Energy spectrum of buoyancy-driven turbulence.
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. PMID:25215829
Energy spectrum of buoyancy-driven turbulence
NASA Astrophysics Data System (ADS)
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 Πu, we demonstrate that, for stably stratified flows, the kinetic energy spectrum Eu(k)˜k-11/5, the potential energy spectrum Eθ(k)˜k-7/5, and Πu(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 Eu(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 Πu(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 Πu(k) and Eu(k)˜k-5/3 for a narrow band of wave numbers.
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.
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.
RESIDUAL ENERGY SPECTRUM OF SOLAR WIND TURBULENCE
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.
Turbulent diffusion phase transition is due to singular energy spectrum.
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
Wavenumber spectrum of whistler turbulence: Particle-in-cell simulation
Saito, S.; Gary, S. Peter; Narita, Y.
2010-12-15
The forward cascade of decaying whistler turbulence is studied in low beta plasma to understand essential properties of the energy spectrum at electron scales, by using a two-dimensional electromagnetic particle-in-cell (PIC) simulation. This simulation demonstrates turbulence in which the energy cascade rate is greater than the dissipation rate at the electron inertial length. The PIC simulation shows that the magnetic energy spectrum of forward-cascaded whistler turbulence at electron inertial scales is anisotropic and develops a very steep power-law spectrum which is consistent with recent solar wind observations. A comparison of the simulated spectrum with that predicted by a phenomenological turbulence scaling model suggests that the energy cascade at the electron inertial scale depends on both magnetic fluctuations and electron velocity fluctuations, as well as on the whistler dispersion relation. Thus, not only kinetic Alfven turbulence but also whistler turbulence may explain recent solar wind observations of very steep magnetic spectra at short scales.
The spatio-temporal spectrum of turbulent flows.
Clark di Leoni, P; Cobelli, P J; Mininni, P D
2015-12-01
Identification and extraction of vortical structures and of waves in a disorganised flow is a mayor challenge in the study of turbulence. We present a study of the spatio-temporal behavior of turbulent flows in the presence of different restitutive forces. We show how to compute and analyse the spatio-temporal spectrum from data stemming from numerical simulations and from laboratory experiments. Four cases are considered: homogeneous and isotropic turbulence, rotating turbulence, stratified turbulence, and water wave turbulence. For homogeneous and isotropic turbulence, the spectrum allows identification of sweeping by the large-scale flow. For rotating and for stratified turbulence, the spectrum allows identification of the waves, precise quantification of the energy in the waves and in the turbulent eddies, and identification of physical mechanisms such as Doppler shift and wave absorption in critical layers. Finally, in water wave turbulence the spectrum shows a transition from gravity-capillary waves to bound waves as the amplitude of the forcing is increased. PMID:26701711
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.
Calculation of turbulence-driven secondary motion in ducts with arbitrary cross-section
NASA Technical Reports Server (NTRS)
Demuren, A. O.
1990-01-01
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.
Lagrangian Frequency Spectrum as a Diagnostic for Magnetohydrodynamic Turbulence Dynamics
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.
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.
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.
The theoretical model of atmospheric turbulence spectrum in surface layer
NASA Astrophysics Data System (ADS)
Liu, Shida; Liu, Shikuo; Xin, Guojun; Liang, Fuming
1994-12-01
It is shown that the slope of energy spectrum obtained from the velocity solution of Kdv—Burgers equation lies between —5/3 and—2 in the dilogarithmic coordinates paper. The spectrum is very close to one of Kolmogorov's isotropic turbulence and Frisch's intermittent turbulence in inertial region. In this paper, the Kdv-Burgers equation to describe atmospheric boundary layer turbulence is obtained. In the equation, the 1 / R e corresponds to dissipative coefficient v, R /2 t to dispersive coefficient β, then ( v/2 β)2 corresponds to 1 / R 2 e • Ri. We prove that the wave number corresponding to maximum energy spectrum S(k) decreases with the decrease of stability (i.e., the increase of ( v / 2 β)2 in eddy—containing region. And the spectrim amplitude decreases with the increase of ( v / 2 β)2 (i.e., the decrease of stability). These results are consistent with actual turbulence spectrum of atmospheric surface layer from turbulence data.
Quantum Turbulence: Vortex Bundle Collapse and Kolmogorov Spectrum
NASA Astrophysics Data System (ADS)
Nemirovskii, Sergey K.
2015-12-01
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}.
Energy spectrum of stably-stratified and convective turbulent flows
NASA Astrophysics Data System (ADS)
Verma, Mahendra; Kumar, Abhishek
2015-11-01
In the inertial range of fluid turbulence, the energy flux is constant, while the energy spectrum scales as k - 5 / 3 (k=wavenumber). The buoyancy however could change the phenomenology dramatically. Bolgiano and Obukhov (1959) had conjectured that stably stratified flows (as in atmosphere) exhibits a decrease in the energy flux as k - 4 / 5 due to the conversion of kinetic energy to the potential energy, consequently, the energy spectrum scales as k - 11 / 5. We show using detailed numerical analysis that the stably stratified flows indeed exhibit k - 11 / 5 energy spectrum for Froude numbers Fr near unity. The flow becomes anisotropic for small Froude numbers. For weaker buoyancy (large Fr), the kinetic energy follows Kolmogorov's spectrum with a constant energy flux. However, in convective turbulence, the energy flux is a nondecreasing function of wavenumber since the buoyancy feeds positively into the kinetic energy. Hence, the kinetic energy spectrum is Kolmogorov-like (k - 5 / 3) or shallower. We also demonstrate the above scaling using a shell model of buoyancy-driven turbulence.
Spectrums and Diffusion in a Round Turbulent Jet
NASA Technical Reports Server (NTRS)
Corrsin, Stanley; Uberoi, Mahinder S
1950-01-01
In a round turbulent jet at room temperature, measurement of the shear correlation coefficient as a function of frequency (through bandpass filters) has given a rather direct verification of Kolmogoroff's local-isotropy hypothesis. One-dimensional power spectrums of velocity and temperature fluctuations, measured in unheated and heated jets, respectively, have been contrasted. Under the same conditions, the two corresponding transverse correlation functions have been measured and compared. Finally, measurements have been made of the mean thermal wakes behind local (line) heat sources in the unheated turbulent jet, and the order of magnitude of the temperature fluctuations has been determined. (author)
Anomalous k⊥(-8/3) spectrum in electron magnetohydrodynamic turbulence.
Meyrand, Romain; Galtier, Sébastien
2013-12-27
Electron magnetohydrodynamic turbulence is investigated under the presence of a relatively strong external magnetic field b0e∥ and through three-dimensional direct numerical simulations. Our study reveals the emergence of a k⊥(-8/3) scaling for the magnetic energy spectrum at scales k∥(D)≤k⊥≤k⊥(D), where k∥(D) and k⊥(D) are, respectively, the typical largest dissipative scales along and transverse to the b0 direction. Unlike standard magnetohydrodynamic, this turbulence regime is characterized by filaments of electric currents parallel to b0. The anomalous scaling is in agreement with a heuristic model in which the transfer in the parallel direction is negligible. Implications for solar wind turbulence are discussed. PMID:24483798
Weak turbulent Kolmogorov spectrum for surface gravity waves.
Dyachenko, A I; Korotkevich, A O; Zakharov, V E
2004-04-01
We study the long-time evolution of surface gravity waves on deep water excited by a stochastic external force concentrated in moderately small wave numbers. We numerically implemented the primitive Euler equations for the potential flow of an ideal fluid with free surface written in Hamiltonian canonical variables, using the expansion of the Hamiltonian in powers of nonlinearity of terms up to fourth order. We show that because of nonlinear interaction processes a stationary Fourier spectrum of a surface elevation close to <|eta(k)|(2)> approximately k(-7/2) is formed. The observed spectrum can be interpreted as a weak-turbulent Kolmogorov spectrum for a direct cascade of energy. PMID:15089618
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.
Testing the Clauser-Horne-Shimony-Holt inequality using observables with arbitrary spectrum
NASA Astrophysics Data System (ADS)
Ketterer, A.; Keller, A.; Coudreau, T.; Milman, P.
2015-01-01
The Clauser-Horne-Shimony-Holt inequality applies when measurements with binary outcomes are performed on physical systems under the assumption of local realism. Testing such inequalities in the quantum realm usually involves either measurements of two-valued quantum observables or predefining a context-dependent binning procedure. Here we establish the conditions to test the Clauser-Horne-Shimony-Holt inequality using any quantum observable. Our result applies to observables with an arbitrary spectrum, and no prior knowledge of their underlying Hilbert space's dimension is required. Finally, we demonstrate the proposed general measurement strategy, that can be seen as positive operator-valued measurements performed on the system, using the formalism of modular variables applied to the transverse degrees of freedom of single photons.
Testing Clauser-Horne-Shimony-Holt inequalities using observables with arbitrary spectrum
NASA Astrophysics Data System (ADS)
Ketterer, Andreas; Keller, Arne; Coudreau, Thomas; Milman, Pérola
2015-03-01
The Clauser-Horne-Shimony and Holt inequality applies when measurements with binary outcomes are performed on physical systems under the assumption of local realism. Testing such inequalities in the quantum realm involves either measurements of two-valued quantum observables or pre-defining a context dependent binning procedure. Here we establish the conditions to test the Clauser-Horne-Shimony and Holt inequality using any quantum observable. Our result applies to observables with an arbitrary spectrum and no prior knowledge of their Hilbert space's dimension is required. Finally, we demonstrate the proposed general measurement strategy, that can be seen as positive operator valued measurements performed on the system, using the formalism of modular variables applied to the transverse degrees of freedom of photon pairs.
Scaling of pressure spectrum in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Patwardhan, Saurabh S.; Ramesh, O. N.
2014-04-01
Scaling of pressure spectrum in zero-pressure-gradient turbulent boundary layers is discussed. Spatial DNS data of boundary layer at one time instant (Reθ = 4500) are used for the analysis. It is observed that in the outer regions the pressure spectra tends towards the -7/3 law predicted by Kolmogorov's theory of small-scale turbulence. The slope in the pressure spectra varies from -1 close to the wall to a value close to -7/3 in the outer region. The streamwise velocity spectra also show a -5/3 trend in the outer region of the flow. The exercise carried out to study the amplitude modulation effect of the large scales on the smaller ones in the near-wall region reveals a strong modulation effect for the streamwise velocity, but not for the pressure fluctuations. The skewness of the pressure follows the same trend as the amplitude modulation coefficient, as is the case for the velocity. In the inner region, pressure spectra were seen to collapse better when normalized with the local Reynolds stress than when scaled with the local turbulent kinetic energy
NASA Astrophysics Data System (ADS)
Zamek, Steve; Yitzhaky, Yitzhak
2006-08-01
In remote sensing, atmospheric turbulence and aerosols limit the image quality. For many practical cases turbulence is shown to be dominant, especially for horizontal close-to-earth imaging in hot environments. In a horizontal long-range imaging it is usually impractical to measure path-averaged refractive index structure constant C n2 (which characterizes the turbulence strength) with conventional equipment. In this paper we propose a method for estimation of C n2 based just on the available recorded turbulence-degraded image sequence. The method exploits the turbulence-induced image "dancing". C n2 is extracted from the estimated image shifts variance. Experimental comparison with C n2 measurements using a scintillometer shows reliable estimation results. We also estimate image motion with sub-pixel accuracy for the purpose of obtaining a high-resolution image by applying a simple super-resolution procedure. Results of super-resolution for real imagery are presented.
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.
SOLAR WIND TURBULENT SPECTRUM AT PLASMA KINETIC SCALES
Alexandrova, O.; Lacombe, C.; Mangeney, A.; Maksimovic, M.; Grappin, R.
