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Sample records for arbitrary turbulence spectrum

  1. Lyapunov spectrum in turbulent combustion

    NASA Astrophysics Data System (ADS)

    Hassanaly, Malik; Raman, Venkat

    2016-11-01

    Transient flame evolution is an important flow problem for many practical applications (for example high-altitude relight, ignition in internal combustion engines, unstart in scramjets). Current approaches to combustion modeling utilize assumptions that are valid mainly for statistically stationary processes. In order to understand the transient problem, a dynamic systems approach is followed here. The propagation of a flame in a turbulent channel flow is used as a canonical turbulent combustion system and is analyzed with the Lyapunov theory. In particular, the Lyapunov spectrum for this flow is computed using multiple coordinated simulations. For a range of flow conditions, dimensionality of the state-space is determined. It is shown that the internal structure of the flame plays a critical role in determining the response of the system to perturbations in the flow.

  2. Sparse spectrum model for a turbulent phase.

    PubMed

    Charnotskii, Mikhail

    2013-03-01

    Monte Carlo (MC) simulation of phase front perturbations by atmospheric turbulence finds numerous applications for design and modeling of the adaptive optics systems, laser beam propagation simulations, and evaluating the performance of the various optical systems operating in the open air environment. Accurate generation of two-dimensional random fields of turbulent phase is complicated by the enormous diversity of scales that can reach five orders of magnitude in each coordinate. In addition there is a need for generation of the long "ribbons" of turbulent phase that are used to represent the time evolution of the wave front. This makes it unfeasible to use the standard discrete Fourier transform-based technique as a basis for the MC simulation algorithm. We propose a new model for turbulent phase: the sparse spectrum (SS) random field. The principal assumption of the SS model is that each realization of the random field has a discrete random spectral support. Statistics of the random amplitudes and wave vectors of the SS model are arranged to provide the required spectral and correlation properties of the random field. The SS-based MC model offers substantial reduction of computer costs for simulation of the wide-band random fields and processes, and is capable of generating long aperiodic phase "ribbons." We report the results of model trials that determine the number of sparse components, and the range of wavenumbers that is necessary to accurately reproduce the random field with a power-law spectrum.

  3. Energy spectrum of buoyancy-driven turbulence.

    PubMed

    Kumar, Abhishek; Chatterjee, Anando G; Verma, Mahendra K

    2014-08-01

    Using high-resolution direct numerical simulation and arguments based on the kinetic energy flux Π(u), we demonstrate that, for stably stratified flows, the kinetic energy spectrum E(u)(k)∼k(-11/5), the potential energy spectrum E(θ)(k)∼k(-7/5), and Π(u)(k)∼k(-4/5) are consistent with the Bolgiano-Obukhov scaling. This scaling arises due to the conversion of kinetic energy to the potential energy by buoyancy. For weaker buoyancy, this conversion is weak, hence E(u)(k) follows Kolmogorov's spectrum with a constant energy flux. For Rayleigh-Bénard convection, we show that the energy supply rate by buoyancy is positive, which leads to an increasing Π(u)(k) with k, thus ruling out Bolgiano-Obukhov scaling for the convective turbulence. Our numerical results show that convective turbulence for unit Prandt number exhibits a constant Π(u)(k) and E(u)(k)∼k(-5/3) for a narrow band of wave numbers.

  4. A multiple-time-scale turbulence model based on variable partitioning of turbulent kinetic energy spectrum

    NASA Technical Reports Server (NTRS)

    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.

  5. Spectrum and energy transfer in steady Burgers turbulence

    NASA Technical Reports Server (NTRS)

    Girimaji, Sharath S.; Zhou, YE

    1995-01-01

    The spectrum, energy transfer, and spectral interactions in steady Burgers turbulence are studied using numerically generated data. The velocity field is initially random and the turbulence is maintained steady by forcing the amplitude of a band of low wavenumbers to be invariant in time, while permitting the phase to change as dictated by the equation. The spectrum, as expected, is very different from that of Navier-Stokes turbulence. It is demonstrated that the far range of the spectrum scales as predicted by Burgers. Despite the difference in their spectra, in matters of the spectral energy transfer and triadic interactions Burgers turbulence is similar to Navier-Stokes turbulence.

  6. Calculation of turbulence-driven secondary motion in ducts with arbitrary cross section

    NASA Technical Reports Server (NTRS)

    Demuren, A. O.

    1989-01-01

    Calculation methods for turbulent duct flows are generalized for ducts with arbitrary cross-sections. The irregular physical geometry is transformed into a regular one in computational space, and the flow equations are solved with a finite-volume numerical procedure. The turbulent stresses are calculated with an algebraic stress model derived by simplifying model transport equations for the individual Reynolds stresses. Two variants of such a model are considered. These procedures enable the prediction of both the turbulence-driven secondary flow and the anisotropy of the Reynolds stresses, in contrast to some of the earlier calculation methods. Model predictions are compared to experimental data for developed flow in triangular duct, trapezoidal duct and a rod-bundle geometry. The correct trends are predicted, and the quantitative agreement is mostly fair. The simpler variant of the algebraic stress model procured better agreement with the measured data.

  7. Turbulent diffusion phase transition is due to singular energy spectrum.

    PubMed Central

    Wallstrom, T C

    1995-01-01

    The phase transition for turbulent diffusion, reported by Avellaneda and Majda [Avellaneda, M. & Majda, A. J. (1994) Philos. Trans. R. Soc. London A 346, 205-233, and several earlier papers], is traced to a modeling assumption in which the energy spectrum of the turbulent fluid is singularly dependent on the viscosity in the inertial range. Phenomenological models of turbulence and intermittency, by contrast, require that the energy spectrum be independent of the viscosity in the inertial range. When the energy spectrum is assumed to be consistent with the phenomenological models, there is no phase transition for turbulent diffusion. Images Fig. 2 PMID:11607590

  8. Turbulent diffusion phase transition is due to singular energy spectrum.

    PubMed

    Wallstrom, T C

    1995-11-21

    The phase transition for turbulent diffusion, reported by Avellaneda and Majda [Avellaneda, M. & Majda, A. J. (1994) Philos. Trans. R. Soc. London A 346, 205-233, and several earlier papers], is traced to a modeling assumption in which the energy spectrum of the turbulent fluid is singularly dependent on the viscosity in the inertial range. Phenomenological models of turbulence and intermittency, by contrast, require that the energy spectrum be independent of the viscosity in the inertial range. When the energy spectrum is assumed to be consistent with the phenomenological models, there is no phase transition for turbulent diffusion.

  9. RESIDUAL ENERGY SPECTRUM OF SOLAR WIND TURBULENCE

    SciTech Connect

    Chen, C. H. K.; Bale, S. D.; Salem, C. S.; Maruca, B. A.

    2013-06-20

    It has long been known that the energy in velocity and magnetic field fluctuations in the solar wind is not in equipartition. In this paper, we present an analysis of 5 yr of Wind data at 1 AU to investigate the reason for this. The residual energy (difference between energy in velocity and magnetic field fluctuations) was calculated using both the standard magnetohydrodynamic (MHD) normalization for the magnetic field and a kinetic version, which includes temperature anisotropies and drifts between particle species. It was found that with the kinetic normalization, the fluctuations are closer to equipartition, with a mean normalized residual energy of {sigma}{sub r} = -0.19 and mean Alfven ratio of r{sub A} = 0.71. The spectrum of residual energy, in the kinetic normalization, was found to be steeper than both the velocity and magnetic field spectra, consistent with some recent MHD turbulence predictions and numerical simulations, having a spectral index close to -1.9. The local properties of residual energy and cross helicity were also investigated, showing that globally balanced intervals with small residual energy contain local patches of larger imbalance and larger residual energy at all scales, as expected for nonlinear turbulent interactions.

  10. Heat Transfer in the Turbulent Incompressible Boundary Layer. 3; Arbitrary Wall Temperature and Heat Flux

    NASA Technical Reports Server (NTRS)

    Reynolds, W. C.; Kays, W. M.; Kline, S. J.

    1958-01-01

    Superposition techniques are used to calculate the rate of heat transfer from a flat plate to a turbulent incompressible boundary layer for several cases of variable surface temperature. The predictions of a number of these calculations are compared with experimental heat- transfer rates, and good agreement is obtained. A simple computing procedure for determining the heat-transfer rates from surfaces with arbitrary wall-temperature distributions is presented and illustrated by two examples. The inverse problem of determining the temperature distribution from an arbitrarily prescribed heat flux is also treated, both experimentally and analytically.

  11. Statistic of a Gaussian beam from an arbitrary rough target in the single passage atmospheric turbulence

    NASA Astrophysics Data System (ADS)

    Xiang, NingJing; Wu, ZhenSen; Wang, MingJun

    2014-10-01

    The extended Huygens-Fresnel principle and Goodman model was utilized for target surface to derive the mutual coherence function (MCF) of a Gaussian beam reflected from an arbitrary rough target in atmospheric turbulence. According to the MCF, expressions of the mean irradiance and average speckle size at the receiver were obtained. The analysis indicated that the mean intensity is closely related to the ratio of root mean square (rms) height to the lateral correlation length. In addition, the speckle size at the receiver is associated with turbulence strength, propagation distance and roughness of the target. The results can be reduced to the result of a Gaussian beam illuminating rough target and scattering from a target in free space.

  12. Simulating wave-turbulence on thin elastic plates with arbitrary boundary conditions

    NASA Astrophysics Data System (ADS)

    van Rees, Wim M.; Mahadevan, L.

    2016-11-01

    The statistical characteristics of interacting waves are described by the theory of wave turbulence, with the study of deep water gravity wave turbulence serving as a paradigmatic physical example. Here we consider the elastic analog of this problem in the context of flexural waves arising from vibrations of a thin elastic plate. Such flexural waves generate the unique sounds of so-called thunder machines used in orchestras - thin metal plates that make a thunder-like sound when forcefully shaken. Wave turbulence in elastic plates is typically investigated numerically using spectral simulations with periodic boundary conditions, which are not very realistic. We will present the results of numerical simulations of the dynamics of thin elastic plates in physical space, with arbitrary shapes, boundary conditions, anisotropy and inhomogeneity, and show first results on wave turbulence beyond the conventionally studied rectangular plates. Finally, motivated by a possible method to measure ice-sheet thicknesses in the open ocean, we will further discuss the behavior of a vibrating plate when floating on an inviscid fluid.

  13. Lagrangian Frequency Spectrum as a Diagnostic for Magnetohydrodynamic Turbulence Dynamics

    SciTech Connect

    Busse, Angela; Mueller, Wolf-Christian; Gogoberidze, Grigol

    2010-12-03

    For the phenomenological description of magnetohydrodynamic turbulence competing models exist, e.g., Boldyrev [Phys. Rev. Lett. 96, 115002 (2006)] and Gogoberidze [Phys. Plasmas 14, 022304 (2007)], which predict the same Eulerian inertial-range scaling of the turbulent energy spectrum although they employ fundamentally different basic interaction mechanisms. A relation is found that links the Lagrangian frequency spectrum with the autocorrelation time scale of the turbulent fluctuations {tau}{sub ac} and the associated cascade time scale {tau}{sub cas}. Thus, the Lagrangian energy spectrum can serve to identify weak ({tau}{sub ac}<<{tau}{sub cas}) and strong ({tau}{sub ac{approx}{tau}cas}) interaction mechanisms providing insight into the turbulent energy cascade. The new approach is illustrated by results from direct numerical simulations of two- and three-dimensional incompressible MHD turbulence.

  14. Strain-Induced Landau Levels in Arbitrary Dimensions with an Exact Spectrum.

    PubMed

    Rachel, Stephan; Göthel, Ilja; Arovas, Daniel P; Vojta, Matthias

    2016-12-23

    Certain nonuniform strain applied to graphene flakes has been shown to induce pseudo-Landau levels in the single-particle spectrum, which can be rationalized in terms of a pseudomagnetic field for electrons near the Dirac points. However, this Landau level structure is, in general, approximate and restricted to low energies. Here, we introduce a family of strained bipartite tight-binding models in arbitrary spatial dimension d and analytically prove that their entire spectrum consists of perfectly degenerate pseudo-Landau levels. This construction generalizes the case of triaxial strain on graphene's honeycomb lattice to arbitrary d; in d=3, our model corresponds to tetraxial strain on the diamond lattice. We discuss general aspects of pseudo-Landau levels in arbitrary d.

  15. Strain-Induced Landau Levels in Arbitrary Dimensions with an Exact Spectrum

    NASA Astrophysics Data System (ADS)

    Rachel, Stephan; Göthel, Ilja; Arovas, Daniel P.; Vojta, Matthias

    2016-12-01

    Certain nonuniform strain applied to graphene flakes has been shown to induce pseudo-Landau levels in the single-particle spectrum, which can be rationalized in terms of a pseudomagnetic field for electrons near the Dirac points. However, this Landau level structure is, in general, approximate and restricted to low energies. Here, we introduce a family of strained bipartite tight-binding models in arbitrary spatial dimension d and analytically prove that their entire spectrum consists of perfectly degenerate pseudo-Landau levels. This construction generalizes the case of triaxial strain on graphene's honeycomb lattice to arbitrary d ; in d =3 , our model corresponds to tetraxial strain on the diamond lattice. We discuss general aspects of pseudo-Landau levels in arbitrary d .

  16. Visibility moments and power spectrum of turbulence velocity

    NASA Astrophysics Data System (ADS)

    Dutta, Prasun

    2016-02-01

    Here we introduce moments of visibility function and discuss how those can be used to estimate the power spectrum of the turbulent velocity of external spiral galaxies. We perform numerical simulation to confirm the credibility of this method and found that for galaxies with lower inclination angles it works fine. The estimator outlined here is unbiased and has the potential to recover the turbulent velocity spectrum completely from radio interferometric observations.

  17. A multiple-time-scale turbulence model based on variable partitioning of turbulent kinetic energy spectrum

    NASA Technical Reports Server (NTRS)

    Kim, S.-W.; Chen, C.-P.

    1987-01-01

    A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model.

  18. Spectrum analysis of rectangular pulse in the atmospheric turbulence propagation

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Ni, Xiaolong; Jiang, Huilin; Wang, Junran; Liu, Zhi

    2016-11-01

    Atmospheric turbulence has a great influence on the performance of the atmospheric laser communication system reducing the signal to noise ratio (SNR) and increasing the bit error rate (BER). However, there is rarely study on the effect of atmospheric turbulence on the power spectrum of the rectangular pulse. In this paper, a spectral analyzing method is used to analyze the influence of atmospheric turbulence on the signal. An experiment of laser beam propagation characteristic is carried out on a 6km horizontal atmospheric link, the wavelength is 808 nm. The signal is 100MHz rectangular pulse. The waveform of the rectangular pulse is collected by the oscilloscope, and the power spectral density of the signal is calculated and analyzed by the method of periodogram. Experimental results show that the response and noise characteristics of the laser and photoelectric detector have a great influence on the signal power spectrum distribution which can increase the noise component in the 10^6 Hz frequency range. After the atmospheric turbulence propagation, the signal power decreases in the whole frequency range. However, as the existence of atmospheric turbulence, the signal power increases in the atmospheric turbulence characteristic frequency (tens to hundreds of Hz). The noise power increases in the high frequency range (10^7 10^8 Hz).

  19. Quantum Turbulence: Vortex Bundle Collapse and Kolmogorov Spectrum

    NASA Astrophysics Data System (ADS)

    Nemirovskii, Sergey K.

    2016-12-01

    The statement of problem is motivated by the idea of modeling the classical turbulence with a set of chaotic quantized vortex filaments in superfluids. Among various arguments supporting the idea of quasi-classic behavior of quantum turbulence, the strongest, probably, is the k dependence of the spectra of energy, E(k)∝ k^{-5/3} obtained in numerical simulations and experiments. At the same time, the mechanism of classical vs. quantum turbulence is not clarified and the source of the k^{-5/3} dependence is unclear. In this work, we concentrated on the nonuniform vortex bundles. This choice is related to the actively discussed question concerning a role of collapses in the vortex dynamics in formation of turbulent spectra. We demonstrate that the nonuniform vortex bundles, which appear in result of nonlinear vortex dynamics, generates an energy spectrum which is close to the Kolmogorov dependence ∝ k^{-5/3}.

  20. Collapsing vortex filaments and the spectrum of quantum turbulence

    NASA Astrophysics Data System (ADS)

    Andryushchenko, V. A.; Nemirovskii, S. K.

    2017-01-01

    The method of correlation functions and the method of quantum vortex configurations are used to calculate the energy spectrum of a three-dimensional velocity field that is induced by collapsing (immediately before reconnection) vortex filaments. The formulation of this problem is motivated by the idea of modeling classical turbulence by a set of chaotic quantized vortex filaments. Among the various arguments that support the idea of quasi-classical behavior for quantum turbulence, the most persuasive is probably the resulting Kolmogorov energy spectrum resembling E ( k ) ∝ k - 5 / 3 that was obtained in a number of numerical studies. Another goal is associated with an important and intensely studied theme that relates to the role of hydrodynamic collapse in the formation of turbulence spectra. Calculations have demonstrated that vortex filaments create a velocity field at the moment of contact, which has a singularity. This configuration of vortex filaments generates the spectrum E(k), which bears the resemblance to the Kolmogorov law. A possible cause for this observation is discussed, as well as the likely reasons behind any deviations. The obtained results are discussed from the perspective of both classical and quantum turbulence.

  1. Sparse spectrum model for the turbulent phase simulations

    NASA Astrophysics Data System (ADS)

    Charnotskii, Mikhail

    2013-05-01

    Monte-Carlo simulation of phase front perturbations by atmospheric turbulence finds numerous applications for design and modeling of the adaptive optics systems, laser beams propagation simulations, and evaluating the performance of the various optical systems operating in the open air environment. Accurate generation of two-dimensional random fields of turbulent phase is complicated by the enormous diversity of scales that can reach five orders in magnitude in each coordinate. In addition there is a need for generation of the long "ribbons" of turbulent phase that are used to represent the time evolution of the wave front. This makes it unfeasible to use the standard discrete Fourier transform-based technique as a basis for the Monte-Carlo simulation algorithm. We propose a novel concept for turbulent phase - the Sparse Spectrum (SS) random field. The principle assumption of the SS model is that each realization of the random field has a discrete random spectral support. Statistics of the random amplitudes and wave vectors of the SS model are arranged to provide the required spectral and correlation properties of the random field. The SS-based Monte-Carlo model offers substantial reduction of computer costs for simulation of the wide-band random fields and processes, and is capable of generating long aperiodic phase "ribbons". We report the results of model trials that determine the number of sparse components, and the range of wavenumbers that is necessary to accurately reproduce the random field with a power-law spectrum.

  2. Universality of energy spectrum in turbulent Rayleigh-Benard convection

    NASA Astrophysics Data System (ADS)

    Bai, Kunlun; Hoeller, Judith; Brown, Eric

    2016-11-01

    We present study of energy spectrum in turbulent Rayleigh-Benard convection, in both cylindrical and cubic containers, tilting and non-tilting conditions, and with Rayleigh number ranging from 0 . 5 ×109 to 1 ×1010 . For these different conditions of geometry, tilt, and Rayleigh number, the temperature spectra measured on the system side walls are significantly different from each other. Even for the same condition, the spectrum varies depending on whether the sensors locate in the path of large-scale circulations. However, quite interestingly, once the signals of large-scale circulations are subtracted from the raw temperature, all spectra display a universal shape, regardless of system geometry, tilt, Rayleigh number, and location of sensors. It suggests that one could model the large-scale circulations and small-scale fluctuations separately in turbulent Rayleigh-Benard convection.

  3. Energy spectrum transfer equations of solar wind turbulence

    NASA Technical Reports Server (NTRS)

    Tu, C.-Y.

    1995-01-01

    The recent studies of transfer equations for solar wind magnetohydrodynamic (MHD) turbulence are reviewed with emphasis on the comparison with the statistical observational results. Helios and Voyager missions provide an opportunity to study the the radial evolution of the power spectrum. the cross-helicity the Alfven ratio and the minimum variance direction. Spectrum transfer equations are considered as a tool to explore the nature of this radial evolution of the fluctuations. The transfer equations are derived from incompressible MHD equations. Generally one needs to make assumptions about the nature of the fluctuations and the nature of the turbulent non-linear interactions to obtain numerical results which can be compared with the observations. Some special model results for several simple cases SUCH as for structures or strong mixing. for Alfven waves with weak turbulent interactions. and for a superposition of structures and Alfven waves. are discussed. The difference between the various approaches to derive and handle the transfer equations are also addressed. Finally some theoretical description of the compressible fluctuations are also briefly reviewed.

  4. Inertial range spectrum of field-aligned whistler turbulence

    NASA Astrophysics Data System (ADS)

    Dwivedi, Navin Kumar; Singh, Shobhana

    2017-03-01

    An analytical model to study the whistler turbulence spectrum and inertial range spectral scalings related with the electric and magnetic field spectra in a weakly non-collisional magnetized plasma is developed. In the present model, the dispersion relation of whistler wave propagating along the background magnetic field is exploited to derive the inertial range scaling laws corresponding to the electric field and magnetic field fluctuations. The model is based on the concept of Iroshnikov–Kraichnan inertial range magnetohydrodynamic turbulence. The present phenomenological turbulence scaling model suggests the energy spectra associated with the whistler wave electric field fluctuations and magnetic field fluctuations pursue ‑1 and ‑3 power-laws, respectively. Moreover, the results obtained by the present analytical model reasonably able to explain and compare the observational energy spectra in the wave number domain. The observational and analytical results support the whistler dominated turbulence with the similar spectral index ‑1 of the electric field spectra, whereas, the magnetic field spectral indices in the wave number domain are found -13/3 and ‑3 for the observational and analytical approach, respectively.

  5. A Computer Program for Calculating Three-Dimensional Compressible Laminar and Turbulent Boundary Layers on Arbitrary Wings

    NASA Technical Reports Server (NTRS)

    Cebeci, T.; Kaups, K.; Ramsey, J. A.

    1977-01-01

    A computer program for calculating three dimensional compressible laminar and turbulent boundary layers on arbitrary wings is described and presented. The computer program consists of three separate programs, namely, a geometry program to represent the wing analytically, a velocity program to compute the external velocity components from a given experimental pressure distribution and a finite difference boundary layer method to solve the governing equations for compressible flows. To illustrate the usage of the computer program, three different test cases are presented and the preparation of the input data as well as the computed output data is discussed in some detail.

  6. Investigation of Turbulence Behaviour in the Stable Boundary Layer Using Arbitrary-Order Hilbert Spectra

    NASA Astrophysics Data System (ADS)

    Wei, W.; Zhang, H. S.; Schmitt, F. G.; Huang, Y. X.; Cai, X. H.; Song, Y.; Huang, X.; Zhang, H.

    2017-01-01

    The CASES-99 experimental data are used to analyze turbulence behaviour under a range of stable conditions using an adaptive method based on Hilbert spectral analysis. The characteristic scales of intrinsic mode functions vary between different stratifications. The second-order Hilbert marginal spectra display clear separation between fine-scale turbulence and large-scale motions. After removing the large-scale motions, the statistical characteristics of the reconstructed signals confirm the distinction of different stratifications in the fine-scale range. The correlation coefficient analyses reveal that the Hilbert spectral analysis method separates turbulence from large-scale motions in the stable boundary layer.

  7. Oscillator strength spectrum of hydrogen in strong magnetic and electric fields with arbitrary mutual orientation

    SciTech Connect

    Guan Xiaoxu

    2006-08-15

    We present oscillator strength spectra of the hydrogen Balmer {alpha} series in crossed strong magnetic and electric fields. Field strength regimes of interest ({gamma}{<=}0.02 a.u. and F{<=}1x10{sup 8} V/m) are the characteristic strengths observed on the surface of white dwarf stars. Based on the pseudospectral discretization technique, two independent methods have been developed to achieve reliable oscillator strengths in crossed fields. The effect of relative orientation between the magnetic and electric fields is clarified. Compared to the parallel configuration, we have observed that for the field strength regimes of interest, the perpendicular component of electric fields only results in a weaker coupling between the states belonging to the different subspaces of magnetic quantum numbers. This observation explains why the spectrum of oscillator strengths in crossed electric and magnetic fields with arbitrary mutual orientation shows similar behavior compared to that in parallel fields. However, a careful analysis shows that the two stronger transition lines at 5546 and 5620 A ring previously attributed to the Balmer {alpha} series are now identified to belong to the Balmer {beta} series. An effective scheme has also been suggested to calculate the bound-free opacities of hydrogen atoms in crossed fields.

  8. A multiple-time-scale turbulence model based on variable partitioning of the turbulent kinetic energy spectrum

    NASA Technical Reports Server (NTRS)

    Kim, S.-W.; Chen, C.-P.

    1989-01-01

    A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model.

  9. Inertial Alfvén wave localization and turbulent spectrum

    NASA Astrophysics Data System (ADS)

    Sharma, R. P.; Kumari, Anju; Yadav, Nitin

    2014-09-01

    The localization of pump inertial Alfvén wave (IAW) in low β plasmas (β ≪ me/ mi) has been investigated by developing a model based on weak IAW and finite amplitude background density fluctuations. When IAW is perturbed by these fluctuations which are in the form of magnetosonic and ion acoustic waves, its phase velocity gets modified and IAW breaks up into localized structures of very high intensity. Numerical simulation has been carried out to analyze the localized structures and magnetic fluctuation spectrum of pump IAW. We have also developed a simplified model to understand the physical insight into evolution pattern of IAW. Results obtained from simulation reveal that turbulent spectrum up to k⊥λe ≈ 1 follows Kolmogorov power law. Furthermore, at shorter wavelengths, dispersion starts and spectrum steepens with power law index ˜ - 3.8. Energy transport to smaller length scales through this mechanism may be accountable for the observed parallel electron heating in low β plasmas. Results obtained from the numerical simulation are consistent with the observations of various spacecraft like FAST and Hawkeye.

  10. Anisotropic power spectrum of refractive-index fluctuation in hypersonic turbulence.

    PubMed

    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.

  11. Sensitivity of neutrinos to the supernova turbulence power spectrum: Point source statistics

    SciTech Connect

    Kneller, James P.; Kabadi, Neel V.

    2015-07-16

    The neutrinos emitted from the proto-neutron star created in a core-collapse supernova must run through a significant amount of turbulence before exiting the star. Turbulence can modify the flavor evolution of the neutrinos imprinting itself upon the signal detected here at Earth. The turbulence effect upon individual neutrinos, and the correlation between pairs of neutrinos, might exhibit sensitivity to the power spectrum of the turbulence, and recent analysis of the turbulence in a two-dimensional hydrodynamical simulation of a core-collapse supernova indicates the power spectrum may not be the Kolmogorov 5 /3 inverse power law as has been previously assumed. In this paper we study the effect of non-Kolmogorov turbulence power spectra upon neutrinos from a point source as a function of neutrino energy and turbulence amplitude at a fixed postbounce epoch. We find the two effects of turbulence upon the neutrinos—the distorted phase effect and the stimulated transitions—both possess strong and weak limits in which dependence upon the power spectrum is absent or evident, respectively. Furthermore, since neutrinos of a given energy will exhibit these two effects at different epochs of the supernova each with evolving strength, we find there is sensitivity to the power spectrum present in the neutrino burst signal from a Galactic supernova.

  12. Sensitivity of neutrinos to the supernova turbulence power spectrum: Point source statistics

    DOE PAGES

    Kneller, James P.; Kabadi, Neel V.

    2015-07-16

    The neutrinos emitted from the proto-neutron star created in a core-collapse supernova must run through a significant amount of turbulence before exiting the star. Turbulence can modify the flavor evolution of the neutrinos imprinting itself upon the signal detected here at Earth. The turbulence effect upon individual neutrinos, and the correlation between pairs of neutrinos, might exhibit sensitivity to the power spectrum of the turbulence, and recent analysis of the turbulence in a two-dimensional hydrodynamical simulation of a core-collapse supernova indicates the power spectrum may not be the Kolmogorov 5 /3 inverse power law as has been previously assumed. Inmore » this paper we study the effect of non-Kolmogorov turbulence power spectra upon neutrinos from a point source as a function of neutrino energy and turbulence amplitude at a fixed postbounce epoch. We find the two effects of turbulence upon the neutrinos—the distorted phase effect and the stimulated transitions—both possess strong and weak limits in which dependence upon the power spectrum is absent or evident, respectively. Furthermore, since neutrinos of a given energy will exhibit these two effects at different epochs of the supernova each with evolving strength, we find there is sensitivity to the power spectrum present in the neutrino burst signal from a Galactic supernova.« less

  13. A robust and accurate numerical method for transcritical turbulent flows at supercritical pressure with an arbitrary equation of state

    SciTech Connect

    Kawai, Soshi; Terashima, Hiroshi; Negishi, Hideyo

    2015-11-01

    This paper addresses issues in high-fidelity numerical simulations of transcritical turbulent flows at supercritical pressure. The proposed strategy builds on a tabulated look-up table method based on REFPROP database for an accurate estimation of non-linear behaviors of thermodynamic and fluid transport properties at the transcritical conditions. Based on the look-up table method we propose a numerical method that satisfies high-order spatial accuracy, spurious-oscillation-free property, and capability of capturing the abrupt variation in thermodynamic properties across the transcritical contact surface. The method introduces artificial mass diffusivity to the continuity and momentum equations in a physically-consistent manner in order to capture the steep transcritical thermodynamic variations robustly while maintaining spurious-oscillation-free property in the velocity field. The pressure evolution equation is derived from the full compressible Navier–Stokes equations and solved instead of solving the total energy equation to achieve the spurious pressure oscillation free property with an arbitrary equation of state including the present look-up table method. Flow problems with and without physical diffusion are employed for the numerical tests to validate the robustness, accuracy, and consistency of the proposed approach.

  14. Transition from thermal to turbulent equilibrium with a resulting electromagnetic spectrum

    SciTech Connect

    Ziebell, L. F.; Yoon, P. H.; Gaelzer, R.; Pavan, J.

    2014-01-15

    A recent paper [Ziebell et al., Phys. Plasmas 21, 010701 (2014)] discusses a new type of radiation emission process for plasmas in a state of quasi-equilibrium between the particles and enhanced Langmuir turbulence. Such a system may be an example of the so-called “turbulent quasi-equilibrium.” In the present paper, it is shown on the basis of electromagnetic weak turbulence theory that an initial thermal equilibrium state (i.e., only electrostatic fluctuations and Maxwellian particle distributions) transitions toward the turbulent quasi-equilibrium state with enhanced electromagnetic radiation spectrum, thus demonstrating that the turbulent quasi-equilibrium discussed in the above paper correctly describes the weakly turbulent plasma dynamically interacting with electromagnetic fluctuations, while maintaining a dynamical steady-state in the average sense.

  15. The spectrum of a turbulent passive scalar in the viscous-convective range

    NASA Astrophysics Data System (ADS)

    Qian, J.

    1990-08-01

    The closed equations of isotropic turbulence, obtained by the method of nonequilibrium statistical mechanics and a perturbation-variation approach (Qian 1983, 1985, 1988), are applied to the study of the spectrum dynamics of a turbulent passive scalar in the viscous-convective range. Batchelor's 1/k spectrum is further confirmed. Moreover, the effective average value of the least principal rate of strain gamma in Batchelor's spectrum function is theoretically evaluated, and the results are in agreement with experimental data reported by Grant et al. (1968) and Williams and Paulson (1977).

  16. Nonlinear relativistic single-electron Thomson scattering power spectrum for incoming laser of arbitrary intensity

    SciTech Connect

    Alvarez-Estrada, R. F.; Pastor, I.; Guasp, J.; Castejon, F.

    2012-06-15

    The classical nonlinear incoherent Thomson scattering power spectrum from a single relativistic electron with incoming laser radiation of any intensity, investigated numerically by the present authors in a previous publication, displayed both an approximate quadratic behavior in frequency and a redshift of the power spectrum for high intensity incoming radiation. The present work is devoted to justify, in a more general setup, those numerical findings. Those justifications are reinforced by extending suitably analytical approaches, as developed by other authors. Moreover, our analytical treatment exhibits differences between the Doppler-like frequencies for linear and circular polarization of the incoming radiation. Those differences depend nonlinearly on the laser intensity and on the electron initial velocity and do not appear to have been displayed by previous authors. Those Doppler-like frequencies and their differences are validated by new Monte Carlo computations beyond our previuos ones and reported here.

  17. THE TURBULENCE VELOCITY POWER SPECTRUM OF NEUTRAL HYDROGEN IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Chepurnov, A.; Lazarian, A.; Stanimirovic, S.; Burkhart, B.

    2015-09-01

    We present the results of the Velocity Coordinate Spectrum (VCS) technique to calculate the velocity power spectrum of turbulence in the Small Magellanic Cloud (SMC) in 21 cm emission. We present an updated version of the VCS technique that takes into account regular motions, which is an important factor in our SMC VCS analysis. We have obtained a velocity spectral index of −3.85, a cold phase sonic Mach number of 5.6, and an injection scale of 2.3 kpc. The spectral index is steeper than the Kolmogorov index, which is expected for shock-dominated turbulence. The injection scale of 2.3 kpc suggests that HI supershells or tidal interactions with the Large Magellanic Cloud are the dominant drivers of turbulence in this dwarf galaxy. This implies that turbulence may be driven by multiple mechanisms in galaxies and that galaxy–galaxy interactions may play an important role in addition to supernova feedback.

  18. Spectrum analysis of turbulence in the canine ascending aorta measured with a hot-film anemometer.

    PubMed

    Yamaguchi, T; Kikkawa, S; Tanishita, K; Sugawara, M

    1988-01-01

    We measured turbulence velocity in the canine ascending aorta using a hot-film anemometer. Blood flow velocity was measured at various points across the ascending aorta approximately 1.5-2 times the diameter downstream from the aortic valve. The turbulence spectrum was calculated and its characteristics were examined in connection with the mean Reynolds number and/or measuring positions. In the higher wave number range the values of the turbulence spectra were higher at larger mean Reynolds number. In the higher wave number range, the values of the turbulence spectra were higher at points closer to the centerline of the aorta, when the mean Reynolds number was relatively large. The patterns of the turbulence spectra at various points outside the boundary layer on the aortic wall were similar.

  19. Calculation of three-dimensional compressible laminar and turbulent boundary layers. Calculation of three-dimensional compressible boundary layers on arbitrary wings

    NASA Technical Reports Server (NTRS)

    Cebeci, T.; Kaups, K.; Ramsey, J.; Moser, A.

    1975-01-01

    A very general method for calculating compressible three-dimensional laminar and turbulent boundary layers on arbitrary wings is described. The method utilizes a nonorthogonal coordinate system for the boundary-layer calculations and includes a geometry package that represents the wing analytically. In the calculations all the geometric parameters of the coordinate system are accounted for. The Reynolds shear-stress terms are modeled by an eddy-viscosity formulation developed by Cebeci. The governing equations are solved by a very efficient two-point finite-difference method used earlier by Keller and Cebeci for two-dimensional flows and later by Cebeci for three-dimensional flows.

  20. TURBULENCE SPECTRA FROM DOPPLER-BROADENED SPECTRAL LINES: TESTS OF THE VELOCITY CHANNEL ANALYSIS AND VELOCITY COORDINATE SPECTRUM TECHNIQUES

    SciTech Connect

    Chepurnov, A.; Lazarian, A.

    2009-03-10

    Turbulent motions induce Doppler shifts of observable emission and absorption lines motivating studies of turbulence using precision spectroscopy. We provide numerical testing of the two most promising techniques, velocity channel analysis and velocity coordinate spectrum (VCS). We obtain an expression for the shot noise that the discretization of the numerical data entails and successfully test it. We show that the numerical resolution required for recovering the underlying turbulent spectrum from observations depend on the spectral index of velocity fluctuations, which makes low-resolution testing misleading. We demonstrate numerically that, when dealing with absorption lines, sampling of turbulence along just a dozen directions provides a high quality spectrum with the VCS technique.

  1. Upstream turbulence and the particle spectrum at CME-driven Shocks

    SciTech Connect

    Li Gang; Hu, Q.; Zank, G.P.

    2005-08-01

    Particle spectra at a CME-driven shock often exhibit a power law to certain energies, then roll over exponentially beyond. However, there are cases where a spectrum evolves to another power law above a certain energy (e.g. the Oct. 29th, 2003 event). Here we introduce an effective 'loss term' into the particle transport equation and study the consequent particle spectra behavior at a CME-driven shock. The loss term represents the effect of particle leaking out from a finite shock and is related to the turbulence power at and near the shock. We show that the shape of particle spectra are tightly related to the form of upstream turbulence. Under certain circumstances, broken power-law spectrum can be obtained. The physical meaning of the 'loss term' and its relationship to the upstream turbulence is discussed.

  2. Hierarchical Bayesian analysis of the velocity power spectrum in supersonic turbulence

    NASA Astrophysics Data System (ADS)

    Konstandin, L.; Shetty, R.; Girichidis, P.; Klessen, R. S.

    2015-01-01

    Turbulence is a dominant feature operating in gaseous flows across nearly all scales in astrophysical environments. Accordingly, accurately estimating the statistical properties of such flows is necessary for developing a comprehensive understanding of turbulence. We develop and employ a hierarchical Bayesian fitting method to estimate the parameters describing the scaling relationships of the velocity power spectra of supersonic turbulence. We demonstrate the accuracy and other advantages of this technique compared with ordinary linear regression methods. Using synthetic power spectra, we show that the Bayesian method provides accurate parameter and error estimates. Commonly used normal linear regression methods can provide estimates that fail to recover the underlying slopes, up to 70 per cent of the instances, even when considering the 2σ uncertainties. Additionally, we apply the Bayesian methods to analyse the statistical properties of compressible turbulence in three-dimensional numerical simulations. We model driven, isothermal, turbulence with root-mean-square Mach numbers in the highly supersonic regime {M}≈ 15. We study the influence of purely solenoidal (divergence-free) and purely compressive (curl-free) forcing on the scaling exponent of the power spectrum. In simulations with solenoidal forcing and 10243 resolution, our results indicate that there is no extended inertial range with a constant scaling exponent. The bottleneck effect results in a curved power spectrum at all wave numbers and is more pronounced in the transversal modes compared with the longitudinal modes. Therefore, this effect is stronger in stationary turbulent flows driven by solenoidal forcing compared to the compressive one. The longitudinal spectrum driven with compressive forcing is the only spectrum with constant scaling exponent ζ = -1.94 ± 0.01, corresponding to slightly shallower slopes than the Burger prediction.

  3. Energy Spectrum in the Dissipation Range of Fluid Turbulence

    NASA Technical Reports Server (NTRS)

    Martinez, D. O.; Chen, S.; Doolen, G. D.; Kraichnan, R. H.; Wang, L.-P.; Zhou, Y.

    1996-01-01

    High resolution, direct numerical simulations of the three-dimensional incompressible Navier-Stokes equations are carried out to study the energy spectrum in the dissipation range. An energy spectrum of the form A(k/k( sub d))(sup alpha) exp[- betak/k(sub d) is confirmed. The possible values of the parameters alpha and beta, as well as their dependence on Revnolds numbers and length scales, are investigated, showing good agreement with recent theoretical predictions. A "bottleneck'-type effect is reported at k/k(sub d) approximately 4, exhibiting a possible transition from near-dissipation to far- dissipation.

  4. Phase noise effects on turbulent weather radar spectrum parameter estimation

    NASA Technical Reports Server (NTRS)

    Lee, Jonggil; Baxa, Ernest G., Jr.

    1990-01-01

    Accurate weather spectrum moment estimation is important in the use of weather radar for hazardous windshear detection. The effect of the stable local oscillator (STALO) instability (jitter) on the spectrum moment estimation algorithm is investigated. Uncertainty in the stable local oscillator will affect both the transmitted signal and the received signal since the STALO provides transmitted and reference carriers. The proposed approach models STALO phase jitter as it affects the complex autocorrelation of the radar return. The results can therefore by interpreted in terms of any source of system phase jitter for which the model is appropriate and, in particular, may be considered as a cumulative effect of all radar system sources.

  5. A Microthermal Device for Measuring the Spatial Power Spectrum of Atmospheric Optical Turbulence

    NASA Astrophysics Data System (ADS)

    Turner, Jonathan; McGraw, J.; Zimmer, P.; Williams, T.; Claver, C.; Krabbendam, V.; Wiecha, O.; Andrew, J.; Warner, M.

    2010-01-01

    The Measurement Astrophysics group at UNM designed and built a novel microthermal device for characterizing atmospheric optical turbulence at astronomical observatories. This instrument is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors. The device makes differential temperature measurements which are directly related to the index of refraction structure constant, Cn2, which quantifies the strength of optical turbulence. The device is designed to work in two modes. In horizontal mode temperature differentials are measured between adjacent sensors. Measurements are combined to recover the differences over all pairwise sensor baselines. These measurements result in a spatial spectrum of turbulence. Measured turbulent spectra are then fit to standard turbulence models which yield estimates of the outer scale of turbulence and the slope of the power spectra. In vertical mode the device operates with pairs of microthermal sensors distributed vertically, each pair being separated horizontally by approximately one meter. Sensor pairs are suspended at multiple heights above the ground allowing measurement of atmospheric turbulence power as a function of altitude. This device was used to monitor optical turbulence during a site testing campaign at the future LSST site on Cerro Pachón. We present preliminary results from operation in both vertical and horizontal modes from October 2008 to December 2009. The microthermal array remains in operation on Cerro Pachón, and continues to produce valuable atmospheric measurements. Our results support the conclusion that Cerro Pachón is an excellent observatory site. The vertical turbulence profile decreases monotonically with height as expected, and the surface layer does not contribute a significant amount to the overall seeing measured at the site. This work was supported by Air Force Grant No. FA9451-04-2-0355. Instrumentation and travel support was provided in part by

  6. Height dependence of the observed spectrum of radar backscatter from HF-induced ionospheric Langmuir turbulence

    NASA Astrophysics Data System (ADS)

    Fejer, J. A.; Sulzer, M. P.; Djuth, F. T.

    1991-09-01

    Results are presented of observations of the spectrum of the 430-MHz radar backscatter from HF-induced Langmuir turbulence with height discrimination. During very stable ionospheric conditions under which the height of the below-threshold backscatter spectrum changed by less than 300 m during a 7-min period, a 20-s-long temporary increase in the HF power from 3 MW ERP to 38-MW-equivalent-radiated HF power is found to result in subsequent strong above-threshold spectra extending to heights up to 1200 m greater than the height of the below-threshold spectrum for more than a minute. The generation of irregularities in the plasma density during the 20 s of enhanced HF power is suggested as a possible cause of this persistence of strong above-threshold spectra at greater heights. The initial temporal evolution of the backscatter spectrum from Langmuir turbulence after the start of HF transmissions is observed for different heights. The observational results are compared with the predictions of existing theories of Langmuir turbulence.

  7. Height dependence of the observed spectrum of radar backscatter from HF-induced ionospheric Langmuir turbulence

    SciTech Connect

    Fejer, J.A. ); Sulzer, M.P. ); Djuth, F.T. )

    1991-09-01

    Observations of the spectrum of 430-MHz radar backscatter from HF-induced Langmuir turbulence with height discrimination are described. During very stable ionospheric conditions under which the height of the below-threshold backscatter spectrum had changed by less than 300 m during a 7-min period, a 20-s-long temporary increase in the HF power from 3 MW ERP to 38 MW equivalent radiated HF power resulted in subsequent strong above-threshold spectra extending to heights up to 1200 m greater than the height of the below-threshold spectrum for more than a minute. The generation of irregularities in the plasma density during the 20 s of enhanced HF power is suggested as a possible cause of this persistence of strong above-threshold spectra at greater heights. The initial temporal evolution of the backscatter spectrum from Langmuir turbulence after the start of HF transmissions was observed for different heights. The observational results are compared with the predictions of existing theories of Langmuir turbulence.

  8. Shaping the X-ray spectrum of galaxy clusters with AGN feedback and turbulence

    NASA Astrophysics Data System (ADS)

    Gaspari, M.

    2015-07-01

    The hot plasma filling galaxy clusters emits copious X-ray radiation. The classic unheated and unperturbed cooling flow model predicts dramatic cooling rates and an isobaric X-ray spectrum with constant differential luminosity distribution. The observed cores of clusters (and groups) show instead a strong deficit of soft X-ray emission: dLx/dT ∝ (T/Thot)α = 2 ± 1. Using 3D hydrodynamic simulations, we show that such deficit arises from the tight self-regulation between thermal instability condensation and AGN outflow injection: condensing clouds boost the AGN outflows, which quench cooling as they thermalize through the core. The resultant average distribution slope is α ≃ 2, oscillating within the observed 1 < α < 3. In the absence of thermal instability, the X-ray spectrum remains isothermal (α ≳ 8), while unopposed cooling drives a too shallow slope, α < 1. AGN outflows deposit their energy inside-out, releasing more heat in the inner cooler phase; radially distributed heating alone induces a declining spectrum, 1 < α < 2. Turbulence further steepens the spectrum and increases the scatter: the turbulent Mach number in the hot phase is subsonic, while it becomes transonic in the cooler phase, making perturbations to depart from the isobaric mode. Such increase in dln P/dln T leads to α ≈ 3. Self-regulated AGN outflow feedback can address the soft X-ray problem through the interplay of heating and turbulence.

  9. Turbulence spectrum observed by a fast-rotating wind-turbine blade

    SciTech Connect

    Connell, J.R.

    1980-06-01

    The spectrum of turbulence encountered by a point on a fast-rotating wind turbine blade is shown to be possibly quite different from that measured by a stationary anemometer. The physically reasonable expectations are supported quantitatively by experiments using Pacific Northwest Laboratory's vertical-plane anemometer array. The measurements indicate that the blade encounters energy densities in two regions of the turbulence spectrum much different than those seen by stationary anemometers. For typical turbine types and wind conditions, the spectral energy redistribution phenomenon may be significant only for turbine blade diameters larger than 10 m. The spectral shift should also affect gust statistics for rotting blades; the duration of gusts that are smaller than the diameter of the disk of blade rotation will decrease. Correspondingly, the rise rate will increase by a factor of about ten.

  10. A Microthermal Device for Measuring the Spatial Power Spectrum of Atmospheric Turbulence

    NASA Astrophysics Data System (ADS)

    Turner, Jonathan; McGraw, J.; Zimmer, P.; Williams, T.; Claver, C.; Krabbendam, V.; Wiecha, O.; Andrew, J.; Warner, M.

    2009-01-01

    The Measurement Astrophysics group at UNM designed and built a novel microthermal device for the purpose of characterizing atmospheric turbulence at astronomical observatories. This instrument is based on the Wheatstone bridge and uses fine wire tungsten filaments as resistance temperature detectors. The device is designed to work in two data taking modes: with a horizontal array of microthermal sensors, or with a vertical array of sensors. In horizontal mode differential measurements are made between adjacent sensors, then these measurements are combined to recover the differences between all non-adjacent sensor pairs. The result of these measurements is microthermal data over many independent baselines which comprise a spatial spectrum of turbulence. The measured turbulent spectra are then fit to standard turbulence models which yield estimates of the outer scale of turbulence and the slope of the power spectra. Measurements in horizontal mode are made with 14 sensors over baselines of up to 30 meters. In addition probes can be repositioned to provide additional baselines. In vertical mode the device operates as microthermals traditionally have in the past: differential measurements are made between a pair of resistance temperature detectors. Sensor pairs are suspended at different heights above the ground allowing measurement of atmospheric turbulence as a function of altitude. Measurements in vertical mode are made with 14 sensor pairs which can be elevated up to 30 meters above ground. Data were taken with the device in a variety of test configurations, and the device is being used in a site testing campaign at Cerro Pachon. We will present the design, prototyping, and testing of this instrument as well as preliminary results from our campaign on Cerro Pachon.

  11. Multimode stretched spiral vortex and nonequilibrium energy spectrum in homogeneous shear flow turbulence

    NASA Astrophysics Data System (ADS)

    Horiuti, Kiyosi; Ozawa, Tetsuya

    2011-03-01

    The stretched spiral vortex [T. S. Lundgren, "Strained spiral vortex model for turbulent structures," Phys. Fluids 25, 2193 (1982)] is identified in turbulence in homogeneous shear flow and the spectral properties of this flow are studied using direct-numerical simulation data. The effects of mean shear on the genesis, growth, and annihilation processes of the spiral vortex are elucidated, and the role of the spiral vortex in the generation of turbulence is shown. As in homogeneous isotropic turbulence [K. Horiuti and T. Fujisawa, "The multi mode stretched spiral vortex in homogeneous isotropic turbulence," J. Fluid Mech. 595, 341 (2008)], multimodes of the spiral vortex are extracted. Two symmetric modes of configurations with regard to the vorticity alignment along the vortex tube in the core region and dual vortex sheets spiraling around the tube are often educed. One of the two symmetric modes is created by a conventional rolling-up of a single spanwise shear layer. Another one is created by the convergence of the recirculating flow or streamwise roll [F. Waleffe, "Homotopy of exact coherent structures in plane shear flows," Phys. Fluids 15, 1517 (2003)] caused by the upward and downward motions associated with the streaks. The vortex tube is formed by axial straining and lowering of pressure in the recirculating region. The spanwise shear layers are entrained by the tube and they form spiral turns. The latter symmetric mode tends to be transformed into the former mode with lapse of time due to the action of the pressure Hessian term. The power law in the inertial subrange energy spectrum is studied. The base steady spectrum fits the equilibrium Kolmogorov -5/3 spectrum, to which a nonequilibrium component induced by the fluctuation of the dissipation rate ɛ is added. This component is extracted using the conditional sampling on ɛ, and it is shown that it fits the -7/3 power in accordance with the statistical theory. The correlation between these spectra and

  12. SPECTRUM AND ANISOTROPY OF TURBULENCE FROM MULTI-FREQUENCY MEASUREMENT OF SYNCHROTRON POLARIZATION

    SciTech Connect

    Lazarian, A.; Pogosyan, D.

    2016-02-20

    We consider turbulent synchrotron-emitting media that also exhibit Faraday rotation and provide a statistical description of synchrotron polarization fluctuations. In particular, we consider these fluctuations as a function of the spatial separation of the direction of the measurements and as a function of wavelength for the same line of sight. On the basis of our general analytical approach, we introduce several measures that can be used to obtain the spectral slopes and correlation scales of both the underlying magnetic turbulence responsible for emission and the spectrum of the Faraday rotation fluctuations. We show the synergetic nature of these measures and discuss how the study can be performed using sparsely sampled interferometric data. We also discuss how additional characteristics of turbulence can be obtained, including the turbulence anisotropy and the three-dimensional direction of the mean magnetic field. In addition, we consider the cases when the synchrotron emission and Faraday rotation regions are spatially separated. Appealing to our earlier study, we explain that our new results are applicable to a wide range of spectral indexes of relativistic electrons responsible for synchrotron emission. We expect wide application of our techniques, both with existing synchrotron data sets and with big forthcoming data sets from LOFAR and SKA.

  13. Universality of spectrum of passive scalar variance at very high Schmidt number in isotropic steady turbulence

    NASA Astrophysics Data System (ADS)

    Gotoh, Toshiyuki

    2012-11-01

    Spectrum of passive scalar variance at very high Schmidt number up to 1000 in isotropic steady turbulence has been studied by using very high resolution DNS. Gaussian random force and scalar source which are isotropic and white in time are applied at low wavenumber band. Since the Schmidt number is very large, the system was integrated for 72 large eddy turn over time for the system to forgot the initial state. It is found that the scalar spectrum attains the asymptotic k-1 spectrum in the viscous-convective range and the constant CB is found to be 5.7 which is larger than 4.9 obtained by DNS under the uniform mean scalar gradient. Reasons for the difference are inferred as the Reynolds number effect, anisotropy, difference in the scalar injection, duration of time average, and the universality of the constant is discussed. The constant CB is also compared with the prediction by the Lagrangian statistical theory for the passive scalar. The scalar spectrum in the far diffusive range is found to be exponential, which is consistent with the Kraichnan's spectrum. However, the Kraichnan spectrum was derived under the assumption that the velocity field is white in time, therefore theoretical explanation of the agreement needs to be explored. Grant-in-Aid for Scientific Research No. 21360082, Ministry of Education, Culture, Sports, Science and Technology of Japan.

  14. Elementary models for turbulent diffusion with complex physical features: eddy diffusivity, spectrum and intermittency.

    PubMed

    Majda, Andrew J; Gershgorin, Boris

    2013-01-13

    This paper motivates, develops and reviews elementary models for turbulent tracers with a background mean gradient which, despite their simplicity, have complex statistical features mimicking crucial aspects of laboratory experiments and atmospheric observations. These statistical features include exact formulas for tracer eddy diffusivity which is non-local in space and time, exact formulas and simple numerics for the tracer variance spectrum in a statistical steady state, and the transition to intermittent scalar probability density functions with fat exponential tails as certain variances of the advecting mean velocity are increased while satisfying important physical constraints. The recent use of such simple models with complex statistics as unambiguous test models for central contemporary issues in both climate change science and the real-time filtering of turbulent tracers from sparse noisy observations is highlighted throughout the paper.

  15. On the cross-helicity dependence of the energy spectrum in magnetohydrodynamic turbulence

    SciTech Connect

    Podesta, J. J.

    2011-01-15

    Phenomenological theories of strong incompressible magnetohydrodynamic (MHD) turbulence derived by Goldreich and Sridhar (GS) in 1995 and by Boldyrev in 2006 are only applicable to turbulence with vanishing cross-helicity. In this study, these two theories are generalized to treat turbulence with nonvanishing cross-helicity in such a way that the relation (w{sup +}/w{sup -}){sup 2}=({epsilon}{sup +}/{epsilon}{sup -}){sup 2} observed in numerical simulations is satisfied. The average energy (second order structure function) in the generalized GS theory is E(r{sub perpendicular})={phi}{sub 1}({sigma}{sub c})({epsilon}r{sub perpendicular}){sup 2/3} and that in the generalized Boldyrev theory is E(r{sub perpendicular})={phi}{sub 2}({sigma}{sub c})(v{sub A{epsilon}}r{sub perpendicular}){sup 1/2}, where the function {phi}({sigma}{sub c}) describes the dependence on the normalized cross-helicity {sigma}{sub c}. The form of the function {phi}({sigma}{sub c}) is derived through a renormalization of the variable {sigma}{sub c} that yields a one parameter family of solutions. The theory derived by Lithwick, Goldreich, and Sridhar (LGS) in 2007 is a special case of the generalized GS theory derived here; however, other generalizations of the GS theory are obtained that have a different cross-helicity dependence than the LGS theory. This new class of solutions and similar generalizations of Boldyrev's theory are investigated to see how the energy cascade rate {epsilon} changes as a function of {sigma}{sub c} when the energy at a given scale is held fixed. The generalization of Boldyrev's theory derived here is applicable to homogeneous MHD turbulence in the solar wind, for example, and can be used to obtain the turbulent dissipation rate {epsilon} from measurements of the energy spectrum and the normalized cross-helicity.

  16. Universality of solar-wind turbulent spectrum from MHD to electron scales.

    PubMed

    Alexandrova, O; Saur, J; Lacombe, C; Mangeney, A; Mitchell, J; Schwartz, S J; Robert, P

    2009-10-16

    To investigate the universality of magnetic turbulence in space plasmas, we analyze seven time periods in the free solar wind under different plasma conditions. Three instruments on Cluster spacecraft operating in different frequency ranges give us the possibility to resolve spectra up to 300 Hz. We show that the spectra form a quasiuniversal spectrum following the Kolmogorov's law approximately k(-5/3) at MHD scales, a approximately k(-2.8) power law at ion scales, and an exponential approximately exp[-sqrt[k(rho)e

  17. Self-similar formation of the Kolmogorov spectrum in the Leith model of turbulence

    NASA Astrophysics Data System (ADS)

    Nazarenko, S. V.; Grebenev, V. N.

