillation index and average bit error rate with respect to changes in propagation distance, wavelength, beam size, and average signal to noise ratio are exhibited. Our results indicated that small advantage can be achieved in weak atmospheric marine when focal length equals to propagation distance and when the order of flatness is small value.
Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels
Benkhelifa, Fatma
2013-01-27
In this paper, we study the ergodic capacity of free space optical communication systems over Gamma-Gamma atmospheric turbulence fading channels with perfect channel state information at both the transmitter and the receiver. In our framework, we mainly focus on the low signal-to-noise ratio range and show that the ergodic capacity scales proportionally to SNR log^4(1/SNR). We show also that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-o ff power control scheme.
Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels
Benkhelifa, Fatma
2013-02-23
In this paper, we study the ergodic capacity of free space optical communication systems over Gamma-Gamma atmospheric turbulence fading channels with perfect channel state information at both the transmitter and the receiver. In our framework, we mainly focus on the low signal-to-noise ratio range and show that the ergodic capacity scales proportionally to SNR log^4(1/SNR). We show also that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-off power control scheme.
1991-01-11
distribution unlimited Prepared for: Naval Research Laboratory Washington, D.C. 20375 WL/ARCA Kirtland Air Force Base New Mexico 97117 NAVAL POSTGRADUATE...AFB ELEMENT NO NO NO :CCESSON NO 20375 New Mexico 87117 11 TITLE (Include Security Classification) ATMOSPHERIC OPTICAL TURBULENCE MEASUREMENTS TAKEN...Value Dominant % >= (UTC) (mm) Conditions "Good" I (urad) Conditions "Good" 13 91.6 Mediocre(74%) 25 1 11.86 Medio /Good(49%)49 14 77.5 MBdiocre(89%) 8
Smalikho, Igor N.; Banakh, Viktor A.
2017-11-01
The method and results of lidar studies of spatiotemporal variability of wind turbulence in the atmospheric boundary layer are reported. The measurements were conducted by a Stream Line pulsed coherent Doppler lidar (PCDL) with the use of conical scanning by a probing beam around the vertical axis. Lidar data are used to estimate the kinetic energy of turbulence, turbulent energy dissipation rate, integral scale of turbulence, and momentum fluxes. The dissipation rate was determined from the azimuth structure function of radial velocity within the inertial subrange of turbulence. When estimating the kinetic energy of turbulence from lidar data, we took into account the averaging of radial velocity over the sensing volume. The integral scale of turbulence was determined on the assumption that the structure of random irregularities of the wind field is described by the von Kármán model. The domain of applicability of the used method and the accuracy of the estimation of turbulence parameters were determined. Turbulence parameters estimated from Stream Line lidar measurement data and from data of a sonic anemometer were compared.
Avila, R.; Avilés, J. L.; Wilson, R. W.; Chun, M.; Butterley, T.; Carrasco, E.
2008-07-01
We report the development and first results of an instrument called Low Layer SCIDAR (Scintillation Detection and Ranging) (LOLAS) which is aimed at the measurement of optical-turbulence profiles in the atmospheric boundary layer with high altitude resolution. The method is based on the Generalized SCIDAR (GS) concept, but unlike the GS instruments which need a 1-m or larger telescope, LOLAS is implemented on a dedicated 40-cm telescope, making it an independent instrument. The system is designed for widely separated double-star targets, which enables the high altitude resolution. Using a 200-arcsec-separation double star, we have obtained turbulence profiles with unprecedented 12-m resolution. The system incorporates necessary novel algorithms for autoguiding, autofocus and image stabilization. The results presented here were obtained at Mauna Kea Observatory. They show LOLAS capabilities but cannot be considered as representative of the site. A forthcoming paper will be devoted to the site characterization. The instrument was built as part of the Ground Layer Turbulence Monitoring Campaign on Mauna Kea for Gemini Observatory.
Sound propagation in a turbulent atmosphere near the ground: a parabolic equation approach.
Ostashev, V E; Salomons, E M; Clifford, S F; Lataitis, R J; Wilson, D K; Blanc-Benon, P; Juvé, D
2001-05-01
The interference of the direct wave from the point source to the receiver and the wave reflected from the impedance ground in a turbulent atmosphere is studied. A parabolic equation approach for calculating the sound pressure p at the receiver is formulated. Then, the parabolic equation is solved by the Rytov method yielding expressions for the complex phases of direct and ground-reflected waves. Using these expressions, a formula for the mean squared sound pressure [absolute value(p)2] is derived for the case of anisotropic spectra of temperature and wind velocity fluctuations. This formula contains the "coherence factor," which characterizes the coherence between direct and ground-reflected waves. It is shown that the coherence factor is equal to the normalized coherence function of a spherical sound wave for line-of-sight propagation. For the case of isotropic turbulence, this result allows one to obtain analytical formulas for [absolute value(p)2] for the Kolmogorov, Gaussian, and von Karman spectra of temperature and wind velocity fluctuations. Using these formulas, the effects of temperature and wind velocity fluctuations, and the effects of different spectra of these fluctuations on the mean squared sound pressure, are numerically studied. Also the effect of turbulent anisotropy on the interference of direct and ground reflected waves is numerically studied. Finally, it is shown that the mean squared sound pressure [absolute value(p)2] calculated for the von Karman spectrum of temperature fluctuations agrees well with experimental data obtained in a laboratory experiment.
The formation of snow streamers in the turbulent atmosphere boundary layer
Huang, Ning; Wang, Zheng-Shi
2016-12-01
The drifting snow in the turbulent atmosphere boundary layer is an important type of aeolian multi-phase flow. Current theoretical and numerical studies of drifting snow mostly consider the flow field as steady wind velocity. Whereas, little is known about the effects of turbulent wind structures on saltating snow particles. In this paper, a 3-D drifting snow model based on Large Eddy Simulation is established, in which the trajectory of every snow grain is calculated and the coupling effect between wind field and snow particles is considered. The results indicate that the saltating snow particles are re-organized by the suction effect of high-speed rotating vortexes, which results in the local convergence of particle concentration, known as snow streamers. The turbulent wind leads to the spatial non-uniform of snow particles lifted by aerodynamic entrainment, but this does not affect the formation of snow streamers. Whereas the stochastic grain-bed interactions make a great contribution to the final shapes of snow streamers. Generally, snow streamers display a characteristic length about 0.5 m and a characteristic width of approximately 0.16 m, and their characteristic sizes are not sensitive to the wind speed. Compared to the typical sand streamer, snow streamer is slightly narrower and the occurrence of other complex streamer patterns is later than that of sand streamers due to the better follow performance of snow grains with air flow.
Statistics of atmospheric turbulence at Cerro Pachon using the GeMS profiler
Rodriguez, Ignacio; Neichel, Benoit; Béchet, Clémentine; Guzmán, Dani; Guesalaga, Andrés.
2014-08-01
The knowledge of the atmospheric turbulence profile directly above the telescope using the telemetry from wide-field Adaptive Optics (AO) measurements can be extremely useful for the optimization of the correction in the new generation of AO systems. For this purpose, two techniques have been recently implemented at the Gemini South MCAO System (GeMS); both based on the SLODAR method. The first technique uses a matrix inversion approach of the slopes covariance matrices and the second deconvolves the cross-correlation functions between all combinations of slopes using the auto-correlation responses. The deconvolution approach has proved to be more reliable that the one based on matrices inversion, so we use it for estimating the profiles from on-sky telemetry gathered over three years (2012 - 2014), obtaining statistical parameters of the turbulence at Cerro Pachón. These results are summarized in this article. Particular attention is paid to the occurrence of turbulence in the dome of the Gemini South telescope.
Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts.
Piacsek, Andrew A
2002-01-01
The propagation and subsequent distortion of sonic booms with rippled wave fronts are investigated theoretically using a nonlinear time-domain finite-difference scheme. This work seeks to validate the rippled wave front approach as a method for explaining the significant effects of turbulence on sonic booms [A. S. Pierce and D. J. Maglieri, J. Acoust. Soc. Am. 51, 702-721 (1971)]. A very simple description of turbulence is employed in which velocity perturbations within a shallow layer of the atmosphere form strings of vortices characterized by their size and speed. Passage of a steady-state plane shock front through such a vortex layer produces a periodically rippled wave front which, for the purposes of the present investigation, serves as the initial condition for a finite-difference propagation scheme. Results show that shock strength and ripple curvature determine whether ensuing propagation leads to wave front folding. High resolution images of the computed full wave field provide insights into the spiked and rounded features seen in sonic booms that have propagated through turbulence.
On the Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels Using OOK Signaling
Directory of Open Access Journals (Sweden)
Antonio García-Zambrana
2010-01-01
Full Text Available A new upper bound on the capacity of power- and bandwidth-constrained optical wireless links over gamma-gamma atmospheric turbulence channels with intensity modulation and direct detection is derived when on-off keying (OOK formats are used. In this free-space optical (FSO scenario, unlike previous capacity bounds derived from the classic capacity of the well-known additive white Gaussian noise (AWGN channel with uniform input distribution, a new closed-form upper bound on the capacity is found by bounding the mutual information subject to an average optical power constraint and not only to an average electrical power constraint, showing the fact that the input distribution that maximizes the mutual information varies with the turbulence strength and the signal-to-noise ratio (SNR. Additionally, it is shown that an increase of the peak-to-average optical power ratio (PAOPR provides higher capacity values. Simulation results for the mutual information are further demonstrated to confirm the analytical results under several turbulence conditions.
Energy Technology Data Exchange (ETDEWEB)
J. KAO; D. COOPER; ET AL
2000-11-01
As lidar technology is able to provide fast data collection at a resolution of meters in an atmospheric volume, it is imperative to promote a modeling counterpart of the lidar capability. This paper describes an integrated capability based on data from a scanning water vapor lidar and a high-resolution hydrodynamic model (HIGRAD) equipped with a visualization routine (VIEWER) that simulates the lidar scanning. The purpose is to better understand the spatial and temporal representativeness of the lidar measurements and, in turn, to extend their utility in studying turbulence fields in the atmospheric boundary layer. Raman lidar water vapor data collected over the Pacific warm pool and the simulations with the HIGRAD code are used for identifying the underlying physics and potential aliasing effects of spatially resolved lidar measurements. This capability also helps improve the trade-off between spatial-temporal resolution and coverage of the lidar measurements.
Strauss, Lukas; Serafin, Stefano; Haimov, Samuel; Grubišić, Vanda
2015-10-01
Atmospheric turbulence generated in flow over mountainous terrain is studied using airborne in situ and cloud radar measurements over the Medicine Bow Mountains in southeast Wyoming, USA. During the NASA Orographic Clouds Experiment (NASA06) in 2006, two complex mountain flow cases were documented by the University of Wyoming King Air research aircraft carrying the Wyoming Cloud Radar. The structure of turbulence and its intensity across the mountain range are described using the variance of vertical velocity σw2 and the cube root of the energy dissipation rate ɛ1/3 (EDR). For a quantitative analysis of turbulence from the cloud radar, the uncertainties in the Doppler wind retrieval have to be taken into account, such as the variance of hydrometeor fall speed and the contamination of vertical Doppler velocity by the horizontal wind. A thorough analysis of the uncertainties shows that 25% accuracy or better can be achieved in regions of moderate to severe turbulence in the lee of the mountains, while only qualitative estimates of turbulence intensity can be obtained outside the most turbulent regions. Two NASA06 events exhibiting large-amplitude mountain waves, mid-tropospheric wave breaking, and rotor circulations are examined. Moderate turbulence is found in a wave-breaking region with σw2 and EDR reaching 4.8 m2 s-2 and 0.25 m2/3 s-1, respectively. Severe turbulence is measured within the rotor circulations with σw2 and EDR respectively in the ranges of 7.8-16.4 m2 s-2 and 0.50-0.77 m2/3 s-1. A unique result of this study is the quantitative estimation of the intensity of turbulence and its spatial distribution in the interior of atmospheric rotors, provided by the radar-derived turbulence fields.
Han, Jongil; Arya, S. Pal; Shaohua, Shen; Lin, Yuh-Lang; Proctor, Fred H. (Technical Monitor)
2000-01-01
Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.
Zheng, Guo; Wang, Jue; Wang, Lin; Zhou, Muchun; Chen, Yanru; Song, Minmin
2018-03-01
The scintillation index of pseudo-Bessel-Gaussian Schell-mode (PBGSM) beams propagating through atmospheric turbulence is analyzed with the help of wave optics simulation due to the analytic difficulties. It is found that in the strong fluctuation regime, the PBGSM beams are more resistant to the turbulence with the appropriate parameters β and δ . However, the case is contrary in the weak fluctuation regime. Our simulation results indicate that the PBGSM beams may be applied to free-space optical (FSO) communication systems only when the turbulence is strong or the propagation distance is long.
Guo, Ying; Xie, Cailang; Liao, Qin; Zhao, Wei; Zeng, Guihua; Huang, Duan
2017-08-01
The survival of Gaussian quantum states in a turbulent atmospheric channel is of crucial importance in free-space continuous-variable (CV) quantum key distribution (QKD), in which the transmission coefficient will fluctuate in time, thus resulting in non-Gaussian quantum states. Different from quantum hacking of the imperfections of practical devices, here we propose a different type of attack by exploiting the security loopholes that occur in a real lossy channel. Under a turbulent atmospheric environment, the Gaussian states are inevitably afflicted by decoherence, which would cause a degradation of the transmitted entanglement. Therefore, an eavesdropper can perform an intercept-resend attack by applying an entanglement-distillation operation on the transmitted non-Gaussian mixed states, which allows the eavesdropper to bias the estimation of the parameters and renders the final keys shared between the legitimate parties insecure. Our proposal highlights the practical CV QKD vulnerabilities with free-space quantum channels, including the satellite-to-earth links, ground-to-ground links, and a link from moving objects to ground stations.
Profiles of Wind and Turbulence in the Coastal Atmospheric Boundary Layer of Lake Erie
Wang, H
2014-06-16
Prediction of wind resource in coastal zones is difficult due to the complexity of flow in the coastal atmospheric boundary layer (CABL). A three week campaign was conducted over Lake Erie in May 2013 to investigate wind characteristics and improve model parameterizations in the CABL. Vertical profiles of wind speed up to 200 m were measured onshore and offshore by lidar wind profilers, and horizontal gradients of wind speed by a 3-D scanning lidar. Turbulence data were collected from sonic anemometers deployed onshore and offshore. Numerical simulations were conducted with the Weather Research Forecasting (WRF) model with 2 nested domains down to a resolution of 1-km over the lake. Initial data analyses presented in this paper investigate complex flow patterns across the coast. Acceleration was observed up to 200 m above the surface for flow coming from the land to the water. However, by 7 km off the coast the wind field had not yet reached equilibrium with the new surface (water) conditions. The surface turbulence parameters over the water derived from the sonic data could not predict wind profiles observed by the ZephlR lidar located offshore. Horizontal wind speed gradients near the coast show the influence of atmospheric stability on flow dynamics. Wind profiles retrieved from the 3-D scanning lidar show evidence of nocturnal low level jets (LLJs). The WRF model was able to capture the occurrence of LLJ events, but its performance varied in predicting their intensity, duration, and the location of the jet core.
Gorlé, C.; van Beeck, J.; Rambaud, P.; Van Tendeloo, G.
When considering the modelling of small particle dispersion in the lower part of the Atmospheric Boundary Layer (ABL) using Reynolds Averaged Navier Stokes simulations, the particle paths depend on the velocity profile and on the turbulence kinetic energy, from which the fluctuating velocity components are derived to predict turbulent dispersion. It is therefore important to correctly reproduce the ABL, both for the velocity profile and the turbulence kinetic energy profile. For RANS simulations with the standard k- ɛ model, Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k-ɛ turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46-47, 145-153.) proposed a set of boundary conditions which result in horizontally homogeneous profiles. The drawback of this method is that it assumes a constant profile of turbulence kinetic energy, which is not always consistent with field or wind tunnel measurements. Therefore, a method was developed which allows the modelling of a horizontally homogeneous turbulence kinetic energy profile that is varying with height. By comparing simulations performed with the proposed method to simulations performed with the boundary conditions described by Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k-ɛ turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46-47, 145-153.), the influence of the turbulence kinetic energy on the dispersion of small particles over flat terrain is quantified.
Directory of Open Access Journals (Sweden)
P. Paradisi
2012-02-01
Full Text Available We investigate the time intermittency of turbulent transport associated with the birth-death of self-organized coherent structures in the atmospheric boundary layer. We apply a threshold analysis on the increments of turbulent fluctuations to extract sequences of rapid acceleration events, which is a marker of the transition between self-organized structures.
The inter-event time distributions show a power-law decay ψ(τ ~ 1/τ^{μ}, with a strong dependence of the power-law index μ on the threshold.
A recently developed method based on the application of event-driven walking rules to generate different diffusion processes is applied to the experimental event sequences. At variance with the power-law index μ estimated from the inter-event time distributions, the diffusion scaling H, defined by ⟨ X^{2}⟩ ~ t^{2H}, is independent from the threshold.
From the analysis of the diffusion scaling it can also be inferred the presence of different kind of events, i.e. genuinely transition events and spurious events, which all contribute to the diffusion process but over different time scales. The great advantage of event-driven diffusion lies in the ability of separating different regimes of the scaling H. In fact, the greatest H, corresponding to the most anomalous diffusion process, emerges in the long time range, whereas the smallest H can be seen in the short time range if the time resolution of the data is sufficiently accurate.
The estimated diffusion scaling is also robust under the change of the definition of turbulent fluctuations and, under the assumption of statistically independent events, it corresponds to a self-similar point process with a well-defined power-law index μ_{D} ~ 2.1, where D denotes that μ_{D} is derived from the diffusion scaling. We argue that
Paradisi, P.; Cesari, R.; Donateo, A.; Contini, D.; Allegrini, P.
2012-02-01
We investigate the time intermittency of turbulent transport associated with the birth-death of self-organized coherent structures in the atmospheric boundary layer. We apply a threshold analysis on the increments of turbulent fluctuations to extract sequences of rapid acceleration events, which is a marker of the transition between self-organized structures. The inter-event time distributions show a power-law decay ψ(τ) ~ 1/τμ, with a strong dependence of the power-law index μ on the threshold. A recently developed method based on the application of event-driven walking rules to generate different diffusion processes is applied to the experimental event sequences. At variance with the power-law index μ estimated from the inter-event time distributions, the diffusion scaling H, defined by ⟨ X2⟩ ~ t2H, is independent from the threshold. From the analysis of the diffusion scaling it can also be inferred the presence of different kind of events, i.e. genuinely transition events and spurious events, which all contribute to the diffusion process but over different time scales. The great advantage of event-driven diffusion lies in the ability of separating different regimes of the scaling H. In fact, the greatest H, corresponding to the most anomalous diffusion process, emerges in the long time range, whereas the smallest H can be seen in the short time range if the time resolution of the data is sufficiently accurate. The estimated diffusion scaling is also robust under the change of the definition of turbulent fluctuations and, under the assumption of statistically independent events, it corresponds to a self-similar point process with a well-defined power-law index μD ~ 2.1, where D denotes that μD is derived from the diffusion scaling. We argue that this renewal point process can be associated to birth and death of coherent structures and to turbulent transport near the ground, where the contribution of turbulent coherent structures becomes dominant.
National Research Council Canada - National Science Library
Auvermann, Harry
2001-01-01
The objective of one portion of the Army Research Laboratory program on acoustic propagation on the battlefield is to develop an advanced method of accounting for the effects of anisotropic inhomogeneous turbulence...
Chatterjee, Monish R.; Mohamed, Fathi H. A.
2014-12-01
The impact of atmospheric phase turbulence on Gaussian beam propagation along propagation paths of varying lengths is examined using multiple random phase screens. The work is motivated by research involving generation and encryption of acousto-optic chaos, and the interest in examining propagation of such chaotic waves through atmospheric turbulence. A phase screen technique is used to simulate perturbations to the refractive index of the medium through the propagation path. A power spectral density based on the modified von Karman spectrum model for turbulence is used to describe the random phase behavior of the medium. In recent work, results for the numerical simulation of phase turbulence over a narrow region of space implemented by placing a planar aperture representing a (narrow) random phase screen were presented. Results are presented pertinent to extended phase screens (via multiple random-phase apertures) through which an incident Gaussian beam propagates incrementally via alternate phase transmission and diffraction along the propagation path. Additionally, for profiled electromagnetic waves (such as Gaussian), the scintillation index is evaluated for extended phase turbulence, and finally, fringe visibility due to the interference of double-Gaussian beams passing through extended turbulence is examined.
Directory of Open Access Journals (Sweden)
S. Yahaya
2003-10-01
Full Text Available This paper deals with the characteristics of turbulent flow over two agricultural plots with various tillage treatments in a fallow, semiarid area (Central Aragon, Spain. The main dynamic characteristics of the Atmospheric Surface Layer (ASL measured over the experimental site (friction velocity, roughness length, etc., and energy budget, have been presented previously (Frangi and Richard, 2000. The current study is based on experimental measurements performed with cup anemometers located in the vicinity of the ground at 5 different levels (from 0.25 to 4 m and sampled at 1 Hz. It reveals that the horizontal wind variance, the Eulerian integral scales, the frequency range of turbulence and the turbulent kinetic energy dissipation rate are affected by the surface roughness. In the vicinity of the ground surface, the horizontal wind variance logarithmically increases with height, directly in relation to the friction velocity and the roughness length scale. It was found that the time integral scale (and subsequently the length integral scale increased with the surface roughness and decreased with the anemometer height. These variations imply some shifts in the meteorological spectral gap and some variations of the spectral peak length scale. The turbulent energy dissipation rate, affected by the soil roughness, shows a z-less stratification behaviour under stable conditions. In addition to the characterization of the studied ASL, this paper intends to show which turbulence characteristics, and under what conditions, are accessible through the cup anemometer.Key words. Meteorology and atmospheric dynamics (climatology, turbulence, instruments and techniques
Directory of Open Access Journals (Sweden)
S. Yahaya
Full Text Available This paper deals with the characteristics of turbulent flow over two agricultural plots with various tillage treatments in a fallow, semiarid area (Central Aragon, Spain. The main dynamic characteristics of the Atmospheric Surface Layer (ASL measured over the experimental site (friction velocity, roughness length, etc., and energy budget, have been presented previously (Frangi and Richard, 2000. The current study is based on experimental measurements performed with cup anemometers located in the vicinity of the ground at 5 different levels (from 0.25 to 4 m and sampled at 1 Hz. It reveals that the horizontal wind variance, the Eulerian integral scales, the frequency range of turbulence and the turbulent kinetic energy dissipation rate are affected by the surface roughness. In the vicinity of the ground surface, the horizontal wind variance logarithmically increases with height, directly in relation to the friction velocity and the roughness length scale. It was found that the time integral scale (and subsequently the length integral scale increased with the surface roughness and decreased with the anemometer height. These variations imply some shifts in the meteorological spectral gap and some variations of the spectral peak length scale. The turbulent energy dissipation rate, affected by the soil roughness, shows a z-less stratification behaviour under stable conditions. In addition to the characterization of the studied ASL, this paper intends to show which turbulence characteristics, and under what conditions, are accessible through the cup anemometer.
Key words. Meteorology and atmospheric dynamics (climatology, turbulence, instruments and techniques
Influence of Evaporating Droplets in the Turbulent Marine Atmospheric Boundary Layer
Peng, Tianze; Richter, David
2017-08-01
Sea-spray droplets ejected into the marine atmospheric boundary layer take part in a series of complex transport processes. By capturing the air-droplet coupling and feedback, we focus on how droplets modify the total heat transfer across a turbulent boundary layer. We implement a high-resolution Eulerian-Lagrangian algorithm with varied droplet size and mass loading in a turbulent open-channel flow, revealing that the influence from evaporating droplets varies for different dynamic and thermodynamic characteristics of droplets. Droplets that both respond rapidly to the ambient environment and have long suspension times are able to modify the latent and sensible heat fluxes individually, however the competing signs of this modification lead to an overall weak effect on the total heat flux. On the other hand, droplets with a slower thermodynamic response to the environment are less subjected to this compensating effect. This indicates a potential to enhance the total heat flux, but the enhancement is highly dependent on the concentration and suspension time.
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
Energy Technology Data Exchange (ETDEWEB)
Berman, Gennady P [Los Alamos National Laboratory; Gorshkov, V. N. [NATL' TECH. UNIV. OF UA; Torous, S. V. [NATL' TECH. UNIV. OF UA
2010-12-14
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams (PCBs), including the optical vortices, propagating in turbulent atmospheres, The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. A method for significantly reducing the SI, by averaging the signal at the detector over a set of PCBs, is described, This novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the SI is effectively suppressed without any high-frequency modulators.
DEFF Research Database (Denmark)
Zhu, Jiajian; Gao, Jinlong; Ehn, Andreas
2017-01-01
of the glow-type discharge is the same as that of the electronic power dissipated in the plasma column. The glow-type discharge can transfer into a spark discharge characterized by a sharp peak current of several amperes and a sudden increase of the brightness in the plasma column. Transitions can also......A gliding arc discharge was generated in a turbulent air flow at atmospheric pressure driven by a 35 kHz alternating current (AC) electric power. The spatiotemporally resolved characteristics of the gliding arc discharge, including glow-type discharges, spark-type discharges, short-cutting events...... be found to take place from spark-type discharges to glow-type discharges. Short-cutting events were often observed as the intermediate states formed during the spark-glow transition. Three different types of short-cutting events have been observed to generate new current paths between two plasma channel...
PIV Measurements of Atmospheric Turbulence and Pollen Dispersal Above a Corn Canopy
Zhu, W.; van Hout, R.; Luznik, L.; Katz, J.
2003-12-01
Dispersal of pollen grains by wind and gravity (Anemophilous) is one of the oldest means of plant fertilization available in nature. Recently, the growth of genetically modified foods has raised questions on the range of pollen dispersal in order to limit cross-fertilization between organically grown and transgenic crops. The distance that a pollen grain can travel once released from the anther is determined, among others, by the aerodynamic parameters of the pollen and the characteristics of turbulence in the atmosphere in which it is released. Turbulence characteristics of the flow above a pollinating corn field were measured using Particle Image Velocimetry (PIV). The measurements were performed on the eastern shore of the Chesapeake Bay, in Maryland, during July 2003. Two PIV systems were used simultaneously, each with an overall sample area of 18x18 cm. The spacing between samples was about equal to the field of view. The PIV instrumentation, including CCD cameras, power supply and laser sheets forming optics were mounted on a measurement platform, consisting of a hydraulic telescopic arm that could be extended up to 10m. The whole system could be rotated in order to align it with the flow. The flow was seeded with smoke generated about 30m upstream of the sample areas. Measurements were carried out at several elevations, from just below canopy height up to 1m above canopy. The local meteorological conditions around the test site were monitored by other sensors including sonic anemometers, Rotorod pollen counters and temperature sensors. Each processed PIV image provides an instantaneous velocity distribution containing 64x64 vectors with a vector spacing of ~3mm. The pollen grains (~100mm) can be clearly distinguished from the smoke particles (~1mm) based on their size difference. The acquired PIV data enables calculation of the mean flow and turbulence characteristics including Reynolds stresses, spectra, turbulent kinetic energy and dissipation rate. Data
Due to their highly-structured canopy, turbulent characteristics within and above vineyards, may not conform to those typically exhibited by other agricultural and natural ecosystems. Using data collected as a part of the Grape Remote sensing and Atmospheric Profiling and Evapotranspiration Experime...
Energy Technology Data Exchange (ETDEWEB)
Berlowitz, D.R.
1996-11-01
In the last few decades the negative impact by humans on the thin atmospheric layer enveloping the earth, the basis for life on this planet, has increased steadily. In order to halt, or at least slow down this development, the knowledge and study of these anthropogenic influence has to be increased and possible remedies have to be suggested. An important tool for these studies are computer models. With their help the atmospheric system can be approximated and the various processes, which have led to the current situation can be quantified. They also serve as an instrument to assess short or medium term strategies to reduce this human impact. However, to assure efficiency as well as accuracy, a careful analysis of the numerous processes involved in the dispersion of pollutants in the atmosphere is called for. This should help to concentrate on the essentials and also prevent excessive usage of sometimes scarce computing resources. The basis of the presented work is the EUMAC Zooming Model (ETM), and particularly the component calculating the dispersion of pollutants in the atmosphere, the model MARS. The model has two main parts: an explicit solver, where the advection and the horizontal diffusion of pollutants are calculated, and an implicit solution mechanism, allowing the joint computation of the change of concentration due to chemical reactions, coupled with the respective influence of the vertical diffusion of the species. The aim of this thesis is to determine particularly the influence of the horizontal components of the turbulent diffusion on the existing implicit solver of the model. Suggestions for a more comprehensive inclusion of the full three dimensional diffusion operator in the implicit solver are made. This is achieved by an appropriate operator splitting. A selection of numerical approaches to tighten the coupling of the diffusion processes with the calculation of the applied chemical reaction mechanisms are examined. (author) figs., tabs., refs.
Friedrich, Katja; Lundquist, Julie K.; Aitken, Matthew; Kalina, Evan A.; Marshall, Robert F.
2012-02-01
When monitoring winds and atmospheric stability for wind energy applications, remote sensing instruments present some advantages to in-situ instrumentation such as larger vertical extent, in some cases easy installation and maintenance, measurements of vertical humidity profiles throughout the boundary layer, and no restrictions on prevailing wind directions. In this study, we compare remote sensing devices, Windcube lidar and microwave radiometer, to meteorological in-situ tower measurements to demonstrate the accuracy of these measurements and to assess the utility of the remote sensing instruments in overcoming tower limitations. We compare temperature and wind observations, as well as calculations of Brunt-Väisälä frequency and Richardson numbers for the instrument deployment period in May-June 2011 at the U.S. Department of Energy National Renewable Energy Laboratory's National Wind Technology Center near Boulder, Colorado. The study reveals that a lidar and radiometer measure wind and temperature with the same accuracy as tower instruments, while also providing advantages for monitoring stability and turbulence. We demonstrate that the atmospheric stability is determined more accurately when the liquid-water mixing ratio derived from the vertical humidity profile is considered under moist-adiabatic conditions.
Jee, M. James; Tyson, J. Anthony
2011-05-01
The weak-lensing science of the Large Synoptic Survey Telescope (LSST) project drives the need to carefully model and separate the instrumental artifacts from the intrinsic shear signal caused by gravitational lensing. The dominant source of the systematics for all ground-based telescopes is the spatial correlation of the point-spread function (PSF) modulated by both atmospheric turbulence and optical aberrations in the telescope and camera system. In this article, we present a full field-of-view simulation of the LSST images by modeling both the atmosphere and the system optics with the most current data for the telescope and camera specifications and the environment. To simulate the effects of atmospheric turbulence, we generated six-layer Kolmogorov/von Kármán phase screens with the parameters estimated from the on-site measurements. LSST will continuously sample the wavefront, correcting the optics alignment and focus. For the optics, we combined the ray-tracing tool ZEMAX and our simulated focal-plane data to introduce realistic residual aberrations and focal-plane height variations. Although this expected focal-plane flatness deviation for LSST is small compared with that of other existing cameras, the fast focal ratio of the LSST optics cause this focal-plane flatness variation and the resulting PSF discontinuities across the CCD boundaries to be significant challenges in our removal of the PSF-induced systematics. We resolve this complication by performing principal component analysis (PCA) CCD by CCD and by interpolating the basis functions derived from the analysis using conventional polynomials. We demonstrate that this PSF correction scheme reduces the residual PSF ellipticity correlation below 10-7 over the cosmologically interesting (dark-matter-dominated) scale 10‧-3°. From a null test using the Hubble Space Telescope (HST) Ultra Deep Field (UDF) galaxy images without input shear, we verify that the amplitude of the galaxy ellipticity
Drake, Marvin D.; Bas, Christophe F.; Gervais, David; Renda, Priscilla F.; Townsend, Daniel; Rushanan, Joseph J.; Francoeur, Joe; Donnangelo, Nick; Stenner, Michael D.
2013-05-01
We describe an experimental laboratory system that generates and distributes random binary sequence bit streams between two optical terminals (labeled Alice and Bob). The random binary sequence is generated through probing the optical channel of a turbulent atmosphere between the two terminals with coincident laser beams. The two laser beams experience differential phase delays while propagating through the atmospheric optical channel. The differential phase delays are detected and sampled at each terminal to yield raw random bit streams. The random bit streams are processed to remove bit errors and, through privacy amplification, to yield a bit stream known only to Alice and Bob. The same chaotic physical mechanism that provides randomness also provides confidentiality. The laboratory system yielded secret key bit rates of a few bits/second. For external optical channels over longer channel lengths with atmospheric turbulence levels, secret bit rates of 10 s of bits/second are predicted.
Li, Ya-qing; Wang, Li-guo
2017-11-01
On the basis of the extended Huygens-Fresnel principle and the cross-spectral density function (CSDF), the intensity and average orbital angular momentum (OAM) of the partially coherent flat-topped vortex beams in the slant atmospheric turbulence are presented. The effects of the order, topological charge, waist radius, and propagation distance of the beam on the intensity and average OAM are discussed. Results obtained show that the intensity of the partially coherent flat-topped vortex beam is changed due to the variations of the propagation distance, waist radius, topological charge and beam order, the average OAM is constant during the beam propagation in the atmospheric turbulence and related only to the waist radius and beam order. Results obtained by this paper may serve as theory bases for future applications in the atmospheric optical communication.
Litt, Maxime; Sicart, Jean-Emmanuel; Six, Delphine; Wagnon, Patrick; Helgason, Warren D.
2017-04-01
Over Saint-Sorlin Glacier in the French Alps (45° N, 6.1° E; ˜ 3 km2) in summer, we study the atmospheric surface-layer dynamics, turbulent fluxes, their uncertainties and their impact on surface energy balance (SEB) melt estimates. Results are classified with regard to large-scale forcing. We use high-frequency eddy-covariance data and mean air-temperature and wind-speed vertical profiles, collected in 2006 and 2009 in the glacier's atmospheric surface layer. We evaluate the turbulent fluxes with the eddy-covariance (sonic) and the profile method, and random errors and parametric uncertainties are evaluated by including different stability corrections and assuming different values for surface roughness lengths. For weak synoptic forcing, local thermal effects dominate the wind circulation. On the glacier, weak katabatic flows with a wind-speed maximum at low height (2-3 m) are detected 71 % of the time and are generally associated with small turbulent kinetic energy (TKE) and small net turbulent fluxes. Radiative fluxes dominate the SEB. When the large-scale forcing is strong, the wind in the valley aligns with the glacier flow, intense downslope flows are observed, no wind-speed maximum is visible below 5 m, and TKE and net turbulent fluxes are often intense. The net turbulent fluxes contribute significantly to the SEB. The surface-layer turbulence production is probably not at equilibrium with dissipation because of interactions of large-scale orographic disturbances with the flow when the forcing is strong or low-frequency oscillations of the katabatic flow when the forcing is weak. In weak forcing when TKE is low, all turbulent fluxes calculation methods provide similar fluxes. In strong forcing when TKE is large, the choice of roughness lengths impacts strongly the net turbulent fluxes from the profile method fluxes and their uncertainties. However, the uncertainty on the total SEB remains too high with regard to the net observed melt to be able to
Chatterjee, Monish R.; Mohamed, Ali A.
2017-05-01
In recent research, anisoplanatic electromagnetic (EM) wave propagation along a slanted path in the presence of low atmosphere phase turbulence (modified von Karman spectrum or MVKS) has been investigated assuming a Hufnagel-Valley (HV) type structure parameter. Preliminary results indicate a strong dependence on the slant angle especially for long range transmission and relatively strong turbulence. The investigation was further divided into two regimes, viz. (a) one where the EM source consisted of a plane wave modulated with a digitized image, which is propagated along the turbulent path and recovered via demodulation at the receiver; and (b) transmit the plane wave without modulation along the turbulent path through an image transparency and a thin lens designed to gather the received image in the focal plane. In this paper, we reexamine the same problem (part (a) only) in the presence of a chaotic optical carrier where the chaos is generated in the feedback loop of an acousto-optic Bragg cell. The image information is encrypted within the chaos wave, and subsequently propagated along a similar slant path and identical turbulence conditions. The recovered image extracted via heterodyning from the received chaos is compared quantitatively (through image cross-correlations and mean-squared error measures) for the non-chaotic versus the chaotic approaches. Generally, "packaging" the information in chaos improves performance through turbulent propagation, and results are discussed from this perspective. Concurrently, we will also examine the effect of a non-encrypted plane EM wave propagation through a transparency-lens combination. These results are also presented with appropriate comparisons with the cases involving lensless transmission of imagery through corresponding turbulent and non-turbulent layers.