2012-12-01
The description of the turbulent spectrum of magnetic fluctuations in the solar wind in the kinetic range of scales is not yet completely established. Here, we perform a statistical study of 100 spectra measured by the STAFF instrument on the Cluster mission, which allows us to resolve turbulent fluctuations from ion scales down to a fraction of electron scales, i.e., from {approx}10{sup 2} km to {approx}300 m. We show that for k {rho} {sub e} in [0.03, 3] (which corresponds approximately to the frequency in the spacecraft frame f in [3, 300] Hz), all the observed spectra can be described by a general law E(k ){proportional_to}k {sup -8/3} exp (- k {rho} {sub e}), where k is the wavevector component normal to the background magnetic field and {rho} {sub e} the electron Larmor radius. This exponential tail found in the solar wind seems compatible with the Landau damping of magnetic fluctuations onto electrons.
On the technique for the recovery of the spectrum of turbulence in astrophysical discs
NASA Astrophysics Data System (ADS)
Bisikalo, D. V.; Kurbatov, E. P.; Pavlyuchenkov, Ya. N.; Zhilkin, A. G.; Kaygorodov, P. V.
2016-06-01
We present a method that can be used to recover the spectrum of turbulence from observations of optically thin emission lines formed in astrophysical discs. Within this method, we analyse how line intensity fluctuations depend on the angular resolution of the instrument, used for the observations. The method allows us to restore the slope of the power spectrum of velocity turbulent pulsations and estimate the upper boundary of the turbulence scale.
NASA Astrophysics Data System (ADS)
Wei, W.; Schmitt, F. G.; Huang, Y. X.; Zhang, H. S.
2016-05-01
Turbulent characteristics in the atmospheric surface layer are investigated using a data-driven method, Hilbert spectral analysis. The results from empirical mode decomposition display a set of intrinsic mode functions whose characteristic scales suggest a dyadic filter-bank property. It can be concluded from the joint probability density function of the intrinsic mode functions that the turbulent properties are totally different under different stratifications: the amplitudes (or energies) are arranged according to the stability parameter [InlineEquation not available: see fulltext.] for stable conditions, but tend to cluster randomly for unstable cases. The intermittency analyses reveal that second-order Hilbert marginal spectra display a power-law behaviour in the inertial subrange, and that the scaling exponent functions deviate from the theoretical values due to the strong intermittency in the stable boundary layer.
NASA Astrophysics Data System (ADS)
Wei, Wei; Schmitt, François G.; Huang, Yongxiang; Zhang, Hongsheng
2016-04-01
Turbulent characteristics in the atmospheric surface layer are investigated using a data-driven method, Hilbert spectral analysis. The results from empirical mode decomposition display a set of intrinsic mode functions whose characteristic scales suggest a dyadic filter-bank property. It can be concluded from the joint probability density function of the intrinsic mode functions that the turbulent properties are totally different under different stratifications: the amplitudes (or energies) are arranged according to the stability parameter z/L for stable conditions, but tend to cluster randomly for unstable cases. The intermittency analyses reveal that second-order Hilbert marginal spectra display a power-law behaviour in the inertial subrange, and that the scaling exponent functions present deviation, from the theoretical values due to the strong intermittency in the stable boundary layer.
Sensitivity of neutrinos to the supernova turbulence power spectrum: Point source statistics
NASA Astrophysics Data System (ADS)
Kneller, James P.; Kabadi, Neel V.
2015-07-01
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. 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.
Time Correlations and the Frequency Spectrum of Sound Radiated by Turbulent Flows
NASA Technical Reports Server (NTRS)
Rubinstein, Robert; Zhou, Ye
1997-01-01
Theories of turbulent time correlations are applied to compute frequency spectra of sound radiated by isotropic turbulence and by turbulent shear flows. The hypothesis that Eulerian time correlations are dominated by the sweeping action of the most energetic scales implies that the frequency spectrum of the sound radiated by isotropic turbulence scales as omega(exp 4) for low frequencies and as omega(exp -3/4) for high frequencies. The sweeping hypothesis is applied to an approximate theory of jet noise. The high frequency noise again scales as omega(exp -3/4), but the low frequency spectrum scales as omega(exp 2). In comparison, a classical theory of jet noise based on dimensional analysis gives omega(exp -2) and omega(exp 2) scaling for these frequency ranges. It is shown that the omega(exp -2) scaling is obtained by simplifying the description of turbulent time correlations. An approximate theory of the effect of shear on turbulent time correlations is developed and applied to the frequency spectrum of sound radiated by shear turbulence. The predicted steepening of the shear dominated spectrum appears to be consistent with jet noise measurements.
Transition from thermal to turbulent equilibrium with a resulting electromagnetic spectrum
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.
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.
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.
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.
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.
Coherent structures and turbulent spectrum in solar wind plasmas
Sharma, R. P.; Yadav, N.; Kumari, Anju
2013-08-15
The present paper investigates the localization of a uniform plane kinetic Alfvén wave (KAW) due to the coupling with the density/magnetic field fluctuations associated with a magnetosonic wave propagating in the transverse direction, i.e., perpendicular to the background magnetic field. To gain the physical insight into this evolution, a simplified analytical model based on the Mathieu equation has also been studied. Numerical method has also been used to analyse the evolution of KAW. The magnetic fluctuation spectrum follows Kolmogorovian scaling above the proton gyroradius scalelength, which is regarded as the inertial range. Below this scale, a steepened spectrum has been obtained in the dispersive range with power law index ∼−2.5, which continues up to the dissipation range. Our results reveal that the proposed mechanism may be an interesting physical mechanism for transferring the energy from larger lengthscales to smaller lengthscales in the solar wind plasmas. Relevance of the present study with Cluster spacecraft observations has also been discussed.
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.
Enhanced damping of Alfven waves in the solar corona by a turbulent wave spectrum
NASA Technical Reports Server (NTRS)
Kleva, Robert G.; Drake, J. F.
1992-01-01
The effect of a background spectrum of Alfven waves on the rate of dissipation of a test shear Alfven wave is numerically calculated. The results demonstrate that as the classical resistivity eta and classical viscosity mu become small, the damping rate of the Alfven wave remains large and depends only on the amplitude for the scalar potential of the wave spectrum and the wavenumber of the Alfven wave. The damping rate is virtually independent of eta and mu. The wave spectrum need not be turbulent or stochastic to affect the damping rate. The dissipation rate is nonlinear enhanced by nonstochastic spectra as well as by stochastic spectra if two conditions are met. First, the perpendicular magnetic field associated with Alfven wave spectrum must exceed a certain collision-frequency threshold and second, for nonstochastic spectra only, the magnetic field must exceed a threshold proportional to the parallel wavenumber of the shear Alfven wave. These conditions can be easily satisfied in the solar corona.
Chandran
2000-11-27
Scattering rates for a Goldreich-Sridhar (GS) spectrum of anisotropic, incompressible, magnetohydrodynamic turbulence are calculated in the quasilinear approximation. Because the small-scale fluctuations are constrained to have wave vectors nearly perpendicular to the background magnetic field, scattering is too weak to provide either the mean-free paths commonly used in Galactic cosmic-ray propagation models or the mean-free paths required for acceleration of cosmic rays at quasiparallel shocks. Where strong pitch-angle scattering occurs, it is due to fluctuations not described by the GS spectrum, such as fluctuations generated by streaming cosmic rays. PMID:11082620
NASA Astrophysics Data System (ADS)
Ofman, Leon; Ozak, Nataly; Viñas, Adolfo F.
2016-03-01
Near the Sun (< 10Rs) the acceleration, heating, and propagation of the solar wind are likely affected by the background inhomogeneities of the magnetized plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super-Alfvénic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.
Turbulence in the solar wind: what controls the slope of the energy spectrum?
NASA Astrophysics Data System (ADS)
Verdini, Andrea; Grappin, Roland
2016-04-01
The spectrum of solar wind fluctuations is well described by a power law with an average spectral index -5/3 for periods between a few hours and a few minutes. However, the spectral index varies with stream speed and with the correlation of velocity and magnetic field fluctuations (Alfvénicity): the spectrum is softer in fast and Alfvénic streams. Roughly, this variation can be understood in term of the turbulent age of fluctuations at a given scale: the faster is the wind or the stronger is the correlation than the younger is the turbulence. Since the coronal spectrum is supposed to be rather flat (at least in the fast solar wind), smaller spectral indices correspond to less evolved spectra. According to this interpretation, one would expect spectral slope to change with distance as the turbulence ages, while observations report fairly stable spectral slopes. In order to quantify the effect of wind speed and Alfvénicity on the spectral slope, we ran a series of numerical simulations of MHD turbulence in the framework of the Expanding Box Model (EBM). In EBM we can vary the expansion rate and the initial correlation of fluctuations so as to investigate the existence of a threshold value for each parameter or for a combination of the two that could explain the observed variation and stability of the spectral index. We present preliminary results that indicate that the expansion rate does control the spectral index of energy when the Alfvénicity is high.
NASA Astrophysics Data System (ADS)
Goto, Susumu; Kida, Shigeo
1999-07-01
The Lagrangian direct-interaction approximation developed previously by the present authors [S. Kida and S. Goto, J. Fluid Mech. 345, 307 (1997)] is applied to a passive scalar field in isotropic turbulence. We examine the behavior of solutions to the resultant closure equations for the correlation function of the scalar field for arbitrary values of the Schmidt number, and show systematically that the solutions are completely consistent with the phenomenological theories on the scalar spectral function by Obukhov (1949), Corrsin (1951), Batchelor et al. (1959), and Batchelor (1959). The universal forms of the function in the statistically stationary state are obtained by solving the closure equations numerically in the whole wave number range for each case of moderate, extremely large, and small values of the Schmidt number.
Spectrum and Anisotropy of Turbulence from Multi-frequency Measurement of Synchrotron Polarization
NASA Astrophysics Data System (ADS)
Lazarian, A.; Pogosyan, D.
2016-02-01
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.
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.
High frequency formulation for the acoustic power spectrum due to cascade-turbulence interaction.
Cheong, Cheolung; Joseph, Phillip; Lee, Soogab
2006-01-01
This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. An analytic formulation for the spectrum of acoustic power of a two-dimensional flat-plate is derived. The main finding of this paper is that the acoustic power spectrum from the cascade of flat airfoils may be split into two distinct frequency regions of low frequency and high frequency, separated by a critical frequency. Below this frequency, cascade effects due to the interaction between neighboring airfoils are shown to be important. At frequencies above the critical frequency, cascade effects are shown to be relatively weak. In this frequency range, acoustic power is shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number, stagger angle, gap-chord ratio, and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction. PMID:16454269
S-process nucleosynthesis in AGB stars with the full spectrum of turbulence scheme for convection.
NASA Astrophysics Data System (ADS)
Yagüe, A.; García-Hernández, D. A.; Ventura, P.; Lugaro, M.
2016-07-01
The chemical evolution of asymptotic giant branch (AGB) stars models depends greatly on the input physics (e.g. convective model, mass loss recipe). Variations of hot bottom burning (HBB) strength, or third dredge-up (TDU) efficiency are among the main consequences of adopting different input physics in the AGB models. The ATON evolutionary code stands apart from others in that it uses the Full Spectrum of Turbulence convective model. Here we present the first results of a newly developed s-process nucleosynthesis module for ATON AGB models. Our results are compared also with observations and theoretical predictions of present AGB nucleosynthesis models using different input physics.
The energy spectrum and geometrical structure of Galactic turbulent magnetic field
NASA Astrophysics Data System (ADS)
Sun, Xiaohui; Gaensler, Bryan; Mcclure-Griffiths, Naomi; Purcell, Cormac; Hill, Alex; Burkhart, Blakesley; Lazarian, Alex
2012-04-01
The energy spectrum and geometrical structure of the turbulent magnetic field can offer a solid test of different theoretical models on the generation and evolution of Galactic magnetic fields. They are also pivotal to understanding the propagation of cosmic-ray particles. However, the energy spectrum has been difficult to determine and the geometrical structure has never been obtained so far, due to lack of proper methods and observations. We aim to infer these quantities by applying our newly developed techniques to polarisation images. These images are required to be observed with high angular resolution and broadband multi-channel polarimetry, which is possible only recently using the ATCA. As a pilot study, we plan to map the 2X2 degree high-latitude field centred at l=255.5 degree and b=-38 degree at 1.1-3.1 GHz in total intensity and polarisation.