    2017-01-01

    The last stage of evolution toward the stationary Kolmogorov spectrum of hydrodynamic turbulence is studied using the Leith model [1]. This evolution is shown to manifest itself as a reflection wave in the wavenumber space propagating from the largest toward the smallest wavenumbers, and is described by a self-similar solution of a new (third) kind. This stage follows the previously studied stage of an initial explosive propagation of the spectral front from the smallest to the largest wavenumbers reaching arbitrarily large wavenumbers in a finite time, and which was described by a self-similar solution of the second kind [2-4]. Nonstationary solutions corresponding to ‘warm cascades’ characterised by a thermalised spectrum at large wavenumbers are also obtained.

  18. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmasa)

    NASA Astrophysics Data System (ADS)

    Lu, Z. X.; Wang, W. X.; Diamond, P. H.; Tynan, G.; Ethier, S.; Gao, C.; Rice, J.

    2015-05-01

    Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear ( s ̂ ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s ̂ . Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s ̂ discharges and that the value of s ̂ c r i t is consistent with the experimental results ŝ c r i t e x p ≈ 0.2 ˜ 0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s ̂ and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s ̂ .

  19. The Energy Spectrum of Energetic Particles Downstream of Turbulent Collisionless Shocks

    NASA Astrophysics Data System (ADS)

    Giacalone, Joe; Neugebauer, Marcia

    2008-01-01

    Using simple analytic considerations, numerical simulations, and data analysis, we discuss the physics of charged-particle acceleration by turbulent, rippled, collisionless shocks. The standard theory of diffusive shock acceleration predicts that the energetic-particle energy spectrum, in the region of shocked plasma, is a function of the plasma density jump. But because of the interaction of the shock with plasma turbulence, the jump in plasma density varies in time and from place to place on the shock front. Here we show that for reasonable parameters, the shape of the energetic-particle energy spectra downstream of any given shock is nearly independent of location along the shock front, even though the density jump varies. This is because energetic particles are mobile and sample many turbulent fluctuations during their acceleration. This result holds for shocks having smaller scale ripples than the large-scale radius of curvature (Dc) of the shock. Thus, it applies to the interpretation of spacecraft observations of traveling interplanetary shocks provided the spacecraft separation is less than Dc. This result is confirmed with simple analytic considerations and numerical simulations that solve the combined magnetohydrodynamic equations for a plasma and energetic test particles using the well-known Parker transport equation. This conclusion is further supported by our analysis of ACE and Geotail observations of a few interplanetary shocks.

  20. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

    SciTech Connect

    Lu, Z. X.; Tynan, G.; Wang, W. X.; Ethier, S.; Diamond, P. H.; Gao, C.; Rice, J.

    2015-05-15

    Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (s{sup ^}) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s{sup ^}. Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s{sup ^} discharges and that the value of s{sup ^}{sub crit} is consistent with the experimental results s{sup ^}{sub crit}{sup exp}≈0.2∼0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s{sup ^} and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s{sup ^}.

  1. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

    SciTech Connect

    Lu, Z. X.; Wang, W. X.; Diamond, P. H.; Tynan, G.; Ethier, S.; Gao, C.; Rice, J.

    2015-05-04

    We report that intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. Here we focus on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (sˆ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak sˆ . Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak sˆ discharges and that the value of sˆ crit is consistent with the experimental results sˆ expcrit [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. In conclusion, the consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive sˆ .

  2. Anisotropy and nonuniversality in scaling laws of the large-scale energy spectrum in rotating turbulence.

    PubMed

    Sen, Amrik; Mininni, Pablo D; Rosenberg, Duane; Pouquet, Annick

    2012-09-01

    Rapidly rotating turbulent flow is characterized by the emergence of columnar structures that are representative of quasi-two-dimensional behavior of the flow. It is known that when energy is injected into the fluid at an intermediate scale Lf, it cascades towards smaller as well as larger scales. In this paper we analyze the flow in the inverse cascade range at a small but fixed Rossby number, Rof≈0.05. Several numerical simulations with helical and nonhelical forcing functions are considered in periodic boxes with unit aspect ratio. In order to resolve the inverse cascade range with reasonably large Reynolds number, the analysis is based on large eddy simulations which include the effect of helicity on eddy viscosity and eddy noise. Thus, we model the small scales and resolve explicitly the large scales. We show that the large-scale energy spectrum has at least two solutions: one that is consistent with Kolmogorov-Kraichnan-Batchelor-Leith phenomenology for the inverse cascade of energy in two-dimensional (2D) turbulence with a ∼k⊥-5/3 scaling, and the other that corresponds to a steeper ∼k⊥-3 spectrum in which the three-dimensional (3D) modes release a substantial fraction of their energy per unit time to the 2D modes. The spectrum that emerges depends on the anisotropy of the forcing function, the former solution prevailing for forcings in which more energy is injected into the 2D modes while the latter prevails for isotropic forcing. In the case of anisotropic forcing, whence the energy goes from the 2D to the 3D modes at low wave numbers, large-scale shear is created, resulting in a time scale τsh, associated with shear, thereby producing a ∼k-1 spectrum for the total energy with the horizontal energy of the 2D modes still following a ∼k⊥-5/3 scaling.

  3. Localization of Dispersive Alfvén Wave in Solar wind plasmas and Turbulent Spectrum

    NASA Astrophysics Data System (ADS)

    Sharma, Swati; Sharma, R. P.

    2016-07-01

    Solar wind turbulence at large inertial scales is well known for decades and believed to consist of Alfvén cascade. The inertial range of Solar wind turbulence can be described by a magnetohydrodynamic model. But at small scales the MHD description is not valid. At scales of the order of proton inertial length, Alfvén cascade excites kinetic Alfvén wave or fast wave or whistler wave that carries wave energy to smaller scales. On the other hand, parallel propagating right(R) and left(L) circularly polarized Alfvén/ ion cyclotron wave in the framework of Hall MHD are also thought to be essential ingredients of the solar wind turbulence. Recently, He et.al[1] have used the magnetic field data from the STEREO spacecraft to calculate the magnetic helicities in the solar wind turbulence and reported the possible existence of Alfvén -cyclotron waves and their coexistence with the right handed polarized fluctuations. In the present article we intend to study the right circularly polarized dispersive Alfvén wave (DAW) and their role in the solar wind turbulence. The inclusion of the Hall term causes the dispersion of the AW which, in the present study, is considered on account of the finite frequency (frequency comparable to ion gyro frequency) of the pump wave. Filamentation instability has been reported to occur for the case of circularly polarized dispersive Alfvén wave (DAW) propagating parallel to ambient magnetic field. In the present study, the instability arises on account of the transverse density perturbations of the acoustic wave that may couple nonlinearly with the Alfvén wave and the driven ponderomotive force sequentially leads to growth of density perturbations. Numerical simulation involves finite difference method for the time domain and pseudo spectral method for the spatial domain. The power spectrum is investigated which shows a steepening for scales larger than the proton inertial length. These findings have been reported by Alexandrova et al

  4. Large-deviation joint statistics of the finite-time Lyapunov spectrum in isotropic turbulence

    SciTech Connect

    Johnson, Perry L. Meneveau, Charles

    2015-08-15

    One of the hallmarks of turbulent flows is the chaotic behavior of fluid particle paths with exponentially growing separation among them while their distance does not exceed the viscous range. The maximal (positive) Lyapunov exponent represents the average strength of the exponential growth rate, while fluctuations in the rate of growth are characterized by the finite-time Lyapunov exponents (FTLEs). In the last decade or so, the notion of Lagrangian coherent structures (which are often computed using FTLEs) has gained attention as a tool for visualizing coherent trajectory patterns in a flow and distinguishing regions of the flow with different mixing properties. A quantitative statistical characterization of FTLEs can be accomplished using the statistical theory of large deviations, based on the so-called Cramér function. To obtain the Cramér function from data, we use both the method based on measuring moments and measuring histograms and introduce a finite-size correction to the histogram-based method. We generalize the existing univariate formalism to the joint distributions of the two FTLEs needed to fully specify the Lyapunov spectrum in 3D flows. The joint Cramér function of turbulence is measured from two direct numerical simulation datasets of isotropic turbulence. Results are compared with joint statistics of FTLEs computed using only the symmetric part of the velocity gradient tensor, as well as with joint statistics of instantaneous strain-rate eigenvalues. When using only the strain contribution of the velocity gradient, the maximal FTLE nearly doubles in magnitude, highlighting the role of rotation in de-correlating the fluid deformations along particle paths. We also extend the large-deviation theory to study the statistics of the ratio of FTLEs. The most likely ratio of the FTLEs λ{sub 1} : λ{sub 2} : λ{sub 3} is shown to be about 4:1:−5, compared to about 8:3:−11 when using only the strain-rate tensor for calculating fluid volume

  5. Large-deviation joint statistics of the finite-time Lyapunov spectrum in isotropic turbulence

    NASA Astrophysics Data System (ADS)

    Johnson, Perry L.; Meneveau, Charles

    2015-08-01

    One of the hallmarks of turbulent flows is the chaotic behavior of fluid particle paths with exponentially growing separation among them while their distance does not exceed the viscous range. The maximal (positive) Lyapunov exponent represents the average strength of the exponential growth rate, while fluctuations in the rate of growth are characterized by the finite-time Lyapunov exponents (FTLEs). In the last decade or so, the notion of Lagrangian coherent structures (which are often computed using FTLEs) has gained attention as a tool for visualizing coherent trajectory patterns in a flow and distinguishing regions of the flow with different mixing properties. A quantitative statistical characterization of FTLEs can be accomplished using the statistical theory of large deviations, based on the so-called Cramér function. To obtain the Cramér function from data, we use both the method based on measuring moments and measuring histograms and introduce a finite-size correction to the histogram-based method. We generalize the existing univariate formalism to the joint distributions of the two FTLEs needed to fully specify the Lyapunov spectrum in 3D flows. The joint Cramér function of turbulence is measured from two direct numerical simulation datasets of isotropic turbulence. Results are compared with joint statistics of FTLEs computed using only the symmetric part of the velocity gradient tensor, as well as with joint statistics of instantaneous strain-rate eigenvalues. When using only the strain contribution of the velocity gradient, the maximal FTLE nearly doubles in magnitude, highlighting the role of rotation in de-correlating the fluid deformations along particle paths. We also extend the large-deviation theory to study the statistics of the ratio of FTLEs. The most likely ratio of the FTLEs λ1 : λ2 : λ3 is shown to be about 4:1:-5, compared to about 8:3:-11 when using only the strain-rate tensor for calculating fluid volume deformations. The results

  6. Energy spectrum in high-resolution direct numerical simulations of turbulence

    NASA Astrophysics Data System (ADS)

    Ishihara, Takashi; Morishita, Koji; Yokokawa, Mitsuo; Uno, Atsuya; Kaneda, Yukio

    2016-12-01

    A study is made about the energy spectrum E (k ) of turbulence on the basis of high-resolution direct numerical simulations (DNSs) of forced incompressible turbulence in a periodic box using a Fourier spectral method with the number of grid points and the Taylor scale Reynolds number Rλ up to 12 2883 and approximately 2300, respectively. The DNS data show that there is a wave-number range (approximately 5 ×10-3 2 /3k-5 /3] =c (kL ) m , where <ɛ > is the mean energy dissipation rate per unit mass; L is the integral length scale; and m ≈-0.12 . The coefficient c is independent of k , but has a Rλ dependence, such as c =C Rλζ , where C ≈0.9 and ζ ≈0.14 .

  7. Temporal power spectrum of irradiance fluctuations for a Gaussian-beam wave propagating through non-Kolmogorov turbulence.

    PubMed

    Tan, Liying; Zhai, Chao; Yu, Siyuan; Ma, Jing; Lu, Gaoyuan

    2015-05-04

    In the past decades, both the increasing experimental evidence and some results of theoretical investigation on non-Kolmogorov turbulence have been reported. This has prompted the study of optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, based on the thin phase screen model and a non-Kolmogorov power spectrum which owns a generalized power law instead of standard Kolmogorov power law value 11/3 and a generalized amplitude factor instead of constant value 0.033, the temporal power spectrum of irradiance fluctuations for a Gaussian-beam wave is derived in the weak fluctuation regime for a horizontal path. The analytic expressions are obtained and then used to analyze the influence of spectral power law variations on the temporal power spectrum of irradiance fluctuations.

  8. Turbulence

    NASA Astrophysics Data System (ADS)

    Frisch, Uriel

    1996-01-01

    Written five centuries after the first studies of Leonardo da Vinci and half a century after A.N. Kolmogorov's first attempt to predict the properties of flow, this textbook presents a modern account of turbulence, one of the greatest challenges in physics. "Fully developed turbulence" is ubiquitous in both cosmic and natural environments, in engineering applications and in everyday life. Elementary presentations of dynamical systems ideas, probabilistic methods (including the theory of large deviations) and fractal geometry make this a self-contained textbook. This is the first book on turbulence to use modern ideas from chaos and symmetry breaking. The book will appeal to first-year graduate students in mathematics, physics, astrophysics, geosciences and engineering, as well as professional scientists and engineers.

  9. Comparison of techniques to measure the low wavenumber wall pressure spectrum of a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Martini, K. F.; Leehey, P.; Moeller, M.

    1984-08-01

    The agreement between low wavenumber measurements of the turbulent wall pressure spectrum by various investigators has not been too good. Different techniques have been used in different facilities and have yielded data in different nondimensional frequency and wavenumber ranges. The current measurement program has utilized the wavenumber filtering techniques used by three primary investigators, the Martin plate, the Jameson plate and the Farabee and Geib 6-element microphone array in the same facility. Also a 12-element collinear and stagger array and a lateral array were used. The agreement between the different techniques in the M.I.T. facility is generally good. In addition, the difference of results between facilities has been reduced by displaying the data in a non-dimensional form that does not include the effect of boundary layer thickness. However, there was still a significant scatter in the data for each technique. Scatter is believed to be due to variation of each filter's wavenumber response away from the main acceptance lobe where the filter is responding to the acoustic and convective contamination and also the variation of the contamination with flow speed.

  10. Weak turbulant theory estimation for non-linear energy, wave action and momentum fluxes in wind wave spectrum

    NASA Astrophysics Data System (ADS)

    Lavrenov, I.

    2003-04-01

    Direct numerical simulations of the Hasselmann kinetic equation for gravity waves in water surface confirms basic predictions of the weak-turbulent theory. Three different stages can be defined in the wave spectrum evolution.. At the first stage the spectrum unstable growth is observed within the range of the external force input. High frequency spectrum development is observed at the second stage of spectrum evolution. The frequency spectrum is becoming larger within high frequency range and a spectral growth is penetrated to a larger frequency range. After that the spectrum remains almost constant at high frequency range. In both isotropic and non-isotropic cases the spectra are found out to be close to the Zakharov-Filonenko spectrum pow(w,-4) not only in the universal range, but in the range of wave energy input. Formation of this asymptotic spectrum happens explosively. The third stage of spectrum evolution is revealed for a larger time period. It is characterized by a slow spectrum evolution into a low frequency range. The spectrum value becomes larger penetrating to a smaller frequency range with decreasing speed in accordance with experimental data. In low frequency range a power spectrum is revealed for both isotropic and non-isotropic cases with the spectra close to the Zakharov-Zaslavskii spectrum pow(w,-11/3). Main energy flux is directed to the high frequency range. Its value makes up 77 per cent of total value of wave energy input coming from external source. Main wave action flux is directed to low frequency range. Its relative value is equal to 75 per cents of total wave action flux input. 25 per cents of wave action is directed to high frequency range. Almost all wave momentum (up to 98 per cents) is directed to high frequency range. The investigations are supported by the Grants: RFBR 01-05-64846, and INTAS-(99)-666, INTAS - (01)-234, INTAS-(01)-2156.

  11. SENSITIVITY OF COSMIC-RAY PROTON SPECTRA TO THE LOW-WAVENUMBER BEHAVIOR OF THE 2D TURBULENCE POWER SPECTRUM

    SciTech Connect

    Engelbrecht, N. E.; Burger, R. A.

    2015-12-01

    In this study, a novel ab initio cosmic ray (CR) modulation code that solves a set of stochastic transport equations equivalent to the Parker transport equation, and that uses output from a turbulence transport code as input for the diffusion tensor, is introduced. This code is benchmarked with a previous approach to ab initio modulation. The sensitivity of computed galactic CR proton spectra at Earth to assumptions made as to the low-wavenumber behavior of the two-dimensional (2D) turbulence power spectrum is investigated using perpendicular mean free path expressions derived from two different scattering theories. Constraints on the low-wavenumber behavior of the 2D power spectrum are inferred from the qualitative comparison of computed CR spectra with spacecraft observations at Earth. Another key difference from previous studies is that observed and inferred CR intensity spectra at 73 AU are used as boundary spectra instead of the usual local interstellar spectrum. Furthermore, the results presented here provide a tentative explanation as to the reason behind the unusually high galactic proton intensity spectra observed in 2009 during the recent unusual solar minimum.

  12. Density fluctuation spectrum of solar wind turbulence between ion and electron scales.

    PubMed

    Chen, C H K; Salem, C S; Bonnell, J W; Mozer, F S; Bale, S D

    2012-07-20

    We present a measurement of the spectral index of density fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1 AU was found to be -2.75±0.06, steeper than predictions for pure whistler or kinetic Alfvén wave turbulence but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.

  13. Two-time correlation of heat release rate and spectrum of combustion noise from turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Liu, Yu

    2015-09-01

    The spectral characteristics of combustion noise are dictated by the temporal correlation of the overall change of heat release rate fluctuations which has not received sufficient attention in prior studies. In this work, the two-time correlation of the volumetric heat release rate fluctuations within the flame brush and its role in modeling combustion noise spectrum are investigated by analyzing direct numerical simulation (DNS) data of turbulent premixed V-flames. This two-time correlation can be well represented by Gaussian-type functions and it captures the slow global variation of the fluctuating heat release rate and hence the low-frequency noise sources of unsteady combustion. The resulting correlation model is applied to predict the far-field noise spectrum from test open flames, and different reference time scales are used to scale this correlation from the DNS data to the test flames. The comparison between predictions and measurements indicates that the correlation models of all reference time scales are capable of reproducing the essential spectral shape including the low- and high-frequency dependencies. Reasonable agreement in the peak frequency, peak sound pressure level, and the Strouhal number scaling of peak frequency is also achieved for two turbulent time scales. A promising convective time scale shows great potential for characterizing the spectral features, yet its predictive capabilities are to be further verified through a longer DNS signal of a bounded flame configuration.

  14. Turbulent cosmic ray reacceleration and the curved radio spectrum of the radio relic in the Sausage Cluster

    NASA Astrophysics Data System (ADS)

    Fujita, Yutaka; Akamatsu, Hiroki; Kimura, Shigeo S.

    2016-06-01

    It has often been thought that the northern radio relic in the galaxy cluster CIZA J2242.8+5301 (the "Sausage" Cluster) is associated with cosmic ray (CR) electrons that are accelerated at a shock through the diffusive shock acceleration (DSA) mechanism. However, recent radio observations have shown that the radio spectrum is curved, which is inconsistent with the prediction of a simple DSA model. Moreover, the CR electron spectrum before being affected by radiative cooling seems to be too hard for DSA. In this study, we show that these facts are natural consequences if the electrons are reaccelerated in turbulence downstream of the shock. In this model, DSA is not the main mechanism for generating high-energy electrons. We find that the mean free path of the electrons should be much shorter than the Coulomb mean free path for efficient reacceleration. The scale of the turbulent eddies must be smaller than the width of the relic. We also predict hard X-ray spectra of inverse Compton scattering of photons.

  15. Localization of finite frequency inertial Alfvén wave and turbulent spectrum in low beta plasmas

    NASA Astrophysics Data System (ADS)

    Rinawa, M. L.; Sharma, R. P.; Modi, K. V.

    2015-05-01

    In the present paper, we have investigated nonlinear interaction of inertial Alfvén wave with ion acoustic wave, for low β-plasma ( β≪ m e / m i ) where β is the thermal to magnetic pressure ratio. We have developed the dynamical equation of inertial Alfvén wave by considering the finite frequency as well as finite ion temperature correction. The dynamical equation of ion acoustic wave, propagating at an angle with respect to the background magnetic field, in the presence of ponderomotive nonlinearity due to inertial Alfvén wave is also derived. Numerical simulation has been carried out to study the effect of nonlinear coupling between these waves which results in the formation of localized structures and turbulent spectrum, applicable to auroral region. The result reveals that the localized structures become complex and intense in nature (quasi-steady state). Further, we have studied the turbulent spectrum which follows spectral index (˜ k -4.46) at smaller scales. Relevance of the obtained results has been shown with the observations reported by various spacecrafts like Hawkeye and HEOS-2 (Highly Eccentric Orbiting Satellite-2).

  16. Frequency-wavenumber spectrum of the free surface of shallow turbulent flows over a rough boundary

    NASA Astrophysics Data System (ADS)

    Dolcetti, G.; Horoshenkov, K. V.; Krynkin, A.; Tait, S. J.

    2016-10-01

    Data on the frequency-wavenumber spectra and dispersion relation of the dynamic water surface in an open channel flow are very scarce. In this work, new data on the frequency-wavenumber spectra were obtained in a rectangular laboratory flume with a rough bottom boundary, over a range of subcritical Froude numbers. These data were used to study the dispersion relation of the surface waves in such shallow turbulent water flows. The results show a complex pattern of surface waves, with a range of scales and velocities. When the mean surface velocity is faster than the minimum phase velocity of gravity-capillary waves, the wave pattern is dominated by stationary waves that interact with the static rough bed. There is a coherent three-dimensional pattern of radially propagating waves with the wavelength approximately equal to the wavelength of the stationary waves. Alongside these waves, there are freely propagating gravity-capillary waves that propagate mainly parallel to the mean flow, both upstream and downstream. In the flow conditions where the mean surface velocity is slower than the minimum phase velocity of gravity-capillary waves, patterns of non-dispersive waves are observed. It is suggested that these waves are forced by turbulence. The results demonstrate that the free surface carries information about the underlying turbulent flow. The knowledge obtained in this study paves the way for the development of novel airborne methods of non-invasive flow monitoring.

  17. Transition from geostrophic turbulence to inertia–gravity waves in the atmospheric energy spectrum

    PubMed Central

    Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver

    2014-01-01

    Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth’s rotation and the atmosphere’s stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia–gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia–gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia–gravity waves dominate at scales smaller than 500 km. PMID:25404349

  18. Quenching the X-ray spectrum of hot halos with AGN outflows and turbulence

    NASA Astrophysics Data System (ADS)

    Gaspari, M.

    2016-06-01

    I highlight recent advancements in the astrophysics of AGN outflow feedback and diffuse hot gas. Thanks to XMM RGS resolution, we know that the X-ray cores of clusters, groups, and massive galaxies have a strong deficit of soft X-ray emission compared with the classic cooling flow prediction: dL_{x}/dT ∝ (T/T_{hot})^{2±1}. Using 3D hydrodynamic simulations, I show that such deficit arises from the tight self-regulation between thermal instability condensation and AGN outflow feedback. Multiphase filaments condense out of the hot plasma, they rain onto the central SMBH, and boost the AGN outflows via chaotic cold accretion. The sub-relativistic outflows thermalize in the core via shocks and turbulence, releasing more heat in the inner cooler phase, thus inducing the observed soft X-ray decline. I discuss how we can leverage XMM capabilities in the next decade by probing turbulence, conduction, AGN accretion and outflows via the information contained in X-ray spectra and surface brightness. I focus on the importance of selecting a few objects with Ms exposure and how we can unveil multiphase halos through the synergy between simulations and multiwavelength observations.

  19. Solar-cycle dependence of a model turbulence spectrum using IMP and ACE observations over 38 years

    NASA Astrophysics Data System (ADS)

    Burger, R. A.; Nel, A. E.; Engelbrecht, N. E.

    2014-12-01

    Ab initio modulation models require a number of turbulence quantities as input for any reasonable diffusion tensor. While turbulence transport models describe the radial evolution of such quantities, they in turn require observations in the inner heliosphere as input values. So far we have concentrated on solar minimum conditions (e.g. Engelbrecht and Burger 2013, ApJ), but are now looking at long-term modulation which requires turbulence data over at a least a solar magnetic cycle. As a start we analyzed 1-minute resolution data for the N-component of the magnetic field, from 1974 to 2012, covering about two solar magnetic cycles (initially using IMP and then ACE data). We assume a very simple three-stage power-law frequency spectrum, calculate the integral from the highest to the lowest frequency, and fit it to variances calculated with lags from 5 minutes to 80 hours. From the fit we then obtain not only the asymptotic variance at large lags, but also the spectral index of the inertial and the energy, as well as the breakpoint between the inertial and energy range (bendover scale) and between the energy and cutoff range (cutoff scale). All values given here are preliminary. The cutoff range is a constraint imposed in order to ensure a finite energy density; the spectrum is forced to be either flat or to decrease with decreasing frequency in this range. Given that cosmic rays sample magnetic fluctuations over long periods in their transport through the heliosphere, we average the spectra over at least 27 days. We find that the variance of the N-component has a clear solar cycle dependence, with smaller values (~6 nT2) during solar minimum and larger during solar maximum periods (~17 nT2), well correlated with the magnetic field magnitude (e.g. Smith et al. 2006, ApJ). Whereas the inertial range spectral index (-1.65 ± 0.06) does not show a significant solar cycle variation, the energy range index (-1.1 ± 0.3) seems to be anti-correlated with the variance

  20. FRAME DEPENDENCE OF THE ELECTRIC FIELD SPECTRUM OF SOLAR WIND TURBULENCE

    SciTech Connect

    Chen, C. H. K.; Bale, S. D.; Salem, C.; Mozer, F. S.

    2011-08-20

    We present the first survey of electric field data using the ARTEMIS spacecraft in the solar wind to study inertial range turbulence. It was found that the average perpendicular spectral index of the electric field depends on the frame of measurement. In the spacecraft frame it is -5/3, which matches the magnetic field due to the large solar wind speed in Lorentz transformation. In the mean solar wind frame, the electric field is primarily due to the perpendicular velocity fluctuations and has a spectral index slightly shallower than -3/2, which is close to the scaling of the velocity. These results are an independent confirmation of the difference in scaling between the velocity and magnetic field, which is not currently well understood. The spectral index of the compressive fluctuations was also measured and found to be close to -5/3, suggesting that they are not only passive to the velocity but may also interact nonlinearly with the magnetic field.

  1. Universal Spectrum of Two-Dimensional Turbulence on a Rotating Sphere and Some Basic Features of Atmospheric Circulation on Giant Planets

    NASA Astrophysics Data System (ADS)

    Sukoriansky, Semion; Galperin, Boris; Dikovskaya, Nadejda

    2002-08-01

    The Kolmogorov-Batchelor-Kraichnan (KBK) theory of two-dimensional turbulence is generalized for turbulence on the surface of a rotating sphere. The energy spectrum develops considerable anisotropy; a steep -5 slope emerges in the zonal direction, while in all others the classical KBK scaling prevails. This flow regime in robust steady state is reproduced in simulations with linear drag. The conditions favorable for this regime may be common for giant planets' atmospheric circulations; the same steep spectra are found in their observed zonal velocity profiles and utilized to explain their basic characteristics.

  2. Experimental study on spectrum and multi-scale nature of wall pressure and velocity in turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Zheng, Xiao-Bo; Jiang, Nan

    2015-06-01

    When using a miniature single sensor boundary layer probe, the time sequences of the stream-wise velocity in the turbulent boundary layer (TBL) are measured by using a hot wire anemometer. Beneath the fully developed TBL, the wall pressure fluctuations are attained by a microphone mechanism with high spatial resolution. Analysis on the statistic and spectrum properties of velocity and wall pressure reveals the relationship between the wall pressure fluctuation and the energy-containing structure in the buffer layer of the TBL. Wavelet transform shows the multi-scale natures of coherent structures contained in both signals of velocity and pressure. The most intermittent wall pressure scale is associated with the coherent structure in the buffer layer. Meanwhile the most energetic scale of velocity fluctuation at y+ = 14 provides a specific frequency f9 ≈ 147 Hz for wall actuating control with Reτ = 996. Project supported by the National Basic Research Program of China (Grant Nos. 2012CB720101 and 2012CB720103) and the National Natural Science Foundation of China (Grant Nos. 11272233, 11332006, and 11411130150).

  3. Quantum Turbulence

    NASA Astrophysics Data System (ADS)

    Tsubota, Makoto

    2008-11-01

    The present article reviews the recent developments in the physics of quantum turbulence. Quantum turbulence (QT) was discovered in superfluid 4He in the 1950s, and the research has tended toward a new direction since the mid 90s. The similarities and differences between quantum and classical turbulence have become an important area of research. QT is comprised of quantized vortices that are definite topological defects, being expected to yield a model of turbulence that is much simpler than the classical model. The general introduction of the issue and a brief review on classical turbulence are followed by a description of the dynamics of quantized vortices. Then, we discuss the energy spectrum of QT at very low temperatures. At low wavenumbers, the energy is transferred through the Richardson cascade of quantized vortices, and the spectrum obeys the Kolmogorov law, which is the most important statistical law in turbulence; this classical region shows the similarity to conventional turbulence. At higher wavenumbers, the energy is transferred by the Kelvin-wave cascade on each vortex. This quantum regime depends strongly on the nature of each quantized vortex. The possible dissipation mechanism is discussed. Finally, important new experimental studies, which include investigations into temperature-dependent transition to QT, dissipation at very low temperatures, QT created by vibrating structures, and visualization of QT, are reviewed. The present article concludes with a brief look at QT in atomic Bose-Einstein condensates.

  4. Arbitrary Metrics in Psychology

    ERIC Educational Resources Information Center

    Blanton, Hart; Jaccard, James

    2006-01-01

    Many psychological tests have arbitrary metrics but are appropriate for testing psychological theories. Metric arbitrariness is a concern, however, when researchers wish to draw inferences about the true, absolute standing of a group or individual on the latent psychological dimension being measured. The authors illustrate this in the context of 2…

  5. Wave turbulence

    NASA Astrophysics Data System (ADS)

    Nazarenko, Sergey

    2015-07-01

    Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.

  6. Study of one-dimensional spectral dynamic equations of the Reynolds stresses in homogeneous anisotropic turbulence: Application to split-spectrum modeling

    NASA Technical Reports Server (NTRS)

    Schiestel, R.

    1987-01-01

    The CTR numerical data base generated by direct simulation of homogeneous anisotropic turbulence was used to calculate all of the terms in the spectral balance equations for the turbulent Reynolds stresses. The aim in not only to test the main closure assumptions used in the split-spectrum models, but also to try to devise improved hypotheses deduced from the statistical information. Numerical simulations of turbulent flows provide a large amount of data, a thought provoking wealth of information. The main advantage of this type of comparison is that a great variety of flows can be considered, and this is necessary to test closure hypotheses. Moreover various initial conditions can be introduced in the calculation, even if they are not experimentally feasible. All the terms in the spectral equations can be calculated. The limited Reynolds numbers of the simulations and the statistical noise caused by a small sample, particularly at the large scales, causes some difficulty in the interpretation of the results, but the method of approach proved to be a powerful tool for testing and improving spectral closures.

  7. On the decay of homogeneous isotropic turbulence

    NASA Astrophysics Data System (ADS)

    Skrbek, L.; Stalp, Steven R.

    2000-08-01

    Decaying homogeneous, isotropic turbulence is investigated using a phenomenological model based on the three-dimensional turbulent energy spectra. We generalize the approach first used by Comte-Bellot and Corrsin [J. Fluid Mech. 25, 657 (1966)] and revised by Saffman [J. Fluid Mech. 27, 581 (1967); Phys. Fluids 10, 1349 (1967)]. At small wave numbers we assume the spectral energy is proportional to the wave number to an arbitrary power. The specific case of power 2, which follows from the Saffman invariant, is discussed in detail and is later shown to best describe experimental data. For the spectral energy density in the inertial range we apply both the Kolmogorov -5/3 law, E(k)=Cɛ2/3k-5/3, and the refined Kolmogorov law by taking into account intermittency. We show that intermittency affects the energy decay mainly by shifting the position of the virtual origin rather than altering the power law of the energy decay. Additionally, the spectrum is naturally truncated due to the size of the wind tunnel test section, as eddies larger than the physical size of the system cannot exist. We discuss effects associated with the energy-containing length scale saturating at the size of the test section and predict a change in the power law decay of both energy and vorticity. To incorporate viscous corrections to the model, we truncate the spectrum at an effective Kolmogorov wave number kη=γ(ɛ/v3)1/4, where γ is a dimensionless parameter of order unity. We show that as the turbulence decays, viscous corrections gradually become more important and a simple power law can no longer describe the decay. We discuss the final period of decay within the framework of our model, and show that care must be taken to distinguish between the final period of decay and the change of the character of decay due to the saturation of the energy containing length scale. The model is applied to a number of experiments on decaying turbulence. These include the downstream decay of turbulence in

  8. Ocean Turbulence. Part 4; Mesoscale Modeling in Isopycnal Coordinates the role of the Spectrum of Vertical Shear

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Dubovikov, M. S.

    1999-01-01

    We study the tracer subgrid term in isopycnal coordinates, S(sub I). We employ two ingredients: the experimental data on vertical spectra of ocean turbulence measured by Gargett et al.(1981) and the stochastic approach recently developed by Dukowicz and Smith (1997). Our result confirms that S(sub I) is made of two parts: an advection and a diffusion term. However, the tracer bolus velocity u** consists of two terms u** = u(sub 1) + u(sub 2) while in the GM model there is only a term related to u(sub 1) which is shown to be: u(sub 1) = k(bar-q)(sup -1)(delta)(sub rho) where bar-q is the thickness weighted average potential vorticity, a result in agreement with the recent suggestions by Treguier et al. (1997), Lee et al. (1997) and Greatbatch (1998). The second component u(sub 2) IS new. We compute it in the geostrophic approximation using the Gargett et al. data (1981) on ocean vertical turbulence. We find that u(sub 2) much greater than u(sub 1) and that u(sub 2) is orthogonal to u(sub 1).

  9. A Simple Theory of Capillary-Gravity Wave Turbulence

    NASA Technical Reports Server (NTRS)

    Glazman, Roman E.

    1995-01-01

    Employing a recently proposed 'multi-wave interaction' theory, inertial spectra of capillary gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The absence of scale invariance makes this and some other problems of wave turbulence (e.g., nonlinear inertia gravity waves) intractable by small-perturbation techniques, even in the weak-turbulence limit. The analytical solution obtained in the present work for an arbitrary degree of nonlinearity is shown to be in reasonable agreement with experimental data. The theory explains the dependence of the wave spectrum on wind input and describes the accelerated roll-off of the spectral density function in the narrow sub-range separating scale-invariant regimes of purely gravity and capillary waves, while the appropriate (long- and short-wave) limits yield power laws corresponding to the Zakharov-Filonenko and Phillips spectra.

  10. Radio wave scattering observations of the solar corona First-order measurements of expansion velocity and turbulence spectrum using Viking and Mariner 10 spacecraft

    NASA Technical Reports Server (NTRS)

    Tyler, G. L.; Vesecky, J. F.; Plume, M. A.; Howard, H. T.; Barnes, A.

    1981-01-01

    Radio wave scattering data were collected at 3.6 and 13 cm wavelengths by means of the radio link between the Viking orbiters and the earth during the Nov. 25, 1976 solar conjunction of Mars, which occurred near the beginning of solar cycle 21; Mariner 10 solar activity observations during 1974 are also used. It is found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma, and the spectral index of electron density turbulence is obtained. The measurements of solar wind velocity and spectral index cover 78 days for Viking and 49 days for Mariner 10 and show the combined effects of changing heliocentric distance, solar latitude, and solar longitude as well as solar activity. It is concluded that the observational velocity profile differs significantly from the theoretical profiles in two ways: (1) the theoretical profile does not show the abrupt change in velocity at about 15 solar radii, and (2) the observational profile shows acceleration at larger radial distances than the model profiles. The observational profiles indicate velocities of less than about 150 km/sec out to 15 solar radii.

  11. How arbitrary is language?

    PubMed Central

    Monaghan, Padraic; Shillcock, Richard C.; Christiansen, Morten H.; Kirby, Simon

    2014-01-01

    It is a long established convention that the relationship between sounds and meanings of words is essentially arbitrary—typically the sound of a word gives no hint of its meaning. However, there are numerous reported instances of systematic sound–meaning mappings in language, and this systematicity has been claimed to be important for early language development. In a large-scale corpus analysis of English, we show that sound–meaning mappings are more systematic than would be expected by chance. Furthermore, this systematicity is more pronounced for words involved in the early stages of language acquisition and reduces in later vocabulary development. We propose that the vocabulary is structured to enable systematicity in early language learning to promote language acquisition, while also incorporating arbitrariness for later language in order to facilitate communicative expressivity and efficiency. PMID:25092667

  12. Numerical Simulation of Turbulent Fluid Flows

    NASA Technical Reports Server (NTRS)

    Leonard, A.

    1983-01-01

    Numerical simulation of turbulent flows is discussed. Computational requirements for the direct simulaton of turbulence, simulation of arbitrary homogeneous flows, an expansion technique for wall bounded flows with application to pipe flow, and possibilities of flow representations or modeling techniques that allow the simulation of high Reynolds number flows with a relatively small number of dependent variables are included.

  13. Turbulence in quantum fluids

    NASA Astrophysics Data System (ADS)

    Tsubota, Makoto

    2014-02-01

    This paper reviews briefly the recent important developments in the physics of quantum turbulence (QT) in superfluid helium and atomic Bose-Einstein condensates (BECs). After giving the basics of quantum hydrodynamics, we discuss energy spectrum, QT created by vibrating structures, and visualization among the topics on superfluid helium. For atomic BECs we review three-dimensional QT, two-component BECs, and spin turbulence in spinor BECs. The last part is devoted to some perspectives of this issue.

  14. Turbulent mix experiments and simulations

    SciTech Connect

    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.

  15. A Simple Arbitrary Solid Slicer

    SciTech Connect

    Yao, J

    2005-06-23

    The intersection of a given plane and an arbitrary (possibly non-convex, with multiple connectivities) meshed solid is exactly expressed by a set of planar cross-sections. A rule for marching on the edges of an arbitrary polyhedron is set for obtaining the topology of the cross-section. The method neither seeks triangulation of the surface mesh nor utilizes look-up tables, therefore it has optimal efficiency.

  16. Phenomenology of turbulent convection

    NASA Astrophysics Data System (ADS)

    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.

  17. Galaxy formation from annihilation-generated supersonic turbulence in the baryon-symmetric big-bang cosmology and the gamma ray background spectrum

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Puget, J. L.

    1972-01-01

    Following the big-bang baryon symmetric cosmology of Omnes, the redshift was calculated to be on the order of 500-600. It is show that, at these redshifts, annihilation pressure at the boundaries between regions of matter and antimatter drives large scale supersonic turbulence which can trigger galaxy formation. This picture is consistent with the gamma-ray background observations discussed previously. Gravitational binding of galaxies then occurs at a redshift of about 70, at which time vortical turbulent velocities of about 3 x 10 to the 7th power cm/s lead to angular momenta for galaxies comparable with measured values.

  18. Turbulence of swarming sperm

    NASA Astrophysics Data System (ADS)

    Creppy, Adama; Praud, Olivier; Druart, Xavier; Kohnke, Philippa L.; Plouraboué, Franck

    2015-09-01

    Collective motion of self-sustained swarming flows has recently provided examples of small-scale turbulence arising where viscous effects are dominant. We report the first observation of universal enstrophy cascade in concentrated swarming sperm consistent with a body of evidence built from various independent measurements. We found a well-defined k-3 power-law decay of a velocity field power spectrum and relative dispersion of small beads consistent with theoretical predictions in 2D turbulence. Concentrated living sperm displays long-range, correlated whirlpool structures of a size that provides an integral scale of turbulence. We propose a consistent explanation for this quasi-2D turbulence based on self-structured laminated flow forced by steric interactions and alignment, a state of active matter that we call "swarming liquid crystal." We develop scaling arguments consistent with this interpretation.

  19. Single-wave-number representation of nonlinear energy spectrum in elastic-wave turbulence of the Föppl-von Kármán equation: energy decomposition analysis and energy budget.

    PubMed

    Yokoyama, Naoto; Takaoka, Masanori

    2014-12-01

    A single-wave-number representation of a nonlinear energy spectrum, i.e., a stretching-energy spectrum, is found in elastic-wave turbulence governed by the Föppl-von Kármán (FvK) equation. The representation enables energy decomposition analysis in the wave-number space and analytical expressions of detailed energy budgets in the nonlinear interactions. We numerically solved the FvK equation and observed the following facts. Kinetic energy and bending energy are comparable with each other at large wave numbers as the weak turbulence theory suggests. On the other hand, stretching energy is larger than the bending energy at small wave numbers, i.e., the nonlinearity is relatively strong. The strong correlation between a mode a(k) and its companion mode a(-k) is observed at the small wave numbers. The energy is input into the wave field through stretching-energy transfer at the small wave numbers, and dissipated through the quartic part of kinetic-energy transfer at the large wave numbers. Total-energy flux consistent with energy conservation is calculated directly by using the analytical expression of the total-energy transfer, and the forward energy cascade is observed clearly.

  20. Dissipation in unsteady turbulence

    NASA Astrophysics Data System (ADS)

    Bos, Wouter J. T.; Rubinstein, Robert

    2017-02-01

    Recent experiments and simulations have shown that unsteady turbulent flows display a universal behavior at short and intermediate times, different from classical scaling relations. The origin of these observations is explained using a nonequilibrium correction to Kolmogorov's energy spectrum, and the exact form of the observed universal scaling is derived.

  1. Critical exponents of Nikolaevskii turbulence

    NASA Astrophysics Data System (ADS)

    Tanaka, Dan

    2005-02-01

    We study the spatial power spectra of Nikolaevskii turbulence in one-dimensional space. First, we show that the energy distribution in wave-number space is extensive in nature. Then, we demonstrate that, when varying a particular parameter, the spectrum becomes qualitatively indistinguishable from that of Kuramoto-Sivashinsky turbulence. Next, we derive the critical exponents of turbulent fluctuations. Finally, we argue that in some previous studies, parameter values for which this type of turbulence does not appear were mistakenly considered, and we resolve inconsistencies obtained in previous studies.

  2. Computation of turbulent near wake for asymmetric airfoils

    NASA Technical Reports Server (NTRS)

    Deiwert, G. S.

    1979-01-01

    A numerical procedure for studying the turbulent near wake of two dimensional airfoil sections is presented. The Reynolds Navier-Stokes equations were written for flow about bodies of arbitrary geometry and solved on an arbitrary nonuniform curvilinear computational mesh. Eddy viscosity and Reynolds stress turbulence transport models are considered. Specific examples are shown for airfoil section by using an algebraic viscosity model with streamwise relaxation and the interactive Reynolds stress model.

  3. Arbitrary shape surface Fresnel diffraction.

    PubMed

    Shimobaba, Tomoyoshi; Masuda, Nobuyuki; Ito, Tomoyoshi

    2012-04-09

    Fresnel diffraction calculation on an arbitrary shape surface is proposed. This method is capable of calculating Fresnel diffraction from a source surface with an arbitrary shape to a planar destination surface. Although such calculation can be readily calculated by the direct integral of a diffraction calculation, the calculation cost is proportional to O(N²) in one dimensional or O(N⁴) in two dimensional cases, where N is the number of sampling points. However, the calculation cost of the proposed method is O(N log N) in one dimensional or O(N² log N) in two dimensional cases using non-uniform fast Fourier transform.

  4. Multiple-scale turbulence modeling of free turbulent flows

    NASA Technical Reports Server (NTRS)

    Fabris, G.; Harsha, P. T.

    1981-01-01

    As part of an investigation into the application of turbulence models to the computation of flows in advanced scramjet combustors, the multiple-scale turbulence model has been applied to a variety of flowfield predictions. The model appears to have a potential for improved predictions in a variety of areas relevant to combustor problems. This potential exists because of the partition of the turbulence energy spectrum that is the major feature of the model and which allows the turbulence energy dissipation rate to be out of phase with turbulent energy production. To establish the general reliability of the approach, it has been tested through comparison of predictions with experimental data. An appreciable overall improvement in the generality of the predictions is observed, as compared to those of the basic two-equation turbulence model. A Mach number-related correction is found to be necessary to satisfactorily predict the spreading rate of the supersonic jet and mixing layer.

  5. Representing Arbitrary Boosts for Undergraduates.

    ERIC Educational Resources Information Center

    Frahm, Charles P.

    1979-01-01

    Presented is a derivation for the matrix representation of an arbitrary boost, a Lorentz transformation without rotation, suitable for undergraduate students with modest backgrounds in mathematics and relativity. The derivation uses standard vector and matrix techniques along with the well-known form for a special Lorentz transformation. (BT)

  6. Kinematic dynamo theory for an arbitrary mean flow

    NASA Astrophysics Data System (ADS)

    Hoyng, P.

    1984-11-01

    Arbitrary, incompressible mean flow (vo) in kinematic dynamo theory is analyzed via stochastic differential equations. When the first order smoothing approximation is made the only effect of a nonzero vo is that in the definition of the tensors the turbulent velocity v is replaced by the effect of passive advection by vo. Dynamo action depends only on velocity correlations measured in a frame comoving with and distorted by the mean flow through passive advection. Conclusions apply when the analysis is extended to arbitrary order, relevant for a long correlation time. The result admits straightforward evaluation for given model mean flows. The shear in vo causes a (kinematic) anisotropy in the tensors. This can be a large effect, which comes on top of the intrinsic (dynamical) anisotropy in the velocity correlation functions. Conditions for applicability are very large magnetic Reynolds number; incompressible flows; stationary vo; and correlation time period of the dynamo.

  7. Physical interpretation of the angle-dependent magnetic helicity spectrum in the solar wind: The nature of turbulent fluctuations near the proton gyroradius scale

    SciTech Connect

    Klein, Kristopher G.; Howes, Gregory G.; TenBarge, Jason M.; Podesta, John J.

    2014-04-20

    Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.

  8. Emission of sound from turbulence convected by a parallel flow in the presence of solid boundaries

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Rosenbaum, B. M.

    1973-01-01

    A theoretical description is given of the sound emitted from an arbitrary point in a parallel or nearly parallel turbulent shear flow confined to a region near solid boundaries. The analysis begins with Lighthill's formulation of aerodynamic noise and assumes that the turbulence is axisymmetric. Specific results are obtained for the sound emitted from an arbitrary point in a turbulent flow within a semi-infinite, open-ended duct.

  9. The effect of finite turbulence spatial scale on the amplification of turbulence by a contracting stream

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Durbin, P. A.

    1980-01-01

    The turbulence downstream of a rapid contraction is calculated for the case when the turbulence scale can have the same magnitude as the mean-flow spatial scale. The approach used is based on the formulation of Goldstein (1978) for turbulence downstream of a contraction, with the added assumptions of a parallel mean flow at downstream infinity and turbulence calculated far enough downstream so that the nonuniformity of the mean flow field has decayed, and by treating the inverse contraction ratio as a small parameter. Consideration is given to the large-contraction-ratio and classical rapid-distortion theory limits, and to results at an arbitrary contraction ratio. It is shown that the amplification effect of the contraction is reduced when the spatial scale of the turbulence increases, with the upstream turbulence actually suppressed for a contraction ratio less than five and a turbulence spatial scale greater than three times the transverse dimensions of the downstream channel.

  10. Unsteady turbulence cascades.

    PubMed

    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.

  11. Unsteady turbulence cascades

    NASA Astrophysics Data System (ADS)

    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), 10.1098/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.

  12. Turbulence forecasting

    NASA Technical Reports Server (NTRS)

    Chandler, C. L.

    1987-01-01

    In order to forecast turbulence, one needs to have an understanding of the cause of turbulence. Therefore, an attempt is made to show the atmospheric structure that often results when aircraft encounter moderate or greater turbulence. The analysis is based on thousands of hours of observations of flights over the past 39 years of aviation meteorology.

  13. Quantitative vortex models of turbulence

    NASA Astrophysics Data System (ADS)

    Pullin, D. I.

    2001-11-01

    This presentation will review attempts to develop models of turbulence, based on compact vortex elements, that can be used both to obtain quantitative estimates of various statistical properties of turbulent fine scales and also to formulate subgrid-transport models for large-eddy simulation (LES). Attention will be focused on a class of stretched-vortex models. Following a brief review of prior work, recent studies of vortex-based modeling of the small-scale behavior of a passive scalar will be discussed. The large-wavenumber spectrum of a passive scalar undergoing mixing by the velocity field of a stretched-spiral vortex will be shown to consist of the sum of two classical power laws, a k-1 Batchelor spectrum for wavenumbers up to the inverse Batchelor scale, and a k-5/3 Obukov-Corrsin spectrum for wavenumbers less than the inverse Kolmogorov scale (joint work with T.S. Lundgren). We will then focus on the use of stretched vortices as the basic subgrid structure in subgrid-scale (SGS) modeling for LES of turbulent flows. An SGS stress model and a vortex-based scalar-flux model for the LES of flows with turbulent mixing will be outlined. Application of these models to the LES of decaying turbulence, channel flow, the mixing of a passive scalar by homogeneous turbulence in the presence of a mean scalar gradient, and to the LES of compressible turbulence will be described.

  14. Perturbative gadgets at arbitrary orders

    NASA Astrophysics Data System (ADS)

    Jordan, Stephen P.; Farhi, Edward

    2008-06-01

    Adiabatic quantum algorithms are often most easily formulated using many-body interactions. However, experimentally available interactions are generally two-body. In 2004, Kempe, Kitaev, and Regev introduced perturbative gadgets, by which arbitrary three-body effective interactions can be obtained using Hamiltonians consisting only of two-body interactions. These three-body effective interactions arise from the third order in perturbation theory. Since their introduction, perturbative gadgets have become a standard tool in the theory of quantum computation. Here we construct generalized gadgets so that one can directly obtain arbitrary k -body effective interactions from two-body Hamiltonians. These effective interactions arise from the k th order in perturbation theory.

  15. Arbitrary bending plasmonic light waves.

    PubMed

    Epstein, Itai; Arie, Ady

    2014-01-17

    We demonstrate the generation of self-accelerating surface plasmon beams along arbitrary caustic curvatures. These plasmonic beams are excited by free-space beams through a two-dimensional binary plasmonic phase mask, which provides the missing momentum between the two beams in the direction of propagation and sets the required phase for the plasmonic beam in the transverse direction. We examine the cases of paraxial and nonparaxial curvatures and show that this highly versatile scheme can be designed to produce arbitrary plasmonic self-accelerating beams. Several different plasmonic beams, which accelerate along polynomial and exponential trajectories, are demonstrated both numerically and experimentally, with a direct measurement of the plasmonic light intensity using a near-field scanning optical microscope.

  16. Turbulence modeling in non-inertial frames of reference

    NASA Technical Reports Server (NTRS)

    Speziale, Charles G.

    1988-01-01

    The effect of an arbitrary change of frame on the structure of turbulence models is examined from a fundamental theoretical standpoint. It is proven, as a rigorous consequence of the Navier-Stokes equations, that turbulence models must be form invariant under arbitrary translational accelerations of the reference frame and should only be affected by rotations through the intrinsic mean vorticity. A direct application of the invariance property along with the Taylor-Proudman Theorem, material frame-indifference in the limit of two-dimensional turbulence and Rapid Distortion Theory is shown to yield powerful constraints on the allowable form of turbulence models. Most of the commonly used turbulence models are demonstrated to be in serious violation of these constraints and consequently are inconsistent with the Navier-Stokes equations in non-inertial frames. Alternative models with improved non-inertial properties are developed and some simple applications to rotating turbulent flows are considered.

  17. Photonic Arbitrary Waveform Generation Technology

    DTIC Science & Technology

    2006-06-01

    filters or ring resonator based technologies [26-29]. Key aspects of the filter technology are the flatness of the filter channel, the crosstalk...photodetectors would also be warranted. 28 References [1] K. Nosu, “ Advanced coherent lightwave technologies ,” IEEE Commun. Magn,, vol. 26...AFRL-SN-RS-TR-2006-208 Final Technical Report June 2006 PHOTONIC ARBITRARY WAVEFORM GENERATION TECHNOLOGY University of

  18. Stellar Spectrum Synthesizer

    ERIC Educational Resources Information Center

    Landegren, G. F.

    1975-01-01

    Describes a device which employs two diffraction gratings and three or four simple lenses to produce arbitrary absorption or emission spectra that may be doppler shifted and spectroscopically examined by students some distance away. It may be regarded as a sort of artificial star whose spectrum may be analyzed as an undergraduate laboratory…

  19. Turbulence patterns and neutrino flavor transitions in high-resolution supernova models

    SciTech Connect

    Borriello, Enrico; Mirizzi, Alessandro; Chakraborty, Sovan; Janka, Hans-Thomas; Lisi, Eligio E-mail: sovan@mppmu.mpg.de E-mail: eligio.lisi@ba.infn.it

    2014-11-01

    During the shock-wave propagation in a core-collapse supernova (SN), matter turbulence may affect neutrino flavor conversion probabilities. Such effects have been usually studied by adding parametrized small-scale random fluctuations (with arbitrary amplitude) on top of coarse, spherically symmetric matter density profiles. Recently, however, two-dimensional (2D) SN models have reached a space resolution high enough to directly trace anisotropic density profiles, down to scales smaller than the typical neutrino oscillation length. In this context, we analyze the statistical properties of a large set of SN matter density profiles obtained in a high-resolution 2D simulation, focusing on a post-bounce time (2 s) suited to study shock-wave effects on neutrino propagation on scales as small as O(100) km and possibly below. We clearly find the imprint of a broken (Kolmogorov-Kraichnan) power-law structure, as generically expected in 2D turbulence spectra. We then compute the flavor evolution of SN neutrinos along representative realizations of the turbulent matter density profiles, and observe no or modest damping of the neutrino crossing probabilities on their way through the shock wave. In order to check the effect of possibly unresolved fluctuations at scales below O(100) km, we also apply a randomization procedure anchored to the power spectrum calculated from the simulation, and find consistent results within ± 1σ fluctuations. These results show the importance of anchoring turbulence effects on SN neutrinos to realistic, fine-grained SN models.

  20. Scale-adaptive subgrid-scale modelling for large-eddy simulation of turbulent flows

    NASA Astrophysics Data System (ADS)

    Yu, Changping; Xiao, Zuoli; Li, Xinliang

    2017-03-01

    The proportionality between the subgrid-scale (SGS) drain rate of kinetic energy and the viscous dissipation rate of the resolved motions is studied a priori by filtering a given fully resolved field and evaluating a generic form of the hypothesized energy spectrum. The ratio of the SGS drain to the resolved dissipation, on which a balance condition for the SGS dissipation across an arbitrary grid scale is founded, is shown to be independent of the turbulence Reynolds number, and can be described by a function in terms of the averaged mesh Reynolds number. Such a balance condition can serve as a physical constraint in the SGS modeling to account for the scale effects of the model coefficient(s). Scale-adaptive dynamic Smagorinsky-Lilly model and mixed nonlinear model are formulated for large-eddy simulation of transitional and/or turbulent flows in such a way that the constraint is satisfied. The newly proposed scale-adaptive dynamic SGS models are validated in simulations of homogeneous isotropic turbulence and turbulent channel flow, and prove to be superior over traditional dynamic SGS models.