Jha, Pankaj Kumar
Wind energy is becoming one of the most significant sources of renewable energy. With its growing use, and social and political awareness, efforts are being made to harness it in the most efficient manner. However, a number of challenges preclude efficient and optimum operation of wind farms. Wind resource forecasting over a long operation window of a wind farm, development of wind farms over a complex terrain on-shore, and air/wave interaction off-shore all pose difficulties in materializing the goal of the efficient harnessing of wind energy. These difficulties are further amplified when wind turbine wakes interact directly with turbines located downstream and in adjacent rows in a turbulent atmospheric boundary layer (ABL). In the present study, an ABL solver is used to simulate different atmospheric stability states over a diurnal cycle. The effect of the turbines is modeled by using actuator methods, in particular the state-of-the-art actuator line method (ALM) and an improved ALM are used for the simulation of the turbine arrays. The two ALM approaches are used either with uniform inflow or are coupled with the ABL solver. In the latter case, a precursor simulation is first obtained and data saved at the inflow planes for the duration the turbines are anticipated to be simulated. The coupled ABL-ALM solver is then used to simulate the turbine arrays operating in atmospheric turbulence. A detailed accuracy assessment of the state-of-the-art ALM is performed by applying it to different rotors. A discrepancy regarding over-prediction of tip loads and an artificial tip correction is identified. A new proposed ALM* is developed and validated for the NREL Phase VI rotor. This is also applied to the NREL 5-MW turbine, and guidelines to obtain consistent results with ALM* are developed. Both the ALM approaches are then applied to study a turbine-turbine interaction problem consisting of two NREL 5-MW turbines. The simulations are performed for two ABL stability
García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz
2010-03-15
Atmospheric turbulence produces fluctuations in the irradiance of the transmitted optical beam, which is known as atmospheric scintillation, severely degrading the link performance. In this paper, a scheme combining transmit laser selection (TLS) and space-time trellis code (STTC) for multiple-input-single-output (MISO) free-space optical (FSO) communication systems with intensity modulation and direct detection (IM/DD) over strong atmospheric turbulence channels is analyzed. Assuming channel state information at the transmitter and receiver, we propose the transmit diversity technique based on the selection of two out of the available L lasers corresponding to the optical paths with greater values of scintillation to transmit the baseline STTCs designed for two transmit antennas. Based on a pairwise error probability (PEP) analysis, results in terms of bit error rate are presented when the scintillation follows negative exponential and K distributions, which cover a wide range of strong atmospheric turbulence conditions. Obtained results show a diversity order of 2L-1 when L transmit lasers are available and a simple two-state STTC with rate 1 bit/(s .Hz) is used. Simulation results are further demonstrated to confirm the analytical results.
Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan
2015-06-20
A theoretical formulation of the spherical-wave two-frequency mutual coherence function (MCF) for a propagation path characterized by a complex ABCD matrix with anisotropic atmospheric turbulence existing somewhere is developed. A specialization of this formulation leads to an expression for the two-frequency MCF of an equivalent pulsed Gaussian beam propagating in weak anisotropic atmospheric turbulence along a horizontal line-of-sight path; relevant closed-form analytical solutions under both near- and far-field conditions are obtained. The small- and large-scale solutions for both the plane- and spherical-wave spatial-coherence radii in either horizontal or vertical direction are derived. Analysis shows that the formula for the on-axis two-frequency MCF of a pulsed Gaussian beam under the weak-turbulence condition in both the near- and far-field regions is distinguished from that applicable in the strong-turbulence limit only by whether the turbulence-induced beam broadening can be thought of as negligible. Under both the near- and far-field conditions, the turbulence-induced increment of the mean-square temporal-pulse half-width is proportional to the effective anisotropy factor of turbulence. The MCF becomes statistically anisotropic due to the anisotropy of turbulence. For the spatial coherence radius of either a plane or spherical wave propagating along a horizontal line-of-sight path in anisotropic atmospheric turbulence, the corresponding small-scale solution is proportional to that for the plane-wave spatial-coherence radius in the isotropic-turbulence case with a proportionality coefficient depending only on the effective anisotropy factor of turbulence. The corresponding large-scale solution is proportional to that for the plane-wave spatial-coherence radius in the isotropic-turbulence case with a proportionality coefficient that depends on both the effective anisotropy factor and spectral index of turbulence.
Blow-out of nonpremixed turbulent jet flames at sub-atmospheric pressures
Wang, Qiang
2016-12-09
Blow-out limits of nonpremixed turbulent jet flames in quiescent air at sub-atmospheric pressures (50–100 kPa) were studied experimentally using propane fuel with nozzle diameters ranging 0.8–4 mm. Results showed that the fuel jet velocity at blow-out limit increased with increasing ambient pressure and nozzle diameter. A Damköhler (Da) number based model was adopted, defined as the ratio of characteristic mixing time and characteristic reaction time, to include the effect of pressure considering the variations in laminar burning velocity and thermal diffusivity with pressure. The critical lift-off height at blow-out, representing a characteristic length scale for mixing, had a linear relationship with the theoretically predicted stoichiometric location along the jet axis, which had a weak dependence on ambient pressure. The characteristic mixing time (critical lift-off height divided by jet velocity) adjusted to the characteristic reaction time such that the critical Damköhler at blow-out conditions maintained a constant value when varying the ambient pressure.
Djordjevic, Ivan B
2007-08-06
We describe a coded power-efficient transmission scheme based on repetition MIMO principle suitable for communication over the atmospheric turbulence channel, and determine its channel capacity. The proposed scheme employs the Q-ary pulse-position modulation. We further study how to approach the channel capacity limits using low-density parity-check (LDPC) codes. Component LDPC codes are designed using the concept of pairwise-balanced designs. Contrary to the several recent publications, bit-error rates and channel capacities are reported assuming non-ideal photodetection. The atmospheric turbulence channel is modeled using the Gamma-Gamma distribution function due to Al-Habash et al. Excellent bit-error rate performance improvement, over uncoded case, is found.
Odeyemi, Kehinde O.; Owolawi, Pius A.; Srivastava, Viranjay M.
2017-01-01
Atmospheric turbulence is a major impairment that degrades the performance of free space optical (FSO) communication systems. Spatial modulation (SM) with receive spatial diversity is considered as a powerful technique to mitigate the fading effect induced by atmospheric turbulence. In this paper, the performance of free space optical spatial modulation (FSO-SM) system under Gamma-Gamma atmospheric turbulence is presented. We studied the Average Bit Error Rate (ABER) for the system by employing spatial diversity combiners such Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) at the receiving end. In particular, we provide a theoretical framework for the system error by deriving Average Pairwise Error Probability (APEP) expression using a generalized infinite power series expansion approach and union bounding technique is applied to obtain the ABER for each combiner. Based on this study, it was found that spatial diversity combiner significantly improved the system error rate where MRC outperforms the EGC. The performance of this system is also compared with other well established diversity combiner systems. The proposed system performance is further improved by convolutional coding technique and our analysis confirmed that the system performance of MRC coded system is enhanced by approximately 20 dB while EGC falls within 17 dB.
Odeyemi, Kehinde O.; Owolawi, Pius A.; Srivastava, Viranjay M.
2017-11-01
Dual-hops transmission is a growing interest technique that can be used to mitigate against atmospheric turbulence along the Free Space Optical (FSO) communication links. This paper analyzes the performance of Decode-and-Forward (DF) dual-hops FSO systems in-conjunction with spatial modulation and diversity combiners over a Gamma-Gamma atmospheric turbulence channel using heterodyne detection. Maximum Ratio Combiner (MRC), Equal Gain Combiner (EGC) and Selection Combiner (SC) are considered at the relay and destination as mitigation tools to improve the system error performance. Power series expansion of modified Bessel function is used to derive the closed form expression for the end-to-end Average Pairwise Error Probability (APEP) expressions for each of the combiners under study and a tight upper bound on the Average Bit Error Rate (ABER) per hop is given. Thus, the overall end-to-end ABER for the dual-hops FSO system is then evaluated. The numerical results depicted that dual-hops transmission systems outperformed the direct link systems. Moreover, the impact of having the same and different combiners at the relay and destination are also presented. The results also confirm that the combination of dual hops transmission with spatial modulation and diversity combiner significantly improves the systems error rate with the MRC combiner offering an optimal performance with respect to variation in atmospheric turbulence, change in links average received SNR and link range of the system.
Energy Technology Data Exchange (ETDEWEB)
Rusakov, Yu.S. [Science and Production Association Typhoon, Obninsk (Russian Federation)
2007-08-15
The backscattering of acoustic waves in the atmosphere has been studied with an absolutely calibrated sodar and a measuring complex at a 300-m meteorological mast (HMM). It has been shown that the backward differential cross-section of the atmosphere and excess attenuation of sound are by an order of magnitude greater than formerly recognized. The effects have been qualitatively justified on the basis of consideration of the small-scale turbulence intermittence and a model of sound scattering on the ensemble of local inhomogeneities. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Vijayakumar, Ganesh [National Renewable Energy Lab. (NREL), Golden, CO (United States); Pennsylvania State Univ., University Park, PA (United States); Brasseur, James [Pennsylvania State Univ., University Park, PA (United States); Univ. of Colorado, Boulder, CO (United States); Lavely, Adam; Jayaraman, Balaji; Craven, Brent
2016-01-04
We describe the response of the NREL 5 MW wind turbine blade boundary layer to the passage of atmospheric turbulence using blade-boundary-layer-resolved computational fluid dynamics with hybrid URANS-LES modeling.
Wang, Xiao-yang; Zhao, Nan; Chen, Nan; Zhu, Chang-hua; Pei, Chang-xing
2018-01-01
In free space quantum channel, with the introduction and implementation of the satellite-ground link transmission, the researches of single-photon transmission have attracted great interest. We propose a single-photon receiving model and analyze the influence of the atmospheric turbulence on the single-photon transmission. We obtain the relationship between single-photon receiving efficiency and atmospheric turbulence, and analyze the influence of the atmospheric turbulence on the quantum channel performance by the single-photon counting. Finally, we present a reasonable simulation analysis. Simulation results show that as the strength of the atmospheric fluctuations increases, the counting distribution gradually broadens, and the utilization of quantum channel drops. Furthermore, the key generation rate and transmission distance decreases sharply in the case of strong turbulence.
Directory of Open Access Journals (Sweden)
Theodore D. Katsilieris
2017-03-01
Full Text Available The terrestrial optical wireless communication links have attracted significant research and commercial worldwide interest over the last few years due to the fact that they offer very high and secure data rate transmission with relatively low installation and operational costs, and without need of licensing. However, since the propagation path of the information signal, i.e., the laser beam, is the atmosphere, their effectivity affects the atmospheric conditions strongly in the specific area. Thus, system performance depends significantly on the rain, the fog, the hail, the atmospheric turbulence, etc. Due to the influence of these effects, it is necessary to study, theoretically and numerically, very carefully before the installation of such a communication system. In this work, we present exactly and accurately approximate mathematical expressions for the estimation of the average capacity and the outage probability performance metrics, as functions of the link’s parameters, the transmitted power, the attenuation due to the fog, the ambient noise and the atmospheric turbulence phenomenon. The latter causes the scintillation effect, which results in random and fast fluctuations of the irradiance at the receiver’s end. These fluctuations can be studied accurately with statistical methods. Thus, in this work, we use either the lognormal or the gamma–gamma distribution for weak or moderate to strong turbulence conditions, respectively. Moreover, using the derived mathematical expressions, we design, accomplish and present a computational tool for the estimation of these systems’ performances, while also taking into account the parameter of the link and the atmospheric conditions. Furthermore, in order to increase the accuracy of the presented tool, for the cases where the obtained analytical mathematical expressions are complex, the performance results are verified with the numerical estimation of the appropriate integrals. Finally, using
Dabiri, Mohammad Taghi; Sadough, Seyed Mohammad Sajad; Khalighi, Mohammad Ali
2017-11-01
In the free-space optical (FSO) links, atmospheric turbulence and pointing errors lead to scintillation in the received signal. Due to its ease of implementation, intensity modulation with direct detection (IM/DD) based on ON-OFF-keying(OOK) is a popular signaling scheme in these systems. For long-haul FSO links, avalanche photo diodes (APDs) are commonly used, which provide an internal gain in photo-detection, allowing larger transmission ranges, as compared with PIN photo-detector (PD) counterparts. Since optimal OOK detection at the receiver requires the knowledge of the instantaneous channel fading coefficient, channel estimation is an important task that can considerably impact the link performance. In this paper, we investigate the channel estimation issue when using an APD at the receiver. Here, optimal signal detection is quite more delicate than in the case of using a PIN PD. In fact, given that APD-based receivers are usually shot-noise limited, the receiver noise will have a different distribution depending on whether the transmitted bit is '0' or '1', and moreover, its statistics are further affected by the scintillation. To deal with this, we first consider minimum mean-square-error (MMSE), maximum a posteriori probability (MAP) and maximum likelihood (ML) channel estimation over an observation window encompassing several consecutive received OOK symbols. Due to the high computational complexity of these methods, in a second step, we propose an ML channel estimator based on the expectation-maximization (EM) algorithm which has a low implementation complexity, making it suitable for high data-rate FSO communications. Numerical results show that for a sufficiently large observation window, by using the proposed EM channel estimator, we can achieve bit error rate performance very close to that with perfect channel state information. We also derive the Cramer-Rao lower bound (CRLB) of MSE of estimation errors and show that for a large enough observation
Sparrow, Victor W.; Pierce, Allan D.
1992-01-01
A theory which gives statistical predictions for how often sonic booms propagating through the earth's turbulent boundary layer will encounter caustics, given the spectral properties of the atmospheric turbulence, is outlined. The theory is simple but approximately accounts for the variation of ray tube areas along ray paths. This theory predicts that the variation of ray tube areas is determined by the product of two similar area factors, psi (x) and phi (x), each satisfying a generic harmonic oscillator equation. If an area factor increases the peak acoustic pressure decreases, and if the factor decreases the peak acoustic pressure increases. Additionally, if an area factor decreases to zero and becomes negative, the ray has propagated through a caustic, which contributes a phase change of 90 degrees to the wave. Thus, it is clear that the number of times that a sonic boom wave passes through a caustic should be related to the distorted boom waveform received on the ground. Examples are given based on a characterization of atmospheric turbulence due to the structure function of Tatarski as modified by Crow.
Vijayakumar, Ganesh
Modern commercial megawatt-scale wind turbines occupy the lower 15-20% of the atmospheric boundary layer (ABL), the atmospheric surface layer (ASL). The current trend of increasing wind turbine diameter and hub height increases the interaction of the wind turbines with the upper ASL which contains spatio-temporal velocity variations over a wide range of length and time scales. Our interest is the interaction of the wind turbine with the energetic integral-scale eddies, since these cause the largest temporal variations in blade loadings. The rotation of a wind turbine blade through the ABL causes fluctuations in the local velocity magnitude and angle of attack at different sections along the blade. The blade boundary layer responds to these fluctuations and in turn causes temporal transients in local sectional loads and integrated blade and shaft bending moments. While the integral scales of the atmospheric boundary layer are ˜ O(10--100m) in the horizontal with advection time scales of order tens of seconds, the viscous surface layer of the blade boundary layer is ˜ O(10 -- 100 mum) with time scales of order milliseconds. Thus, the response of wind turbine blade loadings to atmospheric turbulence is the result of the interaction between two turbulence dynamical systems at extremely disparate ranges of length and time scales. A deeper understanding of this interaction can impact future approaches to improve the reliability of wind turbines in wind farms, and can underlie future improvements. My thesis centers on the development of a computational framework to simulate the interaction between the atmospheric and wind turbine blade turbulence dynamical systems using a two step one-way coupled approach. Pseudo-spectral large eddy simulation (LES) is used to generate a true (equilibrium) atmospheric boundary layer over a flat land with specified surface roughness and heating consistent with the stability state of the daytime lower troposphere. Using the data from the
Mitigating the Effects of Atmospheric Turbulence: Towards More Useful Micro Air Vehicles
2010-07-18
pressures and forces on aerofoils in order to examine the possibility of “feeling” through turbulent air and to also understanding the influence on...10 Adjunct Experiments 11 Dynamic Pressure Measurements on Thin Aerofoils 11 Low Cost Video Tracking Investigation 17 Dynamic...investigating the influence of large scale (> 1m) turbulence of the performance of Low Reynolds number thin aerofoils . Interim results are given
Fine Scale Modeling and Forecasts of Upper Atmospheric Turbulence for Operational Use
2014-11-30
nonequilibrium layer dynamics at fine scales, Phys. Scr. 89 (22pp) 098001 (2014). Observation and simulation of wave breaking in the southern hemispheric ...Clear Air Turbulence (CAT) Solver The Clear Air Turbulence (CAT) Solver performs processing of input HRMM meteorological data using parameters...wavenumber pair (or wavevector), as well as each meteorological profile. This means that the solver can be scaled to run on a high performance
On the study of the FSO link performance under controlled turbulence and fog atmospheric conditions
Rajbhandari, Sujan; Ghassemlooy, Zabih; Perez Soler, Joaquin; Le Minh, Hoa; Leitgeb, Erich; Kandus, Gorazd; Kvicera, V.
2011-01-01
In this paper, the effect of turbulence and fog on the free space optical (FSO) communication systems for on off keying (OOK), pulse amplitude modulation (PAM) and subcarrier intensity modulation (SIM) based on binary phase shift keying (BPSK) is experimentally investigated. The experiment is carried out in a controlled laboratory environment where turbulence and fog could be generated in a dedicated FSO chamber. In comparison to 4 PAM signal, the BPSK and OOK NRZ modulation signalling format...
Ogorzalek, A.; Zhuravleva, I.; Allen, S. W.; Pinto, C.; Werner, N.; Mantz, A. B.; Canning, R. E. A.; Fabian, A. C.; Kaastra, J. S.; de Plaa, J.
2017-12-01
We present significantly improved measurements of turbulent velocities in the hot gaseous haloes of nearby giant elliptical galaxies. Using deep XMM-Newton Reflection Grating Spectrometer (RGS) observations and a combination of resonance scattering and direct line broadening methods, we obtain well bounded constraints for 13 galaxies. Assuming that the turbulence is isotropic, we obtain a best-fitting mean 1D turbulent velocity of ∼110 km s-1. This implies a typical 3D Mach number ∼0.45 and a typical non-thermal pressure contribution of ∼6 per cent in the cores of nearby massive galaxies. The intrinsic scatter around these values is modest - consistent with zero, albeit with large statistical uncertainty - hinting at a common and quasi-continuous mechanism sourcing the velocity structure in these objects. Using conservative estimates of the spatial scales associated with the observed turbulent motions, we find that turbulent heating can be sufficient to offset radiative cooling in the inner regions of these galaxies (X-ray micro-calorimeter observations.
DEFF Research Database (Denmark)
Pena Diaz, Alfredo; Hahmann, Andrea N.
2012-01-01
anemometer at 15 m height and potential temperature differences between the water and the air above. Surface flux estimations from the advanced weather research and forecast (WRF) model are also validated against the sonic and bulk data. The correlation between the sonic and bulk estimates of friction......Direct estimations of turbulent fluxes and atmospheric stability were performed from a sonic anemometer at 50 m height on a meteorological mast at the Horns Rev wind farm in the North Sea. The stability and flux estimations from the sonic measurements are compared with bulk results from a cup...... velocity is high and the highest among all velocity comparisons. From the sonic–bulk–WRF inter‐comparison, it is found that the atmospheric stability measures at the sonic height tend to be closer to the neutral value than the WRF and bulk estimates, which are performed within an air layer closer...
DEFF Research Database (Denmark)
Chougule, Abhijit S.; Mann, Jakob; Kelly, Mark C.
2017-01-01
the eddy lifetime parameterization of Mann to make the model stationary. The buoyant spectral tensor model is driven via five parameters: the viscous dissipation rate epsilon, length scale of energy-containing eddies L, a turbulence anisotropy parameter Gamma, gradient Richardson number (Ri) representing...
Hicks, Micheal M.
A comprehensive analysis of surface-atmosphere flux exchanges over a mixed rural and urban convective environment is conducted at Howard University Beltsville, MD Research Campus. This heterogeneous site consists of rural, suburban and industrial surface covers to its south, east and west, within a 2 km radius of a flux sensor. The eddy covariance method is utilized to estimate surface-atmosphere flux exchanges of momentum, heat and moisture. The attributes of these surface flux exchanges are contrasted to those of classical homogeneous sites and assessed for accuracy, to evaluate the following: (I) their similarity to conventional convective boundary layer (CBL) processes and (II) their representativeness of the surrounding environment's turbulent properties. Both evaluations are performed as a function of upwind surface conditions. In particular, the flux estimates' obedience to spectrum power laws and similarity theory relationships is used for performing the first evaluation, and their ability to close the surface energy balance and accurately model CBL heights is used for the latter. An algorithm that estimates atmospheric boundary layer heights from observed lidar extinction backscatter was developed, tested and applied in this study. The derived lidar based CBL heights compared well with those derived from balloon borne soundings, with an overall Pearson correlation coefficient and standard deviation of 0.85 and 223 m, respectively. This algorithm assisted in the evaluation of the response of CBL processes to surface heterogeneity, by deriving high temporal CBL heights and using them as independent references of the surrounding area averaged sensible heat fluxes. This study found that the heterogeneous site under evaluation was rougher than classical homogeneous sites, with slower dissipation rates of turbulent kinetic energy. Flux measurements downwind of the industrial complexes exhibited enhanced efficiency in surface-atmosphere momentum, heat, and
Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan
2015-09-21
The mean-square angle-of-arrival (AOA) difference between two counter-propagating spherical waves in atmospheric turbulence is theoretically formulated. Closed-form expressions for the path weighting functions are obtained. It is found that the diffraction and refraction effects of turbulent cells make negative and positive contributions to the mean-square AOA difference, respectively, and the turbulent cells located at the midpoint of the propagation path have no contributions to the mean-square AOA difference. If the mean-square AOA difference is separated into the refraction and diffraction parts, the refraction part always dominates the diffraction one, and the ratio of the diffraction part to the refraction one is never larger than 0.5 for any turbulence spectrum. Based on the expressions for the mean-square AOA difference, formulae for the correlation coefficient between the angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are derived. Numerical calculations are carried out by considering that the turbulence spectrum has no path dependence. It is shown that the mean-square AOA difference always approximates to the variance of AOA fluctuations. It is found that the correlation coefficient between the angles of arrival in the x or y direction of two counter-propagating spherical waves ranges from 0.46 to 0.5, implying that the instantaneous angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are far from being perfectly correlated even when the turbulence spectrum does not vary along the path.
Fritts, D. C.; Geller, M. A.; Schoeberl, M. R.; Balsley, B. B.; Chanin, M. L.; Hirota, I.; Holton, J. R.; Kato, S.; Lindzen, R. S.; Vincent, R. A.
1984-01-01
The Alaska Workshop on Gravity Waves and Turbulence in the Middle Atmosphere had as its purpose the assessment of current theoretical understanding and observational capabilities in this field, as well as to suggest what additional studies would further knowledge of these processes and their effects on the large scale circulation of the middle atmosphere. While it is judged that current understanding is primitive, theoretical and modelling studies are held to be able to contribute important quantitative data on gravity wave excitation, propagation, and dissipation mechanisms and effects. The combination of several observational systems is considered capable of expanding the present knowledge of gravity wave and turbulence morphology, parameters, and processes.
Directory of Open Access Journals (Sweden)
G. A. Lehmacher
2011-12-01
Full Text Available Very few sequences of high resolution wind and temperature measurements in the lower thermosphere are available in the literature, which makes it difficult to verify the simulation results of models that would provide better understanding of the complex dynamics of the region. To address this problem the Turbopause experiment used four rockets launched over a period of approximately two hours from Poker Flat Research Range, Alaska (64° N, 147° W on the night of 17–18 February 2009. All four rocket payloads released trimethyl aluminum trails for neutral wind and turbulence measurements, and two of the rockets carried ionization gauges and fixed-bias Langmuir probes measuring neutral and electron densities, small-scale fluctuations and neutral temperatures. Two lidars monitored temperature structure and sodium densities. The observations were made under quiet geomagnetic conditions and show persistence in the wind magnitudes and shears throughout the observing period while being modulated by inertia-gravity waves. High resolution temperature profiles show the winter polar mesosphere and lower thermosphere in a state of relatively low stability with several quasi-adiabatic layers between 74 and 103 km. Temperature and wind data were combined to calculate Richardson number profiles. Evidence for turbulence comes from simultaneous observations of density fluctuations and downward transport of sodium in a mixed layer near 75 km; the observation of turbulent fluctuations and energy dissipation from 87–90 km; and fast and irregular trail expansion at 90–93 km, and especially between 95 to 103 km. The regions of turbulent trails agree well with regions of quasi-adiabatic temperature gradients. Above 103 km, trail diffusion was mainly laminar; however, unusual features and vortices in the trail diffusion were observed up to 118 km that have not been as prevalent or as clearly evident in earlier trail releases.
Representation of the grey zone of turbulence in the atmospheric boundary layer
Honnert, Rachel
2016-04-01
Numerical weather prediction model forecasts at horizontal grid lengths in the range of 100 to 1 km are now possible. This range of scales is the "grey zone of turbulence". Previous studies, based on large-eddy simulation (LES) analysis from the MésoNH model, showed that some assumptions of some turbulence schemes on boundary-layer structures are not valid. Indeed, boundary-layer thermals are now partly resolved, and the subgrid remaining part of the thermals is possibly largely or completely absent from the model columns. First, some modifications of the equations of the shallow convection scheme have been tested in the MésoNH model and in an idealized version of the operational AROME model at resolutions coarser than 500 m. Secondly, although the turbulence is mainly vertical at mesoscale (> 2 km resolution), it is isotropic in LES (AROME, which needs mixing lengths in the formulation. Vertical and horizontal mixing lengths have been calculated from LES of neutral and convective cases at resolutions in the grey zone.
A Dropsonde UAV for Atmospheric Sensing in a Turbulent Environment Project
National Aeronautics and Space Administration — Dropsondes are one of the primary atmospheric measurement tools available to researchers. Current dropsondes are deployed with a free fall parachute trajectory,...
Salomons, E M; Ostashev, V E; Clifford, S F; Lataitis, R J
2001-05-01
A new, rigorous approach is presented for the computation of the fluctuating field of a monopole source in a nonrefracting, turbulent atmosphere above a ground surface. The time-averaged sound pressure level is considered, as well as statistical distributions of the sound pressure level. The computation is based on the Rytov solution of the wave equation for a turbulent medium, evaluated for the half-space above the ground surface. The solution takes into account the ground reflection of scattered waves, which has been neglected in previous work on this subject. The present approach is based on a Fourier-Stieltjes representation of refractive-index fluctuations, and makes use of a turbulent image atmosphere to account for the ground reflection of scattered waves. This approach is rigorous only for a rigid ground surface, but it is shown that it also yields a good approximation for a finite-impedance ground surface. The accuracy of the solution is demonstrated by comparison with results of numerical computations with the parabolic equation method for a turbulent atmosphere. The assumption of a nonrefracting atmosphere implies that direct application of the solution is limited to propagation over relatively small distances. However, this study can also be considered as a basis for a generalized solution for a downward refracting atmosphere, which can be applied for larger propagation distances.
Shapkalijevski, M.M.
2017-01-01
This thesis deals with the representation of the exchange of energy, momentum and chemically reactive compounds between the land, covered by high vegetation, and the lowest part of the atmosphere, named as atmospheric boundary layer (ABL). The study presented in this thesis introduces the roughness
Yura, Harold T; Fields, Renny A
2011-06-20
Level crossing statistics is applied to the complex problem of atmospheric turbulence-induced beam wander for laser propagation from ground to space. A comprehensive estimate of the single-axis wander angle temporal autocorrelation function and the corresponding power spectrum is used to develop, for the first time to our knowledge, analytic expressions for the mean angular level crossing rate and the mean duration of such crossings. These results are based on an extension and generalization of a previous seminal analysis of the beam wander variance by Klyatskin and Kon. In the geometrical optics limit, we obtain an expression for the beam wander variance that is valid for both an arbitrarily shaped initial beam profile and transmitting aperture. It is shown that beam wander can disrupt bidirectional ground-to-space laser communication systems whose small apertures do not require adaptive optics to deliver uniform beams at their intended target receivers in space. The magnitude and rate of beam wander is estimated for turbulence profiles enveloping some practical laser communication deployment options and suggesting what level of beam wander effects must be mitigated to demonstrate effective bidirectional laser communication systems.
Johnson, E. H.
1975-01-01
The optimal design was investigated of simple structures subjected to dynamic loads, with constraints on the structures' responses. Optimal designs were examined for one dimensional structures excited by harmonically oscillating loads, similar structures excited by white noise, and a wing in the presence of continuous atmospheric turbulence. The first has constraints on the maximum allowable stress while the last two place bounds on the probability of failure of the structure. Approximations were made to replace the time parameter with a frequency parameter. For the first problem, this involved the steady state response, and in the remaining cases, power spectral techniques were employed to find the root mean square values of the responses. Optimal solutions were found by using computer algorithms which combined finite elements methods with optimization techniques based on mathematical programming. It was found that the inertial loads for these dynamic problems result in optimal structures that are radically different from those obtained for structures loaded statically by forces of comparable magnitude.
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.
Sun, Xiaole; Djordjevic, Ivan B.; Neifeld, Mark A.
2016-03-01
Free-space optical (FSO) channels can be characterized by random power fluctuations due to atmospheric turbulence, which is known as scintillation. Weak coherent source based FSO quantum key distribution (QKD) systems suffer from the scintillation effect because during the deep channel fading the expected detection rate drops, which then gives an eavesdropper opportunity to get additional information about protocol by performing photon number splitting (PNS) attack and blocking single-photon pulses without changing QBER. To overcome this problem, in this paper, we study a large-alphabet QKD protocol, which is achieved by using pulse-position modulation (PPM)-like approach that utilizes the time-frequency uncertainty relation of the weak coherent photon state, called here TF-PPM-QKD protocol. We first complete finite size analysis for TF-PPM-QKD protocol to give practical bounds against non-negligible statistical fluctuation due to finite resources in practical implementations. The impact of scintillation under strong atmospheric turbulence regime is studied then. To overcome the secure key rate performance degradation of TF-PPM-QKD caused by scintillation, we propose an adaptation method for compensating the scintillation impact. By changing source intensity according to the channel state information (CSI), obtained by classical channel, the adaptation method improves the performance of QKD system with respect to the secret key rate. The CSI of a time-varying channel can be predicted using stochastic models, such as autoregressive (AR) models. Based on the channel state predictions, we change the source intensity to the optimal value to achieve a higher secret key rate. We demonstrate that the improvement of the adaptation method is dependent on the prediction accuracy.
Modeling of High-Pressure Turbulent Multi-Species Mixing Applicable to the Venus Atmosphere
Bellan, J.
2017-11-01
A comprehensive theory of high-pressure multi-species mixing is presented and salient results pertinent to the Venus atmosphere are discussed. The influence of the insights obtained from these results on Venus exploration are addressed.
CSIR Research Space (South Africa)
Griffith, DJ
2013-09-01
Full Text Available services for the Rietvlei campaign were provided by the Advanced Fire Information System (AFIS8). REFERENCES [1] Weiss-Wrana, K. and Balfour, L. S., “Statistical analysis of measurements of atmospheric turbulence in different climates,” Optics...
A Kolmogorov-Brutsaert structure function model for evaporation into a turbulent atmosphere
Katul, Gabriel; Liu, Heping
2017-05-01
In 1965, Brutsaert proposed a model that predicted mean evaporation rate E¯ from rough surfaces to scale with the 3/4 power law of the friction velocity (u∗) and the square-root of molecular diffusivity (Dm) for water vapor. In arriving at these results, a number of assumptions were made regarding the surface renewal rate describing the contact durations between eddies and the evaporating surface, the diffusional mass process from the surface into eddies, and the cascade of turbulent kinetic energy sustaining the eddy renewal process itself. The working hypothesis explored here is that E¯˜Dmu∗3/4 is a direct outcome of the Kolmogorov scaling for inertial subrange eddies modified to include viscous cutoff thereby bypassing the need for a surface renewal assumption. It is demonstrated that Brutsaert's model for E¯ may be more general than its original derivation implied.
Banakh, V A; Smalikho, I N; Falits, A V
2017-09-18
The accuracy of the method of azimuth structure function for estimation of the dissipation rate of the kinetic energy of turbulence from an array of radial velocities measured by low-energy micropulse coherent Doppler lidars with conical scanning by a probing beam around the vertical axis has been studied numerically. The applicability of the method in dependence on the turbulence intensity and the signal-to-noise ratio has been determined. The method of azimuth structure function was applied for estimation of the turbulent energy dissipation rate from radial velocities measured by the lidar in the experiments on the coast of Lake Baikal. Two dimensional time-height patterns of the wind turbulence energy dissipation rate were obtained. Part of them were obtained in presence of the atmospheric internal waves (AIWs) and low-level jet streams. It is observed that the wind turbulence in the area occupied by jet streams is very weak. In the process of dissipation of AIWs the wind turbulence strength increases.
Temporal coherence of a soundfield in the turbulent atmosphere near the ground
DEFF Research Database (Denmark)
Arranz, Marta Galindo; Havelock, Dave I.
1996-01-01
A sound field propagating through the atmosphere changes with time due to the dynamics of the inhomogeneous medium. The coherence time, defined as the time lag beyond which the auto correlation is less than 1/e, is a time scale for dynamics of the medium as well as design criteria for coherent...
Litt, Maxime; Steiner, Jakob F.; Stigter, Emmy E.; Immerzeel, Walter; Shea, Joseph Michael
2017-04-01
Over debris-covered glaciers, water content variations in the debris layer can drive significant changes in its thermal conductivity and significantly impact melt rates. Since sublimation and evaporation are favoured in high-altitude conditions, e.g., low atmospheric pressure and high wind speeds, they are expected to strongly influence the water balance of the debris-layer. Dedicated latent heat fluxes measurements at the debris surface are essential to characterize the debris heat conductivity in order to assess underlying ice melt. Furthermore, the contribution of the turbulent fluxes in the surface energy balance over debris covered glacier remains uncertain since they are generally evaluated through similarity methods which might not be valid in complex terrain. We present the first results of a 15-day eddy-covariance experiment installed at the end of the monsoon (September-October) on a 3-m tower above the debris-covered Lirung glacier in Nepal. The tower also included measurements of the 4 radiation components. The eddy covariance measurements allowed for the characterization of the turbulence in the atmospheric surface layer, as well as the direct measurements of evaporation, sublimation and turbulent sensible heat fluxes. The experiment helps us to evaluate the contribution of turbulent fluxes to the surface energy balance over this debris-covered glacier, through a precise characterization of the overlying turbulent atmospheric surface layer. It also helps to study the role of the debris-layer water content changes through evaporation and sublimation and its feedback on heat conduction in this layer. The large observed turbulent fluxes play a significant role in the energy balance at the debris surface and significantly influence debris moisture, conductivity and subsequently underlying ice melt.
Zhang, Yan; Wang, Ping; Guo, Lixin; Wang, Wei; Tian, Hongxin
2017-08-21
The average bit error rate (ABER) performance of an orbital angular momentum (OAM) multiplexing-based free-space optical (FSO) system with multiple-input multiple-output (MIMO) architecture has been investigated over atmospheric turbulence considering channel estimation and space-time coding. The impact of different types of space-time coding, modulation orders, turbulence strengths, receive antenna numbers on the transmission performance of this OAM-FSO system is also taken into account. On the basis of the proposed system model, the analytical expressions of the received signals carried by the k-th OAM mode of the n-th receive antenna for the vertical bell labs layered space-time (V-Blast) and space-time block codes (STBC) are derived, respectively. With the help of channel estimator carrying out with least square (LS) algorithm, the zero-forcing criterion with ordered successive interference cancellation criterion (ZF-OSIC) equalizer of V-Blast scheme and Alamouti decoder of STBC scheme are adopted to mitigate the performance degradation induced by the atmospheric turbulence. The results show that the ABERs obtained by channel estimation have excellent agreement with those of turbulence phase screen simulations. The ABERs of this OAM multiplexing-based MIMO system deteriorate with the increase of turbulence strengths. And both V-Blast and STBC schemes can significantly improve the system performance by mitigating the distortions of atmospheric turbulence as well as additive white Gaussian noise (AWGN). In addition, the ABER performances of both space-time coding schemes can be further enhanced by increasing the number of receive antennas for the diversity gain and STBC outperforms V-Blast in this system for data recovery. This work is beneficial to the OAM FSO system design.
Brun, Ch.; Chollet, J. P.