The energy spectrum and geometrical structure of Galactic turbulent magnetic field
NASA Astrophysics Data System (ADS)
Sun, Xiaohui; Gaensler, Bryan; Mcclure-Griffiths, Naomi; Purcell, Cormac; Hill, Alex; Burkhart, Blakesley; Lazarian, Alex
2012-10-01
The energy spectrum and geometrical structure of the turbulent magnetic field can offer a solid test of different theoretical models on the generation and evolution of Galactic magnetic fields. They are also pivotal to understanding the propagation of cosmic-ray particles. However, the energy spectrum has been difficult to determine and the geometrical structure has never been obtained so far, due to lack of proper methods and observations. We aim to infer these quantities by applying our newly developed techniques to polarisation images. These images are required to be observed with high angular resolution and broadband multi-channel polarimetry, which is possible only recently using the ATCA. As a pilot study, we plan to map the 2X2 degree high-latitude field centred at l=255.5 degree and b=-38 degree at 1.1-3.1 GHz in total intensity and polarisation.
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 . Basedmore » 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 .« less
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 ^}.
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 ̂ .
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 ^{exp}_{crit} [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 .
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.
NASA Astrophysics Data System (ADS)
Ozak, N.; Ofman, L.; Vinas, A. F.; Maneva, Y. G.
2013-12-01
Remote sensing observations of solar wind plasma show that heavy ions are hotter than protons and that their temperature is anisotropic. In-situ observations of fast solar wind streams at distances of 0.29 AU and beyond by Helios and recently at ~1 AU by STEREO, ACE, and Wind spacecraft provide direct evidence for the presence of turbulent Alfven wave spectrum and of left-hand polarized ion-cyclotron waves in the coronal plasma. The latter can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Furthermore, measurements indicate that Ti,⊥>>Ti,‖, contrary to what is expected in purely adiabatic expansion of the solar wind plasma, which predicts the opposite effect due to conservation of magnetic moment of the expanding ions. Future Solar Probe+ mission will provide in-situ observations of solar wind plasma close to the Sun where it is expected to be inhomogeneous on small scales. Here, we study the heating and the acceleration of solar wind ions (H+, He++) in inhomogeneous plasma with a turbulent spectrum of Alfvénic fluctuations using 2.5D hybrid code. The 2-D model allows us to explore inhomogeneities in the plasma and obliquely propagating waves. We extend previous work (Ofman 2010; Ofman et al. 2011) by including the expansion of the solar wind and study its effect on the perpendicular ion heating and cooling, and on the spectrum of the magnetic fluctuations in the inhomogeneous background wind. We also study the effects of inhomogeneous drift on the heating of the ions. We compare our results to the available observations.
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
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
Large-deviation joint statistics of the finite-time Lyapunov spectrum in isotropic turbulence
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
Shock interactions, turbulence and the origin of the stellar mass spectrum.
Pudritz, Ralph E; Kevlahan, N K-R
2013-11-28
Supersonic turbulence is an essential element in understanding how structure within interstellar gas is created and shaped. In the context of star formation, many computational studies show that the mass spectrum of density and velocity fluctuations within dense clouds, as well as the distribution of their angular momenta, trace their origin to the statistical and physical properties of gas that is lashed with shock waves. In this paper, we review the observations, simulations and theories of how turbulent-like processes can account for the structures we see in molecular clouds. We then compare traditional ideas of supersonic turbulence with a simpler physical model involving the effects of multiple shock waves and their interactions in the interstellar medium. Planar intersecting shock waves produce dense filaments and generate vortex sheets that are essential to create the broad range of density and velocity structure in clouds. As an example, the lower-mass behaviour of the stellar initial mass function can be traced to the tendency of a collection of shock waves to build up a lognormal density distribution (or column density). Vorticity--which is essential to produce velocity structure over a very broad range of length scales in shocked clouds--can also be generated by the passage of curved shocks or intersecting planar shocks through such media. Two major additional physical forces affect the structure of star-forming gas--gravity and feedback processes from young stars. Both of these can produce power-law tails at the high-mass end of the initial mass function. PMID:24146011
NASA Astrophysics Data System (ADS)
Marschalkó, G.; Petrovay, K.; Petrovay, K.
2013-11-01
A simple analytical relation of form α=2κ-1 between the magnetic energy spectral exponent α of the turbulent magnetic field in the solar photosphere and its magnetic flux cancellation exponent κ, valid under certain restrictive assumptions, is tested and extended outside its range of validity in a series of Monte Carlo simulations. In these numerical tests artificial ``magnetograms'' are constructed in 1D and 2D by superposing a discrete set of Fourier modes of the magnetic field distribution with amplitudes following a power law spectrum and measuring the cancellation function on these simulated magnetograms. Our results confirm the validity of the analytical relation and extend it to the domain α<-1 where κ-> 0 as α-> -∞. The observationally derived upper limit of 0.38 on κ implies α<-0.24 in the granular size range, apparently at odds with a small scale dynamo driven in the inertial range.
Tan, Liying; Zhai, Chao; Yu, Siyuan; Ma, Jing; Lu, Gaoyuan
2015-05-01
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. PMID:25969221
DB white dwarf evolution in the frame of the full spectrum turbulence theory
NASA Astrophysics Data System (ADS)
Benvenuto, O. G.; Althaus, L. G.
1997-07-01
We present an analysis of the evolution of carbon-oxygen DB white dwarfs (helium-rich envelope) for a wide range of effective temperatures and luminosities. To this end, we employ a full stellar evolution code, in which we include a new equation of state for helium plasmas recently developed by Saumon, Chabrier & Van Horn and new OPAL radiative opacities. The most important feature of our models is that the transport of energy by convection is described by the full spectrum turbulence theory. In particular, we have adopted two versions of this theory for stellar convection: the Canuto & Mazzitelli theory and the more recent, self-consistent theory developed by Canuto, Goldman & Mazzitelli. Both theories, which have no free parameters and account for the whole spectrum of turbulent eddies, represent a great improvement compared to the mixing-length theory approach used thus far in almost all white dwarf studies. Neutrino energy losses as well as crystallization were taken into account. In order to explore the sensitivity of our results to various input model parameters, we vary the model mass from 0.5 to 1.0Msolar in intervals of 0.1Msolar, and the helium layer mass in the interval of 10^-6≮M_He/ M_*≮10^-2. The emphasis is put mainly on the behaviour of the evolving outer convection zone. In particular, we analyse the dependence of the location of the theoretical blue edge of the instability strip on the various input parameters. We find that the new ingredients we have incorporated in this study - mostly the new formulations for stellar convection - lead to theoretical blue edges in agreement with observations of pulsating DB white dwarfs. In this context, the Canuto, Goldman & Mazzitelli self-consistent theory yields theoretical blue edges somewhat hotter than those given by the Canuto & Mazzitelli theory, which is more consistent with a recent determination of the effective temperature of the hot DBV GD358. Contrary to previous results, we find that
Scaling of the wall-pressure spectrum from turbulent boundary-layer flows over rough surfaces
NASA Astrophysics Data System (ADS)
Chang, Natasha; Forest, Jonathan; Rast, Joshua
2015-11-01
Seafaring applications require predictions of noise and drag from rough surfaces at high Reynolds numbers. Glegg and Devenport (2009) have shown that roughness noise is directly proportional to the wall pressure spectrum. As a means to develop an empirical model of the surface pressure spectra from rough surfaces, experiments were conducted in a fully-developed turbulent boundary layer flow at the Anechoic Flow Facility located at the Naval Surface Warfare Center, Carderock Division in West Bethesda MD. A variety of inhomogeneous roughness types were tested where the momentum thickness Reynolds number ranged from 4000 to 40000 while the flow based non-dimensional equivalent sand grain roughness height, ks+, ranged from 24 to 1500. Mean and fluctuating velocities, as well as fluctuating surface pressure and radiated far-field results were collected and analyzed. The surface pressure spectra are collapsed with inner and outer flow variables in an attempt to obtain an empirical model that can be used to scale the spectra for higher Reynolds number applications. Glegg, S., and Devenport, W., 2009. ``The far-field sound from rough-wall boundary layers.'' Proceedings of the Royal Society, Vol 465, pp 1717 - 1734.
NASA Technical Reports Server (NTRS)
Mathur, Gopal P.; Cannon, Mark R.
1990-01-01
The turbulent boundary layer (TBL) pressure fluctuations represent a dominant source of aircraft interior noise during cruise. The wavenumber-frequency characteristics of the TBL pressure field become important when determining its coupling with the aircraft structure and the resulting sound radiation into the interior of the aircraft. A technique is presented to estimate the TBL pressure wavenumber-frequency spectrum using a fixed probe pair consisting of two microphones. Flight test data from the McDonnel Douglas Ultra High Bypass Demonstrator aircraft were used to estimate the TBL pressure wavenumber-frequency spectra. These data were compared with selected wall pressure prediction models based on the existing wind tunnel data. The estimated in-flight spectral levels for the Demonstrator aircraft were in good agreement with the TBL wall pressure prediction models in the medium wavenumber range. The estimated TBL wavenumber spectral levels were found to be on the higher side in the low wavenumber region when compared with the predicted levels.
Simulation of HF waves reflected from a turbulent ionosphere for spread spectrum systems
Wagen, J.F.O.
1988-01-01
The communication channel established with HF waves reflected by the ionosphere is investigated. The background ionosphere is modeled by a horizontally stratified medium. This model is superimposed with random irregularities. The resulting channel is characterized by a random transfer function. Each frequency component of this transfer function is determined from the received wave, field, knowing the transmitted wave field. The computation of the random fluctuations of the received wave field is performed by using the phase screen-diffraction layer method. This scheme simulates the propagation of an HF wave in the turbulent ionosphere. Based on the forward-scatter approximation, the scheme computes sequentially the effects of phase fluctuations due to the irregularities and the effects of diffraction due to phase mixing. Stepping along the ray path, phase fluctuations are imbedded into a number of phase screens. Diffraction effects are then computed between phase screens using FFT techniques. Special attention is given to the reflection region where the classical WKB approximations are invalid. The computed statistics of the received signal include probability distribution, power spectrum, correlation function and scintillation index.
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.
Roman-Duval, Julia; Jackson, James; Federrath, Christoph; Klessen, Ralf S.; Brunt, Christopher; Heyer, Mark E-mail: jackson@bu.edu E-mail: chfeder@uni-heidelberg.de E-mail: heyer@astro.umass.edu
2011-10-20
Turbulence plays a major role in the formation and evolution of molecular clouds. Observationally, turbulent velocities are convolved with the density of an observed region. To correct for this convolution, we investigate the relation between the turbulence spectrum of model clouds, and the statistics of their synthetic observations obtained from principal component analysis (PCA). We apply PCA to spectral maps generated from simulated density and velocity fields, obtained from hydrodynamic simulations of supersonic turbulence, and from fractional Brownian motion (fBm) fields with varying velocity, density spectra, and density dispersion. We examine the dependence of the slope of the PCA pseudo-structure function, {alpha}{sub PCA}, on intermittency, on the turbulence velocity ({beta}{sub v}) and density ({beta}{sub n}) spectral indexes, and on density dispersion. We find that PCA is insensitive to {beta}{sub n} and to the log-density dispersion {sigma}{sub s}, provided {sigma}{sub s} {<=} 2. For {sigma}{sub s} > 2, {alpha}{sub PCA} increases with {sigma}{sub s} due to the intermittent sampling of the velocity field by the density field. The PCA calibration also depends on intermittency. We derive a PCA calibration based on fBm structures with {sigma}{sub s} {<=} 2 and apply it to 367 {sup 13}CO spectral maps of molecular clouds in the Galactic Ring Survey. The average slope of the PCA structure function, ({alpha}{sub PCA}) = 0.62 {+-} 0.2, is consistent with the hydrodynamic simulations and leads to a turbulence velocity exponent of ({beta}{sub v}) = 2.06 {+-} 0.6 for a non-intermittent, low density dispersion flow. Accounting for intermittency and density dispersion, the coincidence between the PCA slope of the GRS clouds and the hydrodynamic simulations suggests {beta}{sub v} {approx_equal} 1.9, consistent with both Burgers and compressible intermittent turbulence.