  1. Broken symmetry in ideal magnetohydrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1993-01-01

    A numerical study of the long-time evolution of a number of cases of inviscid, isotropic, incompressible, three-dimensional fluid, and magneto-fluid turbulence has been completed. The results confirm that ideal magnetohydrodynamic turbulence is non-ergodic if there is no external magnetic field present. This is due essentially to a canonical symmetry being broken in an arbitrary dynamical representation. The broken symmetry manifests itself as a coherent structure, i.e., a non-zero time-averaged part of the turbulent magnetic field. The coherent structure is observed, in one case, to contain about eighteen percent of the total energy.

  2. The Theories of Turbulence

    NASA Technical Reports Server (NTRS)

    Bass, J; Agostini, L

    1955-01-01

    The theory of turbulence reached its full growth at the end of the 19th century as a result of the work by Boussinesq and Reynolds. It then underwent a long period of stagnation which ended under the impulse given to it by the development of wind tunnels caused by the needs of aviation. Numerous researchers, attempted to put Reynolds' elementary statistical theory into a more precise form. During the war, some isolated scientists - von Weizsacker and Heisenberg in Germany, Kolmogoroff in Russia, Onsager in the U.S.A. - started a program of research. By a system of assumptions which make it possible to approach the structure of turbulence in well-defined limiting conditions quantitatively, they obtained a certain number of laws on the correlations and the spectrum. Since the late reports have improved the mathematical language of turbulence, it was deemed advisable to start with a detailed account of the mathematical methods applicable to turbulence, inspired at first by the work of the French school, above all for the basic principles, then the work of the foreigners, above all for the theory of the spectrum.

  3. Interpretation of second solar spectrum observations of the Sr I 4607 Å line in a quiet region: Turbulent magnetic field strength determination

    NASA Astrophysics Data System (ADS)

    Bommier, V.; Derouich, M.; Landi Degl'Innocenti, E.; Molodij, G.; Sahal-Bréchot, S.

    2005-03-01

    This paper presents and interprets some observations of the limb polarization of Sr I 4607 Å obtained with the spectropolarimeter of the French-Italian telescope THEMIS in quiet regions close to the solar North Pole on 2002 December 7-9. The linear polarization was measured for a series of limb distances ranging from 4 to 160 arcsec, corresponding to heights of optical depth unity in the line core ranging from about 330 to 220 km, respectively, above the τ5000=1 level. To increase the polarimetric sensitivity, the data were averaged along the spectrograph slit (one arcmin long) set parallel to the solar limb. Since the data show no rotation of the linear polarization direction with respect to the limb direction, the observed depolarization is ascribed to the Hanle effect of a turbulent weak magnetic field, the zero-field polarization being derived from a model. The interpretation is performed by means of an algorithm which describes the process of line formation in terms of the atomic density matrix formalism, the solar atmosphere being described by an empirical, plane-parallel model. The collisional rates entering the model (inelastic collisions with electrons, elastic depolarizing collisions with neutral hydrogen), have been computed by applying fast semi-classical methods having a typical accuracy of the order of 20% or better (see Derouich [CITE]), leading to 6% inaccuracy on the magnetic field strength determination. We assume a unimodal distribution for the intensity of the turbulent field. The computed intensity profile has been adjusted to the observed one in both depth and width, by varying both microturbulent and macroturbulent velocities. The best adjustment is obtained for respectively 1.87 km s-1 (micro) and 1.78 km s-1 (macro). The evaluation of the magnetic depolarization leads then to the average value of 46 Gauss for the turbulent magnetic field strength, with a gradient of -0.12 Gauss/km. Our results are in very good agreement with the value of

  4. Double Resonances and Spectral Scaling in the Weak Turbulence Theory of Rotating and Stratified Turbulence

    NASA Technical Reports Server (NTRS)

    Rubinstein, Robert

    1999-01-01

    In rotating turbulence, stably stratified turbulence, and in rotating stratified turbulence, heuristic arguments concerning the turbulent time scale suggest that the inertial range energy spectrum scales as k(exp -2). From the viewpoint of weak turbulence theory, there are three possibilities which might invalidate these arguments: four-wave interactions could dominate three-wave interactions leading to a modified inertial range energy balance, double resonances could alter the time scale, and the energy flux integral might not converge. It is shown that although double resonances exist in all of these problems, they do not influence overall energy transfer. However, the resonance conditions cause the flux integral for rotating turbulence to diverge logarithmically when evaluated for a k(exp -2) energy spectrum; therefore, this spectrum requires logarithmic corrections. Finally, the role of four-wave interactions is briefly discussed.

  5. Light propagation through anisotropic turbulence.

    PubMed

    Toselli, Italo; Agrawal, Brij; Restaino, Sergio

    2011-03-01

    A wealth of experimental data has shown that atmospheric turbulence can be anisotropic; in this case, a Kolmogorov spectrum does not describe well the atmospheric turbulence statistics. In this paper, we show a quantitative analysis of anisotropic turbulence by using a non-Kolmogorov power spectrum with an anisotropic coefficient. The spectrum we use does not include the inner and outer scales, it is valid only inside the inertial subrange, and it has a power-law slope that can be different from a Kolmogorov one. Using this power spectrum, in the weak turbulence condition, we analyze the impact of the power-law variations α on the long-term beam spread and scintillation index for several anisotropic coefficient values ς. We consider only horizontal propagation across the turbulence cells, assuming circular symmetry is maintained on the orthogonal plane to the propagation direction. We conclude that the anisotropic coefficient influences both the long-term beam spread and the scintillation index by the factor ς(2-α).

  6. Mathematic model analysis of Gaussian beam propagation through an arbitrary thickness random phase screen.

    PubMed

    Tian, Yuzhen; Guo, Jin; Wang, Rui; Wang, Tingfeng

    2011-09-12

    In order to research the statistical properties of Gaussian beam propagation through an arbitrary thickness random phase screen for adaptive optics and laser communication application in the laboratory, we establish mathematic models of statistical quantities, which are based on the Rytov method and the thin phase screen model, involved in the propagation process. And the analytic results are developed for an arbitrary thickness phase screen based on the Kolmogorov power spectrum. The comparison between the arbitrary thickness phase screen and the thin phase screen shows that it is more suitable for our results to describe the generalized case, especially the scintillation index.

  7. Vortex burst as a source of turbulence.

    PubMed

    Cuypers, Yannis; Maurel, Agnès; Petitjeans, Philippe

    2003-11-07

    An important issue in turbulence theory is to understand what kinds of elementary flow structures are responsible for the part of the turbulent energy spectrum described by Kolmogorov's celebrated k(-5/3) law. A model for such structure has been proposed by Lundgren [Phys. Fluids 25, 2193-2203 (1982)

  8. Arbitrary Inequality in Reputation Systems

    NASA Astrophysics Data System (ADS)

    Frey, Vincenz; van de Rijt, Arnout

    2016-12-01

    Trust is an essential condition for exchange. Large societies must substitute the trust traditionally provided through kinship and sanctions in small groups to make exchange possible. The rise of internet-supported reputation systems has been celebrated for providing trust at a global scale, enabling the massive volumes of transactions between distant strangers that are characteristic of modern human societies. Here we problematize an overlooked side-effect of reputation systems: Equally trustworthy individuals may realize highly unequal exchange volumes. We report the results of a laboratory experiment that shows emergent differentiation between ex ante equivalent individuals when information on performance in past exchanges is shared. This arbitrary inequality results from cumulative advantage in the reputation-building process: Random initial distinctions grow as parties of good repute are chosen over those lacking a reputation. We conjecture that reputation systems produce artificial concentration in a wide range of markets and leave superior but untried exchange alternatives unexploited.

  9. Arbitrary Inequality in Reputation Systems.

    PubMed

    Frey, Vincenz; van de Rijt, Arnout

    2016-12-20

    Trust is an essential condition for exchange. Large societies must substitute the trust traditionally provided through kinship and sanctions in small groups to make exchange possible. The rise of internet-supported reputation systems has been celebrated for providing trust at a global scale, enabling the massive volumes of transactions between distant strangers that are characteristic of modern human societies. Here we problematize an overlooked side-effect of reputation systems: Equally trustworthy individuals may realize highly unequal exchange volumes. We report the results of a laboratory experiment that shows emergent differentiation between ex ante equivalent individuals when information on performance in past exchanges is shared. This arbitrary inequality results from cumulative advantage in the reputation-building process: Random initial distinctions grow as parties of good repute are chosen over those lacking a reputation. We conjecture that reputation systems produce artificial concentration in a wide range of markets and leave superior but untried exchange alternatives unexploited.

  10. Arbitrary Inequality in Reputation Systems

    PubMed Central

    Frey, Vincenz; van de Rijt, Arnout

    2016-01-01

    Trust is an essential condition for exchange. Large societies must substitute the trust traditionally provided through kinship and sanctions in small groups to make exchange possible. The rise of internet-supported reputation systems has been celebrated for providing trust at a global scale, enabling the massive volumes of transactions between distant strangers that are characteristic of modern human societies. Here we problematize an overlooked side-effect of reputation systems: Equally trustworthy individuals may realize highly unequal exchange volumes. We report the results of a laboratory experiment that shows emergent differentiation between ex ante equivalent individuals when information on performance in past exchanges is shared. This arbitrary inequality results from cumulative advantage in the reputation-building process: Random initial distinctions grow as parties of good repute are chosen over those lacking a reputation. We conjecture that reputation systems produce artificial concentration in a wide range of markets and leave superior but untried exchange alternatives unexploited. PMID:27995957

  11. Generalization of the electronic susceptibility for arbitrary molecular geometries.

    PubMed

    Scherrer, Arne; Dreßler, Christian; Ahlert, Paul; Sebastiani, Daniel

    2016-04-14

    We generalize the explicit representation of the electronic susceptibility χ[R](r, r') for arbitrary molecular geometries R. The electronic susceptibility is a response function that yields the response of the molecular electronic charge density at linear order to an arbitrary external perturbation. We address the dependence of this response function on the molecular geometry. The explicit representation of the molecular geometry dependence is achieved by means of a Taylor expansion in the nuclear coordinates. Our approach relies on a recently developed low-rank representation of the response function χ[R](r, r') which allows a highly condensed storage of the expansion and an efficient application within dynamical chemical environments. We illustrate the performance and accuracy of our scheme by computing the vibrationally induced variations of the response function of a water molecule and its resulting Raman spectrum.

  12. A new approach for turbulent simulations in complex geometries

    NASA Astrophysics Data System (ADS)

    Israel, Daniel M.

    Historically turbulence modeling has been sharply divided into Reynolds averaged Navier-Stokes (RANS), in which all the turbulent scales of motion are modeled, and large-eddy simulation (LES), in which only a portion of the turbulent spectrum is modeled. In recent years there have been numerous attempts to couple these two approaches either by patching RANS and LES calculations together (zonal methods) or by blending the two sets of equations. In order to create a proper bridging model, that is, a single set of equations which captures both RANS and LES like behavior, it is necessary to place both RANS and LES in a more general framework. The goal of the current work is threefold: to provide such a framework, to demonstrate how the Flow Simulation Methodology (FSM) fits into this framework, and to evaluate the strengths and weaknesses of the current version of the FSM. To do this, first a set of filtered Navier-Stokes (FNS) equations are introduced in terms of an arbitrary generalized filter. Additional exact equations are given for the second order moments and the generalized subfilter dissipation rate tensor. This is followed by a discussion of the role of implicit and explicit filters in turbulence modeling. The FSM is then described with particular attention to its role as a bridging model. In order to evaluate the method a specific implementation of the FSM approach is proposed. Simulations are presented using this model for the case of a separating flow over a "hump" with and without flow control. Careful attention is paid to error estimation, and, in particular, how using flow statistics and time series affects the error analysis. Both mean flow and Reynolds stress profiles are presented, as well as the phase averaged turbulent structures and wall pressure spectra. Using the phase averaged data it is possible to examine how the FSM partitions the energy between the coherent resolved scale motions, the random resolved scale fluctuations, and the subfilter

  13. Shell model for buoyancy-driven turbulence.

    PubMed

    Kumar, Abhishek; Verma, Mahendra K

    2015-04-01

    In this paper we present a unified shell model for stably stratified and convective turbulence. Numerical simulation of this model for stably stratified flow shows Bolgiano-Obukhbov scaling in which the kinetic energy spectrum varies as k(-11/5). The shell model of convective turbulence yields Kolmogorov's spectrum. These results are consistent with the energy flux and energy feed due to buoyancy, and are in good agreement with direct numerical simulations of Kumar et al. [Phys. Rev. E 90, 023016 (2014)].

  14. Second solar spectrum of the Sr I 4607 Å line: depth probing of the turbulent magnetic field strength in a quiet region

    NASA Astrophysics Data System (ADS)

    Derouich, M.; Bommier, V.; Malherbe, J. M.; Landi Degl'Innocenti, E.

    2006-10-01

    Aims.This paper is devoted to an interpretation of Quiet-Sun, spatially-resolved spectropolarimetric observations of the Hanle effect in terms of turbulent weak magnetic field determination. Methods: . Observations: the slit was positioned perpendicular to the limb, and the spatial resolution along the slit was 1 arcsec, leading to a depth probing along 132 different limb distances. The new polarimeter of the Pic-du-Midi Turret Dome was used on May 14, 2004 to observe a quiet region at the East limb equator in the resonance line of neutral Strontium at 4607 Å. Results: . For each limb distance, we properly adjusted the theoretical intensity profile obtained by applying a zero-field model to the observed one. Micro- and macroturbulent velocities were thus derived (average values v{micro}=1.77 km s-1 and v{macro}=1.95 km s-1). The magnetic field was determined in a second step by interpreting the Hanle effect on the line center linear polarization degree. The depolarizing collisions with neutral hydrogen were taken fully into account through a semi-classical calculation of their rates. An average value of B=38 Gauss was thus derived. Finally, error bars on the magnetic field values were evaluated from a) the polarimetric inaccuracy, b) the limb distance determination inaccuracy, and c) the uncertainty on our theoretical collisional depolarizing rates that we evaluated. This combination leads to 10-20% as total relative error on the magnetic field determination by the Hanle effect method. Since the inaccuracy due to the model itself was hard to properly evaluate, it was ignored. An uncertainty of ±60 km on the line formation depth was, however, derived from the contribution functions. The magnetic field is found to increase slowly with height in the height range 220-300 km above τ5000=1 and then decrease in the height range 300-370 km.

  15. Diffusion of Heat from a Line Source in Isotropic Turbulence

    NASA Technical Reports Server (NTRS)

    Uberoi, Mahinder S; Corrsin, Stanley

    1953-01-01

    An experimental and analytical study has been made of some features of the turbulent heat diffusion behind a line heated wire stretched perpendicular to a flowing isotropic turbulence. The mean temperature distributions have been measured with systematic variations in wind speed, size of turbulence-producing grid, and downstream location of heat source. The nature of the temperature fluctuation field has been studied. A comparison of Lagrangian and Eulerian analyses for diffusion in a nondecaying turbulence yields an expression for turbulent-heat-transfer coefficient in terms of turbulence velocity and a Lagrangian "scale." the ratio of Eulerian to Lagrangian microscale has been determined theoretically by generalization of a result of Heisenberg and with arbitrary constants taken from independent sources, shows rough agreement with experimental results. A convenient form has been deduced for the criterion of interchangeability of instantaneous space and time derivatives in a flowing turbulence.

  16. Magnetosheath electrostatic turbulence

    NASA Technical Reports Server (NTRS)

    Rodriquez, P.

    1977-01-01

    The spectrum of electrostatic plasma waves in the terrestrial magnetosheath was studied using the plasma wave experiment on the IMP-6 satellite. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz- 70 kHz) r.m.s. field intensities typically 0.01 - 1.0 millivolts/m. Peak intensities of about 1.0 millivolts/m near the electron plasma frequency (30 - 60 kHz) were detected occasionally. The components usually identified in the spectrum of magnetosheath electrostatic turbulence include a high frequency ( or = 30 kHz) component peaking at the electron plasma frequency f sub pe, a low frequency component with a broad intensity maximum below the nominal ion plasma frequency f sub pi (approximately f sub pe/43), and a less well defined intermediate component in the range f sub pi f f sub pe. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath.

  17. Magnetohydrodynamic turbulence: Observation and experiment

    SciTech Connect

    Brown, M. R.; Schaffner, D. A.; Weck, P. J.

    2015-05-15

    We provide a tutorial on the paradigms and tools of magnetohydrodynamic (MHD) turbulence. The principal paradigm is that of a turbulent cascade from large scales to small, resulting in power law behavior for the frequency power spectrum for magnetic fluctuations E{sub B}(f). We will describe five useful statistical tools for MHD turbulence in the time domain: the temporal autocorrelation function, the frequency power spectrum, the probability distribution function of temporal increments, the temporal structure function, and the permutation entropy. Each of these tools will be illustrated with an example taken from MHD fluctuations in the solar wind. A single dataset from the Wind satellite will be used to illustrate all five temporal statistical tools.

  18. Magnetohydrodynamic turbulence: Observation and experimenta)

    NASA Astrophysics Data System (ADS)

    Brown, M. R.; Schaffner, D. A.; Weck, P. J.

    2015-05-01

    We provide a tutorial on the paradigms and tools of magnetohydrodynamic (MHD) turbulence. The principal paradigm is that of a turbulent cascade from large scales to small, resulting in power law behavior for the frequency power spectrum for magnetic fluctuations EB(f ) . We will describe five useful statistical tools for MHD turbulence in the time domain: the temporal autocorrelation function, the frequency power spectrum, the probability distribution function of temporal increments, the temporal structure function, and the permutation entropy. Each of these tools will be illustrated with an example taken from MHD fluctuations in the solar wind. A single dataset from the Wind satellite will be used to illustrate all five temporal statistical tools.

  19. Decay of capillary wave turbulence.

    PubMed

    Deike, Luc; Berhanu, Michael; Falcon, Eric

    2012-06-01

    We report on the observation of freely decaying capillary wave turbulence on the surface of a fluid. The capillary wave turbulence spectrum decay is found to be self-similar in time with the same power law exponent as the one found in the stationary regime, in agreement with weak turbulence predictions. The amplitude of all Fourier modes are found to decrease exponentially with time at the same damping rate. The longest wavelengths involved in the system are shown to be damped by a viscous surface boundary layer. These long waves play the role of an energy source during the decay that sustains nonlinear interactions to keep capillary waves in a wave turbulent state.

  20. Wall Turbulence.

    ERIC Educational Resources Information Center

    Hanratty, Thomas J.

    1980-01-01

    This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)

  1. Quantitative photography of intermittency in surface wave turbulence

    SciTech Connect

    Wright, W.; Budakian, R.; Putterman, S.J.

    1997-12-31

    At high amplitudes of excitation surface waves on water distribute their energy according to a Kolmogorov type of turbulent power spectrum. We have used diffusing light photography to measure the power spectrum and to quantify the presence of large structures in the turbulent state.

  2. Hilbert-Huang Transform in Ocean Turbulence

    NASA Astrophysics Data System (ADS)

    Huang, Yongxiang

    2013-04-01

    Hilbert-Huang Transform is a relative novel time-frequency analysis technique for multi-scale processes. It is a wavelet-like data-driven methodology without a priori basis assumption. This meets the requirement of the analysis of the nonstationary and nonlinear data with short length or irregular sampling time interval. Since it is introduced in 1998 by Dr. N.E Huang, it has been widely applied to different scientific research fields and engineering problems, showing its simplicity and successes. We develop further this method to characterize the scale invariance for turbulence-like/scaling processes, e.g., velocity, temperature, dissolved oxygen observed in ocean, etc. In this talk, we first present a general introduction of this method. The key feature of this Hilbert-based method is that it is free with sub-harmonics when dealing with nonstationary and nonlinear data. This is accomplished by using an Intrawave-Frequency Modulation mechanism to characterize the so-called nonlinear distortion. Therefore, unlike the Fourier based methodologies, artificial energy redistribution in spectral space is constrained. We then show several applications of this method to experimental data from wind tunnel experiments and ocean observations. The interaction between two different scales and two variables are also discussed in statistics sense. The method is general and applicable to other systems, in which the multi-scale is relevant. Reference 1. Huang, N. E.; Shen, Z.; Long, S. R.; Wu, M. C.; Shih, H. H.; Zheng, Q.; Yen, N.; Tung, C. C. & Liu, H. H. The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis Proc. R. Soc. London, Ser. A, Royal Society, 1998, 454, 903-995 2. Huang, Y.; Schmitt, F.; Lu, Z. & Liu, Y. An amplitude-frequency study of turbulent scaling intermittency using Hilbert spectral analysis, Europhys. Lett., 2008, 84, 40010 3. Huang, Y.; Schmitt, F.; Lu, Z.; Fougairolles, P.; Gagne, Y. & Liu, Y. Second

  3. Existence of a persistent background of turbulence

    NASA Technical Reports Server (NTRS)

    Vanzandt, T. E.

    1983-01-01

    A plausible scenario for the existence of a persistent back-ground of turbulence in the free atmosphere is described. The MST radar technique is the only existing technique that can be used to describe the morphology of occurrence of turbulence as a function of altitude, wind speed, shear, weather conditions, geographical location, etc. This technique was used also to assess the degree of universality of shape and amplitude of the buoyancy wave spectrum and the relation between the buoyancy wave spectrum and turbulence.

  4. Numerical solution of the Navier-Stokes equations for arbitrary two-dimensional multi-element airfoils

    NASA Technical Reports Server (NTRS)

    Thompson, J. F.; Turner, L., III; Long, W. S.; Bearden, J. H.

    1979-01-01

    The development of a numerical simulation of time dependent, turbulent, compressible flow about two dimensional multi-element airfoils of arbitrary shape is described. The basis of this simulation is a technique of automatic numerical generation of coordinate systems fitted to the multiple bodies regardless of their number or shape. Procedures developed whereby the coordinate lines are automatically concentrated in the boundary layer at any Reynolds number are discussed. The compressible turbulent solution involves an algebraic eddy viscosity turbulence model. The laminar version was run for transonic flow at free stream Mach numbers up to 0.9.

  5. Mixing in Magnetized Turbulent Media

    NASA Astrophysics Data System (ADS)

    Sur, Sharanya; Pan, Liubin; Scannapieco, Evan

    2014-04-01

    Turbulent motions are essential to the mixing of entrained fluids and are also capable of amplifying weak initial magnetic fields by small-scale dynamo action. Here we perform a systematic study of turbulent mixing in magnetized media, using three-dimensional magnetohydrodynamic simulations that include a scalar concentration field. We focus on how mixing depends on the magnetic Prandtl number, Pm, from 1 to 4 and the Mach number, { {M}}, from 0.3 to 2.4. For all subsonic flows, we find that the velocity power spectrum has a k -5/3 slope in the early kinematic phase, but steepens due to magnetic back reactions as the field saturates. The scalar power spectrum, on the other hand, flattens compared to k -5/3 at late times, consistent with the Obukohov-Corrsin picture of mixing as a cascade process. At higher Mach numbers, the velocity power spectrum also steepens due to the presence of shocks, and the scalar power spectrum again flattens accordingly. Scalar structures are more intermittent than velocity structures in subsonic turbulence, whereas for supersonic turbulence, velocity structures appear more intermittent than the scalars only in the kinematic phase. Independent of the Mach number of the flow, scalar structures are arranged in sheets in both the kinematic and saturated phases of the magnetic field evolution. For subsonic turbulence, scalar dissipation is hindered in the strong magnetic field regions, probably due to Lorentz forces suppressing the buildup of scalar gradients, whereas for supersonic turbulence, scalar dissipation increases monotonically with increasing magnetic field strength. At all Mach numbers, mixing is significantly slowed by the presence of dynamically important small-scale magnetic fields, implying that mixing in the interstellar medium and in galaxy clusters is less efficient than modeled in hydrodynamic simulations.

  6. Arbitrary waveform generation using optical direct digital synthesis

    NASA Astrophysics Data System (ADS)

    Chester-Parsons, J.

    2013-11-01

    The objective of this paper is to describe the progress of a project designed to build on recent photonic capabilities in order to develop an ultra-wide band, true Arbitrary Waveform Generator (AWG) capable of providing radar quality signals in the 500MHz to 20GHz spectrum using photonic integration. Within this scope, it is planned to create a single channel radar environment simulator based on a photonic waveform generator, which will demonstrate the dynamic range, stability, and high signal fidelity required to simulate the modern complex radar environment. The paper will present recent measurements of critical parameters that are vital for the practical realisation of this system on a chip.

  7. Optical arbitrary waveform characterization using linear spectrograms.

    PubMed

    Jiang, Zhi; Leaird, Daniel E; Long, Christopher M; Boppart, Stephen A; Weiner, Andrew M

    2010-08-01

    We demonstrate the first application of linear spectrogram methods based on electro-optic phase modulation to characterize optical arbitrary waveforms generated under spectral line-by-line control. This approach offers both superior sensitivity and self-referencing capability for retrieval of periodic high repetition rate optical arbitrary waveforms.

  8. Numerical solution of the Navier-Stokes equations for arbitrary 2-dimensional multi-element airfoils

    NASA Technical Reports Server (NTRS)

    Thompson, J. F.

    1983-01-01

    Numerical solutions of the Navier-Stokes equations, with an algebraic turbulence model, for time-dependent two dimensional flow about multi-element airfoils were developed. Fundamental to these solutions was the use of numerically-generated boundary-conforming curvilinear coordinate systems to allow bodies of arbitrary shape to be treated. A general two dimensional grid generation code for multiple-body configuration was written as a part of this project and made available through the COSMIC code library.

  9. A Model for Jet-Surface Interaction Noise Using Physically Realizable Upstream Turbulence Conditions

    NASA Technical Reports Server (NTRS)

    Afsar, Mohammed Z.; Leib, Stewart J.; Bozak, Richard F.

    2016-01-01

    This paper is a continuation of previous work in which a generalized Rapid Distortion Theory (RDT) formulation was used to model low-frequency trailing-edge noise. The research was motivated by proposed next-generation aircraft configurations where the exhaust system is tightly integrated with the airframe. Data from recent experiments at NASA on the interaction between high-Reynolds-number subsonic jet flows and an external flat plate showed that the power spectral density (PSD) of the far-field pressure underwent considerable amplification at low frequencies. For example, at the 90deg observation angle, the low-frequency noise could be as much as 10 dB greater than the jet noise itself. In this paper, we present predictions of the noise generated by the interaction of a rectangular jet with the trailing edge of a semi-infinite flat plate. The calculations are based on a formula for the acoustic spectrum of this noise source derived from an exact formal solution of the linearized Euler equations involving (in this case) one arbitrary convected scalar quantity and a Rayleigh equation Green's function. A low-frequency asymptotic approximation for the Green's function based on a two-dimensional mean flow is used in the calculations along with a physically realizable upstream turbulence spectrum, which includes a finite decorrelation region. Numerical predictions of the sound field, based on three-dimensional RANS solutions to determine the mean flow, turbulent kinetic energy and turbulence length and time scales, for a range of subsonic acoustic Mach number jets and nozzle aspect ratios are compared with experimental data. Comparisons of the RANS results with flow data are also presented for selected cases. We find that a finite decorrelation region in the turbulence spectrum increases the low-frequency algebraic decay (the low frequency "roll-off") of the acoustic spectrum with angular frequency thereby producing much closer agreement with noise data for Strouhal

  10. Saturation of the turbulent dynamo.

    PubMed

    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.

  11. Soliton turbulence

    NASA Technical Reports Server (NTRS)

    Tchen, C. M.

    1986-01-01

    Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.

  12. LAMINAR TRANSITIONAL AND TURBULENT BOUNDARY LAYERS FOR COMPRESSIBLE AXISYMMETRIC FLOW

    NASA Technical Reports Server (NTRS)

    Albers, J. A.

    1994-01-01

    This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.

  13. Calculating fusion neutron energy spectra from arbitrary reactant distributions

    NASA Astrophysics Data System (ADS)

    Eriksson, J.; Conroy, S.; Andersson Sundén, E.; Hellesen, C.

    2016-02-01

    The Directional Relativistic Spectrum Simulator (DRESS) code can perform Monte-Carlo calculations of reaction product spectra from arbitrary reactant distributions, using fully relativistic kinematics. The code is set up to calculate energy spectra from neutrons and alpha particles produced in the D(d, n)3He and T(d, n)4He fusion reactions, but any two-body reaction can be simulated by including the corresponding cross section. The code has been thoroughly tested. The kinematics calculations have been benchmarked against the kinematics module of the ROOT Data Analysis Framework. Calculated neutron energy spectra have been validated against tabulated fusion reactivities and against an exact analytical expression for the thermonuclear fusion neutron spectrum, with good agreement. The DRESS code will be used as the core of a detailed synthetic diagnostic framework for neutron measurements at the JET and MAST tokamaks.

  14. Range of turbulence-independent propagation and Rayleigh range of partially coherent beams in atmospheric turbulence.

    PubMed

    Dan, Youquan; Zeng, Shuguang; Hao, Bangyuan; Zhang, Bin

    2010-03-01

    Two characteristic distances for partially coherent beams propagating in atmospheric turbulence have been proposed. The turbulent Rayleigh range is used for characterizing the range over which the beams propagate in turbulence without spreading appreciably; i.e., the concept of the well-known Rayleigh range in free space is extended to the case of turbulence. In this paper the range of turbulence-independent propagation of the beams, in contrast to similar characteristic distances in previous published works, is based on the formula of the beam propagation factor (M(2) factor) and is used for describing the range over which the spatial and angular spreading and the M(2) factor increase due to turbulence are sufficiently small and negligible. Several simple formulas used for calculating the approximate values of these distances are given, and the formulas are applied to Gaussian Schell-model (GSM) beams and illustrated by examples. Furthermore, as a typical example, the effect of the angular spread of GSM beams in turbulence on a thin-lens optical system is also discussed. We show that the turbulent Rayleigh range depends on the Rayleigh range in free space, the waist width, and the spatial power spectrum of the refractive-index fluctuations of the turbulent atmosphere, and that the range of turbulence-independent propagation depends on the waist width, the initial angular spread in the waist plane, and the spatial power spectrum.

  15. Quantum turbulence

    NASA Astrophysics Data System (ADS)

    Skrbek, L.

    2011-12-01

    We review physical properties of quantum fluids He II and 3He-B, where quantum turbulence (QT) has been studied experimentally. Basic properties of QT in these working fluids are discussed within the phenomenological two-fluid model introduced by Landau. We consider counterflows in which the normal and superfluid components flow against each other, as well as co-flows in which the direction of the two fluids is the same. We pay special attention to the important case of zero temperature limit, where QT represents an interesting and probably the simplest prototype of three-dimensional turbulence in fluids. Experimental techniques to explore QT such as second sound attenuation, Andreev reflection, NMR, ion propagation are briefly introduced and results of various experiments on so-called Vinen QT and Kolmogorov QT both in He II and 3He are discussed, emphasizing similarities and differences between classical and quantum turbulence.

  16. Turbulence in Compressible Flows

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.

  17. On Kraichnan's 'direct interaction approximation' and Kolmogoroff's theory in two-dimensional plasma turbulence

    SciTech Connect

    Kulsrud, R.M.; Sudan, R.N.

    1981-04-01

    The nonlinear damping in a strongly turbulent convecting plasma computed by Kraichnan's modified direct inteaction approximation and the power spectrum are rederived in a physically transparent form using Kolmogoroff's theory of turbulence.

  18. Formulation and closure of compressible turbulence equations in the light of kinetic theory

    NASA Technical Reports Server (NTRS)

    Tsuge, S.; Sagara, K.

    1976-01-01

    Fluid-dynamic moment equations, based on a kinetic hierarchy system, are derived governing the interaction between turbulent and thermal fluctuations. The kinetic theory is shown to reduce the inherent complexity of the conventional formalism of compressible turbulence theory and to minimize arbitrariness in formulating the closure condition.

  19. INVERSE CASCADE IN IMBALANCED ELECTRON MAGNETOHYDRODYNAMIC TURBULENCE

    SciTech Connect

    Kim, Hoonkyu; Cho, Jungyeon E-mail: jcho@cnu.ac.kr

    2015-03-10

    Electron magnetohydrodynamics (EMHD) provides a fluid-like description of small-scale magnetized plasmas. Balanced EMHD turbulence has been studied for a long time. However, driven imbalanced EMHD turbulence, in which waves moving in one direction (dominant waves) have higher amplitudes than waves moving in the other direction (sub-dominant waves), has not been well studied. In this paper, we numerically study driven three-dimensional imbalanced weak EMHD turbulence. We find the following results. First, in driven imbalanced EMHD turbulence, we clearly observe inverse cascade of magnetic helicity, as well as magnetic energy. This is because magnetic helicity is a conserved quantity and non-zero magnetic helicity is injected into the system in driven imbalanced EMHD turbulence. Second, the magnetic energy spectrum of the dominant waves on scales larger than the energy injection scale does not show a single power-law spectrum, which indicates that the inverse cascade is not a self-similar process. The peak of the spectrum roughly follows a k {sup –3/2} spectrum, which can be explained by a Kolmogorov-type argument for weak turbulence. Third, a small amount of sub-dominant waves is induced by the dominant waves on large scales and the ratio of helicity densities of the dominant and the sub-dominant waves on large scales seems to converge to a certain value.

  20. Turbulent combustion

    SciTech Connect

    Talbot, L.; Cheng, R.K.

    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.

  1. Turbulence Modeling

    DTIC Science & Technology

    1991-10-01

    and complexity of thermochemistry . Accordingly a practical viewpoint is required to meet near-term work required for use in advanced CFD codes...teachers the opportunity to learn/explore/ teach turbulence issues. While such a product could be an invaluable eductaional tool (university), it also

  2. Turbulence modeling

    NASA Technical Reports Server (NTRS)

    Bardina, Jorge E.

    1995-01-01

    The objective of this work is to develop, verify, and incorporate the baseline two-equation turbulence models which account for the effects of compressibility into the three-dimensional Reynolds averaged Navier-Stokes (RANS) code and to provide documented descriptions of the models and their numerical procedures so that they can be implemented into 3-D CFD codes for engineering applications.

  3. On turbulence in dilatant dispersions

    NASA Astrophysics Data System (ADS)

    Baumert, Helmut Z.; Wessling, Bernhard

    2016-07-01

    This paper presents a new theory on the behaviour of shear-thickening (dilatant) fluids under turbulent conditions. The structure of a dilatant colloidal fluid in turbulent motion may be characterized by (at least) four characteristic length scales: (i) the ‘statistically largest’ turbulent scale, {λ }0, labeling the begin of the inertial part of the wavenumber spectrum; (ii) the energy-containing scale, { L }; (iii) Kolmogorov’s micro-scale, {λ }{ K }, related with the size of the smallest vortices existing for a given kinematic viscosity and forcing; (iv) the inner (‘colloidal’) micro-scale, {λ }i, typically representing a major stable material property of the colloidal fluid. In particular, for small ratios r={λ }i/{λ }{ K }∼ { O }(1), various interactions between colloidal structures and smallest turbulent eddies can be expected. In the present paper we discuss particularly that for ρ ={λ }0/{λ }{ K }\\to { O }(1) turbulence (in the narrow, inertial sense) is strangled and chaotic but less mixing fluid motions remain. We start from a new stochastic, micro-mechanical turbulence theory without empirical parameters valid for inviscid fluids as seen in publications by Baumert in 2013 and 2015. It predicts e.g. von Karman’s constant correctly as 1/\\sqrt{2 π }=0.399. In its generalized version for non-zero viscosity and shear-thickening behavior presented in this contribution, it predicts two solution branches for the steady state: The first characterizes a family of states with swift (inertial) turbulent mixing and small {λ }{ K }, potentially approaching {λ }i. The second branch characterizes a state family with ρ \\to { O }(1) and thus strangled turbulence, ρ ≈ { O }(1). Stability properties and a potential dynamic commuting between the two solution branches had to be left for future research.

  4. Muonium Spectrum Beyond the Nonrelativistic Limit

    SciTech Connect

    Weber, Axel

    2008-07-02

    A generalization of the Gell-Mann-Low theorem is applied to the antimuon-electron system. The bound state spectrum is extracted numerically. As a result, fine and hyperfine structure are reproduced correctly near the nonrelativistic limit (and for arbitrary masses). We compare the spectrum for the relativistic value {alpha} = 0.3 with corresponding calculations in light-front quantization.

  5. Two-dimensional convective turbulence

    SciTech Connect

    Gruzinov, A.V.; Kukharkin, N.; Sudan, R.N.

    1996-02-01

    We show that 2D {bold E{times}B} ionospheric turbulence of the electron density in the equatorial electrojet is isomorphic to the viscous convection of an ordinary fluid in a porous medium due to temperature gradients. Numerical simulations reveal the strong anisotropy in the turbulence, which consists of rising hot bubbles and falling cool bubbles. These bubbles break up into fingers leading to the formation of stable shear flows. After reaching a quasisteady state, the omnidirectional energy spectrum approaches a {ital k}{sup {minus}2} behavior, rather than {ital k}{sup {minus}5/3} as expected from isotropic turbulence. Physical mechanisms that lead to anisotropy are analyzed. {copyright} {ital 1996 The American Physical Society.}

  6. Vortex Burst as a Source of Turbulence

    NASA Astrophysics Data System (ADS)

    Cuypers, Yannis; Maurel, Agnès; Petitjeans, Philippe

    2003-11-01

    An important issue in turbulence theory is to understand what kinds of elementary flow structures are responsible for the part of the turbulent energy spectrum described by Kolmogorov's celebrated k-5/3 law. A model for such structure has been proposed by Lundgren [

    Phys. FluidsPHFLE61070-6631 25, 2193 2203 (1982)
    ] in the form of a vortex with spiral structure subjected to an axially straining field. We report experimental results of a vortex burst in a laminar-flow environment showing that this structure is responsible for a k-5/3 part in the energy spectrum. If there are many experimental evidences of the existence of vortices with spiral structures in turbulent flows, it is the first time that such an elementary structure is experimentally shown to be responsible for the turbulent energy cascade.

  7. From coherent structures to turbulence spectra

    NASA Astrophysics Data System (ADS)

    Lion, Sonny; Alexandrova, Olga; Zaslavsky, Arnaud

    2016-04-01

    Turbulence in the solar wind has been attracting attention since first in-situ measurements in the Heliosphere. Still a lot of open questions remain. In particular, the nature of turbulence around plasma kinetic scales, where self-similarity breaks down and no-power law behaviour of the turbulent spectrum is expected. It is known that approaching these small scales, Probability Distribution Functions (PDF) of magnetic fluctuations deviate strongly from the Gaussian distribution. This is called intermittency and is usually interpreted as presence of coherent structures. Here, using magnetic field waveforms and their wavelet coefficients, we study the nature of these intermittent events. We propose as well a universal description of magnetic fluctuations PDF using a four-parameter function and we describe the evolution of this parameters with increasing frequencies. Using two different approaches we establish the connection between intermittency and the evolution of the turbulent spectrum at ion scales. Finally the relationship between intermittency and ion temperature is discussed.

  8. Magnetofluid Turbulence in the Solar Wind

    NASA Technical Reports Server (NTRS)

    Goldstein, Melvyn L.

    2008-01-01

    The solar wind shows striking characteristics that suggest that it is a turbulent magnetofluid, but the picture is not altogether simple. From the earliest observations, a strong correlation between magnetic fluctuations and plasma velocity fluctuations was noted. The high corrections suggest that the fluctuations are Alfven waves. In addition, the power spectrum of the magnetic fluctuation showed evidence of an inertial range that resembled that seen in fully-developed fluid turbulence. Alfven waves, however, are exact solutions of the equations of incompressible magnetohydrodynamics. Thus, there was a puzzle: how can a magnetofluid consisting of Alfven waves be turbulent? The answer lay in the role of velocity shears in the solar wind that could drive turbulent evolution. Puzzles remain: for example, the power spectrum of the velocity fluctuations is less steep than the slope of the magnetic fluctuations, nor do we understand even now why the solar wind appears to be nearly incompressible with a -5/3 power-spectral index.

  9. Bulk Comptonization by turbulence in accretion discs

    NASA Astrophysics Data System (ADS)

    Kaufman, J.; Blaes, O. M.

    2016-06-01

    Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent `wave' temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, radiation viscous dissipation is suppressed, and the evolution of local photon spectra can be understood in terms of compression and expansion of the strongly coupled photon and gas fluids. We discuss the consequences of these effects for self-consistently resolving and interpreting turbulent Comptonization in spectral calculations in radiation magnetohydrodynamic simulations of high luminosity accretion flows.

  10. Recent developments in plasma turbulence and turbulent transport

    SciTech Connect

    Terry, P.W.

    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.

  11. Creation of arbitrary time-sequenced line spectra with an electro-optic phase modulator.

    PubMed

    Rogers, C E; Carini, J L; Pechkis, J A; Gould, P L

    2011-07-01

    We use a waveguide-based electro-optic phase modulator, driven by a nanosecond-timescale arbitrary waveform generator, to produce an optical spectrum with an arbitrary pattern of peaks. A programmed sequence of linear voltage ramps, with various slopes, is applied to the modulator. The resulting phase ramps give rise to peaks whose frequency offsets relative to the carrier are equal to the slopes of the corresponding linear phase ramps. This simple extension of the serrodyne technique provides multi-line spectra with peak spacings in the 100 MHz range.

  12. Characterizing Wake Turbulence with Staring Lidar Measurements

    NASA Astrophysics Data System (ADS)

    Bastine, D.; Wächter, M.; Peinke, J.; Trabucchi, D.; Kühn, M.

    2015-06-01

    Lidar measurements in the German offshore wind farm Alpha Ventus were performed to investigate the turbulence characteristics of wind turbine wakes. In particular, we compare measurements of the free flow in the surroundings of the wind turbines with measurements in the inner region of a wake flow behind one turbine. Our results indicate that wind turbines modulate the turbulent structures of the flow on a wide range of scales. For the data of the wake flow, the power spectrum as well as the multifractal intermittency coefficient reveal features of homogeneous isotropic turbulence. Thus, we conjecture that on scales of the rotor a new turbulent cascade is initiated, which determines the features of the turbulent wake flow quite independently from the more complex wind flow in the surroundings of the turbine.

  13. Acceleration of particles in imbalanced magnetohydrodynamic turbulence.

    PubMed

    Teaca, Bogdan; Weidl, Martin S; Jenko, Frank; Schlickeiser, Reinhard

    2014-08-01

    The present work investigates the acceleration of test particles, relevant to the solar-wind problem, in balanced and imbalanced magnetohydrodynamic turbulence (terms referring here to turbulent states possessing zero and nonzero cross helicity, respectively). These turbulent states, obtained numerically by prescribing the injection rates for the ideal invariants, are evolved dynamically with the particles. While the energy spectrum for balanced and imbalanced states is known, the impact made on particle heating is a matter of debate, with different considerations giving different results. By performing direct numerical simulations, resonant and nonresonant particle accelerations are automatically considered and the correct turbulent phases are taken into account. For imbalanced turbulence, it is found that the acceleration rate of charged particles is reduced and the heating rate diminished. This behavior is independent of the particle gyroradius, although particles that have a stronger adiabatic motion (smaller gyroradius) tend to experience a larger heating.

  14. Entropic Lattice Boltzmann Algorithms for Turbulence

    NASA Astrophysics Data System (ADS)

    Vahala, George; Yepez, Jeffrey; Soe, Min; Vahala, Linda; Keating, Brian; Carter, Jonathan

    2007-11-01

    For turbulent flows in non-trivial geometry, the scaling of CFD codes (now necessarily non-pseudo spectral) quickly saturate with the number of PEs. By projecting into a lattice kinetic phase space, the turbulent dynamics are simpler and much easier to solve since the underlying kinetic equation has only local algebraic nonlinearities in the macroscopic variables with simple linear kinetic advection. To achieve arbitrary high Reynolds number, a discrete H-theorem constraint is imposed on the collision operator resulting in an entropic lattice Boltzmann (ELB) algorithm that is unconditionally stable and scales almost perfectly with PE's on any supercomputer architecture. At this mesoscopic level, there are various kinetic lattices (ELB-27, ELB-19, ELB-15) which will recover the Navier-Stokes equation to leading order in the Chapman-Enskog asymptotics. We comment on the morphology of turbulence and its correlation to the rate of change of enstrophy as well as simulations on 1600^3 grids.

  15. On stability and turbulence of fluid flows

    NASA Technical Reports Server (NTRS)

    Heisenberg, Werner

    1951-01-01

    This investigation is divided into two parts, the treatment of the stability problem of fluid flows on the one hand, and that of the turbulent motion on the other. The first part summarizes all previous investigations under a unified point of view, that is, sets up as generally as possible the conditions under which a profile possesses unstable or stable characteristics, and indicates the methods for solution of the stability equation for any arbitrary velocity profile and for calculation of the critical Reynolds number for unstable profiles. In the second part, under certain greatly idealizing assumptions, differential equations for the turbulent motions are derived and from them qualitative information about several properties of the turbulent velocity distribution is obtained.

  16. Controlling turbulence

    NASA Astrophysics Data System (ADS)

    Kühnen, Jakob; Hof, Björn

    2015-11-01

    We show that a simple modification of the velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarises. The annihilation of turbulence is achieved by a steady manipulation of the streamwise velocity component alone, greatly reducing control efforts. Several different control techniques are presented: one with a local modification of the flow profile by means of a stationary obstacle, one employing a nozzle injecting fluid through a small gap at the pipe wall and one with a moving wall, where a part of the pipe is shifted in the streamwise direction. All control techniques act on the flow such that the streamwise velocity profile becomes more flat and turbulence gradually grows faint and disappears. In a smooth straight pipe the flow remains laminar downstream of the control. Hence a reduction in skin friction by a factor of 8 and more can be accomplished. Stereoscopic PIV-measurements and movies of the development of the flow during relaminarisation are presented.

  17. Arbitrary order permanent Cartesian multipolar electrostatic interactions

    NASA Astrophysics Data System (ADS)

    Boateng, H. A.; Todorov, I. T.

    2015-01-01

    Recently, there has been a concerted effort to implement advanced classical potential energy surfaces by adding higher order multipoles to fixed point charge electrostatics in a bid to increase the accuracy of simulations of condensed phase systems. One major hurdle is the unwieldy nature of the expressions which in part has limited developers mostly to including only dipoles and quadrupoles. In this paper, we present a generalization of the Cartesian formulation of electrostatic multipolar interactions that enables the specification of an arbitrary order of multipoles. Specifically, we derive formulas for arbitrary order implementation of the particle mesh Ewald method and give a closed form formula for the stress tensor in the reciprocal space. In addition, we provide recurrence relations for common electrostatic potentials employed in molecular simulations, which allows for the generalization to arbitrary order and guarantees a computational cost that scales as O(p3) for Cartesian multipole interactions of order p.

  18. Vortex burst as a source of turbulence

    NASA Astrophysics Data System (ADS)

    Cuypers, Yannis; Maurel, Agnes; Petitjeans, Philippe

    2003-11-01

    An important issue in turbulence is to understand what kinds of elementary structures are responsible for the part of the turbulent energy spectrum described by Kolmogorov'S celebrated k-5/3 law. A model for such a structure has been proposed by Lundgren 1982 in the form of a spiral vortex subjected to an axially straining field . We report experimental results of a vortex burst in a laminar flow environment showing that this structure is responsible for a k-5/3 part in the energy spectrum. If there are many experimental evidences of vortices with spiral structure in turbulent flows, it is the first time that such an elementary structure is experimentally shown to provide an inertial range spectrum of Kolmogorov type.

  19. Simulation of turbulent wall pressure

    NASA Technical Reports Server (NTRS)

    Ash, R. L.

    1978-01-01

    A Monte Carlo procedure was developed to simulate turbulent boundary layer wall pressure fluctuations. The approach utilizes much of the newly available conditional sampling information to construct the required distribution functions. Various disturbance wave forms were examined, as well as the effect of frequency-dependent decay. Good agreement between the simulation and experimental data was achieved for root mean square pressure level, power spectrum, and space time correlation.

  20. Phytoplankton's motion in turbulent ocean.

    PubMed

    Fouxon, Itzhak; Leshansky, Alexander

    2015-07-01

    We study the influence of turbulence on upward motion of phytoplankton. Interaction with the flow is described by the Pedley-Kessler model considering spherical microorganisms. We find a range of parameters when the upward drift is only weakly perturbed or when turbulence completely randomizes the drift direction. When the perturbation is small, the drift is either determined by the local vorticity or is Gaussian. We find a range of parameters where the phytoplankton interaction with the flow can be described consistently as diffusion of orientation in effective potential. By solving the corresponding Fokker-Planck equation we find exponential steady-state distribution of phytoplankton's propulsion orientation. We further identify the range of parameters where phytoplankton's drift velocity with respect to the flow is determined uniquely by its position. In this case, one can describe phytoplankton's motion by a smooth flow and phytoplankton concentrates on fractal. We find fractal dimensions and demonstrate that phytoplankton forms vertical stripes in space with a nonisotropic pair-correlation function of concentration increased in the vertical direction. The probability density function of the distance between two particles obeys power law with the negative exponent given by the ratio of integrals of the turbulent energy spectrum. We find the regime of strong clustering where the exponent is of order one so that turbulence increases the rate of collisions by a large factor. The predictions hold for Navier-Stokes turbulence and stand for testing.

  1. Regimes of turbulence without an energy cascade

    NASA Astrophysics Data System (ADS)

    Barenghi, C. F.; Sergeev, Y. A.; Baggaley, A. W.

    2016-10-01

    Experiments and numerical simulations of turbulent 4He and 3He-B have established that, at hydrodynamic length scales larger than the average distance between quantum vortices, the energy spectrum obeys the same 5/3 Kolmogorov law which is observed in the homogeneous isotropic turbulence of ordinary fluids. The importance of the 5/3 law is that it points to the existence of a Richardson energy cascade from large eddies to small eddies. However, there is also evidence of quantum turbulent regimes without Kolmogorov scaling. This raises the important questions of why, in such regimes, the Kolmogorov spectrum fails to form, what is the physical nature of turbulence without energy cascade, and whether hydrodynamical models can account for the unusual behaviour of turbulent superfluid helium. In this work we describe simple physical mechanisms which prevent the formation of Kolmogorov scaling in the thermal counterflow, and analyze the conditions necessary for emergence of quasiclassical regime in quantum turbulence generated by injection of vortex rings at low temperatures. Our models justify the hydrodynamical description of quantum turbulence and shed light into an unexpected regime of vortex dynamics.

  2. Regimes of turbulence without an energy cascade

    PubMed Central

    Barenghi, C. F.; Sergeev, Y. A.; Baggaley, A. W.

    2016-01-01

    Experiments and numerical simulations of turbulent 4He and 3He-B have established that, at hydrodynamic length scales larger than the average distance between quantum vortices, the energy spectrum obeys the same 5/3 Kolmogorov law which is observed in the homogeneous isotropic turbulence of ordinary fluids. The importance of the 5/3 law is that it points to the existence of a Richardson energy cascade from large eddies to small eddies. However, there is also evidence of quantum turbulent regimes without Kolmogorov scaling. This raises the important questions of why, in such regimes, the Kolmogorov spectrum fails to form, what is the physical nature of turbulence without energy cascade, and whether hydrodynamical models can account for the unusual behaviour of turbulent superfluid helium. In this work we describe simple physical mechanisms which prevent the formation of Kolmogorov scaling in the thermal counterflow, and analyze the conditions necessary for emergence of quasiclassical regime in quantum turbulence generated by injection of vortex rings at low temperatures. Our models justify the hydrodynamical description of quantum turbulence and shed light into an unexpected regime of vortex dynamics. PMID:27761005

  3. Arbitrary segments of absolute negative mobility

    NASA Astrophysics Data System (ADS)

    Chen, Ruyin; Nie, Linru; Chen, Chongyang; Wang, Chaojie

    2017-01-01

    In previous research work, investigators have reported only one or two segments of absolute negative mobility (ANM) in a periodic potential. In fact, many segments of ANM also occur in the system considered here. We investigate transport of an inertial particle in a gating ratchet periodic potential subjected to a constant bias force. Our numerical results show that its mean velocity can decrease with the bias force increasing, i.e. ANM phenomenon. Furthermore, the ANM can take place arbitrary segments, even up to more than thirty. Intrinsic physical mechanism and conditions for arbitrary segments of ANM to occur are discussed in detail.

  4. 3D linear dispersion relation for arbitrary shear currents

    NASA Astrophysics Data System (ADS)

    Ellingsen, Simen; Smeltzer, Benjamin

    2016-11-01

    Dispesion properties of waves can be strongly affected by the presence of a sub-surface shear current. A number of approximation techniques exist to calculate dispersion properties of waves on shear currents, most relying on assumptions such as long wavelength, weak vorticity or near-potentiality. Another approach has been to approximate the shear current by a piecewise linear function, corresponding to dividing the fluid phase into a sequence of layers with constant vorticity in each layer. We discuss the practical implementation of this scheme in 3D for arbitrary wavelengths, and how how it may be applied to 3D linear surface waves problems where the full Fourier spectrum in the horizontal plane is required. Solutions to particular implementation challenges such as optimal choice of layer distribution and the nature and removal of spurious solutions are presented, as are several validation cases and tests of convergence. Applications to ring waves and ship waves are provided as examples. Norwegian Research Council (FRINATEK).

  5. Shell model for buoyancy-driven turbulence

    NASA Astrophysics Data System (ADS)

    Kumar, Abhishek; Verma, Mahendra K.

    2015-04-01

    In this paper we present a unified shell model for stably stratified and convective turbulence. Numerical simulation of this model for stably stratified flow shows Bolgiano-Obukhbov scaling in which the kinetic energy spectrum varies as k-11 /5. The shell model of convective turbulence yields Kolmogorov's spectrum. These results are consistent with the energy flux and energy feed due to buoyancy, and are in good agreement with direct numerical simulations of Kumar et al. [Phys. Rev. E 90, 023016 (2014), 10.1103/PhysRevE.90.023016].

  6. Magnetohydrodynamic Turbulence

    NASA Astrophysics Data System (ADS)

    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.

  7. The residual zonal flow in tokamak plasmas toroidally rotating at arbitrary velocity

    SciTech Connect

    Zhou, Deng

    2014-08-15

    Zonal flows, initially driven by ion-temperature-gradient turbulence, may evolve due to the neoclassic polarization in a collisionless tokamak plasma. In our previous work [D. Zhou, Nucl. Fusion 54, 042002 (2014)], the residual zonal flow in a tokamak plasma rotating toroidally at sonic speed is found to have the same form as that of a static plasma. In the present work, the form of the residual zonal flow is presented for tokamak plasmas rotating toroidally at arbitrary velocity. The gyro-kinetic equation is analytically solved for low speed rotation to give the expression of residual zonal flows, and the expression is then generalized for cases with arbitrary rotating velocity through interpolation. The zonal flow level decreases as the rotating velocity increases. The numerical evaluation is in good agreement with the former simulation result for high aspect ratio tokamaks.

  8. Spectrum of Wind Power Fluctuations

    NASA Astrophysics Data System (ADS)

    Bandi, M. M.