2009-04-01
The behaviour of the Atmospheric Boundary layer (ABL) along alpine valleys is strongly dependent on the day-night thermodynamic cycle and might impact meteorology and air pollution prediction. At night, the ABL is stably stratified and the radiative cooling of the surface yields the development of a katabatic flow (Doran and Horst 1983, Monti et al. 2002). This flow consists of a downslope wall-jet which has the structure of both wall turbulence in the inner-layer zone and shear layer turbulence in the outer-layer zone and enhances a relative mixing eventhough stable stratification is considered (Baines 2005). A full 3D description of such flow by mean of Large Eddy Simulation of turbulence (LES) has not yet been achieved, except recently on relatively simple slopes (Skyllingstad 2003, Smith and Skyllingstad 2005) or including geostrophic wind forcing (Cuxart et al. 2006, Cuxart and Jimenez 2006). This is the purpose of the present study to accurately describe the ABL on a hyperbolic tangent slope with stable stratification. The numerical code used, Meso-NH, has been developed in CNRM/Meteo-France and Laboratoire d'Aérologie Toulouse, and consists of an anelastic non-hydrostatic model solving the pseudo-incompressible Navier-Stokes equations with a Boussinesq approximation. About 5 million grid points are necessary to afford a relatively precise description of the flow in the vicinity of the surface, with a special refinement in the vertical direction to capture the wall-jet developing along the slope. The setting of initial and boundary conditions is crucial for the simulation of stable ABL. Initial conditions consist of air at rest following a stable temperature profile with a constant Brunt-Väisälä frequency N=0.013. At the surface two sets of boundary conditions have been considered, first a rough surface condition, second an ideal case with slip conditions. A constant surface cooling q_w=-30 W/m2 is applied on the stably stratified fluid initially at rest
Preliminary Work in Atmospheric Turbulence Profiles with the Differential Multi-image Motion Monitor
2016-09-01
np import matplotlib.pyplot as plt import scipy.io as sio from OCCIMA.atmosphere.atmosgeo import geo , atmos # T a r g e t s e p a r a t i o n s i n m e...Viscous Fluid for Very Large Reynolds Numbers.” Dokl. Akad. Nauk SSSR, vol. 30, pp. 299–303. 4. Fried, D. L. 1965. “Statistics of a Geometric
Bordiec, Maï; Carpy, Sabrina; Perret, Laurent; Bourgeois, Olivier; Massé, Marion
2017-04-01
The redistribution of surface ice induced the wind flow may lead to the development and migration of periodic bedforms, or "ice ripples", at the surface of ice sheets. In certain cold and dry environments, this redistribution need not involve solid particle transport but may be dominated by sublimation and condensation, inducing mass transfers between the ice surface and the overlying steady boundary layer turbulent flow. These mass transfers diffuse the water vapour sublimated from the ice into the atmosphere and become responsible for the amplification and propagation of ripples in a direction perpendicular to their crests. Such ice ripples, 24 cm in wavelength, have been described in the so-called Blue Ice Areas of Antarctica. In order to understand the mechanisms that generate and develop these periodic bedforms on terrestrial glaciers and to evaluate the plausibility that similar bedforms may develop on Mars, we performed a linear stability analysis applied to a turbulent boundary layer flow perturbed by a wavy ice surface. The model is developed as follow. We first solve the flow dynamics using numerical methods analogous to those used in sand wave models assuming that the airflow is similar in both problems. We then add the transport/diffusion equation of water vapour following the same scheme. We use the Reynolds-averaged description of the equation with a Prandtl-like closure. We insert a damping term in the exponential formula of the Van Driest mixing length, depending on the pressure gradient felt by the flow and related to the thickness of the viscous sublayer at the ice-atmosphere interface. This formulation is an efficient way to properly represent the transitional regime under which the ripples grow. Once the mass flux of water vapour is solved, the phase shift between the ripples crests and the maximum of the flux can be deduced for different environments. The temporal evolution of the ice surface can be expressed from these quantities to infer the
Ren, Yongxiong; Wang, Zhe; Xie, Guodong; Li, Long; Willner, Asher J; Cao, Yinwen; Zhao, Zhe; Yan, Yan; Ahmed, Nisar; Ashrafi, Nima; Ashrafi, Solyman; Bock, Robert; Tur, Moshe; Willner, Alan E
2016-06-01
We explore the mitigation of atmospheric turbulence effects for orbital angular momentum (OAM)-based free-space optical (FSO) communications with multiple-input multiple-output (MIMO) architecture. Such a system employs multiple spatially separated aperture elements at the transmitter/receiver, and each transmitter aperture contains multiplexed data-carrying OAM beams. We propose to use spatial diversity combined with MIMO equalization to mitigate both weak and strong turbulence distortions. In a 2×2 FSO link with each transmitter aperture containing two multiplexed OAM modes of ℓ=+1 and ℓ=+3, we experimentally show that at least two OAM data channels could be recovered under both weak and strong turbulence distortions using selection diversity assisted with MIMO equalization.
DEFF Research Database (Denmark)
Hansen, Kurt Schaldemose; Barthelmie, Rebecca J.; Jensen, Leo E.
2012-01-01
the flow inside the wind farm, and the power deficits along rows of wind turbines have been determined for different inflow directions and wind speed intervals. A method to classify the atmospheric stability based on the Bulk-Ri number has been implemented. Long-term stability conditions have been...... unstable conditions, whereas northerly winds have fewer observations in the stable classes. Stable conditions also tend to be associated with lower levels of turbulence intensity, and this relationship persists as wind speeds increase. Power deficit is a function of ambient turbulence intensity. The level...... of power deficit is strongly dependent on the wind turbine spacing; as turbulence intensity increases, the power deficit decreases. The power deficit is determined for four different wind turbine spacing distances and for stability classified as very stable, stable and others (near neutral to very unstable...
Energy Technology Data Exchange (ETDEWEB)
Baker, K L; Stappaerts, E A; Gavel, D; Tucker, J; Silva, D A; Wilks, S C; Olivier, S S; Olsen, J
2004-08-25
An adaptive optical system used to correct horizontal beam propagation paths has been demonstrated. This system utilizes an interferometric wave-front sensor and a large-actuator-number MEMS-based spatial light modulator to correct the aberrations incurred by the beam after propagation along the path. Horizontal path correction presents a severe challenge to adaptive optics systems due to the short atmospheric transverse coherence length and the high degree of scintillation incurred by laser propagation along these paths. Unlike wave-front sensors that detect phase gradients, however, the interferometric wave-front sensor measures the wrapped phase directly. Because the system operates with nearly monochromatic light and uses a segmented spatial light modulator, it does not require that the phase be unwrapped to provide a correction and it also does not require a global reconstruction of the wave-front to determine the phase as required by gradient detecting wave-front sensors. As a result, issues with branch points are eliminated. Because the atmospheric probe beam is mixed with a large amplitude reference beam, it can be made to operate in a photon noise limited regime making its performance relatively unaffected by scintillation. The MEMS-based spatial light modulator in the system contains 1024 pixels and is controlled to speeds in excess of 800 Hz, enabling its use for correction of horizontal path beam propagation. In this article results are shown of both atmospheric characterization with the system and open loop horizontal path correction of a 1.53 micron laser by the system. To date Strehl ratios of greater than 0.5 have been achieved.
Mukhartova, Juliya; Levashova, Natalia; Volkova, Elena; Olchev, Alexander
2016-04-01
vegetation and land-use types are situated far enough from the domain boundaries. It enabled us to assume that near these boundaries the values of vertical and horizontal wind components are independent on x coordinate. To quantify the possible effects of relief and vegetation heterogeneity on CO2 fluxes the three transects crossing the study area were chosen. For each transect the 2D patterns of wind speed components, turbulent exchange coefficients, CO2 concentrations and fluxes were calculated. The modeled vertical CO2 fluxes were compared with the fluxes calculated without allowing for turbulent disturbances due to relief and vegetation heterogeneity. All modeling experiments were provided for different weather conditions. The results of modeling experiments for different transects under various meteorological conditions showed that relief and vegetation heterogeneity have a significant impact on CO2 fluxes within the atmospheric surface layer and their ignoring can results in uncertainties in flux estimations. This study was supported by the Russian Science Foundation (Grant 14-14-00956).
Mclaren, Jason R W; Thomas, John C; Mackintosh, Jessica L; Mudge, Kerry A; Grant, Kenneth J; Clare, Bradley A; Cowley, William G
2012-09-01
A large number of model probability density functions (PDFs) are used to analyze atmospheric scintillation statistics. We have analyzed scintillation data from two different experimental setups covering a range of scintillation strengths to determine which candidate model PDFs best describe the experimental data. The PDFs were fitted to the experimental data using the method of least squares. The root-mean-squared fitting error was used to monitor the goodness of fit. The results of the fitting were found to depend strongly on the scintillation strength. We find that the log normally modulated Rician and the log normal PDFs are the best fit to the experimental data over the range of scintillation strengths encountered.
Energy Technology Data Exchange (ETDEWEB)
R. L. Street; F. L. Ludwig; Y. Chen
2005-04-11
Our DOE project is one of the efforts comprising the Vertical Transport and Mixing Program of the Environmental Sciences Division of the Office of Biological and Environmental Research in Department of Energy. We used ARPS to simulate flow in the Salt Lake Valley. We simulated the physical processes more accurately so that we can better understand the physics of flow in complex terrain and its effects at larger scales. The simulations provided evidence that atmospheric forcing interacts with the Jordan Narrows, the Traverse Range and other complex mountain terrain at the south end of the Salt Lake Valley to produce lee rotors, hydraulic jumps and other effects. While we have successfully used ARPS to simulate VTMX 2000 flows, we have also used observed data to test the model and identify some of its weaknesses. Those are being addressed in a continuation project supported by DOE.
12th EUROMECH European Turbulence Conference
Eckhardt, Bruno
2009-01-01
This volume comprises the communications presented at the EUROMECH European Turbulence Conference ETC12, held in Marburg in September 2009. The topics covered by the meeting include: Acoustics of turbulent flows Atmospheric turbulence Control of turbulent flows Geophysical and astrophysical turbulence Instability and transition Intermittency and scaling Large eddy simulation and related techniques Lagrangian aspects MHD turbulence Reacting and compressible turbulence Transport and mixing Turbulence in multiphase and non-Newtonian flows Vortex dynamics and structure formation Wall bounded flows
Ding, Zhangwei; Ma, Yaoming; Wen, Zhiping; Ma, Weiqiang; Chen, Shiji
2017-07-01
Banana plantation and alpine meadow ecosystems in southern China and the Tibetan Plateau (TP) are unique in the underlying surfaces they exhibit. In this study, we used eddy covariance and a micrometeorological tower to examine the characteristics of land surface energy exchanges over a banana plantation in southern China and an alpine meadow in the Tibetan Plateau from May 2010 to August 2012. The results showed that the diurnal and seasonal variations in upward shortwave radiation flux and surface soil heat flux were larger over the alpine meadow than over the banana plantation surface. Dominant energy partitioning varied with season. Latent heat flux was the main consumer of net radiation flux in the growing season, whereas sensible heat flux was the main consumer during other periods. The Monin-Obukhov similarity theory was employed for comparative purposes, using sonic anemometer observations of flow over the surfaces of banana plantations in the humid southern China monsoon region and the semi-arid areas of the TP, and was found to be applicable. Over banana plantation and alpine meadow areas, the average surface albedo and surface aerodynamic roughness lengths under neutral atmospheric conditions were ˜0.128 and 0.47 m, and ˜0.223 and 0.01 m, respectively. During the measuring period, the mean annual bulk transfer coefficients for momentum and sensible heat were 1.47 × 10-2 and 7.13 × 10-3, and 2.91 × 10-3 and 1.96 × 10-3, for banana plantation and alpine meadow areas, respectively.
Kwon, Byung Hyuk; Lee, Gyuwon
2010-11-01
The SEMAPHORE (Structure des Echanges Mer-Atmosphère, Propriétés Océaniques/ Recherche Expérimentale) experiment, which took place between 04 Oct. and 17 Nov. 1993, was conducted over the oceanic Azores current located in the Azores basin. The SST (Sea Surface Temperature) field was characterized in the SEMAPHORE area (31°-38°N; 21°-28°W) by a large meander with a SST gradient of about 1°C per 100 km. In order to study the evolution of the MABL (Marine Atmospheric Boundary Layer) over the ocean, the mean and the turbulent data were evaluated by the measurement with two aircraft and a ship in different meteorological conditions. Three cases of low pressure and three cases of high pressure are mainly presented here. For the six cases, the satellite images (NOAA) did not show any relation between the SST field and the cloud cover. At each flight level, the decrease of the SST with the altitude due to the divergence of the infrared radiation flux from the ocean is 0.25°C per 100 m. For the comparison between the two aircraft, the mean thermodynamic and dynamic parameters show a good agreement except for the temperature. The dispersion of the sensible heat flux is larger than that of the latent heat flux due to the weak sensible heat flux over the ocean both in the intercomparison between two aircraft and in the comparison between the aircraft and the ship.
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
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.
Fu, Huihua; Wang, Ping; Liu, Tao; Cao, Tian; Guo, Lixin; Qin, Jiao
2017-08-10
The average bit error rate (ABER) performance of an avalanche-photodiode (APD)-based pulse-position modulation (PPM) free-space optical (FSO) communication system is investigated considering the aperture averaging effect. The approximate ABER expression is theoretically derived in terms of M and exponentiated Weibull (EW) distributions under weak-to-strong turbulent atmosphere conditions with a binary PPM (BPPM) scheme. Union-bound and Hermite polynomials are then considered to estimate the performance of M-ary PPM FSO systems. The system performance is analyzed with the aperture sizes, turbulence strengths, receiver temperatures, and average photon counts taken into account. The results show that an optimal average APD gain, which is affected by receiver temperature, can be chosen to minimize the ABER value. And the impact of aperture averaging on the system performance over M distribution is not so apparent as that over EW distribution for different temperatures, turbulent strengths, and average photon counts. In addition, the present APD-based system can offer better ABER performance than that of a P-i-N-based PPM system over both EW and M fading channels at 300 and 500 K. This work is beneficial to the FSO system design.
Nandi, Tarak Nath
Relevant to utility scale wind turbine functioning and reliability, the present work focuses on enhancing our understanding of wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and rotating blades of a GE 1.5 MW wind turbine using a unique data set from a GE field experiment and computer simulations at two levels of fidelity. Previous studies have shown that the stability state of the lower troposphere has a major impact on the coherent structure of the turbulence eddies, with corresponding differences in wind turbine loading response. In this study, time-resolved aerodynamic data measured locally at the leading edge and trailing edge of three outer blade sections on a GE 1.5 MW wind turbine blade and high-frequency SCADA generator power data from a daytime field campaign are combined with computer simulations that mimic the GE wind turbine within a numerically generated atmospheric boundary layer (ABL) flow field which is a close approximation of the atmospheric turbulence experienced by the wind turbine in the field campaign. By combining the experimental and numerical data sets, this study describes the time-response characteristics of the local loadings on the blade sections in response to nonsteady nonuniform energetic atmospheric turbulence eddies within a daytime ABL which have spatial scale commensurate with that of the turbine blade length. This study is the first of its kind where actuator line and blade boundary layer resolved CFD studies of a wind turbine field campaign are performed with the motivation to validate the numerical predictions with the experimental data set, and emphasis is given on understanding the influence of the laminar to turbulent transition process on the blade loadings. The experimental and actuator line method data sets identify three important response time scales quantified at the blade location: advective passage of energy-dominant eddies (≈25 - 50 s), blade rotation (1P
2009-06-01
Tewksbury-Christlea, Patrick R. Kellya aStarfire Optical Range, Air Force Research Labs, Kirtland Air Force Base, New Mexico , USA ABSTRACT The...from s ingle phase whul data for sclectcd Illrb tlience stre1lgtils . For each CIH’VC, the turbulence strength, gIVen by ro o is held COlls tant
Energy Technology Data Exchange (ETDEWEB)
Lawson, J K; Carrano, C J
2006-06-20
Image data collected near the ground, in the boundary layer, or from low altitude planes must contend with the detrimental effects of atmospheric turbulence on the image quality. So it is useful to predict operating regimes (wavelength, height of target, height of detector, total path distance, day vs. night viewing, etc.) where atmospheric turbulence is expected to play a significant role in image degradation. In these regimes, image enhancement techniques such as speckle processing, deconvolution and Wiener filtering methods can be utilized to recover near instrument-limited resolution in degraded images. We conducted a literature survey of various boundary layer and lower troposphere models for the structure coefficient of the index of refraction (C{sub n}{sup 2}). Using these models, we constructed a spreadsheet tool to estimate the Fried parameter (r{sub 0}) for different scenarios, including slant and horizontal path trajectories. We also created a tool for scenarios where the height along the path crudely accounted for the topology of the path. This would be of particular interest in mountain-based viewing platforms surveying ground targets. The tools that we developed utilized Visual Basic{reg_sign} programming in an Excel{reg_sign} spreadsheet environment for accessibility and ease of use. In this paper, we will discuss the C{sub n}{sup 2} profile models used, describe the tools developed and compare the results obtained for the Fried parameter with those estimated from experimental data.
Jackson, Christopher Robert
"Lucky-region" fusion (LRF) is a synthetic imaging technique that has proven successful in enhancing the quality of images distorted by atmospheric turbulence. The LRF algorithm selects sharp regions of an image obtained from a series of short exposure frames, and fuses the sharp regions into a final, improved image. In previous research, the LRF algorithm had been implemented on a PC using the C programming language. However, the PC did not have sufficient sequential processing power to handle real-time extraction, processing and reduction required when the LRF algorithm was applied to real-time video from fast, high-resolution image sensors. This thesis describes two hardware implementations of the LRF algorithm to achieve real-time image processing. The first was created with a VIRTEX-7 field programmable gate array (FPGA). The other developed using the graphics processing unit (GPU) of a NVIDIA GeForce GTX 690 video card. The novelty in the FPGA approach is the creation of a "black box" LRF video processing system with a general camera link input, a user controller interface, and a camera link video output. We also describe a custom hardware simulation environment we have built to test the FPGA LRF implementation. The advantage of the GPU approach is significantly improved development time, integration of image stabilization into the system, and comparable atmospheric turbulence mitigation.
2012-01-01
Radiometer (AVHRR) and the surface chlorophyll concentrations from MODIS Aqua. Considering the trade-off between uncontaminated images and frequency of...and the albedo following Payne (1972), while the net long wave radiation using Berliand’s formula (see Budiko, 1974 for details) and turbulent...Osborn, T.R.. Cox, C.S., 1972. Oceanic fine structure. Geophys. Fluid Dyn. 3,321 -345. Payne. R.E., 1972. Albedo of the sea surface. J. Atmos. Sei
Geng, Dongxian; Du, Pengfei; Wang, Wei; Gao, Gan; Wang, Tao; Gong, Mali
2014-07-01
A free space duplex communication system with a single laser and a modulated retro-reflector is presented. A method to minimize the echo wave bit error rate (BER) of this system is proposed by setting the optimum threshold automatically based on the measured mean power and irradiance variances with log-normal distribution and the Bayes minimum classification error criterion. Experiments were taken at a distance of 1.55 km in a weak turbulence and the measured BER was 0.0213. The BER performance of this system is studied and the result shows the experimental BER is in good accordance with the theoretical value.
Interdisciplinary aspects of turbulence
Kupka, Friedrich
2008-01-01
What do combustion engines, fusion reactors, weather forecast, ocean flows, our sun, and stellar explosions in outer space have in common? Of course, the physics and the length and time scales are vastly different in all cases, but it is also well known that in all of them, on some relevant length scales, the material flows that govern the dynamical and/or secular evolution of the systems are chaotic and often unpredictable: they are said to be turbulent. The interdisciplinary aspects of turbulence are brought together in this volume containing chapters written by experts from very different fields, including geophysics, astrophysics, and engineering. It covers several subjects on which considerable progress was made during the last decades, from questions concerning the very nature of turbulence to some practical applications. These subjects include: a basic introduction into turbulence, statistical mechanics and nonlinear dynamics, turbulent convection in stars, atmospheric turbulence in the context of nume...
Sarazin, Marc S.; Osborn, James; Chacon-Oelckers, Arlette; Dérie, Frédéric J.; Le Louarn, Miska; Milli, Julien; Navarrete, Julio; Wilson, Richard R. W.
2017-09-01
The Stereo-SCIDAR (Scintillation Detection and Ranging) atmospheric turbulence profiler, built for ESO by Durham University, observes the scintillation patterns of binary elements with one of the four VLT-Interferometer 1.8m auxiliary telescopes at the ESO Paranal Observatory. The primary products are the vertical profiles of the index of refraction structure coefficient and of the wind velocity which allow to compute the wavefront coherence time and the isoplanatic angle with a vertical resolution of 250m. The several thousands of profiles collected during more than 30 nights of operation are grouped following criteria based on the altitude distribution or on principal component analysis. A set of reference profiles representative of the site is proposed as input for the various simulation models developed by the E-ELT (European Extremely Large Telescope) instruments Consortia.
Ding, Jiachen; Li, Mi; Tang, Minghui; Li, Yan; Song, Yuejiang
2013-09-15
Minimum shift keying (MSK) has been widely used in fiber optical communication and free-space optical communication. In order to introduce MSK into satellite laser communication, the bit-error rate (BER) performance of the MSK scheme is investigated in uplink communications under the influence of atmospheric turbulence consisting of weak fluctuation and beam wander. Numerical results indicate that the BER performance of MSK is much better than the performance of on-off keying (OOK). With the laser power being 4 W, the improvement is 5 dB in coherent demodulation and 15 dB in delay coherent demodulation. Furthermore, compared with OOK, optimal values of the divergence angle, receiver diameter, and transmitter beam radius are easier and more practical to achieve in the MSK scheme. The work can benefit ground-to-satellite laser uplink communication system design.
Fritts, D. C.; Geller, M. A.; Balsley, B. B.; Chanin, M. L.; Hirota, I.; Holton, J. R.; Kato, S.; Lindzen, R. S.; Schoeberl, M. R.; Vincent, R. A.
1984-01-01
Internal gravity waves are disturbances whose intrinsic frequencies k(c - u) are smaller than the Brunt-Vaisala frequency (N). Their importance arises because: they are the major components of the total flow and temperature variability fields of the mesosphere (i.e., shears and lapse rates) and hence constitute the likely sources of turbulence; and they are associated with fluxes of momentum that communicate stresses over large distances. For example, gravity waves exert a drag on the flow in the upper mesosphere. However, in order for gravity waves to exert a net drag on the atmosphere, they must be attenuated. There are two general types of processes that seek to attenuate gravity waves: dissipation and saturation. Dissipation is any process that is effective independent of the wave amplitude, while saturation occurs when certain wave amplitude conditions are met. Radiative damping is an example of dissipation, while convective overturning is an example of saturation. The two processes are not mutually exclusive.
Quantitative evaluation of turbulence compensation
Eekeren, A.W.M. van; Schutte, K.; Dijk, J.; Schwering, P.B.W.
2013-01-01
A well-known phenomena that diminishes the recognition range in infrared imagery is atmospheric turbulence. In literature many methods are described that try to compensate for the distortions caused by atmospheric turbulence. Most of these methods use a global processing approach in which they
Stirring turbulence with turbulence
Cekli, H.E.; Joosten, R.F.D.; Water, W. van de
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
Energy Technology Data Exchange (ETDEWEB)
Zhang, Kai [Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Fu, Rong [Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles CA USA; Shaikh, Muhammad J. [Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Ghan, Steven [Pacific Northwest National Laboratory, Richland WA USA; Wang, Minghuai [Institute for Climate and Global Change Research and School of Atmospheric Sciences, Nanjing University, Nanjing China; Collaborative Innovation Center of Climate Change, Nanjing China; Leung, L. Ruby [Pacific Northwest National Laboratory, Richland WA USA; Dickinson, Robert E. [Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Marengo, Jose [Centro Nacional de Monitoramento e Alertas aos Desastres Naturais, São Jose dos Campos Brazil
2017-09-21
We evaluate the Community Atmosphere Model Version 5 (CAM5) with a higher-order turbulence closure scheme, named Cloud Layers Unified By Binomials (CLUBB), and a Multiscale Modeling Framework (MMF) with two different microphysics configurations to investigate their influences on rainfall simulations over Southern Amazonia. The two different microphysics configurations in MMF are the one-moment cloud microphysics without aerosol treatment (SAM1MOM) and two-moment cloud microphysics coupled with aerosol treatment (SAM2MOM). Results show that both MMF-SAM2MOM and CLUBB effectively reduce the low biases of rainfall, mainly during the wet season. The CLUBB reduces low biases of humidity in the lower troposphere with further reduced shallow clouds. The latter enables more surface solar flux, leading to stronger convection and more rainfall. MMF, especially MMF-SAM2MOM, unstablizes the atmosphere with more moisture and higher atmospheric temperatures in the atmospheric boundary layer, allowing the growth of more extreme convection and further generating more deep convection. MMF-SAM2MOM significantly increases rainfall in the afternoon, but it does not reduce the early bias of the diurnal rainfall peak; LUBB, on the other hand, delays the afternoon peak time and produces more precipitation in the early morning, due to more realistic gradual transition between shallow and deep convection. MMF appears to be able to realistically capture the observed increase of relative humidity prior to deep convection, especially with its two-moment configuration. In contrast, in CAM5 and CAM5 with CLUBB, occurrence of deep convection in these models appears to be a result of stronger heating rather than higher relative humidity.
Energy Technology Data Exchange (ETDEWEB)
Malet, F
2005-12-15
The main objectives of PhD work concern the characterisation of hydrogen flame propagation in air-steam mixture representative of reactor containment atmosphere in severe accident situations. Laminar and turbulent flame regimes were investigated with: (1) spherical bomb is used to perform laminar flame tests. Different parameters were identified: the laminar flame velocity, SL{sup 0}, and flame thickness, d, the integral length scale, LT, and intensity of turbulence, the Lewis and Zeldovich numbers, Le, b, the expansion ratio, s, the product speed of sound Csp. (2) ENACCEF facility dedicated to flame acceleration. This facility is highly instrumented (16 optical windows with PMT, 9 pressure transducers) to follow the flame propagation. The lower part of ENACCEF has 6 gas sampling locations. The mixture is ignited by a spark discharge at the bottom-end using electrodes. Tests performed on ENACCEF show the effect of blockage ratio, obstacles shape and gas composition on flame velocity. Some tests performed on the previous facilities were numerically simulated with TONUS CFD code. (author)
Marichal, Y.; De Visscher, I.; Chatelain, P.; Winckelmans, G.
2017-05-01
The objective of the present work is to develop a tool able to predict, in a computationally affordable way, the unsteady wind turbine power production and loads as well as its wake dynamics, as a function of the turbine dynamics and incoming wind conditions. Based on the lessons learned from a previous study about the characterization of the unsteady wake dynamics, the framework for an operational wake model is presented. The approach relies on an underlying vorticity-based skeleton consisting of different components, such as a regularized Vortex Sheet Tube (VST) and Vortex Dipole Line (VDL). Physically based evolution equations, accounting for the various flow phenomena occurring in the wake (such as advection, turbulent diffusion/core spreading, source/sink terms, etc.), are then derived. Once calibrated, the wake model is shown to be in good agreement with results of high-fidelity Large Eddy Simulations (LES) obtained using an Immersed Lifting Line-enabled Vortex Particle-Mesh method.
Directory of Open Access Journals (Sweden)
S. Marcq
2012-02-01
Full Text Available Leads are linear-like structures of open water within the sea ice cover that develop as the result of fracturing due to divergence or shear. Through leads, air and water come into contact and directly exchange latent and sensible heat through convective processes driven by the large temperature and moisture differences between them. In the central Arctic, leads only cover 1 to 2% of the ocean during winter, but account for more than 70% of the upward heat fluxes. Furthermore, narrow leads (several meters are more than twice as efficient at transmitting turbulent heat than larger ones (several hundreds of meters. We show that lead widths are power law distributed, P(X~X^{−a} with a>1, down to very small spatial scales (20 m or below. This implies that the open water fraction is by far dominated by very small leads. Using two classical formulations, which provide first order turbulence closure for the fetch-dependence of heat fluxes, we find that the mean heat fluxes (sensible and latent over open water are up to 55% larger when considering the lead-width distribution obtained from a SPOT satellite image of the ice cover, compared to the situation where the open water fraction constitutes one unique large lead and the rest of the area is covered by ice, as it is usually considered in climate models at the grid scale. This difference may be even larger if we assume that the power law scaling of lead widths extends down to smaller (~1 m scales. Such estimations may be a first step towards a subgrid scale parameterization of the spatial distribution of open water for heat fluxes calculations in ocean/sea ice coupled models.
Brun, Christophe; Chollet, Jean Pierre
2010-05-01
The behaviour of the Atmospheric Boundary layer (ABL) along alpine valleys is strongly dependent on the day-night thermodynamic cycle and might impact meteorology and air pollution prediction. At night, the ABL is stably stratified and the radiative cooling of the surface yields the development of a katabatic flow. This flow consists of a downslope wall-jet which has the structure of both wall turbulence in the inner-layer zone and shear layer turbulence in the outer-layer zone and enhances a relative mixing eventhough stable stratification is considered. A full 3D description of such flow by mean of Large Eddy Simulation of turbulence (LES) has not yet been achieved, except recently on relatively simple slopes (Skyllingstad 2003, Fedorovith and Shapiro 2009) or including geostrophic wind forcing (Cuxart et al. 2006, Cuxart and Jimenez 2006). This is the purpose of the present study to accurately describe the ABL on a curved slope with stable stratification, including passive scalar transport. The numerical code used, Meso-NH, has been developed in CNRM/Meteo-France and Laboratoire d'Aérologie Toulouse, and consists of an anelastic non-hydrostatic model solving the pseudo-incompressible Navier-Stokes equations. About 5 million grid points are necessary to afford a relatively precise description of the flow in the vicinity of the ground surface, with a special refinement down to 1 m in the vertical direction to capture the wall-jet developing along the slope. The setting of initial and boundary conditions is crucial for the simulation of stable ABL. Initial conditions consist of air at rest following a stable temperature profile with a constant Brunt-Väisälä frequency 0.01
Sérazin, Guillaume; Penduff, Thierry; Terray, Laurent; Grégorio, Sandy; Barnier, Bernard; Molines, Jean-Marc
2015-04-01
Ocean-atmosphere heat fluxes are particularly strong in Western Boundary Current (WBC) regions where SST front variations influence basin-scale climate variability. Observed low-frequency fluctuations in latitude and strength of these oceanic jets are classically thought to be essentially atmospherically-driven by wind stress curl variability via the oceanic Rossby wave adjustment. Yet academic eddy-resolving process-oriented models with double-gyre configurations have revealed that an idealized WBC may exhibit low-frequency intrinsic fluctuations without low-frequency external forcing (e.g. Berloff et al., 2007, Dijkstra and Ghil, 2005, etc). Experiments with eddying Ocean General Circulation Models (OGCMs) have also shown that the amount of low-frequency Sea Level Anomaly (SLA) variability is largely intrinsic in WBCs (Penduff et al. 2011; Sérazin et al 2014) and that the frontal-scale (<10°) pattern of the Kuroshio Extension (KE) variability is similar to intrinsic modes (Taguchi et al. 2010). Based on a pair of atmospherically-forced 1/12° OGCM experiments that simulate with accuracy either the intrinsic variability (seasonally-forced) or the observed total variability (forced with the full range of atmospheric timescales), Empirical Orthogonal Function analysis is performed on zonally-averaged SLA fields of four main WBCs (e.g. Gulf Stream, Kuroshio Extension, Agulhas Current and East Australian Current). The first two modes of the KE and GS exhibit a similar spatial structure that is shaped by oceanic intrinsic processes. The frequency content is however different between the intrinsic and total Principal Components, the former containing a wide range of timescales similar to a red noise and the latter being more autocorrelated at interannual-to-decadal timescales. These modes are compared with those obtained from the 20 years of altimetry observation and relationships with low-frequency westward propagative features in the respective oceanic basin are
Stochastic modelling of turbulence
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
This thesis addresses stochastic modelling of turbulence with applications to wind energy in mind. The primary tool is ambit processes, a recently developed class of computationally tractable stochastic processes based on integration with respect to Lévy bases. The subject of ambit processes...... is still undergoing rapid development. Turbulence and wind energy are vast and complicated subjects. Turbulence has structures across a wide range of length and time scales, structures which cannot be captured by a Gaussian process that relies on only second order properties. Concerning wind energy, a wind...... turbine operates in the turbulent atmospheric boundary layer. In this respect, three regimes are of particular interest: modelling the turbulent wind before it interacts with the wind turbine (e.g. to be used in load simulations), modelling of the interaction of the wind with the wind turbine (e...
Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess, D. B.; Mathioudakis, M.
2012-12-01
Using the Rapid Oscillation in the Solar Atmosphere (ROSA) instrument at the Dunn Solar Telescope we have found that the spectra of fluctuations of the G-band (cadence 1.05 s) and Ca II K-line (cadence 4.2 s) intensities show correlated fluctuations above white noise out to frequencies beyond 300 mHz and up to 70 mHz, respectively. The noise-corrected G-band spectrum presents a scaling range (Ultra High Frequency “UHF”) for f = 25-100 mHz, with an exponent consistent with the presence of turbulent motions. The UHF power, is concentrated at the locations of magnetic bright points in the intergranular lanes, it is highly intermittent in time and characterized by a positive kurtosis κ. Combining values of G-band and K-line intensities, the UHF power, and κ, reveals two distinct “states” of the internetwork solar atmosphere. State 1, with κ ≍ 6, which includes almost all the data, is characterized by low intensities and low UHF power. State 2, with κ ≍ 3, including a very small fraction of the data, is characterized by high intensities and high UHF power. Superposed epoch analysis shows that for State 1, the K-line intensity presents 3.5 min chromospheric oscillations with maxima occurring 21 s after G-band intensity maxima implying a 150-210 km effective height difference. For State 2, the G-band and K-line intensity maxima are simultaneous, suggesting that in the highly magnetized environment sites of G-band and K-line emission may be spatially close together. Analysis of observations obtained with Hinode/SOT confirm a scaling range in the G-band spectrum up to 53 mHz also consistent with turbulent motions as well as the identification of two distinct states in terms of the H-line intensity and G-band power as functions of G-band intensity.
Arockia Bazil Raj, A; Arputha Vijaya Selvi, J; Durairaj, S
2015-02-01
Atmospheric parameters strongly affect the performance of free-space optical communication (FSOC) systems when the optical wave is propagating through the inhomogeneous turbulence transmission medium. Developing a model to get an accurate prediction of the atmospheric turbulence strength (C(n)(2)) according to meteorological parameters (weather data) becomes significant to understand the behavior of the FSOC channel during different seasons. The construction of a dedicated free-space optical link for the range of 0.5 km at an altitude of 15.25 m built at Thanjavur (Tamil Nadu) is described in this paper. The power level and beam centroid information of the received signal are measured continuously with weather data at the same time using an optoelectronic assembly and the developed weather station, respectively, and are recorded in a data-logging computer. Existing models that exhibit relatively fewer prediction errors are briefed and are selected for comparative analysis. Measured weather data (as input factors) and C(n)(2) (as a response factor) of size [177,147×4] are used for linear regression analysis and to design mathematical models more suitable in the test field. Along with the model formulation methodologies, we have presented the contributions of the input factors' individual and combined effects on the response surface and the coefficient of determination (R(2)) estimated using analysis of variance tools. An R(2) value of 98.93% is obtained using the new model, model equation V, from a confirmatory test conducted with a testing data set of size [2000×4]. In addition, the prediction accuracies of the selected and the new models are investigated during different seasons in a one-year period using the statistics of day, week-averaged, month-averaged, and seasonal-averaged diurnal Cn2 profiles, and are verified in terms of the sum of absolute error (SAE). A Cn2 prediction maximum average SAE of 2.3×10(-13) m(-2/3) is achieved using the new model in
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)
DEFF Research Database (Denmark)
Keck, Rolf-Erik; de Mare, Martin Tobias; Churchfield, Matthew J.
2015-01-01
agreement with the reference data. A quantitative comparison between the mean flow field of the DWM model with and without the suggested improvements, to that of the AL model, shows that the root-mean-square difference in terms of wind speed and turbulence intensity is reduced on the order of 30% and 40......%, respectively, by including the proposed corrections for a row of eight turbines. Furthermore, it is found that the root-mean-square difference between the AL model and the modified DWM model in terms of wind speed and turbulence intensity does not increase over a row of turbines compared with the root-mean-square...... shear on the wake deficit evolution by including a strain-rate contribution in the wake turbulence calculation. The method to account for the increased turbulence at a wake-affected turbine by basing the wake-added turbulence directly on the Reynolds stresses of the oncoming wake. This also allows...