Density fluctuation spectrum of solar wind turbulence between ion and electron scales.
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. PMID:22861861
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Fujita, Yutaka; Akamatsu, Hiroki; Kimura, Shigeo S.
2016-04-01
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.
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.
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.
Dissipation range turbulent cascades in plasmas
Terry, P. W.; Almagri, A. F.; Forest, C. B.; Nornberg, M. D.; Rahbarnia, K.; Sarff, J. S.; Fiksel, G.; Hatch, D. R.; Jenko, F.; Prager, S. C.; Ren, Y.
2012-05-15
Dissipation range cascades in plasma turbulence are described and spectra are formulated from the scaled attenuation in wavenumber space of the spectral energy transfer rate. This yields spectra characterized by the product of a power law and exponential fall-off, applicable to all scales. Spectral indices of the power law and exponential fall-off depend on the scaling of the dissipation, the strength of the nonlinearity, and nonlocal effects when dissipation rates of multiple fluctuation fields are different. The theory is used to derive spectra for MHD turbulence with magnetic Prandtl number greater than unity, extending previous work. The theory is also applied to generic plasma turbulence by considering the spectrum from damping with arbitrary wavenumber scaling. The latter is relevant to ion temperature gradient turbulence modeled by gyrokinetics. The spectrum in this case has an exponential component that becomes weaker at small scale, giving a power law asymptotically. Results from the theory are compared to three very different types of turbulence. These include the magnetic plasma turbulence of the Madison Symmetric Torus, the MHD turbulence of liquid metal in the Madison Dynamo Experiment, and gyrokinetic simulation of ion temperature gradient turbulence.
Transition from geostrophic turbulence to inertia-gravity waves in the atmospheric energy spectrum.
Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver
2014-12-01
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
Transition from geostrophic turbulence to inertia–gravity waves in the atmospheric energy spectrum
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
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.
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
The Origin of the Stellar Mass Spectrum in Turbulence and Feedback
NASA Astrophysics Data System (ADS)
Krumholz, Mark
The origin of the stellar initial mass function (IMF) is one of the oldest problems in theoretical astrophysics, and one of the most profound. This distribution touches virtually every area of astrophysics, from interpreting observations of integrated starlight, to synthesis of heavy elements, to formation of galaxies, to the development of life. A comprehensive theory of the IMF, and its possible variation, is directly relevant to the NASA mission of understanding our origins, and would also be invaluable for interpreting observations from NASA missions that measure integrated starlight. While the problem of the IMF has stood for a long time, recent developments in both numerical and analytic techniques make the problem ripe for solution. We propose to develop a comprehensive theory for the origin of the IMF that is based on two main ingredients: the statistical properties of the ubiquitous turbulence in interstellar clouds, and the role of stellar radiative feedback in shaping how that gas fragments under the action of self-gravity. This work will proceed on two fronts. Analytically, we will extend the excursion set formalism for turbulence recently developed by Hopkins to account for the effects of local sources of stellar radiative feedback, which have been shown by both simulations and observations to have profound effects on how gas fragments. In parallel, we will conduct adaptive mesh refinement radiation-hydrodynamic simulations to test and guide the development of this analytic framework. The goal will be to develop a predictive theory of the IMF that is capable of explaining both the shape and the normalization of the stellar mass function, and its possible variation with star-forming environment.
NASA Astrophysics Data System (ADS)
Ornigotti, Marco; Conti, Claudio; Szameit, Alexander
2015-10-01
We report on the dependence of the carrier frequency of a nondiffracting optical pulse on the amount of orbital angular momentum it carries. We provide a unified universal form of such a dependence for the cases of both scalar and vector pulses with arbitrary frequency spectra. For the case of paraxial optical pulses we consider two different examples, namely, pulses with exponentially decaying spectra and Gaussian spectra.
The onset of Alfvenic turbulence
NASA Technical Reports Server (NTRS)
Ghosh, S.; Papadopoulos, K.
1987-01-01
An investigation is conducted on how low-frequency MHD oscillations in a warm plasma may undergo a transition from a coherent state to one of turbulence. A driven/dissipative derivative nonlinear Schroedinger equation is derived from the fluid equations. The time evolution of an arbitrary spectrum of waves is analyzed in the case where one k-mode is unstable, with the rest damped. It is found that the transition from order to chaos in the driven/dissipative system is correlated with the existence or absence of 'breathing' solitons in the associated conservative system.
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).
Infrared properties of the energy spectrum in freely decaying isotropic turbulence.
McComb, W D
2016-01-01
The low wave number expansion of the energy spectrum takes the well known form E(k,t)=E_{2}(t)k^{2}+E_{4}(t)k^{4}+⋯, where the coefficients are weighted integrals against the correlation function C(r,t). We show that expressing E(k,t) in terms of the longitudinal correlation function f(r,t) immediately yields E_{2}(t)=0 by cancellation. We verify that the same result is obtained using the correlation function C(r,t), provided only that f(r,t) falls off faster than r^{-3} at large values of r. As power-law forms are widely studied for the purpose of establishing bounds, we consider the family of model correlations f(r,t)=α_{n}(t)r^{-n}, for positive integer n, at large values of the separation r. We find that for the special case n=3, the relationship connecting f(r,t) and C(r,t) becomes indeterminate, and (exceptionally) E_{2}≠0, but that this solution is unphysical in that the viscous term in the Kármán-Howarth equation vanishes. Lastly, we show that E_{4}(t) is independent of time, without needing to assume the exponential decrease of correlation functions at large distances. PMID:26871151
NASA Astrophysics Data System (ADS)
Kyzyurov, Yu.
Motions of neutral gas play the important role in creating irregularities of different scales in the ionospheric plasma. In particular, experimental data reveal that mid-latitude sporadic-E layer is formed by a vertical shear in the horizontal east-west wind due to tides or gravity waves. Below the homopause level (100-120 km) turbulent motions of neutral gas exhibit an essential influence on the layer. Neutral turbulence is responsible for the many-cloud structure of spread sporadic-E layers. This report is devoted to small-scale electron-density fluctuations produced by the turbulence in sporadic-E. Length-scales of the fluctuations correspond to the inertial range of turbulence and are small compared with the local scale of mean plasma-density gradient. We discuss an expected shape of the 1D fluctuation spectrum that can be measured during rocket experiments. The discussion is based on an analytical expression for the spectrum. The main steps necessary for obtaining the expression within the framework of macroscopic description are outlined too. Possible parabolic trajectories of two rockets which can be used for measurements of the sporadic-E electron-density fluctuations in the mid-latitude ionosphere (a magnetic dip angle of 45°) are chosen for a comparison. Parameters of the hypothetical flights were the following: (1) an apogee hmax=180 km, a distance between start and final points R=280 km; and (2) hmax=125 km, R=67 km. Mean values of characteristics for the sporadic-E and the neutral turbulence were fixed at around 97 km in this consideration. We have chosen the layer with a thickness of 2 km, a maximum electron density of 2\\cdot1010 m-3, and concentration of Fe^+ ions of 80 % (i.e. the mean ion mass is about 51 AMU). The mean rate of the turbulent energy dissipation was about 0.1 m^2s-3. Under these circumstances, the rms level of relative fluctuations in electron density may be about 10 % in the range of length-scales 10-400 m. The shape of
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.
Molodij, Guillaume
2011-08-01
A general expression of the spatial correlation functions of quantities related to the phase fluctuations of a wave that have propagated through the atmospheric turbulence are derived. A generalization of the method to integrand containing the product of an arbitrary number of hypergeometric functions is presented. The formalism is able to give the coefficients of phase-expansion functions orthogonal over an arbitrary circularly symmetric weighting function for an isotropic turbulence spectrum, as well as to describe the effect of the finite outer and inner scales of the turbulence and to describe the spherical propagation or to derive the effects of the analytical operators acting on the phase such as the derivatives of any order. The derivation of the generalized integrals with multiparameters is based on the Mellin transforms integration method. PMID:21811336
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.
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…
Tyler, G.L.; Vesecky, J.F.; Plume, M.A.; Howard, H.T.; Barnes, A.
1981-10-01
Solar conjunction of Mars on 1976 November 25 occurred very near the beginning of solar cycle 21, about 4 months after the first Viking spacecraft arrived at the planet. Radio wave scattering data were collected at 3.6 and 13 cm wavelengths, using the radio link between the Viking orbiters and the Earth. These data allow measurements of solar wind properties over a range of heliocentric radial distance from approx.6 to 44 R/sub sun/ with solar latitudes ranging from -17/sup 0/ to +7/sup 0/. Observations with Mariner 10 during a period of moderate solar activity in 1974 cover from 6 to 24 R/sub sun/ and from approx.20/sup 0/ to near 90/sup 0/. We have found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma. This spectrum has an approximately constant low frequency plateau and a power-law high frequency asymptote; the plateau-asymptote intersection frequency provides a measure of the solar wind velocity V. We also obtain the spectral index p of electron density turbulence, Phi/sub N/approx.kappa/sup -p/, where kappa is spatial wavenumber. These results apply to a cylindrical region oriented with its axis along the radio ray path and its center at the point of closest approach to the Sun. The measurements of V and p cover some 78/sup d/ for Viking and 49/sup 2/ for Mariner 10 and show the combined effects of changing heliocentric distance rho, solar latitude theta, and solar longitude Psi, as well as solar activity. The Viking results can be regarded as a function primary of rho and Psi since the observations are concentrated in the equatorial regions when solar activity was near minimum. For Mariner 10, rho, theta, and Psi variations were important. The Viking results show an abrupt change in V(rho) and the turbulence spectral index at approx.15 R/sub sun/.
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).
Hindered Energy Cascade in Highly Helical Isotropic Turbulence
NASA Astrophysics Data System (ADS)
Stepanov, Rodion; Golbraikh, Ephim; Frick, Peter; Shestakov, Alexander
2015-12-01
The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum.
Hindered Energy Cascade in Highly Helical Isotropic Turbulence.
Stepanov, Rodion; Golbraikh, Ephim; Frick, Peter; Shestakov, Alexander
2015-12-01
The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum. PMID:26684120
Turbulent Convection: Old and New Models
NASA Astrophysics Data System (ADS)
Canuto, V. M.
1996-08-01
This paper contains (1) a physical argument to show that the one-eddy MLT model underestimates the convective flux Fc in the high-efficiency regime, while it overestimates Fc in the low-efficiency regime, and (2) a new derivation of the Fc(MLT) using a turbulence model in the one-eddy approximation. (3) We forsake the one-eddy approximation and adopt the Kolmogorov spectrum to represent the turbulent energy spectrum. The resulting Fc > Fc(MLT) in the high-efficiency regime, and Fc
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.
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
Coherent and incoherent scattering by a plume of particles advected by turbulent velocity flow.