    2017-01-01

    Wind power fluctuations for an individual turbine and plant have been widely reported to follow the Kolmogorov spectrum of atmospheric turbulence; both vary with a fluctuation time scale τ as τ2 /3. Yet, this scaling has not been explained through turbulence theory. Using turbines as probes of turbulence, we show the τ2 /3 scaling results from a large scale influence of atmospheric turbulence. Owing to this long-range influence spanning 100s of kilometers, when power from geographically distributed wind plants is summed into aggregate power at the grid, fluctuations average (geographic smoothing) and their scaling steepens from τ2 /3→τ4 /3, beyond which further smoothing is not possible. Our analysis demonstrates grids have already reached this τ4 /3 spectral limit to geographic smoothing.

  9. Aspects of Turbulent / Non-Turbulent Interfaces

    NASA Technical Reports Server (NTRS)

    Bisset, D. K.; Hunt, J. C. R.; Rogers, M. M.; Koen, Dennis (Technical Monitor)

    1999-01-01

    A distinct boundary between turbulent and non-turbulent regions in a fluid of otherwise constant properties is found in many laboratory and engineering turbulent flows, including jets, mixing layers, boundary layers and wakes. Generally, the flow has mean shear in at least one direction within t he turbulent zone, but the non-turbulent zones have no shear (adjacent laminar shear is a different case, e.g. transition in a boundary layer). There may be purely passive differences between the turbulent and non-turbulent zones, e.g. small variations in temperature or scalar concentration, for which turbulent mixing is an important issue. The boundary has several major characteristics of interest for the present study. Firstly, the boundary advances into the non-turbulent fluid, or in other words, nonturbulent fluid is entrained. Secondly, the change in turbulence properties across the boundary is remarkably abrupt; strong turbulent motions come close to the nonturbulent fluid, promoting entrainment. Thirdly, the boundary is irregular with a continually changing convoluted shape, which produces statistical intermittency. Its shape is contorted at all scales of the turbulent motion.

  10. Turbulence and turbulent mixing in natural fluids

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.

    2010-12-01

    Turbulence and turbulent mixing in natural fluids begin with big bang turbulence powered by spinning combustible combinations of Planck particles and Planck antiparticles. Particle prograde accretions on a spinning pair release 42% of the particle rest mass energy to produce more fuel for turbulent combustion. Negative viscous stresses and negative turbulence stresses work against gravity, extracting mass-energy and space-time from the vacuum. Turbulence mixes cooling temperatures until strong-force viscous stresses freeze out turbulent mixing patterns as the first fossil turbulence. Cosmic microwave background temperature anisotropies show big bang turbulence fossils along with fossils of weak plasma turbulence triggered as plasma photon-viscous forces permitting gravitational fragmentation on supercluster to galaxy mass scales. Turbulent morphologies and viscous-turbulent lengths appear as linear gas-protogalaxy-clusters in the Hubble ultra-deep field at z~7. Protogalaxies fragment into Jeans mass clumps of primordial-gas planets at decoupling: the dark matter of galaxies. Shortly after the plasma-to-gas transition, planet mergers produce stars that explode on overfeeding to fertilize and distribute the first life.

  11. Statistical turbulence theory and turbulence phenomenology

    NASA Technical Reports Server (NTRS)

    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.

  12. Ribbon turbulence

    NASA Astrophysics Data System (ADS)

    Venaille, Antoine; Nadeau, Louis-Philippe; Vallis, Geoffrey

    2014-12-01

    We investigate the non-linear equilibration of a two-layer quasi-geostrophic flow in a channel with an initial eastward baroclinically unstable jet in the upper layer, paying particular attention to the role of bottom friction. In the limit of low bottom friction, classical theory of geostrophic turbulence predicts an inverse cascade of kinetic energy in the horizontal with condensation at the domain scale and barotropization in the vertical. By contrast, in the limit of large bottom friction, the flow is dominated by ribbons of high kinetic energy in the upper layer. These ribbons correspond to meandering jets separating regions of homogenized potential vorticity. We interpret these results by taking advantage of the peculiar conservation laws satisfied by this system: the dynamics can be recast in such a way that the initial eastward jet in the upper layer appears as an initial source of potential vorticity levels in the upper layer. The initial baroclinic instability leads to a turbulent flow that stirs this potential vorticity field while conserving the global distribution of potential vorticity levels. Statistical mechanical theory of the 1 1/2 layer quasi-geostrophic model predicts the formation of two regions of homogenized potential vorticity separated by a minimal interface. We explain that cascade phenomenology leads to the same result. We then show that the dynamics of the ribbons results from a competition between a tendency to reach the equilibrium state and baroclinic instability that induces meanders of the interface. These meanders intermittently break and induce potential vorticity mixing, but the interface remains sharp throughout the flow evolution. We show that for some parameter regimes, the ribbons act as a mixing barrier which prevents relaxation toward equilibrium, favouring the emergence of multiple zonal (eastward) jets.

  13. Potential flow about arbitrary biplane wing sections

    NASA Technical Reports Server (NTRS)

    Garrick, I E

    1937-01-01

    A rigorous treatment is given of the problem of determining the two-dimensional potential flow around arbitrary biplane cellules. The analysis involves the use of elliptic functions and is sufficiently general to include the effects of such elements as the section shapes, the chord ratio, gap, stagger, and decalage, which elements may be specified arbitrarily. The flow problem is resolved by making use of the methods of conformal representation. Thus the solution of the problem of transforming conformally two arbitrary contours into two circles is expressed by a pair of simultaneous integral equations, for which a method of numerical solution is outlined. As an example of the numerical process, the pressure distribution over certain arrangements of the NACA 4412 airfoil in biplane combinations is presented and compared with the monoplane pressure distribution.

  14. General Potential Theory of Arbitrary Wing Sections

    NASA Technical Reports Server (NTRS)

    Theodorsen, T.; Garrick, I. E.

    1979-01-01

    The problem of determining the two dimensional potential flow around wing sections of any shape is examined. The problem is condensed into the compact form of an integral equation capable of yielding numerical solutions by a direct process. An attempt is made to analyze and coordinate the results of earlier studies relating to properties of wing sections. The existing approximate theory of thin wing sections and the Joukowski theory with its numerous generalizations are reduced to special cases of the general theory of arbitrary sections, permitting a clearer perspective of the entire field. The method which permits the determination of the velocity at any point of an arbitrary section and the associated lift and moments is described. The method is also discussed in terms for developing new shapes of preassigned aerodynamical properties.

  15. Quantum Fidelity for Arbitrary Gaussian States.

    PubMed

    Banchi, Leonardo; Braunstein, Samuel L; Pirandola, Stefano

    2015-12-31

    We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information, and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.

  16. The arbitrariness and normativity of social conventions.

    PubMed

    Al-Amoudi, Ismael; Latsis, John

    2014-06-01

    This paper investigates a puzzling feature of social conventions: the fact that they are both arbitrary and normative. We examine how this tension is addressed in sociological accounts of conventional phenomena. Traditional approaches tend to generate either synchronic accounts that fail to consider the arbitrariness of conventions, or diachronic accounts that miss central aspects of their normativity. As a remedy, we propose a processual conception that considers conventions as both the outcome and material cause of much human activity. This conceptualization, which borrows from the économie des conventions as well as critical realism, provides a novel perspective on how conventions are nested and defined, and on how they are established, maintained and challenged.

  17. Unsteady aerodynamic modeling for arbitrary motions

    NASA Technical Reports Server (NTRS)

    Edwards, J. W.; Ashley, H.; Breakwell, J. V.

    1977-01-01

    A study is presented on the unsteady aerodynamic loads due to arbitrary motions of a thin wing and their adaptation for the calculation of response and true stability of aeroelastic modes. In an Appendix, the use of Laplace transform techniques and the generalized Theodorsen function for two-dimensional incompressible flow is reviewed. New applications of the same approach are shown also to yield airloads valid for quite general small motions. Numerical results are given for the two-dimensional supersonic case. Previously proposed approximate methods, starting from simple harmonic unsteady theory, are evaluated by comparison with exact results obtained by the present approach. The Laplace inversion integral is employed to separate the loads into 'rational' and 'nonrational' parts, of which only the former are involved in aeroelastic stability of the wing. Among other suggestions for further work, it is explained how existing aerodynamic computer programs may be adapted in a fairly straightforward fashion to deal with arbitrary transients.

  18. Fraunhofer diffraction by arbitrary-shaped obstacles.

    PubMed

    Malinka, Aleksey V; Zege, Eleonora P

    2009-08-01

    We consider Fraunhofer diffraction by an ensemble of large arbitrary-shaped screens that are randomly oriented in the plane of a wavefront and have edges of arbitrary shape. It is shown that far outside the main diffraction peak the differential scattering cross section behaves asymptotically as theta(-3), where theta is the diffraction angle. Moreover, the differential scattering cross section depends only on the length of the contours bordering the screens and does not depend on the shape of the obstacles. As both strictly forward and total diffraction cross sections are specified by obstacle area only, the differential cross section of size-distributed obstacles is expected to be nearly independent of obstacle shape over the entire region of the diffraction angles.

  19. Quantum Fidelity for Arbitrary Gaussian States

    NASA Astrophysics Data System (ADS)

    Banchi, Leonardo; Braunstein, Samuel L.; Pirandola, Stefano

    2015-12-01

    We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information, and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.

  20. Probabilistically teleporting arbitrary two-qubit states

    NASA Astrophysics Data System (ADS)

    Choudhury, Binayak S.; Dhara, Arpan

    2016-12-01

    In this paper we make use of two non-maximally entangled three-qubit channels for probabilistically teleporting arbitrary two particle states from a sender to a receiver. We also calculate the success probability of the teleportation. In the protocol we use two measurements of which one is a POVM and the other is a projective measurement. The POVM provides the protocol with operational advantage.

  1. Turbulent resistivity, diffusion and heating

    NASA Technical Reports Server (NTRS)

    Fried, B. D.; Kennel, C. F.; Mackenzie, K.; Coroniti, F. V.; Kindel, J. M.; Stenzel, R.; Taylor, R. J.; White, R.; Wong, A. Y.; Bernstein, W.

    1971-01-01

    Experimental and theoretical studies are reported on ion acoustic and ion cyclotron turbulence and their roles in anomalous resistivity, viscosity, diffusion and heating and in the structure of collisionless electrostatic shocks. Resistance due to ion acoustic turbulence has been observed in experiments with a streaming cesium plasma in which electron current, potential rise due to turbulent resistivity, spectrum of unstable ion acoustic waves, and associated electron heating were all measured directly. Kinetic theory calculations for an expanding, unstable plasma, give results in agreement with the experiment. In a strong magnetic field, with T sub e/T sub i approximately 1 and current densities typical for present Tokomaks, the plasma is stable to ion acoustic but unstable to current driven electrostatic ion cyclotron waves. Relevant characteristics of these waves are calculated and it is shown that for ion, beta greater than m sub e/m sub i, the electromagnetic ion cyclotron wave has a lower instability threshold than the electrostatic one. However, when ion acoustic turbulence is present experiments with double plasma devices show rapid anomalous heating of an ion beam streaming through a plasma.

  2. Distinguishing Proteins From Arbitrary Amino Acid Sequences

    PubMed Central

    Yau, Stephen S.-T.; Mao, Wei-Guang; Benson, Max; He, Rong Lucy

    2015-01-01

    What kinds of amino acid sequences could possibly be protein sequences? From all existing databases that we can find, known proteins are only a small fraction of all possible combinations of amino acids. Beginning with Sanger's first detailed determination of a protein sequence in 1952, previous studies have focused on describing the structure of existing protein sequences in order to construct the protein universe. No one, however, has developed a criteria for determining whether an arbitrary amino acid sequence can be a protein. Here we show that when the collection of arbitrary amino acid sequences is viewed in an appropriate geometric context, the protein sequences cluster together. This leads to a new computational test, described here, that has proved to be remarkably accurate at determining whether an arbitrary amino acid sequence can be a protein. Even more, if the results of this test indicate that the sequence can be a protein, and it is indeed a protein sequence, then its identity as a protein sequence is uniquely defined. We anticipate our computational test will be useful for those who are attempting to complete the job of discovering all proteins, or constructing the protein universe. PMID:25609314

  3. Inverse energy cascade in rotational turbulence

    NASA Astrophysics Data System (ADS)

    Yu, Huidan (Whitney); Chen, Rou; Wang, Hengjie

    2012-11-01

    Rotation influences large-scale motions in the Earth's atmosphere and oceans and it is also important in many industrial applications such as turbo machinery, rotor-craft, and rotating channel etc. We study rotation effects on decaying isotropic turbulence through direct numerical simulation using lattice Boltzmann method. A Coriolis force characterized by the angular velocity of the frame of reference Ω is included in the lattice Boltzmann equations. The effects of rotation on fundamental turbulence features such as kinetic energy and enstrophy decay, energy spectrum, etc. are studied. The decay laws are quantitatively captured. Inverse energy cascade are observed in the 3D turbulence with and without rotation. The scaling of the inverse energy cascade and its relation to initial energy spectrum are explored. Indiana University-Purdue University Indianapolis (IUPUI).

  4. A model for fully developed turbulence

    NASA Astrophysics Data System (ADS)

    Canuto, V. M.; Goldman, I.; Chasnov, J.

    1987-11-01

    A model for stationary, fully developed turbulence is presented in which the turbulent spectral energy function is completely determined once the time scale for the energy fed into the eddy interaction is known. The form of the eddy correlation time scale determining the turbulent viscosity is suggested by the basic equation of the model itself, up to a dimensionless constant that is fixed by demanding that the coefficient of the spectrum in the Heisenberg-Kolmogoroff inertial range of wavenunmbers be the experimental value. The model makes quantitative predictions that are compared with data on turbulent convection; the k-epsilon and Smagorinsky relations; the spectral function, transfer term, and dissipation term; the skewness factor; the Kolmogoroff and Batchelor constants; and the inertial-conductive and inertial-convective ranges.

  5. Forced organization of flute-type turbulence by convective cell injection

    SciTech Connect

    Iizuka, S.; Huld, T.; Pecseli, H.L.; Rasmussen, J.J.

    1988-03-14

    Nonlinear interactions between flute-type turbulence and an externally excited convective cell in a strongly magnetized plasma are investigated. During the interaction the azimuthal-mode-number spectrum of the turbulence is deformed and a broad spectrum evolves, indicating an inverse cascade. As a result of a modification in phase and amplitude of the fluctuations, an organized structure is created in turbulence. The macroscopic behavior is well explained by a Van der Pol--type equation.

  6. Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Turner, L.

    1981-01-01

    A strong external dc magnetic field introduces a basic anisotropy in incompressible MHD turbulence. The modifications that this is likely to produce in the properties of the turbulence are investigated for high Reynolds numbers. It is found that the turbulent spectrum splits into two parts: (1) an essentially two-dimensional spectrum with both the velocity field and the magnetic fluctuations perpendicular to the dc magnetic field, and (2) a generally weaker and more nearly isotropic spectrum of Alfven waves. These results are discussed in relation to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrorotor tokamak, as well as in relation to measurements of MHD turbulence in the solar wind.

  7. Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Turner, L.

    1981-01-01

    A strong external dc magnetic field introduces a basic anisotropy into incompressible magnetohydrodynamic turbulence. The modifications that this is likely to produce in the properties of the turbulence are explored for the high Reynolds number case. The conclusion is reached that the turbulent spectrum splits into two parts: an essentially two dimensional spectrum with both the velocity field and magnetic fluctuations perpendicular to the dc magnetic field, and a generally weaker and more nearly isotropic spectrum of Alfven waves. A minimal characterization of the spectral density tensors is given. Similarities to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrotor Tokamak are remarked upon, as are certain implications for the Belcher and Davis measurements of magnetohydrodynamic turbulence in the solar wind.

  8. Gaussian entanglement in the turbulent atmosphere

    NASA Astrophysics Data System (ADS)

    Bohmann, M.; Semenov, A. A.; Sperling, J.; Vogel, W.

    2016-07-01

    We provide a rigorous treatment of the entanglement properties of two-mode Gaussian states in atmospheric channels by deriving and analyzing the input-output relations for the corresponding entanglement test. A key feature of such turbulent channels is a nontrivial dependence of the transmitted continuous-variable entanglement on coherent displacements of the quantum state of the input field. Remarkably, this allows one to optimize the entanglement certification by modifying local coherent amplitudes using a finite, but optimal amount of squeezing. In addition, we propose a protocol which, in principle, renders it possible to transfer the Gaussian entanglement through any turbulent channel over arbitrary distances. Therefore, our approach provides the theoretical foundation for advanced applications of Gaussian entanglement in free-space quantum communication.

  9. TURBULENT DISKS ARE NEVER STABLE: FRAGMENTATION AND TURBULENCE-PROMOTED PLANET FORMATION

    SciTech Connect

    Hopkins, Philip F.; Christiansen, Jessie L.

    2013-10-10

    A fundamental assumption in our understanding of disks is that when the Toomre Q >> 1, the disk is stable against fragmentation into self-gravitating objects (and so cannot form planets via direct collapse). But if disks are turbulent, this neglects a spectrum of stochastic density fluctuations that can produce rare, high-density mass concentrations. Here, we use a recently developed analytic framework to predict the statistics of these fluctuations, i.e., the rate of fragmentation and mass spectrum of fragments formed in a turbulent Keplerian disk. Turbulent disks are never completely stable: we calculate the (always finite) probability of forming self-gravitating structures via stochastic turbulent density fluctuations in such disks. Modest sub-sonic turbulence above Mach number M∼0.1 can produce a few stochastic fragmentation or 'direct collapse' events over ∼Myr timescales, even if Q >> 1 and cooling is slow (t{sub cool} >> t{sub orbit}). In transsonic turbulence this extends to Q ∼ 100. We derive the true Q-criterion needed to suppress such events, which scales exponentially with Mach number. We specify to turbulence driven by magneto-rotational instability, convection, or spiral waves and derive equivalent criteria in terms of Q and the cooling time. Cooling times ∼> 50 t{sub dyn} may be required to completely suppress fragmentation. These gravo-turbulent events produce mass spectra peaked near ∼(Q M{sub disk}/M{sub *}){sup 2} M{sub disk} (rocky-to-giant planet masses, increasing with distance from the star). We apply this to protoplanetary disk models and show that even minimum-mass solar nebulae could experience stochastic collapse events, provided a source of turbulence.

  10. Gaussian Quadrature Formulae for Arbitrary Positive Measures

    PubMed Central

    Fernandes, Andrew D.; Atchley, William R.

    2007-01-01

    We present computational methods and subroutines to compute Gaussian quadrature integration formulas for arbitrary positive measures. For expensive integrands that can be factored into well-known forms, Gaussian quadrature schemes allow for efficient evaluation of high-accuracy and -precision numerical integrals, especially compared to general ad hoc schemes. In addition, for certain well-known density measures (the normal, gamma, log-normal, Student’s t, inverse-gamma, beta, and Fisher’s F) we present exact formulae for computing the respective quadrature scheme. PMID:19455218

  11. Confined systems within arbitrary enclosed surfaces

    NASA Astrophysics Data System (ADS)

    Burrows, B. L.; Cohen, M.

    2016-06-01

    A new model of electronic confinement in atoms and molecules is presented. This is based on the electronic flux J which is assumed to vanish on some notional bounding surface of arbitrary shape. J is necessarily calculated using an approximate wave-function, whose parameters are chosen to satisfy the required surface conditions. This model embraces the results of all previous calculations for which the wave-functions or their derivatives vanish on conveniently shaped surfaces, but now extends the theory to more general surfaces. Examples include one-centre hydrogen-like atoms, the valence state of Li and the two centre molecular systems {{{H}}}2+ and {{HeH}}++.

  12. Oceanic turbulence effects on long-exposure and short-exposure imaging

    NASA Astrophysics Data System (ADS)

    Pu, Huan; Ji, Xiaoling

    2016-10-01

    Based on the power spectrum of oceanic turbulence, the modulation transfer functions and the optical resolution for long-exposure and short-exposure imaging through oceanic turbulence are studied in detail. The analytical formulae for the seeing parameter and the tilt variance in oceanic turbulence are derived, and it is found that the relationship between the seeing parameter and the spatial coherence width in oceanic turbulence is just like that in atmospheric turbulence. Furthermore, the model of underwater imaging shown in this paper considers both temperature and salinity fluctuations for oceanic turbulence. It is found that, compared with the dominating salinity-induced turbulence, the range of angular spatial frequency where oceanic turbulence plays the major role rather than particle scattering is higher for the dominating temperature-induced turbulence.

  13. Effects of very high turbulence on convective heat transfer

    NASA Technical Reports Server (NTRS)

    Moffat, R. J.; Maciejewski, P. K.

    1984-01-01

    The effects of high-intensity, large-scale turbulence on turbulent boundary-layer heat transfer are studied. Flow fields were produced with turbulence intensities up to 40% and length scales up to several times the boundary layer thickness. In addition, three different types of turbulence will be compared to see whether they have the same effect on the boundary layer. The three are: the far field of a free jet, flow downstream of a grid, and flow downstream of a simulated gas turbine combustor. Each turbulence field will be characterized by several measures: intensity (by component), scale, and spectrum. Heat transfer will be measured on a 2.5 m long, 0.5 m wide flat plate using the energy-balance technique. The same plate will be used in each of the four flow fields; a low-turbulence tunnel for baseline data, and the three flow situations mentioned.

  14. The energy spectrum for stochastic eddies with gamma distribution

    NASA Astrophysics Data System (ADS)

    Kara, Rukiye; Caglar, Mine

    2012-09-01

    Lundgren (1982) showed that strained spiral vortex model for turbulent fine structure has exponential Kolmogorov energy spectrum form. Caglar (2007) has generalized Cinlar velocity field which defined a similar structure with Lundgren vortex and computed the energy spectrum. In this study, we investigate the energy spectrum of the stochastic velocity field using Gamma distribution for small scale eddies.

  15. Mirror Instability in the Turbulent Solar Wind

    NASA Astrophysics Data System (ADS)

    Hellinger, Petr; Landi, Simone; Matteini, Lorenzo; Verdini, Andrea; Franci, Luca

    2017-04-01

    The relationship between a decaying strong turbulence and the mirror instability in a slowly expanding plasma is investigated using two-dimensional hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and a vanishing correlation between the two fields. A turbulent cascade rapidly develops, magnetic field fluctuations exhibit a Kolmogorov-like power-law spectrum at large scales and a steeper spectrum at sub-ion scales. The imposed expansion (taking a strictly transverse ambient magnetic field) leads to the generation of an important perpendicular proton temperature anisotropy that eventually drives the mirror instability. This instability generates large-amplitude, nonpropagating, compressible, pressure-balanced magnetic structures in a form of magnetic enhancements/humps that reduce the perpendicular temperature anisotropy.

  16. Optical distortions by compressible turbulence

    NASA Astrophysics Data System (ADS)

    Mani, Ali

    Optical distortions induced by refractive index fluctuations in turbulent flows are a serious concern in airborne communication and imaging systems. This project focuses on aero-optical flows in which compressible turbulence is the dominant source of optical distortions. These flows include boundary layers, free shear layers, cavity flows, and wakes typically associated with flight conditions. The present study consists of two theoretical analyses and an extensive numerical investigation of optical distortions by separated shear layers and turbulent wakes. We present an analysis of far-field optical statistics in a general aero-optical framework. Based on this analysis, measures of far-field distortion, such as tilt, spread, and loss of focus-depth, are linked to key flow statistics. By employing these measures, we quantify distortion effects through a set of norms that have provable scaling properties with key optical parameters. The second analysis presents a theoretical estimate of the range of optically important flow scales in an arbitrary aero-optical flowfield. We show that in the limit of high Reynolds numbers, the smallest optically important scale does not depend on the Kolmogorov scale. For a given geometry this length scale depends only on the flow Mach number, freestream refractive index, and the optical wavelength. The provided formula can be used to estimate grid resolution requirements for numerical simulations of aero-optical phenomena. A rough estimate indicates that resolution requirements for accurate prediction of aero-optics is not much higher than typical LES requirements. As a model problem, compressible turbulent flows over a circular cylinder is considered to study the fundamental physics of aero-optical effects. Large-eddy simulation with a high-resolution numerical scheme is employed to compute variations of the refractive index field in the separated shear layers and turbulent wakes in a range of flow Mach numbers (0.2--0.85) and

  17. Computer program for calculating laminar, transitional, and turbulent boundary layers for a compressible axisymmetric flow

    NASA Technical Reports Server (NTRS)

    Albers, J. A.; Gregg, J. L.

    1974-01-01

    A finite-difference program is described for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain the factors of arbitrary Reynolds number, free-stream Mach number, free-stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile.

  18. Determining the alpha dynamo parameter in incompressible homogeneous magnetohydrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Matthaeus, W. H.; Goldstein, M. L.; Lantz, S. R.

    1983-01-01

    Alpha, an important parameter in dynamo theory, is proportional to either the kinetic, current, magnetic, or velocity helicity of the fluctuating magnetic field and fluctuating velocity field. The particular helicity to which alpha is proportional depends on the assumptions used in deriving the first order smoothed equations that describe the alpha effect. In two cases, when alpha is proportional to either the magnetic helicity or velocity helicity, alpha is determined experimentally from two point measurements of the fluctuating fields in incompressible, homogeneous turbulence having arbitrary symmetry. For the other two possibilities, alpha is determined if the turbulence is isotropic.

  19. Statistical theory of turbulent incompressible multimaterial flow

    SciTech Connect

    Kashiwa, B.

    1987-10-01

    Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of kappa-epsilon modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy kappa, and the rate of fluctuational energy dissipation epsilon, for each material. Hence a set of kappa and epsilon equations must be solved, together with mean mass and momentum conservation equations, for each material. Both kappa and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a pipe.

  20. Arbitrary Order Hierarchical Bases for Computational Electromagnetics

    SciTech Connect

    Rieben, R N; White, D; Rodrigue, G

    2002-12-20

    We present a clear and general method for constructing hierarchical vector bases of arbitrary polynomial degree for use in the finite element solution of Maxwell's equations. Hierarchical bases enable p-refinement methods, where elements in a mesh can have different degrees of approximation, to be easily implemented. This can prove to be quite useful as sections of a computational domain can be selectively refined in order to achieve a greater error tolerance without the cost of refining the entire domain. While there are hierarchical formulations of vector finite elements in publication (e.g. [1]), they are defined for tetrahedral elements only, and are not generalized for arbitrary polynomial degree. Recently, Hiptmair, motivated by the theory of exterior algebra and differential forms presented a unified mathematical framework for the construction of conforming finite element spaces [2]. In [2], both 1-form (also called H(curl)) and 2-form (also called H(div)) conforming finite element spaces and the definition of their degrees of freedom are presented. These degrees of freedom are weighted integrals where the weighting function determines the character of the bases, i.e. interpolatory, hierarchical, etc.

  1. Zellweger Spectrum

    MedlinePlus

    ... Resources Conference News Contact Us Donate The Zellweger Spectrum Zellweger Syndrome, Neonatal Adrenoleukodystrophy (NALD), and Infantile Refsum’s ... of severity of disease. What causes the Zellweger spectrum of diseases? As we mentioned, disorders of the ...

  2. Hyperspectral Image Turbulence Measurements of the Atmosphere

    NASA Technical Reports Server (NTRS)

    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.

  3. Spin filter for arbitrary spins by substrate engineering

    NASA Astrophysics Data System (ADS)

    Pal, Biplab; Römer, Rudolf A.; Chakrabarti, Arunava

    2016-08-01

    We design spin filters for particles with potentially arbitrary spin S≤ft(=1/2,1,3/2,\\ldots \\right) using a one-dimensional periodic chain of magnetic atoms as a quantum device. Describing the system within a tight-binding formalism we present an analytical method to unravel the analogy between a one-dimensional magnetic chain and a multi-strand ladder network. This analogy is crucial, and is subsequently exploited to engineer gaps in the energy spectrum by an appropriate choice of the magnetic substrate. We obtain an exact correlation between the magnitude of the spin of the incoming beam of particles and the magnetic moment of the substrate atoms in the chain desired for opening up of a spectral gap. Results of spin polarized transport, calculated within a transfer matrix formalism, are presented for particles having half-integer as well as higher spin states. We find that the chain can be made to act as a quantum device which opens a transmission window only for selected spin components over certain ranges of the Fermi energy, blocking them in the remaining part of the spectrum. The results appear to be robust even when the choice of the substrate atoms deviates substantially from the ideal situation, as verified by extending the ideas to the case of a ‘spin spiral’. Interestingly, the spin spiral geometry, apart from exhibiting the filtering effect, is also seen to act as a device flipping spins—an effect that can be monitored by an interplay of the system size and the period of the spiral. Our scheme is applicable to ultracold quantum gases, and might inspire future experiments in this direction.

  4. A small-scale turbulence model

    NASA Technical Reports Server (NTRS)

    Lundgren, T. S.

    1992-01-01

    A model for the small-scale structure of turbulence is reformulated in such a way that it may be conveniently computed. The model is an ensemble of randomly oriented structured two dimensional vortices stretched by an axially symmetric strain flow. The energy spectrum of the resulting flow may be expressed as a time integral involving only the enstrophy spectrum of the time evolving two-dimensional cross section flow, which may be obtained numerically. Examples are given in which a k(exp -5/3) spectrum is obtained by this method without using large wave number asymptotic analysis. The k(exp -5/3) inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the two-dimensional enstrophy spectrum. The results are insensitive to time dependence of the strain-rate, including even intermittent on-or-off strains.

  5. On the nature of magnetic turbulence in rotating, shearing flows

    NASA Astrophysics Data System (ADS)

    Walker, Justin; Lesur, Geoffroy; Boldyrev, Stanislav

    2016-03-01

    The local properties of turbulence driven by the magnetorotational instability (MRI) in rotating, shearing flows are studied in the framework of a shearing-box model. Based on numerical simulations, we propose that the MRI-driven turbulence comprises two components: the large-scale shear-aligned strong magnetic field and the small-scale fluctuations resembling magnetohydrodynamic (MHD) turbulence. The energy spectrum of the large-scale component is close to k-2, whereas the spectrum of the small-scale component agrees with the spectrum of strong MHD turbulence k-3/2. While the spectrum of the fluctuations is universal, the outer-scale characteristics of the turbulence are not; they depend on the parameters of the system, such as the net magnetic flux. However, there is remarkable universality among the allowed turbulent states - their intensity v0 and their outer scale λ0 satisfy the balance condition v0/λ0 ˜ dΩ/dln r, where dΩ/dln r is the local orbital shearing rate of the flow. Finally, we find no sustained dynamo action in the Pm = 1 zero net-flux case for Reynolds numbers as high as 45 000, casting doubts on the existence of an MRI dynamo in the Pm ≤ 1 regime.

  6. Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers.

    PubMed

    Flowers-Jacobs, Nathan E; Fox, Anna E; Dresselhaus, Paul D; Schwall, Robert E; Benz, Samuel P

    2016-09-01

    The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors.

  7. General description of circularly symmetric Bessel beams of arbitrary order

    NASA Astrophysics Data System (ADS)

    Wang, Jia Jie; Wriedt, Thomas; Lock, James A.; Mädler, Lutz

    2016-11-01

    A general description of circularly symmetric Bessel beams of arbitrary order is derived in this paper. This is achieved by analyzing the relationship between different descriptions of polarized Bessel beams obtained using different approaches. It is shown that a class of circularly symmetric Davis Bessel beams derived using the Hertz vector potentials possesses the same general functional dependence as the aplanatic Bessel beams generated using the angular spectrum representation (ASR). This result bridges the gap between different descriptions of Bessel beams and leads to a general description of circularly symmetric Bessel beams, such that the Davis Bessel beams and the aplanatic Bessel beams are merely the two simplest cases of an infinite number of possible circularly symmetric Bessel beams. Additionally, magnitude profiles of the electric and magnetic fields, the energy density and the Poynting vector are displayed for Bessel beams in both paraxial and nonparaxial cases. The results presented in this paper provide a fresh perspective on the description of Bessel beams and cast some insights into the light scattering and light-matter interactions problems in practice.

  8. Simulation of Rutherford backscattering spectrometry from arbitrary atom structures

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Nordlund, K.; Djurabekova, F.; Zhang, Y.; Velisa, G.; Wang, T. S.

    2016-10-01

    Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop here a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms, Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.

  9. Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers

    PubMed Central

    Flowers-Jacobs, Nathan E.; Fox, Anna E.; Dresselhaus, Paul D.; Schwall, Robert E.; Benz, Samuel P.

    2016-01-01

    The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors. PMID:27453676

  10. Simulation of Rutherford backscattering spectrometry from arbitrary atom structures

    DOE PAGES

    Zhang, S.; Univ. of Helsinki; Nordlund, Kai; ...

    2016-10-25

    Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop in this paper a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms,more » Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Finally, comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.« less

  11. Simulation of Rutherford backscattering spectrometry from arbitrary atom structures

    SciTech Connect

    Zhang, S.; Nordlund, Kai; Djurabekova, Flyura; Zhang, Yanwen; Velisa, Gihan; Wang, T. S.

    2016-10-25

    Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop in this paper a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms, Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Finally, comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.

  12. Generalized anisotropic turbulence spectra and applications in the optical waves' propagation through anisotropic turbulence.

    PubMed

    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.

  13. Generalized sheath criterion for arbitrary degenerate plasmas

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2017-01-01

    In this research, we study the generalized sheath criterion for plasmas with an arbitrary degree of electron degeneracy and temperature, ranging from the classical dilute regime to the fully degenerate quantum plasmas. The latter may be relevant to warm dense matter and/or laboratory high energy density matter or even astrophysical stellar plasmas. The hydrostatic one dimensional model is used to establish the generalized Bohm's criterion for sheath entrance ion speed limits, and the small amplitude theory of the sheath problem, which accurately describes the sheath parameters for lower ion acoustic Mach numbers, is developed. Our results indicate that the sheath characteristic parameters such as electrostatic potential and density profiles, as well as the wall potential and the sheath length, are significantly affected by plasma parameters such as the ion and electron temperature and number densities in the plasma region. In particular, there are fundamental differences between sheath structures of the dilute classical plasmas and those of dense quantum ones.

  14. Aerodynamic shape optimization of arbitrary hypersonic vehicles

    NASA Technical Reports Server (NTRS)

    Dulikravich, George S.; Sheffer, Scott G.

    1991-01-01

    A new method was developed to optimize, in terms of aerodynamic wave drag minimization, arbitrary (nonaxisymmetric) hypersonic vehicles in modified Newtonian flow, while maintaining the initial volume and length of the vehicle. This new method uses either a surface fitted Fourier series to represent the vehicle's geometry or an independent point motion algorithm. In either case, the coefficients of the Fourier series or the spatial locations of the points defining each cross section were varied and a numerical optimization algorithm based on a quasi-Newton gradient search concept was used to determine the new optimal configuration. Results indicate a significant decrease in aerodynamic wave drag for simple and complex geometries at relatively low CPU costs. In the case of a cone, the results agreed well with known analytical optimum ogive shapes. The procedure is capable of accepting more complex flow field analysis codes.

  15. Fast polar decomposition of an arbitrary matrix

    NASA Technical Reports Server (NTRS)

    Higham, Nicholas J.; Schreiber, Robert S.

    1988-01-01

    The polar decomposition of an m x n matrix A of full rank, where m is greater than or equal to n, can be computed using a quadratically convergent algorithm. The algorithm is based on a Newton iteration involving a matrix inverse. With the use of a preliminary complete orthogonal decomposition the algorithm can be extended to arbitrary A. How to use the algorithm to compute the positive semi-definite square root of a Hermitian positive semi-definite matrix is described. A hybrid algorithm which adaptively switches from the matrix inversion based iteration to a matrix multiplication based iteration due to Kovarik, and to Bjorck and Bowie is formulated. The decision when to switch is made using a condition estimator. This matrix multiplication rich algorithm is shown to be more efficient on machines for which matrix multiplication can be executed 1.5 times faster than matrix inversion.

  16. Introduction to quantum turbulence

    PubMed Central

    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

  17. Modeling Compressed Turbulence

    SciTech Connect

    Israel, Daniel M.

    2012-07-13

    From ICE to ICF, the effect of mean compression or expansion is important for predicting the state of the turbulence. When developing combustion models, we would like to know the mix state of the reacting species. This involves density and concentration fluctuations. To date, research has focused on the effect of compression on the turbulent kinetic energy. The current work provides constraints to help development and calibration for models of species mixing effects in compressed turbulence. The Cambon, et al., re-scaling has been extended to buoyancy driven turbulence, including the fluctuating density, concentration, and temperature equations. The new scalings give us helpful constraints for developing and validating RANS turbulence models.

  18. Mixing and turbulent mixing in fluids, plasma and materials: summary of works presented at the 3rd International Conference on Turbulent Mixing and Beyond

    NASA Astrophysics Data System (ADS)

    Gauthier, Serge; Keane, Christopher J.; Niemela, Joseph J.; Abarzhi, Snezhana I.

    2013-07-01

    companion paper Rooker et al provide a very interesting study on the generation and detection of 'whistler waves' induced space plasma turbulence at Gakona (Alaska). Physics of atmosphere. Five papers are devoted to the physics of atmosphere. Byalko presents the first experimental observation of a new hydrodynamic phenomenon, the underwater tornado. Herring and Kimura provide a review on recent results on homogeneous stably stratified turbulence. Pouquet et al use a high-resolution direct numerical simulation of rotating helical turbulence to obtain new numerical results on the inverse energy cascade in rotating flows. Tailleux discusses energy conversion and dissipation in depth in mixing flows. Zagumennyi and Chashechkin study the structure of convective flows driven by density variations in a stratified fluid by means of experiments and numerical simulations. Geophysics and Earth science. Three papers are dedicated to geophysics and Earth science. Jinadasa et al investigate small-scale and lateral intermittency of oceanic microstructure in the pycnocline. Shrira and Townsend review on a plausible mechanism of deep-ocean mixing caused by near-inertial waves in the abyssal ocean. Using numerical simulations, Imazio and Mininni study how helicity affects the spectrum of a passive scalar in rotating turbulent flows. Combustion. Two papers deal with flows with chemical reactions. Meshram used the Lewis-Kraichnan space-time version of Hopf's functional formalism to investigate turbulence with chemical reaction. Watanabe et al carry out experiments on a turbulent plane liquid jet with a second-order chemical reaction. Theoretical aspects of non-equilibrium dynamics. Six papers are devoted to fundamental aspects of non-equilibrium dynamics. Chen et al present state-of-the-art work on exact and direct derivation of macroscopic theoretical description for a flow at arbitrary Knudsen number from the Boltzmann-Bhatnagar-Gross-Krook kinetic theory with constant relaxation time

  19. Turbulent Spots Inside the Turbulent Boundary Layer

    NASA Astrophysics Data System (ADS)

    Skarda, Jinhie; Wu, Xiaohua; Moin, Parviz; Lozano-Duran, Adrian; Wallace, James; Hickey, Jean-Pierre

    2016-11-01

    We present evidence that the buffer region of the canonical turbulent boundary layer is populated by locally generated turbulent spots, which cause strong indentations on the near-wall low-momentum streaks. This evidence is obtained from a spatially-developing direct numerical simulation carrying the inlet Blasius boundary layer through a bypass transition to the turbulent boundary layer state over a moderate Reynolds number range. The turbulent spots are structurally analogous to their transitional counter-parts but without any direct causality connection. High-pass filtered time-history records are used to calculate the period of turbulent spot detection and this period is compared to the boundary layer bursting period reported in hot-wire experiments. The sensitivity of the results to parameters such as the high pass filter frequency and the amplitude discriminator level is examined. The characteristics of these turbulent spots are also quantified using a spatial connectivity based conditional sampling technique. This evidence seems to be at odds with the notion that the buffer region is dominated by quasi-streamwise vortices, and contributes to the potential unification of the studies on near-wall turbulent boundary layer dynamics.

  20. Multidimensional Potential Burgers Turbulence

    NASA Astrophysics Data System (ADS)

    Boritchev, Alexandre

    2016-03-01

    We consider the multidimensional generalised stochastic Burgers equation in the space-periodic setting: partial {u}/partial t+(nabla f({u}) \\cdot nabla) {u}-ν Δ {u}= nabla η, quad t ≥ 0, {x} in{T}^d=({R}/ {Z})^d, under the assumption that u is a gradient. Here f is strongly convex and satisfies a growth condition, ν is small and positive, while η is a random forcing term, smooth in space and white in time. For solutions u of this equation, we study Sobolev norms of u averaged in time and in ensemble: each of these norms behaves as a given negative power of ν. These results yield sharp upper and lower bounds for natural analogues of quantities characterising the hydrodynamical turbulence, namely the averages of the increments and of the energy spectrum. These quantities behave as a power of the norm of the relevant parameter, which is respectively the separation ℓ in the physical space and the wavenumber k in the Fourier space. Our bounds do not depend on the initial condition and hold uniformly in {ν}. We generalise the results obtained for the one-dimensional case in [10], confirming the physical predictions in [4, 30]. Note that the form of the estimates does not depend on the dimension: the powers of {ν, |{{k}}|, ℓ} are the same in the one- and the multi-dimensional setting.

  1. Electron magnetohydrodynamics: Dynamics and turbulence

    NASA Astrophysics Data System (ADS)

    Lyutikov, Maxim

    2013-11-01

    We consider dynamics and turbulent interaction of whistler modes within the framework of inertialess electron magnetohydrodynamics (EMHD). We argue that there is no energy principle in EMHD: any stationary closed configuration is neutrally stable. On the other hand, the relaxation principle, the long term evolution of a weakly dissipative system towards Taylor-Beltrami state, remains valid in EMHD. We consider the turbulent cascade of whistler modes. We show that (i) harmonic whistlers are exact nonlinear solutions; (ii) collinear whistlers do not interact (including counterpropagating); (iii) waves with the same value of the wave vector k1=k2 do not interact; (iv) whistler modes have a dispersion that allows a three-wave decay, including into a zero frequency mode; (v) the three-wave interaction effectively couples modes with highly different wave numbers and propagation angles. In addition, linear interaction of a whistler with a single zero mode can lead to spatially divergent structures via parametric instability. All these properties are drastically different from MHD, so that the qualitative properties of the Alfvén turbulence can not be transferred to the EMHD turbulence. We derive the Hamiltonian formulation of EMHD, and using Bogoliubov transformation reduce it to the canonical form; we calculate the matrix elements for the three-wave interaction of whistlers. We solve numerically the kinetic equation and show that, generally, the EMHD cascade develops within a broad range of angles, while transiently it may show anisotropic, nearly two-dimensional structures. Development of a cascade depends on the forcing (nonuniversal) and often fails to reach a steady state. Analytical estimates predict the spectrum of magnetic fluctuations for the quasi-isotropic cascade ∝k-2. The cascade remains weak (not critically balanced). The cascade is UV local, while the infrared locality is weakly (logarithmically) violated.

  2. Turbulence, Turbulence Control, and Drag Reduction.

    DTIC Science & Technology

    1987-08-01

    Onsager (1945) and Weizs~cker (1948). has made remarkable strides in advancing our understanding of turbulent flows. It is this description of turbulent...tujrbuilce Inl thle lar to thle Intermiittenit trans’ition to turbulence lus.t ,iedipen itlik. N\\N.tern onI the other. O pen0 * ~ ~ h 1 ~ kdinition10 po...Some Studies of Non-Simple Pipe Flows K R SREENIVASAN 2.AR’ .\\ variety o phenooena occrs ’.5’, ,sTecla’., f we stray,’ away from straight circ- lar i es a

  3. Random shearing direction models for isotropic turbulent diffusion

    NASA Astrophysics Data System (ADS)

    Majda, Andrew J.

    1994-06-01

    Recently, a rigorous renormalization theory for various scalar statistics has been developed for special modes of random advection diffusion involving random shear layer velocity fields with long-range spatiotemporal correlations. New random shearing direction models for isotropic turbulent diffusion are introduced here. In these models the velocity field has the spatial second-order statistics of an arbitrary prescribed stationary incompressible isotropic random field including long-range spatial correlations with infrared divergence, but the temporal correlations have finite range. The explicit theory of renormalization for the mean and second-order statistics is developed here. With ɛ the spectral parameter, for -∞<ɛ<4 and measuring the strength of the infrared divergence of the spatial spectrum, the scalar mean statistics rigorously exhibit a phase transition from mean-field behavior for ɛ<2 to anomalous behavior for ɛ with 2<ɛ<4 as conjectured earlier by Avellaneda and the author. The universal inertial range renormalization for the second-order scalar statistics exhibits a phase transition from a covariance with a Gaussian functional form for ɛ with ɛ<2 to an explicit family with a non-Gaussian covariance for ɛ with 2<ɛ<4. These non-Gaussian distributions have tails that are broader than Gaussian as ɛ varies with 2<ɛ<4 and behave for large values like exp(- C c | x|4-ɛ), with C c an explicit constant. Also, here the attractive general principle is formulated and proved that every steady, stationary, zero-mean, isotropic, incompressible Gaussian random velocity field is well approximated by a suitable superposition of random shear layers.

  4. Turbulence kinetic energy equation for dilute suspensions

    NASA Technical Reports Server (NTRS)

    Abou-Arab, T. W.; Roco, M. C.

    1989-01-01

    A multiphase turbulence closure model is presented which employs one transport equation, namely the turbulence kinetic energy equation. The proposed form of this equation is different from the earlier formulations in some aspects. The power spectrum of the carrier fluid is divided into two regions, which interact in different ways and at different rates with the suspended particles as a function of the particle-eddy size ratio and density ratio. The length scale is described algebraically. A mass/time averaging procedure for the momentum and kinetic energy equations is adopted. The resulting turbulence correlations are modeled under less retrictive assumptions comparative to previous work. The closures for the momentum and kinetic energy equations are given. Comparisons of the predictions with experimental results on liquid-solid jet and gas-solid pipe flow show satisfactory agreement.

  5. Developed turbulence and nonlinear amplification of magnetic fields in laboratory and astrophysical plasmas

    PubMed Central

    Meinecke, Jena; Tzeferacos, Petros; Bell, Anthony; Bingham, Robert; Clarke, Robert; Churazov, Eugene; Crowston, Robert; Doyle, Hugo; Drake, R. Paul; Heathcote, Robert; Koenig, Michel; Kuramitsu, Yasuhiro; Kuranz, Carolyn; Lee, Dongwook; MacDonald, Michael; Murphy, Christopher; Notley, Margaret; Park, Hye-Sook; Pelka, Alexander; Ravasio, Alessandra; Reville, Brian; Sakawa, Youichi; Wan, Willow; Woolsey, Nigel; Yurchak, Roman; Miniati, Francesco; Schekochihin, Alexander; Lamb, Don; Gregori, Gianluca

    2015-01-01

    The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe. PMID:26100873

  6. Developed turbulence and nonlinear amplification of magnetic fields in laboratory and astrophysical plasmas.

    PubMed

    Meinecke, Jena; Tzeferacos, Petros; Bell, Anthony; Bingham, Robert; Clarke, Robert; Churazov, Eugene; Crowston, Robert; Doyle, Hugo; Drake, R Paul; Heathcote, Robert; Koenig, Michel; Kuramitsu, Yasuhiro; Kuranz, Carolyn; Lee, Dongwook; MacDonald, Michael; Murphy, Christopher; Notley, Margaret; Park, Hye-Sook; Pelka, Alexander; Ravasio, Alessandra; Reville, Brian; Sakawa, Youichi; Wan, Willow; Woolsey, Nigel; Yurchak, Roman; Miniati, Francesco; Schekochihin, Alexander; Lamb, Don; Gregori, Gianluca

    2015-07-07

    The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe.

  7. COSMIC-RAY TRANSPORT THEORY IN PARTIALLY TURBULENT SPACE PLASMAS WITH COMPRESSIBLE MAGNETIC TURBULENCE

    SciTech Connect

    Casanova, S.; Schlickeiser, R.

    2012-02-01

    Recently, a new transport theory of cosmic rays in magnetized space plasmas extending the quasilinear approximation to the particle orbit has been developed for the case of an axisymmetric incompressible magnetic turbulence. Here, we generalize the approach to the important physical case of a compressible plasma. As previously obtained in the case of an incompressible plasma, we allow arbitrary gyrophase deviations from the unperturbed spiral orbits in the uniform magnetic field. For the case of quasi-stationary and spatially homogeneous magnetic turbulence we derive, in the small Larmor radius approximation, gyrophase-averaged cosmic-ray Fokker-Planck coefficients. Upper limits for the perpendicular and pitch-angle Fokker-Planck coefficients and for the perpendicular and parallel spatial diffusion coefficients are presented.

  8. The Flight of Flexible Aircraft in Turbulence. State-of-the-Art in the Description and Modelling of Atmospheric Turbulence. Addendum

    DTIC Science & Technology

    1988-06-01

    fitting between calculated and measured transfers, spectral densities and coherence, once the adequate turbulence length scale and standart deviation...Turbulence length scale The quantities C(0,•11) and 0 (0) depend of the turbulence-" 2 length scale L and of the standart deviation a. If we want to...get easily the standart deviation. This method is however limited by the scattering of the experimental spectrum values but it gives a rough estimate

  9. Lidar sounding of the optical parameter of atmospheric turbulence

    NASA Astrophysics Data System (ADS)

    Gurvich, A. S.; Fortus, M. I.

    2016-03-01

    The operation of a lidar intended for clear air turbulence (CAT) positioning on the basis of the backscatter enhancement (BSE) effect is analyzed using a turbulence model with a power-law spectrum. Systematic distortions occurring due to a need to regularize the lidar positioning problem solution are estimated. It is shown that the effect of molecular viscosity of air on the positioning result can be neglected if the wave parameter, which characterizes the diffraction manifestation, is higher than 3. This corresponds to sounding ranges of more than 1 km for optical or UV lidars. The analysis results show that the BSE lidar positioning accuracy weakly depends on the exponent in the turbulence spectrum in regions of severe turbulence. The results can justify a physical experiment for the design of an aircraft system for the lidar detection of CAT regions ahead of the flight course.

  10. Turbulence Visualization at the Terascale on Desktop PCs.

    PubMed

    Treib, M; Burger, K; Reichl, F; Meneveau, C; Szalay, A; Westermann, R

    2012-12-01

    Despite the ongoing efforts in turbulence research, the universal properties of the turbulence small-scale structure and the relationships between small- and large-scale turbulent motions are not yet fully understood. The visually guided exploration of turbulence features, including the interactive selection and simultaneous visualization of multiple features, can further progress our understanding of turbulence. Accomplishing this task for flow fields in which the full turbulence spectrum is well resolved is challenging on desktop computers. This is due to the extreme resolution of such fields, requiring memory and bandwidth capacities going beyond what is currently available. To overcome these limitations, we present a GPU system for feature-based turbulence visualization that works on a compressed flow field representation. We use a wavelet-based compression scheme including run-length and entropy encoding, which can be decoded on the GPU and embedded into brick-based volume ray-casting. This enables a drastic reduction of the data to be streamed from disk to GPU memory. Our system derives turbulence properties directly from the velocity gradient tensor, and it either renders these properties in turn or generates and renders scalar feature volumes. The quality and efficiency of the system is demonstrated in the visualization of two unsteady turbulence simulations, each comprising a spatio-temporal resolution of 10244. On a desktop computer, the system can visualize each time step in 5 seconds, and it achieves about three times this rate for the visualization of a scalar feature volume.

  11. Toward the Theory of Turbulence in Magnetized Plasmas

    SciTech Connect

    Boldyrev, Stanislav

    2013-07-26

    The goal of the project was to develop a theory of turbulence in magnetized plasmas at large scales, that is, scales larger than the characteristic plasma microscales (ion gyroscale, ion inertial scale, etc.). Collisions of counter-propagating Alfven packets govern the turbulent cascade of energy toward small scales. It has been established that such an energy cascade is intrinsically anisotropic, in that it predominantly supplies energy to the modes with mostly field-perpendicular wave numbers. The resulting energy spectrum of MHD turbulence, and the structure of the fluctuations were studied both analytically and numerically. A new parallel numerical code was developed for simulating reduced MHD equations driven by an external force. The numerical setting was proposed, where the spectral properties of the force could be varied in order to simulate either strong or weak turbulent regimes. It has been found both analytically and numerically that weak MHD turbulence spontaneously generates a “condensate”, that is, concentration of magnetic and kinetic energy at small k{sub {parallel}}. A related topic that was addressed in the project is turbulent dynamo action, that is, generation of magnetic field in a turbulent flow. We were specifically concentrated on the generation of large-scale magnetic field compared to the scales of the turbulent velocity field. We investigate magnetic field amplification in a turbulent velocity field with nonzero helicity, in the framework of the kinematic Kazantsev-Kraichnan model.

  12. The Dissipation Rate Transport Equation and Subgrid-Scale Models in Rotating Turbulence

    NASA Technical Reports Server (NTRS)

    Rubinstein, Robert; Ye, Zhou

    1997-01-01

    The dissipation rate transport equation remains the most uncertain part of turbulence modeling. The difficulties arc increased when external agencies like rotation prevent straightforward dimensional analysis from determining the correct form of the modelled equation. In this work, the dissipation rate transport equation and subgrid scale models for rotating turbulence are derived from an analytical statistical theory of rotating turbulence. In the strong rotation limit, the theory predicts a turbulent steady state in which the inertial range energy spectrum scales as k(sup -2) and the turbulent time scale is the inverse rotation rate. This scaling has been derived previously by heuristic arguments.

  13. Factorized cumulant expansion approximation method for turbulence with reacting and mixing chemical elements of type A + B → Product

    NASA Astrophysics Data System (ADS)

    Meshram, M. C.

    2013-07-01

    The Lewis-Kraichnan space-time version of Hopf functional formalism is considered for the investigation of turbulence with reacting and mixing chemical elements of type A + B → Product. The equations of motion are written in Fourier space. We first define the characteristic functional (or the moments generating functional) for the joint probability distribution of the velocity vector of the flow field and the reactants’ concentration scalar fields and translate the equations of motion in terms of the differential equations for the characteristic functional. These differential equations for the characteristic functional are further written in terms of the second characteristic functional (or the cumulant generating functional). This helps us in obtaining the equations for various order cumulants. We note from these equations for cumulants the characteristic difficulty of the theory of turbulence that the (n + 1)th order cumulant C(n+1) occurs in the equation for the dynamics of nth order cumulant Cn. We use the factorized cumulant expansion approximation method for the present investigation. Under this approximation an arbitrary nth order cumulant Cn is expressed in terms of the lower-order cumulants C(2), C(3) and C(n-1) and thus we obtain a closed but untruncated system of equations for the cumulants. On using the factorized fourth-cumulant approximation method a closed set of equations for the reactants’ energy spectrum functions and the reactants’ energy transfer functions are derived. These equations are solved numerically and the similarity laws of the solutions are derived analytically. The statistical quantities such as the reactants’ energy, the reactants’ enstrophy, the reactants’ scale of segregations and so on are calculated numerically and the statistical laws of these quantities are discussed. Also, the scope of this tool for investigation of turbulent phenomena not covered in the present study is discussed.