Anderson, William
2017-04-01
Mars is a dry planet with a thin atmosphere. Aeolian processes - wind-driven mobilization of sediment and dust - are the exclusive mode of landscape variability on Mars. Craters are common topographic features on the surface of Mars, and many craters on Mars contain a prominent central mound (NASA's Curiosity rover was landed in Gale crater). Using density-normalized large-eddy simulations, we have modeled turbulent flows over crater-like topographies that feature a central mound. We have also run one simulation of flow over a digital elevation map of Gale crater. Resultant datasets suggest a deflationary mechanism wherein vortices shed from the upwind crater rim are realigned to conform to the crater profile via stretching and tilting. This was accomplished using three-dimensional datasets (momentum and vorticity) retrieved from LES. As a result, helical vortices occupy the inner region of the crater and, therefore, are primarily responsible for aeolian morphodynamics in the crater. We have also used the immersed-boundary method body force distribution to compute the aerodynamic surface stress on the crater. These results suggest that secondary flows - originating from flow separation at the crater - have played an important role in shaping landscape features observed in craters (including the dune fields observed on Mars, many of which are actively evolving).
Calderer, Antoni; Guo, Xin; Shen, Lian; Sotiropoulos, Fotis
2018-02-01
We develop a numerical method for simulating coupled interactions of complex floating structures with large-scale ocean waves and atmospheric turbulence. We employ an efficient large-scale model to develop offshore wind and wave environmental conditions, which are then incorporated into a high resolution two-phase flow solver with fluid-structure interaction (FSI). The large-scale wind-wave interaction model is based on a two-fluid dynamically-coupled approach that employs a high-order spectral method for simulating the water motion and a viscous solver with undulatory boundaries for the air motion. The two-phase flow FSI solver is based on the level set method and is capable of simulating the coupled dynamic interaction of arbitrarily complex bodies with airflow and waves. The large-scale wave field solver is coupled with the near-field FSI solver with a one-way coupling approach by feeding into the latter waves via a pressure-forcing method combined with the level set method. We validate the model for both simple wave trains and three-dimensional directional waves and compare the results with experimental and theoretical solutions. Finally, we demonstrate the capabilities of the new computational framework by carrying out large-eddy simulation of a floating offshore wind turbine interacting with realistic ocean wind and waves.
Dandou, A.; Tombrou, M.; Kalogiros, J.; Bossioli, E.; Biskos, G.; Mihalopoulos, N.; Coe, H.
2017-08-01
The spatial structure of the marine atmospheric boundary layer (MABL) over the Aegean Sea is investigated using the Weather Research and Forecasting (WRF) mesoscale model. Two `first-order' non-local and five `1.5-order' local planetary boundary-layer (PBL) parametrization schemes are used. The predictions from the WRF model are evaluated against airborne observations obtained by the UK Facility for Airborne Atmospheric Measurements BAe-14 research aircraft during the Aegean-GAME field campaign. Statistical analysis shows good agreement between measurements and simulations especially at low altitude. Despite the differences between the predicted and measured wind speeds, they reach an agreement index of 0.76. The simulated wind-speed fields close to the surface differ substantially among the schemes (maximum values range from 13 to 18 m s^{-1} at 150-m height), but the differences become marginal at higher levels. In contrast, all schemes show similar spatial variation patterns in potential temperature fields. A warmer (1-2 K) and drier (2-3 g kg^{-1}) layer than is observed, is predicted by almost all schemes under stable conditions (eastern Aegean Sea), whereas a cooler (up to 2 K) and moister (1-2 g kg^{-1}) layer is simulated under near-neutral to nearly unstable conditions (western Aegean Sea). Almost all schemes reproduce the vertical structure of the PBL and the shallow MABL (up to 300 m) well, including the low-level jet in the eastern Aegean Sea, with non-local schemes being closer to observations. The simulated PBL depths diverge (up to 500 m) due to the different criteria applied by the schemes for their calculation. Under stable conditions, the observed MABL depth corresponds to the height above the sea surface where the simulated eddy viscosity reaches a minimum; under neutral to slightly unstable conditions this is close to the top of the simulated entrainment layer. The observed sensible heat fluxes vary from -40 to 25 W m^{-2}, while the simulated
Large Eddy Simulations of an Airfoil in Turbulent Inflow
DEFF Research Database (Denmark)
Gilling, Lasse; Sørensen, Niels
2008-01-01
Wind turbines operate in the turbulent boundary layer of the atmosphere and due to the rotational sampling effect the blades experience a high level of turbulence [1]. In this project the effect of turbulence is investigated by large eddy simulations of the turbulent flow past a NACA 0015 airfoil...
2015-09-01
providing the metrological and turbulence data presented in this report. 1 1. Site Measurement During the 5-day periods of April 20–24 and May 4–8...result of vehicular travel along the road that boarders the TSI aerosol probe. Figures 16–19 shows the turbulence and metrological data. 13...report will be made available in ASCII form to any interested parties upon request to the authors. 18 1 DEFENSE TECH INFO CTR ( PDF
Time-varying phase diversity turbulence compensation
Eekeren, A.W.M. van; Schutte, K.; Dijk, J.; Schwering, P.B.W.
2011-01-01
Long range object identification needs visual identification over large distances. However, atmospheric turbulence does hinder long range imaging. Therefore it is crucial to compensate the visual artifacts due to atmospheric turbulence. In this paper we propose a new method to compensate these
Turbulence in Natural Environments
Banerjee, Tirtha
Problems in the area of land/biosphere-atmosphere interaction, hydrology, climate modeling etc. can be systematically organized as a study of turbulent flow in presence of boundary conditions in an increasing order of complexity. The present work is an attempt to study a few subsets of this general problem of turbulence in natural environments- in the context of neutral and thermally stratified atmospheric surface layer, the presence of a heterogeneous vegetation canopy and the interaction between air flow and a static water body in presence of flexible protruding vegetation. The main issue addressed in the context of turbulence in the atmospheric surface layer is whether it is possible to describe the macro-states of turbulence such as mean velocity and turbulent velocity variance in terms of the micro-states of the turbulent flow, i.e., a distribution of turbulent kinetic energy across a multitude of scales. This has been achieved by a `spectral budget approach' which is extended for thermal stratification scenarios as well, in the process unifying the seemingly different and unrelated theories of turbulence such as Kolmogorov's hypothesis, Heisenberg's eddy viscosity, Monin Obukhov Similarity Theory (MOST) etc. under a common framework. In the case of a more complex scenario such as presence of a vegetation canopy with edges and gaps, the question that is addressed is in what detail the turbulence is needed to be resolved in order to capture the bulk flow features such as recirculation patterns. This issue is addressed by a simple numerical framework and it has been found out that an explicit prescription of turbulence is not necessary in presence of heterogeneities such as edges and gaps where the interplay between advection, pressure gradients and drag forces are sufficient to capture the first order dynamics. This result can be very important for eddy-covariance flux calibration strategies in non-ideal environments and the developed numerical model can be
2015-09-30
1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Langmuir Turbulence Eric A. D’Asaro, Ramsey Harcourt...definitive experimental tests of the hypothesis that Langmuir Turbulence , specifically the equations of motion with the addition of the Craik-Leibovich...vortex force and advection by the surface wave Stokes drift, can accurately describe turbulence in the upper ocean boundary layer under conditions of
De-trending of turbulence measurements
DEFF Research Database (Denmark)
Hansen, Kurt Schaldemose; Larsen, Gunner Chr.
2006-01-01
The paper presents the results of a comparison between long term raw and de-trended turbulence intensity values recorded at offshore and coastal sites under different weather systems. Within the traditional framework of turbulence interpretation, where turbulence is considered as a stationary...... process imposed on a given constant mean wind speed, measured raw turbulence intensities consist of contributions from the atmospheric turbulence as well as from the change in mean wind speed levels. The change in mean wind speed will appear as a trend in the wind speed time series. Wind resource...... 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...
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.
CSIR Research Space (South Africa)
Sprung, D
2014-09-01
Full Text Available and Industrial Research (CSIR) P O Box 395, Pretoria 0001, South Africa dgriffith@csir.co.za ABSTRACT Optical turbulence represented by the structure function parameter of the refractive index Cn 2 is a relevant parameter for the performance... of these time series Cn 2 was derived. Three instruments were mounted at a portable mast in the center of slant path measurements over a horizontal distance of 1000 m using large aperture scintillometers (Boundary layer scintillometer BLS 900). Averaging over...
Using Indirect Turbulence Measurements for Real-Time Parameter Estimation in Turbulent Air
Martos, Borja; Morelli, Eugene A.
2012-01-01
The use of indirect turbulence measurements for real-time estimation of parameters in a linear longitudinal dynamics model in atmospheric turbulence was studied. It is shown that measuring the atmospheric turbulence makes it possible to treat the turbulence as a measured explanatory variable in the parameter estimation problem. Commercial off-the-shelf sensors were researched and evaluated, then compared to air data booms. Sources of colored noise in the explanatory variables resulting from typical turbulence measurement techniques were identified and studied. A major source of colored noise in the explanatory variables was identified as frequency dependent upwash and time delay. The resulting upwash and time delay corrections were analyzed and compared to previous time shift dynamic modeling research. Simulation data as well as flight test data in atmospheric turbulence were used to verify the time delay behavior. Recommendations are given for follow on flight research and instrumentation.
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.
1997-07-06
THIS IS A SAFETY NOTICE. The guidance contained herein supersedes : the guidance provided in the current edition of Order 7110.65, Air Traffic Control, relating to selected wake turbulence separations and aircraft weight classifications. This Notice ...
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.
Turbulence mitigation methods and their evaluation
Eekeren, A.W.M. van; Dijk, J.; Schutte, K.
2014-01-01
In general, long range detection, recognition and identification in visual and infrared imagery are hampered by turbulence caused by atmospheric conditions. The amount of turbulence is often indicated by the refractive-index structure parameter Cn 2. The value of this parameter and its variation is
DEFF Research Database (Denmark)
Brændholt, Andreas; Larsen, Klaus Steenberg; Ibrom, Andreas
2016-01-01
Abstract Precise quantification of the diurnal and seasonal variation of soil respiration (Rs) is crucial to correctly estimate annual soil carbon fluxes as well as to correctly interpret the response of Rs to biotic and abiotic factors on different time scale. In this study we found a systematic...... day time, i.e. following the course of soil temperatures. This effect on the diurnal pattern was due to low turbulence primarily occurring during night time. We calculated different annual Rs budgets by filtering out fluxes for different levels of u⋆. The highest annual Rs budget was found when...
Directory of Open Access Journals (Sweden)
Valerii Aksenov
2012-01-01
Full Text Available The method is proposed of optical vortex topological charge detection along with a design of a corresponding detector. The developed technique is based on measurements of light field intensity. Mathematical model simulating performance of the detector is described in the paper, and results of numerical experiments are presented which illustrate recognition of a vortex in a turbulent medium and in the presence of amplitude and phase noise in the registered radiation. Influence of shifts of the system optical axis on precision of registration is also considered in the paper.
Lipkens, B; Blackstock, D T
1998-09-01
A model experiment was reported to be successful in simulating the propagation of sonic booms through a turbulent atmosphere [B. Lipkens and D. T. Blackstock, J. Acoust. Soc. Am. 103, 148-158 (1998)]. In this study the effect on N wave characteristics of turbulence intensity and propagation distance through turbulence are investigated. The main parameters of interest are the rise time and the peak pressure. The effect of turbulence intensity and propagation distance is to flatten the rise time and peak pressure distributions. Rise time and peak pressure distributions always have positive skewness after propagation through turbulence. Average rise time grows with turbulence intensity and propagation distance. The scattering of rise time data is one-sided, i.e., rise times are almost always increased by turbulence. Average peak pressure decreases slowly with turbulence intensity and propagation distance. For the reported data a threefold increase in average rise time is observed and a maximum decrease of about 20% in average peak pressure. Rise times more than ten times that of the no turbulence value are observed. At most, the maximum peak pressure doubles after propagation through turbulence, and the minimum peak pressure values are about one-half the no-turbulence values. Rounded waveforms are always more common than peaked waveforms.
High Altitude Clear Air Turbulence Project
National Oceanic and Atmospheric Administration, Department of Commerce — The Air Force Flight Dynamics Laboratory conducted the High Altitude Clear Air Turbulence Project in the mid 1960s with the intention of better understanding air...
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.
Micha, Raphael; Micha, Raphael; Tkachev, Igor I.
2004-01-01
We study, analytically and with lattice simulations, the decay of coherent field oscillations and the subsequent thermalization of the resulting stochastic classical wave-field. The problem of reheating of the Universe after inflation constitutes our prime motivation and application of the results. We identify three different stages of these processes. During the initial stage of ``parametric resonance'', only a small fraction of the initial inflaton energy is transferred to fluctuations in the physically relevant case of sufficiently large couplings. A major fraction is transfered in the prompt regime of driven turbulence. The subsequent long stage of thermalization classifies as free turbulence. During the turbulent stages, the evolution of particle distribution functions is self-similar. We show that wave kinetic theory successfully describes the late stages of our lattice calculation. Our analytical results are general and give estimates of reheating time and temperature in terms of coupling constants and...
DEFF Research Database (Denmark)
Nielsen, Mogens Peter; Shui, Wan; Johansson, Jens
2011-01-01
In this report a new turbulence model is presented.In contrast to the bulk of modern work, the model is a classical continuum model with a relatively simple constitutive equation. The constitutive equation is, as usual in continuum mechanics, entirely empirical. It has the usual Newton or Stokes...... 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...
African Journals Online (AJOL)
Tariff Turbulence. * See also Information File on p. 1340 this issue. licence to practice should he deviate from the norm unduly. The Standard Tariff of fees is reviewed regularly in the light of increased costs, the rise in the cost of living, for the elimination of anomalies and so forth and this tariff for private patients, with its 10% ...
Energy Technology Data Exchange (ETDEWEB)
Talbot, L.; Cheng, R.K. [Lawrence Berkeley Laboratory, CA (United States)
1993-12-01
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
Directory of Open Access Journals (Sweden)
H. Dupuis
Full Text Available Heat flux estimates obtained using the inertial dissipation method, and the profile method applied to radiosonde soundings, are assessed with emphasis on the parameterization of the roughness lengths for temperature and specific humidity. Results from the inertial dissipation method show a decrease of the temperature and humidity roughness lengths for increasing neutral wind speed, in agreement with previous studies. The sensible heat flux estimates were obtained using the temperature estimated from the speed of sound determined by a sonic anemometer. This method seems very attractive for estimating heat fluxes over the ocean. However allowance must be made in the inertial dissipation method for non-neutral stratification. The SOFIA/ASTEX and SEMAPHORE results show that, in unstable stratification, a term due to the transport terms in the turbulent kinetic energy budget, has to be included in order to determine the friction velocity with better accuracy. Using the profile method with radiosonde data, the roughness length values showed large scatter. A reliable estimate of the temperature roughness length could not be obtained. The humidity roughness length values were compatible with those found using the inertial dissipation method.
Learning to soar in turbulent environments.
Reddy, Gautam; Celani, Antonio; Sejnowski, Terrence J; Vergassola, Massimo
2016-08-16
Birds and gliders exploit warm, rising atmospheric currents (thermals) to reach heights comparable to low-lying clouds with a reduced expenditure of energy. This strategy of flight (thermal soaring) is frequently used by migratory birds. Soaring provides a remarkable instance of complex decision making in biology and requires a long-term strategy to effectively use the ascending thermals. Furthermore, the problem is technologically relevant to extend the flying range of autonomous gliders. Thermal soaring is commonly observed in the atmospheric convective boundary layer on warm, sunny days. The formation of thermals unavoidably generates strong turbulent fluctuations, which constitute an essential element of soaring. Here, we approach soaring flight as a problem of learning to navigate complex, highly fluctuating turbulent environments. We simulate the atmospheric boundary layer by numerical models of turbulent convective flow and combine them with model-free, experience-based, reinforcement learning algorithms to train the gliders. For the learned policies in the regimes of moderate and strong turbulence levels, the glider adopts an increasingly conservative policy as turbulence levels increase, quantifying the degree of risk affordable in turbulent environments. Reinforcement learning uncovers those sensorimotor cues that permit effective control over soaring in turbulent environments.
Energy Technology Data Exchange (ETDEWEB)
Baker, K; Stappaerts, E; Gavel, D; Wilks, S; Tucker, J; Silva, D; Olsen, J; Olivier, S; Young, P; Kartz, M; Flath, L; Kruelivitch, P; Crawford, J; Azucena, O
2004-03-04
Atmospheric propagation results for a high-speed, large-actuator-number, adaptive optics system are presented. The system uses a MEMS-based spatial light modulator correction device with 1024 actuators. Tests over a 1.35 km path achieved correction speeds in excess of 800 Hz and Strehl ratios close to 0.5. The wave-front sensor was based on a quadrature interferometer that directly measures phase. This technique does not require global wave-front reconstruction, making it relatively insensitive to scintillation and phase residues. The results demonstrate the potential of large actuator number MEMS-based spatial light modulators to replace conventional deformable mirrors.
Baker, K L; Stappaerts, E A; Gavel, D; Wilks, S C; Tucker, J; Silva, D A; Olsen, J; Olivier, S S; Young, P E; Kartz, M W; Flath, L M; Kruelevitch, P; Crawford, J; Azucena, Oscar
2004-08-01
Results of atmospheric propagation for a high-speed, large-actuator-number adaptive optics system are presented. The system uses a microelectromechanical system- (MEMS-) based spatial light modulator correction device with 1024 actuators. Tests over a 1.35-km path achieved correction speeds in excess of 800 Hz and Strehl ratios close to 0.5. The wave-front sensor was based on a quadrature interferometer that directly measures phase. This technique does not require global wave-front reconstruction, making it relatively insensitive to scintillation and phase residues. The results demonstrate the potential of large-actuator-number MEMS-based spatial light modulators to replace conventional deformable mirrors.
Laguerre Gaussian beam multiplexing through turbulence
Trichili, Abderrahmen; Mhlanga, Thandeka; Naidoo, Darryl; Dudley, Angela; Zghal, Mourad; Forbes, Andrew
2014-10-01
We analyze the effect of atmospheric turbulence on the propagation of multiplexed Laguerre Gaussian modes. We present a method to multiplex Laguerre Gaussian modes using digital holograms and decompose the resulting field after encountering a laboratory simulated atmospheric turbulence. The proposed technique makes use of a single spatial light modulator for the generation of superimposed beam and a second spatial light modulator and a CCD camera for the modal decomposition. The obtained results demonstrate how sensitive the Laguerre Gaussian beams are to atmospheric distortions.
Using random forests to diagnose aviation turbulence.
Williams, John K
Atmospheric turbulence poses a significant hazard to aviation, with severe encounters costing airlines millions of dollars per year in compensation, aircraft damage, and delays due to required post-event inspections and repairs. Moreover, attempts to avoid turbulent airspace cause flight delays and en route deviations that increase air traffic controller workload, disrupt schedules of air crews and passengers and use extra fuel. For these reasons, the Federal Aviation Administration and the National Aeronautics and Space Administration have funded the development of automated turbulence detection, diagnosis and forecasting products. This paper describes a methodology for fusing data from diverse sources and producing a real-time diagnosis of turbulence associated with thunderstorms, a significant cause of weather delays and turbulence encounters that is not well-addressed by current turbulence forecasts. The data fusion algorithm is trained using a retrospective dataset that includes objective turbulence reports from commercial aircraft and collocated predictor data. It is evaluated on an independent test set using several performance metrics including receiver operating characteristic curves, which are used for FAA turbulence product evaluations prior to their deployment. A prototype implementation fuses data from Doppler radar, geostationary satellites, a lightning detection network and a numerical weather prediction model to produce deterministic and probabilistic turbulence assessments suitable for use by air traffic managers, dispatchers and pilots. The algorithm is scheduled to be operationally implemented at the National Weather Service's Aviation Weather Center in 2014.
Huang, Qi-kai; Mei, Hai-ping; Xiao, Shu-mei; Rao, Rui-zhong
2012-10-01
Effects of light propagation in random atmospheric optical turbulence are critical problems for ground based high resolution optical imaging. To get further knowledge of turbulence intensity or structure properties, the concept of fiber optic sensing system is proposed and realized. Different to fine-wire platinum resistance thermometer or laser scintillometer, the system has the ability to make non-contact measurement of optical turbulence up to the frequency of 500Hz during the air gap of 100mm, and has the dynamic range of 10-18 ~ 10-12 . The optic fiber's merit of corrosion resistance is sufficiently demonstrated by one month field test on the seacoast. Some properties of high frequency turbulence power spectrum that have never been observed before in the range of 10cm are reported. In the end, prospects of optical turbulence research by the usage of fiber optic turbulence sensing system are also discussed.
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Lagrangian scale of particle dispersion in turbulence.
Xia, Hua; Francois, Nicolas; Punzmann, Horst; Shats, Michael
2013-01-01
Transport of mass, heat and momentum in turbulent flows by far exceeds that in stable laminar fluid motions. As turbulence is a state of a flow dominated by a hierarchy of scales, it is not clear which of these scales mostly affects particle dispersion. Also, it is not uncommon that turbulence coexists with coherent vortices. Here we report on Lagrangian statistics in laboratory two-dimensional turbulence. Our results provide direct experimental evidence that fluid particle dispersion is determined by a single measurable Lagrangian scale related to the forcing scale. These experiments offer a new way of predicting dispersion in turbulent flows in which one of the low energy scales possesses temporal coherency. The results are applicable to oceanographic and atmospheric data, such as those obtained from trajectories of free-drifting instruments in the ocean.
Time change and universality in turbulence
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole Eiler; Schmiegel, Jürgen
of the probability densities of turbulent velocity increments. Furthermore, the application of a time change in terms of the scale parameter δ of the normal inverse Gaussian distribution results in a collapse of the densities of velocity increments onto Reynolds number independent distributions. We discuss this kind......We discuss a unifying description of the probability densities of turbulent velocity increments for a large number of turbulent data sets that include data from low temperature gaseous helium jet experiments, a wind tunnel experiment, an atmospheric boundary layer experiment and a free air jet...
Directory of Open Access Journals (Sweden)
Chao Gao
2016-01-01
Full Text Available This paper investigates the modulation transfer function of a Gaussian beam propagating through a horizontal path in weak-fluctuation non-Kolmogorov turbulence. Mathematical expressions are obtained based on the generalized modified atmospheric spectrum, which includes the spectral power law value of non-Kolmogorov turbulence, the finite inner and outer scales of turbulence, and other optical parameters of the Gaussian beam. The numerical results indicate that the atmospheric turbulence would produce less negative effects on the wireless optical communication system with an increase in the inner scale of turbulence. Additionally, the increased outer scale of turbulence makes a Gaussian beam influenced more seriously by the atmospheric turbulence.
Energy Technology Data Exchange (ETDEWEB)
Vinkovic, I.
2005-07-15
In order to study atmospheric pollution and the dispersion of industrial stack emissions, a large eddy simulation with the dynamic Smagorinsky-Germano sub-grid-scale model is coupled with Lagrangian tracking of fluid particles containing scalar, solid particles and droplets. The movement of fluid particles at a sub-grid level is given by a three-dimensional Langevin model. The stochastic model is written in terms of sub-grid-scale statistics at a mesh level. By introducing a diffusion model, the coupling between the large-eddy simulation and the modified three-dimensional Langevin model is applied to passive scalar dispersion. The results are validated by comparison with the wind-tunnel experiments of Fackrell and Robins (1982). The equation of motion of a small rigid sphere in a turbulent flow is introduced. Solid particles and droplets are tracked in a Lagrangian way. The velocity of solid particles and droplets is considered to have a large scale component (directly computed by the large-eddy simulation) and a sub-grid scale part. Because of inertia and gravity effects, solid particles and droplets, deviate from the trajectories of the surrounding fluid particles. Therefore, a modified Lagrangian correlation timescale is introduced into the Langevin model previously developed for the sub-grid velocity of fluid particles. Two-way coupling and collisions are taken into account. The results of the large-eddy simulation with solid particles are compared with the wind-tunnel experiments of Nalpanis et al. (1993) and of Taniere et al. (1997) on sand particles in saltation and in modified saltation, respectively. A model for droplet coalescence and breakup is implemented which allows to predict droplet interactions under turbulent flow conditions in the frame of the Euler/Lagrange approach. Coalescence and breakup are considered as a stochastic process with simple scaling symmetry assumption for the droplet radius, initially proposed by Kolmogorov (1941). At high
Statistical turbulence theory and turbulence phenomenology
Herring, J. R.
1973-01-01
The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion about randomness. Two concepts are involved: (1) a modeling of the turbulence as nearly multipoint Gaussian, and (2) a simultaneous introduction of a generalized eddy viscosity operator.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2015-11-16
Theoretical and experimental investigations have shown that the atmospheric turbulence exhibits both anisotropic and non-Kolmogorov properties. In this work, two theoretical atmosphere refractive-index fluctuations spectral models are derived for optical waves propagating through anisotropic non-Kolmogorov atmospheric turbulence. They consider simultaneously the finite turbulence inner and outer scales and the asymmetric property of turbulence eddies in the orthogonal xy-plane throughout the path. Two anisotropy factors which parameterize the asymmetry of turbulence eddies in both horizontal and vertical directions are introduced in the orthogonal xy-plane, so that the circular symmetry assumption of turbulence eddies in the xy-plane is no longer required. Deviations from the classic 11/3 power law behavior in the spectrum model are also allowed by assuming power law value variations between 3 and 4. Based on the derived anisotropic spectral model and the Rytov approximation theory, expressions for the variance of angle of arrival (AOA) fluctuations are derived for optical plane and spherical waves propagating through weak anisotropic non-Kolmogorov turbulence. Calculations are performed to analyze the derived spectral models and the variance of AOA fluctuations.
Quantifying the improvement of turbulence mitigation technology
Kozacik, Stephen; Paolini, Aaron; Sherman, Ariel; Bonnett, James; Kelmelis, Eric
2017-05-01
Atmospheric turbulence degrades imagery by imparting scintillation and warping effects that can reduce the ability to identify key features of the subjects. While visually, a human can intuitively understand the improvement that turbulence mitigation techniques can offer in increasing visual information, this enhancement is rarely quantified in a meaningful way. In this paper, we discuss methods for measuring the potential improvement on system performance video enhancement algorithms can provide. To accomplish this, we explore two metrics. We use resolution targets to determine the difference between imagery degraded by turbulence and that improved by atmospheric correction techniques. By comparing line scans between the data before and after processing, it is possible to quantify the additional information extracted. Advanced processing of this data can provide information about the effective modulation transfer function (MTF) of the system when atmospheric effects are considered and removed, using this data we compute a second metric, the relative improvement in Strehl ratio.
Coherence in Turbulence: New Perspective
Levich, Eugene
2009-07-01
It is claimed that turbulence in fluids is inherently coherent phenomenon. The coherence shows up clearly as strongly correlated helicity fluctuations of opposite sign. The helicity fluctuations have cellular structure forming clusters that are actually observed as vorticity bands and coherent structures in laboratory turbulence, direct numerical simulations and most obviously in atmospheric turbulence. The clusters are named BCC - Beltrami Cellular Clusters - because of the observed nearly total alignment of the velocity and vorticity fields in each particular cell, and hence nearly maximal possible helicity in each cell; although when averaged over all the cells the residual mean helicity in general is small and does not play active dynamical role. The Beltrami like fluctuations are short-lived and stabilize only in small and generally contiguous sub-domains that are tending to a (multi)fractal in the asymptotic limit of large Reynolds numbers, Re → ∞. For the model of homogeneous isotropic turbulence the theory predicts the leading fractal dimension of BCC to be: DF = 2.5. This particular BCC is responsible for generating the Kolmogorov -5/3 power law energy spectrum. The most obvious role that BCC play dynamically is that the nonlinear interactions in them are relatively reduced, due to strong spatial alignment between the velocity field v(r, t) and the vorticity field ω(r, t) = curlv(r, t), while the physical quantities typically best characterizing turbulence intermittency, such as entrophy, vorticity stretching and generation, and energy dissipation are maximized in and near them. The theory quantitatively relates the reduction of nonlinear inter-actions to the BCC fractal dimension DF and subsequent turbulence intermittency. It is further asserted that BCC is a fundamental feature of all turbulent flows, e.g., wall bounded turbulent flows, atmospheric and oceanic flows, and their leading fractal dimension remains invariant and universal in these flows
Clear turbulence forecasting - Towards a union of art and science
Keller, J. L.
1985-01-01
The development of clear air turbulence (CAT) forecasting over the last several decades is reviewed in the context of empirical and theoretical research into the nature of nonconvective turbulence in the free atmosphere, particularly at jet stream levels. Various qualitative CAT forecasting techniques are examined, and prospects for an effective quantitative index to aid aviation meteorologists in jet stream level turbulence monitoring and forecasting are examined. Finally, the use of on-board sensors for short-term warning is discussed.
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.
Efficient Turbulence Modeling for CFD Wake Simulations
DEFF Research Database (Denmark)
van der Laan, Paul
Wind turbine wakes can cause 10-20% annual energy losses in wind farms, and wake turbulence can decrease the lifetime of wind turbine blades. One way of estimating these effects is the use of computational fluid dynamics (CFD) to simulate wind turbines wakes in the atmospheric boundary layer. Since...... wind farm, the simulated results cannot be compared directly with wind farm measurements that have a high uncertainty in the measured reference wind direction. When this uncertainty is used to post-process the CFD results, a fairer comparison with measurements is achieved....... this flow is in the high Reynolds number regime, it is mainly dictated by turbulence. As a result, the turbulence modeling in CFD dominates the wake characteristics, especially in Reynolds-averaged Navier-Stokes (RANS). The present work is dedicated to study and develop RANS-based turbulence models...
Computational fluid dynamics incompressible turbulent flows
Kajishima, Takeo
2017-01-01
This textbook presents numerical solution techniques for incompressible turbulent flows that occur in a variety of scientific and engineering settings including aerodynamics of ground-based vehicles and low-speed aircraft, fluid flows in energy systems, atmospheric flows, and biological flows. This book encompasses fluid mechanics, partial differential equations, numerical methods, and turbulence models, and emphasizes the foundation on how the governing partial differential equations for incompressible fluid flow can be solved numerically in an accurate and efficient manner. Extensive discussions on incompressible flow solvers and turbulence modeling are also offered. This text is an ideal instructional resource and reference for students, research scientists, and professional engineers interested in analyzing fluid flows using numerical simulations for fundamental research and industrial applications. • Introduces CFD techniques for incompressible flow and turbulence with a comprehensive approach; • Enr...
Simultaneous video stabilization and moving object detection in turbulence.
Oreifej, Omar; Li, Xin; Shah, Mubarak
2013-02-01
Turbulence mitigation refers to the stabilization of videos with nonuniform deformations due to the influence of optical turbulence. Typical approaches for turbulence mitigation follow averaging or dewarping techniques. Although these methods can reduce the turbulence, they distort the independently moving objects, which can often be of great interest. In this paper, we address the novel problem of simultaneous turbulence mitigation and moving object detection. We propose a novel three-term low-rank matrix decomposition approach in which we decompose the turbulence sequence into three components: the background, the turbulence, and the object. We simplify this extremely difficult problem into a minimization of nuclear norm, Frobenius norm, and l1 norm. Our method is based on two observations: First, the turbulence causes dense and Gaussian noise and therefore can be captured by Frobenius norm, while the moving objects are sparse and thus can be captured by l1 norm. Second, since the object's motion is linear and intrinsically different from the Gaussian-like turbulence, a Gaussian-based turbulence model can be employed to enforce an additional constraint on the search space of the minimization. We demonstrate the robustness of our approach on challenging sequences which are significantly distorted with atmospheric turbulence and include extremely tiny moving objects.
Deconstructing quantum decoherence in atmospheric turbulence
CSIR Research Space (South Africa)
Roux, FS
2012-06-01
Full Text Available Ψ Ψx,y (x,y) State defined on 2D plane — evolves as function of z Instead of i~ ∂tρ(t) = [H, ρ(t)] we need ∂zρ(z) = iP {ρ(z)} – p. 8/35 Paterson model (PM) Assuming weak scintillation (only affects the phase)a Use single phase screen: Phase screen... o n c u r r e n c e w /r 0 0For point where C → 0: ⊲ If C2n is small⇒ distance z is large ⊲ If distance z small⇒ C2n is large Is the approximation still valid where C → 0? aB.J. Smith and M.G. Raymer, Phys. Rev. A, 74, 062104 (2006) – p. 13/35 Rytov...
Synthetic Aperture Ladar Imaging and Atmospheric Turbulence
2016-06-09
Phase Detectors Task 2.1: Design and build reference targets Figure 6 is a picture of the raging/imaging system on a small wheeled optical table...at https://www.osapublishing.org/abstract.cfm?URI=oe-23-18-23811 (Z.W. Barber’s contributions). 2. New discoveries, inventions , or patent disclosures...Do you have any discoveries, inventions , or patent disclosures to report for this period? No Please describe and include any notable dates Do you plan
Restoration algorithms for imaging through atmospheric turbulence
2017-02-18
which are confirmed by the velocity vector fields given on the second row of each of those figures (the color wheel on the left gives the...media. Decomposition of Oscillatory vs Non-Oscillatory spatio-temporal vector fields", Submitted to SIAM Imaging Journal. New discoveries, inventions ...or patent disclosures: Do you have any discoveries, inventions , or patent disclosures to report for this period? No Please describe and include any
A Survey of Atmospheric Turbulence Characteristics
1981-08-19
appreciation to Dr. Oskar M. Essenwanger for encouragement and helpful suggestions during this project; to Mr. Richard E. Dickson and Dr. George Fichtl...Army Picatinny Arsenal ATTN: SMUPS-TV-3 1 Dover, New Jersey 07801 Florida State University ATTN: Prof. Dr. Gleeson 1 Tallahassee, Florida 32306 "ADTC
Atmospheric Turbulence Estimates from a Pulsed Lidar
Pruis, Matthew J.; Delisi, Donald P.; Ahmad, Nash'at N.; Proctor, Fred H.
2013-01-01
Estimates of the eddy dissipation rate (EDR) were obtained from measurements made by a coherent pulsed lidar and compared with estimates from mesoscale model simulations and measurements from an in situ sonic anemometer at the Denver International Airport and with EDR estimates from the last observation time of the trailing vortex pair. The estimates of EDR from the lidar were obtained using two different methodologies. The two methodologies show consistent estimates of the vertical profiles. Comparison of EDR derived from the Weather Research and Forecast (WRF) mesoscale model with the in situ lidar estimates show good agreement during the daytime convective boundary layer, but the WRF simulations tend to overestimate EDR during the nighttime. The EDR estimates from a sonic anemometer located at 7.3 meters above ground level are approximately one order of magnitude greater than both the WRF and lidar estimates - which are from greater heights - during the daytime convective boundary layer and substantially greater during the nighttime stable boundary layer. The consistency of the EDR estimates from different methods suggests a reasonable ability to predict the temporal evolution of a spatially averaged vertical profile of EDR in an airport terminal area using a mesoscale model during the daytime convective boundary layer. In the stable nighttime boundary layer, there may be added value to EDR estimates provided by in situ lidar measurements.
Anomalous diffusion in geophysical and laboratory turbulence
Directory of Open Access Journals (Sweden)
A. Tsinober
1994-01-01
Full Text Available We present an overview and some new results on anomalous diffusion of passive scalar in turbulent flows (including those used by Richardson in his famous paper in 1926. The obtained results are based on the analysis of the properties of invariant quantities (energy, enstrophy, dissipation, enstrophy generation, helicity density, etc. - i.e. independent of the choice of the system of reference as the most appropriate to describe physical processes - in three different turbulent laboratory flows (grid-flow, jet and boundary layer, see Tsinober et al. (1992 and Kit et al. (1993. The emphasis is made on the relations between the asymptotic properties of the intermittency exponents of higher order moments of different turbulent fields (energy, dissipation, helicity, spontaneous breaking of isotropy and reflexional symmetry and the variability of turbulent diffusion in the atmospheric boundary layer, in the troposphere and in the stratosphere. It is argued that local spontaneous breaking of isotropy of turbulent flow results in anomalous scaling laws for turbulent diffusion (as compared to the scaling law of Richardson which are observed, as a rule, in different atmospheric layers from the atmospheric boundary layer (ABL to the stratosphere. Breaking of rotational symmetry is important in the ABL, whereas reflexional symmetry breaking is dominating in the troposphere locally and in the stratosphere globally. The results are of speculative nature and further analysis is necessary to validate or disprove the claims made, since the correspondence with the experimental results may occur for the wrong reasons as happens from time to time in the field of turbulence.
Anomalous diffusion in geophysical and laboratory turbulence
Tsinober, A.