Palmer, David R
2009-08-01
Studies of acoustic remote sensing of the plumes that result from the injection of particulate matter in the ocean, either naturally or by dumping or dredging activities, have assumed the scattering is incoherent. These plumes are always turbulent, however. The particle density is a passive scalar that is advected by the turbulent velocity flow. The possibility exists, therefore, that the scattered waves from a significant number of particles add coherently as a result of Bragg scattering. In this paper, we investigate this possibility. We derive an expression for the ratio of the coherent intensity to the incoherent one in terms of the turbulent spectrum and the properties of the particles that make up the plume. The sonar is modeled as a high-Q, monostatic, pulsed sonar with arbitrary pulse envelope and arbitrary, but narrow, beam pattern. We apply the formalism to acoustic remote sensing of black smoker hydrothermal plumes. We find that, at most, the coherent intensity is less than 1% of the incoherent one. The implications are that Bragg scattering does not lead to a significant coherent component and in analyses of scattering from this type of plume, one can ignore the complications of turbulence altogether. PMID:19640023
Spectral methods on arbitrary grids
NASA Technical Reports Server (NTRS)
Carpenter, Mark H.; Gottlieb, David
1995-01-01
Stable and spectrally accurate numerical methods are constructed on arbitrary grids for partial differential equations. These new methods are equivalent to conventional spectral methods but do not rely on specific grid distributions. Specifically, we show how to implement Legendre Galerkin, Legendre collocation, and Laguerre Galerkin methodology on arbitrary grids.
Stirring turbulence with turbulence
NASA Astrophysics Data System (ADS)
Cekli, Hakki Ergun; Joosten, René; van de Water, Willem
2015-12-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the Gledzer-Ohkitani-Yamada shell model, which is a simple dynamical model of turbulence that produces a velocity field displaying inertial-range scaling behavior. The range of scales can be adjusted by selection of shells. We find that the largest energy input and the smallest anisotropy are reached when the time scale of the random numbers matches that of the largest eddies of the wind-tunnel turbulence. A large mismatch of these times creates a highly intermittent random flow with interesting but quite anomalous statistics.
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.
A Simple Arbitrary Solid Slicer
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.
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. PMID:26465513
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.
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.
Ising-like models on arbitrary graphs: The Hadamard way
NASA Astrophysics Data System (ADS)
Mosseri, Rémy
2015-01-01
We propose a generic framework to describe classical Ising-like models defined on arbitrary graphs. The energy spectrum is shown to be the Hadamard transform of a suitably defined sparse "coding" vector associated with the graph. We expect that the existence of a fast Hadamard transform algorithm (used, for instance, in image compression processes), together with the sparseness of the coding vector, may provide ways to fasten the spectrum computation. Applying this formalism to regular graphs, such as hypercubic graphs, we obtain a simple recurrence relation for the spectrum, which significantly speeds up its determination. First attempts to analyze partition functions and transfer matrices are also presented.
Scattering theory for arbitrary potentials
Kadyrov, A.S.; Bray, I.; Stelbovics, A.T.; Mukhamedzhanov, A.M.
2005-09-15
The fundamental quantities of potential scattering theory are generalized to accommodate long-range interactions. Definitions for the scattering amplitude and wave operators valid for arbitrary interactions including potentials with a Coulomb tail are presented. It is shown that for the Coulomb potential the generalized amplitude gives the physical on-shell amplitude without recourse to a renormalization procedure.
Arbitrary and Capricious Nonrenewal Decisions.
ERIC Educational Resources Information Center
Phay, Robert E.
This chapter discusses the question, To what degree is the school board limited by the requirement that it not be arbitrary or capricious in deciding not to renew a probationary teacher? When teachers have been notified that their employment contracts will not be renewed, they are responsible for initiating a review of the decision. If the school…
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.
Forced fluid dynamics from gravity in arbitrary dimensions
NASA Astrophysics Data System (ADS)
Ashok, T.
2014-03-01
We consider long wavelength solutions to the Einstein-dilaton system with negative cosmological constant which are dual, under the AdS/CFT correspondence, to solutions of the conformal relativistic Navier-Stokes equations with a dilaton-dependent forcing term. Certain forced fluid flows are known to exhibit turbulence; holographic duals of forced fluid dynamics are therefore of particular interest as they may aid efforts towards an explicit model of holographic steady state turbulence. In recent work, Bhattacharyya et al. have constructed long wavelength asymptotically locally AdS5 bulk space-times with a slowly varying boundary dilaton field which are dual to forced fluid flows on the 4-dimensional boundary. In this paper, we generalise their work to arbitrary space-time dimensions; we explicitly compute the dual bulk metric, the fluid dynamical stress tensor and Lagrangian to second order in a boundary derivative expansion.
Scintillation index in strong oceanic turbulence
NASA Astrophysics Data System (ADS)
Baykal, Yahya
2016-09-01
Scintillation index of spherical wave in strongly turbulent oceanic medium is evaluated. In the evaluation, modified Rytov solution and our recent formulation that expresses the oceanic turbulence parameters by the atmospheric turbulence structure constant, are employed. Variations of the scintillation index in strong oceanic turbulence are examined versus the oceanic turbulence parameters such as the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, viscosity, wavelength, the link length, and the ratio of temperature to salinity contributions to the refractive index spectrum.
Turbulence patterns and neutrino flavor transitions in high-resolution supernova models
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.
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.
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.
Elastic wave turbulence and intermittency
NASA Astrophysics Data System (ADS)
Chibbaro, Sergio; Josserand, Christophe
2016-07-01
We investigate the onset of intermittency for vibrating elastic plate turbulence in the framework of the weak wave turbulence theory using a numerical approach. The spectrum of the displacement field and the structure functions of the fluctuations are computed for different forcing amplitudes. At low forcing, the spectrum predicted by the theory is observed, while the fluctuations are consistent with Gaussian statistics. When the forcing is increased, the spectrum varies at large scales, corresponding to the oscillations of nonlinear structures made of ridges delimited by d cones. In this regime, the fluctuations exhibit small-scale intermittency that can be fitted via a multifractal model. The analysis of the nonlinear frequency shows that the intermittency is linked to the breakdown of the weak turbulence at large scales only.
Elastic wave turbulence and intermittency.
Chibbaro, Sergio; Josserand, Christophe
2016-07-01
We investigate the onset of intermittency for vibrating elastic plate turbulence in the framework of the weak wave turbulence theory using a numerical approach. The spectrum of the displacement field and the structure functions of the fluctuations are computed for different forcing amplitudes. At low forcing, the spectrum predicted by the theory is observed, while the fluctuations are consistent with Gaussian statistics. When the forcing is increased, the spectrum varies at large scales, corresponding to the oscillations of nonlinear structures made of ridges delimited by d cones. In this regime, the fluctuations exhibit small-scale intermittency that can be fitted via a multifractal model. The analysis of the nonlinear frequency shows that the intermittency is linked to the breakdown of the weak turbulence at large scales only. PMID:27575068
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.
On the nature of incompressible magnetohydrodynamic turbulence
Gogoberidze, G.
2007-02-15
A novel model of incompressible magnetohydrodynamic turbulence in the presence of a strong external magnetic field is proposed for the explanation of recent numerical results. According to the proposed model, in the presence of the strong external magnetic field, incompressible magnetohydrodynamic turbulence becomes nonlocal in the sense that low-frequency modes cause decorrelation of interacting high-frequency modes from the inertial interval. It is shown that the obtained nonlocal spectrum of the inertial range of incompressible magnetohydrodynamic turbulence represents an anisotropic analogue of Kraichnan's nonlocal spectrum of hydrodynamic turbulence. Based on the analysis performed in the framework of the weak-coupling approximation, which represents one of the equivalent formulations of the direct interaction approximation, it is shown that incompressible magnetohydrodynamic turbulence could be both local and nonlocal, and therefore anisotropic analogues of both the Kolmogorov and Kraichnan spectra are realizable in incompressible magnetohydrodynamic turbulence.
Horton, W.; Hu, G.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates.
Equientangled bases in arbitrary dimensions
Karimipour, V.; Memarzadeh, L.
2006-01-15
For the space of two identical systems of arbitrary dimensions, we introduce a continuous family of bases with the following properties: (i) the bases are orthonormal (ii) in each basis, all the states have the same values of entanglement, and (iii) they continuously interpolate between the product basis and the maximally entangled basis. The states thus constructed may find applications in many areas related to the quantum information science including quantum cryptography, optimal Bell tests, and the investigation of the enhancement of channel capacity due to entanglement.
Numerical measurement of turbulent responses in drift-Alfven turbulence
Fernandez, E.; Terry, P.W.
1997-07-01
A drift-Alfven magnetoturbulence model that augments reduced magnetohydrodynamics with evolution of electron density under parallel compression and fluid advection has been studied numerically. In the Alfvenic regime, measurement of spectral transfer rates, frequency spectra, energy partitions, and the ensemble-averaged turbulent response reveals both Alfvenic and hydrodynamic characteristics. The rms turbulent frequency is Alfvenic, the energies are equipartitioned, and there is a fast, Alfven-time scale relaxation in the turbulent response. The mean frequency is hydrodynamic, with diamagnetic and eddy straining signatures, and there is an eddy straining decorrelation appearing as a distinct, long time scale branch in the turbulent response. The decay rates and relative fluctuation strengths associated with fast and slow time scale decorrelation are in good agreement with theoretical predictions that posit a Kolmogorov spectrum in the Alfvenic regime. {copyright} {ital 1997 American Institute of Physics.}
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.
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.
Generalization of the electronic susceptibility for arbitrary molecular geometries
NASA Astrophysics Data System (ADS)
Scherrer, Arne; Dreßler, Christian; Ahlert, Paul; Sebastiani, Daniel
2016-04-01
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.
Deffayet, C.; Deser, S.; Esposito-Farese, G.
2010-09-15
We show that scalar, 0-form, Galileon actions--models whose field equations contain only second derivatives--can be generalized to arbitrary even p-forms. More generally, they need not even depend on a single form, but may involve mixed p combinations, including equal p multiplets, where odd p fields are also permitted: We construct, for given dimension D, general actions depending on scalars, vectors, and higher p-form field strengths, whose field equations are of exactly second derivative order. We also discuss and illustrate their curved-space generalizations, especially the delicate nonminimal couplings required to maintain this order. Concrete examples of pure and mixed actions, field equations, and their curved-space extensions are presented.
Resonance capture at arbitrary inclination
NASA Astrophysics Data System (ADS)
Namouni, F.; Morais, M. H. M.
2015-01-01
Resonance capture is studied numerically in the three-body problem for arbitrary inclinations. Massless particles are set to drift from outside the 1:5 resonance with a Jupiter-mass planet thereby encountering the web of the planet's diverse mean motion resonances. Randomly constructed samples explore parameter space for inclinations from 0 to 180° with 5° increments totalling nearly 6 × 105 numerical simulations. 30 resonances internal and external to the planet's location are monitored. We find that retrograde resonances are unexpectedly more efficient at capture than prograde resonances and that resonance order is not necessarily a good indicator of capture efficiency at arbitrary inclination. Capture probability drops significantly at moderate sample eccentricity for initial inclinations in the range [10°,110°]. Orbit inversion is possible for initially circular orbits with inclinations in the range [60°,130°]. Capture in the 1:1 co-orbital resonance occurs with great likelihood at large retrograde inclinations. The planet's orbital eccentricity, if larger than 0.1, reduces the capture probabilities through the action of the eccentric Kozai-Lidov mechanism. A capture asymmetry appears between inner and outer resonances as prograde orbits are preferentially trapped in inner resonances. The relative capture efficiency of retrograde resonance suggests that the dynamical lifetimes of Damocloids and Centaurs on retrograde orbits must be significantly larger than those on prograde orbits implying that the recently identified asteroids in retrograde resonance, 2006 BZ8, 2008 SO218, 2009 QY6 and 1999 LE31 may be among the oldest small bodies that wander between the outer giant planets.
Logistic equation of arbitrary order
NASA Astrophysics Data System (ADS)
Grabowski, Franciszek
2010-08-01
The paper is concerned with the new logistic equation of arbitrary order which describes the performance of complex executive systems X vs. number of tasks N, operating at limited resources K, at non-extensive, heterogeneous self-organization processes characterized by parameter f. In contrast to the classical logistic equation which exclusively relates to the special case of sub-extensive homogeneous self-organization processes at f=1, the proposed model concerns both homogeneous and heterogeneous processes in sub-extensive and super-extensive areas. The parameter of arbitrary order f, where -∞
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)
Magnetohydrodynamic turbulence: Observation and experiment
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.
Anisotropic scaling of magnetohydrodynamic turbulence.