  14. An alternative to Reynolds stresses in turbulent channels

    NASA Astrophysics Data System (ADS)

    Jimenez, Javier

    2016-11-01

    It is remarked that fluxes in conservation laws, such as the Reynolds stresses in the momentum equation of turbulent shear flows, or the spectral energy flux in isotropic turbulence, are only defined up to an arbitrary solenoidal field. While this is not usually significant for long-time averages, it becomes important when fluxes are modelled locally in large-eddy simulations, or in the analysis of intermittency and cascades. As an example, a numerical procedure is introduced to compute fluxes in scalar conservation equations in such a way that their total integrated magnitude is minimised. The result is an irrotational vector field that derives from a potential, thus minimising sterile flux 'circuits'. The algorithm is generalised to tensor fluxes and applied to the transfer of momentum in a turbulent channel. The resulting instantaneous Reynolds stresses are compared with their traditional expressions, and found to be substantially different. Funded by the Coturb project of the ERC.

  15. Transmission spectrum of an optical cavity containing N atoms

    SciTech Connect

    Leslie, Sabrina; Shenvi, Neil; Brown, Kenneth R.; Whaley, K. Birgitta; Stamper-Kurn, Dan M.

    2004-04-01

    The transmission spectrum of a high-finesse optical cavity containing an arbitrary number of trapped atoms is presented in the zero-temperature, low saturation limit. We take spatial and motional effects into account and show that in the limit of strong coupling, the important spectral features can be determined for an arbitrary number of atoms, N. We also show that these results have important ramifications in limiting our ability to determine the number of atoms in the cavity.

  16. A phenomenological treatment of rotating turbulence

    NASA Technical Reports Server (NTRS)

    Zhou, YE

    1995-01-01

    The strong similarity between the magnetohydrodynamic (MHD) turbulence and initially isotropic turbulence subject to rotation is noted. We then apply the MHD phenomenologies of Kraichnan and Matthaeus & Zhou to rotating turbulence. When the turbulence is subject to a strong rotation, the energy spectrum is found to scale as E(k) = C(sub Omega)(Omega(sub epsilon))(sup 1/2)k(sup -2), where Omega is the rotation rate, k is the wavenumber, and epsilon is the dissipation rate. This spectral form is consistent with a recent letter by Zeman. However, here the constant C(sub Omega) is found to be related to the Kolmogorov constant and is estimated in the range 1.22 - 1.87 for the typical values of the latter constant. A 'rule' that relates spectral transfer times to the eddy turnover time and the time scale for decay of the triple correlations is deduced. A hypothesis for the triple correlation decay rate leads to the spectral law which varies between the '-5/3' (without rotation) and '-2' laws (with strong rotation). For intermediate rotation rates, the spectrum varies according to the value of a dimensionless parameter that measures the strength of the rotation wavenumber k(sub Omega) = (Omega(sup 3)/epsiolon)(sup 1/2) relative to the wavenumber k. An eddy viscosity is derived with an explicit dependence on the rotation rate.

  17. MAGNETIC HELICITY OF ION KINETIC TURBULENCE WITH A NONZERO ELECTRON TEMPERATURE

    SciTech Connect

    Markovskii, S. A.; Vasquez, Bernard J. E-mail: bernie.vasquez@unh.edu

    2016-03-20

    Hybrid numerical simulations of strong turbulence with a nonzero electron temperature are carried out in the proton kinetic range. The turbulent cascade is initiated by a large-scale spectrum with a nonzero cross-helicity. The turbulence evolves freely and produces a magnetic helicity spectrum with a peak at smaller scales. Testing is performed to verify that the shape of the peak is not affected by numerical artifacts. The magnetic helicity spectrum is shown to be determined by both the electron and proton thermal pressures, rather than the proton pressure alone. Implications for the observed correlations between the magnetic helicity and the plasma parameters in the solar wind are discussed.

  18. Broadband Phase Spectroscopy over Turbulent Air Paths.

    PubMed

    Giorgetta, Fabrizio R; Rieker, Gregory B; Baumann, Esther; Swann, William C; Sinclair, Laura C; Kofler, Jon; Coddington, Ian; Newbury, Nathan R

    2015-09-04

    Broadband atmospheric phase spectra are acquired with a phase-sensitive dual-frequency-comb spectrometer by implementing adaptive compensation for the strong decoherence from atmospheric turbulence. The compensation is possible due to the pistonlike behavior of turbulence across a single spatial-mode path combined with the intrinsic frequency stability and high sampling speed associated with dual-comb spectroscopy. The atmospheric phase spectrum is measured across 2 km of air at each of the 70,000 comb teeth spanning 233  cm(-1) across hundreds of near-infrared rovibrational resonances of CO(2), CH(4), and H(2)O with submilliradian uncertainty, corresponding to a 10(-13) refractive index sensitivity. Trace gas concentrations extracted directly from the phase spectrum reach 0.7 ppm uncertainty, demonstrated here for CO(2). While conventional broadband spectroscopy only measures intensity absorption, this approach enables measurement of the full complex susceptibility even in practical open path sensing.

  19. Broadband Phase Spectroscopy over Turbulent Air Paths

    NASA Astrophysics Data System (ADS)

    Giorgetta, Fabrizio R.; Rieker, Gregory B.; Baumann, Esther; Swann, William C.; Sinclair, Laura C.; Kofler, Jon; Coddington, Ian; Newbury, Nathan R.

    2015-09-01

    Broadband atmospheric phase spectra are acquired with a phase-sensitive dual-frequency-comb spectrometer by implementing adaptive compensation for the strong decoherence from atmospheric turbulence. The compensation is possible due to the pistonlike behavior of turbulence across a single spatial-mode path combined with the intrinsic frequency stability and high sampling speed associated with dual-comb spectroscopy. The atmospheric phase spectrum is measured across 2 km of air at each of the 70 000 comb teeth spanning 233 cm-1 across hundreds of near-infrared rovibrational resonances of CO2 , CH4 , and H2O with submilliradian uncertainty, corresponding to a 10-13 refractive index sensitivity. Trace gas concentrations extracted directly from the phase spectrum reach 0.7 ppm uncertainty, demonstrated here for CO2 . While conventional broadband spectroscopy only measures intensity absorption, this approach enables measurement of the full complex susceptibility even in practical open path sensing.

  20. ISOTROPICALLY DRIVEN VERSUS OUTFLOW DRIVEN TURBULENCE: OBSERVATIONAL CONSEQUENCES FOR MOLECULAR CLOUDS

    SciTech Connect

    Carroll, Jonathan J.; Frank, Adam; Blackman, Eric G.

    2010-10-10

    Feedback from protostellar outflows can influence the nature of turbulence in star-forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star-forming regions, we previously (Carroll et al.) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here, we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scales effectively reducing the formation of large-scale turbulent density structures. These effects are qualitatively independent of resolution. We have also carried out Principal Component Analysis (PCA) for synthetic data from our simulations. We find that PCA as a tool for identifying the driving scale of turbulence has a misleading bias toward low amplitude large-scale velocity structures even when they are not necessarily the dominant energy containing scales. This bias is absent for isotropically forced turbulence but manifests strongly for collimated outflow driven turbulence.

  1. Solving Nonlinear Euler Equations with Arbitrary Accuracy

    NASA Technical Reports Server (NTRS)

    Dyson, Rodger W.

    2005-01-01

    A computer program that efficiently solves the time-dependent, nonlinear Euler equations in two dimensions to an arbitrarily high order of accuracy has been developed. The program implements a modified form of a prior arbitrary- accuracy simulation algorithm that is a member of the class of algorithms known in the art as modified expansion solution approximation (MESA) schemes. Whereas millions of lines of code were needed to implement the prior MESA algorithm, it is possible to implement the present MESA algorithm by use of one or a few pages of Fortran code, the exact amount depending on the specific application. The ability to solve the Euler equations to arbitrarily high accuracy is especially beneficial in simulations of aeroacoustic effects in settings in which fully nonlinear behavior is expected - for example, at stagnation points of fan blades, where linearizing assumptions break down. At these locations, it is necessary to solve the full nonlinear Euler equations, and inasmuch as the acoustical energy is of the order of 4 to 5 orders of magnitude below that of the mean flow, it is necessary to achieve an overall fractional error of less than 10-6 in order to faithfully simulate entropy, vortical, and acoustical waves.

  2. Understanding rigid body motion in arbitrary dimensions

    NASA Astrophysics Data System (ADS)

    Leyvraz, Francois

    2015-05-01

    Why would anyone wish to generalize the already unappetizing subject of rigid body motion to an arbitrary number of dimensions? At first sight, the subject seems to be both repellent and superfluous. The author will try to argue that an approach involving no specific three-dimensional constructs is actually easier to grasp than the traditional approach and might thus be generally useful to understand rigid body motion both in three dimensions and in the general case. Specific differences between the viewpoint suggested here and the usual one include the following: here angular velocities are systematically treated as antisymmetric matrices, a symmetric tensor I quite different from the moment of inertia tensor plays a central role, whereas the latter is shown to be a far more complex object, namely a tensor of rank four. A straightforward way to define it is given. The Euler equation is derived and the use of Noether’s theorem to obtain conserved quantities is illustrated. Finally the equations of motion for a heavy top as well as for two bodies linked by a spherical joint are derived to display the simplicity and the power of the method.

  3. Heterotic string in an arbitrary background field

    NASA Astrophysics Data System (ADS)

    Sen, Ashoke

    1985-10-01

    An expression for the light-cone gauge action for the first-quantized heterotic string in the presence of arbitrary background gauge, gravitational, and antisymmetric tensor fields is derived. The result is a two-dimensional local field theory with N=1/2 supersymmetry. The constraints imposed on the background fields in order to make this theory one-loop finite are derived. These constraints are identical to the equations of motion for the massless fields at the linearized level. Finally, it is shown that if there is no background antisymmetric tensor field, and if the gauge connection is set equal to the spin connection, the effective action is that of an N=1 supersymmetric nonlinear and N=2 supersymmetric Georgi-Glashow models the occurrence of the fermion fractionization is the necessity; the ignorance of it results in the inconsistency in the perturbative calculation of the mass splittings among the members of the supermultiplets. The notable feature of our result is that the degeneracy due to the Jackiw-Rebbi zero mode is not independent of the one required by the supersymmetry, suggesting a nontrivial structure in embedding the topology of Higgs fields into supersymmetric gauge theories.

  4. Turbulence generation by waves

    SciTech Connect

    Kaftori, D.; Nan, X.S.; Banerjee, S.

    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.

  5. One-dimensional turbulence

    SciTech Connect

    Kerstein, A.R.

    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.

  6. Diffusion of Sound Waves in a Turbulent Atmosphere

    NASA Technical Reports Server (NTRS)

    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.

  7. Interaction of turbulence with a detonation wave

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.; Hussaini, M. Y.; Ribner, H. S.

    1993-01-01

    This paper addresses a specific reactive-flow configuration, namely, the interaction of a detonation wave with convected homogeneous isotropic weak turbulence (which can be constructed by a Fourier synthesis of small-amplitude vorticity waves). The effect of chemical heat release on the rms fluctuations downstream of the detonation is presented as a function of Mach number. In addition, for the particular case of the von Karman spectrum, the one-dimensional power spectra of these flow quantities are given.

  8. Renormalization group analysis of turbulence. I - Basic theory

    NASA Astrophysics Data System (ADS)

    Yakhot, Victor; Orszag, Steven A.

    The dynamic renormalization group (RNG) method is developed for hydrodynamic turbulence. This procedure, which uses dynamic scaling and invariance together with iterated perturbation methods, permits the evaluation of transport coefficients and transport equations for the large-scale (slow) modes. The RNG theory, which does not include any experimentally adjustable parameters, gives the following numerical values for important constants of turbulent flows: Kolmogorov constant for the inertial-range spectrum = 1.617; turbulent Prandtl number for high-Reynolds-number heat transfer = 0.7179; Batchelor constant = 1.161; and skewness factor = 0.4878. A differential transport model, is derived which is particularly useful near walls.

  9. Energy Spectra of Strongly Stratified and Rotating Turbulence

    NASA Technical Reports Server (NTRS)

    Mahalov, Alex; Nicolaenko, Basil; Zhou, Ye

    1998-01-01

    Turbulence under strong stratification and rotation is usually characterized as quasi-two dimensional turbulence. We develop a "quasi-two dimensional" energy spectrum which changes smoothly between the Kolmogorov -5/3 law (no stratification), the -2 scalings of Zhou for the case of strong rotation, as well as the -2 scalings for the case of strong rotation and stratification. For strongly stratified turbulence, the model may give the -2 scaling predicted by Herring; and the -5/3 scaling indicated by some mesoscale observations.

  10. A soliton gas model for astrophysical magnetized plasma turbulence

    NASA Astrophysics Data System (ADS)

    Spangler, S. R.; Sheerin, J. P.

    1982-06-01

    Plasma turbulence is considered as an ensemble of solitons. The derivation of the Alfven soliton by Spangler and Sheering (1981) is reviewed, and expressions are derived for the magnetic irregularity spectrum and the relationship between the magnetic and density irregularity power spectra. A derived expression also provides the answer to the question of the correlation between magnetic field and density enhancements. The properties of the turbulence model are compared with observations of plasma turbulence in the solar wind, and are found to reasonably account for them.

  11. Imbalanced relativistic force-free magnetohydrodynamic turbulence

    SciTech Connect

    Cho, Jungyeon; Lazarian, A.

    2014-01-01

    When magnetic energy density is much larger than that of matter, as in pulsar/black hole magnetospheres, the medium becomes force-free and we need relativity to describe it. As in non-relativistic magnetohydrodynamics (MHD), Alfvénic MHD turbulence in the relativistic limit can be described by interactions of counter-traveling wave packets. In this paper, we numerically study strong imbalanced MHD turbulence in such environments. Here, imbalanced turbulence means the waves traveling in one direction (dominant waves) have higher amplitudes than the opposite-traveling waves (sub-dominant waves). We find that (1) spectrum of the dominant waves is steeper than that of sub-dominant waves, (2) the anisotropy of the dominant waves is weaker than that of sub-dominant waves, and (3) the dependence of the ratio of magnetic energy densities of dominant and sub-dominant waves on the ratio of energy injection rates is steeper than quadratic (i.e., b{sub +}{sup 2}/b{sub −}{sup 2}∝(ϵ{sub +}/ϵ{sub −}){sup n} with n > 2). These results are consistent with those obtained for imbalanced non-relativistic Alfvénic turbulence. This corresponds well to the earlier reported similarity of the relativistic and non-relativistic balanced magnetic turbulence.

  12. Classes of Hydrodynamic and Magnetohydrodynamic Turbulent Decay

    NASA Astrophysics Data System (ADS)

    Brandenburg, Axel; Kahniashvili, Tina

    2017-02-01

    We perform numerical simulations of decaying hydrodynamic and magnetohydrodynamic turbulence. We classify our time-dependent solutions by their evolutionary tracks in parametric plots between instantaneous scaling exponents. We find distinct classes of solutions evolving along specific trajectories toward points on a line of self-similar solutions. These trajectories are determined by the underlying physics governing individual cases, while the infrared slope of the initial conditions plays only a limited role. In the helical case, even for a scale-invariant initial spectrum (inversely proportional to wave number k ), the solution evolves along the same trajectory as for a Batchelor spectrum (proportional to k4).

  13. Spectrum Recombination.

    ERIC Educational Resources Information Center

    Greenslade, Thomas B., Jr.

    1984-01-01

    Describes several methods of executing lecture demonstrations involving the recombination of the spectrum. Groups the techniques into two general classes: bringing selected portions of the spectrum together using lenses or mirrors and blurring the colors by rapid movement or foreshortening. (JM)

  14. A mesh partitioning algorithm for preserving spatial locality in arbitrary geometries

    NASA Astrophysics Data System (ADS)

    Nivarti, Girish V.; Salehi, M. Mahdi; Bushe, W. Kendal

    2015-01-01

    A space-filling curve (SFC) is a proximity preserving linear mapping of any multi-dimensional space and is widely used as a clustering tool. Equi-sized partitioning of an SFC ignores the loss in clustering quality that occurs due to inaccuracies in the mapping. Often, this results in poor locality within partitions, especially for the conceptually simple, Morton order curves. We present a heuristic that improves partition locality in arbitrary geometries by slicing a Morton order curve at points where spatial locality is sacrificed. In addition, we develop algorithms that evenly distribute points to the extent possible while maintaining spatial locality. A metric is defined to estimate relative inter-partition contact as an indicator of communication in parallel computing architectures. Domain partitioning tests have been conducted on geometries relevant to turbulent reactive flow simulations. The results obtained highlight the performance of our method as an unsupervised and computationally inexpensive domain partitioning tool.

  15. Turbulence in astrophysics

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.

    1990-01-01

    Some of the astrophysical scenarios in which turbulence plays an important role are discussed in view of the comparative advantages of currently available models of turbulence phenomena; attention is given to a specific model that has undergone continuous refinement since 1985. The desideratum in this inquiry is a turbulence model which incorporates the best features of an a priori deterministic model, as well as a redundant set of results from full numerical simulations for a wide variety of turbulent flows; there should also be a simplification of the former, and an enlargement of the complexities of the latter.

  16. Tactical missile turbulence problems

    NASA Technical Reports Server (NTRS)

    Dickson, Richard E.

    1987-01-01

    Of particular interest is atmospheric turbulence in the atmospheric boundary layer, since this affects both the launch and terminal phase of flight, and the total flight for direct fire systems. Brief discussions are presented on rocket artillery boost wind problems, mean wind correction, turbulent boost wind correction, the Dynamically Aimed Free Flight Rocket (DAFFR) wind filter, the DAFFR test, and rocket wake turbulence problems. It is concluded that many of the turbulence problems of rockets and missiles are common to those of aircraft, such as structural loading and control system design. However, these problems have not been solved at this time.

  17. String Theory and Turbulence

    NASA Astrophysics Data System (ADS)

    Jejjala, Vishnu; Minic, Djordje; Ng, Y. Jack; Tze, Chia-Hsiung

    We propose a string theory of turbulence that explains the Kolmogorov scaling in 3+1 dimensions and the Kraichnan and Kolmogorov scalings in 2+1 dimensions. This string theory of turbulence should be understood in light of the AdS/CFT dictionary. Our argument is crucially based on the use of Migdal's loop variables and the self-consistent solutions of Migdal's loop equations for turbulence. In particular, there is an area law for turbulence in 2+1 dimensions related to the Kraichnan scaling.

  18. User's guide for a personal computer model of turbulence at a wind turbine rotor

    NASA Astrophysics Data System (ADS)

    Connell, J. R.; Powell, D. C.; Gower, G. L.

    1989-08-01

    This document is primarily: (1) a user's guide for the personal computer (PC) version of the code for the PNL computational model of the rotationally sampled wind speed (RODASIM11), and (2) a brief guide to the growing literature on the subject of rotationally sampled turbulence, from which the model is derived. The model generates values of turbulence experienced by single points fixed in the rotating frame of reference of an arbitrary wind turbine blade. The character of the turbulence depends on the specification of mean wind speed, the variance of turbulence, the crosswind and along-wind integral scales of turbulence, mean wind shear, and the hub height, radius, and angular speed of rotation of any point at which wind fluctuation is to be calculated.

  19. User's guide for a personal computer model of turbulence at a wind turbine rotor

    SciTech Connect

    Connell, J.R.; Powell, D.C.; Gower, G.L.

    1989-08-01

    This document is primarily (1) a user's guide for the personal computer (PC) version of the code for the PNL computational model of the rotationally sampled wind speed (RODASIM11) and (2) a brief guide to the growing literature on the subject of rotationally sampled turbulence, from which the model is derived. The model generates values of turbulence experienced by single points fixed in the rotating frame of reference of an arbitrary wind turbine blade. The character of the turbulence depends on the specification of mean wind speed, the variance of turbulence, the crosswind and along-wind integral scales of turbulence, mean wind shear, and the hub height, radius, and angular speed of rotation of any point at which wind fluctuation is to be calculated. 13 refs., 4 figs., 4 tabs.

  20. Demonstration That Calibration of the Instrument Response to Polarizations Parallel and Perpendicular to the Object Space Projected Slit of an Imaging Spectrometer Enable Measurement of the Atmospheric Absorption Spectrum in Region of the Weak CO2 Band for the Case of Arbitrary Polarization: Implication for the Geocarb Mission

    NASA Astrophysics Data System (ADS)

    Kumer, J. B.; Rairden, R. L.; Polonsky, I. N.; O'Brien, D. M.

    2014-12-01

    The Tropospheric Infrared Mapping Spectrometer (TIMS) unit rebuilt to operate in a narrow spectral region, approximately 1603 to 1615 nm, of the weak CO2 band as described by Kumer et al. (2013, Proc. SPIE 8867, doi:10.1117/12.2022668) was used to conduct the demonstration. An integrating sphere (IS), linear polarizers and quarter wave plate were used to confirm that the instrument's spectral response to unpolarized light, to 45° linearly polarized light and to circular polarized light are identical. In all these cases the intensity components Ip = Is where Ip is the component parallel to the object space projected slit and Is is perpendicular to the slit. In the circular polarized case Ip = Is in the time averaged sense. The polarizer and IS were used to characterize the ratio Rθ of the instrument response to linearly polarized light at the angle θ relative to parallel from the slit, for increments of θ from 0 to 90°, to that of the unpolarized case. Spectra of diffusely reflected sunlight passed through the polarizer in increments of θ, and divided by the respective Rθ showed identical results, within the noise limit, for solar spectrum multiplied by the atmospheric transmission and convolved by the Instrument Line Shape (ILS). These measurements demonstrate that unknown polarization in the diffusely reflected sunlight on this small spectral range affect only the slow change across the narrow band in spectral response relative to that of unpolarized light and NOT the finely structured / high contrast spectral structure of the CO2 atmospheric absorption that is used to retrieve the atmospheric content of CO2. The latter is one of the geoCARB mission objectives (Kumer et al, 2013). The situation is similar for the other three narrow geoCARB bands; O2 A band 757.9 to 768.6 nm; strong CO2 band 2045.0 to 2085.0 nm; CH4 and CO region 2300.6 to 2345.6 nm. Polonsky et al have repeated the mission simulation study doi:10.5194/amt-7-959-2014 assuming no use of a geo

  1. Ion trajectory simulation for electrode configurations with arbitrary geometries.

    PubMed

    Wu, Guangxiang; Cooks, R Graham; Ouyang, Zheng; Yu, Meng; Chappell, William J; Plass, Wolfgang R

    2006-09-01

    A multi-particle ion trajectory simulation program ITSIM 6.0 is described, which is capable of ion trajectory simulations for electrode configurations with arbitrary geometries. The electrode structures are input from a 3D drawing program AutoCAD and the electric field is calculated using a 3D field solver COMSOL. The program CreatePot acts as interface between the field solver and ITSIM 6.0. It converts the calculated electric field into a field array file readable by ITSIM 6.0 and ion trajectories are calculated by solving Newton's equation using Runge-Kutta integration methods. The accuracy of the field calculation is discussed for the ideal quadrupole ion trap in terms of applied mesh density. Electric fields of several different types of devices with 3D geometry are simulated, including ion transport through an ion optical system as a function of pressure. Ion spatial distributions, including the storage of positively charged ions only and simultaneous storage of positively/negatively charged ions in commercial linear ion traps with various geometries, are investigated using different trapping modes. Inelastic collisions and collision induced dissociation modeled using RRKM theory are studied, with emphasis on the fragmentation of n-butylbenzene inside an ideal quadrupole ion trap. The mass spectrum of 1,3-dichlorobenzene is simulated for the rectilinear ion trap device and good agreement is observed between the simulated and the experimental mass spectra. Collisional cooling using helium at different pressures is found to affect mass resolution in the rectilinear ion trap.

  2. Arbitrary Shape Deformation in CFD Design

    NASA Technical Reports Server (NTRS)

    Landon, Mark; Perry, Ernest

    2014-01-01

    Sculptor(R) is a commercially available software tool, based on an Arbitrary Shape Design (ASD), which allows the user to perform shape optimization for computational fluid dynamics (CFD) design. The developed software tool provides important advances in the state-of-the-art of automatic CFD shape deformations and optimization software. CFD is an analysis tool that is used by engineering designers to help gain a greater understanding of the fluid flow phenomena involved in the components being designed. The next step in the engineering design process is to then modify, the design to improve the components' performance. This step has traditionally been performed manually via trial and error. Two major problems that have, in the past, hindered the development of an automated CFD shape optimization are (1) inadequate shape parameterization algorithms, and (2) inadequate algorithms for CFD grid modification. The ASD that has been developed as part of the Sculptor(R) software tool is a major advancement in solving these two issues. First, the ASD allows the CFD designer to freely create his own shape parameters, thereby eliminating the restriction of only being able to use the CAD model parameters. Then, the software performs a smooth volumetric deformation, which eliminates the extremely costly process of having to remesh the grid for every shape change (which is how this process had previously been achieved). Sculptor(R) can be used to optimize shapes for aerodynamic and structural design of spacecraft, aircraft, watercraft, ducts, and other objects that affect and are affected by flows of fluids and heat. Sculptor(R) makes it possible to perform, in real time, a design change that would manually take hours or days if remeshing were needed.

  3. A controlled laboratory environment to study EO signal degradation due to underwater turbulence

    NASA Astrophysics Data System (ADS)

    Matt, Silvia; Hou, Weilin; Goode, Wesley; Liu, Guigen; Han, Ming; Kanaev, Andrey; Restaino, Sergio

    2015-05-01

    Temperature microstructure in the ocean can lead to localized changes in the index of refraction and can distort underwater electro-optical (EO) signal transmission. A similar phenomenon is well-known from atmospheric optics and generally referred to as "optical turbulence". Though turbulent fluctuations in the ocean distort EO signal transmission and can impact various underwater applications, from diver visibility to active and passive remote sensing, there have been few studies investigating the subject. To provide a test bed for the study of impacts from turbulent flows on underwater EO signal transmission, and to examine and mitigate turbulence effects, we set up a laboratory turbulence environment allowing the variation of turbulence intensity. Convective turbulence is generated in a large Rayleigh- Bénard tank and the turbulent flow is quantified using high-resolution Acoustic Doppler Velocimeter profilers and fast thermistor probes. The turbulence measurements are complemented by computational fluid dynamics simulations of convective turbulence emulating the tank environment. These numerical simulations supplement the sparse laboratory measurements. The numerical data compared well to the laboratory data and both conformed to the Kolmogorov spectrum of turbulence and the Batchelor spectrum of temperature fluctuations. The controlled turbulence environment can be used to assess optical image degradation in the tank in relation to turbulence intensity, as well as to apply adaptive optics techniques. This innovative approach that combines optical techniques, turbulence measurements and numerical simulations can help understand how to mitigate the effects of turbulence impacts on underwater optical signal transmission, as well as advance optical techniques to probe oceanic processes.

  4. Computation of large-scale statistics in decaying isotropic turbulence

    NASA Technical Reports Server (NTRS)

    Chasnov, Jeffrey R.

    1993-01-01

    We have performed large-eddy simulations of decaying isotropic turbulence to test the prediction of self-similar decay of the energy spectrum and to compute the decay exponents of the kinetic energy. In general, good agreement between the simulation results and the assumption of self-similarity were obtained. However, the statistics of the simulations were insufficient to compute the value of gamma which corrects the decay exponent when the spectrum follows a k(exp 4) wave number behavior near k = 0. To obtain good statistics, it was found necessary to average over a large ensemble of turbulent flows.

  5. Comparison of Four Mixed Layer Mesoscale Parameterizations and the Equation for an Arbitrary Tracer

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Dubovikov, M. S.

    2011-01-01

    In this paper we discuss two issues, the inter-comparison of four mixed layer mesoscale parameterizations and the search for the eddy induced velocity for an arbitrary tracer. It must be stressed that our analysis is limited to mixed layer mesoscales since we do not treat sub-mesoscales and small turbulent mixing. As for the first item, since three of the four parameterizations are expressed in terms of a stream function and a residual flux of the RMT formalism (residual mean theory), while the fourth is expressed in terms of vertical and horizontal fluxes, we needed a formalism to connect the two formulations. The standard RMT representation developed for the deep ocean cannot be extended to the mixed layer since its stream function does not vanish at the ocean's surface. We develop a new RMT representation that satisfies the surface boundary condition. As for the general form of the eddy induced velocity for an arbitrary tracer, thus far, it has been assumed that there is only the one that originates from the curl of the stream function. This is because it was assumed that the tracer residual flux is purely diffusive. On the other hand, we show that in the case of an arbitrary tracer, the residual flux has also a skew component that gives rise to an additional bolus velocity. Therefore, instead of only one bolus velocity, there are now two, one coming from the curl of the stream function and other from the skew part of the residual flux. In the buoyancy case, only one bolus velocity contributes to the mean buoyancy equation since the residual flux is indeed only diffusive.

  6. Plume rise, entrainment and dispersion in turbulent winds

    NASA Astrophysics Data System (ADS)

    Netterville, Dennett D. J.

    This paper describes a new analytical model which combines within one theoretical framework several aspects of the phenomena of plume rise, dispersion, thermal stratification and ambient turbulence. The model is based in part on knowledge gained from recent investigations of flow within free shear layers. The observations suggest a simple model for the turbulent mixing process, which accounts for the known entrainment of air into smoke plumes by plume-generated turbulence. More importantly, the model also predicts a path by which ambient turbulence causes reverse entrainment of plume material into the surrounding fluids. This gives rise to a new 'extrainment' term in each of the plume momentum and buoyancy equations. These equations are solved for a turbulent atmosphere of arbitrary thermal stability, and yield plume trajectories which gradually level off at final rise heights that depend on the degree of thermal stratification and on the scale and intensity of ambient turbulence. A link between plume rise and dispersion is identified by means of the concentration species equation, which is solved to show that the plume acts along its length as a distributed source of passively dispersing material. The new theory, specialized for an adiabatic atmosphere, plus the familiar x2/3 law and a semi-empirical final rise theory from the literature, are all compared against full-scale data on plume rise in turbulent winds. The new theory significantly improves the accuracy of estimates of plume trajectory and final plume height. The price for this improved predictive ability is the need to evaluate the air temperature and its gradient at plume level, and the corresponding intensity and scale of turbulent air movement. This is no longer a technical obstacle since recently developed SODAR and RASS remote sensors have this capability.

  7. Turbulence Studies of a Rectangular Slotted Noise-Suppressor Nozzle

    NASA Technical Reports Server (NTRS)

    Laurence, James C.

    1960-01-01

    The problem of noise suppression of turbojet engines has shown a need for turbulence data within the flow field of various types of nozzles used in ad hoc investigations of the sound power. The result of turbulence studies in a nozzle configuration of four parallel rectangular slots is presented in this report with special attention to the effect of the spacing of the nozzles on the intensity of turbulence, scale of turbulence, spectrum of turbulence, and the mean stream velocity. Taylor's hypothesis, which describes the convection of the turbulence eddies, was tested and found correct within experimental error and certain experimental and theoretical limitations. The convection of the pressure patterns was also investigated, and the value of the convection velocity was found to be about 0.43 times the central core velocity of the jets. The effect of the spacing-to-width ratio of the nozzles upon the turbulence intensity, the scale of turbulence, and the spectral distribution of the noise was found in general to produce a maximum change for spacing-to-width ratios of 1.5 to 2.0. These changes may be the cause of the reduction in sound power reported for similar full-scale nozzles and test conditions under actual (static) engine operation. A noise reduction parameter is defined from Lighthill's theory which gives qualitative agreement with experiments which show the noise reduction is greatest for spacing-to-width ratios of 1.5 to 2.0.

  8. Helicopter rotor noise due to ingestion of atmospheric turbulence

    NASA Technical Reports Server (NTRS)

    Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.

    1986-01-01

    A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor noise due to the ingestion of atmospheric turbulence. This study incorporates an atmospheric turbulence model, a rotor mean flow contraction model and a rapid distortion turbulence model which together determine the statistics of the non-isotropic turbulence at the rotor plane. Inputs to the combined mean inflow and turbulence models are controlled by atmospheric wind characteristics and helicopter operating conditions. A generalized acoustic source model was used to predict the far field noise generated by the non-isotropic flow incident on the rotor. Absolute levels for acoustic spectra and directivity patterns were calculated for full scale helicopters, without the use of empirical or adjustable constants. Comparisons between isotropic and non-isotropic turbulence at the rotor face demonstrated pronounced differences in acoustic spectra. Turning and contraction of the flow for hover and low speed vertical ascent cases result in a 3 dB increase in the acoustic spectrum energy and a 10 dB increase in tone levels. Compared to trailing edge noise, turbulence ingestion noise is the dominant noise mechanism below approximately 30 rotor harmonics, while above 100 harmonics, trailing edge noise levels exceed turbulence ingestion noise by 25 dB.

  9. Zombie Turbulence and More in Stratified Couette Flow

    NASA Astrophysics Data System (ADS)

    Marcus, Philip; Barranco, Joe; Pei, Suyang; Jiang, Chung-Hsiang

    2016-11-01

    Zombie turbulence occurs in rotating, shearing vertically-stratified flows such as stratified Couette flows. The turbulence is triggered by a neutrally-stable eigenmode with a critical layer receptive to finite-amplitude perturbations. Once excited, the critical layer becomes a vortex layer pair that rolls up into discrete vortices. Those vortices excite new critical layers, and the process repeats ad infinitum. When the vortex amplitudes become sufficiently large, the flow becomes turbulent. Although possessing a mid-range energy spectrum with E (k) k - 5 / 3 , the turbulence is non-Kolmogorov, highly anisotropic, and with large turbulent, but coherent, structures that retain the length scales of the spacing between the critical layers. The motivation for this study is protoplanetary disks (PPDs) where new stars form. In the PPD the Brunt-Vaisala frequency N increases as a function of distance from the midplane where it is zero. We cannot trigger the initial finite amplitude instability where N is small (close to the midplane). However, computations in PPDs and Couette flows show that zombie turbulence forms where N is large, and then a new type of turbulence, that is neither zombie nor Kolmogorov turbulence, fills in the remainder of the domain even where N = 0 .

  10. A Model for Jet-Surface Interaction Noise Using Physically Realizable Upstream Turbulence Conditions

    NASA Technical Reports Server (NTRS)

    Afsar, Mohammed Z.; Leib, Stewart J.; Bozak, Richard F.

    2015-01-01

    This paper is a continuation of previous work in which a generalized Rapid Distortion Theory (RDT) formulation was used to model low-frequency trailing-edge noise. The research was motivated by proposed next-generation aircraft configurations where the exhaust system is tightly integrated with the airframe. Data from recent experiments at NASA on the interaction between high-Reynolds-number subsonic jet flows and an external flat plate showed that the power spectral density (PSD) of the far-field pressure underwent considerable amplification at low frequencies. For example, at the 900 observation angle, the low-frequency noise could be as much as 10dB greater than the jet noise itself. In this paper, we present predictions of the noise generated by the interaction of a rectangular jet with the trailing edge of a semi-infinite flat plate. The calculations are based on a formula for the acoustic spectrum of this noise source derived from an exact formal solution of the linearized Euler equations involving (in this case) one arbitrary convected scalar quantity and a Rayleigh equation Green's function. A low-frequency asymptotic approximation for the Green's function based on a two-dimensional mean flow is used in the calculations along with a physically realizable upstream turbulence spectrum, which includes a finite de-correlation region. Numerical predictions, based on three-dimensional RANS solutions for a range of subsonic acoustic Mach number jets and nozzle aspect ratios are compared with experimental data. Comparisons of the RANS results with flow data are also presented for selected cases. We find that a finite decorrelation region increases the low-frequency algebraic decay (the low frequency "rolloff") of the acoustic spectrum with angular frequency thereby producing much closer agreement with noise data for Strouhal numbers less than 0.1. Secondly, the large-aspectratio theory is able to predict the low-frequency amplification due to the jet

  11. MHD turbulent processes

    NASA Technical Reports Server (NTRS)

    Montgomery, David

    1988-01-01

    Three areas of study in MHD turbulence are considered. These are the turbulent relaxation of the toroidal Z pinch, density fluctuations in MHD fluids, and MHD cellular automata. A Boolean computer game that updates a cellular representation in parallel and that has macroscopic averages converging to solutions of the two-dimensional MHD equations is discussed.

  12. Scattering of radio frequency waves by turbulence in fusion plasmas

    NASA Astrophysics Data System (ADS)

    Ram, Abhay K.

    2016-10-01

    In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments and incoherent fluctuations due to turbulence are routinely observed in the scrape-off layer. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near the wall of a tokamak, have to propagate through the scrape-off layer before reaching the core of the plasma. While the effect of fluctuations on RF waves has not been quantified experimentally, there are telltale signs, arising from differences between results from simulations and from experiments, that fluctuations can modify the spectrum of RF waves. Any effect on RF waves in the scrape-off layer can have important experimental consequences. For example, electron cyclotron waves are expected to stabilize the deleterious neoclassical tearing mode (NTM) in ITER. Spectral and polarization changes due to scattering will modify the spatial location and profile of the current driven by the RF waves, thereby affecting the control of NTMs. Pioneering theoretical studies and complementary computer simulations have been pursued to elucidate the impact of fluctuations on RF waves. From the full complement of Maxwell's equations for cold, magnetized plasmas, it is shown that the Poynting flux in the wake of filaments develops spatial structure due to diffraction and shadowing. The uniformity of power flow into the plasma is affected by side-scattering, modifications to the wave spectrum, and coupling to plasma waves other than the incident RF wave. The Snell's law and the Fresnel equations have been reformulated within the context of magnetized plasmas. They are distinctly different from their counterparts in scalar dielectric media, and reveal new and important physical insight into the scattering of RF waves. The Snell's law and Fresnel equations are the basis for the Kirchhoff approximation necessary to determine properties of the scattered waves. Furthermore, this theory is also relevant for studying back

  13. Elasto-inertial turbulence

    PubMed Central

    Samanta, Devranjan; Dubief, Yves; Holzner, Markus; Schäfer, Christof; Morozov, Alexander N.; Wagner, Christian; Hof, Björn

    2013-01-01

    Turbulence is ubiquitous in nature, yet even for the case of ordinary Newtonian fluids like water, our understanding of this phenomenon is limited. Many liquids of practical importance are more complicated (e.g., blood, polymer melts, paints), however; they exhibit elastic as well as viscous characteristics, and the relation between stress and strain is nonlinear. We demonstrate here for a model system of such complex fluids that at high shear rates, turbulence is not simply modified as previously believed but is suppressed and replaced by a different type of disordered motion, elasto-inertial turbulence. Elasto-inertial turbulence is found to occur at much lower Reynolds numbers than Newtonian turbulence, and the dynamical properties differ significantly. The friction scaling observed coincides with the so-called “maximum drag reduction” asymptote, which is exhibited by a wide range of viscoelastic fluids. PMID:23757498

  14. MHD turbulent mixing layers

    SciTech Connect

    Esquivel, A.; Lazarian, A.; Benjamin, R.A.; Cho, J.; Leitner, S.N.

    2005-09-28

    Turbulent mixing layers have been proposed to explain observations of line ratios of highly ionized elements in the interstellar medium. We present preliminary results of numerical simulations of turbulent mixing layers in a magnetized medium. We developed a MHD code with radiative cooling. The magnetic field is expected to be a controlling factor by suppressing instabilities that lead to the turbulent mixing. Our results suggest that the difference in turbulent mixing in the unmagnetized case as compared to the case of a weak magnetic field, {beta} = Pgas/Pmag {approx} 10, is insignificant. With a more thorough exploration of parameter space, this work will provide more reliable diagnostics of turbulent mixing layers than those available today.

  15. Microwave beam power transmission at an arbitrary range

    NASA Technical Reports Server (NTRS)

    Pinero, L. R.; Christian, J. L., Jr.; Acosta, R. J.

    1992-01-01

    The power transfer efficiency between two circular apertures at an arbitrary range is obtained numerically. The apertures can have generally different sizes and arbitrary taper illuminations. The effects of distance and taper illumination on the transmission efficiency are investigated for equal size apertures. The result shows that microwave beam power is more effective at close ranges, namely distances less than 2D(exp 2)/lambda. Also shown was the power transfer efficiency increase with taper illumination for close range distances. A computer program was developed for calculating the power transfer efficiency at an arbitrary range.

  16. Turbulent Flow Past Spinning Cylinders

    NASA Astrophysics Data System (ADS)

    Mehmedagic, Igbal; Carlucci, Donald; Carlucci, Pasquale; Thangam, Siva

    2009-11-01

    Flow past cylinders aligned along their axis where a base freely spins while attached to a non-spinning forebody is considered from a computational and experimental point of view. The time-averaged equations of motion and energy are solved using the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation with an efficient finite-volume algorithm. An anisotropic two-equation Reynolds-stress model that incorporates the effect of rotation-modified energy spectrum and swirl is used to perform computations for the flow past axially rotating cylinders. Both rigid cylinders as well as that of cylinders with free-spinning base are considered from a computational point of view. A subsonic wind tunnel with a forward-sting mounted spinning cylinder is used for experiments. Experiments are performed for a range of spin rates and free stream flow conditions. The experimental results of Carlucci & Thangam (2001) are used to benchmark flow over spinning cylinders. The data is extended to munitions spinning in the wake of other munitions. Applications involving the design of projectiles are discussed.

  17. Sequential recall of meaningful and arbitrary sequences by orangutans and human children: Does content matter?

    PubMed

    Renner, Elizabeth; Price, Elizabeth E; Subiaul, Francys

    2016-01-01

    Do visual cues such as size, color, and number facilitate sequential recall in orangutans and human children? In Experiment 1, children and adult orangutans solved two types of sequences, arbitrary (unrelated pictures) and meaningful (pictures varied along a spectrum according to the size, color, or number of items shown), in a touchscreen paradigm. It was found that visual cues did not increase the percentage of correct responses for either children or orangutans. In order to demonstrate that the failure to spontaneously seriate along these dimensions was not due to a general inability to perceive the dimensions nor to an inability to seriate items, in Experiment 2, orangutans were trained on one type of sequence and tested on novel sequences organized according to the same rule (i.e., pictures varied on the number spectrum only). The orangutans performed significantly better on novel meaningful sequences in this task than on novel arbitrary sequences. These results indicate that, while orangutans and human children share the ability to learn how to order items according to their size, color, or number, both orangutans and humans lack a cognitive propensity to spontaneously (i.e., without prior training or enculturation) order multiple items by size, color, or number.

  18. Inverse scattering problem in turbulent magnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Treumann, Rudolf A.; Baumjohann, Wolfgang; Narita, Yasuhito

    2016-08-01

    We apply a particular form of the inverse scattering theory to turbulent magnetic fluctuations in a plasma. In the present note we develop the theory, formulate the magnetic fluctuation problem in terms of its electrodynamic turbulent response function, and reduce it to the solution of a special form of the famous Gelfand-Levitan-Marchenko equation of quantum mechanical scattering theory. The last of these applies to transmission and reflection in an active medium. The theory of turbulent magnetic fluctuations does not refer to such quantities. It requires a somewhat different formulation. We reduce the theory to the measurement of the low-frequency electromagnetic fluctuation spectrum, which is not the turbulent spectral energy density. The inverse theory in this form enables obtaining information about the turbulent response function of the medium. The dynamic causes of the electromagnetic fluctuations are implicit to it. Thus, it is of vital interest in low-frequency magnetic turbulence. The theory is developed until presentation of the equations in applicable form to observations of turbulent electromagnetic fluctuations as input from measurements. Solution of the final integral equation should be done by standard numerical methods based on iteration. We point to the possibility of treating power law fluctuation spectra as an example. Formulation of the problem to include observations of spectral power densities in turbulence is not attempted. This leads to severe mathematical problems and requires a reformulation of inverse scattering theory. One particular aspect of the present inverse theory of turbulent fluctuations is that its structure naturally leads to spatial information which is obtained from the temporal information that is inherent to the observation of time series. The Taylor assumption is not needed here. This is a consequence of Maxwell's equations, which couple space and time evolution. The inversion procedure takes advantage of a particular

  19. Beyond the Maltese Cross: Geometry of Turbulence Between 0.2 and 1 au

    NASA Astrophysics Data System (ADS)

    Verdini, Andrea; Grappin, Roland

    2016-11-01

    The spectral anisotropy of turbulent structures has been measured in the solar wind since 1990, relying on the assumption of axisymmetry about the mean magnetic field, B 0. However, several works indicate that this hypothesis might be partially wrong, thus raising two questions: (i) is it correct to interpret measurements at 1 au (the so-called Maltese cross) in term of a sum of slab and two-dimensional (2D) turbulence; and (ii) what information is really contained in the Maltese cross? We solve direct numerical simulations of the magnetohydrodynamic equations including the transverse stretching exerted by the solar wind flow and study the genuine 3D anisotropy of turbulence as well as that one resulting from the assumption of axisymmetry about B 0. We show that the evolution of the turbulent spectrum from 0.2 to 1 au depends strongly on its initial anisotropy. An axisymmetric spectrum with respect to B 0 keeps its axisymmetry, i.e., resists stretching perpendicular to radial, while an isotropic spectrum becomes essentially axisymmetric with respect to the radial direction. We conclude that close to the Sun, slow-wind turbulence has a spectrum that is axisymmetric around B 0 and the measured 2D component at 1 au describes the real shape of turbulent structures. In contrast, fast-wind turbulence has a more isotropic spectrum at the source and becomes radially symmetric at 1 au. Such structure is hidden by the symmetrization applied to the data that instead returns a slab geometry.

  20. Introducing the concept of anisotropy at different scales for modeling optical turbulence.

    PubMed

    Toselli, Italo

    2014-08-01

    In this paper, the concept of anisotropy at different atmospheric turbulence scales is introduced. A power spectrum and its associated structure function with inner and outer scale effects and anisotropy are also shown. The power spectrum includes an effective anisotropic parameter ζ(eff) to describe anisotropy, which is useful for modeling optical turbulence when a non-Kolmogorov power law and anisotropy along the direction of propagation are present.

  1. Implementation and Validation of the BHR Turbulence Model in the FLAG Hydrocode

    SciTech Connect

    Denissen, Nicholas A.; Fung, Jimmy; Reisner, Jon M.; Andrews, Malcolm J.

    2012-08-29

    The BHR-2 turbulence model, developed at Los Alamos National Laboratory for variable density and compressible flows, is implemented in an Arbitrary Lagrangian-Eulerian hydrocode, FLAG. The BHR-2 formulation is discussed, with emphasis on its connection to multi-component flow formulations that underlie FLAG's treatment of multi-species flow. One-dimensional and two-dimensional validation tests are performed and compared to experiment and Eulerian simulations. Turbulence is an often studied and ubiquitous phenomenon in nature, and modeling its effects is essential in many practical applications. Specifically the behavior of turbulence in the presence of strong density gradients and compressibility is of fundamental importance in applications ranging from Inertial Confinement Fusion (ICF) [1], supernovae [2], and atmospheric flows. The BHR closure approach [3] seeks to model the physical processes at work in variable density turbulence including Kelvin-Helmholtz (KH) [4], Rayleigh-Taylor (RT) [5], and Richtmyer-Meshkov (RM) [6], driven turbulence. The effectiveness of the BHR-2 implementation has been demonstrated for variable density mixing in the KH, RT, and RM cases in an Eulerian framework [7]. The primary motivation of the present work is to implement the BHR-2 turbulence model in the Arbitrary Lagrangian-Eulerian (ALE) hydrodynamics code FLAG. The goal is not only to demonstrate results in agreement with previous Eulerian calculations, but also document behavior that arises from the underlying differences in code philosophy.

  2. Diff-invariant kinetic terms in arbitrary dimensions

    NASA Astrophysics Data System (ADS)

    Barbero G., J. Fernando; Villaseñor, Eduardo J.

    2002-06-01

    We study the physical content of quadratic diff-invariant Lagrangians in arbitrary dimensions by using covariant symplectic techniques. This paper extends previous results in dimension four. We discuss the difference between the even and odd dimensional cases.

  3. Statistics of intense turbulent vorticity events.

    PubMed

    Moriconi, L

    2004-08-01

    We investigate statistical properties of vorticity fluctuations in fully developed turbulence, which are known to exhibit a strong intermittent behavior. Taking as the starting point the Navier-Stokes equations with a random force term correlated at large scales, we obtain in the high Reynolds number regime a closed analytical expression for the probability distribution function of an arbitrary component of the vorticity field. The central idea underlying the analysis consists in the restriction of the velocity configurational phase-space to a particular sector where the rate of strain and the rotation tensors can be locally regarded as slow and fast degrees of freedom, respectively. This prescription is implemented along the Martin-Siggia-Rose functional framework, whereby instantons and perturbations around them are taken into account within a steepest-descent approach.

  4. Edge turbulence in tokamaks

    NASA Astrophysics Data System (ADS)

    Nedospasov, A. V.

    1992-12-01

    Edge turbulence is of decisive importance for the distribution of particle and energy fluxes to the walls of tokamaks. Despite the availability of extensive experimental data on the turbulence properties, its nature still remains a subject for discussion. This paper contains a review of the most recent theoretical and experimental studies in the field, including mainly the studies to which Wootton (A.J. Wooton, J. Nucl. Mater. 176 & 177 (1990) 77) referred to most in his review at PSI-9 and those published later. The available theoretical models of edge turbulence with volume dissipation due to collisions fail to fully interpret the entire combination of experimental facts. In the scrape-off layer of a tokamak the dissipation prevails due to the flow of current through potential shifts near the surface of limiters of divertor plates. The different origins of turbulence at the edge and in the core plasma due to such dissipation are discussed in this paper. Recent data on the electron temperature fluctuations enabled one to evaluate the electric probe measurements of turbulent flows of particles and heat critically. The latest data on the suppression of turbulence in the case of L-H transitions are given. In doing so, the possibility of exciting current instabilities in biasing experiments (rather than only to the suppression of existing turbulence) is given some attention. Possible objectives of further studies are also discussed.

  5. Turbulent scaling in fluids

    SciTech Connect

    Ecke, R.; Li, Ning; Chen, Shiyi; Liu, Yuanming

    1996-11-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project was a study of turbulence in fluids that are subject to different body forces and to external temperature gradients. Our focus was on the recent theoretical prediction that the Kolomogorov picture of turbulence may need to be modified for turbulent flows driven by buoyancy and subject to body forces such as rotational accelerations. Models arising from this research are important in global climate modeling, in turbulent transport problems, and in the fundamental understanding of fluid turbulence. Experimentally, we use (1) precision measurements of heat transport and local temperature; (2) flow visualization using digitally- enhanced optical shadowgraphs, particle-image velocimetry, thermochromic liquid-crystal imaging, laser-doppler velocimetry, and photochromic dye imaging; and (3) advanced image- processing techniques. Our numerical simulations employ standard spectral and novel lattice Boltzmann algorithms implemented on parallel Connection Machine computers to simulate turbulent fluid flow. In laboratory experiments on incompressible fluids, we measure probability distribution functions and two-point spatial correlations of temperature T and velocity V (both T-T and V-T correlations) and determine scaling relations for global heat transport with Rayleigh number. We also explore the mechanism for turbulence in thermal convection and the stability of the thermal boundary layer.

  6. Modeling turbulent flame propagation

    SciTech Connect

    Ashurst, W.T.

    1994-08-01

    Laser diagnostics and flow simulation techniques axe now providing information that if available fifty years ago, would have allowed Damkoehler to show how turbulence generates flame area. In the absence of this information, many turbulent flame speed models have been created, most based on Kolmogorov concepts which ignore the turbulence vortical structure, Over the last twenty years, the vorticity structure in mixing layers and jets has been shown to determine the entrainment and mixing behavior and these effects need to be duplicated by combustion models. Turbulence simulations reveal the intense vorticity structure as filaments and simulations of passive flamelet propagation show how this vorticity Creates flame area and defines the shape of the expected chemical reaction surface. Understanding how volume expansion interacts with flow structure should improve experimental methods for determining turbulent flame speed. Since the last decade has given us such powerful new tools to create and see turbulent combustion microscopic behavior, it seems that a solution of turbulent combustion within the next decade would not be surprising in the hindsight of 2004.

  7. Classical Vs. Superfluid Turbulence

    NASA Astrophysics Data System (ADS)

    Roche, P.-E.

    2008-11-01

    Thanks to a zero-viscosity, superfluids offer a unique testing ground for hydrodynamic models, in particular for turbulence ones. In Kolmogorov's turbulence model, viscosity is well known to damp the kinetic energy of the smallest eddies, and thus to introduce a cut-off at one end of the turbulent cascade. Significant differences between this ``classical'' turbulence and the turbulence of a superfluid are therefore expected, but --surprisingly- most experiments rather evidenced strong similarities. We will give an overview of a set of experiments designed to compare in details the classical versus superfluid turbulences, up to a record mass flow of superfluid (700g/s of He @ 1.6K). Then, we will focus on some unexpected vorticity measurements, which can be interpreted assuming that the superfluid vortices are passively advected by the largest scales of the flow, in contrast with the ``classical'' turbulence counterpart. Numerical simulations -based on regular DNS- will be presented to complete this interpretation. In collaboration with C. Barenghi, University of Newcastle; B. Castaing and E. Levèque, ENSL, Lyon; S. David, IEF, CNRS, Orsay; B. Rousset, SBT/CEA, Grenoble; and P. Tabeling, H. Willaime MMN, ESPCI, Paris.

  8. Wall turbulence control

    NASA Technical Reports Server (NTRS)

    Wilkinson, Stephen P.; Lindemann, A. Margrethe; Beeler, George B.; Mcginley, Catherine B.; Goodman, Wesley L.; Balasubramanian, R.

    1986-01-01

    A variety of wall turbulence control devices which were experimentally investigated are discussed; these include devices for burst control, alteration of outer flow structures, large eddy substitution, increased heat transfer efficiency, and reduction of wall pressure fluctuations. Control of pre-burst flow was demonstrated with a single, traveling surface depression which is phase-locked to elements of the burst production process. Another approach to wall turbulence control is to interfere with the outer layer coherent structures. A device in the outer part of a boundary layer was shown to suppress turbulence and reduce drag by opposing both the mean and unsteady vorticity in the boundary layer. Large eddy substitution is a method in which streamline curvature is introduced into the boundary layer in the form of streamwise vortices. Riblets, which were already shown to reduce turbulent drag, were also shown to exhibit superior heat transfer characteristics. Heat transfer efficiency as measured by the Reynolds Analogy Factor was shown to be as much as 36 percent greater than a smooth flat plate in a turbulent boundary layer. Large Eddy Break-Up (LEBU) which are also known to reduce turbulent drag were shown to reduce turbulent wall pressure fluctuation.

  9. Turbulence and Global Properties of the Solar Wind

    NASA Technical Reports Server (NTRS)

    Goldstein, Melvyn L.

    2010-01-01

    The solar wind shows striking characteristics that suggest that it is a turbulent magnetofluid, but the picture is not altogether simple. From the earliest observations, a strong correlation between magnetic fluctuations and plasma velocity fluctuations was noted. The high corrections suggest that the fluctuations are Alfven waves. In addition, the power spectrum of the magnetic fluctuation showed evidence of an inertial range that resembled that seen in fully-developed fluid turbulence. Alfven waves, however, are exact solutions of the equations of incompressible magnetohydrodynamics. Thus, there was a puzzle: how can a magnetofluid consisting of Alfven waves be turbulent? The answer lay in the role of velocity shears in the solar wind that could drive turbulent evolution. Puzzles remain: for example, the power spectrum of the velocity fluctuations is less steep than the slope of the magnetic fluctuations. The plasma in the magnetic tail of Earth's magnetosphere also shows aspects of turbulence, as does the plasma in the dayside magnetosphere near the poles the dayside cusps. Recently, new analyses of high time resolution magnetic field data from Cluster have offered a glimpse of how turbulence is dissipated, thus heating the ambient plasma.