We present an overview and some new results on anomalous diffusion of passive scalar in turbulent flows (including those used by Richardson in his famous paper in 1926). The obtained results are based on the analysis of the properties of invariant quantities (energy, enstrophy, dissipation, enstrophy generation, helicity density, etc.) - i.e. independent of the choice of the system of reference as the most appropriate to describe physical processes - in three different turbulent laboratory flows (grid-flow, jet and boundary layer, see Tsinober et al. (1992) and Kit et al. (1993). The emphasis is made on the relations between the asymptotic properties of the intermittency exponents of higher order moments of different turbulent fields (energy, dissipation, helicity, spontaneous breaking of isotropy and reflexional symmetry) and the variability of turbulent diffusion in the atmospheric boundary layer, in the troposphere and in the stratosphere. It is argued that local spontaneous breaking of isotropy of turbulent flow results in anomalous scaling laws for turbulent diffusion (as compared to the scaling law of Richardson) which are observed, as a rule, in different atmospheric layers from the atmospheric boundary layer (ABL) to the stratosphere. Breaking of rotational symmetry is important in the ABL, whereas reflexional symmetry breaking is dominating in the troposphere locally and in the stratosphere globally. The results are of speculative nature and further analysis is necessary to validate or disprove the claims made, since the correspondence with the experimental results may occur for the wrong reasons as happens from time to time in the field of turbulence.
Kolmogorov Spectrum of Quantum Turbulence
Kobayashi, Michikazu; Tsubota, Makoto
2005-01-01
There is a growing interest in the relation between classical turbulence and quantum turbulence. Classical turbulence arises from complicated dynamics of eddies in a classical fluid. In contrast, quantum turbulence consists of a tangle of stable topological defects called quantized vortices, and thus quantum turbulence provides a simpler prototype of turbulence than classical turbulence. In this paper, we investigate the dynamics and statistics of quantized vortices in quantum turbulence by n...
National Research Council Canada - National Science Library
Drikakis, D; Geurts, Bernard
2002-01-01
... discretization 3 A test-case: turbulent channel flow 4 Conclusions 75 75 82 93 98 4 Analysis and control of errors in the numerical simulation of turbulence Sandip Ghosal 1 Introduction 2 Source...
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....
Introduction to quantum turbulence
Barenghi, Carlo F.; Skrbek, Ladislav; Sreenivasan, Katepalli R.
2014-01-01
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose–Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics. PMID:24704870
Turbulent kinetic energy during wildfires in the north central and north-eastern US
Warren E. Heilman; Xindi. Bian
2010-01-01
The suite of operational fire-weather indices available for assessing the atmospheric potential for extreme fire behaviour typically does not include indices that account for atmospheric boundary-layer turbulence or wind gustiness that can increase the erratic behaviour of fires. As a first step in testing the feasibility of using a quantitative measure of turbulence...
Numerical modeling of the boundary layer Ekman using explicit algebraic turbulence model
Kurbatskii, Albert; Kurbatskaya, Lyudmila
2017-10-01
Modeling turbulence is an important object of environmental sciences for describing an essential turbulent transport of heat and momentum in the boundary layer of the atmosphere. The many turbulence model used in the simulation of flows in the environment, based on the concept of eddy viscosity, and buoyancy effects are often included in the expression for the turbulent fluxes through empirical functions, based on the similarity theory of Monin-Obukhov, fair, strictly speaking, only in the surface layer. Furthermore, significant progress has been made in recent years in the development broader than standard hypothesis turbulent viscosity models for the eddy diffusivity momentum and heat, as a result of the recording of differential equations for the Reynolds stresses and vector turbulent heat flux in a weakly-equilibrium approximation, which neglects advection and the diffusion of certain dimensionless quantities. Explicit algebraic model turbulent Reynolds stresses and heat flux vector for the planetary boundary layer is tested in the neutral atmospheric boundary layer over the homogeneous rough surface. The present algebraic model of turbulence built on physical principles RANS (Reynolds Average Navier Stokes) approach for stratified turbulence uses three prognostic equations and shows correct reproduction of the main characteristics of the Ekman neutral planetary boundary layer (PBL): the components average of wind velocity, the angle of wind turn, turbulence statistics. Test calculations shows that this turbulence model can be used for the purposeful researches of the atmospheric boundary layer for solving of various problems of the environment.
Energy Technology Data Exchange (ETDEWEB)
Kerstein, A.R. [Sandia National Lab., Livermore, CA (United States)
1996-12-31
One-Dimensional Turbulence is a new turbulence modeling strategy involving an unsteady simulation implemented in one spatial dimension. In one dimension, fine scale viscous and molecular-diffusive processes can be resolved affordably in simulations at high turbulence intensity. The mechanistic distinction between advective and molecular processes is thereby preserved, in contrast to turbulence models presently employed. A stochastic process consisting of mapping {open_quote}events{close_quote} applied to a one-dimensional velocity profile represents turbulent advection. The local event rate for given eddy size is proportional to the velocity difference across the eddy. These properties cause an imposed shear to induce an eddy cascade analogous in many respects to the eddy cascade in turbulent flow. Many scaling and fluctuation properties of self-preserving flows, and of passive scalars introduced into these flows, are reproduced.
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.
Actuator Line Simulation of Wake of Wind Turbine Operating in Turbulent Inflow
DEFF Research Database (Denmark)
Troldborg, Niels; Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming
2007-01-01
The wake of a wind turbine operating in an atmospheric turbulent inflow without mean shear is simulated using a numerical method, which combines large eddy simulations with an actuator line technique. A turbulent inflow with the same spectral characteristics as the atmosphere is produced by intro......The wake of a wind turbine operating in an atmospheric turbulent inflow without mean shear is simulated using a numerical method, which combines large eddy simulations with an actuator line technique. A turbulent inflow with the same spectral characteristics as the atmosphere is produced...... by introducing time varying body forces in a plane upstream the rotor. The results of the simulation are compared to those obtained on a wind turbine in uniform inflow at the same mean wind speed and from this comparison a number of features of the influence of inflow turbulence on wake dynamics are deduced...
Effect of oceanic turbulence on polarization of stochastic beams
Korotkova, Olga; Farwell, Nathan
2011-04-01
On the basis of the extended Huygens-Fresnel principle and the unified theory of coherence and polarization of light we determine the changes in various polarization properties of stochastic beams propagating through the turbulent clear-water ocean. The ocean-induced fluctuations in the refractive index are described via the recently developed power spectrum which takes into account both temperature and salinity variations. Numerical examples of changes in the spectral density, the degree of polarization and in the polarization ellipse are given for electromagnetic Gaussian Schell-model beams. We demonstrate, in particular, how polarization of the propagating beam is affected by statistical properties of the source and by several parameters of oceanic turbulence. We find that propagation of light beams in the oceanic turbulence resembles that in the atmospheric turbulence qualitatively, however evolution and asymptotic saturation of polarization in the oceanic turbulence occurs at much shorter distances.
Comparing multiple turbulence restoration algorithms performance on noisy anisoplanatic imagery
Rucci, Michael A.; Hardie, Russell C.; Dapore, Alexander J.
2017-05-01
In this paper, we compare the performance of multiple turbulence mitigation algorithms to restore imagery degraded by atmospheric turbulence and camera noise. In order to quantify and compare algorithm performance, imaging scenes were simulated by applying noise and varying levels of turbulence. For the simulation, a Monte-Carlo wave optics approach is used to simulate the spatially and temporally varying turbulence in an image sequence. A Poisson-Gaussian noise mixture model is then used to add noise to the observed turbulence image set. These degraded image sets are processed with three separate restoration algorithms: Lucky Look imaging, bispectral speckle imaging, and a block matching method with restoration filter. These algorithms were chosen because they incorporate different approaches and processing techniques. The results quantitatively show how well the algorithms are able to restore the simulated degraded imagery.
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...
Yang, Chunyong; Xu, Chuang; Ni, Wenjun; Gan, Yu; Hou, Jin; Chen, Shaoping
2017-10-16
A novel scheme is proposed to mitigate the atmospheric turbulence effect in free space optical (FSO) communication employing orbital angular momentum (OAM) multiplexing. In this scheme, the Gaussian beam is used as an auxiliary light with a common-path to obtain the distortion information caused by atmospheric turbulence. After turbulence, the heterodyne coherent detection technology is demonstrated to realize the turbulence mitigation. With the same turbulence distortion, the OAM beams and the Gaussian beam are respectively utilized as the signal light and the local oscillation light. Then the turbulence distortion is counteracted to a large extent. Meanwhile, a phase matching method is proposed to select the specific OAM mode. The discrimination between the neighboring OAM modes is obviously improved by detecting the output photocurrent. Moreover, two methods of beam size adjustment have been analyzed to achieve better performance for turbulence mitigation. Numerical results show that the system bit error rate (BER) can reach 10-5 under strong turbulence in simulation situation.
Snowflakes as inertial particles in turbulence
Coletti, Filippo; Nemes, Andras; Dasari, Teja; Hong, Jiarong; Guala, Michele
2016-11-01
We report on the first direct measurements of trajectories and settling velocity of snow particles in the atmospheric surface layer. During a nocturnal snowfall we deploy an imaging system consisting of a searchlight and high speed cameras to illuminate and track thousands of snowflakes over a 7 m by 4 m vertical plane. We simultaneously characterize their shape and size using digital holography, while recording the air turbulence properties via sonic anemometry. We show that, in the meteorological conditions in object, the snowflake motion exhibits hallmark features identified by fundamental studies of particle-laden turbulence in both the Lagrangian and the Eulerian framework. The acceleration distribution displays stretched exponential tails, and by comparing with previous laboratory and computational studies we infer the Stokes number and aerodynamic response time of the snowflakes. The fall speed is found to be much greater than the expected value in still air, indicating that turbulence enhances settling according to the preferential sweeping mechanism. These observations demonstrate the major role of turbulence in determining the snow fall speed, and create the basis for leveraging results from particle-laden turbulence research towards improved snow precipitation models.
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
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 9; Issue 10. Turbulence and Dispersion. K S Gandhi. General Article Volume 9 Issue 10 October 2004 pp 48-61. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/009/10/0048-0061. Keywords. Turbulent ...
Theoretical analysis of quantum ghost imaging through turbulence
Energy Technology Data Exchange (ETDEWEB)
Chan, Kam Wai Clifford [Rochester Optical Manufacturing Company, 1260 Lyell Avenue, Rochester, New York 14606 (United States); Simon, D. S.; Sergienko, A. V. [Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Hardy, Nicholas D.; Shapiro, Jeffrey H. [Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Eberly, Joseph H. [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); O' Sullivan, Malcolm N.; Rodenburg, Brandon [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Boyd, Robert W. [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5 (Canada)
2011-10-15
Atmospheric turbulence generally affects the resolution and visibility of an image in long-distance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon et al., Phys. Rev. A 83, 051803 (2011)], it was found that the effect of the turbulence can nevertheless be mitigated under certain conditions. This paper gives a detailed theoretical analysis to the setup and results reported in the experiment. Entangled photons with a finite correlation area and a turbulence model beyond the phase screen approximation are considered.
Cheng, Mingjian; Zhang, Yixin; Gao, Jie; Wang, Fei; Zhao, Fengsheng
2014-06-20
We model the average channel capacity of optical wireless communication systems for cases of weak to strong turbulence channels, using the exponentiation Weibull distribution model. The joint effects of the beam wander and spread, pointing errors, atmospheric attenuation, and the spectral index of non-Kolmogorov turbulence on system performance are included. Our results show that the average capacity decreases steeply as the propagation length L changes from 0 to 200 m and decreases slowly down or tends to a stable value as the propagation length L is greater than 200 m. In the weak turbulence region, by increasing the detection aperture, we can improve the average channel capacity and the atmospheric visibility as an important issue affecting the average channel capacity. In the strong turbulence region, the increase of the radius of the detection aperture cannot reduce the effects of the atmospheric turbulence on the average channel capacity, and the effect of atmospheric visibility on the channel information capacity can be ignored. The effect of the spectral power exponent on the average channel capacity in the strong turbulence region is higher than weak turbulence region. Irrespective of the details determining the turbulent channel, we can say that pointing errors have a significant effect on the average channel capacity of optical wireless communication systems in turbulence channels.
Turbulent Mixing in Stably Stratified Flows
2008-03-01
is top-heavy in salt, a fluid parcel from the top will flow downward. As the parcel convects downward it will exchange heat, but negligible salt...analytique de la chaleur , volume 2, p. 172. Gauthier-Villars, Paris, 1903. .1. D. Boyd. Properties of thermal staircase off the northeast coast of South...ments. J. Phys. Oceanogr., 10:83 89, 1980. R. V. Ozmidov. On the turbulent exchange in a stable stratified ocean. Izv. Atmospheric and Oceanic Physics
Warren E. Heilman; Xindi. Bain
2013-01-01
Recent research suggests that high levels of ambient near-surface atmospheric turbulence are often associated with rapid and sometimes erratic wildland fire spread that may eventually lead to large burn areas. Previous research has also examined the feasibility of using near-surface atmospheric turbulent kinetic energy (TKEs) alone or in...
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.
DEFF Research Database (Denmark)
Gilling, Lasse
. However, it turns out that the velocities in the inner part of the boundary layer only increase slightly, and there is no effect on the obtained surface pressures or lift coefficients. It appears that the resolved turbulence has a too large length scale to cause the effect as seen in experiments...... 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...
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.
DEFF Research Database (Denmark)
Højstrup, Jørgen; Hansen, Kurt S.; Pedersen, Bo Juul
1999-01-01
The pdf's of atmosperic turbulence have somewhat wider tails than a Gaussian, especially regarding accelerations, whereas velocities are close to Gaussian. This behaviour has been investigated using data from a large WEB-database in order to quantify the amount of non-gaussianity. Models for non......-Gaussian turbulence has been developed, by which artificial turbulence can be generated with specific 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....
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
Zare, Armin; Georgiou, Tryphon T
2016-01-01
Second-order statistics of turbulent flows can be obtained either experimentally or via direct numerical simulations. Statistics reflect fundamentals of flow physics and can be used to develop low-complexity turbulence models. Due to experimental or numerical limitations it is often the case that only partial flow statistics can be reliably known, i.e., only certain correlations between a limited number of flow field components are available. Thus, it is of interest to complete the statistical signature of the flow field in a way that is consistent with the known dynamics. This is an inverse problem and our approach utilizes stochastically-forced linearization around turbulent mean velocity profile. In general, white-in-time stochastic forcing is not sufficient to explain turbulent flow statistics. In contrast, colored-in-time forcing of the linearized equations allows for exact matching of available correlations. To accomplish this, we develop dynamical models that generate the required stochastic excitation...
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
Nakamichi, A.; Morikawa, M.
2009-05-01
We aim for a consistent understanding of various scaling relations reported for self-gravitating systems, based on the proposal that the collisionless dark matter fluid turns into a turbulent state, i.e. dark turbulence, after crossing the caustic surface in the non-linear stage. Kolmogorov scaling laws with a constant energy flow per mass of 0.3 cm^2/s3 are suggested from observations.
Turbulent Plasmoid Reconnection
Widmer, Fabien; Yokoi, Nobumitsu
2016-01-01
The plasmoid instability may lead to fast magnetic reconnection through long current sheets(CS). It is well known that large-Reynolds-number plasmas easily become turbulent. We address the question whether turbulence enhances the energy conversion rate of plasmoid-unstable current sheets. We carry out appropriate numerical MHD simulations, but resolving simultaneously the relevant large-scale (mean-) fields and the corresponding small-scale, turbulent, quantities by means of direct numerical simulations (DNS) is not possible. Hence we investigate the influence of small scale turbulence on large scale MHD processes by utilizing a subgrid-scale (SGS) turbulence model. We verify the applicability of our SGS model and then use it to investigate the influence of turbulence on the plasmoid instability. We start the simulations with Harris-type and force-free CS equilibria in the presence of a finite guide field in the direction perpendicular to the reconnection plane. We use the DNS results to investigate the growt...
Cui, Linyan; Xue, Bindang
2015-09-01
Theoretical and experimental investigations have shown that the atmospheric turbulence exhibits both anisotropic and non-Kolmogorov properties. Very recent analyses of angle of arrival (AOA) fluctuations of an optical wave in anisotropic non-Kolmogorov turbulence have adopted the assumption that the propagation path was in the z-direction with circular symmetry of turbulence cells maintained in the orthogonal xy-plane throughout the path, and one single anisotropy factor was adopted in the orthogonal xy-plane to parameterize the asymmetry of turbulence cells or eddies in both horizontal and vertical directions. In this work, the circular symmetry assumption of turbulence cells or eddies in the orthogonal xy-plane is no longer required, and two anisotropy parameters are introduced in the orthogonal xy-plane to investigate the AOA fluctuations. In addition, deviations from the classic 11/3 spectral power law behavior for Kolmogorov turbulence are allowed by assuming spectral power law value variations between 3 and 4. With the Rytov approximation theory, new theoretical models for the variance of AOA fluctuations are developed for optical plane and spherical waves propagating through weak anisotropic non-Kolmogorov atmospheric turbulence. When the two anisotropic parameters are equal to each other, they reduce correctly to the recently published results (the circular symmetry assumption of turbulence cells or eddies in the orthogonal xy-plane was adopted). Furthermore, when these two anisotropic parameters equal one, they reduce correctly to the previously published analytic expressions for the cases of optical wave propagation through weak isotropic non-Kolmogorov turbulence.
DEFF Research Database (Denmark)
Bille, Mikkel; Bjerregaard, Peter; Sørensen, Tim Flohr
2015-01-01
The article introduces the special issue on staging atmospheres by surveying the philosophical, political and anthropological literature on atmosphere, and explores the relationship between atmosphere, material culture, subjectivity and affect. Atmosphere seems to occupy one of the classic...
Shapkalijevski, M.; Moene, A.F.; Ouwersloot, Huug; Patton, E.G.; Vilà-Guerau De Arellano, J.
2016-01-01
In this observational study, the role of tree phenology on the atmospheric turbulence parameterization over 10-m-tall and relatively sparse deciduous vegetation is quantified. Observations from the Canopy Horizontal Array Turbulence Study (CHATS) field experiment are analyzed to establish the
Goto, Susumu; Vassilicos, J C
2016-11-01
We have run a total of 311 direct numerical simulations (DNSs) of decaying three-dimensional Navier-Stokes turbulence in a periodic box with values of the Taylor length-based Reynolds number up to about 300 and an energy spectrum with a wide wave-number range of close to -5/3 power-law dependence at the higher Reynolds numbers. On the basis of these runs, we have found a critical time when (i) the rate of change of the square of the integral length scale turns from increasing to decreasing, (ii) the ratio of interscale energy flux to high-pass filtered turbulence dissipation changes from decreasing to very slowly increasing in the inertial range, (iii) the signature of large-scale coherent structures disappears in the energy spectrum, and (iv) the scaling of the turbulence dissipation changes from the one recently discovered in DNSs of forced unsteady turbulence and in wind tunnel experiments of turbulent wakes and grid-generated turbulence to the classical scaling proposed by G. I. Taylor [Proc. R. Soc. London, Ser. A 151, 421 (1935)1364-502110.1098/rspa.1935.0158] and A. N. Kolmogorov [Dokl. Akad. Nauk SSSR 31, 538 (1941)]. Even though the customary theoretical basis for this Taylor-Kolmogorov scaling is a statistically stationary cascade where large-scale energy flux balances dissipation, this is not the case throughout the entire time range of integration in all our DNS runs. The recently discovered dissipation scaling can be reformulated physically as a situation in which the dissipation rates of the small and large scales evolve together. We advance two hypotheses that may form the basis of a theoretical approach to unsteady turbulence cascades in the presence of large-scale coherent structures.
Digital Repository Service at National Institute of Oceanography (India)
Levy, M.; Resplandy, L.; Lengaigne, M.
Observed phytoplankton interannual variability has been commonly related to atmospheric variables and climate indices. Here we showed that such relation is highly hampered by internal variability associated with oceanic mesoscale turbulence...
Simulations and Data Analysis for Air Force Optical Turbulence Forecasting Applications
National Research Council Canada - National Science Library
Werne, Joseph; Fritts, David; Lund, Thomas
2007-01-01
We completed a series of Direct-Numerical and Large-Eddy Simulations (DNS and LES) of wind-shear instability and gravity wave breaking and associated analysis to characterize atmospheric turbulence and its optical impacts...
Magnetic reconnection in turbulence: from Cluster to MMS and beyond
Retino, Alessandro; Sundkvist, David; Matthaeus, William; Vaivads, Andris; Califano, Francesco; Khotyaintsev, Yuri; Le Contel, Olivier; Sorriso-valvo, Luca; Chasapis, Alexandros; Lavraud, Benoit; Valentini, Francesco; Servidio, Sergio; Rossi, Claudia; Camporeale, Enrico
2016-07-01
Magnetic reconnection is a universal energy dissipation mechanism occurring in space and astrophysical magnetized plasmas. Such plasmas are frequently in a turbulent state, raising the fundamental question of the role reconnection for energy dissipation in turbulence. Understanding reconnection in turbulence is of pivotal importance to explain phenomena such as particle acceleration in stellar atmospheres, the heating of interplanetary and interstellar media as well as particle energization in accretion disks and cosmic rays acceleration. Many numerical simulations support the role of reconnection for efficiently dissipate turbulent energy and heat and accelerated particles. Such simulations indicate that reconnection occurs in small-scale current sheets spontaneously forming within the turbulence. Yet experimental evidence of reconnection in turbulence has been provided only recently thanks to high resolution in situ measurements by modern spacecraft. Here we present ESA/Cluster and more recent NASA/MMS observations in near-Earth space showing evidence of reconnection in turbulence and its importance for energy dissipation and particle energization. We also discuss implications for upcoming spacecraft missions such as Solar Orbiter and Solar Probe Plus, as well as for missions currently under study pahse such as ESA/THOR.
Statistical energy conservation principle for inhomogeneous turbulent dynamical systems.
Majda, Andrew J
2015-07-21
Understanding the complexity of anisotropic turbulent processes over a wide range of spatiotemporal scales in engineering shear turbulence as well as climate atmosphere ocean science is a grand challenge of contemporary science with important societal impact. In such inhomogeneous turbulent dynamical systems there is a large dimensional phase space with a large dimension of unstable directions where a large-scale ensemble mean and the turbulent fluctuations exchange energy and strongly influence each other. These complex features strongly impact practical prediction and uncertainty quantification. A systematic energy conservation principle is developed here in a Theorem that precisely accounts for the statistical energy exchange between the mean flow and the related turbulent fluctuations. This statistical energy is a sum of the energy in the mean and the trace of the covariance of the fluctuating turbulence. This result applies to general inhomogeneous turbulent dynamical systems including the above applications. The Theorem involves an assessment of statistical symmetries for the nonlinear interactions and a self-contained treatment is presented below. Corollary 1 and Corollary 2 illustrate the power of the method with general closed differential equalities for the statistical energy in time either exactly or with upper and lower bounds, provided that the negative symmetric dissipation matrix is diagonal in a suitable basis. Implications of the energy principle for low-order closure modeling and automatic estimates for the single point variance are discussed below.
Estimating the atmospheric correlation length with stochastic parallel gradient descent algorithm.
Yazdani, R; Hajimahmoodzadeh, M; Fallah, H R
2014-03-01
The atmospheric turbulence measurement has received much attention in various fields due to its effects on wave propagation. One of the interesting parameters for characterization of the atmospheric turbulence is the Fried parameter or the atmospheric correlation length. We numerically investigate the feasibility of estimating the Fried parameter using a simple and low-cost system based on the stochastic parallel gradient descent (SPGD) algorithm without the need for wavefront sensing. We simulate the atmospheric turbulence using Zernike polynomials and employ a wavefront sensor-less adaptive optics system based on the SPGD algorithm and report the estimated Fried parameter after compensating for atmospheric-turbulence-induced phase distortions. Several simulations for different atmospheric turbulence strengths are presented to validate the proposed method.
Turbulent complex (dusty) plasma
Zhdanov, Sergey; Schwabe, Mierk
2017-04-01
As a paradigm of complex system dynamics, solid particles immersed into a weakly ionized plasma, so called complex (dusty) plasmas, were (and continue to be) a subject of many detailed studies. Special types of dynamical activity have been registered, in particular, spontaneous pairing, entanglement and cooperative action of a great number of particles resulting in formation of vortices, self-propelling, tunneling, and turbulent movements. In the size domain of 1-10 mkm normally used in experiments with complex plasmas, the characteristic dynamic time-scale is of the order of 0.01-0.1 s, and these particles can be visualized individually in real time, providing an atomistic (kinetic) level of investigations. The low-R turbulent flow induced either by the instability in a complex plasma cloud or formed behind a projectile passing through the cloud is a typical scenario. Our simulations showed formation of a fully developed system of vortices and demonstrated that the velocity structure functions scale very close to the theoretical predictions. As an important element of self-organization, cooperative and turbulent particle motions are present in many physical, astrophysical, and biological systems. Therefore, experiments with turbulent wakes and turbulent complex plasma oscillations are a promising mean to observe and study in detail the anomalous transport on the level of individual particles.
Phenomenology of turbulent convection
Verma, Mahendra; Chatterjee, Anando; Kumar, Abhishek; Samtaney, Ravi
2016-11-01
We simulate Rayleigh-Bénard convection (RBC) in which a fluid is confined between two thermally conducting plates. We report results from direct numerical simulation (DNS) of RBC turbulence on 40963 grid, the highest resolution hitherto reported, on 65536 cores of Cray XC40, Shaheen II, at KAUST. The non-dimensional parameters of our simulation are: the Rayleigh number Ra = 1 . 1 ×1011 (the highest ever for a pseudo-spectral simulation) and Prandtl number of unity. We present energy flux diagnostics of shell-to-shell (in wave number space) transfer. Furthermore, noting that convective flows are anisotropic due to buoyancy, we quantify anisotropy by subdividing each wavenumber shell into rings and quantify ring energy spectrum. An outstanding question in convective turbulence is the wavenumber scaling of the energy spectrum. Our pseudo-spectral simulations of turbulent thermal convection coupled with novel energy transfer diagnostics have provided a definitive answer to this question. We conclude that convective turbulence exhibits behavior similar to fluid turbulence, that is, Kolmogorov's k - 5 / 3 spectrum with forward and local energy transfers, along with a nearly isotropic energy distribution. The supercomputer Shaheen at KAUST was utilized for the simulations.
Toyoshima, Morio
2003-01-01
This study is devoted to lightwave propagation in the presence of random pointing jitter and atmospheric turbulence. The intrinsic narrow beam/high gain nature of free-space laser communications produces several extremely valuable advantages when compared to microwaves, but also requires a very high tracking and pointing accuracy. Furthermore, space-to-ground optical communications are strongly affected by scintillation effects due to the turbulent atmosphere. The purpose of this study is to ...
Directory of Open Access Journals (Sweden)
C. M. Hall
Full Text Available By measuring fading times of radar echoes from underdense meteor trails, it is possible to deduce the ambipolar diffusivities of the ions responsible for these radar echoes. It could be anticipated that these diffusivities increase monotonically with height akin to neutral viscosity. In practice, this is not always the case. Here, we investigate the capability of neutral turbulence to affect the meteor trail diffusion rate.
Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence
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.
PREFACE Turbulent Mixing and Beyond
Abarzhi, Snezhana I.; Gauthier, Serge; Niemela, Joseph J.
2010-12-01
The goals of the International Conference 'Turbulent Mixing and Beyond', TMB-2009, are to expose the generic problem of non-equilibrium turbulent processes to a broad 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 turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together researchers from different areas, which include but are not limited to fluid dynamics, plasmas, high energy density physics, astrophysics, material science, combustion, atmospheric and Earth sciences, nonlinear and statistical physics, applied mathematics, probability and statistics, data processing and computations, optics and telecommunications, and to have their attention focused on the long-standing formidable task of non-equilibrium processes. Non-equilibrium turbulent processes play a key role in a broad variety of phenomena spanning astrophysical to atomistic scales and high or low energy density regimes. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, strong shocks and explosions, material transformation under high strain rate, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, non-canonical wall-bounded flows, hypersonic and supersonic boundary layers, dynamics of atmosphere and oceanography, are just a few examples. A grip on non-equilibrium turbulent processes is crucial for cutting-edge technology such as laser micro-machining, nano-electronics, free-space optical telecommunications, and for industrial applications in the areas of aeronautics and aerodynamics. Non-equilibrium turbulent processes are anisotropic, non-local, multi-scale and multi-phase, and often are driven by shocks or
Wind Shear/Turbulence Inputs to Flight Simulation and Systems Certification
Bowles, Roland L. (Editor); Frost, Walter (Editor)
1987-01-01
The purpose of the workshop was to provide a forum for industry, universities, and government to assess current status and likely future requirements for application of flight simulators to aviation safety concerns and system certification issues associated with wind shear and atmospheric turbulence. Research findings presented included characterization of wind shear and turbulence hazards based on modeling efforts and quantitative results obtained from field measurement programs. Future research thrusts needed to maximally exploit flight simulators for aviation safety application involving wind shear and turbulence were identified. The conference contained sessions on: Existing wind shear data and simulator implementation initiatives; Invited papers regarding wind shear and turbulence simulation requirements; and Committee working session reports.
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.
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.
Information Content of Turbulence
Cerbus, Rory; Goldburg, Walter
2013-03-01
This work is one of the few attempts to treat turbulence as an information source that can be controlled experimentally. As the Reynolds number Re is increased, more degrees of freedom are excited and participate in the turbulent cascade. One might therefore expect that on raising Re , the system becomes more random, thereby increasing the Shannon entropy H. However, because the excited modes are correlated, H is a decreasing function of Re , as is experimentally shown in a study of turbulence in a flowing soap film. A parallel analysis was made of the logistic map, where H is calculated as a function of the control parameter r in the equation xn + 1 = rxn (1 -xn) . There, as expected, H is an increasing function of r. This work is supported by NSF grant No. 1044105, a Mellon fellowship, and the Okinawa Institute of Science and Technology.
Clumps in drift wave turbulence
DEFF Research Database (Denmark)
Pecseli, H. L.; Mikkelsen, Torben
1986-01-01
is proposed in terms of conditional eddies, in order to discriminate turbulent flows where macro-clumps may be observed. The analysis is illustrated by results from experimental investigations of strongly turbulent, resistive drift-wave fluctuations. The related problem for electrostatic turbulence...
Recent progress in compressible turbulence
Chen, S.; Xia, Z.; Wang, Jianchun; Yang, Yantao
2015-01-01
In this paper, we review some recent studies on compressible turbulence conducted by the authors’ group, which include fundamental studies on compressible isotropic turbulence (CIT) and applied studies on developing a constrained large eddy simulation (CLES) for wall-bounded turbulence. In the first
Adaptive free-space optical communications through turbulence using self-healing Bessel beams
Li, Shuhui; Wang, Jian
2017-01-01
We present a scheme to realize obstruction- and turbulence-tolerant free-space orbital angular momentum (OAM) multiplexing link by using self-healing Bessel beams accompanied by adaptive compensation techniques. Compensation of multiple 16-ary quadrature amplitude modulation (16-QAM) data carrying Bessel beams through emulated atmospheric turbulence and obstructions is demonstrated. The obtained experimental results indicate that the compensation scheme can effectively reduce the inter-channel crosstalk, improve the bit-error rate (BER) performance, and recuperate the nondiffracting property of Bessel beams. The proposed scheme might be used in future high-capacity OAM links which are affected by atmospheric turbulence and obstructions. PMID:28230076
Reflection driven wave turbulence in an open field and the structure of solar wind
Asgari-Targhi, M.; van Ballegooijen, A. A.
2016-12-01
We present results from an extensive study of an open magnetic field line positioned at the center of a coronal hole. We test the hypothesis that reflection-driven wave turbulence can provide the energy needed for heating the coronal plasma in the acceleration region of the fast solar wind. We use the reduced magnetohydrodynamic simulations to describe the wave turbulence where the simulated wave dissipation rates are compared with those needed to sustain the background atmosphere. We consider the effects of density fluctuations, which may significantly increase the turbulent heating rate. These density variations simulate the effects of compressive MHD waves on the Alfvén waves. We find that such variations significantly enhance the wave reflection and thereby the turbulent dissipation rates, producing enough heat to maintain the background atmosphere. We conclude that interactions between Alfvén and compressive waves may play an important role in the turbulent heating of the fast solar wind.
The impact of forest canopy structure on simulations of atmosphere-biosphere NO
Firanj, Ana; Lalic, Branislava; Ganzeveld, Laurens; Podrascanin, Zorica
2015-01-01
The concentrations and fluxes of reactive nitrogen species in the land-atmosphere system are controlled by complex interactions between emissions, turbulent transfer, dry deposition and chemical transformations. The forest canopy can significantly affect turbulent fluxes between the atmosphere,
The simulation of turbulence effect based on the technology of optical wavefront control
Zhao, Hongming; Fei, Jindong; Du, Huijie; Yu, Hong; Du, Jian; Hu, Xinqi; Dong, Bing
2013-09-01
In the process of high-resolution astronomical observation and space optical mapping, the wavefront aberrations caused by atmosphere turbulence effect lead to reduced resolution of optical imaging sensor. Firstly, on the base of influence of atmosphere turbulence effect for the optical observation system, this paper investigates and analyses the development and technical characteristics of deformable mirror, which is the key device of optical wavefront control technology. In this part, the paper describes the basic principles of wavefront control and measurement using the current production line of deformable mirror, including micro-electromechanical systems (MEMS) deformable mirror which is one of the most promising technology for wavefront modulation and Shack-Hartmann wavefront sensors. Secondly, a new method based on the technology of optical wavefront control and the data of optical path difference (OPD) for simulating the effect of optical transmission induced by turbulence is presented in this paper. The modeling and characteristics of atmosphere turbulence effect applied for optical imagery detector of astronomical observation and space optical mapping has been obtained. Finally, based on the theory model of atmosphere turbulence effects and digital simulation results, a preliminary experiment was done and the results verify the feasibility of the new method. The OPD data corresponding to optical propagation effect through turbulent atmosphere can be achieved by the calculation based on the method of ray-tracing and principle of physical optics. It is a common practice to decompose aberrated wavefronts in series over the Zernike polynomials. These data will be applied to the drive and control of the deformable mirror. This kind of simulation method can be applied to simulate the optical distortions effect, such as the dithering and excursion of light spot, in the space based earth observation with the influence of turbulent atmosphere. With the help of the
Turbulence characteristics inside a turbulent spot in plane Poiseuille flow
Henningson, Dan S.; Kim, John
1989-01-01
Turbulence characteristics inside a turbulent spot in plane Poiseuille flow are investigated by analyzing a database obtained from a direct simulation. The spot area is divided into two distinct regions - a turbulent area and a wave area. It is found that the flow structures inside the turbulent area have strong resemblance to those found in the fully-developed turbulent channel flow. A suitably defined mean and rms fluctuations as well as the internal shear-layer structures are found to be similar to the turbulent counterpart. In the wave area the inflexional mean spanwise profiles cause a rapid growth of oblique waves, which break down to turbulence. The rms fluctuations and Reynolds stress are found to be higher in that area, and the shear-layer structures are similar to those observed in the secondary instability of two-dimensional Tollmien-Schlichting waves.
Higher order mode laser beam intensity fluctuations in strong oceanic turbulence
Baykal, Yahya
2017-05-01
Intensity fluctuations of the higher order mode laser beams are evaluated when these beams propagate in a medium exhibiting strong oceanic turbulence. Our formulation involves the modified Rytov solution that extends the Rytov solution to cover strong turbulence as well, and our recently reported expression that relates the atmospheric turbulence structure constant to the oceanic turbulence parameters and oceanic wireless optical communication link parameters. The variations of the intensity fluctuations are reported against the changes of the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, viscosity and the source size of the higher order mode laser beam. Our results indicate that under any oceanic turbulence parameters, it is advantageous to employ higher order laser modes in reducing the scintillation noise in wireless optical communication links operating in a strongly turbulent ocean.
Experimental detection of turbulent thermaldiffusion of aerosols in non-isothermal flows
Directory of Open Access Journals (Sweden)
A. Eidelman
2006-01-01
Full Text Available We studied experimentally a new phenomenon of turbulent thermal diffusion of particles which can cause formation of the large-scale aerosol layers in the vicinity of the atmospheric temperature inversions. This phenomenon was detected experimentally in oscillating grids turbulence in air flow. Three measurement techniques were used to study turbulent thermal diffusion in strongly inhomogeneous temperature fields, namely Particle Image Velocimetry to determine the turbulent velocity field, an image processing technique to determine the spatial distribution of aerosols, and an array of thermocouples for the temperature field. Experiments are presented for both, stably and unstably stratified fluid flows, by using both directions of the imposed mean vertical temperature gradient. We demonstrated that even in strongly inhomogeneous temperature fields particles in turbulent fluid flow accumulate at the regions with minimum of mean temperature of surrounding fluids due to the phenomenon of turbulent thermal diffusion.
Bushnell, D. M.