Horbury, Timothy S; Forman, Miriam; Oughton, Sean
2008-10-24
We present a quantitative estimate of the anisotropic power and scaling of magnetic field fluctuations in inertial range magnetohydrodynamic turbulence, using a novel wavelet technique applied to spacecraft measurements in the solar wind. We show for the first time that, when the local magnetic field direction is parallel to the flow, the spacecraft-frame spectrum has a spectral index near 2. This can be interpreted as the signature of a population of fluctuations in field-parallel wave numbers with a k(-2)_(||) spectrum but is also consistent with the presence of a "critical balance" style turbulent cascade. We also find, in common with previous studies, that most of the power is contained in wave vectors at large angles to the local magnetic field and that this component of the turbulence has a spectral index of 5/3. PMID:18999759
Quantitative photography of intermittency in surface wave turbulence
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.
Airplane wing vibrations due to atmospheric turbulence
NASA Technical Reports Server (NTRS)
Pastel, R. L.; Caruthers, J. E.; Frost, W.
1981-01-01
The magnitude of error introduced due to wing vibration when measuring atmospheric turbulence with a wind probe mounted at the wing tip was studied. It was also determined whether accelerometers mounted on the wing tip are needed to correct this error. A spectrum analysis approach is used to determine the error. Estimates of the B-57 wing characteristics are used to simulate the airplane wing, and von Karman's cross spectrum function is used to simulate atmospheric turbulence. It was found that wing vibration introduces large error in measured spectra of turbulence in the frequency's range close to the natural frequencies of the wing.
Mixing in magnetized turbulent media
Sur, Sharanya; Scannapieco, Evan; Pan, Liubin E-mail: evan.scannapieco@asu.edu
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 {sup –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 {sup –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.
Anisotropic turbulence in the solar wind
NASA Technical Reports Server (NTRS)
Matthaeus, W. H.; Bieber, J. W.; Zank, G. P.
1995-01-01
Solar wind turbulence has been viewed traditionally as composed of parallel propagating ('slab' fluctuations) or otherwise as isotropic turbulence. A variety of recent investigations, reviewed here, indicate that the spectrum may contain a significant admixture of two dimensional fluctuations, having variations mainly perpendicular to the local magnetic field. These indications come from simulations, from the theory of nearly incompressible MHD, from cosmic ray transport studies and from transport theory for solar wind turbulence, as well as from interpretations of direct observations. Thus, solar wind turbulence may be more like bundles of spaghetti than like parallel phase fronts.
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
Turbulent cascade in a two-ion plasma
Qiu, Xin; Liu, San-Qiu; Yu, Ming-Yang
2014-11-15
It is shown that small but finite-amplitude drift wave turbulence in a two-ion-species plasma can be modeled by a Hasegawa-Mima equation. The mode cascade process and resulting turbulent spectrum are investigated. The spectrum is found to be similar to that of a two-component plasma, but the space and time scales of the turbulent cascade process can be quite different since they are rescaled by the presence of the second ion species.
Simulation of atmospheric turbulence layers with phase screens by JAVA
NASA Astrophysics Data System (ADS)
Zhang, Xiaofang; Chen, Wenqin; Yu, Xin; Yan, Jixiang
2008-03-01
In multiconjugate Adaptive Optics (MCAO), the phase screens are used to simulate atmospheric turbulence layers to study the optimal turbulence delamination and the determination of layer boundary position. In this paper, the method of power spectrum inversion and sub-harmonic compensation were used to simulate atmospheric turbulence layers and results can be shown by grey map. The simulation results showed that, with the increase of turbulence layers, the RMS of adaptive system decreased, but the amplitude diminished. So the atmospheric turbulence can be split into 2-3 layers and be modeled by phase screens. Otherwise, a small simulation atmospheric turbulence delamination system was realized by JAVA.
Pulsar timing noise from superfluid turbulence
NASA Astrophysics Data System (ADS)
Melatos, Andrew; Link, Bennett
2014-01-01
Shear-driven turbulence in the superfluid interior of a neutron star exerts a fluctuating torque on the rigid crust, causing the rotational phase to walk randomly. The phase fluctuation spectrum is calculated analytically for incompressible Kolmogorov turbulence and is found to be red; the half-power point is set by the observed spin-down rate, the crust-superfluid lag and the dynamical response time of the superfluid. Preliminary limits are placed on the latter quantities using selected time- and frequency-domain data. It is found that measurements of the normalization and slope of the power spectrum are reproduced for reasonable choices of the turbulence parameters. The results point preferentially to the neutron star interior containing a turbulent superfluid rather than a turbulent Navier-Stokes fluid. The implications for gravitational wave detection by pulsar timing arrays are discussed briefly.
Influence of atmospheric turbulence on OAM-based FSO system with use of realistic link model
NASA Astrophysics Data System (ADS)
Li, Ming; Yu, Zhongyuan; Cvijetic, Milorad
2016-04-01
We study the influence of atmospheric turbulence on OAM-based free-space optical (FSO) communication by using the Pump turbulence spectrum model which accurately characterizes the realistic FSO link. A comprehensive comparison is made between the Pump and Kolmogorov spectrum models with respect to the turbulence impact. The calculated results show that obtained turbulence-induced crosstalk is lower, which means that a higher channel capacity is projected when the realistic Pump spectrum is used instead of the Kolmogorov spectrum. We believe that our results prove that performance of practical OAM-based FSO is better than one predicted by using the original Kolmogorov turbulence model.
Effective kinematic viscosity of turbulent He II
Chagovets, T. V.; Gordeev, A. V.; Skrbek, L.
2007-08-15
The temperature dependence of the effective kinematic viscosity of turbulent He II, {nu}{sub eff}(T), is deduced from second sound attenuation data using the late stage of decay of thermally induced counterflow He II turbulence in two channels of square cross section. It is shown to qualitatively agree with the published data for {nu}{sub eff}(T) calculated based on experiments on decaying-grid-generated He II turbulence [Niemela et al., J. Low Temp. Phys. 138, 537 (2005)]. Corrections to these data due to the 'sine squared' law that describes attenuation of the second sound wave propagating along an arbitrary direction with respect to the direction of the core of a quantized vortex in turbulent He II are discussed and applied.
Sandia's Arbitrary Waveform MEMO Actuator
Energy Science and Technology Software Center (ESTSC)
2003-08-07
SAMA is a multichannel, arbitrary waveform generator program for driving microelectromechanical systems (MEMS). It allows the user to piece together twelve available wave parts, thereby permitting the user to create practically any waveform, or upload a previously constructed signal. The waveforms (bundled together as a signal) may simultaneously be output through four different channels to actuate MEMS devices, and the number of output channels may be increased depending on the DAQ card or instrument utilized.more » Additionally, real-time changes may be made to the frequency and amplitude. The signal may be paused temporarily. The waveform may be saved to file for future uploading. Recent work for this version has focused on modifications that will allow loading previously generated arbitrary waveforms, independent channel waveform amplification, adding a pause function, separating the "modify waveform: and "end program" functions, and simplifying the user interface by adding test blocks with statements to help the user program and output the desired signals. The program was developed in an effort to alleviate some of the limitations of Micro Driver. For example, Micro Driver will not allow the user to select a segment of a sine wave, but rather the user is limited to choosing either a whole or half sine wave pattern. It therefore becomes quite difficult ot construct partial sine wave patterns out of a "ramp" waveparts for several reasons. First, one must determine on paper how many data points each ramp will cover, and what the slopes of these ramps will be. Second, from what was observed, Micro Driver has difficulty processing more than six distinct waveparts during sequencing. The program will allow the user to input the various waves into the desired sequence; however, it will not allow the user to compile them (by clicking "ok" and returning to the main screen). Third, should the user decide that they want to increase the amplitute of the output signal
In situ measurements of wind and current speed and relationship between output power and turbulence
NASA Astrophysics Data System (ADS)
Duran Medina, Olmo; Schmitt, François G.; Sentchev, Alexei; Calif, Rudy
2015-04-01
In a context of energy transition, wind and tidal energy are sources of clean energy with the potential of partially satisfying the growing demand. The main problem of this type of energy, and other types of renewable energy remains the discontinuity of the electric power produced in different scales, inducing large fluctuations also called intermittency. This intermittency of wind and tidal energy is inherent to the turbulent nature of wind and marine currents. We consider this intermittent power production in strong relation with the turbulent intermittency of the resource. The turbulence theory is multifractal energy cascades models, a classic in physics of turbulence. From earlier studies in atmospheric sciences, we learn that wind speed and the aggregate power output are intermittent and multifractal over a wide range of scales [Calif and Schmitt 2014]. We want to extend this study to a marine current turbine and compare the scaling properties for those renewable energy sources. We consider here coupling between simultaneous velocity time series and output power from a wind turbine and a marine current turbine. Wind turbine data were obtained from Denmark and marine current data from Western Scheldt, Belgium where a prototype of a vertical and horizontal marine current turbines are tested. After an estimation of their Fourier density power spectra, we study their scaling properties in Kolmogorov's theory and the framework of fully developed turbulence. Hence, we employ a Hilbert-based methodology, namely arbitrary-order Hilbert spectral analysis [Calif et al. 2013a, 2013b] to characterize the intermittent property of the wind and marine current velocity in order to characterize the intermittent nature of the fluid. This method is used in order to obtain the spectrum and the corresponding power law for non-linear and non-stationary time series. The goal is to study the non-linear transfer characteristics in a multi-scale and multi-intensity framework.
Spectra of noise and amplified turbulence emanating from shock-turbulence interaction: Two scenarios
NASA Technical Reports Server (NTRS)
Ribner, H. S.
1986-01-01
This work is a small extension of NACA studies of the early fifties that predicted amplification of turbulence on passing through a shock wave (observed for turbulent boundary layers), as well as the generation of intense noise (observed for supersonic jets). The first solved the basic gasdynamics problem of the interaction of an infinite planar shock with a single three-dimensional spectrum component of turbulence (an oblique sinusoidal shear wave). The second developed the comprehensive 3D spectrum analysis necessary to generalize the scenario to the interaction of a shock wave with convected homogeneous turbulence. Numerical calculations were carried out to yield curves (vs. Mach number) of rms sound pressure, temperature fluctuation, and two components of turbulent velocity downstream of the shock, for two cases of preshock turbulence. The present numerical study reproduces these for one case and provides in addition their one-dimensional power spectra (vs. wavenumber or frequency). Ratios of the several postshock spectra to the longitudinal preshock turbulence spectrum (1D) have been computed for a wide range of Mach numbers; curves vs. wavenumber are presented for two scenarios of preshock turbulence: isotropy and axisymmetry, both based on the von Karman 3D spectrum.
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
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.
Saturation of the turbulent dynamo.
Schober, J; Schleicher, D R G; Federrath, C; Bovino, S; Klessen, R S
2015-08-01
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence. PMID:26382506
Turbulent energy flux generated by shock/homogeneous-turbulence interaction
NASA Astrophysics Data System (ADS)
Sinha, Krishnendu; Quadros, Russell; Larsson, Johan
2015-11-01
High-speed turbulent flows with shock waves are characterized by high localized surface heat transfer rates. Computational predictions are often inaccurate due to the limitations in modeling of the unclosed turbulent energy flux in the highly non-equilibrium regions of shock interaction. In this paper, we investigate the turbulent energy flux generated when homogeneous isotropic turbulence passes through a nominally normal shock wave. We use linear interaction analysis where the incoming turbulence is idealized as being composed of a collection of two-dimensional planar vorticity waves, and the shock wave is taken to be a discontinuity. The nature of the post-shock turbulent energy flux is predicted to be strongly dependent on the incidence angle of the incoming waves. The energy flux correlation is also decomposed into its vortical, entropy and acoustic contributions to understand its rapid non-monotonic variation behind the shock. Three-dimensional statistics, calculated by integrating two-dimensional results over a prescribed upstream energy spectrum, are compared with available direct numerical simulation data. A detailed budget of the governing equation is also considered in order to gain insight into the underlying physics.