  10. Skin effect with arbitrary specularity in Maxwellian plasma

    SciTech Connect

    Latyshev, A. V.; Yushkanov, A. A.

    2010-11-15

    The problem of the skin effect with arbitrary specularity in Maxwellian plasma with specular-diffuse boundary conditions is solved. A new analytical method is developed that makes it possible to obtain a solution up to an arbitrary degree of accuracy. The method is based on the idea of symmetric continuation of not only the electric field, but also electron distribution function. The solution is obtained in a form of von Neumann series.

  11. Closed description of arbitrariness in resolving quantum master equation

    NASA Astrophysics Data System (ADS)

    Batalin, Igor A.; Lavrov, Peter M.

    2016-07-01

    In the most general case of the Delta exact operator valued generators constructed of an arbitrary Fermion operator, we present a closed solution for the transformed master action in terms of the original master action in the closed form of the corresponding path integral. We show in detail how that path integral reduces to the known result in the case of being the Delta exact generators constructed of an arbitrary Fermion function.

  12. Macroscopic effects of the spectral structure in turbulent flows

    NASA Astrophysics Data System (ADS)

    Tran, Tuan; Chakraborty, Pinaki; Guttenberg, Nicholas; Prescott, Alisia; Kellay, Hamid; Goldburg, Walter; Goldenfeld, Nigel; Gioia, Gustavo

    2010-06-01

    There is a missing link between the macroscopic properties of turbulent flows, such as the frictional drag of a wall-bounded flow, and the turbulent spectrum. The turbulent spectrum is a power law of exponent α (the `spectral exponent') that gives the characteristic velocity of a turbulent fluctuation (or `eddy') of size s as a function of s (ref. 1). Here we seek the missing link by comparing the frictional drag in soap-film flows, where α=3 (refs 9, 10), and in pipe flows, where α=5/3 (refs 11, 12). For moderate values of the Reynolds number Re, we find experimentally that in soap-film flows the frictional drag scales as Re-1/2, whereas in pipe flows the frictional drag scales as Re-1/4. Each of these scalings may be predicted from the attendant value of α by using a new theory, in which the frictional drag is explicitly linked to the turbulent spectrum.

  13. PECASE - Multi-Scale Experiments and Modeling in Wall Turbulence

    DTIC Science & Technology

    2014-12-23

    characterizing the three-dimensional spectrum of the streamwise velocity fluctuations using time-resolved particle image velocimetry at a range of...spectrum of the streamwise velocity fluctuations using time-resolved particle image velocimetry at a range of wall-normal locations, and extending a two...in canonical and non-canonical turbulent boundary layers using fast Particle Image Velocimetry in order to identify the influence of multi-scale

  14. Modeling of turbulent chemical reaction

    NASA Technical Reports Server (NTRS)

    Chen, J.-Y.

    1995-01-01

    Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

  15. Lagrangian turbulence and the Brownian motion paradox

    NASA Astrophysics Data System (ADS)

    Viecelli, J. A.

    1991-11-01

    The unique properties of three-dimensional hydrodynamic turbulence depend on the nature of the long-range time correlations as well as the spatial correlations. Although Kolmogorov's second similarity hypothesis predicts a power-law spatial scaling exponent for the Eulerian velocity fluctuations in agreement with experiments, it also leads, via the Lagrangian velocity time structure function relationship, to particle dispersion predictions that are inconsistent with enhanced diffusion. Recently, a new computational technique has been developed which can generate random power-law correlated fields in any number of dimensions with unlimited scale range. This new method is used to explore the consequences of a proposed set of assumptions about the nature of the time correlations and their relationship to the spatial correlations. In particular, the Brownian motion paradox is examined and it is shown that it can be resolved if the time domain constraint part of Kolmogorov's second hypothesis is relaxed and replaced with an assumption of space-time isotropy. The proposed modification preserves the observed one-dimensional k-5/3 spatial energy spectrum, allows for enhanced diffusion consistent with Richardson's law, is consistent with Taylor's frozen turbulence assumption under the appropriate conditions, and yields an ω-5/3 frequency spectrum for the velocity fluctuations in a frame at rest with respect to the turbulence.

  16. Universal constants and equations of turbulent motion

    NASA Astrophysics Data System (ADS)

    Baumert, Helmut

    2011-11-01

    For turbulence at high Reynolds number we present an analogy with the kinetic theory of gases, with dipoles made of vortex tubes as frictionless, incompressible but deformable quasi-particles. Their movements are governed by Helmholtz' elementary vortex rules applied locally. A contact interaction or ``collision'' leads either to random scatter of a trajectory or to the formation of two likewise rotating, fundamentally unstable whirls forming a dissipative patch slowly rotating around its center of mass, the latter almost at rest. This approach predicts von Karman's constant as 1/sqrt(2 pi) = 0.399 and the spatio-temporal dynamics of energy-containing time and length scales controlling turbulent mixing [Baumert 2005, 2009]. A link to turbulence spectra was missing so far. In the present contribution it is shown that the above image of dipole movements is compatible with Kolmogorov's spectra if dissipative patches, beginning as two likewise rotating eddies, evolve locally into a space-filling bearing in the sense of Herrmann [1990], i.e. into an ``Apollonian gear.'' Its parts and pieces are are frictionless, excepting the dissipative scale of size zero. Our approach predicts the dimensionless pre-factor in the 3D Eulerian wavenumber spectrum (in terms of pi) as 1.8, and in the Lagrangian frequency spectrum as the integer number 2. Our derivations are free of empirical relations and rest on geometry, methods from many-particle physics, and on elementary conservation laws only. Department of the Navy Grant, ONR Global

  17. Computation of beam propagation in turbulent field

    NASA Astrophysics Data System (ADS)

    Yang, Yao; Cen, Zhaofeng; Li, Xiaotong

    2016-10-01

    The split-step Fourier method (SSFM) is introduced to analyze the beam propagation in a relatively large-sized turbulent filed, whose refractive-index profile is already detected. The numerical method is achieved by fast Fourier transform (FFT).To obtain the optimal sampling number, we propose an adaptive spread-spectrum method as an optimization. The SSFM is widely used for solving the nonlinear Schrödinger equation [1].The advantage of the SSFM is apparently its simple formalism and suitability to our situation. The direct numerical solution of the Helmholtz equation, derived from this method, yields detailed information of the spatial and angular properties of the propagation beam. On the other hand, a set of approximations restrict its applicability, the requirements for the accurate application of the method are summarized and a set of formulas is generalized in this paper. The efficiency of the SSFM depends on the sampling number, the adaptive spread-spectrum method yields optimal sampling number to increase the computational efficiency .To testify the accuracy of our algorithm, we use graded-index medium as the turbulent filed, for the reason that the beam propagation in turbulent field with random refractive-index profile is ruleless and has no unified reference. The simulation result testifies our algorithm is tremendously accurate, capable of selecting the optimal N automatically and much more computationally efficient than the original algorithm.

  18. Near isotropic behavior of turbulent thermal convection

    NASA Astrophysics Data System (ADS)

    Nath, Dinesh; Pandey, Ambrish; Kumar, Abhishek; Verma, Mahendra K.

    2016-10-01

    We investigate the anisotropy in turbulent convection in a three-dimensional (3D) box using direct numerical simulation. We compute the anisotropic parameter A =u⊥2/(2 u∥2) , where u⊥ and u∥ are the components of velocity perpendicular and parallel to the buoyancy direction, the shell and ring spectra, and shell-to-shell energy transfers. We observe that the flow is nearly isotropic for the Prandtl number Pr ≈1 , but the anisotropy increases with the Prandtl number. For Pr =∞ ,A ≈0.3 , anisotropy is not very significant even in extreme cases. We also observe that u∥ feeds energy to u⊥ via pressure. The computation of shell-to-shell energy transfers reveals that the energy transfer in turbulent convection is local and forward, similar to hydrodynamic turbulence. These results are consistent with the Kolmogorov's spectrum observed by Kumar et al. [Phys. Rev. E 90, 023016 (2014), 10.1103/PhysRevE.90.023016] for turbulent convection.

  19. Spectra and statistics in compressible isotropic turbulence

    NASA Astrophysics Data System (ADS)

    Wang, Jianchun; Gotoh, Toshiyuki; Watanabe, Takeshi

    2017-01-01

    Spectra and one-point statistics of velocity and thermodynamic variables in isotropic turbulence of compressible fluid are examined by using numerical simulations with solenoidal forcing at the turbulent Mach number Mt from 0.05 to 1.0 and at the Taylor Reynolds number Reλ from 40 to 350. The velocity field is decomposed into a solenoidal component and a compressible component in terms of the Helmholtz decomposition, and the compressible velocity component is further decomposed into a pseudosound component, namely, the hydrodynamic component associated with the incompressible field and an acoustic component associated with sound waves. It is found that the acoustic mode dominates over the pseudosound mode at turbulent Mach numbers Mt≥0.4 in our numerical simulations. At turbulent Mach numbers Mt≤0.4 , there exists a critical wave number kc beyond which the pseudosound mode dominates while the acoustic mode dominates at small wave numbers k spectrum scales as Mt4k-3 in the inertial range. It is also found that in the inertial range, the spectra of pressure, density, and temperature exhibit a k-7 /3 scaling for Mt≤0.3 and a k-5 /3 scaling for Mt≥0.5 .

  20. Inverse turbulent cascade in swarming sperm

    NASA Astrophysics Data System (ADS)

    Creppy, Adama; Praud, Olivier; Druart, Xavier; Kohnke, Philippa; Plouraboue, Franck; Inra, Cnrs, Umr, F-37380 Nouzilly, France Team; Université de Toulouse, Inpt, Ups, Imft, Umr 5502, France Team

    2014-11-01

    Collective motion of self-sustained swarming flows has recently provided examples of small scale turbulence arising where viscosity effects are dominant. We report the first observation of an universal inverse enstrophy cascade in concentrated swarming sperm consistent with a body of evidence built from various independent measurements. We found a well-defined k-3 power-law decay of velocity field power-spectrum and relative dispersion of small beads consistent with theoretical predictions in two-dimensional turbulence. Concentrated living sperm displays long-range, correlated whirlpool structures the size of which provides turbulence's integral scale. We propose a consistent explanation for this quasi-two-dimensional turbulence based on self-structured laminated flow forced by steric interaction and alignment, a state of active matter that we call ``swarming liquid crystal.'' We develop scaling arguments consistent with this interpretation. The implication of multi-scale collective dynamics of sperm's collective motility for fertility assessment is discussed. This work has been supported by the French Agence Nationale pour la Recherche (ANR) in the frame of the Contract MOTIMO (ANR-11-MONU-009-01). We thank Pierre Degond, Eric Climent, Laurent Lacaze and Frédéric Moulin for interesting discussions.

  1. Vortex annihilation and inverse cascades in two dimensional superfluid turbulence

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew; Chesler, Paul M.

    2015-03-01

    The dynamics of a dilute mixture of vortices and antivortices in a turbulent two-dimensional superfluid at finite temperature is well described by first order Hall-Vinen-Iordanskii equations, or dissipative point vortex dynamics. These equations are governed by a single dimensionless parameter: the ratio of the strength of drag forces to Magnus forces on vortices. When this parameter is small, we demonstrate using numerical simulations that the resulting superfluid enjoys an inverse energy cascade where small scale stirring leads to large scale vortex clustering. We argue analytically and numerically that the vortex annihilation rate in a laminar flow may be parametrically smaller than the rate in a turbulent flow with an inverse cascade. This suggests a new way to detect inverse cascades in experiments on two-dimensional superfluid turbulence using cold atomic gases, where traditional probes of turbulence such as the energy spectrum are not currently accessible.

  2. Test particle study of ion transport in drift type turbulence

    SciTech Connect

    Vlad, M.; Spineanu, F.

    2013-12-15

    Ion transport regimes in drift type turbulence are determined in the frame of a realistic model for the turbulence spectrum based on numerical simulations. The model includes the drift of the potential with the effective diamagnetic velocity, turbulence anisotropy, and dominant waves. The effects of the zonal flow modes are also analyzed. A semi-analytical method that is able to describe trajectory stochastic trapping or eddying is used for obtaining the transport coefficients as function of the parameters of the turbulence. Analytical approximations of the transport coefficients are derived from the results. They show the transition from Bohm to gyro-Bohm scaling as plasma size increases in very good agreement with the numerical simulations.

  3. RF wave propagation and scattering in turbulent tokamak plasmas

    SciTech Connect

    Horton, W. Michoski, C.; Peysson, Y.; Decker, J.

    2015-12-10

    Drift wave turbulence driven by the steep electron and ion temperature gradients in H-mode divertor tokamaks produce scattering of the RF waves used for heating and current drive. The X-ray emission spectra produced by the fast electrons require the turbulence broaden RF wave spectrum. Both the 5 GHz Lower Hybrid waves and the 170 GHz electron cyclotron [EC] RF waves experience scattering and diffraction by the electron density fluctuations. With strong LHCD there are bifurcations in the coupled turbulent transport dynamics giving improved steady-state confinement states. The stochastic scattering of the RF rays makes the prediction of the distribution of the rays and the associated particle heating a statistical problem. Thus, we introduce a Fokker-Planck equation for the probably density of the RF rays. The general frame work of the coupled system of coupled high frequency current driving rays with the low-frequency turbulent transport determines the profiles of the plasma density and temperatures.

  4. NON-LOCALITY OF HYDRODYNAMIC AND MAGNETOHYDRODYNAMIC TURBULENCE

    SciTech Connect

    Cho, Jungyeon

    2010-12-20

    We compare non-locality of interactions between different scales in hydrodynamic (HD) turbulence and magnetohydrodynamic (MHD) turbulence in a strongly magnetized medium. We use three-dimensional incompressible direct numerical simulations to evaluate non-locality of interactions. Our results show that non-locality in MHD turbulence is much more pronounced than that in HD turbulence. Roughly speaking, non-local interactions count for more than 10% of total interactions in our MHD simulation on a grid of 512{sup 3} points. However, there is no evidence that non-local interactions are important in our HD simulation with the same numerical resolution. We briefly discuss how non-locality affects the energy spectrum.

  5. On the Development of Turbulent Wakes from Vortex Streets

    NASA Technical Reports Server (NTRS)

    Roshko, Anatol

    1954-01-01

    Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At r=40 to 150, called the stable range, regular vortex streets are formed and no turbulent velocity fluctuations accompany the periodic formation of vortices. The range r=150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. The transition first occurs in the range r=150 to 300. Spectrum and statistical measurements were made to study the velocity fluctuations.

  6. Turbulent flow through screens

    NASA Technical Reports Server (NTRS)

    Mehta, R. D.

    1984-01-01

    A detailed experimental investigation has been carried out on the effects of different types of screens on turbulent flow, in particular turbulent boundary layers. The effect of a screen on a turbulent boundary layer is to give it a 'new lease of life'. The boundary layer turbulence is reorganized and the thickness reduced, thus making it less susceptible to separation. The aerodynamic properties of plastic screens are found to differ significantly from those of the conventional metal screens, evidently because of differences in the weaving properties. The 'overshoot' in mean velocity profile near the boudnary layer edge is shown to be a result of the effect of screen inclination on pressure drop coefficient. A more accurate formulation for the deflection coefficient of a screen is also proposed.

  7. Containerless Ripple Turbulence

    NASA Technical Reports Server (NTRS)

    Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles

    2002-01-01

    One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear

  8. Inflow Turbulence Generation Methods

    NASA Astrophysics Data System (ADS)

    Wu, Xiaohua

    2017-01-01

    Research activities on inflow turbulence generation methods have been vigorous over the past quarter century, accompanying advances in eddy-resolving computations of spatially developing turbulent flows with direct numerical simulation, large-eddy simulation (LES), and hybrid Reynolds-averaged Navier-Stokes–LES. The weak recycling method, rooted in scaling arguments on the canonical incompressible boundary layer, has been applied to supersonic boundary layer, rough surface boundary layer, and microscale urban canopy LES coupled with mesoscale numerical weather forecasting. Synthetic methods, originating from analytical approximation to homogeneous isotropic turbulence, have branched out into several robust methods, including the synthetic random Fourier method, synthetic digital filtering method, synthetic coherent eddy method, and synthetic volume forcing method. This article reviews major progress in inflow turbulence generation methods with an emphasis on fundamental ideas, key milestones, representative applications, and critical issues. Directions for future research in the field are also highlighted.

  9. Containerless Ripple Turbulence

    NASA Astrophysics Data System (ADS)

    Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles

    2002-11-01

    One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear

  10. Strained spiral vortex model for turbulent fine structure

    NASA Technical Reports Server (NTRS)

    Lundgren, T. S.

    1982-01-01

    A model for the intermittent fine structure of high Reynolds number turbulence is proposed. The model consists of slender axially strained spiral vortex solutions of the Navier-Stokes equation. The tightening of the spiral turns by the differential rotation of the induced swirling velocity produces a cascade of velocity fluctuations to smaller scale. The Kolmogorov energy spectrum is a result of this model.

  11. Anisotropy in MHD turbulence due to a mean magnetic field

    NASA Technical Reports Server (NTRS)

    Shebalin, J. V.; Matthaeus, W. H.; Montgomery, D.

    1982-01-01

    The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.

  12. Flavor evolution of supernova neutrinos in turbulent matter

    SciTech Connect

    Lund, Tina; Kneller, James P.

    2014-01-01

    The neutrino signal from the next galactic supernova carries with it an enormous amount of information on the explosion mechanism of a core-collapse supernova, as well as on the stellar progenitor and on the neutrinos themselves. In order to extract this information we need to know how the neutrino flavor evolves over time due to the interplay of neutrino self-interactions and matter effects. Additional turbulence in the supernova matter may impart its own signatures on the neutrino spectrum, and could partly obscure the imprints of collective and matter effects. We investigate the neutrino flavor evolution due to neutrino self-interactions, matter effects due to the shock wave propagation, and turbulence in three progenitors with masses of 8.8 M⊙, 10.8 M⊙ and 18.0 M⊙. In the lightest progenitor we find that the impact of moderate turbulence of the order 10% is limited and occurs only briefly early on. This makes the signatures of collective and matter interactions relatively straightforward to interpret. Similarly, with moderate turbulence the two heavier progenitors exhibit only minor changes in the neutrino spectrum, and collective and matter signatures persists. However, when the turbulence is increased to 30% and 50% the high density matter resonance features in the neutrino spectrum get obscured, while new features arise in the low density resonance channel and in the non-resonant channels. We conclude that with moderate amounts of turbulence spectral features of collective and matter interactions survive in all three progenitors. For the larger amounts of turbulence in the 10.8 M⊙ and 18.0 M⊙ progenitor new features arise, as others disappear.

  13. Mimicking Natural Laminar to Turbulent Flow Transition: A Systematic CFD Study Using PAB3D

    NASA Technical Reports Server (NTRS)

    Pao, S. Paul; Abdol-Hamid, Khaled S.

    2005-01-01

    For applied aerodynamic computations using a general purpose Navier-Stokes code, the common practice of treating laminar to turbulent flow transition over a non-slip surface is somewhat arbitrary by either treating the entire flow as turbulent or forcing the flow to undergo transition at given trip locations in the computational domain. In this study, the possibility of using the PAB3D code, standard k-epsilon turbulence model, and the Girimaji explicit algebraic stresses model to mimic natural laminar to turbulent flow transition was explored. The sensitivity of flow transition with respect to two limiters in the standard k-epsilon turbulence model was examined using a flat plate and a 6:1 aspect ratio prolate spheroid for our computations. For the flat plate, a systematic dependence of transition Reynolds number on background turbulence intensity was found. For the prolate spheroid, the transition patterns in the three-dimensional boundary layer at different flow conditions were sensitive to the free stream turbulence viscosity limit, the reference Reynolds number and the angle of attack, but not to background turbulence intensity below a certain threshold value. The computed results showed encouraging agreements with the experimental measurements at the corresponding geometry and flow conditions.

  14. Statistical Study of Turbulence: Spectral Functions and Correlation Coefficients

    NASA Technical Reports Server (NTRS)

    Frenkiel, Francois N.

    1958-01-01

    In reading the publications on turbulence of different authors, one often runs the risk of confusing the various correlation coefficients and turbulence spectra. We have made a point of defining, by appropriate concepts, the differences which exist between these functions. Besides, we introduce in the symbols a few new characteristics of turbulence. In the first chapter, we study some relations between the correlation coefficients and the different turbulence spectra. Certain relations are given by means of demonstrations which could be called intuitive rather than mathematical. In this way we demonstrate that the correlation coefficients between the simultaneous turbulent velocities at two points are identical, whether studied in Lagrange's or in Euler's systems. We then consider new spectra of turbulence, obtained by study of the simultaneous velocities along a straight line of given direction. We determine some relations between these spectra and the correlation coefficients. Examining the relation between the spectrum of the turbulence measured at a fixed point and the longitudinal-correlation curve given by G. I. Taylor, we find that this equation is exact only when the coefficient is very small.

  15. Nonlinear Flow Generation By Electrostatic Turbulence In Tokamaks

    SciTech Connect

    Wang, W. X.; Diamond, P. H.; Hahm, T. S.; Ethier, S.; Rewoldt, G.; Tang, W. M.

    2010-07-07

    Global gyrokinetic simulations have revealed an important nonlinear flow generation process due to the residual stress produced by electrostatic turbulence of ion temperature gradient (ITG) modes and trapped electron modes (TEM). In collisionless TEM (CTEM) turbulence, nonlinear residual stress generation by both the fluctuation intensity and the intensity gradient in the presence of broken symmetry in the parallel wave number spectrum is identified for the first time. Concerning the origin of the symmetry breaking, turbulence self-generated low frequency zonal flow shear has been identified to be a key, universal mechanism in various turbulence regimes. Simulations reported here also indicate the existence of other mechanisms beyond E × B shear. The ITG turbulence driven “intrinsic” torque associated with residual stress is shown to increase close to linearly with the ion temperature gradient, in qualitative agreement with experimental observations in various devices. In CTEM dominated regimes, a net toroidal rotation is driven in the cocurrent direction by “intrinsic” torque, consistent with the experimental trend of observed intrinsic rotation. The finding of a “flow pinch” in CTEM turbulence may offer an interesting new insight into the underlying dynamics governing the radial penetration of modulated flows in perturbation experiments. Finally, simulations also reveal highly distinct phase space structures between CTEM and ITG turbulence driven momentum, energy and particle fluxes, elucidating the roles of resonant and non-resonant particles.

  16. Charge pariticle transport in the non-isotropic turbulences

    NASA Astrophysics Data System (ADS)

    Sun, P.; Jokipii, J. R.

    2015-12-01

    The scattering and diffusion of energetic charged particles is not only important for understanding phenomena such as diffusive shock acceleration but it also is a natural probe of the statistical characteristics of magnetohydrodynamic (MHD) turbulence. Although Parker's transport equation (Parker 1965) allows us to describe the propagation of charged particles, the transport coefficients needed in the equation must be determined. Using Quasi-Linear Theory (QLT, e.g. Jokipii (1966)), one finds that coefficients can be related to the correlation function or power spectrum of homogeneous magnetic turbulence. However, different turbulence models will generally have a different influence on particle's scattering and diffusion. Among those models developed in MHD Turbulence, such as isotropic, Slab plus 2D (Tu & Marsch 1993; Gray et al 1996; Bieber et al 1996), etc. Here, using test-particle orbit simulations to calculate the transport coefficients, we study particle transport in synthesized asymmetric turbulence using the form first proposed by Goldreich & Sridhar (1995). We developed and introduce a systematic method to synthesize scale-dependent non-isotropic magnetic turbulences. We also developed and introduce a method to synthesize the 3d turbulent magnetic field from the observed solar wind time series dataset. We present the comparison of their effects on charge particle transport with previous theories and models.

  17. The decay of isotropic turbulence in a rapidly rotating frame

    NASA Technical Reports Server (NTRS)

    Speziale, C. G.; Mansour, N. N.; Rogallo, R. S.

    1987-01-01

    A direct numerical simulation of the decay of initially isotropic turbulence in a rapidly rotating frame was conducted. This 128 x 128 x 128 simulation was completed for a Reynolds number Re sub lambda = 15.3 and a Rossby number Ro sub lambda = 0.07 based on the initial turbulent kinetic energy and Taylor microscale. The numerical results indicate that the turbulence remains essentially isotropic during the major part of the decay (i.e., beyond the point where the turbulent kinetic energy has decayed to less than 10 percent of its initial value). The rapid rotation has the primary effect of shutting off the energy transfer so that the turbulence dissipation (and hence the rate of decay of the turbulent kinetic energy) is substantially reduced. Consequently, the anisotropy tensor remains essentially unchanged while the energy spectrum undergoes a nearly linear viscous decay (the same results that are predicted by Rapid Distortion Theory which is only formally valid for much shorter elapsed times. Surprisingly, no Taylor-Proudman reorganization of the flow to a two-dimensional state is observed. The implications that these results have on turbulence modeling are discussed briefly along with prospective future research.

  18. Spectrum of the Open Asymmetric Simple Exclusion Process with Arbitrary Boundary Parameters

    NASA Astrophysics Data System (ADS)

    Wen, Fa-Kai; Yang, Zhan-Ying; Cui, Shuai; Cao, Jun-Peng; Yang, Wen-Li

    2015-05-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11375141, 11475135, 11434013 and 11425522, the Ministry of Education Doctoral Program Fund under Grant No 20126101110004, and the Northwest University Graduate Student Innovation Fund under Grant No YZZ14104.

  19. General scale-dependent anisotropic turbulence and its impact on free space optical communication system performance.

    PubMed

    Toselli, Italo; Korotkova, Olga

    2015-06-01

    We generalize a recently introduced model for nonclassic turbulent spatial power spectrum involving anisotropy along two mutually orthogonal axes transverse to the direction of beam propagation by including two scale-dependent weighting factors for these directions. Such a turbulent model may be pertinent to atmospheric fluctuations in the refractive index in stratified regions well above the boundary layer and employed for air-air communication channels. When restricting ourselves to an unpolarized, coherent Gaussian beam and a weak turbulence regime, we examine the effects of such a turbulence type on the OOK FSO link performance by including the results on scintillation flux, probability of fade, SNR, and BERs.

  20. Bidirectional Energy Cascades and the Origin of Kinetic Alfvenic and Whistler Turbulence in the Solar Wind

    NASA Technical Reports Server (NTRS)

    Che, H.; Goldstein, M. L.; Vinas, A. F.

    2014-01-01

    The observed steep kinetic scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quiet time suggest them as a possible source of free energy to drive kinetic turbulence. Using particle-in-cell simulations, we explore how the free energy released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler turbulence are excited that evolve through inverse and forward magnetic energy cascades.

  1. A small-scale turbulence model

    NASA Technical Reports Server (NTRS)

    Lundgren, T. S.

    1993-01-01

    A previously derived analytical model for the small-scale structure of turbulence is reformulated in such a way that the energy spectrum may be computed. The model is an ensemble of two-dimensional (2D) vortices with internal spiral structure, each stretched by an axially symmetric strain flow. Stretching and differential rotation produce an energy cascade to smaller scales in which the stretching represents the effect of instabilities and the spiral structure is the source of dissipation at the end of the cascade. The energy spectrum of the resulting flow may be expressed as a time integration involving only the enstrophy spectrum of the time evolving 2D cross section flow, which may be obtained numerically. Examples are given in which a k exp -5/3 spectrum is obtained by this method. The k exp -5/3 inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the 2D enstrophy spectrum. The results are found to be insensitive to time dependence of the strain rate, including even intermittent on-or-off strains.

  2. The dynamics of interacting nonlinearities governing long wavelength driftwave turbulence

    SciTech Connect

    Newman, David E.

    1993-09-01

    Because of the ubiquitous nature of turbulence and the vast array of different systems which have turbulent solutions, the study of turbulence is an area of active research. Much present day understanding of turbulence is rooted in the well established properties of homogeneous Navier-Stokes turbulence, which, due to its relative simplicity, allows for approximate analytic solutions. This work examines a group of turbulent systems with marked differences from Navier-Stokes turbulence, and attempts to quantify some of their properties. This group of systems represents a variety of drift wave fluctuations believed to be of fundamental importance in laboratory fusion devices. From extensive simulation of simple local fluid models of long wavelength drift wave turbulence in tokamaks, a reasonably complete picture of the basic properties of spectral transfer and saturation has emerged. These studies indicate that many conventional notions concerning directions of cascades, locality and isotropy of transfer, frequencies of fluctuations, and stationarity of saturation are not valid for moderate to long wavelengths. In particular, spectral energy transfer at long wavelengths is dominated by the E x B nonlinearity, which carries energy to short scale in a manner that is highly nonlocal and anisotropic. In marked contrast to the canonical self-similar cascade dynamics of Kolmogorov, energy is efficiently passed between modes separated by the entire spectrum range in a correlation time. At short wavelengths, transfer is dominated by the polarization drift nonlinearity. While the standard dual cascade applies in this subrange, it is found that finite spectrum size can produce cascades that are reverse directed and are nonconservative in enstrophy and energy similarity ranges. In regions where both nonlinearities are important, cross-coupling between the nolinearities gives rise to large no frequency shifts as well as changes in the spectral dynamics.

  3. Perturbing turbulence beyond collapse

    NASA Astrophysics Data System (ADS)

    Kühnen, Jakob; Scarselli, Davide; Hof, Björn; Nonlinear Dynamics; Turbulence Group Team

    2016-11-01

    Wall-bounded turbulent flows are considered to be in principle stable against perturbations and persist as long as the Reynolds number is sufficiently high. We show for the example of pipe flow that a specific perturbation of the turbulent flow field disrupts the genesis of new turbulence at the wall. This leads to an immediate collapse of the turbulent flow and causes complete relaminarisation further downstream. The annihilation of turbulence is effected by a steady manipulation of the streamwise velocity component only, greatly simplifying control efforts which usually require knowledge of the highly complex three dimensional and time dependent velocity fields. We present several different control schemes from laboratory experiments which achieve the required perturbation of the flow for total relaminarisation. Transient growth, a linear amplification mechanism measuring the efficiency of eddies in redistributing shear that quantifies the maximum perturbation energy amplification achievable over a finite time in a linearized framework, is shown to set a clear-cut threshold below which turbulence is impeded in its formation and thus permanently annihilated.

  4. Anisotropic Particles in Turbulence

    NASA Astrophysics Data System (ADS)

    Voth, Greg A.; Soldati, Alfredo

    2017-01-01

    Anisotropic particles are common in many industrial and natural turbulent flows. When these particles are small and neutrally buoyant, they follow Lagrangian trajectories while exhibiting rich orientational dynamics from the coupling of their rotation to the velocity gradients of the turbulence field. This system has proven to be a fascinating application of the fundamental properties of velocity gradients in turbulence. When particles are not neutrally buoyant, they experience preferential concentration and very different preferential alignment than neutrally buoyant tracer particles. A vast proportion of the parameter range of anisotropic particles in turbulence is still unexplored, with most existing research focusing on the simple foundational cases of axisymmetric ellipsoids at low concentrations in homogeneous isotropic turbulence and in turbulent channel flow. Numerical simulations and experiments have recently developed a fairly comprehensive picture of alignment and rotation in these cases, and they provide an essential foundation for addressing more complex problems of practical importance. Macroscopic effects of nonspherical particle dynamics include preferential concentration in coherent structures and drag reduction by fiber suspensions. We review the models used to describe nonspherical particle motion, along with numerical and experimental methods for measuring particle dynamics.

  5. Characterizing glottal jet turbulence.

    PubMed

    Alipour, Fariborz; Scherer, Ronald C

    2006-02-01

    Air pressure associated with airflow from the lungs drives the vocal folds into oscillation and allows the air to exit the glottis as a turbulent jet, even though laminar flow may enter the glottis from the trachea. The separation of the turbulence from the deterministic portion of the glottal jet was investigated in the excised canine larynx model. The present study is methodological in that the main goal was to examine three methods of obtaining reasonable representations of both the deterministic signal and the residual turbulence portion: (a) smoothing, (b) wavelet denoising, and (c) ensemble averaging. Ensemble averaging resulted in a deterministic signal that disregarded gross cyclic alterations while exaggerating the turbulence intensity. Wavelet denoising can perform an excellent analysis and synthesis of the glottal velocity, but was problematic in determining which levels of analysis to choose to represent both the deterministic and turbulence appropriately. Smoothing appeared to be the most appropriate for phonation velocities because it preserved gross cyclic variations important to perturbations and modulations, while extracting turbulence at what appears to be reasonable levels.

  6. Multifractal energy exchange between gravity waves and turbulence in an upper tropospheric front

    NASA Astrophysics Data System (ADS)

    Koch, Steven

    2014-05-01

    Intermittent generation of strong turbulence measured by reconnaissance aircraft occurred in association with a wide spectrum of upward propagating gravity waves above the core of an upper level jet stream. The turbulence generation process could be described as an energy cascade process, initiated as gravity-inertia waves were produced in a region of diagnosed unbalanced upper-level frontogenesis near a tropopause fold. High resolution numerical weather prediction model forecasts produced bimodal waves with dominant wavelengths of 120-216 km and 1-20 km, the latter of which perturbed the atmosphere to create conditions conducive to turbulence generation. Cross spectral, wavelet transformation, and polarization analysis of the in situ aircraft data allowed unambiguous determination of the presence of the spectrum of gravity waves, reconstruction of the waves' evolving character, and identification of intermittent wave packets. Introduction of wavelet cross spectrum into the Stokes parameter theory shed light on how turbulence production was intimately related to increasing levels of polarization, only to be followed by sudden reduction of polarization as turbulence arose. Wavelet and structure function analysis indicated that episodes of high turbulent kinetic energy were the result of upscale feedback effects ("inverse energy cascade" processes linked to wave breaking). The bi-fractal nature of the gravity waves and turbulence suggest new approaches for parameterizing sub grid-scale effects caused by the interaction of waves and turbulence in numerical models.

  7. Turbulent Flow Past Projectiles: A Computational Investigation

    NASA Astrophysics Data System (ADS)

    Mehmedagic, Igbal; Carlucci, Donald; Buckley, Liam; Carlucci, Pasquale; Thangam, Siva

    2010-11-01

    Projectiles with free spinning bases are often used for smart munitions to provide effective control, stability and terminal guidance. Computational investigations are performed for flow past cylinders aligned along their axis where a base freely spins while attached to and separated at various distances from a non-spinning fore-body. The energy spectrum is modified to incorporate the effects of swirl and rotation using a parametric characterization of the model coefficients. An efficient finite-volume algorithm is used to solve the time-averaged equations of motion and energy along with the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation. Computations are performed for both rigid cylinders as well as cylinders with free-spinning bases. Experimental data for a range of spin rates and free stream flow conditions obtained from subsonic wind tunnel with sting-mounted spinning cylinders is used for validating the computational findings.

  8. Imbalanced magnetohydrodynamic turbulence modified by velocity shear in the solar wind

    NASA Astrophysics Data System (ADS)

    Gogoberidze, G.; Voitenko, Y. M.

    2016-11-01

    We study incompressible imbalanced magnetohydrodynamic turbulence in the presence of background velocity shears. Using scaling arguments, we show that the turbulent cascade is significantly accelerated when the background velocity shear is stronger than the velocity shears in the subdominant Alfvén waves at the injection scale. The spectral transport is then controlled by the background shear rather than the turbulent shears and the Tchen spectrum with spectral index -1 is formed. This spectrum extends from the injection scale to the scale of the spectral break where the subdominant wave shear becomes equal to the background shear. The estimated spectral breaks and power spectra are in good agreement with those observed in the fast solar wind. The proposed mechanism can contribute to enhanced turbulent cascades and modified -1 spectra observed in the fast solar wind with strong velocity shears. This mechanism can also operate in many other astrophysical environments where turbulence develops on top of non-uniform plasma flows.

  9. Universal equations and constants of turbulent motion

    NASA Astrophysics Data System (ADS)

    Baumert, H. Z.

    2013-07-01

    This paper presents a parameter-free theory of shear-generated turbulence at asymptotically high Reynolds numbers in incompressible fluids. It is based on a two-fluids concept. Both components are materially identical and inviscid. The first component is an ensemble of quasi-rigid dipole-vortex tubes (vortex filaments, excitations) as quasi-particles in chaotic motion. The second is a superfluid performing evasive motions between the tubes. The local dipole motions follow Helmholtz' law. The vortex radii scale with the energy-containing length scale. Collisions between quasi-particles lead either to annihilation (likewise rotation, turbulent dissipation) or to scattering (counterrotation, turbulent diffusion). There are analogies with birth and death processes of population dynamics and their master equations and with Landau's two-fluid theory of liquid helium. For free homogeneous decay the theory predicts the turbulent kinetic energy to follow t-1. With an adiabatic wall condition it predicts the logarithmic law with von Kármán's constant as 1/\\sqrt {2\\,\\pi }= 0.399 . Likewise rotating couples form localized dissipative patches almost at rest (→ intermittency) wherein under local quasi-steady conditions the spectrum evolves into an ‘Apollonian gear’ as discussed first by Herrmann (1990 Correlation and Connectivity (Dordrecht: Kluwer) pp 108-20). Dissipation happens exclusively at scale zero and at finite scales this system is frictionless and reminds of Prigogine's (1947 Etude Thermodynamique des Phenomenes Irreversibles (Liege: Desoer) p 143) law of minimum (here: zero) entropy production. The theory predicts further the prefactor of the 3D-wavenumber spectrum (a Kolmogorov constant) as \\frac {1}{3}(4\\,\\pi )^{2/3}=1.802 , well within the scatter range of observational, experimental and direct numerical simulation results.

  10. Wave turbulence in shallow water models

    NASA Astrophysics Data System (ADS)

    Clark di Leoni, P.; Cobelli, P. J.; Mininni, P. D.

    2014-06-01

    We study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids with up to 20482 points. In all simulations, the Froude number varies between 0.015 and 0.05, while the Reynolds number and level of dispersion are varied in a broader range to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, nonlinear waves are nondispersive and the spectrum of potential energy is compatible with ˜k-2 scaling. For deeper (Boussinesq) flows, the nonlinear dispersion relation as directly measured from the wave and frequency spectrum (calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, ˜k-4/3. In this latter case, the nonlinear dispersion relation differs from the linear one and has two branches, which we explain with a simple qualitative argument. Finally, we study probability density functions of the surface height and find that in all cases the distributions are asymmetric. The probability density function can be approximated by a skewed normal distribution as well as by a Tayfun distribution.

  11. Inverse Energy Cascades in Rotating Turbulence

    NASA Astrophysics Data System (ADS)

    Rosenberg, D. L.; Marino, R.; Mininni, P.; Pouquet, A.

    2013-12-01

    We present the results of direct numerical simulations (DNS) of rapidly rotating turbulent flows on grids of 20483 grid points that are forced at intermediate scales. Injection of energy at such scales at small Rossby numbers (~0.04) leads to a direct cascade toward small scales and an inverse cascade toward large scales. These results essentially validate those obtained using large eddy simulation (LES) (Sen et al., PRE 86:036319 (2012)): for a (helical) forcing that injects energy largely in 2D modes, the large scale energy spectrum scales as kperp-5/3, consistent with Kolmogorov-Kraichnan-Batchelor-Leith phenomenology; for a nonhelical isotropic forcing, the large scale energy spectrum scales as kperp-3. The (helical) anisotropic forcing DNS solution, like that of the LES models, shows a k-1 isotropic energy spectrum, which Sen et al. attribute to a large scale shear. The higher resolution of the DNS runs allows us to carry out probability distribution and conditional analyses that show that this interpretation may, in fact, be consistent with wall-bounded turbulent shear flow.

  12. Transport Bifurcation in Plasma Interchange Turbulence

    NASA Astrophysics Data System (ADS)

    Li, Bo

    2016-10-01

    Transport bifurcation and mean shear flow generation in plasma interchange turbulence are explored with self-consistent two-fluid simulations in a flux-driven system with both closed and open field line regions. The nonlinear evolution of interchange modes shows the presence of two confinement regimes characterized by the low and high mean flow shear. By increasing the input heat flux above a certain threshold, large-amplitude oscillations in the turbulent and mean flow energy are induced. Both clockwise and counter-clockwise types of oscillations are found before the transition to the second regime. The fluctuation energy is decisively transferred to the mean flows by large-amplitude Reynolds power as turbulent intensity increases. Consequently, a transition to the second regime occurs, in which strong mean shear flows are generated in the plasma edge. The peak of the spectrum shifts to higher wavenumbers as the large-scale turbulent eddies are suppressed by the mean shear flow. The transition back to the first regime is then triggered by decreasing the input heat flux to a level much lower than the threshold for the forward transition, showing strong hysteresis. During the back transition, the mean flow decreases as the energy transfer process is reversed. This transport bifurcation, based on a field-line-averaged 2D model, has also been reproduced in our recent 3D simulations of resistive interchange turbulence, in which the ion and electron temperatures are separated and the parallel current is involved. Supported by the MOST of China Grant No. 2013GB112006, US DOE Contract No. DE-FC02-08ER54966, US DOE by LLNL under Contract DE-AC52-07NA2734.

  13. Plasma shaping effects on tokamak scrape-off layer turbulence

    NASA Astrophysics Data System (ADS)

    Riva, Fabio; Lanti, Emmanuel; Jolliet, Sébastien; Ricci, Paolo

    2017-03-01

    The impact of plasma shaping on tokamak scrape-off layer (SOL) turbulence is investigated. The drift-reduced Braginskii equations are written for arbitrary magnetic geometries, and an analytical equilibrium model is used to introduce the dependence of turbulence equations on tokamak inverse aspect ratio (ε ), Shafranov’s shift (Δ), elongation (κ), and triangularity (δ). A linear study of plasma shaping effects on the growth rate of resistive ballooning modes (RBMs) and resistive drift waves (RDWs) reveals that RBMs are strongly stabilized by elongation and negative triangularity, while RDWs are only slightly stabilized in non-circular magnetic geometries. Assuming that the linear instabilities saturate due to nonlinear local flattening of the plasma gradient, the equilibrium gradient pressure length {L}p=-{p}e/{{\

  14. Response of a rigid aircraft to nonstationary atmospheric turbulence.

    NASA Technical Reports Server (NTRS)

    Verdon, J. M.; Steiner, R.

    1973-01-01

    The plunging response of an aircraft to a type of nonstationary turbulent excitation is considered. The latter consists of stationary Gaussian noise modulated by a well-defined envelope function. The intent of the investigation is to model the excitation experienced by an airplane flying through turbulence of varying intensity and to examine the influence of intensity variations on exceedance frequencies of the gust velocity and the airplane's plunging velocity and acceleration. One analytical advantage of the proposed model is that the Gaussian assumption for the gust excitation is retained. The analysis described herein is developed in terms of an envelope function of arbitrary form; however, numerical calculations are limited to the case of harmonic modulation.

  15. Equilibrium energy spectrum of point vortex motion with remarks on ensemble choice and ergodicity

    NASA Astrophysics Data System (ADS)

    Esler, J. G.

    2017-01-01

    The dynamics and statistical mechanics of N chaotically evolving point vortices in the doubly periodic domain are revisited. The selection of the correct microcanonical ensemble for the system is first investigated. The numerical results of Weiss and McWilliams [Phys. Fluids A 3, 835 (1991), 10.1063/1.858014], who argued that the point vortex system with N =6 is nonergodic because of an apparent discrepancy between ensemble averages and dynamical time averages, are shown to be due to an incorrect ensemble definition. When the correct microcanonical ensemble is sampled, accounting for the vortex momentum constraint, time averages obtained from direct numerical simulation agree with ensemble averages within the sampling error of each calculation, i.e., there is no numerical evidence for nonergodicity. Further, in the N →∞ limit it is shown that the vortex momentum no longer constrains the long-time dynamics and therefore that the correct microcanonical ensemble for statistical mechanics is that associated with the entire constant energy hypersurface in phase space. Next, a recently developed technique is used to generate an explicit formula for the density of states function for the system, including for arbitrary distributions of vortex circulations. Exact formulas for the equilibrium energy spectrum, and for the probability density function of the energy in each Fourier mode, are then obtained. Results are compared with a series of direct numerical simulations with N =50 and excellent agreement is found, confirming the relevance of the results for interpretation of quantum and classical two-dimensional turbulence.

  16. Computer program for solving compressible nonsimilar-boundary-layer equations for laminar, transitional, or turbulent flows of a perfect gas

    NASA Technical Reports Server (NTRS)

    Price, J. M.; Harris, J. F.

    1972-01-01

    A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity.

  17. Turbulent transport measurements with a laser Doppler velocimeter

    NASA Technical Reports Server (NTRS)

    Edwards, R. V.; Angus, J. C.; Dunning, J. W., Jr.

    1972-01-01

    The power spectrum of phototube current from a laser Doppler velocimeter operating in the heterodyne mode has been computed. The spectrum is obtained in terms of the space time correlation function of the fluid. The spectral width and shape predicted by the theory are in agreement with experiment. For normal operating parameters the time average spectrum contains information only for times shorter than the Lagrangian integral time scale of the turbulence. To examine the long time behavior, one must use either extremely small scattering angles, much longer wavelength radiation or a different mode of signal analysis, e.g., FM detection.

  18. Numerical Simulation of the turbulent flow around a wing

    NASA Astrophysics Data System (ADS)

    Auerswald, Torsten; Bange, Jens

    2014-05-01

    In this talk the simulation of turbulent flow around a 3D-wing will be presented. For the simulations the compressible flow model TAU is used which is developed by the German Aerospace Center DLR. The model domain consists of two grids which are communicating with each other by using the chimera technique. The primary grid is the unstructured body-fitted grid that contains the wing and the secondary grid is a cartesian grid upstream of the wing on which the turbulent flow is simulated. During the simulation the cartesian grid is moved towards the wing and in a short distance in front of the wing the grid is stopped and the turbulent flow is passed to the primary grid where it can interact with the wing. Since, the earth surface is not simulated there is no source for atmospheric turbulence in the model. That means that the simulation has to be initialised with an already turbulent wind field. For this purpose a synthetic turbulence generator is used that takes the statistics of measurement data from the atmospheric boundary layer and generates a three-dimensional wind field with the same statistics. The statistics used as input comprise the energy spectrum, the correlation matrix and the variances. In the future it is planned to improve the turbulence generator to also consider coherent structures of the turbulent flow. With this simulation strategy it is possible to simulate the flight of a wing through realistic atmospheric boundary layer turbulence in different weather situations and investigate the effects of the turbulence on the wing. Especially during flights with high angle of attack and at low altitudes it is of interest to investigate how the angle of stall is influenced by the turbulent flow and which scales of the turbulence have an significant effect on the lift and drag produced by the wing. The talk will cover the simulation strategy with TAU and the generation of the synthetic turbulent wind fields based on measurements. Furthermore, results from

  19. Photonic arbitrary waveform generator based on Taylor synthesis method.

    PubMed

    Liao, Shasha; Ding, Yunhong; Dong, Jianji; Yan, Siqi; Wang, Xu; Zhang, Xinliang

    2016-10-17

    Arbitrary waveform generation has been widely used in optical communication, radar system and many other applications. We propose and experimentally demonstrate a silicon-on-insulator (SOI) on chip optical arbitrary waveform generator, which is based on Taylor synthesis method. In our scheme, a Gaussian pulse is launched to some cascaded microrings to obtain first-, second- and third-order differentiations. By controlling amplitude and phase of the initial pulse and successive differentiations, we can realize an arbitrary waveform generator according to Taylor expansion. We obtain several typical waveforms such as square waveform, triangular waveform, flat-top waveform, sawtooth waveform, Gaussian waveform and so on. Unlike other schemes based on Fourier synthesis or frequency-to-time mapping, our scheme is based on Taylor synthesis method. Our scheme does not require any spectral disperser or large dispersion, which are difficult to fabricate on chip. Our scheme is compact and capable for integration with electronics.

  20. Multiple-scale turbulence modeling of boundary layer flows for scramjet applications

    NASA Technical Reports Server (NTRS)

    Fabris, G.; Harsha, P. T.; Edelman, R. B.

    1981-01-01

    As part of an investigation into the application of turbulence models to the computation of flows in advanced scramjet combustors, the multiple-scale turbulence model was applied to a variety of flowfield predictions. The model appears to have a potential for improved predictions in a variety of areas relevant to combustor problems. This potential exists because of the partition of the turbulence energy spectrum that is the major feature of the model and which allows the turbulence energy dissipation rate to be out of phase with turbulent energy production. The computations were made using a consistent method of generating experimentally unavailable initial conditions. An appreciable overall improvement in the generality of the predictions is observed, as compared to those of the basic two-equation turbulence model. A Mach number-related correction is found to be necessary to satisfactorily predict the spreading rate of the supersonic jet and mixing layer.

  1. Wind speed power spectrum analysis for Bushland, Texas

    SciTech Connect

    Eggleston, E.D.

    1996-12-31

    Numerous papers and publications on wind turbulence have referenced the wind speed spectrum presented by Isaac Van der Hoven in his article entitled Power Spectrum of Horizontal Wind Speed Spectrum in the Frequency Range from 0.0007 to 900 Cycles per Hour. Van der Hoven used data measured at different heights between 91 and 125 meters above the ground, and represented the high frequency end of the spectrum with data from the peak hour of hurricane Connie. These facts suggest we should question the use of his power spectrum in the wind industry. During the USDA - Agricultural Research Service`s investigation of wind/diesel system power storage, using the appropriate wind speed power spectrum became a significant issue. We developed a power spectrum from 13 years of hourly average data, 1 year of 5 minute average data, and 2 particularly gusty day`s 1 second average data all collected at a height of 10 meters. While the general shape is similar to the Van der Hoven spectrum, few of his peaks were found in the Bushland spectrum. While higher average wind speeds tend to suggest higher amplitudes in the high frequency end of the spectrum, this is not always true. Also, the high frequency end of the spectrum is not accurately described by simple wind statistics such as standard deviation and turbulence intensity. 2 refs., 5 figs., 1 tab.

  2. Turbulence in Natural Environments

    NASA Astrophysics Data System (ADS)

    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

  3. Linearly Forced Isotropic Turbulence

    NASA Technical Reports Server (NTRS)

    Lundgren, T. S.

    2003-01-01

    Stationary isotropic turbulence is often studied numerically by adding a forcing term to the Navier-Stokes equation. This is usually done for the purpose of achieving higher Reynolds number and longer statistics than is possible for isotropic decaying turbulence. It is generally accepted that forcing the Navier-Stokes equation at low wave number does not influence the small scale statistics of the flow provided that there is wide separation between the largest and smallest scales. It will be shown, however, that the spectral width of the forcing has a noticeable effect on inertial range statistics. A case will be made here for using a broader form of forcing in order to compare computed isotropic stationary turbulence with (decaying) grid turbulence. It is shown that using a forcing function which is directly proportional to the velocity has physical meaning and gives results which are closer to both homogeneous and non-homogeneous turbulence. Section 1 presents a four part series of motivations for linear forcing. Section 2 puts linear forcing to a numerical test with a pseudospectral computation.

  4. Gyrokinetic turbulent heating

    SciTech Connect

    Hinton, F. L.; Waltz, R. E.

    2006-10-15

    Expressions for particle and energy fluxes and heating rates due to turbulence are derived. These fluxes and heating rates are identified from moments of an extended drift-kinetic equation for the equilibrium distribution function. These include neoclassical as well as turbulent diffusion and heating. Phase-space conservation is demonstrated, allowing the drift-kinetic equation to be expressed in conservative form. This facilitates taking moments with few approximations, mainly those consistent with drift kinetics for the equilibrium distribution function and the relative smallness of the fluctuations. The turbulent heating is uniquely defined by choosing the standard gyrokinetic definition for the energy flux. With this definition, most of the heating can be expressed in the form of ohmic heating from turbulent parallel and perpendicular current density perturbations. The latter current is identified with grad-B and curvature drifts, plus terms involving magnetic perturbations (which are smaller for low beta). A small contribution to the heating comes from the divergence of an energy flux that is dependent on the finite gyroradius of the ions. The fluxes and heating rates are expressed in a form that can be easily evaluated from gyrokinetic turbulence simulations.

  5. Turbulence and fossil turbulence in oceans and lakes

    NASA Astrophysics Data System (ADS)

    Leung, Pak Tao; Gibson, Carl H.

    2013-01-01

    Turbulence is defined as an eddy-like state of fluid motion where the intertial-vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Energy cascades of irrotational flows from large scales to small are non-turbulent, even if they supply energy to turbulence. Turbulent flows are rotational and cascade from small scales to large, with feedback. Viscous forces limit the smallest turbulent eddy size to the Kolmogorov scale. In stratified fluids, buoyancy forces limit large vertical overturns to the Ozmidov scale and convert the largest turbulent eddies into a unique class of saturated, non-propagating, internal waves, termed fossil-vorticity-turbulence. These waves have the same energy but different properties and spectral forms than the original turbulence patch. The Gibson (1980, 1986) theory of fossil turbulence applies universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified fluid as its growth is constrained and fossilized by buoyancy forces. Quantitative hydrodynamic-phase-diagrams (HPDs) from the theory are used to classify microstructure patches according to their hydrodynamic states. When analyzed in HPD space, previously published oceanic datasets showed their dominant microstructure patches are fossilized at large scales in all layers. Laboratory and field measurements suggested phytoplankton species with different swimming abilities adjust their growth strategies by pattern recognition of turbulence-fossil-turbulence dissipation and persistence times that predict survival-relevant surface layer sea changes. New data collected near a Honolulu waste-water outfall showed the small-to-large evolution of oceanic turbulence microstructure from active to fossil states, and revealed the ability of fossil-density-tubulence patches to absorb, and vertically radiate, internal wave energy, information, and enhanced turbulent

  6. Volumetric Lattice Boltzmann Simulation for Fluid dynamics and Turbulence in Practical Syringes

    NASA Astrophysics Data System (ADS)

    Lima, Everton; Deep, Debanjan; Yu, Huidan (Whitney)

    2012-11-01

    We conduct numerical experiments to study fluid dynamics and turbulence in syringes using volumetric lattice Boltzmann method (VLBM) that is developed for dealing with arbitrary moving boundaries. Several common used medical syringes are used to predict the efficiency and safety of syringes experiencing low flow infusion rates. It is found that smaller size syringes reach a steady flow rate much sooner than larger ones, which are in quantitative agreement with experimental results. The relation between the syringe size and its steady flow rate is revealed. At low flow rates, corner vortices are observed. We explore conditions that lead to turbulent flow aiming to aid safer syringe application in nursing practices.

  7. The alpha dynamo parameter and measurability of helicities in magnetohydrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Matthaeus, W. H.; Goldstein, M. L.; Lantz, S. R.

    1986-01-01

    Alpha, an important parameter in dynamo theory, is shown to be proportional to either the kinetic, current, magnetic, or velocity helicities of the fluctuating magnetic field and fluctuating velocity field. The particular helicity to which alpha is proportional depends on the assumptions used in deriving the first-order smoothed equations that describe the alpha effect. In two cases, viz., when alpha is proportional to either the magnetic helicity or velocity helicity, alpha can be determined experimentally from two-point measurements of the fluctuating fields in incompressible, homogeneous turbulence with arbitrary rotational symmetry. For the other two possibilities, alpha can be determined if the turbulence is isotropic.

  8. Nonrelativistic equations of motion for particles with arbitrary spin

    SciTech Connect

    Fushchich, V.I.; Nikitin, A.G.