1984-01-01
The paper reviews the area of body-turbulence interaction with particular emphasis upon the influence of the body upon an incident turublent field. Cases considered include two-dimensional (high and low fineness ratio, porous, and impervious) and three-dimensional bodies in-stream, adjacent to, and attached to walls. Particular physics common to several geometric and incident flow configurations include (1) eddy severing at relatively sharp leading edges, (2) production of vorticity of the opposite sense on bluff bodies, and (3) body region production of control vortices which affect the incident turbulence field for the order of 100 boundary-layer thicknesses downstream. The major local effects of the body upon the incident turbulent field include (1) a blocking effect, (2) influence of the body momentum deficit/near wake, (3) distortion due to the body time-averaged flow field, and (4) unsteady body circulation. The review may be of particular interest for turbulence alteration/control using fixed geometry in applications such as drag reduction, separation control, noise reduction, and augmentor optimization.
Turbulence compressibility corrections
Coakley, T. J.; Horstman, C. C.; Marvin, J. G.; Viegas, J. R.; Bardina, J. E.; Huang, P. G.; Kussoy, M. I.
1994-01-01
The basic objective of this research was to identify, develop and recommend turbulence models which could be incorporated into CFD codes used in the design of the National AeroSpace Plane vehicles. To accomplish this goal, a combined effort consisting of experimental and theoretical phases was undertaken. The experimental phase consisted of a literature survey to collect and assess a database of well documented experimental flows, with emphasis on high speed or hypersonic flows, which could be used to validate turbulence models. Since it was anticipated that this database would be incomplete and would need supplementing, additional experiments in the NASA Ames 3.5-Foot Hypersonic Wind Tunnel (HWT) were also undertaken. The theoretical phase consisted of identifying promising turbulence models through applications to simple flows, and then investigating more promising models in applications to complex flows. The complex flows were selected from the database developed in the first phase of the study. For these flows it was anticipated that model performance would not be entirely satisfactory, so that model improvements or corrections would be required. The primary goals of the investigation were essentially achieved. A large database of flows was collected and assessed, a number of additional hypersonic experiments were conducted in the Ames HWT, and two turbulence models (kappa-epsilon and kappa-omega models with corrections) were determined which gave superior performance for most of the flows studied and are now recommended for NASP applications.
Multilevel turbulence simulations
Energy Technology Data Exchange (ETDEWEB)
Tziperman, E. [Princeton Univ., NJ (United States)
1994-12-31
The authors propose a novel method for the simulation of turbulent flows, that is motivated by and based on the Multigrid (MG) formalism. The method, called Multilevel Turbulence Simulations (MTS), is potentially more efficient and more accurate than LES. In many physical problems one is interested in the effects of the small scales on the larger ones, or in a typical realization of the flow, and not in the detailed time history of each small scale feature. MTS takes advantage of the fact that the detailed simulation of small scales is not needed at all times, in order to make the calculation significantly more efficient, while accurately accounting for the effects of the small scales on the larger scale of interest. In MTS, models of several resolutions are used to represent the turbulent flow. The model equations in each coarse level incorporate a closure term roughly corresponding to the tau correction in the MG formalism that accounts for the effects of the unresolvable scales on that grid. The finer resolution grids are used only a small portion of the simulation time in order to evaluate the closure terms for the coarser grids, while the coarse resolution grids are then used to accurately and efficiently calculate the evolution of the larger scales. The methods efficiency relative to direct simulations is of the order of the ratio of required integration time to the smallest eddies turnover time, potentially resulting in orders of magnitude improvement for a large class of turbulence problems.
Cygankiewicz, Iwona
2013-01-01
Heart rate turbulence (HRT) is a baroreflex-mediated biphasic reaction of heart rate in response to premature ventricular beats. Heart rate turbulence is quantified by: turbulence onset (TO) reflecting the initial acceleration of heart rate following premature beat and turbulence slope (TS) describing subsequent deceleration of heart rate. Abnormal HRT identifies patients with autonomic dysfunction or impaired baroreflex sensitivity due to variety of disorders, but also may reflect changes in autonomic nervous system induced by different therapeutic modalities such as drugs, revascularization, or cardiac resynchronization therapy. More importantly, impaired HRT has been shown to identify patients at high risk of all-cause mortality and sudden death, particularly in postinfarction and congestive heart failure patients. It should be emphasized that abnormal HRT has a well-established role in stratification of postinfarction and heart failure patients with relatively preserved left ventricular ejection fraction. The ongoing clinical trials will document whether HRT can be used to guide implantation of cardioverter-defibrillators in this subset of patients, not covered yet by ICD guidelines. This review focuses on the current state-of-the-art knowledge regarding clinical significance of HRT in detection of autonomic dysfunction and regarding the prognostic significance of this parameter in predicting all-cause mortality and sudden death. © 2013.
Incremental Similarity and Turbulence
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole E.; Hedevang, Emil; Schmiegel, Jürgen
This paper discusses the mathematical representation of an empirically observed phenomenon, referred to as Incremental Similarity. We discuss this feature from the viewpoint of stochastic processes and present a variety of non-trivial examples, including those that are of relevance for turbulence...
Turbulence and Flying Machines
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 4; Issue 11. Turbulence and Flying Machines. Rama Govindarajan. General Article Volume 4 Issue 11 November 1999 pp 54-62. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/004/11/0054-0062 ...
Large-eddy simulation of atmospheric flow over complex terrain
Energy Technology Data Exchange (ETDEWEB)
Bechmann, A.
2006-11-15
The present report describes the development and validation of a turbulence model designed for atmospheric flows based on the concept of Large-Eddy Simulation (LES). The background for the work is the high Reynolds number k - epsilon model, which has been implemented on a finite-volume code of the incompressible Reynolds-averaged Navier-Stokes equations (RANS). The k - epsilon model is traditionally used for RANS computations, but is here developed to also enable LES. LES is able to provide detailed descriptions of a wide range of engineering flows at low Reynolds numbers. For atmospheric flows, however, the high Reynolds numbers and the rough surface of the earth provide difficulties normally not compatible with LES. Since these issues are most severe near the surface they are addressed by handling the near surface region with RANS and only use LES above this region. Using this method, the developed turbulence model is able to handle both engineering and atmospheric flows and can be run in both RANS or LES mode. For LES simulations a time-dependent wind field that accurately represents the turbulent structures of a wind environment must be prescribed at the computational inlet. A method is implemented where the turbulent wind field from a separate LES simulation can be used as inflow. To avoid numerical dissipation of turbulence special care is paid to the numerical method, e.g. the turbulence model is calibrated with the specific numerical scheme used. This is done by simulating decaying isotropic and homogeneous turbulence. Three atmospheric test cases are investigated in order to validate the behavior of the presented turbulence model. Simulation of the neutral atmospheric boundary layer, illustrates the turbulence model ability to generate and maintain the turbulent structures responsible for boundary layer transport processes. Velocity and turbulence profiles are in good agreement with measurements. Simulation of the flow over the Askervein hill is also
Aircraft Dynamic Modeling in Turbulence
Morelli, Eugene A.; Cunninham, Kevin
2012-01-01
A method for accurately identifying aircraft dynamic models in turbulence was developed and demonstrated. The method uses orthogonal optimized multisine excitation inputs and an analytic method for enhancing signal-to-noise ratio for dynamic modeling in turbulence. A turbulence metric was developed to accurately characterize the turbulence level using flight measurements. The modeling technique was demonstrated in simulation, then applied to a subscale twin-engine jet transport aircraft in flight. Comparisons of modeling results obtained in turbulent air to results obtained in smooth air were used to demonstrate the effectiveness of the approach.
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
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.
Inhomogeneity of optical turbulence over False Bay (South Africa)
Ullwer, Carmen; Sprung, Detlev; van Eijk, Alexander M. J.; Gunter, Willi; Stein, Karin
2017-09-01
Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the vertical and horizontal distribution (inhomogeneity) of the optical turbulence. In the framework of the First European South African Transmission ExpeRiment (FESTER) optical turbulence was measured between June 2015 and February 2016 on a 2 km over-water link over False Bay. The link ran from the Institute of Maritime Technology (IMT) in Simons Town to the lighthouse at Roman Rock Island. Three Boundary layer scintillometers (BLS900) allowed assessing the vertical distribution of optical turbulence at three different heights between 5 and 12 m above the water surface. The expected decrease of Cn2 with height is not always found. These results are analyzed in terms of the meteorological scenarios, and a comparison is made with a fourth optical link providing optical turbulence data over a 8.7 km path from IMT to Kalk Bay, roughly 36° to the north of the three 2 km paths. The results are related to the inhomogeneous meteorological conditions over the Bay as assessed with the numerical weather prediction tool, the Weather Forecast and Research model WRF.
Turbulent boundary layer in high Rayleigh number convection in air.
du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian
2014-03-28
Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.
Preferrential Concentration of Particles in Protoplanetary Nebula Turbulence
Hartlep, Thomas; Cuzzi, Jeffrey N.
2015-01-01
Preferential concentration in turbulence is a process that causes inertial particles to cluster in regions of high strain (in-between high vorticity regions), with specifics depending on their stopping time or Stokes number. This process is thought to be of importance in various problems including cloud droplet formation and aerosol transport in the atmosphere, sprays, and also in the formation of asteroids and comets in protoplanetary nebulae. In protoplanetary nebulae, the initial accretion of primitive bodies from freely-floating particles remains a problematic subject. Traditional growth-by-sticking models encounter a formidable "meter-size barrier" [1] in turbulent nebulae. One scenario that can lead directly from independent nebula particulates to large objects, avoiding the problematic m-km size range, involves formation of dense clumps of aerodynamically selected, typically mm-size particles in protoplanetary turbulence. There is evidence that at least the ordinary chondrite parent bodies were initially composed entirely of a homogeneous mix of such particles generally known as "chondrules" [2]. Thus, while it is arcane, turbulent preferential concentration acting directly on chondrule size particles are worthy of deeper study. Here, we present the statistical determination of particle multiplier distributions from numerical simulations of particle-laden isotopic turbulence, and a cascade model for modeling turbulent concentration at lengthscales and Reynolds numbers not accessible by numerical simulations. We find that the multiplier distributions are scale dependent at the very largest scales but have scale-invariant properties under a particular variable normalization at smaller scales.
Atmospheric Circulation of Exoplanets
Showman, A. P.; Cho, J. Y.-K.; Menou, K.
2010-12-01
We survey the basic principles of atmospheric dynamics relevant to explaining existing and future observations of exoplanets, both gas giant and terrestrial. Given the paucity of data on exoplanet atmospheres, our approach is to emphasize fundamental principles and insights gained from solar system studies that are likely to be generalizable to exoplanets. We begin by presenting the hierarchy of basic equations used in atmospheric dynamics, including the Navier-Stokes, primitive, shallow-water, and two-dimensional nondivergent models. We then survey key concepts in atmospheric dynamics, including the importance of planetary rotation, the concept of balance, and simple scaling arguments to show how turbulent interactions generally produce large-scale east-west banding on rotating planets. We next turn to issues specific to giant planets, including their expected interior and atmospheric thermal structures, the implications for their wind patterns, and mechanisms to pump their east-west jets. Hot Jupiter atmospheric dynamics are given particular attention, as these close-in planets have been the subject of most of the concrete developments in the study of exoplanetary atmospheres. We then turn to the basic elements of circulation on terrestrial planets as inferred from solar system studies, including Hadley cells, jet streams, processes that govern the large-scale horizontal temperature contrasts, and climate, and we discuss how these insights may apply to terrestrial exoplanets. Although exoplanets surely possess a greater diversity of circulation regimes than seen on the planets in our solar system, our guiding philosophy is that the multidecade study of solar system planets reviewed here provides a foundation upon which our understanding of more exotic exoplanetary meteorology must build.
Zilitinkevich, S S; Kleeorin, N; Rogachevskii, I; Esau, I
2011-01-01
In this paper we advance physical background of the EFB turbulence closure and present its comprehensive description. It is based on four budget equations for the second moments: turbulent kinetic and potential energies (TKE and TPE) and vertical turbulent fluxes of momentum and buoyancy; a new relaxation equation for the turbulent dissipation time-scale; and advanced concept of the inter-component exchange of TKE. The EFB closure is designed for stratified, rotating geophysical flows from neutral to very stable. In accordance to modern experimental evidence, it grants maintaining turbulence by the velocity shear at any gradient Richardson number Ri, and distinguishes between the two principally different regimes: "strong turbulence" at Ri 1 typical of the free atmosphere or deep ocean, where Pr_T asymptotically linearly increases with increasing Ri that implies strong suppressing of the heat transfer compared to momentum transfer. For use in different applications, the EFB turbulence closure is formulated a...
Faeth, G. M.
1989-01-01
Measurements and predictions of the structure of several multiphase flows are considered. The properties of dense sprays near the exits of pressure-atomizing injectors and of noncombusting and combusting dilute dispersed flows in round-jet configurations are addressed. It is found that the properties of dense sprays exhibit structure and mixing properties similar to variable-density single-phase flows at high Reynolds numbers within the atomization regime. The degree of development and turbulence levels at the injector exit have a surprisingly large effect on the structure and mixing properties of pressure-atomized sprays, particularly when the phase densities are large. Contemporary stochastic analysis of dilute multiphase flows provides encouraging predictions of turbulent dispersion for a wide variety of jetlike flows, particle-laden jets in gases and liquids, noncondensing and condensing bubbly jets, and nonevaporating, evaporating, and combusting sprays.
van Wijngaarden, L.
When bubbles rise in a vertical turbulent liquid flow, their trajectories are affected by the turbulence. In addition, the motion of the bubbles relative to the liquid causes velocity fluctuations in the latter. This is commonly called ``pseudoturbulence.'' Over the past decades measurements of pseudoturbulence have been reported (Theofanous and Sullivan, 1982; Lance and Bataille, 1991; Stewart, 1995). For the bubbles used in the majority of these experiments the relative motion can, as far as the rise of isolated bubbles is concerned, be described by potential flow together with thin boundary layers to accommodate the tangential stress difference between liquid and gas. With the help of this same description an approximate calculation is made of the kinetic energy in the pseudoturbulence. Except for a very low gas concentration, this turns out to be much smaller than the measurements indicate. A tentative explanation of this phenomenon is presented, based on the observed behavior (Duineveld, 1994) of bubbles encountering another bubble or a solid wall.
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...
Cascades in helical turbulence
Ditlevsen, P D
2001-01-01
The existence of a second quadratic inviscid invariant, the helicity, in a turbulent flow leads to coexisting cascades of energy and helicity. An equivalent of the four-fifth law for the longitudinal third order structure function, which is derived from energy conservation, is easily derived from helicity conservation cite{Procaccia,russian}. The ratio of dissipation of helicity to dissipation of energy is proportional to the wave-number leading to a different Kolmogorov scale for helicity than for energy. The Kolmogorov scale for helicity is always larger than the Kolmogorov scale for energy so in the high Reynolds number limit the flow will always be helicity free in the small scales, much in the same way as the flow will be isotropic and homogeneous in the small scales. A consequence is that a pure helicity cascade is not possible. The idea is illustrated in a shell model of turbulence.
Controlled-Turbulence Bioreactors
Wolf, David A.; Schwartz, Ray; Trinh, Tinh
1989-01-01
Two versions of bioreactor vessel provide steady supplies of oxygen and nutrients with little turbulence. Suspends cells in environment needed for sustenance and growth, while inflicting less damage from agitation and bubbling than do propeller-stirred reactors. Gentle environments in new reactors well suited to delicate mammalian cells. One reactor kept human kidney cells alive for as long as 11 days. Cells grow on carrier beads suspended in liquid culture medium that fills cylindrical housing. Rotating vanes - inside vessel but outside filter - gently circulates nutrient medium. Vessel stationary; magnetic clutch drives filter cylinder and vanes. Another reactor creates even less turbulence. Oxygen-permeable tubing wrapped around rod extending along central axis. Small external pump feeds oxygen to tubing through rotary coupling, and oxygen diffuses into liquid medium.
Estimation of turbulence from time-lapse imagery
McCrae, Jack E.; Bose-Pillai, Santasri R.; Fiorino, Steven T.
2017-07-01
Atmospheric turbulence parameters are estimated for an imaging path based on time-lapse imaging results. Atmospheric turbulence causes frame-to-frame shifts of the entire image as well as parts of the image. The statistics of these shifts encode information about the turbulence strength (as characterized by Cn2, the refractive index structure function constant) along the optical path. The shift variance observed is simply proportional to the variance of the tilt of the optical field averaged over the area being tracked and averaged over the camera aperture. By presuming this turbulence follows the Kolmogorov spectrum, weighting functions, which relate the turbulence strength along the path to the shifts measured, are derived. These weighting functions peak at the camera and fall to zero at the object. The larger the area observed, the more quickly the weighting function decays. One parameter we would like to estimate is r0 (the Fried parameter or atmospheric coherence diameter.) The weighting functions derived for pixel sized or larger parts of the image all fall faster than the weighting function appropriate for estimating the spherical wave r0. If we were to presume that Cn2 is constant along the path, then an estimate for r0 could be obtained for each area tracked, but since the weighting function for r0 differs substantially from that for every realizable tracked area, it can be expected that this approach would yield a poor estimate. Instead, the weighting functions for a number of different patch sizes can be combined through the Moore-Penrose pseudoinverse to create a weighting function that yields the least-squares optimal linear combination of measurements for the estimation of r0. This approach is carried out for one example and is shown to give noisy results. A modified version of this approach that creates larger patches by averaging several smaller patches together solves this noise issue. This approach can also work to estimate other atmospheric
Beresnyak, Andrey
2013-01-01
Astrophysical fluids are conductive, magnetized and turbulent. This entails a variety of phenomena, two most basic of which is the dynamo and the energy cascade. Very well known empirically in hydrodynamics so called "zeroth law of turbulence" states that even if viscosity goes to zero, energy dissipation does not, but goes to a constant. It turns out that in MHD not only this still holds true, but another basic law, which I call "zeroth law of dynamo", is valid, namely that if Reynolds numbers are sufficiently high and magnetic energy is low, the latter will grow at a constant rate, which is a fraction of the total dissipation rate. Another point of interest for an astrophysicist is the properties of MHD cascade in the inertial range. I will argue that both theory and numerics favor Kolmogorov -5/3 slope and not -3/2 slope that was reported earlier. The most challenging problem is so-called imbalanced, or cross-helical case which appear whenever there is a localized source of perturbations, such as the Sun for the solar wind turbulence or the central engine in AGN jets. The standard Goldreich-Sridhar model does not apply in this case and it eluded theoretical description for a long time. The keys to understand energy cascades in the imbalanced case are the anisotropies of the Elsasser fields which turn out to be different. I will show the results of one of the highest resolution simulations ever performed, which were very helpful in discriminating between various viable models of MHD turbulence.
Random functions and turbulence
Panchev, S
1971-01-01
International Series of Monographs in Natural Philosophy, Volume 32: Random Functions and Turbulence focuses on the use of random functions as mathematical methods. The manuscript first offers information on the elements of the theory of random functions. Topics include determination of statistical moments by characteristic functions; functional transformations of random variables; multidimensional random variables with spherical symmetry; and random variables and distribution functions. The book then discusses random processes and random fields, including stationarity and ergodicity of random
Using Reconstructed POD Modes as Turbulent Inflow for LES Wind Turbine Simulations
Nielson, Jordan; Bhaganagar, Kiran; Juttijudata, Vejapong; Sirisup, Sirod
2016-11-01
Currently, in order to get realistic atmospheric effects of turbulence, wind turbine LES simulations require computationally expensive precursor simulations. At times, the precursor simulation is more computationally expensive than the wind turbine simulation. The precursor simulations are important because they capture turbulence in the atmosphere and as stated above, turbulence impacts the power production estimation. On the other hand, POD analysis has been shown to be capable of capturing turbulent structures. The current study was performed to determine the plausibility of using lower dimension models from POD analysis of LES simulations as turbulent inflow to wind turbine LES simulations. The study will aid the wind energy community by lowering the computational cost of full scale wind turbine LES simulations, while maintaining a high level of turbulent information and being able to quickly apply the turbulent inflow to multi turbine wind farms. This will be done by comparing a pure LES precursor wind turbine simulation with simulations that use reduced POD mod inflow conditions. The study shows the feasibility of using lower dimension models as turbulent inflow of LES wind turbine simulations. Overall the power production estimation and velocity field of the wind turbine wake are well captured with small errors.
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.
Modeling the turbulent kinetic energy equation for compressible, homogeneous turbulence
Aupoix, B.; Blaisdell, G. A.; Reynolds, William C.; Zeman, Otto
1990-01-01
The turbulent kinetic energy transport equation, which is the basis of turbulence models, is investigated for homogeneous, compressible turbulence using direct numerical simulations performed at CTR. It is shown that the partition between dilatational and solenoidal modes is very sensitive to initial conditions for isotropic decaying turbulence but not for sheared flows. The importance of the dilatational dissipation and of the pressure-dilatation term is evidenced from simulations and a transport equation is proposed to evaluate the pressure-dilatation term evolution. This transport equation seems to work well for sheared flows but does not account for initial condition sensitivity in isotropic decay. An improved model is proposed.
Statistical properties of turbulence: An overview
Indian Academy of Sciences (India)
We present an introductory overview of several challenging problems in the statistical characterization of turbulence. We provide examples from fluid turbulence in three and two dimensions, from the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the ...
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
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...
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...
Surface Temperature and Surface-Layer Turbulence in a Convective Boundary Layer
Garai, A.; Pardyjak, E.; Steeneveld, G.J.; Kleissl, J.
2013-01-01
Previous laboratory and atmospheric experiments have shown that turbulence influences the surface temperature in a convective boundary layer. The main objective of this study is to examine land-atmosphere coupled heat transport mechanism for different stability conditions. High frequency infrared
Measuring turbulent cascades in Jupiter's weather layer
Young, Roland M. B.; Read, Peter L.
2017-10-01
Jupiter's atmosphere has often been compared with a classical quasi-two-dimensional, geostrophically turbulent fluid, in which kinetic energy is transferred upscale, with zonal jets emerging due to the spherical curvature of the planet. In a new analysis of 2D wind fields obtained from Cassini cloud images taken during closest approach to Jupiter at the time of the December 2000 fly-by, we have determined 2nd and 3rd order structure functions and spectral transfers of kinetic energy and enstrophy (squared vorticity) across scales ranging from ~1000 km to the scale of the planet itself. These confirm the upscale transfer of kinetic energy from eddies on scales ≥ 3000 km up to the scales of the zonal jets, with ~90% of the energy being transferred into the jets themselves, accompanied by downscale transfer of enstrophy from all scales. For scales ≤ 3000 km or so, however, kinetic energy is transferred downscale, indicating a strong source of kinetic energy at a scale ~2000-3000 km, comparable with the internal Rossby deformation radius. This suggests an important role for baroclinic instability in energising Jupiter's turbulent atmosphere.
The turbulent decay of trailing vortex pairs in stably stratified environments
Energy Technology Data Exchange (ETDEWEB)
Holzaepfel, F.; Gerz, T.; Baumann, R.
2000-03-01
The decay of trailing vortex pairs in thermally stably stratified environments is investigated by means of large eddy simulations. Results of in-situ measurements in the wakes of different aircraft are used to find appropriate intitializations for the simulation of wake turbulence in the quiescent atmosphere. Furthermore, cases with weak atmospheric turbulence are investigated. It is shown that the early development of the vortices is not affected by turbulence and develops almost identically as in 2D simulations. In a quiescent atmosphere the subsequent vortex decay is controlled by the interaction of short-wave disturbances, owing to the aircraft induced turbulence, and baroclinic vorticity, owing to stable stratification. As a consequence, vertical vorticity streaks between the vortices are induced which are substantially intensified by vortex stretching and finally lead to rapid turbulent wake-vortex decay. When in addition also atmospheric turbulence is present, the long-wave instability is dominantly promoted. For very strong stratification (Fr < 1) it is observed that wake vortices may rebound but lose most of their strength before reaching the flight level. Finally, the simulation results are compared to the predictive capabilities of Greene's approximate model. (orig.)
Front dynamics in turbulent media
Martí, A C; Sancho, J M
1997-01-01
A study of a stable front propagating in a turbulent medium is presented. The front is generated through a reaction-diffusion equation, and the turbulent medium is statistically modeled using a Langevin equation. Numerical simulations indicate the presence of two different dynamical regimes. These regimes appear when the turbulent flow either wrinkles a still rather sharp propagating interfase or broadens it. Specific dependences of the propagating velocities on stirring intensities appropriate to each case are found and fitted when possible according to theoretically predicted laws. Different turbulent spectra are considered.
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.
Turbulent Dynamos and Magnetic Helicity
Energy Technology Data Exchange (ETDEWEB)
Ji, Hantao
1999-04-01
It is shown that the turbulent dynamo alpha-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is elcetrostatic or due to the elcetron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity expect for a battery effect which vanishes in the limit of magnetohydrodynamics. Implications for astrophysical situations, especially for the solar dynamo, are discussed.
Anisotropic power spectrum of refractive-index fluctuation in hypersonic turbulence.
Li, Jiangting; Yang, Shaofei; Guo, Lixin; Cheng, Mingjian
2016-11-10
An anisotropic power spectrum of the refractive-index fluctuation in hypersonic turbulence was obtained by processing the experimental image of the hypersonic plasma sheath and transforming the generalized anisotropic von Kármán spectrum. The power spectrum suggested here can provide as good a fit to measured spectrum data for hypersonic turbulence as that recorded from the nano-planar laser scattering image. Based on the newfound anisotropic hypersonic turbulence power spectrum, Rytov approximation was employed to establish the wave structure function and the spatial coherence radius model of electromagnetic beam propagation in hypersonic turbulence. Enhancing the anisotropy characteristics of the hypersonic turbulence led to a significant improvement in the propagation performance of electromagnetic beams in hypersonic plasma sheath. The influence of hypersonic turbulence on electromagnetic beams increases with the increase of variance of the refractive-index fluctuation and the decrease of turbulence outer scale and anisotropy parameters. The spatial coherence radius was much smaller than that in atmospheric turbulence. These results are fundamental to understanding electromagnetic wave propagation in hypersonic turbulence.
Wavefront sensing for anisotropic turbulence using digital holography
Thurman, Samuel T.; Gatt, Philip; Alley, Thomas
2016-09-01
We report on digital holographic imaging through atmospheric turbulence. Data recorded with aberrations is corrected during post processing using an iterative sharpness-metric maximization algorithm. Assuming the correction cancels the actual wavefront error, this process is equivalent to wavefront sensing. Much of our past work focused on imaging through isotropic turbulence with phase corrections using a Zernike-polynomial expansion. Here, we describe algorithm modifications for imaging through anisotropic turbulence, similar to what is seen when looking through the aero-optic boundary layer surrounding a moving aircraft. Specifically, we explore tradeoffs associated with switching from a Zernike representation to Karhunen-Loève basis functions. In some cases, the dimensionality of the phase correction estimation algorithm can be reduced significantly by this change. This reduces the computational burden
Unraveling the Mysteries of Turbulence Transport in a Wind Farm
Directory of Open Access Journals (Sweden)
Pankaj K. Jha
2015-06-01
Full Text Available A true physical understanding of the mysteries involved in the recovery process of the wake momentum deficit, downstream of utility-scale wind turbines in the atmosphere, has not been obtained to date. Field data are not acquired at sufficient spatial and temporal resolutions to dissect some of the mysteries of wake turbulence. It is here that the actuator line method has evolved to become the technology standard in the wind energy community. This work presents the actuator line method embedded into an Open source Field Operation and Manipulation (OpenFOAM large-eddy simulation solver and applies it to two small wind farms, the first one consisting of an array of two National Renewable Energy Laboratory 5 Megawatt (NREL 5-MW turbines separated by seven rotor diameters in neutral and unstable atmospheric boundary-layer flow and the second one consisting of five NREL 5-MW wind turbines in unstable atmospheric conditions arranged in two staggered arrays of two and three turbines, respectively. Detailed statistics involving power spectral density (PSD of turbine power along with standard deviations reveal the effects of atmospheric turbulence and its space and time scales. High-resolution surface data extracts provide new insight into the complex recovery process of the wake momentum deficit governed by turbulence transport phenomena.
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.
Energy Technology Data Exchange (ETDEWEB)
Deng Peng; Yuan Xiuhua; Zeng Yanan; Zhao Ming; Luo Hanjun, E-mail: yuanxh@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei (China)
2011-02-01
In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal, affecting link performance. Most theoretical treatments have been described by Kolmogorov's power spectral density model through weak turbulence with constant wind speed. However, several experiments showed that Kolmogorov theory is sometimes incomplete to describe atmospheric turbulence properly, especially through the strong turbulence with variable wind speed, which is known to contribute significantly to the turbulence in the atmosphere. We present an optical turbulence model that incorporates into variable wind speed instead of constant value, a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/3, and a generalized amplitude factor instead of constant value 0.033. The free space optical communication performance for a Gaussian beam wave of scintillation index, mean signal-to-noise ratio
DEFF Research Database (Denmark)
Wieczorek, Izabela
2015-01-01
Through the coupling of dispositif with atmosphere this paper engages in a discussion of the atmospherics as both a form of knowledge and a material practice. In doing so the objective is to provide an inventory of tools and methodologies deployed in the construction of atmosphere understood......, the conceptual foundations and protocols for the production of atmosphere in architecture might be found beneath the surface of contemporary debates. In this context, the notion of atmospheric dispositif – illustrated through an oeuvre of the German architect Werner Ruhnau and its theoretical and historical...
Turbulence and sediment transport over sand dunes and ripples
Bennis, A.; Le Bot, S.; lafite, R.; Bonneton, P.; Ardhuin, F.
2013-12-01
Several bedforms are present near to the surfzone of natural beaches. Dunes and ripples are frequently observed. Understanding the turbulence over these forms is essential for the sediment transport. The turbulent flow and the suspended sand particles interact with each other. At the moment, the modelling strategy for turbulence is still a challenge. According to the spatial scales, some different methods to model the turbulence are employed, in particular the RANS (Reynolds Averaged Navier-Stokes) and the LES (Large Eddy Simulation). A hybrid method combining both RANS and LES is set up here. We have adapted this method, initially developed for atmospheric flow, to the oceanic flow. This new method is implemented inside the 3D hydrodynamic model, MARS 3D, which is forced by waves. LES is currently the best way to simulate turbulent flow but its higher cost prevents it from being used for large scale applications. So, here we use RANS near the bottom while LES is set elsewhere. It allows us minimize the computational cost and ensure a better accuracy of the results than with a fully RANS model. In the case of megaripples, the validation step was performed with two sets of field data (Sandy Duck'97 and Forsoms'13) but also with the data from Dune2D model which uses only RANS for turbulence. The main findings are: a) the vertical profiles of the velocity are similar throughout the data b) the turbulent kinetic energy, which was underestimated by Dune2D, is in line with the observations c) the concentration of the suspended sediment is simulated with a better accuracy than with Dune2D but this remains lower than the observations.
Direct Simulations of Turbulent Particle-Laden Flows
Wang, Lian-Ping
2004-11-01
Turbulent particle-laden flows had traditionally been treated with empirical and phenomenological approaches and advances in fundamental understanding were limited. In the last 15 years, direct simulations and advanced measurement techniques have provided much needed, first-principle based field data from which new insights and better modeling strategies could be developed. In this talk, I will first provide an overview of using direct simulations as an independent research tool for turbulent particle-laden flows. Applications to particle transport, dispersion, sedimentation, collision/coalescence, and flow modulation will be briefly discussed. The second part of the talk will focus on an on-going study in which direct simulations of turbulent particle-laden flow is being used to address several effects of air turbulence on warm rain formation in the atmosphere, including effects of turbulence on droplet-droplet relative motion, preferential concentration, droplet settling velocity and how these may enhance the geometric collision rates and collision efficiencies of cloud droplets.
Aspects of the atmospheric surface layers on Mars and Earth
DEFF Research Database (Denmark)
Larsen, Søren Ejling; Ejsing Jørgensen, Hans; Landberg, L.
2002-01-01
and mean flow on Mars is found to obey the same scaling laws as on Earth. The largest micrometeorological differences between the two atmospheres are associated with the low air density of the Martian atmosphere. Together with the virtual absence of water vapour, it reduces the importance......The structures of mean flow and turbulence in the atmospheric surface boundary layer have been extensively studied on Earth, and to a far less extent on Mars, where only the Viking missions and the Pathfinder mission have delivered in-situ data. Largely the behaviour of surface-layer turbulence...
MHD turbulence and distributed chaos
Bershadskii, A
2016-01-01
It is shown, using results of recent direct numerical simulations, that spectral properties of distributed chaos in MHD turbulence with zero mean magnetic field are similar to those of hydrodynamic turbulence. An exception is MHD spontaneous breaking of space translational symmetry, when the stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$ has $\\beta=4/7$.
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.
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...
Magnetized Turbulent Dynamo in Protogalaxies
Energy Technology Data Exchange (ETDEWEB)
Leonid Malyshkin; Russell M. Kulsrud
2002-01-28
The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached.
Stochastic Subspace Modelling of Turbulence
DEFF Research Database (Denmark)
Sichani, Mahdi Teimouri; Pedersen, B. J.; Nielsen, Søren R.K.
2009-01-01
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...... an empirical cross spectral density function for the along-wind turbulence component over the wind field area is taken as the starting point. The spectrum is spatially discretized in terms of a Hermitian cross-spectral density matrix for the turbulence state vector which turns out not to be positive definite...... 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...
Organized motion in turbulent flow
Cantwell, B. J.
A review of organized motion in turbulent flow indicates that the transport properties of most shear flows are dominated by large-scale vortex nonrandom motions. The mean velocity profile of a turbulent boundary layer consists of a viscous sublayer, buffer layer, and a logarithmic outer layer; an empirical formula of Coles (1956) applies to various pressure gradients. The boundary layer coherent structure was isolated by the correlation methods of Townsend (1956) and flow visualization by direct observations of complex unsteady turbulent motions. The near-wall studies of Willmart and Wooldridge (1962) used the space-time correlation for pressure fluctuations at the wall under a thick turbulent boundary layer; finally, organized motion in free shear flows and transition-control of mixing demonstrated that the Reynolds number invariance of turbulence shows wide scatter.
Magnetohydrodynamic Turbulence and the Geodynamo
Shebalin, John V.
2016-01-01
Recent research results concerning forced, dissipative, rotating magnetohydrodynamic (MHD) turbulence will be discussed. In particular, we present new results from long-time Fourier method (periodic box) simulations in which forcing contains varying amounts of magnetic and kinetic helicity. Numerical results indicate that if MHD turbulence is forced so as to produce a state of relatively constant energy, then the largest-scale components are dominant and quasistationary, and in fact, have an effective dipole moment vector that aligns closely with the rotation axis. The relationship of this work to established results in ideal MHD turbulence, as well as to models of MHD turbulence in a spherical shell will also be presented. These results appear to be very pertinent to understanding the Geodynamo and the origin of its dominant dipole component. Our conclusion is that MHD turbulence, per se, may well contain the origin of the Earth's dipole magnetic field.
Sokolov, Andrey; Nishiguchi, Daiki; Aronson, Igor
Living systems represented by ensembles of motile organisms demonstrate a transition from a chaotic motion to a highly ordered state. Examples of such living systems include suspensions of bacteria, schools of fish, flocks of birds and even crowds of people. In spite of significant differences in interacting mechanisms and motion scales, ordered living systems have many similarities: short-range alignment of organism, turbulent-like motion, emergence of large-scale flows and dynamic vortices. In this work, we rectify a turbulent dynamics in suspensions of swimming bacteria Bacillus subtilis by imposing periodical constraints on bacterial motion. Bacteria, swimming between periodically placed microscopic vertical pillars, may self-organize in a stable lattice of vortices. We demonstrate the emergence of a strong anti-ferromagnetic order of bacterial vortices in a rectangular lattice of pillars. Hydrodynamic interaction between vortices increases the stability of an emerged pattern. The highest stability of vortices in the anti-ferromagnetic lattice and the fastest vortices speed were observed in structures with the periods comparable with a correlation length of bacterial unconstrained motion. A.S and I.A were supported by the US DOE, Office of Basic Energy Sciences, Division of Materials Science And Engineering, under contract No. DE AC02-06CH11357 and D.N was supported by ALPS and JSPS Grant No. 26-9915.