Adams, Allan; Chesler, Paul M; Liu, Hong
2014-04-18
We construct turbulent black holes in asymptotically AdS4 spacetime by numerically solving Einstein's equations. Using the AdS/CFT correspondence we find that both the dual holographic fluid and bulk geometry display signatures of an inverse cascade with the bulk geometry being well approximated by the fluid-gravity gradient expansion. We argue that statistically steady-state black holes dual to d dimensional turbulent flows have horizons whose area growth has a fractal-like structure with fractal dimension D=d+4/3. PMID:24785028
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.
Coherence in Turbulence: New Perspective
NASA Astrophysics Data System (ADS)
Levich, Eugene
2009-07-01
It is claimed that turbulence in fluids is inherently coherent phenomenon. The coherence shows up clearly as strongly correlated helicity fluctuations of opposite sign. The helicity fluctuations have cellular structure forming clusters that are actually observed as vorticity bands and coherent structures in laboratory turbulence, direct numerical simulations and most obviously in atmospheric turbulence. The clusters are named BCC - Beltrami Cellular Clusters - because of the observed nearly total alignment of the velocity and vorticity fields in each particular cell, and hence nearly maximal possible helicity in each cell; although when averaged over all the cells the residual mean helicity in general is small and does not play active dynamical role. The Beltrami like fluctuations are short-lived and stabilize only in small and generally contiguous sub-domains that are tending to a (multi)fractal in the asymptotic limit of large Reynolds numbers, Re → ∞. For the model of homogeneous isotropic turbulence the theory predicts the leading fractal dimension of BCC to be: DF = 2.5. This particular BCC is responsible for generating the Kolmogorov -5/3 power law energy spectrum. The most obvious role that BCC play dynamically is that the nonlinear interactions in them are relatively reduced, due to strong spatial alignment between the velocity field v(r, t) and the vorticity field ω(r, t) = curlv(r, t), while the physical quantities typically best characterizing turbulence intermittency, such as entrophy, vorticity stretching and generation, and energy dissipation are maximized in and near them. The theory quantitatively relates the reduction of nonlinear inter-actions to the BCC fractal dimension DF and subsequent turbulence intermittency. It is further asserted that BCC is a fundamental feature of all turbulent flows, e.g., wall bounded turbulent flows, atmospheric and oceanic flows, and their leading fractal dimension remains invariant and universal in these flows
Turbulence transport with nonlocal interactions
Linn, R.R.; Clark, T.T.; Harlow, F.H.; Turner, L.
1998-03-01
This preliminary report describes a variety of issues in turbulence transport analysis with particular emphasis on closure procedures that are nonlocal in wave-number and/or physical space. Anomalous behavior of the transport equations for large scale parts of the turbulence spectrum are resolved by including the physical space nonlocal interactions. Direct and reverse cascade processes in wave-number space are given a much richer potential for realistic description by the nonlocal formulations. The discussion also describes issues, many still not resolved, regarding new classes of self-similar form functions.
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.
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.
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.
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.
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.
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.
Outflow Driven Turbulence in Star Forming Clouds
NASA Astrophysics Data System (ADS)
Frank, Adam
Setting young stellar object jets and outflows in their broadest context requires an understanding of outflows as “feedback” in the development of molecular cloud turbulence and the determination of star formation efficiencies. In this contribution I review our group’s recent studies exploring relationships between protostellar outflows and turbulence in molecular clouds. We first present studies of turbulence and fossil cavities driven by YSO outflows using numerical simulations which track the evolution of single transient jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. These studies demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Next we present simulations of multiple interacting jets. We show that turbulence can readily be sustained by these interactions and show that it is possible to broadly characterize an effective driving scale of the outflows. Comparing the velocity spectrum obtained in our studies to that of an isotropically forced control we show that in outflow driven turbulence a power law of the form E(k) ∝ k - β is indeed achieved. However we find a steeper spectrum β ˜ 3 is obtained in outflow driven turbulence models than in isotropically forced simulations β ˜ 2. 0. Taken together both studies provide broad support for the conclusion that fossil cavities driven by decaying jets can provide a source of turbulence and feedback which mediate star formation processes in molecular clouds. Whether this does obtain in real clouds remains a point which must be demonstrated
Performance of wind turbines in a turbulent atmosphere
NASA Technical Reports Server (NTRS)
Sundar, R. M.; Sullivan, J. P.
1981-01-01
The effect of atmospheric turbulence on the power fluctuations of large wind turbines was studied. The significance of spatial non-uniformities of the wind is emphasized. The turbulent wind with correlation in time and space is simulated on the computer by Shinozukas method. The wind turbulence is modelled according to the Davenport spectrum with an exponential spatial correlation function. The rotor aerodynamics is modelled by simple blade element theory. Comparison of the spectrum of power output signal between 1-D and 3-D turbulence, shows the significant power fluctuations centered around the blade passage frequency.
Two-dimensional convective turbulence
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.}
Electron magnetohydrodynamic turbulence: universal features
NASA Astrophysics Data System (ADS)
Shivamoggi, Bhimsen K.
2015-02-01
The energy cascade of electron magnetohydrodynamic (EMHD) turbulence is considered. Fractal and multi-fractal models for the energy dissipation field are used to determine the spatial intermittency corrections to the scaling behavior in the high-wavenumber (electron hydrodynamic limit) and low-wavenumber (magnetization limit) asymptotic regimes of the inertial range. Extrapolation of the multi-fractal scaling down to the dissipative microscales confirms in these asymptotic regimes a dissipative anomaly previously indicated by the numerical simulations of EMHD turbulence. Several basic features of the EMHD turbulent system are found to be universal which seem to transcend the existence of the characteristic length scale d e (which is the electron skin depth) in the EMHD problem: equipartition spectrum; Reynolds-number scaling of the dissipative microscales; scaling of the probability distribution function (PDF) of the electron-flow velocity (or magnetic field) gradient (even with intermittency corrections); dissipative anomaly; and critical exponent scaling.
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.
Aspects of wave turbulence in preheating
Crespo, José A.; De Oliveira, H.P. E-mail: oliveira@dft.if.uerj.br
2014-06-01
In this work we have studied the nonlinear preheating dynamics of several inflationary models. It is well established that after a linear stage of preheating characterized by the parametric resonance, the nonlinear dynamics becomes relevant driving the system towards turbulence. Wave turbulence is the appropriated description of this phase since the matter contents are fields instead of usual fluids. Turbulence develops due to the nonlinear interations of waves, here represented by the small inhomogeneities of the scalar fields. We present relevant aspects of wave turbulence such as the Kolmogorov-Zakharov spectrum in frequency and wave number that indicates the energy transfer through scales. From the power spectrum of the matter energy density we were able to estimate the temperature of the thermalized system.
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.
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.
NASA Technical Reports Server (NTRS)
Rubesin, Morris W.
1987-01-01
Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.
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.
Recent developments in plasma turbulence and turbulent transport
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.
Energy spectra in bubbly turbulence
NASA Astrophysics Data System (ADS)
Luther, Stefan; van den Berg, Thomas H.; Rensen, Judith; Lohse, Detlef
2004-11-01
The energy spectrum of single phase turbulent flow - apart from intermittency corrections - has been known since Kolomogorov 1941, E(k) ∝ k-5/3. How do bubbles modify this spectrum? To answer this question, we inject micro bubbles (radius 100 μm) in fully turbulent flow (Re_λ=200) up to volume concentrations of 0.3 %. Energy spectra and velocity structure functions are measured with hot-film anemometry. Under our experimental conditions, we find an enhancement of energy on small scales confirming numerical predictions by Mazzitelli, Lohse, and Toschi [Phys. Fluids 15, L5 (2003)]. They propose a mechanism in which bubbles are clustering most likely in downflow regions. This clustering is a lift force effect suppressing large vortical structures, while enhancing energy input on small scales.
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.
Energy spectra in microbubbly turbulence
NASA Astrophysics Data System (ADS)
van den Berg, Thomas H.; Luther, Stefan; Lohse, Detlef
2006-03-01
Microbubbles (R0=100μm) are injected in fully developed turbulence (Reλ=200) up to a volume concentration of 0.3%. An enhancement of the energy on small scales and a reduction on the large scales is observed, confirming theoretical prediction by I. Mazzitelli, D. Lohse, and F. Toschi [Phys. Fluids 15, L5 (2003)]. The result is a (nonuniversal) less steep slope than -5/3 in the power spectrum.
Phytoplankton's motion in turbulent ocean
NASA Astrophysics Data System (ADS)
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.
Phytoplankton's motion in turbulent ocean.
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. PMID:26274279
Whistler Wave Turbulence in Solar Wind Plasma
NASA Astrophysics Data System (ADS)
Shaikh, Dastgeer; Zank, G. P.
2010-03-01
Whistler waves are present in solar wind plasma. These waves possess characteristic turbulent fluctuations that are characterized typically by the frequency and length scales that are respectively bigger than ion gyro frequency and smaller than ion gyro radius. The electron inertial length is an intrinsic length scale in whistler wave turbulence that distinguishably divides the high frequency solar wind turbulent spectra into scales smaller and bigger than the electron inertial length. We present nonlinear three dimensional, time dependent, fluid simulations of whistler wave turbulence to investigate their role in solar wind plasma. Our simulations find that the dispersive whistler modes evolve entirely differently in the two regimes. While the dispersive whistler wave effects are stronger in the large scale regime, they do not influence the spectral cascades which are describable by a Kolmogorov-like k-7/3 spectrum. By contrast, the small scale turbulent fluctuations exhibit a Navier-Stokes like evolution where characteristic turbulent eddies exhibit a typical k-5/3 hydrodynamic turbulent spectrum. By virtue of equipartition between the wave velocity and magnetic fields, we quantify the role of whistler waves in the solar wind plasma fluctuations.
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.
Shell model for buoyancy-driven turbulence.
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)]. PMID:25974587
Explosive turbulent magnetic reconnection.
Higashimori, K; Yokoi, N; Hoshino, M
2013-06-21
We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence. PMID:23829741
Spin in an arbitrary gravitational field
NASA Astrophysics Data System (ADS)
Obukhov, Yuri N.; Silenko, Alexander J.; Teryaev, Oleg V.
2013-10-01
We study the quantum mechanics of a Dirac fermion on a curved spacetime manifold. The metric of the spacetime is completely arbitrary, allowing for the discussion of all possible inertial and gravitational field configurations. In this framework, we find the Hermitian Dirac Hamiltonian for an arbitrary classical external field (including the gravitational and electromagnetic ones). In order to discuss the physical content of the quantum-mechanical model, we further apply the Foldy-Wouthuysen transformation, and derive the quantum equations of motion for the spin and position operators. We analyze the semiclassical limit of these equations and compare the results with the dynamics of a classical particle with spin in the framework of the standard Mathisson-Papapetrou theory and in the classical canonical theory. The comparison of the quantum-mechanical and classical equations of motion of a spinning particle in an arbitrary gravitational field shows their complete agreement.
Engineering arbitrary pure and mixed quantum states
Pechen, Alexander
2011-10-15
Controlled manipulation by atomic- and molecular-scale quantum systems has attracted a lot of research attention in recent years. A fundamental problem is to provide deterministic methods for controlled engineering of arbitrary quantum states. This work proposes a deterministic method for engineering arbitrary pure and mixed states of a wide class of quantum systems. The method exploits a special combination of incoherent and coherent controls (incoherent and coherent radiation) and has two properties which are specifically important for manipulating by quantum systems: it realizes the strongest possible degree of their state control, complete density matrix controllability, meaning the ability to steer arbitrary pure and mixed initial states into any desired pure or mixed final state, and it is all-to-one, such that each particular control transfers all initial system states into one target state.
Arbitrariness, Iconicity, and Systematicity in Language.