    1981-09-01

    First- and second-order Galileo-invariant systems of differential equations which describe the motion of nonrelativistic particles of arbitrary spin are derived. The equations can be derived from a Lagrangian and describe the dipole, quadrupole, and spin-orbit interaction of the particles with an external field; these interactions have traditionally been regarded as purely relativistic effects. The problem of the motion of a nonrelativistic particle of arbitrary spin in a homogeneous magnetic field is solved exactly on the basis of the obtained equations. The generators of all classes of irreducible representations of the Galileo group are found.

  9. Quark-gluon vertex in arbitrary gauge and dimension

    NASA Astrophysics Data System (ADS)

    Davydychev, A. I.; Osland, P.; Saks, L.

    2001-01-01

    One-loop off-shell contributions to the quark-gluon vertex are calculated, in an arbitrary covariant gauge and in arbitrary space-time dimension, including quark-mass effects. It is shown how one can get results for all on-shell limits of interest directly from the off-shell expressions. In order to demonstrate that the Ward-Slavnov-Taylor identity for the quark-gluon vertex is satisfied, we have also calculated the corresponding one-loop contribution involving the quark-quark-ghost-ghost vertex.

  10. Small scale dynamics of isotropic viscoelastic turbulence

    NASA Astrophysics Data System (ADS)

    Nguyen, M. Quan; Delache, Alexandre; Simoëns, Serge; Bos, Wouter J. T.; El Hajem, Mamoud

    2016-12-01

    The comparison of the results of direct numerical simulations of isotropic turbulence of Newtonian and viscoelastic fluid provides evidence that viscoelasticity modifies qualitatively the behavior of the smallest scales: we observe a power law in the far dissipation range of the fluid kinetic energy spectrum and we show that it is a robust feature, roughly independent of the large scale dynamics. A detailed analysis of the energy transfer shows that at these scales energy is injected into the fluid flow through polymer relaxation. It is further shown that a part of the total energy is transferred among scales through an interaction of the velocity field with the polymer field.

  11. Macroscopic effects of the spectral structure in turbulent flows

    NASA Astrophysics Data System (ADS)

    Tran, T.; Chakraborty, P.; Guttenberg, N.; Prescott, A.; Kellay, H.; Goldburg, W.; Goldenfeld, N.; Gioia, G.

    2010-11-01

    There is a missing link between macroscopic properties of turbulent flows, such as the frictional drag of a wall-bounded flow, and the turbulent spectrum. To seek the missing link we carry out unprecedented experimental measurements of the frictional drag in turbulent soap-film flows over smooth walls. These flows are effectively two-dimensional, and we are able to create soap-film flows with the two types of turbulent spectrum that are theoretically possible in two dimensions: the "enstrophy cascade," for which the spectral exponent α= 3, and the "inverse energy cascade," for which the spectral exponent α= 5/3. We find that the functional relation between the frictional drag f and the Reynolds number Re depends on the spectral exponent: where α= 3, f ˜Re-1/2; where α= 5/3, f ˜Re-1/4. Each of these scalings may be predicted from the attendant value of α by using a recently proposed spectral theory of the frictional drag. In this theory the frictional drag of turbulent flows on smooth walls is predicted to be f ˜Re^(1-α)/(1+α).

  12. Turbulence and Global Properties of the Solar Wind

    NASA Technical Reports Server (NTRS)

    Goldstein, Melvyn L.

    2007-01-01

    The solar wind shows striking characteristics that suggest that it is a turbulent magnetofluid, but the picture is not altogether simple. From the earliest observations, a strong correlation between magnetic fluctuations and plasma velocity fluctuations as noted. The high corrections suggest that the fluctuations are Alven waves. In addition, the power spectrum of the magnetic fluctuation showed evidence of an inertial range that resembled that seen in fully-developed fluid turbulence. Alfven waves, however, are exact solutions of the equations of an incompressible magnetohydrodynamics. Thus, there was a puzzle: how can a magnetofluid consisting of Alfven waves be turbulent? The answer lay in the role of velocity shears in the solar wind that could drive turbulent evolution. Puzzles remain: for example, the power spectrum of the velocity fluctuations is less steep than the slope of the magnetic fluctuations. The plasma in the magnetic tail of Earth's magnetosphere also shows aspects of turbulence, as does the plasma in the dayside magnetosphere near the poles--the so-called dayside cusps.

  13. An experimental investigation of turbulent boundary layers along curved surfaces

    NASA Technical Reports Server (NTRS)

    So, R. M. C.; Mellor, G. L.

    1972-01-01

    A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.

  14. Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating

    SciTech Connect

    Kane, D.J. ); Trebino, R. )

    1993-02-01

    The authors introduce a new technique, which they call frequency-resolved optical gating (FROG), for characterizing and displaying arbitrary femtosecond pulses. The method is simple, general, broad-band, and does not require a reference pulse. Using virtually any instantaneous nonlinear-optical effect, FROG involves measuring the spectrum of the signal pulse as a function of the delay between two input pulses. The resulting trace of intensity versus frequency and delay is related to the pulse's spectrogram, a visually intuitive transform containing both time and frequency information. They prove, using phase retrieval concepts, that the FROG trace yields the full intensity l(t) and phase [var phi](t) of an arbitrary ultrashort pulse with no physically significant ambiguities. They argue, in analogy with acoustics problems, that the FROG trace is in many ways as useful a representation of the pulse as the field itself. FROG appears to have temporal resolution limited only by the response of the nonlinear medium. They demonstrate the method using self-diffraction via the electronic Kerr effect in BK-7 glass and few [mu]J, 620 nm, linearly chirped, [approximately]200 fs pulses.

  15. Evolution of perturbations and cosmological constraints in decaying dark matter models with arbitrary decay mass products

    SciTech Connect

    Aoyama, Shohei; Sekiguchi, Toyokazu; Sugiyama, Naoshi; Ichiki, Kiyotomo E-mail: toyokazu.sekiguchi@nagoya-u.jp E-mail: naoshi@nagoya-u.jp

    2014-07-01

    Decaying dark matter (DDM) is a candidate which can solve the discrepancies between predictions of the concordance ΛCDM model and observations at small scales such as the number counts of companion galaxies of the Milky Way and the density profile at the center of galaxies. Previous studies are limited to the cases where the decay particles are massless and/or have almost degenerate masses with that of mother particles. Here we expand the DDM models so that one can consider the DDM with arbitrary lifetime and the decay products with arbitrary masses. We calculate the time evolutions of perturbed phase-space distribution functions of decay products for the first time and study effects of DDM on the temperature anisotropy in the cosmic microwave background and the matter power spectrum at present. From a recent observational estimate of σ{sub 8}, we derive constraints on the lifetime of DDM and the mass ratio between the decay products and DDM. We also discuss implications of the DDM model for the discrepancy in the measurements of σ{sub 8} recently claimed by the Planck satellite collaboration.

  16. An analysis of the vertical structure equation for arbitrary thermal profiles

    NASA Technical Reports Server (NTRS)

    Cohn, Stephen E.; Dee, Dick P.

    1987-01-01

    The vertical structure equation is a singular Sturm-Liouville problem whose eigenfunctions describe the vertical dependence of the normal modes of the primitive equations linearized about a given thermal profile. The eigenvalues give the equivalent depths of the modes. The spectrum of the vertical structure equation and the appropriateness of various upper boundary conditions, both for arbitrary thermal profiles were studied. The results depend critically upon whether or not the thermal profile is such that the basic state atmosphere is bounded. In the case of a bounded atmosphere it is shown that the spectrum is always totally discrete, regardless of details of the thermal profile. For the barotropic equivalent depth, which corresponds to the lowest eigen value, upper and lower bounds which depend only on the surface temperature and the atmosphere height were obtained. All eigenfunctions are bounded, but always have unbounded first derivatives. It was proved that the commonly invoked upper boundary condition that vertical velocity must vanish as pressure tends to zero, as well as a number of alternative conditions, is well posed. It was concluded that the vertical structure equation always has a totally discrete spectrum under the assumptions implicit in the primitive equations.

  17. REVIEWS OF TOPICAL PROBLEMS: The nature of accretion disks of close binary stars: overreflection instability and developed turbulence

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Bisikalo, D. V.

    2008-06-01

    The current status of the physics of accretion disks in close binary stars is reviewed, with an emphasis on the hydrodynamic overreflection instability, which is a factor leading to the accretion disk turbulence. The estimated turbulent viscosity coefficients are in good agreement with observations and explain the high angular momentum transfer rate and the measured accretion rate. Based on the observations, a power-law spectrum for the developed turbulence is obtained.

  18. Propagation of electromagnetic waves in Kolmogorov and non-Kolmogorov atmospheric turbulence: three-layer altitude model.

    PubMed

    Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S

    2008-12-01

    Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere.

  19. Propagation of electromagnetic waves in Kolmogorov and non-Kolmogorov atmospheric turbulence: three-layer altitude model

    SciTech Connect

    Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S

    2008-12-01

    Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere.

  20. Turbulent black holes.

    PubMed

    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.

  1. Bacterial turbulence in motion

    NASA Astrophysics Data System (ADS)

    Rusconi, Roberto; Smriga, Steven; Stocker, Roman; Secchi, Eleonora; Buzzaccaro, Stefano; Piazza, Roberto

    2014-11-01

    Dense suspensions of motile bacteria exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence, yet this analogy has remained largely qualitative. Here we present experiments in which a dense suspension of Bacillus subtilis bacteria was flown through narrow microchannels and the velocity statistics of the flowing suspension were accurately quantified with a recently developed velocimetry technique. This revealed a robust intermittency phenomenon, whereby the average velocity profile of the flowing suspension oscillated between a plug-like flow and a parabolic flow. This intermittency is a hallmark of classic turbulence and was associated with the presence of collective structures in the suspension. Furthermore, quantification of the Reynolds stress profile revealed a direct link between the turbulent nature of the suspension and its anomalous viscosity.

  2. Turbulence Structure in the Wake Region of a Meteorological Tower

    NASA Astrophysics Data System (ADS)

    Barthlott, Christian; Fiedler, Franz

    A meteorological tower significantly modifies the air flow, the mean windspeed and wind direction as well as the turbulencestructure of the air. Suchchanges can be noticed in particular in the wake region of the tower.Measurementson the 200 m tower ofForschungszentrum Karlsruhewere carried outusing Solent sonic anemometers in the lee of the towerand cup anemometers on both sides.In the wake region, spectral energydensity is increased in the high-frequency range. Superposition of this disturbance spectrum on the undisturbedspectrum yields a `knee' in the resulting spectrum. In the case of low turbulence intensity with stable stratification,a plateau with a constant energy content is observed in front of the knee.This effect is caused by the new production of turbulence energy from the mean flow as well as by an energy transfer fromlarger to smaller vortices. Power spectra in strongly stable conditionsshow a more rapid decrease of intensity in the region where the inertialsubrange is expected.The relevant scales of wake turbulence are derived from the maximum of the disturbance spectrum.Locations of the high-frequency peak do not depend on atmospheric stability,but are controlled mainly by mean wind speed.Apart from the reduction of the mean wind speed, the spectra and cospectra exhibit a strong anisotropy for such cases.The results demonstrate the significant influence of a tower on turbulence spectra in the wake region.

  3. Structure and mechanism of turbulence under dynamical restriction in plane Poiseuille flow

    NASA Astrophysics Data System (ADS)

    Constantinou, Navid; Farrell, Brian; Ioannou, Petros; Jimenez, Javier; Lozano-Duran, Adrian; Nikolaidis, Marios-Andreas

    2016-11-01

    The perspective of Statistical State Dynamics (SSD) is used to investigate plane Poiseuille turbulence at moderately high Reynolds numbers (Reτ 940). Simulations of a quasi-linear restricted nonlinear dynamics (RNL), which is an approximation to the full SSD, provide insight into the mechanism and structure of turbulent flow. RNL dynamics spontaneously limits the support of its turbulence to a small set of streamwise Fourier components giving rise to a natural minimal representation of its turbulence dynamics. Although greatly simplified, this RNL turbulence exhibits natural-looking structures and turbulent statistics. RNL turbulence at the Reynolds numbers studied is dominated by the roll/streak structure in the buffer layer and similar very-large-scale structure (VLSM) in the outer layer. Diagnostics of the structure, spectrum and energetics of RNL and DNS turbulence are used to demonstrate that the roll/streak dynamics supporting the turbulence in the buffer and logarithmic layer is essentially similar in RNL and DNS. This mechanism, which has analytical expression in the SSD, comprises a cooperative interaction between the coherent streamwise mean flow and the incoherent turbulent perturbations.

  4. Joint Agency Turbulence Experiment.

    DTIC Science & Technology

    1985-01-21

    Time Series of Aircraft Longitudinal Gust Data For Penetration 1 on 1 July 1981 63 C5. Time Series of Turbulence Severity Estimates Derived From 400 m...spectral analysis of aircraft longitudinal gust data is shown in Figure B1. Figure B2 shows a modeled turbulence field. The model displays the expected...centered about Location C o %-. -. °,4 0- S E - oo -12 -4 - to 20 so O so s 7D -U. TIME (sec) Figure C4. Time Series of Aircraft Longitudinal Gust Data

  5. Electromagnetic strong plasma turbulence

    SciTech Connect

    Melatos, A.; Jenet, F. A.; Robinson, P. A.

    2007-02-15

    The first large-scale simulations of continuously driven, two-dimensional electromagnetic strong plasma turbulence are performed, for electron thermal speeds 0.01c{<=}v{<=}0.57c, by integrating the Zakharov equations for coupled Langmuir and transverse (T) waves near the plasma frequency. Turbulence scalings and wave number spectra are calculated, a transition is found from a mix of trapped and free T eigenstates for v{>=}0.1c to just free eigenstates for v{<=}0.1c, and wave energy densities are observed to undergo slow quasiperiodic oscillations.

  6. Turbulence in Reynolds' flashes

    NASA Astrophysics Data System (ADS)

    Cerbus, Rory; Liu, Chien-Chia; Gioia, Gustavo; Chakraborty, Pinaki

    2016-11-01

    Osborne Reynolds' seminal work from 1883 revealed that the transition from quiescent, laminar flow to a turbulent pipe filled with roiling eddies is mediated by localized flashes of fluctuations. Later work has unveiled many features of these flashes: they proliferate or fade away, maintain their shape or continually expand. The nature of the fluctuations in the flashes, however, has remained mysterious. Here, using measures traditionally attributed to high Reynolds number (Re) flows, we present experimental results on the fluctuations of the flashes. Our results suggest that the transition to turbulence is the low Re limit of the high Re, fully developed flow. Okinawa Institute of Science and Technology.

  7. Fission Spectrum

    DOE R&D Accomplishments Database

    Bloch, F.; Staub, H.

    1943-08-18

    Measurements of the spectrum of the fission neutrons of 25 are described, in which the energy of the neutrons is determined from the ionization produced by individual hydrogen recoils. The slow neutrons producing fission are obtained by slowing down the fast neutrons from the Be-D reaction of the Stanford cyclotron. In order to distinguish between fission neutrons and the remaining fast cyclotron neutrons both the cyclotron current and the pusle amplifier are modulated. A hollow neutron container, in which slow neutrons have a lifetime of about 2 milliseconds, avoids the use of large distances. This method results in much higher intensities than the usual modulation arrangement. The results show a continuous distribution of neutrons with a rather wide maximum at about 0.8 MV falling off to half of its maximum value at 2.0 MV. The total number of netrons is determined by comparison with the number of fission fragments. The result seems to indicate that only about 30% of the neutrons have energies below .8 MV. Various tests are described which were performed in order to rule out modification of the spectrum by inelastic scattering. Decl. May 4, 1951

  8. Electrokinetic turbulence in a microchannel at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Zhao, Wei; Yang, Fang; Wang, Guiren

    2015-11-01

    Turbulence is commonly viewed as a type of macroflow phenomenon under a sufficiently high Reynolds number (Re). On the other hand, it has been widely perceived in science, engineering and medicine that there is never any turbulence in low Re flow for Newtonian fluids. There is even difficulty to characterize turbulence in microchannels with current available velocimeters, due to the requirement of simultaneously high spatial and temporal resolution. Recently, we generated micro-electrokinetic (EK) turbulence in a microchannel when a pressure driven flow at low Re on the order of unity is electrokinetically forced. We also developed a novel velocimeter, i.e. laser induced fluorescence photobleaching anemometer (LIFPA) that enables us to measure the velocity fluctuations with simultaneously high spatial and temporal resolution. Here we surprisingly observed with LIFPA that the corresponding micro EK turbulence can also have some features of high Re flows, such as Kolmogorov -5/3 spectrum and the exponential tail of probability density function of velocity fluctuation, and the scaling behavior of velocity structure function. This work could provide a new perspective on turbulence. The work was supported by NSF under grant no. CAREER CBET-0954977, MRI CBET-1040227.

  9. On the dynamics of homogeneous turbulence near a surface

    NASA Astrophysics Data System (ADS)

    Flores, Oscar; Riley, James J.

    2011-11-01

    It is becoming increasing clear that stably-stratified flows can support a stratified turbulence k - 5 / 3 inertial range, different from Kolmogorov's. Stratification inhibits vertical motions, but the large-scale quasi-horizontal motions produce strong vertical shearing and small-scale instabilities. The result is a k - 5 / 3 horizontal spectrum for the horizontal velocities at scales larger than the Ozmidov scale, the largest scale that can overturn. For smaller scales, the classical Kolmogorov k - 5 / 3 applies. Inspired by data taken near the water surface in a tidal river, we here explore to what extent the dynamics of the nonlinear spectral energy transfer of near-surface turbulence with no mean shear (i.e., horizontally isotropic turbulence bounded by free-slip and no-slip surfaces) is analogous to stably stratified turbulence. To that end, we perform DNS of decaying isotropic turbulence with Reλ ~ 100 , but bounded by a non-slip surface and a free slip surface. The behavior of the flow near the free-slip surface is similar to stratified turbulence, with a tentative k - 5 / 3 range, but the same is not true for the no-slip surface at the present Reynolds numbers. This research was supported by ARO and NSF. Chickadel et al. (2011) to appear in IEEE Geosci. Remote Sens. Lett.

  10. Mean flow and anisotropic cascades in decaying 2D turbulence

    NASA Astrophysics Data System (ADS)

    Liu, Chien-Chia; Cerbus, Rory; Gioia, Gustavo; Chakraborty, Pinaki

    2015-11-01

    Many large-scale atmospheric and oceanic flows are decaying 2D turbulent flows embedded in a non-uniform mean flow. Despite its importance for large-scale weather systems, the affect of non-uniform mean flows on decaying 2D turbulence remains unknown. In the absence of mean flow it is well known that decaying 2D turbulent flows exhibit the enstrophy cascade. More generally, for any 2D turbulent flow, all computational, experimental and field data amassed to date indicate that the spectrum of longitudinal and transverse velocity fluctuations correspond to the same cascade, signifying isotropy of cascades. Here we report experiments on decaying 2D turbulence in soap films with a non-uniform mean flow. We find that the flow transitions from the usual isotropic enstrophy cascade to a series of unusual and, to our knowledge, never before observed or predicted, anisotropic cascades where the longitudinal and transverse spectra are mutually independent. We discuss implications of our results for decaying geophysical turbulence.

  11. Energy dynamics in a simulation of LAPD turbulence

    SciTech Connect

    Friedman, B.; Carter, T. A.; Schaffner, D.; Umansky, M. V.; Dudson, B.

    2012-10-15

    Energy dynamics calculations in a 3D fluid simulation of drift wave turbulence in the linear Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] illuminate processes that drive and dissipate the turbulence. These calculations reveal that a nonlinear instability dominates the injection of energy into the turbulence by overtaking the linear drift wave instability that dominates when fluctuations about the equilibrium are small. The nonlinear instability drives flute-like (k{sub Parallel-To }=0) density fluctuations using free energy from the background density gradient. Through nonlinear axial wavenumber transfer to k{sub Parallel-To }{ne}0 fluctuations, the nonlinear instability accesses the adiabatic response, which provides the requisite energy transfer channel from density to potential fluctuations as well as the phase shift that causes instability. The turbulence characteristics in the simulations agree remarkably well with experiment. When the nonlinear instability is artificially removed from the system through suppressing k{sub Parallel-To }=0 modes, the turbulence develops a coherent frequency spectrum which is inconsistent with experimental data. This indicates the importance of the nonlinear instability in producing experimentally consistent turbulence.

  12. On the Development of Turbulent Wakes from Vortex Streets

    NASA Technical Reports Server (NTRS)

    Roshko, Anatol

    1953-01-01

    Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hotwire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. The range R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300. Spectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream. It was found that in the stable range the vortex street has a periodic spanwise structure. The dependence of shedding frequency on velocity was successfully used to measure flow velocity. Measurements in the wake of a ring showed that an annular vortex street is developed.

  13. Daytime turbulent exchange between the Amazon forest and the atmosphere

    NASA Technical Reports Server (NTRS)

    Fitzjarrald, David R.; Moore, Kathleen E.; Cabral, Osvaldo M. R.; Scolar, Jose; Manzi, Antonio O.; Deabreusa, Leonardo D.

    1989-01-01

    Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain.

  14. Daytime turbulent exchange between the Amazon forest and the atmosphere

    NASA Technical Reports Server (NTRS)

    Fitzjarrald, David R.; Moore, Kathleen E.; Cabral, Osvaldo M. R.; Scolar, Jose; Manzi, Antonio

    1990-01-01

    Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain.

  15. Magnetohydrodynamic turbulence: Generalized formulation and extension to compressible cases

    SciTech Connect

    Shivamoggi, Bhimsen K.

    2008-06-15

    A general framework that incorporates the Iroshnikov-Kraichnan (IK) and Goldreich-Sridhar (GS) phenomenalogies of magnetohydrodynamic (MHD) turbulence is developed. This affords a clarification of the regimes of validity of the IK and GS models and hence help resolve some controversies on this aspect. This general formulation appears to have a certain robustness as revealed here by its form invariance with respect to inclusion of compressible effects. Generalizations of the IK and GS spectra to compressible MHD turbulence are given. These two branches are shown to merge with the MHD shockwave spectrum, as to be expected, in the infinite compressibility limit.

  16. Freely decaying weak turbulence for sea surface gravity waves.

    PubMed

    Onorato, M; Osborne, A R; Serio, M; Resio, D; Pushkarev, A; Zakharov, V E; Brandini, C

    2002-09-30

    We study the long-time evolution of deep-water ocean surface waves in order to better understand the behavior of the nonlinear interaction processes that need to be accurately predicted in numerical models of wind-generated ocean surface waves. Of particular interest are those nonlinear interactions which are predicted by weak turbulence theory to result in a wave energy spectrum of the form of [k](-2.5). We numerically implement the primitive Euler equations for surface waves and demonstrate agreement between weak turbulence theory and the numerical results.

  17. Unveiling Reality of the Mind: Cultural Arbitrary of Consumerism

    ERIC Educational Resources Information Center

    Choi, Su-Jin

    2012-01-01

    This paper discusses the cultural arbitrary of consumerism by focusing on a personal realm. That is, I discuss what consumerism appeals to and how it flourishes in relation to our minds. I argue that we need to unveil reality of the mind, be aware of ourselves in relation to the perpetuation of consumerism, in order to critically intervene in the…

  18. Arbitrary unitary transformations on optical states using a quantum memory

    SciTech Connect

    Campbell, Geoff T.; Pinel, Olivier; Hosseini, Mahdi; Buchler, Ben C.; Lam, Ping Koy

    2014-12-04

    We show that optical memories arranged along an optical path can perform arbitrary unitary transformations on frequency domain optical states. The protocol offers favourable scaling and can be used with any quantum memory that uses an off-resonant Raman transition to reversibly transfer optical information to an atomic spin coherence.

  19. Information balance in quantum teleportation with an arbitrary pure state

    SciTech Connect

    Li Li; Chen Zengbing

    2005-07-15

    We study a general teleportation scheme with an arbitrary two-party pure state and derive a tight bound of the teleportation fidelity with a predesigned estimation of the unknown state to be teleported. This bound shows a piecewise balance between information gain and state disturbance. We also explain possible physical significance of the balance.

  20. Chaotic correlations in barrier billiards with arbitrary barriers

    NASA Astrophysics Data System (ADS)

    Osbaldestin, A. H.; Adamson, L. N. C.

    2013-06-01

    We study autocorrelation functions in symmetric barrier billiards for golden mean trajectories with arbitrary barriers. Renormalization analysis reveals the presence of a chaotic invariant set and thus that, for a typical barrier, there are chaotic correlations. The chaotic renormalization set is the analogue of the so-called orchid that arises in a generalized Harper equation.

  1. The energy spectrum in a barotropic atmosphere

    NASA Astrophysics Data System (ADS)

    Kurgansky, M. V.

    2008-03-01

    In a forced-dissipative barotropic model of the atmosphere on a spherical planet, by following mathematical techniques in (Thompson, P. D.: The equilibrium energy spectrum of randomly forced two-dimensional turbulence, Journal of the Atmospheric Sciences, 30, 1593-1598, 1973) but applying them in a novel context of the discrete spectrum on a rotating sphere, the "minus 2" energy spectrum for wavenumbers much greater than a characteristic wavenumber of the baroclinic forcing has been obtained if the forcing is taken in the simplest and most fundamental form. Some observation-based atmospheric kinetic energy spectra, with their slopes lying between "minus 2" and "minus 3" laws, are discussed from the perspective of the deduced "minus 2" energy spectrum.

  2. Scaling laws in decaying helical hydromagnetic turbulence

    NASA Astrophysics Data System (ADS)

    Christensson, M.; Hindmarsh, M.; Brandenburg }%, A.

    2005-07-01

    We study the evolution of growth and decay laws for the magnetic field coherence length ξ, energy E_M and magnetic helicity H in freely decaying 3D MHD turbulence. We show that with certain assumptions, self-similarity of the magnetic power spectrum alone implies that ξ σm t1/2. This in turn implies that magnetic helicity decays as Hσm t-2s, where s=(ξ_diff/ξH)2, in terms of ξ_diff, the diffusion length scale, and ξ_H, a length scale defined from the helicity power spectrum. The relative magnetic helicity remains constant, implying that the magnetic energy decays as E_M σm t-1/2-2s. The parameter s is inversely proportional to the magnetic Reynolds number Re_M, which is constant in the self-similar regime.

  3. Cooling by discrete and porous injection into a turbulent, supersonic boundary layer

    NASA Technical Reports Server (NTRS)

    Clark, K. J.; Nardo, C. T.; Jaffe, N. A.; Covington, M. A.

    1974-01-01

    A summary is provided of an experimental investigation which was carried out to determine the cooling effectiveness of an injection of water through slotted and porous surfaces into a turbulent, supersonic boundary layer. Correlations, based on the experimental data and the supporting analysis, were incorporated into a computer-code model. The model is used to compute discrete injection coolant flow rate requirements for arbitrary slot sizes and heating environments.

  4. Turbulence characteristics inside a turbulent spot in plane Poiseuille flow

    NASA Technical Reports Server (NTRS)

    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.

  5. Universality of the frequency spectrum of laminates

    NASA Astrophysics Data System (ADS)

    Shmuel, Gal; Band, Ram

    2016-07-01

    We show that the frequency spectrum of two-component elastic laminates admits a universal structure, independent of the geometry of the periodic-cell and the specific physical properties. The compactness of the structure enables us to rigorously derive the maximal width, the expected width, and the density of the band-gaps - ranges of frequencies at which waves cannot propagate. In particular, we find that the density of these band-gaps is a universal property of classes of laminates. Rules for tailoring laminates according to desired spectrum properties thereby follow. We show that the frequency spectrum of various finitely deformed laminates are also endowed with the same compact structure. Finally, we explain how our results generalize for laminates with an arbitrary number of components, based on the form of their dispersion relation.

  6. Analytical and phenomenological studies of rotating turbulence

    NASA Technical Reports Server (NTRS)

    Mahalov, Alex; Zhou, YE

    1995-01-01

    A framework, which combines mathematical analysis, closure theory, and phenomenological treatment, is developed to study the spectral transfer process and reduction of dimensionality in turbulent flows that are subject to rotation. First, we outline a mathematical procedure that is particularly appropriate for problems with two disparate time scales. The approach which is based on the Green's method leads to the Poincare velocity variables and the Poincare transformation when applied to rotating turbulence. The effects of the rotation are now reflected in the modifications to the convolution of a nonlinear term. The Poincare transformed equations are used to obtain a time-dependent analog of the Taylor-Proudman theorem valid in the asymptotic limit when the non-dimensional parameter mu is identical to Omega(t) approaches infinity (Omega is the rotation rate and t is the time). The 'split' of the energy transfer in both direct and inverse directions is established. Secondly, we apply the Eddy-Damped-Quasinormal-Markovian (EDQNM) closure to the Poincare transformed Euler/Navier-Stokes equations. This closure leads to expressions for the spectral energy transfer. In particular, an unique triple velocity decorrelation time is derived with an explicit dependence on the rotation rate. This provides an important input for applying the phenomenological treatment of Zhou. In order to characterize the relative strength of rotation, another non-dimensional number, a spectral Rossby number, which is defined as the ratio of rotation and turbulence time scales, is introduced. Finally, the energy spectrum and the spectral eddy viscosity are deduced.

  7. Spreading of correlations in exactly solvable quantum models with long-range interactions in arbitrary dimensions

    NASA Astrophysics Data System (ADS)

    Cevolani, Lorenzo; Carleo, Giuseppe; Sanchez-Palencia, Laurent

    2016-09-01

    We study the out-of-equilibrium dynamics induced by quantum quenches in quadratic Hamiltonians featuring both short- and long-range interactions. The spreading of correlations in the presence of algebraic decaying interactions, 1/R α , is studied for lattice Bose models in arbitrary dimension D. These models are exactly solvable and provide useful insight in the universal description of more complex systems as well as comparisons to the known universal upper bounds for the spreading of correlations. Using analytical calculations of the dominant terms and full numerical integration of all quasi-particle contributions, we identify three distinct dynamical regimes. For strong decay of interactions, α \\gt D+1, we find a causal regime, qualitatively similar to what previously found for short-range interactions. This regime is characterized by ballistic (linear cone) spreading of the correlations with a cone velocity equal to twice the maximum group velocity of the quasi-particles. For weak decay of interactions, α < D, we find instantaneous activation of correlations at arbitrary distance. This signals the breaking of causality, which can be associated with the divergence of the quasi-particle energy spectrum. Finite-size scaling of the activation time precisely confirms this interpretation. For intermediate decay of interactions, D\\lt α \\lt D+1, we find a sub-ballistic, algebraic (bent cone) spreading and determine the corresponding exponent as a function of α. These outcomes generalize existing results for one-dimensional systems to arbitrary dimension. We precisely relate the three regimes to the first- and second-order divergences of the quasi-particle energy spectrum for any dimension. The long-range transverse Ising model in dimensions D = 1, 2, and 3 in the (quadratic) spin-wave approximation is more specifically studied and we also discuss the shape of the correlation front in dimension higher than one. Our results apply to several condensed

  8. Flows, Turbulence, and Mixing

    NASA Astrophysics Data System (ADS)

    Lazarian, Alex

    2003-07-01

    HST and FUSE spectra of distant UV-bright sources reveal interstellar absorption lines of high stages of ionization {O VI, C IV, N V, Si IV} arising in many different astrophysical environments such as superbubbles, interstellar chimneys, high-velocity clouds, galaxy halos and cosmic filaments. Turbulence, always present in the magnetized ISM, must mix the hot { 10^6 K} gas with cooler gas within "turbulent mixing layers". Present theory, based on 1D steady-state flows, suggest the line ratios in these layers differ significantly from photoionized gas, radiative shocks, cooling zones, or conduction fronts. These models are use to infer mass and energy fluxes important to understanding the ISM. We propose to develop a suite of 3D time-dependent models that properly calculate turbulent mixing. We will produce synthetic UV absorption lines and optical emission lines directly relevant to HST observations that use GHRS, STIS, and eventually, COS. These models will allow us to explore the sensitivity of the spectral diagnostics to magnetic field strength, turbulence intensity, and relative velocity of the hot and cold gas. We will publish the resulting grid of spectral diagnostics and make them available through the Web.

  9. Chemically Reacting Turbulent Flow.

    DTIC Science & Technology

    1987-04-14

    two stages of gen I tubes equipped with P-47 phosphor screens The detector chosen for the camera was a Reticon RL128S* line detectoI- .,hich consists...the Stud’, of Turbulent Mixing," William M. Pitts, Nuclear Engineering Seminar of the Department of Chemical and Nuclear Engineering, University of

  10. Multilevel turbulence simulations

    SciTech Connect

    Tziperman, E.

    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.

  11. Spirituality in Turbulent Times.

    ERIC Educational Resources Information Center

    Wheatley, Margaret J.

    2002-01-01

    Discusses the importance of spiritual leadership in turbulent, uncertain times. Describes several spiritual principles--for example, life is cyclical; all life is interconnected. Offers six suggestions for personal health: Start day peacefully, learn to be mindful, slow things down, create own measures, expect surprise, practice gratefulness. (PKP)

  12. Heart rate turbulence.

    PubMed

    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.

  13. Workshop on Computational Turbulence Modeling

    NASA Technical Reports Server (NTRS)

    1993-01-01

    This document contains presentations given at Workshop on Computational Turbulence Modeling held 15-16 Sep. 1993. The purpose of the meeting was to discuss the current status and future development of turbulence modeling in computational fluid dynamics for aerospace propulsion systems. Papers cover the following topics: turbulence modeling activities at the Center for Modeling of Turbulence and Transition (CMOTT); heat transfer and turbomachinery flow physics; aerothermochemistry and computational methods for space systems; computational fluid dynamics and the k-epsilon turbulence model; propulsion systems; and inlet, duct, and nozzle flow.

  14. Aircraft Dynamic Modeling in Turbulence

    NASA Technical Reports Server (NTRS)

    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.

  15. Remarks on turbulent constitutive relations

    NASA Technical Reports Server (NTRS)

    Shih, Tsan-Hsing; Lumley, John L.

    1993-01-01

    The paper demonstrates that the concept of turbulent constitutive relations can be used to construct general models for various turbulent correlations. Some of the Generalized Cayley-Hamilton formulas for relating tensor products of higher extension to tensor products of lower extension are introduced. The combination of dimensional analysis and invariant theory can lead to 'turbulent constitutive relations' (or general turbulence models) for, in principle, any turbulent correlations. As examples, the constitutive relations for Reynolds stresses and scalar fluxes are derived. The results are consistent with ones from Renormalization Group (RNG) theory and two-scale Direct-Interaction Approximation (DIA) method, but with a more general form.

  16. Analytic improvements to the atmospheric turbulence optical transfer function

    NASA Astrophysics Data System (ADS)

    Tofsted, David H.

    2003-09-01

    The standard method used for modeling optical turbulence effects on imaging uses an optical transfer function (OTF). To model this function the short- and long-exposure limiting cases exist. The short-exposure case is handled by modifying the long-exposure case to remove wavefront tilt assessed at the sensor entrance pupil. Then, depending on whether one is in the "near-field" or the "far-field," one of two subcases is used. These evaluations require a model of the refractive index spectrum. Typically this model is assumed to be the Kolmogorov spectrum where an inner scale is set to zero and outer scale is infinite. However, for real atmospheres the inner and outer scales affect turbulence predictions through a modified spectrum. The difficulty using non-limiting values for these parameters is that double integrals must then be assessed. However, in this paper analytic forms are developed to describe the spectrum, permitting analytic solutions to these integrals. The result is that we can express quantities such as the Fried coherence diameter in closed form accounting for both inner and outer scale effects. Also, expressions for the inner and outer scales of turbulence can be written as functions of the atmospheric surface layer stability. Lastly, it is shown that the near/far-field effect does not easily subdivide into two cases. In fact, the distance dependence of the tilt effect is shown to span a range of 107 in the governing dimensionless parameter. To model this continuum a unified treatment is considered.

  17. Turbulence Modeling Workshop

    NASA Technical Reports Server (NTRS)

    Rubinstein, R. (Editor); Rumsey, C. L. (Editor); Salas, M. D. (Editor); Thomas, J. L. (Editor); Bushnell, Dennis M. (Technical Monitor)

    2001-01-01

    Advances in turbulence modeling are needed in order to calculate high Reynolds number flows near the onset of separation and beyond. To this end, the participants in this workshop made the following recommendations. (1) A national/international database and standards for turbulence modeling assessment should be established. Existing experimental data sets should be reviewed and categorized. Advantage should be taken of other efforts already under-way, such as that of the European Research Community on Flow, Turbulence, and Combustion (ERCOFTAC) consortium. Carefully selected "unit" experiments will be needed, as well as advances in instrumentation, to fill the gaps in existing datasets. A high priority should be given to document existing turbulence model capabilities in a standard form, including numerical implementation issues such as grid quality and resolution. (2) NASA should support long-term research on Algebraic Stress Models and Reynolds Stress Models. The emphasis should be placed on improving the length-scale equation, since it is the least understood and is a key component of two-equation and higher models. Second priority should be given to the development of improved near-wall models. Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) would provide valuable guidance in developing and validating new Reynolds-averaged Navier-Stokes (RANS) models. Although not the focus of this workshop, DNS, LES, and hybrid methods currently represent viable approaches for analysis on a limited basis. Therefore, although computer limitations require the use of RANS methods for realistic configurations at high Reynolds number in the foreseeable future, a balanced effort in turbulence modeling development, validation, and implementation should include these approaches as well.

  18. On Using Shaped Honeycombs for Experimental Generation of Arbitrary Velocity Profiles in Test Facilities

    NASA Astrophysics Data System (ADS)

    Safaripour, Alireza; Olson, David; Naguib, Ahmed; Koochesfahani, Manoochehr

    2016-11-01

    It is common to use a uniform approach flow in the study of most problems in aerodynamics. Motivated by situations where the approach flow is not uniform, the focus of the current work is on the experimental generation of arbitrary velocity profiles in a flow facility (water tunnel) using the shaped honeycomb technique originally proposed by Kotansky (1966). Employing further refinement of this approach, multiple honeycomb devices are designed and fabricated to produce prescribed velocity profiles. The performance of these devices is assessed in terms of their agreement with the desired velocity profiles and the level of turbulence they produce. Single-component molecular tagging velocimetry (1c-MTV) is used to characterize the resulting mean and fluctuating streamwise velocity profiles and their streamwise development. The shaped honeycomb technique is shown to be effective in producing the desired velocity profiles with high fidelity while maintaining velocity fluctuations level at or below that of the freestream prior to installation of the devices. This work was supported by AFOSR Award Number FA9550-15-1-0224.

  19. A mesh partitioning algorithm for preserving spatial locality in arbitrary geometries

    SciTech Connect

    Nivarti, Girish V. Salehi, M. Mahdi; Bushe, W. Kendal

    2015-01-15

    Highlights: •An algorithm for partitioning computational meshes is proposed. •The Morton order space-filling curve is modified to achieve improved locality. •A spatial locality metric is defined to compare results with existing approaches. •Results indicate improved performance of the algorithm in complex geometries. -- Abstract: A space-filling curve (SFC) is a proximity preserving linear mapping of any multi-dimensional space and is widely used as a clustering tool. Equi-sized partitioning of an SFC ignores the loss in clustering quality that occurs due to inaccuracies in the mapping. Often, this results in poor locality within partitions, especially for the conceptually simple, Morton order curves. We present a heuristic that improves partition locality in arbitrary geometries by slicing a Morton order curve at points where spatial locality is sacrificed. In addition, we develop algorithms that evenly distribute points to the extent possible while maintaining spatial locality. A metric is defined to estimate relative inter-partition contact as an indicator of communication in parallel computing architectures. Domain partitioning tests have been conducted on geometries relevant to turbulent reactive flow simulations. The results obtained highlight the performance of our method as an unsupervised and computationally inexpensive domain partitioning tool.

  20. Modeling of Turbulence Generated Noise in Jets

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas; Bridges, James

    2004-01-01

    A numerically calculated Green's function is used to predict jet noise spectrum and its far-field directivity. A linearized form of Lilley's equation governs the non-causal Green s function of interest, with the non-linear terms on the right hand side identified as the source. In this paper, contributions from the so-called self- and shear-noise source terms will be discussed. A Reynolds-averaged Navier-Stokes solution yields the required mean flow as well as time- and length scales of a noise-generating turbulent eddy. A non-compact source, with exponential temporal and spatial functions, is used to describe the turbulence velocity correlation tensors. It is shown that while an exact non-causal Green's function accurately predicts the observed shift in the location of the spectrum peak with angle as well as the angularity of sound at moderate Mach numbers, at high subsonic and supersonic acoustic Mach numbers the polar directivity of radiated sound is not entirely captured by this Green's function. Results presented for Mach 0.5 and 0.9 isothermal jets, as well as a Mach 0.8 hot jet conclude that near the peak radiation angle a different source/Green's function convolution integral may be required in order to capture the peak observed directivity of jet noise.

  1. Time-development of energy spectra in the simulation of quantum turbulence

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shinji; Tsubota, Makoto; Vinen, W. F.

    2012-12-01

    Bradley et al. studied experimentally the emission of vortex rings by a vibrating grid in superfluid 3He-B.1. They observed a sharp transition from ballistic propagation of vortex rings at low grid velocities to a cloud of quantum turbulence at higher velocities, the turbulence being generated by coalescence of the rings. This behaviour is consistent with the results of a full Biot-Savart numerical simulation with the vortex filament model.2 Bradley et al suggested that in the quantum turbulent regime a Kolmogorov energy spectrum develops at small wave numbers (presumably less than 2π/l, where l is the vortex line spacing) and they suggested that the observed rate of free decay of the turbulence is consistent with this idea. In this work we have studied numerically the time-development of the energy spectrum. For the separated rings the spectrum contains very little energy at small wave numbers. After the transition to turbulence the energy at small wavenumbers increases, but it remains much less than would be the case for a Kolmogorov spectrum. We consider why the assumptions underlying the numerical simulations do not lead to the generation of a Kolmogorov spectrum.

  2. Group-kinetic theory of turbulence

    NASA Technical Reports Server (NTRS)

    Tchen, C. M.

    1986-01-01

    The two phases are governed by two coupled systems of Navier-Stokes equations. The couplings are nonlinear. These equations describe the microdynamical state of turbulence, and are transformed into a master equation. By scaling, a kinetic hierarchy is generated in the form of groups, representing the spectral evolution, the diffusivity and the relaxation. The loss of memory in formulating the relaxation yields the closure. The network of sub-distributions that participates in the relaxation is simulated by a self-consistent porous medium, so that the average effect on the diffusivity is to make it approach equilibrium. The kinetic equation of turbulence is derived. The method of moments reverts it to the continuum. The equation of spectral evolution is obtained and the transport properties are calculated. In inertia turbulence, the Kolmogoroff law for weak coupling and the spectrum for the strong coupling are found. As the fluid analog, the nonlinear Schrodinger equation has a driving force in the form of emission of solitons by velocity fluctuations, and is used to describe the microdynamical state of turbulence. In order for the emission together with the modulation to participate in the transport processes, the non-homogeneous Schrodinger equation is transformed into a homogeneous master equation. By group-scaling, the master equation is decomposed into a system of transport equations, replacing the Bogoliubov system of equations of many-particle distributions. It is in the relaxation that the memory is lost when the ensemble of higher-order distributions is simulated by an effective porous medium. The closure is thus found. The kinetic equation is derived and transformed into the equation of spectral flow.

  3. SUB-ALFVENIC NON-IDEAL MAGNETOHYDRODYNAMIC TURBULENCE SIMULATIONS WITH AMBIPOLAR DIFFUSION. III. IMPLICATIONS FOR OBSERVATIONS AND TURBULENT ENHANCEMENT

    SciTech Connect

    Li, Pak Shing; Klein, Richard I.; McKee, Christopher F. E-mail: cmckee@astro.berkeley.edu

    2012-01-01

    Ambipolar diffusion (AD) is believed to be a crucial process for redistributing magnetic flux in the dense molecular gas that occurs in regions of star formation. We carry out numerical simulations of this process in regions of low ionization using the heavy-ion approximation. The simulations are for regions of strong field (plasma {beta} = 0.1) and mildly supersonic turbulence (M=3, corresponding to an Alfven Mach number of 0.67). The velocity power spectrum of the neutral gas changes from an Iroshnikov-Kraichnan spectrum in the case of ideal MHD to a Burgers spectrum in the case of a shock-dominated hydrodynamic system. The magnetic power spectrum shows a similar behavior. We use a one-dimensional radiative transfer code to post-process our simulation results; the simulated emission from the CS J = 2-1 and H{sup 13}CO{sup +} J = 1-0 lines shows that the effects of AD are observable in principle. Linewidths of ions are observed to be less than those of neutrals, and we confirm previous suggestions that this is due to AD. We show that AD is unlikely to affect the Chandrasekhar-Fermi method for inferring field strengths unless the AD is stronger than generally observed. Finally, we present a study of the enhancement of AD by turbulence, finding that AD is accelerated by factor 2-4.5 for non-self-gravitating systems with the level of turbulence we consider.

  4. Satellite sensing of submerged fossil turbulence and zombie turbulence

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.

    2004-11-01

    Surface brightness anomalies from a submerged municipal wastewater outfall trapped by buoyancy in an area 0.1 km^2 are surprisingly detected from space satellites in areas > 200 km^2. How is this possible? Microstructure measurements near the outfall diffuser reveal enhanced turbulence and temperature dissipation rates above the 50 m trapping depth. Near-vertical radiation of internal waves by fossil and zombie turbulence microstructure patches produce wind ripple smoothing with 30-50 m internal wave patterns in surface Fourier brightness anomalies near the outfall. Detections at 10-14 km distances are at 100-220 m bottom boundary layer (BBL) fossil turbulence scales. Advected outfall fossils form zombie turbulence patches in internal wave patterns as they extract energy, vorticity, turbulence and ambient vertical internal wavelength information as their density gradients are tilted by the waves. As the zombies fossilize, patterned energy radiates near-vertically to produce the detected Fourier anomalies. Zombie turbulence patches beam extracted energy in a preferred direction with a special frequency, like energized metastable molecules in a chemical maser. Thus, kilowatts to produce the submerged field of advected fossil outfall turbulence patches are amplified by beamed zombie turbulence maser action (BZTMA) into megawatts of turbulence dissipation to affect sea surface brightness on wide surface areas using gigawatts of BBL fossil turbulence wave energy available.

  5. Microelectrokinetic turbulence in microfluidics at low Reynolds number.

    PubMed

    Wang, Guiren; Yang, Fang; Zhao, Wei

    2016-01-01

    There is commonly no turbulence in microfluidics, and the flows are believed to be either laminar or chaotic, since Reynolds number (Re) in microflows is usually on the order of unity or lower. However, we recently demonstrated that it is possible to achieve turbulence with low Re (based on the measured flow velocity and the width of the channel entrance) when a pressure-driven flow is electrokinetically forced in a quasi T-microchannel. To be able to measure high frequency velocity fluctuations in microchannels, a velocimeter with submicrometer spatial resolution and microsecond temporal resolution, called a laser-induced fluorescence photobleaching anemometer, is developed. Here we characterize the microelectrokinetic turbulence and observe some typical and important features of high Re flows, such as Kolmogorov -5/3 spectrum of velocity fluctuation, which usually can be realized only at very high Re in macroturbulent flows.

  6. Turbulent transport of alpha particles in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Croitoru, A.; Palade, D. I.; Vlad, M.; Spineanu, F.

    2017-03-01

    We investigate the \\boldsymbol{E}× \\boldsymbol{B} diffusion of fusion born α particles in tokamak plasmas. We determine the transport regimes for a realistic model that has the characteristics of the ion temperature gradient (ITG) or of the trapped electron mode (TEM) driven turbulence. It includes a spectrum of potential fluctuations that is modeled using the results of the numerical simulations, the drift of the potential with the effective diamagnetic velocity and the parallel motion. Our semi-analytical statistical approach is based on the decorrelation trajectory method (DTM), which is adapted to the gyrokinetic approximation. We obtain the transport coefficients as a function of the parameters of the turbulence and of the energy of the α particles. According to our results, significant turbulent transport of the α particles can appear only at energies of the order of 100 KeV. We determine the corresponding conditions.

  7. Stretching in a model of a turbulent flow

    NASA Astrophysics Data System (ADS)

    Baggaley, Andrew W.; Barenghi, Carlo F.; Shukurov, Anvar

    2009-03-01

    Using a multi-scaled, chaotic flow known as the KS model of turbulence [J.C.H. Fung, J.C.R. Hunt, A. Malik, R.J. Perkins, Kinematic simulation of homogeneous turbulence by unsteady random fourier modes, J. Fluid Mech. 236 (1992) 281-318], we investigate the dependence of Lyapunov exponents on various characteristics of the flow. We show that the KS model yields a power law relation between the Reynolds number and the maximum Lyapunov exponent, which is similar to that for a turbulent flow with the same energy spectrum. Our results show that the Lyapunov exponents are sensitive to the advection of small eddies by large eddies, which can be explained by considering the Lagrangian correlation time of the smallest scales. We also relate the number of stagnation points within a flow to the maximum Lyapunov exponent, and suggest a linear dependence between the two characteristics.

  8. Direct numerical simulation and analysis of shock turbulence interaction

    NASA Technical Reports Server (NTRS)

    Lee, Sangsan; Lele, Sanjiva K.; Moin, Parviz

    1991-01-01

    Two kinds of linear analysis, rapid distortion theory (RDT) and linear interaction analysis (LIA), were used to investigate the effects of a shock wave on turbulence. Direct numerical simulations of two-dimensional isotropic turbulence interaction with a normal shock were also performed. The results from RDT and LIA are in good agreement for weak shock waves, where the effects of shock front curvature and shock front unsteadiness are not significant in producing vorticity. The linear analyses predict wavenumber-dependent amplification of the upstream one-dimensional energy spectrum, leading to turbulence scale length scale decrease through the interaction. Instantaneous vorticity fields show that vortical structures are enhanced while they are compressed in the shock normal direction. Entrophy amplfication through the shock wave compares favorably with the results of linear analyses.

  9. REDUCTION OF DRIFT EFFECTS DUE TO SOLAR WIND TURBULENCE

    SciTech Connect

    Burger, R. A.; Visser, D. J.

    2010-12-10

    Gradient and curvature drift play a key role in the modulation of cosmic rays. Reduction in the drift coefficient due to turbulence has been demonstrated unambiguously through direct numerical simulations, but a theory that can explain these results is still lacking. We introduce a parameterized form of the drift coefficient based on direct numerical simulations and show that good agreement with observed proton energy spectra at Earth can be found when it is used in a numerical modulation model. We show that the turbulence ultrascale, for which no observations currently exist, plays an important role in drift reduction. The magnitude at Earth and spatial dependence of this quantity required to fit cosmic-ray observations at Earth are argued to be plausible based on the required properties of the two-dimensional turbulence spectrum at large scales.

  10. On 4 D, =1 massless gauge superfields of arbitrary superhelicity

    NASA Astrophysics Data System (ADS)

    Gates, S. James; Koutrolikos, Konstantinos

    2014-06-01

    We present an alternative method of exploring the component structure of an arbitrary super-helicity (integer Y = s, or half odd integer Y = s+1 /2 for any integer s) irreducible representation of the Super-Poincaré group. We use it to derive the component action and the SUSY transformation laws. The effectiveness of this approach is based on the equations of motion and their properties, like the Bianchi identities. These equations are generated by the superspace action when it is expressed in terms of prepotentials. For that reason we reproduce the superspace action for arbitrary superhelicity, using unconstrained superfields. The appropriate, to use, superfields are dictated by the representation theory of the group and the requirement that there is a smooth limit between the massive and massless case.

  11. Bistatic synthetic aperture radar imaging for arbitrary flight trajectories.

    PubMed

    Yarman, Can Evren; Yazici, Birsen; Cheney, Margaret

    2008-01-01

    In this paper, we present an analytic, filtered backprojection (FBP) type inversion method for bistatic synthetic aperture radar (BISAR). We consider a BISAR system where a scene of interest is illuminated by electromagnetic waves that are transmitted, at known times, from positions along an arbitrary, but known, flight trajectory and the scattered waves are measured from positions along a different flight trajectory which is also arbitrary, but known. We assume a single-scattering model for the radar data, and we assume that the ground topography is known but not necessarily flat. We use microlocal analysis to develop the FBP-type reconstruction method. We analyze the computational complexity of the numerical implementation of the method and present numerical simulations to demonstrate its performance.

  12. Arbitrary multicolor photodetection by hetero-integrated semiconductor nanostructures.

    PubMed

    Sang, Liwen; Hu, Junqing; Zou, Rujia; Koide, Yasuo; Liao, Meiyong

    2013-01-01

    The typical photodetectors can only detect one specific optical spectral band, such as InGaAs and graphene-PbS quantum dots for near-infrared (NIR) light detection, CdS and Si for visible light detection, and ZnO and III-nitrides for UV light detection. So far, none of the developed photodetector can achieve the multicolor detection with arbitrary spectral selectivity, high sensitivity, high speed, high signal-to-noise ratio, high stability, and simplicity (called 6S requirements). Here, we propose a universal strategy to develop multicolor photodetectors with arbitrary spectral selectivity by integrating various semiconductor nanostructures on a wide-bandgap semiconductor or an insulator substrate. Because the photoresponse of each spectral band is determined by each semiconductor nanostructure or the semiconductor substrate, multicolor detection satisfying 6S requirements can be readily satisfied by selecting the right semiconductors.

  13. Rapid Teaching of Arbitrary Matching in Individuals with Intellectual Disabilities

    PubMed Central

    Morro, Greg; Mackay, Harry A.; Carlin, Michael T.

    2014-01-01

    This research extended to arbitrary matching-to-sample procedures a method that was successful in rapidly establishing identity matching in children with and without intellectual disabilities (Mackay et al., 2002). The method involves increasing the number of identical comparison stimuli in a choice array in order to create a homogenous background that makes the target more salient, thus likely to prompt selection. The number of comparison stimuli then is faded systematically contingent on accurate responding. This method unites cognitive research on visual search and behavior analytic research on conditional stimulus control. Two experiments examined use of the method to teach arbitrary relations between visual stimuli (numerals and colors and their printed names) and between visual and auditory stimuli (e.g., numerals and colors and their dictated names). Results demonstrated the generality of the method to symbolic matching. This finding is important for conceptual reasons and for its relevance to special education. PMID:25408559

  14. Arbitrary Multicolor Photodetection by Hetero-integrated Semiconductor Nanostructures

    PubMed Central

    Sang, Liwen; Hu, Junqing; Zou, Rujia; Koide, Yasuo; Liao, Meiyong

    2013-01-01

    The typical photodetectors can only detect one specific optical spectral band, such as InGaAs and graphene-PbS quantum dots for near-infrared (NIR) light detection, CdS and Si for visible light detection, and ZnO and III-nitrides for UV light detection. So far, none of the developed photodetector can achieve the multicolor detection with arbitrary spectral selectivity, high sensitivity, high speed, high signal-to-noise ratio, high stability, and simplicity (called 6S requirements). Here, we propose a universal strategy to develop multicolor photodetectors with arbitrary spectral selectivity by integrating various semiconductor nanostructures on a wide-bandgap semiconductor or an insulator substrate. Because the photoresponse of each spectral band is determined by each semiconductor nanostructure or the semiconductor substrate, multicolor detection satisfying 6S requirements can be readily satisfied by selecting the right semiconductors. PMID:23917790

  15. Locally indistinguishable orthogonal product bases in arbitrary bipartite quantum system

    PubMed Central

    Xu, Guang-Bao; Yang, Ying-Hui; Wen, Qiao-Yan; Qin, Su-Juan; Gao, Fei

    2016-01-01

    As we know, unextendible product basis (UPB) is an incomplete basis whose members cannot be perfectly distinguished by local operations and classical communication. However, very little is known about those incomplete and locally indistinguishable product bases that are not UPBs. In this paper, we first construct a series of orthogonal product bases that are completable but not locally distinguishable in a general m ⊗ n (m ≥ 3 and n ≥ 3) quantum system. In particular, we give so far the smallest number of locally indistinguishable states of a completable orthogonal product basis in arbitrary quantum systems. Furthermore, we construct a series of small and locally indistinguishable orthogonal product bases in m ⊗ n (m ≥ 3 and n ≥ 3). All the results lead to a better understanding of the structures of locally indistinguishable product bases in arbitrary bipartite quantum system. PMID:27503634

  16. Delivering sound energy along an arbitrary convex trajectory.

    PubMed

    Zhao, Sipei; Hu, Yuxiang; Lu, Jing; Qiu, Xiaojun; Cheng, Jianchun; Burnett, Ian

    2014-10-15

    Accelerating beams have attracted considerable research interest due to their peculiar properties and various applications. Although there have been numerous research on the generation and application of accelerating light beams, few results have been published on the generation of accelerating acoustic beams. Here we report on the experimental observation of accelerating acoustic beams along arbitrary convex trajectories. The desired trajectory is projected to the spatial phase profile on the boundary which is discretized and sampled spatially. The sound field distribution is formulated with the Green function and the integral equation method. Both the paraxial and the non-paraxial regimes are examined and observed in the experiments. The effect of obstacle scattering in the sound field is also investigated and the results demonstrate that the approach is robust against obstacle scattering. The realization of accelerating acoustic beams will have an impact on various applications where acoustic information and energy are required to be delivered along an arbitrary convex trajectory.