Directory of Open Access Journals (Sweden)
Ming Chen
Full Text Available Gaussian distribution is used to describe the power law along the propagation path and phase screen of the non-Kolmogorov turbulence is proposed based on the equivalent refractive-index structure constants. Various simulations of Gaussian beam propagation in Kolmogorov and non-Kolmogorov turbulence are used for telling the difference between isotropic and anisotropic turbulence. The results imply that the non-Kolmogorov turbulence makes a great influence on the simulations via power law in spectrum and the number of phase screens. Furthermore, the influence is mainly reflected in light intensity and beam drift. Statistics suggest that when Gaussian beam propagate through single phase screen of non-Kolmogorov, maximum and uniformity of light intensity increase first and then decrease with power law, and beam drift firstly increases and then to stabilize. When Gaussian beam propagate through multiple phase screens, relative errors of beam drift decrease with the number of phase screens. And scintillation indices in non-Kolmogorov turbulence is larger than that in Kolmogorov turbulence when the number is small. When the number is big, the scintillation indices in non-Kolmogorov turbulence is smaller than that in Kolmogorov turbulence. The results shown in this paper demonstrate the effect of the non-Kolmogorov turbulence on laser atmospheric transmissions. Thus, this paper suggests a possible direction of the improvement of the laser transmission accuracy over a long distance through the atmosphere.
Lipkens, Bart
2002-01-01
In previous papers, we have shown that model experiments are successful in simulating the propagation of sonic booms through the atmospheric turbulent boundary layer. The results from the model experiment, pressure wave forms of spark-produced N waves and turbulence characteristics of the plane jet, are used to test various sonic boom models for propagation through turbulence. Both wave form distortion models and rise time prediction models are tested. Pierce's model [A. D. Pierce, "Statistical theory of atmospheric turbulence effects on sonic boom rise times," J. Acoust. Soc. Am. 49, 906-924 (1971)] based on the wave front folding mechanism at a caustic yields an accurate prediction for the rise time of the mean wave form after propagation through the turbulence.
GENERATION OF GROUND ATMOSPHERE α-, β- AND γ-FIELDS BY NATURAL ATMOSPHERIC RADIONUCLIDES
Directory of Open Access Journals (Sweden)
V.S. Yakovleva
2014-06-01
Full Text Available The results of numerical investigation of influence of atmospheric turbulence, wind speed and direction as well as radon and thoron flux density from the soil on characteristics of atmospheric α-, β- and γ-radiation fields, which created by atmospheric radon, thoron and their short-lived decay products, are represented and analyzed in the work. It was showed that variation of radon and thoron flux densities from the earth surface changes yields and flux densities of α-, β- and γ-radiation in the ground atmosphere proportionally but does not change a form of their vertical profile.
Numerical model of sonic boom in 3D kinematic turbulence
Coulouvrat, François; Luquet, David; Marchiano, Régis
2015-10-01
Sonic boom is one of the key issues to be considered in the development of future supersonic or hypersonic civil aircraft concepts. The classical sonic boom, typical for Concorde with an N-wave shape and a ground amplitude of the order of 100 Pa, prevents overland flight. Future concepts target carefully shaped sonic booms with low amplitude weak shocks. However, sonic boom when perceived at the ground level is influenced not only by the aircraft characteristics, but also by atmospheric propagation. In particular, the effect of atmospheric turbulence on sonic boom propagation near the ground is not well characterized. Flight tests performed as early as the 1960s demonstrated that classical sonic booms are sensitive to atmospheric turbulence. However, this sensitivity remains only partially understood. This is related to the fact that i) turbulence is a random process that requires a statistical approach, ii) standard methods used to predict sonic booms, mainly geometrical acoustics based on ray tracing, are inadequate within the turbulent planetary boundary layer. Moreover, the ray theory fails to predict the acoustical field in many areas of interest, such as caustics or shadow zones. These zones are of major interest for sonic boom acceptability (highest levels, lateral extent of zone of impact). These limitations outline the need for a numerical approach that is sufficiently efficient to perform a large number of realizations for a statistical approach, but that goes beyond the limitations of ray theory. With this in view, a 3D one-way numerical method solving a nonlinear scalar wave equation established for heterogeneous, moving and absorbing atmosphere, is used to assess the effects of a 3D kinematic turbulence on sonic boom in various configurations. First, a plane N-wave is propagated in the free field through random realizations of kinematic fluctuations. Then the case of a more realistic Atmospheric Boundary Layer (ABL) is investigated, with a mean
Twisted photon entanglement through turbulent air across Vienna
Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Zeilinger, Anton
2015-01-01
Photons with a twisted phase front can carry a discrete, in principle unbounded amount of orbital angular momentum (OAM). The large state space allows for complex types of entanglement, interesting both for quantum communication and for fundamental tests of quantum theory. However, the distribution of such entangled states over large distances was thought to be infeasible due to influence of atmospheric turbulence, indicating a serious limitation on their usefulness. Here we show that it is p...
Collisions of Small Drops in a Turbulent Flow. Part III: Relative Droplet Fluxes and Swept Volumes.
Pinsky, M. B.; Khain, A. P.; Grits, B.; Shapiro, M.
2006-08-01
Swept volumes of cloud droplets with radii below 20 μm are calculated under conditions typical of atmospheric cloud turbulence characterized by enormous values of Reynolds numbers, high turbulent intermittency, and characteristic values of the dissipation rate. To perform the calculations, the motion equation for small droplets proposed by Maxey is generalized for Stokes numbers St > 0.1, which allows one to simulate relative droplet motion even for very high turbulence intensities typical of deep cumulus clouds. Analytical considerations show that droplet motion is fully determined by turbulent shears and the Lagrangian accelerations.A new statistical representation of a turbulent flow has been proposed based on the results of the scale analysis of turbulence characteristics and those related to the droplet motion. According to the method proposed, statistical properties of turbulent flow are represented by a set of noncorrelated samples of turbulent shears and Lagrangian accelerations. Each sample can be assigned to a certain point of the turbulent flow. Each such point can be surrounded by a small “elementary” volume with linear length scales of the Kolmogorov length scale, in which the Lagrangian acceleration and turbulent shears can be considered as uniform in space and invariable in time.This present study (Part III) investigates the droplet collisions in a turbulent flow when hydrodynamic droplet interaction (HDI) is disregarded. Using a statistical model, long series of turbulent shears and accelerations were generated, reproducing probability distribution functions (PDF) at high Reynolds numbers, as they were obtained in recent laboratory and theoretical studies. Swept volumes of droplets are calculated for each sample of an acceleration shear pair, and the PDF of swept volumes is calculated for turbulent parameters typical of cloud turbulence. The effect of turbulent flow intermittency manifests itself in two aspects: 1) an increase of swept volume
DEFF Research Database (Denmark)
Kinch, Sofie
2011-01-01
This paper presents an architectural approach to designing computational interfaces by articulating the notion of atmosphere in the field of interaction design. It draws upon the concept of kinesthetic interaction and a philosophical notion on atmosphere emphasizing the importance of bodily exper......” implications and qualities of the approach are identified through concrete examples of a design case, which also investigates the qualities and implications of addressing atmospheres both as design concern and user experience.......This paper presents an architectural approach to designing computational interfaces by articulating the notion of atmosphere in the field of interaction design. It draws upon the concept of kinesthetic interaction and a philosophical notion on atmosphere emphasizing the importance of bodily...... experience in space, presented as middle ground experience. In the field of HCI, middle ground experiences complete the unarticulated spectrum between designing for foreground of attention or background awareness. When “Articulating Atmospheres through Middle Ground Experiences in Interaction Design...
Performance of different detrending methods in turbulent flux estimation
Donateo, Antonio; Cava, Daniela; Contini, Daniele
2015-04-01
The eddy covariance is the most direct, efficient and reliable method to measure the turbulent flux of a scalar (Baldocchi, 2003). Required conditions for high-quality eddy covariance measurements are amongst others stationarity of the measured data and a fully developed turbulence. The simplest method for obtaining the fluctuating components for covariance calculation according to Reynolds averaging rules under ideal stationary conditions is the so called mean removal method. However steady state conditions rarely exist in the atmosphere, because of the diurnal cycle, changes in meteorological conditions, or sensor drift. All these phenomena produce trends or low-frequency changes superimposed to the turbulent signal. Different methods for trend removal have been proposed in literature; however a general agreement on how separate low frequency perturbations from turbulence has not yet been reached. The most commonly applied methods are the linear detrending (Gash and Culf, 1996) and the high-pass filter, namely the moving average (Moncrieff et al., 2004). Moreover Vickers and Mahrt (2003) proposed a multi resolution decomposition method in order to select an appropriate time scale for mean removal as a function of atmospheric stability conditions. The present work investigates the performance of these different detrending methods in removing the low frequency contribution to the turbulent fluxes calculation, including also a spectral filter by a Fourier decomposition of the time series. The different methods have been applied to the calculation of the turbulent fluxes for different scalars (temperature, ultrafine particles number concentration, carbon dioxide and water vapour concentration). A comparison of the detrending methods will be performed also for different measurement site, namely a urban site, a suburban area, and a remote area in Antarctica. Moreover the performance of the moving average in detrending time series has been analyzed as a function of the
Chalmers, J Alan
1957-01-01
Atmospheric Electricity brings together numerous studies on various aspects of atmospheric electricity. This book is composed of 13 chapters that cover the main problems in the field, including the maintenance of the negative charge on the earth and the origin of the charges in thunderstorms. After a brief overview of the historical developments of atmospheric electricity, this book goes on dealing with the general principles, results, methods, and the MKS system of the field. The succeeding chapters are devoted to some aspects of electricity in the atmosphere, such as the occurrence and d
Directory of Open Access Journals (Sweden)
Takaaki Kajita
2012-01-01
Full Text Available Atmospheric neutrinos are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the atmosphere. Electron-neutrinos and muon-neutrinos are produced mainly by the decay chain of charged pions to muons to electrons. Atmospheric neutrino experiments observed zenith angle and energy-dependent deficit of muon-neutrino events. It was found that neutrino oscillations between muon-neutrinos and tau-neutrinos explain these data well. This paper discusses atmospheric neutrino experiments and the neutrino oscillation studies with these neutrinos.
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.
Simnett, G.
1982-10-01
The sun is a stable, mediocre star with a diameter of 1.4 x 10 to the 6th km, mass 2 x 10 to the 30th kg, spectral class early G, and not too far removed on the main sequence of the Hertzsprung-Russell diagram from the category of stars known as red dwarfs. It is said to be stable only when it is compared with other stars in the Galaxy, some of which are clearly very unsteady. However, despite its poor showing in the league table of variability, now that the means of probing the sun through the ingenuity of modern science are available, it is discovered that by terrestrial standards the sun is more violent and turbulent than anything which could be conceived by man.
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.
Sudden viscous dissipation of compressing turbulence
Davidovits, S.; Fisch, N. J.
2015-01-01
Compression of turbulent plasma can amplify the turbulent kinetic energy, if the compression is fast compared to the viscous dissipation time of the turbulent eddies. A sudden viscous dissipation mechanism is demonstrated, whereby this amplified turbulent kinetic energy is rapidly converted into thermal energy, suggesting a new paradigm for fast ignition inertial fusion.
Sudden Viscous Dissipation of Compressing Turbulence.
Davidovits, Seth; Fisch, Nathaniel J
2016-03-11
Compression of turbulent plasma can amplify the turbulent kinetic energy, if the compression is fast compared to the viscous dissipation time of the turbulent eddies. A sudden viscous dissipation mechanism is demonstrated, whereby this amplified turbulent kinetic energy is rapidly converted into thermal energy, suggesting a new paradigm for fast ignition inertial fusion.
Turbulent reconnection and its implications.
Lazarian, A; Eyink, G; Vishniac, E; Kowal, G
2015-05-13
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700-718 (doi:10.1086/307233)) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate
Turbulent Mixing of Multiphase Flow
Young, Y.-N.; Ferziger, J.; Ham, F. E.; Herrmann, M.
2003-01-01
Thus we conduct numerical simulations of multiphase fluids stirred by two-dimensional turbulence to assess the possibility of self-similar drop size distribution in turbulence. In our turbulence simulations, we also explore the non-diffusive limit, where molecular mobility for the interface is vanishing. Special care is needed to transport the non-diffusive interface. Numerically, we use the particle level set method to evolve the interface. Instead of using the usual methods to calculate the surface tension force from the level set function, we reconstruct the interface based on phase- field modeling, and calculate the continuum surface tension forcing from the reconstructed interface.
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
On Lean Turbulent Combustion Modeling
Directory of Open Access Journals (Sweden)
Constantin LEVENTIU
2014-06-01
Full Text Available This paper investigates a lean methane-air flame with different chemical reaction mechanisms, for laminar and turbulent combustion, approached as one and bi-dimensional problem. The numerical results obtained with Cantera and Ansys Fluent software are compared with experimental data obtained at CORIA Institute, France. First, for laminar combustion, the burn temperature is very well approximated for all chemical mechanisms, however major differences appear in the evaluation of the flame front thickness. Next, the analysis of turbulence-combustion interaction shows that the numerical predictions are suficiently accurate for small and moderate turbulence intensity.
The role of turbulence in explosive magma-water mixing
Mastin, L. G.; Walder, J. S.; Stern, L. A.
2003-12-01
Juvenile tephra from explosive hydromagmatic eruptions differs from that of dry magmatic eruptions by its fine average grain size and highly variable vesicularity. These characteristics are generally interpreted to indicate that fragmentation, which occurs in dry magmas by bubble growth, is supplemented in hydromagmatic eruptions by quench-fracturing. Quench fragmentation is thought to accelerate heat transfer to water, driving violent steam expansion and increasing eruptive violence. Although some observed hydromagmatic events (e.g. at Surtsey) are indeed violent, others (e.g. quiescent entry of lava into the ocean at Kilauea) are not. We suggest that the violence of magma-water mixing and the grain size and dispersal of hydromagmatic tephras are controlled largely by the turbulence of magma-water mixing. At Surtsey, fine-grained, widely dispersed hydromagmatic tephras were produced primarily during continuous uprush events in which turbulent jets of magma and gas passed through shallow water (Thorarinsson, 1967). During Kilauea's current eruption, videos show generation of fine-grained tephras when turbulent jets of magma, steam, and seawater exited through skylights at the coastline. Turbulence intensity, or the fraction of total jet kinetic energy contained in fine-scale turbulent velocity oscillations, has long been known to control the scale of atomization in spray nozzles and the rate of heat transfer and chemical reaction in fuel injectors. We hypothesize that turbulence intensity also influences grain size and heat transfer rate in magma-water mixing, though such processes are complicated by boiling (in water) and quench fracturing (in magma). We are testing this hypothesis in experiments involving turbulent injection of water (a magma analog) into liquid nitrogen (a water analog). We also suggest that turbulent mixing influences relative proportions of magma and water in hydromagmatic eruptions. Empirical studies indicate that pressure-neutral turbulent
Turbulence Modeling Verification and Validation
Rumsey, Christopher L.
2014-01-01
Computational fluid dynamics (CFD) software that solves the Reynolds-averaged Navier-Stokes (RANS) equations has been in routine use for more than a quarter of a century. It is currently employed not only for basic research in fluid dynamics, but also for the analysis and design processes in many industries worldwide, including aerospace, automotive, power generation, chemical manufacturing, polymer processing, and petroleum exploration. A key feature of RANS CFD is the turbulence model. Because the RANS equations are unclosed, a model is necessary to describe the effects of the turbulence on the mean flow, through the Reynolds stress terms. The turbulence model is one of the largest sources of uncertainty in RANS CFD, and most models are known to be flawed in one way or another. Alternative methods such as direct numerical simulations (DNS) and large eddy simulations (LES) rely less on modeling and hence include more physics than RANS. In DNS all turbulent scales are resolved, and in LES the large scales are resolved and the effects of the smallest turbulence scales are modeled. However, both DNS and LES are too expensive for most routine industrial usage on today's computers. Hybrid RANS-LES, which blends RANS near walls with LES away from walls, helps to moderate the cost while still retaining some of the scale-resolving capability of LES, but for some applications it can still be too expensive. Even considering its associated uncertainties, RANS turbulence modeling has proved to be very useful for a wide variety of applications. For example, in the aerospace field, many RANS models are considered to be reliable for computing attached flows. However, existing turbulence models are known to be inaccurate for many flows involving separation. Research has been ongoing for decades in an attempt to improve turbulence models for separated and other nonequilibrium flows. When developing or improving turbulence models, both verification and validation are important
Turbulence Measurements in a Tropical Zoo Hall
Eugster, Werner; Denzler, Basil; Bogdal, Christian
2017-04-01
The Masoala rainforest hall of the Zurich Zoo, Switzerland, covers a ground surface area of 10,856 m2 and reaches 30 m in height. With its transparent ETFE foiled roof it provides a tropical climate for a large diversity of plants and animals. In combination with an effort to estimate dry deposition of elemental mercury, we made an attempt to measure turbulent transfer velocity with an ultrasonic anemometer inside the hall. Not surprising, the largest turbulence elements were on the order of the hall dimension. Although the dimensions of the hall seem to be small (200,000 m3) for eddy covariance flux measurements and the air circulation inside the hall was extremely weak, the spectra of wind velocity components and virtual (sonic) temperature obeyed the general statistical description expected under unconstrained outdoor measurement conditions. We will present results from a two-week measurement campaign in the Masoala rainforest hall and make a suggestion for the deposition velocity to be used to estimate dry deposition of atmospheric components to the tropical vegetation surface.
Modeling Turbulence Generation in the Atmospheric Surface and Boundary Layers
2015-10-01
order of kilometers—requiring on the order of 1018 computational cells—would be practically impossible given even today’s supercomputing resources . Thus...fairly easily from web resources . The mnemonics for these variables were selected as follows: LATTNE is latitude of the site of interest in degrees north...w(t)] = ∞∫ 0 e− stw (t) dt = W (s). (4.4) Standard transform and inverse-transform tables will be used to provide the results needed to express the
Comparison of Recent Measurements of Atmospheric Optical Turbulence
2005-06-01
components: one is centered at the origin, and the two others are separated by OH and -OH, respectively, where d is the angular separation of the double star , and...The factors a and b are given by 1+a2 O•-O~ a = -- b -a= 10- (7) where Am is the magnitude difference of the double star . Eq. (6) shows that all the...information needed to retrieve C, (h) is contained in a radial section of C** (r) along the double star separation. Furthermore, we wish to eliminate
Comparison of Radar and In Situ Measurements of Atmospheric Turbulence
National Research Council Canada - National Science Library
Zink, Florian
2004-01-01
We compare measurements of refractive index structure constant C (2)(n) and energy dissipation rate e by VHF radar with in situ observations by high-resolution thermosondes during a campaign near Adelaide, Australia, in August 1998...
Characteristics of turbulence driven atmospheric blur over coastal water
Jong, A.N. de; Schwering, P.B.W.; Benoist, K.W.; Gunter, W.H.; Vrahimis, G.; October, F.J.
2014-01-01
For users of Electro-Optical (EO) sensors at sea, knowledge on their resolution is of key operational importance for the prediction of the obtainable classification ranges. Small targets may be located at ranges of 20 km and more and the present day sensor pixel size may be as small as 10 μrad. In
Propagation of Polarization Modulated Beams Through a Turbulent Atmosphere
2014-11-24
conductivity in phthalocyanines using light polarization. Nature, 301, 694-5, 1983. Barron, L.D., pp. 271-331, Chap. 6 in R.J.H. Clark & R.E. Hester ...1293, 1999. Mortensen, S. & Hassing, S., pp. 1-60 in Advances in Infrared and Raman Spectroscopy, Vol. 6, R.T.H. Clark & R.E. Hester (eds), Heyden
Profiler measurements of turbulence and wind shear in a snowstorm
Energy Technology Data Exchange (ETDEWEB)
Rogers, R.R. [McGill Univ., Montreal, PQ (Canada). Dept. of Atmospheric and Oceanic Sciences; Leblanc, S.G. [McGill Univ., Montreal, PQ (Canada). Dept. of Atmospheric and Oceanic Sciences; Cohn, S.A. [McGill Univ., Montreal, PQ (Canada). Dept. of Atmospheric and Oceanic Sciences; Ecklund, W.L. [Colorado Univ., Boulder, CO (United States). Cooperative Inst. for Research in Environmental Sciences; Carter, D.A. [National Oceanic and Atmospheric Administration, Boulder, CO (United States). Aeronomy Lab.; Wilson, J.S. [Colorado Univ., Boulder, CO (United States). Cooperative Inst. for Research in Environmental Sciences
1996-02-01
Observations of a large and vigorous snowstorm with a UHF wind profiler were used to investigate the intensity of atmospheric turbulence and its relation to the vertical wind shear. Turbulence was estimated from the spread of the Doppler spectrum in the vertical beam of the profiler, after correcting for the contribution of the horizontal wind speed to the spread. Wind shear was computed directly from the measured wind profiles. Over the 24 h duration of the storm, shear values exceeding 0.02 s{sup -1} existed nearly continuously in the lowest few hundred meters of the atmosphere and in a broad elevated layer that slowly descended from 4 km to 2 km. The pattern of Doppler spread in time-height coordinates closely resembled the pattern of wind shear, though a detailed, point-by-point comparison of these two quantities by linear regression yielded a correlation coefficient of only 0.4. Focusing on just the observations in the lowest few hundred meters gave a higher correlation coefficient. The Richardson number as a function of height and time was computed by combining the measured wind shear values with temperature profiles generated by a mesoscale numerical model. We found evidence of weak turbulence even in regions with Ri>1, but a value close to the theoretical threshold of Ri=1/4 separates the more intense turbulence from the weaker. Estimates of the turbulent energy dissipation rate, {epsilon}, based on the Doppler spread, range as high as 500 cm{sup 2} s{sup -3}, the largest values being near the ground. (orig.)
Measurements of turbulent dissipation during the Bahamas Optical Turbulence Experiment
Matt, Silvia; Hou, Weilin; Woods, Sarah; Jarosz, Ewa; Goode, Wesley; Weidemann, Alan
2013-06-01
The Bahamas Optical Turbulence Experiment (BOTEX) was conducted in the summer of 2011 to investigate the impact of turbulence on underwater optical imaging. Underwater optical properties can be affected by turbulence in the water, due to localized changes in the index of refraction. We discuss measurements of current velocity and temperature, made with a Nortek Vector Acoustic Doppler Velocimeter (ADV) and PME Conductivity- Temperature (CT) probe, as well as observations made with a Rockland Oceanographic Vertical Microstructure Profiler (VMP). The instruments were deployed in close proximity in the field and in the context of measurements of optical target clarity. Turbulent kinetic energy dissipation (TKED) and temperature dissipation (TD) rates are calculated from the ADV/CT measurements and compared to TKED and TD estimated from the data collected with the VMP. The results show reasonable agreement between the two methods; differences are attributed to turbulence patchiness and intermittence, as well as sampling challenges. The study also highlights the importance of collecting concurrent data on temperature, current velocity, and current shear to assess the turbulence impact on underwater optical properties.
Gandy, Matthew
2017-07-01
What is an urban atmosphere? How can we differentiate an 'atmosphere' from other facets of urban consciousness and experience? This essay explores some of the wider cultural, political, and philosophical connotations of atmospheres as a focal point for critical reflections on space and subjectivity. The idea of an 'affective atmosphere' as a distinctive kind of mood or shared corporeal phenomenon is considered in relation to recent developments in phenomenology, extended conceptions of agency, and new understandings of materialism. The essay draws in particular on the changing characteristics of air and light to reflect on different forms of sensory experience and their wider cultural and political connotations. The argument highlights some of the tensions and anomalies that permeate contemporary understandings of urban atmospheres.
SWiFT site atmospheric characterization
Energy Technology Data Exchange (ETDEWEB)
Kelley, Christopher Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ennis, Brandon Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
Historical meteorological tall tower data are analyzed from the Texas Tech University 200 m tower to characterize the atmospheric trends of the Scaled Wind Farm Technologies (SWiFT) site. In this report the data are analyzed to reveal bulk atmospheric trends, temporal trends and correlations of atmospheric variables. Through this analysis for the SWiFT turbines the site International Electrotechnical Commission (IEC) classification is determined to be class III-C. Averages and distributions of atmospheric variables are shown, revealing large fluctuations and the importance of understanding the actual site trends as opposed to simply using averages. The site is significantly directional with the average wind speed from the south, and particularly so in summer and fall. Site temporal trends are analyzed from both seasonal (time of the year) to daily (hour of the day) perspectives. Atmospheric stability is seen to vary most with time of day and less with time of year. Turbulence intensity is highly correlated with stability, and typical daytime unstable conditions see double the level of turbulence intensity versus that experienced during the average stable night. Shear, veer and atmospheric stability correlations are shown, where shear and veer are both highest for stable atmospheric conditions. An analysis of the Texas Tech University tower anemometer measurements is performed which reveals the extent of the tower shadow effects and sonic tilt misalignment.
Gust alleviation using direct turbulence measurements
Rynaski, E. G.; Andrisani, D., II; Eulrich, B. J.
1979-01-01
The research reported upon in this paper describes an effective method of gust alleviation using direct measurements of atmospheric turbulence to drive the aircraft control surfaces in a way that attempts to directly counter or cancel those forces and moments produced on the aircraft by gusts. The method yields a feedforward or open loop control law, simple to mechanize and relatively insensitive to changes in flight condition. When applied directly, the resulting control law effectively gust-alleviates in the low frequency phugoid and short period range but has a tendency to amplify structural mode vehicle motions due to the phase lag of the actuators. A method of design based upon the use of a diagonal or Jordan form of the equations of motion enables the designer to avoid this problem of structural mode excitation.
Flow Structure and Turbulence in Wind Farms
Stevens, Richard J. A. M.; Meneveau, Charles
2017-01-01
Similar to other renewable energy sources, wind energy is characterized by a low power density. Hence, for wind energy to make considerable contributions to the world's overall energy supply, large wind farms (on- and offshore) consisting of arrays of ever larger wind turbines are being envisioned and built. From a fluid mechanics perspective, wind farms encompass turbulent flow phenomena occurring at many spatial and temporal scales. Of particular interest to understanding mean power extraction and fluctuations in wind farms are the scales ranging from 1 to 10 m that comprise the wakes behind individual wind turbines, to motions reaching 100 m to kilometers in scale, inherently associated with the atmospheric boundary layer. In this review, we summarize current understanding of these flow phenomena (particularly mean and second-order statistics) through field studies, wind tunnel experiments, large-eddy simulations, and analytical modeling, emphasizing the most relevant features for wind farm design and operation.
Effects of coastal forcing on turbulence and boundary- layer structure
Strom, Linda Maria Viktoria
Coastal mountains of significant elevation impose constraints for the surrounding flow. The aim of this study is to describe the modifications of the marine atmospheric boundary layer that occur offshore of the west coast of the United States. Aircraft measurements, up to 1000 km off the coast from two experiments, are used. This boundary layer is capped by a subsidence inversion, which slopes down toward the coast and produces large thermal winds. Low-level wind maxima (i.e. jets) are typical for these conditions, commonly a 40-50% increase relative to the 30 m wind speed. The effects of coastal forcing on low-level winds cancel in average when no regard is taken for position relative a cape or point. The variability of the low-level wind speed increases nevertheless significantly toward the coast, the standard deviation is +/-40% of the offshore value. The scale of the adjustment downstream of a cape or point is specifically addressed. Some measurements support a formulation of the coastal extent based on an inviscid shallow-water concept; mean variables (i.e. 30 m wind speed and boundary-layer depth) and turbulent parameters (i.e. dissipation and shear production of turbulent kinetic energy) vary in a uniform, predicted manner. The effects of coastal forcing on winds result in cold sea surface temperatures at the coast, due to upwelling. Stability becomes a function of offshore distance. Surface-layer turbulence statistics and spectra (and cospectra) of turbulence variables are presented. Across- and along-wind sampled spectra (and cospectra) show that large wind shear and shallow boundary layer affect the scales of the turbulence eddies. The relation between the standard deviations of wind components are affected. The turbulence appears to be non-local in some aspects, entrainment fluxes are proposed to be important due to a shallow boundary layer with a sharp, sloping inversion and a low-level jet.
Broken Ergodicity in MHD Turbulence
Shebalin, John V.
2010-01-01
Ideal magnetohydrodynamic (MHD) turbulence may be represented by finite Fourier series, where the inherent periodic box serves as a surrogate for a bounded astrophysical plasma. Independent Fourier coefficients form a canonical ensemble described by a Gaussian probability density function containing a Hermitian covariance matrix with positive eigenvalues. The eigenvalues at lowest wave number can be very small, resulting in a large-scale coherent structure: a turbulent dynamo. This is seen in computations and a theoretical explanation in terms of 'broken ergodicity' contains Taylor s theory of force-free states. An important problem for future work is the case of real, i.e., dissipative flows. In real flows, broken ergodicity and coherent structure are still expected to occur in MHD turbulence at the largest scale, as suggested by low resolution simulations. One challenge is to incorporate coherent structure at the largest scale into the theory of turbulent fluctuations at smaller scales.
Optimizing Stellarators for Turbulent Transport
Energy Technology Data Exchange (ETDEWEB)
H.E. Mynick, N.Pomphrey, and P. Xanthopoulos
2010-05-27
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
Energy Technology Data Exchange (ETDEWEB)
Novikov, E.A. [Univ. of California, San Diego, La Jolla, CA (United States)
1995-12-31
The {open_quotes}vortex strings{close_quotes} scale l{sub s} {approximately} LRe{sup -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).
TEM turbulence optimisation in stellarators
Proll, J H E; Xanthopoulos, P; Lazerson, S A; Faber, B J
2015-01-01
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 adressed 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 [C.D. Beidler $\\textit{et al}$ Fusion Technology $\\bf{17}$, 148 (1990)] 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 [D.A. Spong $\\textit{et al}$ Nucl. Fusion $\\bf{41}$, 711 (2001)] code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stella...
Optimizing stellarators for turbulent transport.
Mynick, H E; Pomphrey, N; Xanthopoulos, P
2010-08-27
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. Two initial proof-of-principle configurations are obtained, reducing the level of ion temperature gradient turbulent transport from the National Compact Stellarator Experiment baseline design by a factor of 2-2.5.
Variable density turbulence tunnel facility
Bodenschatz, E.; Bewley, G. P.; Nobach, H.; Sinhuber, M.; Xu, H.
2014-09-01
The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10-4 m2/s and 10-7 m2/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids 51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number Rλ ≈ 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to Rλ ≈ 8000.
Variable density turbulence tunnel facility.
Bodenschatz, E; Bewley, G P; Nobach, H; Sinhuber, M; Xu, H
2014-09-01
The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10(-4) m(2)/s and 10(-7) m(2)/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids 51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number R(λ) ≈ 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to R(λ) ≈ 8000.
Particle Acceleration by MHD Turbulence
Cho, Jungyeon; Lazarian, A.
2005-01-01
Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call for revisions in the picture of particle acceleration. We make use of the recently established scaling of slow and fast MHD modes in strong and weak MHD turbulence to provide a systematic study of particle acceleration in magnetic pressure (low-$\\beta$) and gaseous pressure (high-$\\beta$) dominated plasmas. We consider the acceleration by large scale compressions in both slow and fast particle diffusion limits. We c...
Mountain Wave-Induced Turbulence - "Lower Turbulent Zones" Revisited
Strauss, Lukas; Grubišić, Vanda; Serafin, Stefano; Mühlgassner, Rita
2014-05-01
In their seminal 1974 paper on "Lower Turbulent Zones Associated with Mountain Lee Waves" P. F. Lester and W. A. Fingerhut attempted to characterize regions of low-level turbulence in the lee of mountain ranges that are commonly associated with large-amplitude mountain waves aloft. For their study, they made extensive use of airborne measurements with small research aircraft that penetrated into the "lower turbulent zone" (LTZ). The Lester and Fingerhut study complemented previous work on wave-induced LTZs by J. P. Kuettner and others in the 1950s who were among the first to employ sailplanes as scientific measurement platforms. Given the limitations of scientific instrumentation on research aircraft in the 1970s (e.g., no GPS) and, in particular, on sailplanes in the 1950s, credit has to be given to these authors for their remarkably detailed account and classification of LTZs. Ever since then, scientists have been trying to refine the conceptual model of the LTZ and shed more light on the origin of turbulence therein. The Terrain-Induced Rotor Experiment (T-REX, Sierra Nevada, California, 2006) is the most recent, major effort organized to investigate the characteristics of LTZs by studying the coupled mountain-wave, rotor, and boundary-layer system. During T-REX, comprehensive ground-based and airborne, in situ and remote sensing measurements were collected during 15 Intensive Observation Periods (IOPs). In this study, we make use of the extensive T-REX datasets to revisit the LTZ concept. During T-REX IOPs, the University of Wyoming King Air (UWKA) research aircraft flew straight-and-level legs aligned with the mean wind direction to document the variation of flow and turbulence over and downwind of the Sierra Nevada. In order to characterize the structure and intensity of turbulence within the LTZ, turbulent kinetic energy (TKE) and eddy-dissipation rate (EDR) were computed from UWKA research flights. In contrast to the rough average values of TKE and EDR
Manipulating the anisotropy of turbulence
Chang, Kelken; Bodenschatz, Eberhard
2011-01-01
Most turbulence theories apply only to the ideal state of statistically homogeneous and isotropic turbulence. Almost all natural flows, including laboratory flows, are neither. In order to know the extent of the validity of the theories, we need to understand the influence of deviations from this ideal state. In this paper, we describe an experiment in which we not only generate isotropic turbulence, but also turbulence whose level of anisotropy can be varied systematically, while maintaining a certain degree of homogeneity. As a first step toward understanding the effect of anisotropy on turbulence, we report on the isotropy of the velocity structure functions for scales smaller than a characteristic length scale describing the large-scale motions of the flow. Our apparatus was nearly spherical, was filled with air, and generated axisymmetric turbulence. We set the ratio of axial to radial velocity fluctuation amplitudes to various values between 0.6 and 2.3. We then measured two-point velocity structure fun...
Kim, S.-W.; Chen, C.-P.
1988-01-01
The paper presents a multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method. Consideration is given to a class of turbulent boundary layer flows and of separated and/or swirling elliptic turbulent flows. For the separated and/or swirling turbulent flows, the present turbulence model yielded significantly improved computational results over those obtained with the standard k-epsilon turbulence model.
DEFF Research Database (Denmark)
Roald, Tone; Pedersen, Ida Egmose; Levin, Kasper
2017-01-01
In this article we establish intersubjective meaning-making in infancy as atmospheric. Through qualitative descriptions of five mother–infant dyads in a video-recorded, experimental setting when the infant is 4, 7, 10, and 13 months, we discovered atmospheric appearances with a developmental...... pattern of atmospheric variations. These appearances, we argue, are contextual and intersubjective monologues. The monologues are similar to what Daniel Stern describes with his concept of “vitality affects,” but they arise as a unified force that envelops the mother and child. As such, we present a new...
Flow, turbulence, and pollutant dispersion in urban atmospheresa)
Fernando, H. J. S.; Zajic, D.; Di Sabatino, S.; Dimitrova, R.; Hedquist, B.; Dallman, A.
2010-05-01
The past half century has seen an unprecedented growth of the world's urban population. While urban areas proffer the highest quality of life, they also inflict environmental degradation that pervades a multitude of space-time scales. In the atmospheric context, stressors of human (anthropogenic) origin are mainly imparted on the lower urban atmosphere and communicated to regional, global, and smaller scales via transport and turbulence processes. Conversely, changes in all scales are transmitted to urban regions through the atmosphere. The fluid dynamics of the urban atmospheric boundary layer and its prediction is the theme of this overview paper, where it is advocated that decision and policymaking in urban atmospheric management must be based on integrated models that incorporate cumulative effects of anthropogenic forcing, atmospheric dynamics, and social implications (e.g., health outcomes). An integrated modeling system juxtaposes a suite of submodels, each covering a particular range of scales while communicating with models of neighboring scales. Unresolved scales of these models need to be parametrized based on flow physics, for which developments in fluid dynamics play an indispensible role. Illustrations of how controlled laboratory, outdoor (field), and numerical experiments can be used to understand and parametrize urban atmospheric processes are presented, and the utility of predictive models is exemplified. Field experiments in real urban areas are central to urban atmospheric research, as validation of predictive models requires data that encapsulate four-dimensional complexities of nature.
Impacts of Ocean Waves on the Atmospheric Surface Layer: Simulations and Observations
National Research Council Canada - National Science Library
Sullivan, Peter P; McWilliams, James C; Melville, W. K
2008-01-01
.... Our long term scientific objective was to explore the nature of intermittence, coherent structures, and turbulent fluxes and their coupling in the surface layers of the marine atmospheric and oceanic...
Modeling of Long-Range Atmospheric Lasercom Links Between Static and Mobile Platforms
Energy Technology Data Exchange (ETDEWEB)
Scharlemann, E T; Breitfeller, E F; Henderson, J R; Kallman, J S; Morris, J R; Ruggiero, A J
2003-07-29
We describe modeling and simulation of long-range terrestrial laser communications links between static and mobile platforms. Atmospheric turbulence modeling, along with pointing, tracking and acquisition models are combined to provide an overall capability to estimate communications link performance.
Turbulent Region Near Jupiter's Great Red Spot
1997-01-01
True and false color mosaics of the turbulent region west of Jupiter's Great Red Spot. The Great Red Spot is on the planetary limb on the right hand side of each mosaic. The region west (left) of the Great Red Spot is characterized by large, turbulent structures that rapidly change in appearance. The turbulence results from the collision of a westward jet that is deflected northward by the Great Red Spot into a higher latitude eastward jet. The large eddies nearest to the Great Red Spot are bright, suggesting that convection and cloud formation are active there.The top mosaic combines the violet (410 nanometers) and near infrared continuum (756 nanometers) filter images to create a mosaic similar to how Jupiter would appear to human eyes. Differences in coloration are due to the composition and abundance of trace chemicals in Jupiter's atmosphere. The lower mosaic uses the Galileo imaging camera's three near-infrared (invisible) wavelengths (756 nanometers, 727 nanometers, and 889 nanometers displayed in red, green, and blue) to show variations in cloud height and thickness. Light blue clouds are high and thin, reddish clouds are deep, and white clouds are high and thick. Purple most likely represents a high haze overlying a clear deep atmosphere. Galileo is the first spacecraft to distinguish cloud layers on Jupiter.The mosaic is centered at 16.5 degrees south planetocentric latitude and 85 degrees west longitude. The north-south dimension of the Great Red Spot is approximately 11,000 kilometers. The smallest resolved features are tens of kilometers in size. North is at the top of the picture. The images used were taken on June 26, 1997 at a range of 1.2 million kilometers (1.05 million miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech
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.
Reinterpreting aircraft measurements in anisotropic scaling turbulence
Directory of Open Access Journals (Sweden)
S. J. Hovde
2009-07-01
Full Text Available Due to both systematic and turbulent induced vertical fluctuations, the interpretation of atmospheric aircraft measurements requires a theory of turbulence. Until now virtually all the relevant theories have been isotropic or "quasi isotropic" in the sense that their exponents are the same in all directions. However almost all the available data on the vertical structure shows that it is scaling but with exponents different from the horizontal: the turbulence is scaling but anisotropic. In this paper, we show how such turbulence can lead to spurious breaks in the scaling and to the spurious appearance of the vertical scaling exponent at large horizontal lags.
We demonstrate this using 16 legs of Gulfstream 4 aircraft near the top of the troposphere following isobars each between 500 and 3200 km in length. First we show that over wide ranges of scale, the horizontal spectra of the aircraft altitude are nearly k^{-5/3}. In addition, we show that the altitude and pressure fluctuations along these fractal trajectories have a high degree of coherence with the measured wind (especially with its longitudinal component. There is also a strong phase relation between the altitude, pressure and wind fluctuations; for scales less than ≈40 km (on average the wind fluctuations lead the pressure and altitude, whereas for larger scales, the pressure fluctuations leads the wind. At the same transition scale, there is a break in the wind spectrum which we argue is caused by the aircraft starting to accurately follow isobars at the larger scales. In comparison, the temperature and humidity have low coherencies and phases and there are no apparent scale breaks, reinforcing the hypothesis that it is the aircraft trajectory that is causally linked to the scale breaks in the wind measurements.
Using spectra and structure functions for the wind, we then estimate their exponents (β, H at small (5/3, 1/3 and large scales (2
Random forcing of geostrophic motion in rotating stratified turbulence
Waite, Michael L.
2017-12-01
Random forcing of geostrophic motion is a common approach in idealized simulations of rotating stratified turbulence. Such forcing represents the injection of energy into large-scale balanced motion, and the resulting breakdown of quasi-geostrophic turbulence into inertia-gravity waves and stratified turbulence can shed light on the turbulent cascade processes of the atmospheric mesoscale. White noise forcing is commonly employed, which excites all frequencies equally, including frequencies much higher than the natural frequencies of large-scale vortices. In this paper, the effects of these high frequencies in the forcing are investigated. Geostrophic motion is randomly forced with red noise over a range of decorrelation time scales τ, from a few time steps to twice the large-scale vortex time scale. It is found that short τ (i.e., nearly white noise) results in about 46% more gravity wave energy than longer τ, despite the fact that waves are not directly forced. We argue that this effect is due to wave-vortex interactions, through which the high frequencies in the forcing are able to excite waves at their natural frequencies. It is concluded that white noise forcing should be avoided, even if it is only applied to the geostrophic motion, when a careful investigation of spontaneous wave generation is needed.
Fluctuations of a passive scalar in a turbulent mixing layer
Attili, Antonio
2013-09-19
The turbulent flow originating downstream of the Kelvin-Helmholtz instability in a mixing layer has great relevance in many applications, ranging from atmospheric physics to combustion in technical devices. The mixing of a substance by the turbulent velocity field is usually involved. In this paper, a detailed statistical analysis of fluctuations of a passive scalar in the fully developed region of a turbulent mixing layer from a direct numerical simulation is presented. Passive scalar spectra show inertial ranges characterized by scaling exponents −4/3 and −3/2 in the streamwise and spanwise directions, in agreement with a recent theoretical analysis of passive scalar scaling in shear flows [Celani et al., J. Fluid Mech. 523, 99 (2005)]. Scaling exponents of high-order structure functions in the streamwise direction show saturation of intermittency with an asymptotic exponent ζ∞=0.4 at large orders. Saturation of intermittency is confirmed by the self-similarity of the tails of the probability density functions of the scalar increments at different scales r with the scaling factor r−ζ∞ and by the analysis of the cumulative probability of large fluctuations. Conversely, intermittency saturation is not observed for the spanwise increments and the relative scaling exponents agree with recent results for homogeneous isotropic turbulence with mean scalar gradient. Probability density functions of the scalar increments in the three directions are compared to assess anisotropy.
Improved observations of turbulence dissipation rates from wind profiling radars
Directory of Open Access Journals (Sweden)
K. McCaffrey
2017-07-01
Full Text Available Observations of turbulence dissipation rates in the planetary boundary layer are crucial for validation of parameterizations in numerical weather prediction models. However, because dissipation rates are difficult to obtain, they are infrequently measured through the depth of the boundary layer. For this reason, demonstrating the ability of commonly used wind profiling radars (WPRs to estimate this quantity would be greatly beneficial. During the XPIA field campaign at the Boulder Atmospheric Observatory, two WPRs operated in an optimized configuration, using high spectral resolution for increased accuracy of Doppler spectral width, specifically chosen to estimate turbulence from a vertically pointing beam. Multiple post-processing techniques, including different numbers of spectral averages and peak processing algorithms for calculating spectral moments, were evaluated to determine the most accurate procedures for estimating turbulence dissipation rates using the information contained in the Doppler spectral width, using sonic anemometers mounted on a 300 m tower for validation. The optimal settings were determined, producing a low bias, which was later corrected. Resulting estimations of turbulence dissipation rates correlated well (R2 = 0. 54 and 0. 41 with the sonic anemometers, and profiles up to 2 km from the 449 MHz WPR and 1 km from the 915 MHz WPR were observed.
Wave-turbulence interaction-induced vertical mixing and its effects in ocean and climate models.
Qiao, Fangli; Yuan, Yeli; Deng, Jia; Dai, Dejun; Song, Zhenya
2016-04-13
Heated from above, the oceans are stably stratified. Therefore, the performance of general ocean circulation models and climate studies through coupled atmosphere-ocean models depends critically on vertical mixing of energy and momentum in the water column. Many of the traditional general circulation models are based on total kinetic energy (TKE), in which the roles of waves are averaged out. Although theoretical calculations suggest that waves could greatly enhance coexisting turbulence, no field measurements on turbulence have ever validated this mechanism directly. To address this problem, a specially designed field experiment has been conducted. The experimental results indicate that the wave-turbulence interaction-induced enhancement of the background turbulence is indeed the predominant mechanism for turbulence generation and enhancement. Based on this understanding, we propose a new parametrization for vertical mixing as an additive part to the traditional TKE approach. This new result reconfirmed the past theoretical model that had been tested and validated in numerical model experiments and field observations. It firmly establishes the critical role of wave-turbulence interaction effects in both general ocean circulation models and atmosphere-ocean coupled models, which could greatly improve the understanding of the sea surface temperature and water column properties distributions, and hence model-based climate forecasting capability. © 2016 The Authors.
Linear stability analysis of swirling turbulent flows with turbulence models
Gupta, Vikrant; Juniper, Matthew
2013-11-01
In this paper, we consider the growth of large scale coherent structures in turbulent flows by performing linear stability analysis around a mean flow. Turbulent flows are characterized by fine-scale stochastic perturbations. The momentum transfer caused by these perturbations affects the development of larger structures. Therefore, in a linear stability analysis, it is important to include the perturbations' influence. One way to do this is to include a turbulence model in the stability analysis. This is done in the literature by using eddy viscosity models (EVMs), which are first order turbulence models. We extend this approach by using second order turbulence models, in this case explicit algebraic Reynolds stress models (EARSMs). EARSMs are more versatile than EVMs, in that they can be applied to a wider range of flows, and could also be more accurate. We verify our EARSM-based analysis by applying it to a channel flow and then comparing the results with those from an EVM-based analysis. We then apply the EARSM-based stability analysis to swirling pipe flows and Taylor-Couette flows, which demonstrates the main benefit of EARSM-based analysis. This project is supported by EPSRC and Rolls-Royce through a Dorothy Hodgkin Research Fellowship.
Schlögl, Sebastian; Mott, Rebecca; Lehning, Michael
2017-04-01
The surface energy balance of a snow cover significantly changes once the snow cover gets patchy. The substantial progress in knowledge about the surface energy balance of patchy snow covers is a mandatory requirement to reduce biases in flux parameterizations in larger scale meteorological or climatological models. The aim of this project was to numerically improve energy balance calculations late in the melting season when the spatial variability of turbulent fluxes is especially high owing to the complex feedback between bare/snow-covered areas and the atmosphere above. In order to account for the feedback between the atmosphere and the patchy snow-cover we calculated three-dimensional air temperature and wind velocity fields with the non-hydrostatic atmospheric model ARPS for an idealized flat test site initialized with different snow distributions and atmospheric conditions. The physics-based surface process model Alpine3D has been forced with these atmospheric fields close to the snow surface in order to resolve the small-scale spatial variability. We further initialized the model with atmospheric fields above the blending height as a reference case. The numerical analysis shows that for simulations initialized with fully-resolved atmospheric fields below the blending height, turbulent sensible heat fluxes are up to 50 W/m2 larger than for calculations forced without resolved atmospheric fields. This difference in turbulent sensible heat fluxes over snow increase with increasing number of snow patches and decreasing snow-cover fraction. This is mainly attributed to an increase in the mean near-surface air temperature over snow due to horizontal and vertical exchange processes induced by the heterogeneous land-surface. We used flux footprint estimations to analyse turbulence data measured during three ablation periods in the Dischma valley (Switzerland). This fundamental theory was deployed for eddy-covariance measurements revealing the origin of the measured
Directory of Open Access Journals (Sweden)
Lukas Pauscher
2018-01-01
Full Text Available This study investigates turbulence characteristics as observed at a 200 m tall mast at a hilly and complex site. It thereby concentrates on turbulence statistics, which are important for the site suitability analysis of a wind turbine. The directional variations in terrain are clearly reflected in the observed turbulence intensities and drag. Integral turbulence statistics showed some variations from their typical flat terrain values. Footprint modelling was used to model the area of effect and to relate the observed turbulence characteristics to the ruggedness and roughness within the estimated fetch area. Among the investigated turbulence quantities, the normalised standard deviation of the wind velocity along the streamlines showed the highest correlation with the effective roughness and ruggedness within the footprint followed by the normalised friction velocity and normalised standard deviation of the vertical wind speed. A differentiation between the effects of roughness and ruggedness was not possible, as forest cover and complex orography are highly correlated at the investigated site. An analysis of turbulence intensity by wind speed indicated a strong influence of atmospheric stability. Stable conditions lead to an overall reduction in turbulence intensity for a wind speed range between approx. 6–12 m s−1 when compared to neutral stratification. The variance of the horizontal wind speed strongly varied over the height range which is typical for a modern wind turbine and was in the order of the differences between different standard turbulence classes for wind turbines.
A new low-turbulence wind tunnel for animal and small vehicle flight experiments
Quinn, Daniel B.; Watts, Anthony; Nagle, Tony; Lentink, David
2017-03-01
Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s-1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s-1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.
A new low-turbulence wind tunnel for animal and small vehicle flight experiments.
Quinn, Daniel B; Watts, Anthony; Nagle, Tony; Lentink, David
2017-03-01
Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s-1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s-1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.
Highway measurements of vehicle-induced turbulence (VIT) and enhanced mixing in the surface layer
Miller, S. J.; Gordon, M.; Staebler, R. M.; Li-Chee-Ming, J.; Taylor, P.
2016-12-01
Motor vehicles generate vehicle-induced turbulence (VIT) while in motion, which affects the mixing and transport of emitted trace gases, heat and momentum. During July, 2016 a 40Hz sonic anemometer (ATI) and a co-located 20Hz open path CO2/H2O gas analyzer (LICOR) were assembled and driven on highways in the Greater Toronto Area. An ultra-high sensitivity aerosol spectrometer was employed to measure the total number concentration of particles between 60 and 1000nm at the position of the gas analyzer and sonic anemometer. A video camera with GPS capabilities was also utilized to assess the surrounding features while chasing a specific vehicle type. The following distance of each chased vehicle is calculated as a function of pixel location, with the back edge of each followed vehicle being identified as the initial contrast between the vehicle's shadow and the roadway. Combining the sonic anemometer data with the GPS data allows turbulence statistics to be developed and correlations with vehicle type and following distance to be examined. Vehicle-induced turbulence is assessed using turbulent kinetic energy (TKE), a measure of turbulent mixing, which maximizes near the followed vehicle and decreases with increasing following distance. Vehicle exhaust plumes are identified using the measured CO2 concentration. The CO2 concentration data in conjunction with TKE and turbulent fluxes are used to explore the potential impacts of vehicle-induced turbulence on atmospheric mixing within the surface layer.
Multi-instrument characterization of optical turbulence at the Ali observatory
Liu, L.-Y.; Yao, Y.-Q.; Vernin, J.; Wang, H.-S.; Yin, J.; Qian, X.
2015-04-01
In order to characterize the atmospheric optical turbulence at Ali observatory, we have deployed multi-instruments, which are able to continuously monitor the optical turbulence for site evaluation. These instruments include the DIMM, MASS, Single Star SCIDAR and Polaris seeing monitor, and we also plan to install SNODAR and Micro-thermal sensors for the turbulence on surface layer by the end of this year. This configuration allows us to collect a substantial database and make cross-comparison of the results. We have successfully obtained the profiles of optical turbulence and wind speed with Single Star SCIDAR, as well as the key parameters for adaptive optics application, such as seeing, coherence time, and isoplanatic angle. The DIMM seeing measurements are also carried out simultaneously. The median seeing measured by the DIMM and SSS in 2013 is 0.69 and 0.79 arcsec, respectively.
Directory of Open Access Journals (Sweden)
Ummul K.R.
2017-01-01
Full Text Available This paper focus on mitigating the atmospheric turbulence effect in free space optical communication using a dual diffuser modulation (DDM technique. The most deteriorate the FSOC is scintillation where it affected the wave front cause to fluctuating signal and ultimately receiver can turn into saturate or loss signal. DD approach enhances the detecting bit ‘1’ and bit ‘0’ and improves the power received to combat with turbulence effect. The performance focus on Signal-to-Noise (SNR and Bit Error Rate (BER by using the Kolmogorov’s scintillation theory. The numerical result shows that the DD approach improves the range where estimated approximately 40% improvement under weak turbulence and 80% under strong turbulence.
Decoupling of mass flux and turbulent wind fluctuations in drifting snow
Paterna, E.; Crivelli, P.; Lehning, M.
2016-05-01
The wind-driven redistribution of snow has a significant impact on the climate and mass balance of polar and mountainous regions. Locally, it shapes the snow surface, producing dunes and sastrugi. Sediment transport has been mainly represented as a function of the wind strength, and the two processes assumed to be stationary and in equilibrium. The wind flow in the atmospheric boundary layer is unsteady and turbulent, and drifting snow may never reach equilibrium. Our question is therefore: what role do turbulent eddies play in initiating and maintaining drifting snow? To investigate the interaction between drifting snow and turbulence experimentally, we conducted several wind tunnel measurements of drifting snow over naturally deposited snow covers. We observed a coupling between snow transport and turbulent flow only in a weak saltation regime. In stronger regimes it self-organizes developing its own length scales and efficiently decoupling from the wind forcing.
Signatures of dynamical processes in Raman lidar profiles of the atmosphere
Philbrick, C. Russell; Hallen, Hans D.
2017-05-01
Raman lidar measurements provide profiles of several different tracers of spatial and temporal variations, which are excellent signatures for studies of dynamical processes in the atmosphere. An examination of Raman lidar data collected during the last four decades clearly show signatures of atmospheric planetary waves, gravity waves, low-level jets, weather fronts, turbulence from wind shear at surfaces and at the interface of the boundary layer with the free troposphere. Water vapor profiles are found to be important as a tracer of the sources of turbulence eddies associated with thermal convection, pressure waves, and wind shears, which result from surface heating, winds, weather systems, orographic forcing, and regions of reduced atmospheric stability. Examples of these processes are selected to show the influence of turbulence on profiles of atmospheric properties. Turbulence eddies generated in the wind shear region near the top of the boundary layer are found to mix into the atmospheric boundary layer. Results from several prior research projects are examined to gain a better understanding of processes impacting optical propagation through the many sources of turbulence observed in the lower atmosphere. Advances in lasers, detectors, and particularly in high-speed electronics now available are expected to provide important opportunities to improve our understanding of the formation processes, as well as for tracking of the sources and dissipation of turbulence eddies.
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.
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.
Turbulent character of wind energy.
Milan, Patrick; Wächter, Matthias; Peinke, Joachim
2013-03-29
Wind turbines generate electricity from turbulent wind. Large fluctuations, and, more importantly, frequent wind gusts cause a highly fluctuating electrical power feed into the grid. Such effects are the hallmark of high-frequency turbulence. Here we show evidence that it is the complex structure of turbulence that dominates the power output for one single wind turbine as well as for an entire wind farm. We illustrate the highly intermittent, peaked nature of wind power fed into the grid. Multifractal scaling is observed, as described initially by Kolmogorov's 1962 theory of turbulence. In parallel, we propose a stochastic model that converts wind speed signals into power output signals with appropriate multifractal statistics. As more and more wind turbines become integrated into our electric grids, a proper understanding of this intermittent power source must be worked out to ensure grid stability in future networks. Thus, our results stress the need for a profound understanding of the physics of turbulence and its impact on wind energy.
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)].
Magnetic Reconnection and Intermittent Turbulence
Osman, K.; Matthaeus, W. H.; Kiyani, K. H.; Gosling, J. T.; Chapman, S. C.; Hnat, B.; Greco, A.; Servidio, S.; Phan, T. D.; Khotyaintsev, Y. V.
2014-12-01
The relationship between magnetic reconnection and plasma turbulence is investigated using in-situ measurements both in the solar wind and within a high-speed reconnection jet in the terrestrial magnetotail. In the solar wind, reconnection events and current sheets are found for the first time to be concentrated in intervals of intermittent turbulence: within the most non-Gaussian 1% of magnetic field fluctuations, 87-92% of reconnection exhausts and about 9% of current sheets are found. Also, the likelihood that an identified current sheet will also correspond to a reconnection exhaust increases dramatically as the least intermittent fluctuations are removed. Hence, the turbulent solar wind contains a hierarchy of intermittent magnetic field structures that are increasingly linked to current sheets, which in turn are progressively more likely to correspond to sites of magnetic reconnection. In a magnetotail reconnection jet, the work done by electromagnetic fields on the particles, J·E, is found for the first time to have a non-Gaussian heavy tailed probability density function. Furthermore, J·E is non-uniform and concentrated in regions of high electric current density. This suggests magnetic energy is converted to kinetic energy within the reconnection jet in a manner that is intermittent, and could be analogous to fluid-like turbulent phenomenology where dissipation proceeds via coherent structures generated by an intermittent cascade. These results could have far reaching implications for space and astrophysical plasmas where turbulence and magnetic reconnection are ubiquitous.
Energy Technology Data Exchange (ETDEWEB)
Kajita, Takaaki [Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa, Chiba 277-8582 (Japan)
2004-12-01
Neutrino oscillation was discovered through the study of atmospheric neutrinos. Atmospheric neutrinos are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the atmosphere. Electron neutrinos and muon neutrinos are produced mainly by the decay chain of charged pions to muons and electrons. Depending on the energy of the neutrinos, atmospheric neutrinos are observed as fully contained events, partially contained events and upward-going muon events. The energy range covered by these events is from a few hundred MeV to >1 TeV. Data from various experiments showed zenith angle- and energy-dependent deficit of {nu}{sub {mu}} events, while {nu}{sub e} events did not show any such effect. It was also shown that the {nu}{sub {mu}} survival probability obeys the sinusoidal function as predicted by neutrino oscillations. Two-flavour {nu}{sub {mu}} {r_reversible} {nu}{sub {tau}} oscillations, with sin{sup 2} 2{theta} > 0.90 and {delta}m{sup 2} in the region of 1.9 x 10{sup -3} to 3.0 x 10{sup -3} eV{sup 2}, explain all these data. Various detailed studies using high statistics atmospheric neutrino data excluded the alternative hypotheses that were proposed to explain the {nu}{sub {mu}} deficit.
Significant Atmospheric Boundary Layer Change Observed above an Agulhas Current Warm Cored Eddy
Directory of Open Access Journals (Sweden)
C. Messager
2016-01-01
Full Text Available The air-sea impact of a warm cored eddy ejected from the Agulhas Retroflection region south of Africa was assessed through both ocean and atmospheric profiling measurements during the austral summer. The presence of the eddy causes dramatic atmospheric boundary layer deepening, exceeding what was measured previously over such a feature in the region. This deepening seems mainly due to the turbulent heat flux anomaly above the warm eddy inducing extensive deep and persistent changes in the atmospheric boundary layer thermodynamics. The loss of heat by turbulent processes suggests that this kind of oceanic feature is an important and persistent source of heat for the atmosphere.
On the turbulent energy cascade in anisotropic magnetohydrodynamic turbulence
Carbone, V; Marino, R
2010-01-01
The problem of the occurrence of an energy cascade for Alfv\\'enic turbulence in solar wind plasmas was hystorically addressed by using phenomenological arguments based to the weakness of nonlinear interactions and the anisotropy of the cascade in wave vectors space. Here, this paradox is reviewed through the formal derivation of a Yaglom relation from anisotropic Magnetohydrodynamic equation. The Yaglom relation involves a third-order moment calculated from velocity and magnetic fields and involving both Els\\"asser vector fields, and is particularly useful to be used as far as spacecraft observations of turbulence are concerned.
Helicity in the atmospheric boundary layer
Kurgansky, Michael; Koprov, Boris; Koprov, Victor; Chkhetiani, Otto
2017-04-01
An overview is presented of recent direct field measurements at the Tsimlyansk Scientific Station of A.M. Obukhov Institute of Atmospheric Physics in Moscow of turbulent helicity (and potential vorticity) using four acoustic anemometers positioned, within the atmospheric surface-adjacent boundary layer, in the vertices of a rectangular tetrahedron, with an approximate 5 m distance between the anemometers and a 5.5 m elevation of the tetrahedron base above the ground surface (Koprov, Koprov, Kurgansky and Chkhetiani. Izvestiya, Atmospheric and Oceanic Physics, 2015, Vol.51, 565-575). The same ideology was applied in a later field experiment in Tsimlyansk with the tetrahedron's size of 0.7 m and variable elevation over the ground from 3.5 to 25 m. It is illustrated with examples of the statistical distribution of instantaneous (both positive and negative) turbulent helicity values. A theory is proposed that explains the measured mean turbulent helicity sign, including the sign of contribution to helicity from the horizontal and vertical velocity & vorticity components, respectively, and the sign of helicity buoyant production term. By considering a superposition of the classic Ekman spiral solution and a jet-like wind profile that mimics a shallow breeze circulation over a non-uniformly heated Earth surface, a possible explanation is provided, why the measured mean turbulent helicity sign is negative. The pronounced breeze circulation over the Tsimlyansk polygon which is located nearby the Tsimlyansk Reservoir was, indeed, observed during the measurements period. Whereas, essentially positive helicity is injected into the boundary layer from the free atmosphere in the Northern Hemisphere.
Iribarne, J V
1973-01-01
The thermodynamics of the atmosphere is the subject of several chapters in most textbooks on dynamic meteorology, but there is no work in English to give the subject a specific and more extensive treatment. In writing the present textbook, we have tried to fill this rather remarkable gap in the literature related to atmospheric sciences. Our aim has been to provide students of meteorology with a book that can playa role similar to the textbooks on chemical thermodynamics for the chemists. This implies a previous knowledge of general thermodynamics, such as students acquire in general physics courses; therefore, although the basic principles are reviewed (in the first four chapters), they are only briefly discussed, and emphasis is laid on those topics that will be useful in later chapters, through their application to atmospheric problems. No attempt has been made to introduce the thermodynamics of irreversible processes; on the other hand, consideration of heterogeneous and open homogeneous systems permits a...
Approximate Augmentation of Turbulent Law-of-the-Wall by Periodic Free-Stream Disturbances
Energy Technology Data Exchange (ETDEWEB)
Dechant, Lawrence J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-12-01
We examine the role of periodic sinusoidal free-stream disturbances on the inner law law-of-the-wall (log-law) for turbulent boundary layers. This model serves a surrogate for the interaction of flight vehicles with atmospheric disturbances. The approximate skin friction expression that is derived suggests that free-stream disturbances can cause enhancement of the mean skin friction. Considering the influence of grid generated free stream turbulence in the laminar sublayer/log law region (small scale/high frequency) the model recovers the well-known shear layer enhancement suggesting an overall validity for the approach. The effect on the wall shear associated with the lower frequency due to the passage of the vehicle through large (vehicle scale) atmospheric disturbances is likely small i.e. on the order 1% increase for turbulence intensities on the order of 2%. The increase in wall pressure fluctuation which is directly proportional to the wall shear stress is correspondingly small.
Two highly singular intermittent structures: Rain and turbulence
Waymire, Edward C.
2006-06-01
Rainfall charges soil moisture and river basins among its many roles with respect to the hydrologic cycle. Research aimed at improved understanding and modeling of surface water processes includes attention to rainfall at a variety of space-time scales. Given the atmospheric environment in which rain events are observed, some similarities between certain rainfall data structures and fluid turbulence can be expected. So the space-time intermittency and large fluctuations observed in both rain rates and energy dissipation rates have provided an interest among hydrologists in developing physical theories, experiments, and mathematical models. In response to a request for insights into multiplicative cascade models, the main goal of this article is to single out a special mathematical transformation, namely, "size biasing" (or "tilting"), which has proven to be very powerful in the mathematical analysis of multiplicative cascades and which has also been successfully exploited within the context of turbulence from a physical perspective.
Turbulence and entrainment length scales in large wind farms.
Andersen, Søren J; Sørensen, Jens N; Mikkelsen, Robert F
2017-04-13
A number of large wind farms are modelled using large eddy simulations to elucidate the entrainment process. A reference simulation without turbines and three farm simulations with different degrees of imposed atmospheric turbulence are presented. The entrainment process is assessed using proper orthogonal decomposition, which is employed to detect the largest and most energetic coherent turbulent structures. The dominant length scales responsible for the entrainment process are shown to grow further into the wind farm, but to be limited in extent by the streamwise turbine spacing, which could be taken into account when developing farm layouts. The self-organized motion or large coherent structures also yield high correlations between the power productions of consecutive turbines, which can be exploited through dynamic farm control.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).
Wind shear and turbulence on Titan: Huygens analysis
Lorenz, Ralph D.
2017-10-01
Wind shear measured by Doppler tracking of the Huygens probe is evaluated, and found to be within the range anticipated by pre-flight assessments (namely less than two times the Brunt-Väisälä frequency). The strongest large-scale shear encountered was ∼5 m/s/km, a level associated with 'Light' turbulence in terrestrial aviation. Near-surface winds (below 4 km) have small-scale fluctuations of ∼0.1 m/s on 1 s timescales, indicated both by probe tilt and Doppler tracking, and the characteristics of the fluctuation, of interest for future missions to Titan, can be reproduced with a simple autoregressive (AR(1)) model. The turbulent dissipation rate at an altitude of ∼500 m is found to be ∼0.2 cm2/s3, which may be a useful benchmark for atmospheric circulation models.
Turbulence and entrainment length scales in large wind farms
Andersen, Søren J.; Sørensen, Jens N.; Mikkelsen, Robert F.
2017-03-01
A number of large wind farms are modelled using large eddy simulations to elucidate the entrainment process. A reference simulation without turbines and three farm simulations with different degrees of imposed atmospheric turbulence are presented. The entrainment process is assessed using proper orthogonal decomposition, which is employed to detect the largest and most energetic coherent turbulent structures. The dominant length scales responsible for the entrainment process are shown to grow further into the wind farm, but to be limited in extent by the streamwise turbine spacing, which could be taken into account when developing farm layouts. The self-organized motion or large coherent structures also yield high correlations between the power productions of consecutive turbines, which can be exploited through dynamic farm control. This article is part of the themed issue 'Wind energy in complex terrains'.
Direct numerical simulation of coalescing droplets in turbulence
Li Sing How, Melanie; Collins, Lance
2017-11-01
There is a rich body of numerical, experimental and theoretical work looking at the role of turbulence in particle collisions, with a particular emphasis on how it might accelerate the evolution of clouds in the atmosphere. This study is a continuation of that lineage. We perform direct numerical simulations of isotropic turbulence with embedded droplets that, upon collision, coalesce to produce a daughter droplet that conserves the mass and momentum of the parent droplets. As a consequence of coalescence, the droplet size distribution evolves over time from its monodisperse initial condition. The work is an extension of Reade and Collins (J. Fluid Mech. 415:45-64, 2000), which considered the same problem at a much lower Reynolds number. We observe important effects of intermittency at Reynolds numbers that are several-fold higher. The collisions do not yet take into account the effect of the lubricating gas layer, which will be the topic of future work. NSF Award CBET-1605195.
Nocturnal low-level jets: sporadic turbulence on complex terrain
Jimenez, M. A.; Cuxart, J.
2009-04-01
Under weak pressure gradient conditions and clear-sky nights the development of locally generated circulations is favourished, specially in complex terrain. As night advances, the layer close to the ground cools down and stably stratified conditions prevail, with weak and usually sporadic or intermittent turbulence. In this work this phenomena is studied through high-resolution mesoscale simulations that are verified with data from weather stations and satellite information. The chosen domain is the island of Majorca, located in the western Mediterranean sea. A large variety of circulations is observed in the three main basins of the island, with drainage flows and organization at the basin scale. These low-level jet structures occasionaly cause turbulent bursts and very efficient mixing in the vertical, leading to significant changes of the atmospheric conditions close to the ground.
IUTAM Symposium on Hamiltonian Dynamics, Vortex Structures, Turbulence
Borisov, Alexey V; Mamaev, Ivan S; Sokolovskiy, Mikhail A; IUTAM BOOKSERIES : Volume 6
2008-01-01
This work brings together previously unpublished notes contributed by participants of the IUTAM Symposium on Hamiltonian Dynamics, Vortex Structures, Turbulence (Moscow, 25-30 August 2006). The study of vortex motion is of great interest to fluid and gas dynamics: since all real flows are vortical in nature, applications of the vortex theory are extremely diverse, many of them (e.g. aircraft dynamics, atmospheric and ocean phenomena) being especially important. The last few decades have shown that serious possibilities for progress in the research of real turbulent vortex motions are essentially related to the combined use of mathematical methods, computer simulation and laboratory experiments. These approaches have led to a series of interesting results which allow us to study these processes from new perspectives. Based on this principle, the papers collected in this proceedings volume present new results on theoretical and applied aspects of the processes of formation and evolution of various flows, wave a...
Direct simulation of the stably stratified turbulent Ekman layer
Coleman, G. N.; Ferziger, J. H.; Spalart, P. R.
1992-01-01
The Navier-Stokes equations and the Boussinesq approximation were used to compute a 3D time-dependent turbulent flow in the stably stratified Ekman layer over a smooth surface. The simulation data are found to be in very good agreement with atmospheric measurements when nondimensionalized according to Nieuwstadt's local scaling scheme. Results suggest that, when Reynolds number effects are taken into account, the 'constant Froud number' stable layer model (Brost and Wyngaard, 1978) and the 'shearing length' stable layer model (Hunt, 1985) for the dissipitation rate of turbulent kinetic energy are both valid. It is concluded that there is good agreement between the direct numerical simulation results and large-eddy simulation results obtained by Mason and Derbyshire (1990).
Assessment of Global Annual Atmospheric Energy Balance from Satellite Observations
Lin, Bing; Stackhouse, Paul; Minnis, Patrick; Wielicki, Bruce A.; Hu, Yongxiang; Sun, Wenbo; Fan, Tai-Fang (Alice); Hinkelman, Laura
2008-01-01
Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface and latent and sensible heat over oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Global annual means of the TOA net radiation obtained from both direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 Watts per square meter, respectively. The estimated atmospheric and surface heat imbalances are about -8 9 Watts per square meter, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements significantly reduces the bias errors in the observed global energy budgets of the climate system.
Thornton, Douglas E.; Spencer, Mark F.; Perram, Glen P.
2017-09-01
The effects of deep turbulence in long-range imaging applications presents unique challenges to properly measure and correct for aberrations incurred along the atmospheric path. In practice, digital holography can detect the path-integrated wavefront distortions caused by deep turbulence, and di erent recording geometries offer different benefits depending on the application of interest. Previous studies have evaluated the performance of the off-axis image and pupil plane recording geometries for deep-turbulence sensing. This study models digital holography in the on-axis phase shifting recording geometry using wave optics simulations. In particular, the analysis models spherical-wave propagation through varying deep-turbulence conditions to estimate the complex optical field, and performance is evaluated by calculating the field-estimated Strehl ratio and RMS wavefront error. Altogether, the results show that digital holography in the on-axis phase shifting recording geometry is an effective wavefront-sensing method in the presence of deep turbulence.
Anisotropic Intermittency of Magnetohydrodynamic Turbulence
Osman, K T; Chapman, S C; Hnat, B
2013-01-01
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 Els\\"asser field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multi-exponent 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.
Electron magnetohydrodynamic turbulence: universal features
Shivamoggi, Bhimsen K.
2015-02-01
The energy cascade of electron magnetohydrodynamic (EMHD) turbulence is considered. Fractal and multi-fractal models for the energy dissipation field are used to determine the spatial intermittency corrections to the scaling behavior in the high-wavenumber (electron hydrodynamic limit) and low-wavenumber (magnetization limit) asymptotic regimes of the inertial range. Extrapolation of the multi-fractal scaling down to the dissipative microscales confirms in these asymptotic regimes a dissipative anomaly previously indicated by the numerical simulations of EMHD turbulence. Several basic features of the EMHD turbulent system are found to be universal which seem to transcend the existence of the characteristic length scale d e (which is the electron skin depth) in the EMHD problem: equipartition spectrum; Reynolds-number scaling of the dissipative microscales; scaling of the probability distribution function (PDF) of the electron-flow velocity (or magnetic field) gradient (even with intermittency corrections); dissipative anomaly; and critical exponent scaling.
Turbulent mix experiments and simulations
Energy Technology Data Exchange (ETDEWEB)
Dimonte, G.; Schneider, M.; Frerking, C.E.
1995-08-01
Hydrodynamic instabilities produce material mixing that can significantly degrade weapons performance. We investigate the Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) instabilities in the turbulent regime in two experimental venues. RM experiments are conducted on the Nova laser with strong radiatively driven shocks (Mach > 20) in planar, two fluid targets. Interfacial perturbations are imposed with single sinusoidal modes to test linear theory and with three dimensional (3D) random modes to produce turbulent mix. RT experiments are conducted on a new facility, the Linear Electric Motor (LEM), in which macroscopic fluids are accelerated with arbitrary temporal profiles. This allows detailed diagnosis of the turbulence over a wide range of conditions. The Nova experiments study the high compression regime whereas the LEM experiments are incompressible. The results are compared to hydrodynamic simulations with the arbitrary Lagrangian-Eulerian code (CALE). The goal is to develop and test engineering models of mix.
ANISOTROPIC INTERMITTENCY OF MAGNETOHYDRODYNAMIC TURBULENCE
Energy Technology Data Exchange (ETDEWEB)
Osman, K. T.; Kiyani, K. H.; Chapman, S. C.; Hnat, B., E-mail: k.t.osman@warwick.ac.uk [Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry CV4 7AL (United Kingdom)
2014-03-10
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.