  17. Adaptive reconnection-based arbitrary Lagrangian Eulerian method

    DOE PAGES

    Bo, Wurigen; Shashkov, Mikhail

    2015-07-21

    We present a new adaptive Arbitrary Lagrangian Eulerian (ALE) method. This method is based on the reconnection-based ALE (ReALE) methodology of Refs. [35], [34] and [6]. The main elements in a standard ReALE method are: an explicit Lagrangian phase on an arbitrary polygonal (in 2D) mesh in which the solution and positions of grid nodes are updated; a rezoning phase in which a new grid is defined by changing the connectivity (using Voronoi tessellation) but not the number of cells; and a remapping phase in which the Lagrangian solution is transferred onto the new grid. Furthermore, in the standard ReALEmore » method, the rezoned mesh is smoothed by using one or several steps toward centroidal Voronoi tessellation, but it is not adapted to the solution in any way.« less

  18. Adaptive reconnection-based arbitrary Lagrangian Eulerian method

    SciTech Connect

    Bo, Wurigen; Shashkov, Mikhail

    2015-07-21

    We present a new adaptive Arbitrary Lagrangian Eulerian (ALE) method. This method is based on the reconnection-based ALE (ReALE) methodology of Refs. [35], [34] and [6]. The main elements in a standard ReALE method are: an explicit Lagrangian phase on an arbitrary polygonal (in 2D) mesh in which the solution and positions of grid nodes are updated; a rezoning phase in which a new grid is defined by changing the connectivity (using Voronoi tessellation) but not the number of cells; and a remapping phase in which the Lagrangian solution is transferred onto the new grid. Furthermore, in the standard ReALE method, the rezoned mesh is smoothed by using one or several steps toward centroidal Voronoi tessellation, but it is not adapted to the solution in any way.

  19. Creating arbitrary quantum vibrational states in a carbon nanotube

    NASA Astrophysics Data System (ADS)

    Wang, Heng; Burkard, Guido

    2016-11-01

    We theoretically study the creation of single- and multiphonon Fock states and arbitrary superpositions of quantum phonon states in a nanomechanical carbon nanotube (CNT) resonator. In our model, a doubly clamped CNT resonator is initialized in the ground state, and a single electron is trapped in a quantum dot which is formed by an electric gate potential and brought into the magnetic field of a micromagnet. The preparation of arbitrary quantum phonon states is based on the coupling between the mechanical motion of the CNT and the electron spin which acts as a nonlinearity. We assume that electrical driving pulses with different frequencies are applied on the system. The quantum information is transferred from the spin qubit to the mechanical motion by the spin-phonon coupling, and the electron spin qubit can be reset by the single-electron spin resonance. We describe Wigner tomography which can be applied at the end to obtain the phase information of the prepared phonon states.

  20. Collisionless Plasma Modeling in an Arbitrary Potential Energy Distribution

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    A new technique for calculating a collisionless plasma along a field line is presented. The primary feature of the new model is that it can handle an arbitrary (including nonmonotonic) potential energy distribution. This was one of the limiting constraints on the existing models in this class, and these constraints are generalized for an arbitrary potential energy composition. The formulation for relating current density to the field-aligned potential as well as formulas for density, temperature and energy flux calculations are presented for several distribution functions, ranging from a bi-Lorentzian with a loss cone to an isotropic Maxwellian. A comparison of these results with previous models shows that the formulation reduces.to the earlier models under similar assumptions.

  1. Fast RBF OGr for solving PDEs on arbitrary surfaces

    NASA Astrophysics Data System (ADS)

    Piret, Cécile; Dunn, Jarrett

    2016-10-01

    The Radial Basis Functions Orthogonal Gradients method (RBF-OGr) was introduced in [1] to discretize differential operators defined on arbitrary manifolds defined only by a point cloud. We take advantage of the meshfree character of RBFs, which give us a high accuracy and the flexibility to represent complex geometries in any spatial dimension. A large limitation of the RBF-OGr method was its large computational complexity, which greatly restricted the size of the point cloud. In this paper, we apply the RBF-Finite Difference (RBF-FD) technique to the RBF-OGr method for building sparse differentiation matrices discretizing continuous differential operators such as the Laplace-Beltrami operator. This method can be applied to solving PDEs on arbitrary surfaces embedded in ℛ3. We illustrate the accuracy of our new method by solving the heat equation on the unit sphere.

  2. Convergence Rates for Arbitrary Statistical Moments of Random Quantum Circuits

    NASA Astrophysics Data System (ADS)

    Brown, Winton G.; Viola, Lorenza

    2010-06-01

    We consider a class of random quantum circuits where at each step a gate from a universal set is applied to a random pair of qubits, and determine how quickly averages of arbitrary finite-degree polynomials in the matrix elements of the resulting unitary converge to Haar measure averages. This is accomplished by mapping the superoperator that describes t order moments on n qubits to a multilevel SU(4t) Lipkin-Meshkov-Glick Hamiltonian. We show that, for arbitrary fixed t, the ground-state manifold is exactly spanned by factorized eigenstates and, under the assumption that a mean-field ansatz accurately describes the low-lying excitations, the spectral gap scales as 1/n in the thermodynamic limit. Our results imply that random quantum circuits yield an efficient implementation of γ approximate unitary t designs.

  3. Chordwise and compressibility corrections for arbitrary planform slender wings

    NASA Technical Reports Server (NTRS)

    Levin, D.; Seginer, A.

    1982-01-01

    The Lomax and Sluder method for adapting slender-wing theory to delta or rectangular wings by making chordwise and compressibility corrections is extended to cover wings of any arbitrary planform in subsonic and supersonic flows. The numerical accuracy of the present work is better than that of the Lomax-Sluder results. Comparison of the results of this work with those of the vortex-lattice method and Kernel function method for a family of Gothic and arrowhead wings shows good agreement. A universal curve is proposed for the evaluation of the lift coefficient of a low aspect ratio wing of an arbitrary planform in subsonic flow. The location of the center of pressure can also be estimated.

  4. Sum uncertainty relations for arbitrary N incompatible observables

    PubMed Central

    Chen, Bin; Fei, Shao-Ming

    2015-01-01

    We formulate uncertainty relations for arbitrary N observables. Two uncertainty inequalities are presented in terms of the sum of variances and standard deviations, respectively. The lower bounds of the corresponding sum uncertainty relations are explicitly derived. These bounds are shown to be tighter than the ones such as derived from the uncertainty inequality for two observables [Phys. Rev. Lett. 113, 260401 (2014)]. Detailed examples are presented to compare among our results with some existing ones. PMID:26370360

  5. Exact equation for curved stationary flames with arbitrary gas expansion.

    PubMed

    Kazakov, Kirill A

    2005-03-11

    An exact equation describing freely propagating stationary flames with arbitrary values of the gas expansion coefficient is obtained. This equation respects all conservation laws at the flame front, and provides a consistent nonperturbative account of the effect of vorticity produced by the curved flame on the front structure. It is verified that the new equation is in agreement with the approximate equations derived previously in the case of weak gas expansion.

  6. Adaptive Haar transforms with arbitrary time and scale splitting

    NASA Astrophysics Data System (ADS)

    Egiazarian, Karen O.; Astola, Jaakko T.

    2001-05-01

    The Haar transform is generalized to the case of an arbitrary time and scale splitting. To any binary tree we associate an orthogonal system of Haar-type functions - tree-structured Haar (TSH) functions. Unified fast algorithm for computation of the introduced tree-structured Haar transforms is presented. It requires 2(N - 1) additions and 3N - 2 multiplications, where N is transform order or, equivalently, the number of leaves of the binary tree.

  7. Arbitrary waveform generator to improve laser diode driver performance

    SciTech Connect

    Fulkerson, Jr, Edward Steven

    2015-11-03

    An arbitrary waveform generator modifies the input signal to a laser diode driver circuit in order to reduce the overshoot/undershoot and provide a "flat-top" signal to the laser diode driver circuit. The input signal is modified based on the original received signal and the feedback from the laser diode by measuring the actual current flowing in the laser diode after the original signal is applied to the laser diode.

  8. Light evolution in arbitrary two-dimensional waveguide arrays

    SciTech Connect

    Szameit, Alexander; Pertsch, Thomas; Dreisow, Felix; Nolte, Stefan; Tuennermann, Andreas; Peschel, Ulf; Lederer, Falk

    2007-05-15

    We introduce an analytical formula for the dynamics of light propagation in a two-dimensional waveguide lattice including diagonal coupling. A superposition of infinite arrays created by imaginary sources is used to derive an expression for boundary reflections. It is shown analytically that for large propagation distances the propagating field reaches uniformity. Furthermore, periodic field recovery is studied and discrete anomalous refraction and diffraction are investigated in arbitrary two-dimensional lattices.

  9. A Dynamically Adaptive Arbitrary Lagrangian-Eulerian Method for Hydrodynamics

    SciTech Connect

    Anderson, R W; Pember, R B; Elliott, N S

    2002-10-19

    A new method that combines staggered grid Arbitrary Lagrangian-Eulerian (ALE) techniques with structured local adaptive mesh refinement (AMR) has been developed for solution of the Euler equations. The novel components of the combined ALE-AMR method hinge upon the integration of traditional AMR techniques with both staggered grid Lagrangian operators as well as elliptic relaxation operators on moving, deforming mesh hierarchies. Numerical examples demonstrate the utility of the method in performing detailed three-dimensional shock-driven instability calculations.

  10. A Dynamically Adaptive Arbitrary Lagrangian-Eulerian Method for Hydrodynamics

    SciTech Connect

    Anderson, R W; Pember, R B; Elliott, N S

    2004-01-28

    A new method that combines staggered grid Arbitrary Lagrangian-Eulerian (ALE) techniques with structured local adaptive mesh refinement (AMR) has been developed for solution of the Euler equations. The novel components of the combined ALE-AMR method hinge upon the integration of traditional AMR techniques with both staggered grid Lagrangian operators as well as elliptic relaxation operators on moving, deforming mesh hierarchies. Numerical examples demonstrate the utility of the method in performing detailed three-dimensional shock-driven instability calculations.

  11. Self-forces on static bodies in arbitrary dimensions

    NASA Astrophysics Data System (ADS)

    Harte, Abraham I.; Flanagan, Éanna É.; Taylor, Peter

    2016-06-01

    We derive exact expressions for the scalar and electromagnetic self-forces and self-torques acting on arbitrary static extended bodies in arbitrary static spacetimes with any number of dimensions. Nonperturbatively, our results are identical in all dimensions. Meaningful point particle limits are quite different in different dimensions, however. These limits are defined and evaluated, resulting in simple "regularization algorithms" which can be used in concrete calculations. In these limits, self-interaction is shown to be progressively less important in higher numbers of dimensions; it generically competes in magnitude with increasingly high-order extended-body effects. Conversely, we show that self-interaction effects can be relatively large in 1 +1 and 2 +1 dimensions. Our motivations for this work are twofold: First, no previous derivation of the self-force has been provided in arbitrary dimensions, and heuristic arguments presented by different authors have resulted in conflicting conclusions. Second, the static self-force problem in arbitrary dimensions provides a valuable test bed with which to continue the development of general, nonperturbative methods in the theory of motion. Several new insights are obtained in this direction, including a significantly improved understanding of the renormalization process. We also show that there is considerable freedom to use different "effective fields" in the laws of motion—a freedom which can be exploited to optimally simplify specific problems. Different choices give rise to different inertias, gravitational forces, and electromagnetic or scalar self-forces, but there is a sense in which none of these quantities are individually accessible to experiment. Certain combinations are observable, however, and these remain invariant under all possible field redefinitions.

  12. Irreducible Cartesian tensors of highest weight, for arbitrary order

    NASA Astrophysics Data System (ADS)

    Mane, S. R.

    2016-03-01

    A closed form expression is presented for the irreducible Cartesian tensor of highest weight, for arbitrary order. Two proofs are offered, one employing bookkeeping of indices and, after establishing the connection with the so-called natural tensors and their projection operators, the other one employing purely coordinate-free tensor manipulations. Some theorems and formulas in the published literature are generalized from SO(3) to SO(n), for dimensions n ≥ 3.

  13. Unsteady aerodynamic modeling for arbitrary motions. [for active control techniques

    NASA Technical Reports Server (NTRS)

    Edwards, J. W.

    1977-01-01

    Results indicating that unsteady aerodynamic loads derived under the assumption of simple harmonic motions executed by airfoil or wing can be extended to arbitrary motions are summarized. The generalized Theodorsen (1953) function referable to loads due to simple harmonic oscillations of a wing section in incompressible flow, the Laplace inversion integral for unsteady aerodynamic loads, calculations of root loci of aeroelastic loads, and analysis of generalized compressible transient airloads are discussed.

  14. Scattering of point source illumination by an arbitrary configuration

    NASA Technical Reports Server (NTRS)

    Solakiewicz, Richard

    1994-01-01

    The problem of electromagnetic scattering of an incident plane wave by an arbitrary configuration of obstacles was solved by Twersky. In this report, the results are extended to point source incidence corresponding to a Hertz dipole. Knowledge of the response of a fixed configuration of scatterers excited by a point source may provide insight to improve the accuracy of the values of bulk parameters for clouds which have been found using plane wave excitation.

  15. Modeling Transition to Turbulence using the Turbulent Potential Model

    NASA Astrophysics Data System (ADS)

    Chang, Wang; Perot, Blair

    2001-11-01

    While transition is a very different phenomenon from fully developed turbulence, it is governed, on average, by equations with are mathematically the same as the RANS equations for fully turbulent flow. It is therefore theoretically possible for RANS equation systems to display transition-like behavior a very rapid growth in turbulent kinetic energy levels, skin friction, etc. In this work, the ability of the turbulent potential model to accurately predict laminar to turbulent transition in flat plate boundary layers is examined. The model accurately predicts the entire range of free-stream turbulence levels from strong bypass transition (6natural transition (0.03It shows correct sensitivity to favorable and adverse pressure gradients, as well as acoustic noise levels. Past results indicated the ability of the model to relaminarize the flow. Recent work has focused attention on the model’s ability to predict transition in mixing layers.

  16. Bidirectional energy cascades and the origin of kinetic Alfvénic and whistler turbulence in the solar wind.

    PubMed

    Che, H; Goldstein, M L; Viñas, A F

    2014-02-14

    The observed steep kinetic scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quiet time suggest them as a possible source of free energy to drive kinetic turbulence. Using particle-in-cell simulations, we explore how the free energy released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler turbulence are excited that evolve through inverse and forward magnetic energy cascades.

  17. Radiation force of an arbitrary acoustic beam on an elastic sphere in a fluid

    PubMed Central

    Sapozhnikov, Oleg A.; Bailey, Michael R.

    2013-01-01

    A theoretical approach is developed to calculate the radiation force of an arbitrary acoustic beam on an elastic sphere in a liquid or gas medium. First, the incident beam is described as a sum of plane waves by employing conventional angular spectrum decomposition. Then, the classical solution for the scattering of a plane wave from an elastic sphere is applied for each plane-wave component of the incident field. The net scattered field is expressed as a superposition of the scattered fields from all angular spectrum components of the incident beam. With this formulation, the incident and scattered waves are superposed in the far field to derive expressions for components of the radiation stress tensor. These expressions are then integrated over a spherical surface to analytically describe the radiation force on an elastic sphere. Limiting cases for particular types of incident beams are presented and are shown to agree with known results. Finally, the analytical expressions are used to calculate radiation forces associated with two specific focusing transducers. PMID:23363086

  18. Resonant ultrasound spectroscopy for materials with high damping and samples of arbitrary geometry

    SciTech Connect

    Remillieux, Marcel C.; Ulrich, T. J.; Payan, Cédric; Rivière, Jacques; Lake, Colton R.; Le Bas, Pierre -Yves

    2015-07-23

    This paper describes resonant ultrasound spectroscopy (RUS) as a powerful and established technique for measuring elastic constants of a material with general anisotropy. The first step of this technique consists of extracting resonance frequencies and damping from the vibrational frequency spectrum measured on a sample with free boundary conditions. An inversion technique is then used to retrieve the elastic tensor from the measured resonance frequencies. As originally developed, RUS has been mostly applicable to (i) materials with small damping such that the resonances of the sample are well separated and (ii) samples with simple geometries for which analytical solutions exist. In this paper, these limitations are addressed with a new RUS approach adapted to materials with high damping and samples of arbitrary geometry. Resonances are extracted by fitting a sum of exponentially damped sinusoids to the measured frequency spectrum. The inversion of the elastic tensor is achieved with a genetic algorithm, which allows searching for a global minimum within a discrete and relatively wide solution space. First, the accuracy of the proposed approach is evaluated against numerical data simulated for samples with isotropic symmetry and transversely isotropic symmetry. Subsequently, the applicability of the approach is demonstrated using experimental data collected on a composite structure consisting of a cylindrical sample of Berea sandstone glued to a large piezoelectric disk. In the proposed experiments, RUS is further enhanced by the use of a 3-D laser vibrometer allowing the visualization of most of the modes in the frequency band studied.

  19. Resonant ultrasound spectroscopy for materials with high damping and samples of arbitrary geometry

    DOE PAGES

    Remillieux, Marcel C.; Ulrich, T. J.; Payan, Cédric; ...

    2015-07-23

    This paper describes resonant ultrasound spectroscopy (RUS) as a powerful and established technique for measuring elastic constants of a material with general anisotropy. The first step of this technique consists of extracting resonance frequencies and damping from the vibrational frequency spectrum measured on a sample with free boundary conditions. An inversion technique is then used to retrieve the elastic tensor from the measured resonance frequencies. As originally developed, RUS has been mostly applicable to (i) materials with small damping such that the resonances of the sample are well separated and (ii) samples with simple geometries for which analytical solutions exist.more » In this paper, these limitations are addressed with a new RUS approach adapted to materials with high damping and samples of arbitrary geometry. Resonances are extracted by fitting a sum of exponentially damped sinusoids to the measured frequency spectrum. The inversion of the elastic tensor is achieved with a genetic algorithm, which allows searching for a global minimum within a discrete and relatively wide solution space. First, the accuracy of the proposed approach is evaluated against numerical data simulated for samples with isotropic symmetry and transversely isotropic symmetry. Subsequently, the applicability of the approach is demonstrated using experimental data collected on a composite structure consisting of a cylindrical sample of Berea sandstone glued to a large piezoelectric disk. In the proposed experiments, RUS is further enhanced by the use of a 3-D laser vibrometer allowing the visualization of most of the modes in the frequency band studied.« less

  20. Growing multiplex networks with arbitrary number of layers

    NASA Astrophysics Data System (ADS)

    Momeni, Naghmeh; Fotouhi, Babak

    2015-12-01

    This paper focuses on the problem of growing multiplex networks. Currently, the results on the joint degree distribution of growing multiplex networks present in the literature pertain to the case of two layers and are confined to the special case of homogeneous growth and are limited to the state state (that is, the limit of infinite size). In the present paper, we first obtain closed-form solutions for the joint degree distribution of heterogeneously growing multiplex networks with arbitrary number of layers in the steady state. Heterogeneous growth means that each incoming node establishes different numbers of links in different layers. We consider both uniform and preferential growth. We then extend the analysis of the uniform growth mechanism to arbitrary times. We obtain a closed-form solution for the time-dependent joint degree distribution of a growing multiplex network with arbitrary initial conditions. Throughout, theoretical findings are corroborated with Monte Carlo simulations. The results shed light on the effects of the initial network on the transient dynamics of growing multiplex networks and takes a step towards characterizing the temporal variations of the connectivity of growing multiplex networks, as well as predicting their future structural properties.

  1. A compact, multichannel, and low noise arbitrary waveform generator

    NASA Astrophysics Data System (ADS)

    Govorkov, S.; Ivanov, B. I.; Il'ichev, E.; Meyer, H.-G.

    2014-05-01

    A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation.

  2. A compact, multichannel, and low noise arbitrary waveform generator.

    PubMed

    Govorkov, S; Ivanov, B I; Il'ichev, E; Meyer, H-G

    2014-05-01

    A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation.

  3. A compact, multichannel, and low noise arbitrary waveform generator

    SciTech Connect

    Govorkov, S.; Ivanov, B. I.; Il'ichev, E.; Meyer, H.-G.

    2014-05-15

    A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation.

  4. Controlled-Turbulence Bioreactors

    NASA Technical Reports Server (NTRS)

    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.

  5. Homogeneous quantum electrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1992-01-01

    The electromagnetic field equations and Dirac equations for oppositely charged wave functions are numerically time-integrated using a spatial Fourier method. The numerical approach used, a spectral transform technique, is based on a continuum representation of physical space. The coupled classical field equations contain a dimensionless parameter which sets the strength of the nonlinear interaction (as the parameter increases, interaction volume decreases). For a parameter value of unity, highly nonlinear behavior in the time-evolution of an individual wave function, analogous to ideal fluid turbulence, is observed. In the truncated Fourier representation which is numerically implemented here, the quantum turbulence is homogeneous but anisotropic and manifests itself in the nonlinear evolution of equilibrium modal spatial spectra for the probability density of each particle and also for the electromagnetic energy density. The results show that nonlinearly interacting fermionic wave functions quickly approach a multi-mode, dynamic equilibrium state, and that this state can be determined by numerical means.

  6. Turbulent nonreacting swirling flows

    NASA Astrophysics Data System (ADS)

    Ramos, J. I.

    1984-06-01

    Numerical results for incompressible confined swirling flows in a model combustor were obtained using the k-epsilon and k-l models of turbulence developed by Ramos (1980, 1981). Calculations were performed for a model combustor consisting of a 3.43-cm diameter inner pipe and a 14.5-cm diameter outer pipe. The outside diameter of the inner pipe is 3.86 cm. It is shown that the k-epsilon model does predict a recirculation zone for both coswirl and counterswirl flow conditions if suitable inlet conditions are used. Both turbulence models predict a nonexistent recirculation zone under coswirl conditions. The calculated mean axial and tangential velocity profiles are compared with the experimental data of Vu and Gouldin (1980).

  7. Measurements of Turbulent Dissipation During the Bahamas Optical Turbulence Experiment

    DTIC Science & Technology

    2013-07-16

    Bahamas Optical Turbulence Experiment 0601153N 73-6604-03-5 Silvia Matt, Weilin Hou, Sarah Woods, Ewa Jarosz, Wesley Goode and Alan Weidemann Naval...of turbulent dissipation during the Bahamas Optical Turbulence Experiment Silvia Matt 1,2, Weilin Hou 2, Sarah Woods 3, Ewa Jarosz 2, Wesley Goode 2...SPEC Inc., Boulder, CO, USA Corresponding author: Silvia Matt: E-mail: silvia.matt.ctr.de@nrlssc.navy.mil Figure 1. Location of stations during BOTEX

  8. Symmetries in Turbulent Boundary Layer Flows

    NASA Technical Reports Server (NTRS)

    Oberlack, M.

    1996-01-01

    The objective is the development of a new theory which enables the algorithmic computation of all self-similar mean velocity profiles. The theory is based on Liegroup analysis and unifies a large set of self-similar solutions for the mean velocity of stationary parallel turbulent shear flows. The results include the logarithmic law of the wall, an algebraic law, the viscous sublayer, the linear region in the middle of a Couette flow and in the middle of a rotating channel flow, and a new exponential mean velocity profile not previously reported. Experimental results taken in the outer parts of a high Reynolds number flat-plate boundary layer, strongly support the exponential profile. From experimental as well as from DNS data of a turbulent channel flow the algebraic scaling law could be confirmed in both the center region and in the near wall region. In the case of the logarithmic law of the wall, the scaling with the wall distance arises as a result of the analysis and has not been assumed in the derivation. The crucial part of the derivation of all the different mean velocity profiles is to consider the invariance of the equation for the velocity fluctuations at the same time as the invariance of the equation for the velocity product equations. The latter is the dyad product of the velocity fluctuations with the equation for the velocity fluctuations. It has been proven that all the invariant solutions are also consistent with similarity of all velocity moment equations up to any arbitrary order.

  9. Covariance statistics of turbulence velocity components for wind-energy-conversion system design-homogeneous, isotropic case

    SciTech Connect

    Fichtl, G.H.

    1983-09-01

    When designing a wind energy converison system (WECS), it may be necessary to take into account the distribution of wind across the disc of rotation. The specific engineering applications include structural strength, fatigue, and control. This wind distribution consists of two parts, namely that associated with the mean wind profile and that associated with the turbulence velocity fluctuation field. The work reported herein is aimed at the latter, namely the distribution of turbulence velocity fluctuations across the WECS disk of rotation. A theory is developed for the two-time covariance matrix for turbulence velocity vector components for wind energy conversion system (WECS) design. The theory is developed for homogeneous and iotropic turbulance with the assumption that Taylor's hypothesis is valid. The Eulerian turbulence velocity vector field is expanded about the hub of the WECS. Formulae are developed for the turbulence velocity vector component covariance matrix following the WECS blade elements. It is shown that upon specification of the turbulence energy spectrum function and the WECS rotation rate, the two-point, two-time covariance matrix of the turbulent flow relative to the WECS bladed elements is determined. This covariance matrix is represented as the sum of nonstationary and stationary contributions. Generalized power spectral methods are used to obtain two-point, double frequency power spectral density functions for the turbulent flow following the blade elements. The Dryden turbulence model is used to demonstrate the theory. A discussion of linear system response analysis is provided to show how the double frequency turbulence spectra might be used to calculate response spectra of a WECS to turbulent flow. Finally the spectrum of the component of turbulence normal to the WECS disc of rotation, following the blade elements, is compared with experimental results.

  10. TURBULENT GENERAL MAGNETIC RECONNECTION

    SciTech Connect

    Eyink, G. L.

    2015-07-10

    Plasma flows with a magnetohydrodynamic (MHD)-like turbulent inertial range, such as the solar wind, require a generalization of general magnetic reconnection (GMR) theory. We introduce the slip velocity source vector per unit arclength of field line, the ratio of the curl of the non-ideal electric field in the generalized Ohm’s Law and magnetic field strength. It diverges at magnetic nulls, unifying GMR with null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of quasi-potential (which is the integral of parallel electric field along magnetic field lines). In a turbulent inertial range, the non-ideal field becomes tiny while its curl is large, so that line slippage occurs even while ideal MHD becomes accurate. The resolution is that ideal MHD is valid for a turbulent inertial range only in a weak sense that does not imply magnetic line freezing. The notion of weak solution is explained in terms of renormalization group (RG) type theory. The weak validity of the ideal Ohm’s law in the inertial range is shown via rigorous estimates of the terms in the generalized Ohm’s Law. All non-ideal terms are irrelevant in the RG sense and large-scale reconnection is thus governed solely by ideal dynamics. We discuss the implications for heliospheric reconnection, in particular for deviations from the Parker spiral model. Solar wind observations show that reconnection in a turbulence-broadened heliospheric current sheet, which is consistent with Lazarian–Vishniac theory, leads to slip velocities that cause field lines to lag relative to the spiral model.

  11. Turbulence Environment Characterization

    DTIC Science & Technology

    1979-06-01

    of ro is consistent with the simultaneous measurement made with the Seeing Monitor. An average turbulent profile developed primarily from microthermal ...data. The operation of the routine meteorological instrumentation, microthermal probes, acoustic sounder, Seeing Monitor and Star Sensor have been...and J. Spencer of RADC gave sub- stantial support and assistance with the microthermal probes, acoustic sounder and PDP-8 software. We acknowledge R

  12. Fountain-Jet Turbulence.

    DTIC Science & Technology

    1980-09-01

    and 3 times higher than expected from free- jet results. Hill et al., (Reference 6) in work with foun- tain jets impacting fuselage models, detected ...delineate the origins of the turbulent anomalies associated with fountain jets by extending the previous studies. The results are presented herein...jet velocities were detected with a Thermal Systems Inc. Model 1050 dual-channel constant-temperature anemometer equipped with a Thermal Systems Inc

  13. Interaction of a turbulent-jet noise source with transverse modes in a rectangular duct

    NASA Technical Reports Server (NTRS)

    Succi, G. P.; Baumeister, K. J.; Ingard, K. U.

    1978-01-01

    A turbulent jet was used to excite transverse acoustic modes in a rectangular duct. The pressure spectrum showed asymmetric singularities (pressure spikes) at the resonant frequencies of the duct modes. This validates previously published theoretical results. These pressure spikes occurred over a range of jet velocities, orientations, and inlet turbulence levels. At the frequency of the spike, the measured transverse pressure shape matched the resonant mode shape.

  14. SIMPLE ANALYTICAL FORMS OF THE PERPENDICULAR DIFFUSION COEFFICIENT FOR TWO-COMPONENT TURBULENCE. I. MAGNETOSTATIC TURBULENCE

    SciTech Connect

    Shalchi, A.

    2013-09-01

    We explore perpendicular diffusion based on the unified nonlinear transport theory. We derive simple analytical forms for the perpendicular mean free path and investigate the influence of different model spectra. We show that for cases where the field line random walk is normal diffusive, the perpendicular diffusion coefficient consists of only two transport regimes. Details of the spectral shape are less important, especially those of the inertial range. Only the macroscopic properties of the turbulence spectrum control the perpendicular diffusion coefficient. Simple formulae for the perpendicular diffusion coefficient are derived which can easily be implemented in solar modulation or shock acceleration codes.

  15. Sound radiation from a high speed axial flow fan due to the inlet turbulence quadrupole interaction

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Rosenbaum, B. M.; Albers, L. U.

    1974-01-01

    A formula is obtained for the total acoustic power spectra radiated out the front of the fan as a function of frequency. The formula involves the design parameters of the fan as well as the statistical properties of the incident turbulence. Numerical results are calculated for values of the parameters in the range of interest for quiet fans tested at the Lewis Research Center. As in the dipole analysis, when the turbulence correlation lengths become equal to the interblade spacing, the predicted spectra exhibit peaks around the blade passing frequency and its harmonics. There has recently been considerable conjecture about whether the stretching of turbulent eddies as they enter a stationary fan could result in the inlet turbulence being the dominant source of pure tones from nontranslating fans. The results of the current analysis show that, unless the turbulent eddies become quite elongated, this noise source contributes predominantly to the broadband spectrum.

  16. Optical diagnostics for turbulent and multiphase flows: Particle image velocimetry and photorefractive optics

    SciTech Connect

    O`Hern, T.J.; Torczynski, J.R.; Shagam, R.N.; Blanchat, T.K.; Chu, T.Y.; Tassin-Leger, A.L.; Henderson, J.A.

    1997-01-01

    This report summarizes the work performed under the Sandia Laboratory Directed Research and Development (LDRD) project ``Optical Diagnostics for Turbulent and Multiphase Flows.`` Advanced optical diagnostics have been investigated and developed for flow field measurements, including capabilities for measurement in turbulent, multiphase, and heated flows. Particle Image Velocimetry (PIV) includes several techniques for measurement of instantaneous flow field velocities and associated turbulence quantities. Nonlinear photorefractive optical materials have been investigated for the possibility of measuring turbulence quantities (turbulent spectrum) more directly. The two-dimensional PIV techniques developed under this LDRD were shown to work well, and were compared with more traditional laser Doppler velocimetry (LDV). Three-dimensional PIV techniques were developed and tested, but due to several experimental difficulties were not as successful. The photorefractive techniques were tested, and both potential capabilities and possible problem areas were elucidated.

  17. Analysis of temporal power spectra for optical waves propagating through weak anisotropic non-Kolmogorov turbulence.

    PubMed

    Cui, Linyan

    2015-06-01

    Analytic expressions for the temporal power spectra of irradiance fluctuations and angle of arrival (AOA) fluctuations are derived for optical waves propagating through weak anisotropic non-Kolmogorov atmospheric turbulence. In the derivation, the anisotropic non-Kolmogorov spectrum is adopted, which adopts the assumption of circular symmetry in the orthogonal plane throughout the path and the same degree of anisotropy along the propagation direction for all the turbulence cells. The final expressions consider simultaneously the anisotropic factor and general spectral power law values. When the anisotropic factor equals one (corresponding to the isotropic turbulence), the derived temporal power spectral models have good consistency with the known results for the isotropic turbulence. Numerical calculations show that the increased anisotropic factor alleviates the atmospheric turbulence's influence on the final expressions.

  18. Gyrokinetic simulations of solar wind turbulence from ion to electron scales.

    PubMed

    Howes, G G; TenBarge, J M; Dorland, W; Quataert, E; Schekochihin, A A; Numata, R; Tatsuno, T

    2011-07-15

    A three-dimensional, nonlinear gyrokinetic simulation of plasma turbulence resolving scales from the ion to electron gyroradius with a realistic mass ratio is presented, where all damping is provided by resolved physical mechanisms. The resulting energy spectra are quantitatively consistent with a magnetic power spectrum scaling of k(-2.8) as observed in in situ spacecraft measurements of the "dissipation range" of solar wind turbulence. Despite the strongly nonlinear nature of the turbulence, the linear kinetic Alfvén wave mode quantitatively describes the polarization of the turbulent fluctuations. The collisional ion heating is measured at subion-Larmor radius scales, which provides evidence of the ion entropy cascade in an electromagnetic turbulence simulation.

  19. Synergies between Asteroseismology and Three-dimensional Simulations of Stellar Turbulence

    NASA Astrophysics Data System (ADS)

    Arnett, W. David; Moravveji, E.

    2017-02-01

    Turbulent mixing of chemical elements by convection has fundamental effects on the evolution of stars. The standard algorithm at present, mixing-length theory (MLT), is intrinsically local, and must be supplemented by extensions with adjustable parameters. As a step toward reducing this arbitrariness, we compare asteroseismically inferred internal structures of two Kepler slowly pulsating B stars (SPBs; M∼ 3.25{M}ȯ ) to predictions of 321D turbulence theory, based upon well-resolved, truly turbulent three-dimensional simulations that include boundary physics absent from MLT. We find promising agreement between the steepness and shapes of the theoretically predicted composition profile outside the convective region in 3D simulations and in asteroseismically constrained composition profiles in the best 1D models of the two SPBs. The structure and motion of the boundary layer, and the generation of waves, are discussed.

  20. Controllability of flow turbulence.

    PubMed

    Guan, Shuguang; Wei, G W; Lai, C-H

    2004-06-01

    In this paper, we study the controllability of real-world flow turbulence governed by the two-dimensional Navier-Stokes equations, using strategies developed in chaos control. A case of control/synchronization of turbulent dynamics is observed when only one component of the velocity field vector is unidirectionally coupled to a target state, while the other component is uncoupled. Unlike previous results, it is shown that the dynamics of the whole velocity field cannot be completely controlled/synchronized to the target, even in the limit of long time and strong coupling strength. It is further revealed that the controlled component of the velocity field can be fully controlled/synchronized to the target, but the other component, which is not directly coupled to the target, can only be partially controlled/synchronized to the target. By extending an auxiliary method to distributed dynamic systems, the partial synchronization of two turbulent orbits in the present study can be categorized in the domain of generalized synchronization of spatiotemporal dynamics.

  1. Anomalous anisotropies of cosmic rays from turbulent magnetic fields.

    PubMed

    Ahlers, Markus

    2014-01-17

    The propagation of cosmic rays (CRs) in turbulent interstellar magnetic fields is typically described as a spatial diffusion process. This formalism predicts only a small deviation from an isotropic CR distribution in the form of a dipole in the direction of the CR density gradient or relative background flow. We show that the existence of a global CR dipole moment necessarily generates a spectrum of higher multipole moments in the local CR distribution. These anomalous anisotropies are a direct consequence of Liouville's theorem in the presence of a local turbulent magnetic field. We show that the predictions of this model are in excellent agreement with the observed power spectrum of multi-TeV CRs.

  2. Suppression of turbulent resistivity in turbulent Couette flow

    SciTech Connect

    Si, Jiahe Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.

    2015-07-15

    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.

  3. APPLICATIONS OF LASERS AND OTHER TOPICS IN LASER PHYSICS AND TECHNOLOGY: Adaptive compensation of atmospheric phase distortions using the spatial spectrum of images

    NASA Astrophysics Data System (ADS)

    Anufriev, A. V.; Zimin, Yu A.; Tolmachev, Alexei I.

    1987-10-01

    A theoretical investigation is reported of an algorithm for adaptive compensation of atmospheric phase distortions using the spatial spectrum of images. This algorithm can be used to reconstruct images of incoherently illuminated objects of arbitrary shape.

  4. An improved arbitrary primed PCR method for rapid characterization of transposon insertion sites.

    PubMed

    Das, Sankar; Noe, Jody C; Paik, Sehmi; Kitten, Todd

    2005-10-01

    Modifications were made to published arbitrary primed polymerase chain reaction (AP-PCR) procedures that resulted in increased specificity and sensitivity. Several arbitrary primer sequences were also evaluated, resulting in recommendations for primer design.

  5. Mueller matrix for an ensemble of particles of arbitrary shape with an arbitrary square integrable orientation distribution function

    SciTech Connect

    Paramonov, L.E.

    1994-12-01

    Scattering of electromagnetic radiation from the elementary volume containing particles of an arbitrary shape with an arbitrary square integrable orientation distribution function is considered. Based on the T-matrix approach and the quantum theory of angular momentum, an analytical method is suggested for estimating the Mueller matrix elements and the Stokes vector of radiation scattered from an ensemble of particles in the case of an arbituary number of incident radiation sources. The constructive existence theorem is proved for the expansion of the scattering matrix elements as a power series in Wigner functions in the elementary volume having a rotational symmetry relative to the direction of the incident radiation propagation. Corollaries of the results obtained are considered. 24 refs.

  6. On the Two Components of Turbulent Mixing Noise from Supersonic Jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Golebiowski, Michel; Seiner, J. M.

    1996-01-01

    It is argued that because of the lack of intrinsic length and time scales in the core part of the jet flow, the radiated noise spectrum of a high-speed jet should exhibit similarity. A careful analysis of all the axisymmetric supersonic jet noise spectra in the data-bank of the Jet Noise Laboratory of the NASA Langley Research Center has been carried out. Two similarity spectra, one for the noise from the large turbulence structures/instability waves of the jet flow, the other for the noise from the fine-scale turbulence, are identified. The two similarity spectra appear to be universal spectra for axisymmetric jets. They fit all the measured data including those from subsonic jets. Experimental evidence are presented showing that regardless of whether a jet is supersonic or subsonic the noise characteristics and generation mechanisms are the same. There is large turbulence structures/instability waves noise from subsonic jets. This noise component can be seen prominently inside the cone of silence of the fine-scale turbulence noise near the jet axis. For imperfectly expanded supersonic jets, a shock cell structure is formed inside the jet plume. Measured spectra are provided to demonstrate that the presence of a shock cell structure has little effect on the radiated turbulent mixing noise. The shape of the noise spectrum as well as the noise intensity remain practically the same as those of a fully expanded jet. However, for jets undergoing strong screeching, there is broadband noise amplification for both turbulent mixing noise components. It is discovered through a pilot study of the noise spectrum of rectangular and elliptic supersonic jets that the turbulent mixing noise of these jets is also made up of the same two noise components found in axisymmetric jets. The spectrum of each individual noise component also fits the corresponding similarity spectrum of axisymmetric jets.

  7. Investigation of the frozen-turbulence hypothesis for temperature spectra in a convectively mixed layer

    NASA Astrophysics Data System (ADS)

    Deardorff, J. W.; Willis, G. E.

    1982-01-01

    Taylor's frozen turbulence hypothesis is investigated in a laboratory free-convection mixed layer which can simulate buoyancy-driven turbulence in an atmospheric mixed layer (of height h) for mean wind speeds of up to several meters per second. For large turbulence intensities the temperature spectra at the height 0.1h are found to be spuriously enhanced at higher wavenumbers based on the frozen turbulence hypothesis, as deduced theoretically by previous investigators. The excess is borrowed from spectral intensities within the energy-containing range. A theory based on the concept of longitudinal-temporal isotropy, after proper scaling of the coordinates, is shown to predict a simple shift of the entire spectrum toward higher wavenumbers with increasing turbulence intensity. The failure of the observed spectra to behave this simply is associated with a complicated structure of the correlation coefficient as a function of longitudinal-temporal lag coordinates when the former is measured relative to a frame moving with the mean flow speed. The temperature spectrum based on the frozen-turbulence hypothesis appears to be a satisfactory representation of the true spectrum in wavenumber space, in tubulence dominated by thermal convection, if the mean wind speed exceeds 2.7-3.6 times the root-mean-square horizontal velocity fluctuation.

  8. Scatter Broadening of Pulsars and Implications on the Interstellar Medium Turbulence

    NASA Astrophysics Data System (ADS)

    Xu, Siyao; Zhang, Bing

    2017-01-01

    Observations reveal a uniform Kolmogorov turbulence throughout the diffuse ionized interstellar medium (ISM) and supersonic turbulence preferentially located in the Galactic plane. Correspondingly, we consider the Galactic distribution of electron density fluctuations consisting of not only a Kolmogorov density spectrum but also a short-wave-dominated density spectrum with the density structure formed at small scales due to shocks. The resulting dependence of the scatter broadening time on the dispersion measure (DM) naturally interprets the existing observational data for both low- and high-DM pulsars. According to the criteria that we derive for a quantitative determination of scattering regimes over wide ranges of DMs and frequencies ν, we find that the pulsars with low DMs are primarily scattered by the Kolmogorov turbulence, while those at low Galactic latitudes with high DMs undergo more enhanced scattering dominated by the supersonic turbulence, where the corresponding density spectrum has a spectral index of ≈ 2.6. Furthermore, by considering a volume filling factor of the density structures with the dependence on ν as \\propto {ν }1.4 in the supersonic turbulence, our model can also explain the observed shallower ν scaling of the scattering time than the Kolmogorov scaling for the pulsars with relatively large DMs. The comparison between our analytical results and the scattering measurements of pulsars in turn makes a useful probe of the properties of the large-scale ISM turbulence, e.g., an injection scale of ∼100 pc, and also characteristics of small-scale density structures.

  9. Developing `Superbeams’ for Improved Propagation Through Turbulence

    DTIC Science & Technology

    2008-01-31

    Gaussian Schell - model sources). Furthermore, there is an additional ambiguity in studies of partially coherent fields in turbulence, especially when...in action is shown in Fig. 4. Several realizations of a Gaussian Schell - model field in the source plane are pictured. The pictures are separated in...the angular spectrum method result while the dashed curve is based on a standard propagation method for Gaussian beams. The dashed-dotted curve shows

  10. Decay of Pure Quantum Turbulence in Superfluid {sup 3}He-B

    SciTech Connect

    Bradley, D.I.; Clubb, D.O.; Fisher, S.N.; Guenault, A.M.; Haley, R.P.; Matthews, C.J.; Pickett, G.R.; Tsepelin, V.; Zaki, K.

    2006-01-27

    We describe measurements of the decay of pure superfluid turbulence in superfluid {sup 3}He-B, in the low temperature regime where the normal fluid density is negligible. We follow the decay of the turbulence generated by a vibrating grid as detected by vibrating wire resonators. Despite the absence of any classical normal fluid dissipation processes, the decay is consistent with turbulence having the classical Kolmogorov energy spectrum and is remarkably similar to that measured in superfluid {sup 4}He at relatively high temperatures. Further, our results strongly suggest that the decay is governed by the superfluid circulation quantum rather than kinematic viscosity.

  11. Phase-synchronization, energy cascade, and intermittency in solar-wind turbulence.

    PubMed

    Perri, S; Carbone, V; Vecchio, A; Bruno, R; Korth, H; Zurbuchen, T H; Sorriso-Valvo, L

    2012-12-14

    The energy cascade in solar wind magnetic turbulence is investigated using MESSENGER data in the inner heliosphere. The decomposition of magnetic field time series in intrinsic functions, each characterized by a typical time scale, reveals phase reorganization. This allows for the identification of structures of all sizes generated by the nonlinear turbulent cascade, covering both the inertial and the dispersive ranges of the turbulent magnetic power spectrum. We find that the correlation (or anticorrelation) of phases occurs between pairs of neighboring time scales, whenever localized peaks of magnetic energy are present at both scales, consistent with the local character of the energy transfer process.

  12. A new look at decomposition of turbulence forcing field and the structural response

    NASA Technical Reports Server (NTRS)

    Lin, Y. K.; Maekawa, S.

    1976-01-01

    Measured cross-spectrum of a turbulence field usually shows some decay in the statistical correlation in addition to convection at a characteristic velocity. It is shown that a decaying turbulence can be decomposed into frozen-pattern components thus permitting a simpler way to calculate the structural response. This procedure also provides a relationship whereby the measured input spectra can be incorporated. The theory is applied to an infinite beam which is backed on one side by a fluid filled cavity and is exposed on the other side by the turbulence excitation. The effect of the free stream velocity is also taken into consideration.

  13. Study of Nonlinear Interaction and Turbulence of Alfven Waves in LAPD Experiments

    SciTech Connect

    Boldyrev, Stanislav; Perez, Jean Carlos

    2013-11-29

    The complete project had two major goals — investigate MHD turbulence generated by counterpropagating Alfven modes, and study such processes in the LAPD device. In order to study MHD turbulence in numerical simulations, two codes have been used: full MHD, and reduced MHD developed specialy for this project. Quantitative numerical results are obtained through high-resolution simulations of strong MHD turbulence, performed through the 2010 DOE INCITE allocation. We addressed the questions of the spectrum of turbulence, its universality, and the value of the so-called Kolmogorov constant (the normalization coefficient of the spectrum). In these simulations we measured with unprecedented accuracy the energy spectra of magnetic and velocity fluctuations. We also studied the so-called residual energy, that is, the difference between kinetic and magnetic energies in turbulent fluctuations. In our analytic work we explained generation of residual energy in weak MHD turbulence, in the process of random collisions of counterpropagating Alfven waves. We then generalized these results for the case of strong MHD turbulence. The developed model explained generation of residual energy is strong MHD turbulence, and verified the results in numerical simulations. We then analyzed the imbalanced case, where more Alfven waves propagate in one direction. We found that spectral properties of the residual energy are similar for both balanced and imbalanced cases. We then compared strong MHD turbulence observed in the solar wind with turbulence generated in numerical simulations. Nonlinear interaction of Alfv´en waves has been studied in the upgraded Large Plasma Device (LAPD). We have simulated the collision of the Alfven modes in the settings close to the experiment. We have created a train of wave packets with the apltitudes closed to those observed n the experiment, and allowed them to collide. We then saw the generation of the second harmonic, resembling that observed in the

  14. Daytime turbulent exchange between the Amazon forest and the atmosphere

    SciTech Connect

    Fitzjarrald, D.R.; Moore, K.E. ); Cabral, M.R. ); Scolar, J. ); Manzi, A.O.; de Abreau Sa, L.D. )

    1990-09-20

    Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high-frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum and the relationship between the horizontal wind speed and its standard deviation are well described by dry convective boundary layer similarity hypotheses originally found to apply in flat terrain. Diurnal changes in the sign of the vertical velocity skewness observed above and inside the canopy are shown to be plausibly explained by considering the skewness budget. Simple empirical formulas that relate observed turbulent heat fluxes to horizontal wind speed and variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented in three case studies. Even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during midday.

  15. Turbulence in the Earth's cusp region: k-filtering analysis

    NASA Astrophysics Data System (ADS)

    Wang, T.; Cao, J.; Fu, H.; Liu, W.

    2013-12-01

    On April 13 2002, four Cluster spacecraft with separation up to 127 km measured similar turbulence in the Earth's mid-altitude cusp region during southward IMF Bz. Using the k-filtering technique, we obtain the propagation angle and dispersion relation of the turbulence. The propagation angle is quite large and ranges from 80° to 92°, meaning that the turbulence propagates perpendicularly to the background magnetic field. By comparing the dispersion relationship with the linear solution of the Vlasov kinetic theory obtained by WHAMP, we conclude that the turbulence is Kinetic Alfvén mode (KAWs). The regions of KAWs are located within an inhomogeneous high density plasma background, suggesting that it is the ion drift, not field aligned ion beam that plays an important role in the wave generation. The magnetic flied fluctuation spectrum resembles the classical Kolmogorov power law under the proton gyrofrequency ωci, but breaks and steepens near ωci, indicating that the KAW may be powered by a turbulent cascade transverse to the magnetic field from large MHD scales to proton gyroradius scales.

  16. Turbulent processes in Earth's magnetosheath by Cluster mission measurements

    NASA Astrophysics Data System (ADS)

    Kozak, L. V.; Lui, A. T. Y.; Kronberg, E. A.; Prokhorenkov, A. S.

    2017-02-01

    Methods and approaches which can be used for the analysis of hydrodynamic and magnetohydrodynamic turbulent flows are chosen for this study. It is defined that the best methods for determination of turbulent process types are the methods of statistical physics. Within the statistical approach the fractal analysis (height of the maximum of probability density fluctuations of the studied parameters) and multifractal analysis (study of a power dependence of high order statistical moments and construction of multifractal spectrum) are considered. It is indicated that the statistical analysis of turbulent process properties can be supplemented with spectral studies (wavelet analysis). Physical processes in the transition regions of the magnetosphere: foreshock, shock, post-shock and magnetosheath are investigated using high frequency measurements by Cluster satellites. Extended self-similarity analysis and structure function analysis demonstrate the presence of super-diffusion processes and the highest values of generalized diffusion coefficients observed in post-shock region. It can be noted that different approaches for the analysis of turbulent processes give similar results and indicate the presence of super-diffusion processes in the transition region of the Earth's magnetosphere. This fact must be taken into account when constructing quantitative models of a transfer process. Wavelet analysis shows the presence of cascade and inverse cascade processes in the Earth's magnetosheath. Good agreement with other studies and our new results contribute to improvement of our understanding of turbulence.

  17. OH* imager response to turbulence-induced temperature fluctuations

    NASA Astrophysics Data System (ADS)

    Gardner, Chester S.; Vargas, Fabio A.

    2016-12-01

    The layer of the excited state hydroxyl radical (OH*) is formed in the mesopause region by the reaction of ozone (O3) and atomic hydrogen (H). We derive the theoretical expressions for the OH* brightness and rotational temperature (T*) responses to high-frequency atmospheric temperature perturbations. The theory is used to calculate the 1-D and 2-D horizontal wave number spectra of the OH* and T* image fluctuations induced by atmospheric turbulence. By applying the theory to images of a breaking gravity wave packet, acquired by the Utah State University Advanced Mesospheric Temperature Mapper, we show that existing infrared OH* imager technology can observe the evolution of gravity wave breakdown and characterize the resulting turbulent eddies in the source region and in the inertial subrange of the turbulence spectrum. For the example presented here, the RMS OH* brightness fluctuations induced by the gravity wave packet was 2.90% and by the associated turbulence was 1.07%. Unfortunately, the T* fluctuations induced by turbulence are usually too small to be observed in the OH* rotational temperature maps.

  18. Control quantum evolution speed of a single dephasing qubit for arbitrary initial states via periodic dynamical decoupling pulses

    PubMed Central

    Song, Ya-Ju; Tan, Qing-Shou; Kuang, Le-Man

    2017-01-01

    We investigate the possibility to control quantum evolution speed of a single dephasing qubit for arbitrary initial states by the use of periodic dynamical decoupling (PDD) pulses. It is indicated that the quantum speed limit time (QSLT) is determined by initial and final quantum coherence of the qubit, as well as the non-Markovianity of the system under consideration during the evolution when the qubit is subjected to a zero-temperature Ohmic-like dephasing reservoir. It is shown that final quantum coherence of the qubit and the non-Markovianity of the system can be modulated by PDD pulses. Our results show that for arbitrary initial states of the dephasing qubit with non-vanishing quantum coherence, PDD pulses can be used to induce potential acceleration of the quantum evolution in the short-time regime, while PDD pulses can lead to potential speedup and slow down in the long-time regime. We demonstrate that the effect of PDD on the QSLT for the Ohmic or sub-Ohmic spectrum (Markovian reservoir) is much different from that for the super-Ohmic spectrum (non-Markovian reservoir). PMID:28272546

  19. Control quantum evolution speed of a single dephasing qubit for arbitrary initial states via periodic dynamical decoupling pulses

    NASA Astrophysics Data System (ADS)

    Song, Ya-Ju; Tan, Qing-Shou; Kuang, Le-Man

    2017-03-01

    We investigate the possibility to control quantum evolution speed of a single dephasing qubit for arbitrary initial states by the use of periodic dynamical decoupling (PDD) pulses. It is indicated that the quantum speed limit time (QSLT) is determined by initial and final quantum coherence of the qubit, as well as the non-Markovianity of the system under consideration during the evolution when the qubit is subjected to a zero-temperature Ohmic-like dephasing reservoir. It is shown that final quantum coherence of the qubit and the non-Markovianity of the system can be modulated by PDD pulses. Our results show that for arbitrary initial states of the dephasing qubit with non-vanishing quantum coherence, PDD pulses can be used to induce potential acceleration of the quantum evolution in the short-time regime, while PDD pulses can lead to potential speedup and slow down in the long-time regime. We demonstrate that the effect of PDD on the QSLT for the Ohmic or sub-Ohmic spectrum (Markovian reservoir) is much different from that for the super-Ohmic spectrum (non-Markovian reservoir).

  20. Dynamic multiscaling in magnetohydrodynamic turbulence.

    PubMed

    Ray, Samriddhi Sankar; Sahoo, Ganapati; Pandit, Rahul

    2016-11-01

    We present a study of the multiscaling of time-dependent velocity and magnetic-field structure functions in homogeneous, isotropic magnetohydrodynamic (MHD) turbulence in three dimensions. We generalize the formalism that has been developed for analogous studies of time-dependent structure functions in fluid turbulence to MHD. By carrying out detailed numerical studies of such time-dependent structure functions in a shell model for three-dimensional MHD turbulence, we obtain both equal-time and dynamic scaling exponents.