Dingemanse, Mark; Blasi, Damián E; Lupyan, Gary; Christiansen, Morten H; Monaghan, Padraic
2015-10-01
The notion that the form of a word bears an arbitrary relation to its meaning accounts only partly for the attested relations between form and meaning in the languages of the world. Recent research suggests a more textured view of vocabulary structure, in which arbitrariness is complemented by iconicity (aspects of form resemble aspects of meaning) and systematicity (statistical regularities in forms predict function). Experimental evidence suggests these form-to-meaning correspondences serve different functions in language processing, development, and communication: systematicity facilitates category learning by means of phonological cues, iconicity facilitates word learning and communication by means of perceptuomotor analogies, and arbitrariness facilitates meaning individuation through distinctive forms. Processes of cultural evolution help to explain how these competing motivations shape vocabulary structure. PMID:26412098
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.
The residual zonal flow in tokamak plasmas toroidally rotating at arbitrary velocity
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.
Wavelet analysis of atmospheric turbulence
Hudgins, L.H.
1992-12-31
After a brief review of the elementary properties of Fourier Transforms, the Wavelet Transform is defined in Part I. Basic results are given for admissable wavelets. The Multiresolution Analysis, or MRA (a mathematical structure which unifies a large class of wavelets with Quadrature Mirror Filters) is then introduced. Some fundamental aspects of wavelet design are then explored. The Discrete Wavelet Transform is discussed and, in the context of an MRA, is seen to supply a Fast Wavelet Transform which competes with the Fast Fourier Transform for efficiency. In Part II, the Wavelet Transform is developed in terms of the scale number variable s instead of the scale length variable a where a = 1/s. Basic results such as the admissibility condition, conservation of energy, and the reconstruction theorem are proven in this context. After reviewing some motivation for the usual Fourier power spectrum, a definition is given for the wavelet power spectrum. This `spectral density` is then intepreted in the context of spectral estimation theory. Parseval`s theorem for Wavelets then leads naturally to the Wavelet Cross Spectrum, Wavelet Cospectrum, and Wavelet Quadrature Spectrum. Wavelet Transforms are then applied in Part III to the analysis of atmospheric turbulence. Data collected over the ocean is examined in the wavelet transform domain for underlying structure. A brief overview of atmospheric turbulence is provided. Then the overall method of applying Wavelet Transform techniques to time series data is described. A trace study is included, showing some of the aspects of choosing the computational algorithm, and selection of a specific analyzing wavelet. A model for generating synthetic turbulence data is developed, and seen to yield useful results in comparing with real data for structural transitions. Results from the theory of Wavelet Spectral Estimation and Wavelength Cross-Transforms are applied to studying the momentum transport and the heat flux.
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.
Arbitrary Steady-State Solutions with the K-epsilon Model
NASA Technical Reports Server (NTRS)
Rumsey, Christopher L.; Pettersson Reif, B. A.; Gatski, Thomas B.
2006-01-01
Widely-used forms of the K-epsilon turbulence model are shown to yield arbitrary steady-state converged solutions that are highly dependent on numerical considerations such as initial conditions and solution procedure. These solutions contain pseudo-laminar regions of varying size. By applying a nullcline analysis to the equation set, it is possible to clearly demonstrate the reasons for the anomalous behavior. In summary, the degenerate solution acts as a stable fixed point under certain conditions, causing the numerical method to converge there. The analysis also suggests a methodology for preventing the anomalous behavior in steady-state computations.
Turbulent eddy viscosity modeling in transonic shock/boundary-layer interactions
NASA Technical Reports Server (NTRS)
Inger, G. R.
1989-01-01
The treatment of turbulence effects on transonic shock/turbulent boundary layer interaction is addressed within the context of a triple deck approach valid for arbitrary practical Reynolds numbers between 1000 and 10 billion. The modeling of the eddy viscosity and basic turbulent boundary profile effects in each deck is examined in detail using Law-of-the-Wall/Law-of-the-Wake concepts as the foundation. Results of parametric studies showing how each of these turbulence model aspects influences typical interaction zone property distributions (wall pressure, displacement thickness and local skin friction) are presented and discussed.
... the Zellweger spectrum result from defects in the assembly of a cellular structure called the peroxisome, and ... Zellweger spectrum are caused by defects in the assembly of the peroxisome. There are at least 12 ...
Signal modeling of turbulence-distorted imagery
NASA Astrophysics Data System (ADS)
Young, S. Susan; Driggers, Ronald G.; Krapels, Keith; Espinola, Richard L.; Reynolds, Joseph P.; Cha, Jae
2009-05-01
Understanding turbulence effects on wave propagation and imaging systems has been an active research area for more than 50 years. Conventional atmospheric optics methods use statistical models to analyze image degradation effects that are caused by turbulence. In this paper, we intend to understand atmospheric turbulence effects using a deterministic signal processing and imaging theory point of view and modeling. The model simulates the formed imagery by a lens by tracing the optical rays from the target through a band of turbulence. We examine the nature of the turbulence-degraded image, and identify its characteristics as the parameters of the band of turbulence, e.g., its width, angle, and index of refraction, are varied. Image degradation effects due to turbulence, such as image blurring and image dancing, are revealed by this signal modeling. We show that in fact these phenomena can be related not only to phase errors in the frequency domain of the image but also a 2D modulation effect in the image spectrum. Results with simulated and realistic data are provided.
Shock-turbulence interaction and the generation of noise
NASA Technical Reports Server (NTRS)
Ribner, H S
1954-01-01
Interaction of convected field of turbulence with shock wave is analyzed to yield modified turbulence, entropy spottiness, and noise generated downstream of the shock. Analysis is generalization of single-spectrum-wave treatment of NACA-TN-2864. Formulas for spectra and correlations are obtained. Numerical calculations yield curves of rms velocity components, temperature, pressure, and noise in db against Mach number for m = 1 to infinity; both isotropic and strongly axisymmetric (lateral/longitudinal = 36/1) initial turbulence are treated. In either case, turbulence of 0.1 percent longitudinal component generates about 120 dbs of noise.
Reflective ghost imaging through turbulence
Hardy, Nicholas D.; Shapiro, Jeffrey H.
2011-12-15
Recent work has indicated that ghost imaging may have applications in standoff sensing. However, most theoretical work has addressed transmission-based ghost imaging. To be a viable remote-sensing system, the ghost imager needs to image rough-surfaced targets in reflection through long, turbulent optical paths. We develop, within a Gaussian-state framework, expressions for the spatial resolution, image contrast, and signal-to-noise ratio of such a system. We consider rough-surfaced targets that create fully developed speckle in their returns and Kolmogorov-spectrum turbulence that is uniformly distributed along all propagation paths. We address both classical and nonclassical optical sources, as well as a computational ghost imager.
Forced organization of flute-type turbulence by convective cell injection
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.
Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow
NASA Astrophysics Data System (ADS)
Hawkins, Christopher; Angheluta, Luiza; Krotkiewski, Marcin; Jamtveit, Bjørn
2016-04-01
In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity KL, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of KL(Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the KL(Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing
2016-08-01
Rytov theory was employed to establish the transmission model for the optical vortices carried by Bessel-Gaussian (BG) beams in weak anisotropic turbulence based on the generalized anisotropic von Karman spectrum. The influences of asymmetry anisotropic turbulence eddies and source parameters on the signal orbital angular momentum (OAM) mode detection probability of partially coherent BG beams in anisotropic turbulence were discussed. Anisotropic characteristics of the turbulence could enhance the OAM mode transmission performance. The spatial partially coherence of the beam source would increase turbulent aberration's effect on the optical vortices. BG beams could dampen the influences of the turbulence because of their nondiffraction and self-healing characteristics. PMID:27505641
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.
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.
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.
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.
Fraunhofer diffraction by arbitrary-shaped obstacles.
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. PMID:19649110
Quantum Fidelity for Arbitrary Gaussian States.
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. PMID:26764978
Arbitrary Lagrangian Eulerian Adaptive Mesh Refinement
Koniges, A.; Eder, D.; Masters, N.; Fisher, A.; Anderson, R.; Gunney, B.; Wang, P.; Benson, D.; Dixit, P.
2009-09-29
This is a simulation code involving an ALE (arbitrary Lagrangian-Eulerian) hydrocode with AMR (adaptive mesh refinement) and pluggable physics packages for material strength, heat conduction, radiation diffusion, and laser ray tracing developed a LLNL, UCSD, and Berkeley Lab. The code is an extension of the open source SAMRAI (Structured Adaptive Mesh Refinement Application Interface) code/library. The code can be used in laser facilities such as the National Ignition Facility. The code is alsi being applied to slurry flow (landslides).
Distinguishing Proteins From Arbitrary Amino Acid Sequences
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
Felten, T.; Schlickeiser, R.
2013-10-15
Using the general expressions for the magnetic fluctuation spectrum from uncorrelated plasma particles, it is shown that an isotropic, unmagnetized plasma with arbitrary momentum distribution function spontaneously emits an aperiodic, collective, transverse, damped mode. The collective mode with the dispersion relation γ(k) provides the strongest contribution to the magnetic field fluctuation spectrum. Its existence has been proven before for Maxwellian and Lorentzian plasma distribution functions. Here it is demonstrated that this collective aperiodic mode exists in any isotropic unmagnetized, irrespective of the explicit form of the momentum distribution of plasma particles.
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.
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.
Ohira, Yutaka
2013-04-10
We consider particle acceleration by large-scale incompressible turbulence with a length scale larger than the particle mean free path. We derive an ensemble-averaged transport equation of energetic charged particles from an extended transport equation that contains the shear acceleration. The ensemble-averaged transport equation describes particle acceleration by incompressible turbulence (turbulent shear acceleration). We find that for Kolmogorov turbulence, the turbulent shear acceleration becomes important on small scales. Moreover, using Monte Carlo simulations, we confirm that the ensemble-averaged transport equation describes the turbulent shear acceleration.
Geophysical and astrophysical turbulence
NASA Astrophysics Data System (ADS)
Moffatt, H. K.
Spiral structures in two-dimensional turbulence are studied and a theory (Moffatt, 1985, 1986) which regards fully three-dimensional turbulence as an agglomeration of 'random vortex sheets and coherent helical structures' is reviewed. Consideration is given to the process by which current-sheet discontinuities may appear during magnetic relaxation. Within the framework of dynamo theory, the determination of the generation coefficient and the turbulent diffusivity in mean-field electrodynamics for turbulence with helicity in the limit of a large magnetic Reynolds number is discussed. Certain features of 'chromospheric turbulence' (i.e., turbulence in the solar atmosphere outside the photosphere) are also examined.
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.
TURBULENT DISKS ARE NEVER STABLE: FRAGMENTATION AND TURBULENCE-PROMOTED PLANET FORMATION
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.
The Dissipation Range of Interstellar Turbulence
NASA Astrophysics Data System (ADS)
Spangler, Steven R.; Buffo, J. J.
2013-06-01
Turbulence may play an important role in a number of interstellar processes. One of these is heating of the interstellar gas, as the turbulent energy is dissipated and changed into thermal energy of the gas, or at least other forms of energy. There have been very promising recent results on the mechanism for dissipation of turbulence in the Solar Wind (Howes et al, Phys. Plasm. 18, 102305, 2011). In the Solar Wind, the dissipation arises because small-scale irregularities develop properties of kinetic Alfven waves, and apparently damp like kinetic Alfven waves. A property of kinetic Alfven waves is that they become significantly compressive on size scales of order the ion Larmor radius. Much is known about the plasma properties of ionized components of interstellar medium such as HII regions and the Diffuse Ionized Gas (DIG) phase, including information on the turbulence in these media. The technique of radio wave scintillations can yield properties of HII region and DIG turbulence on scales of order the ion Larmor radius, which we refer to as the dissipation scale. In this paper, we collect results from a number of published radio scattering measurements of interstellar turbulence on the dissipation scale. These studies show evidence for a spectral break on the dissipation scale, but no evidence for enhanced compressibility of the fluctuations. The simplest explanation of our result is that turbulence in the ionized interstellar medium does not possess properties of kinetic Alfven waves. This could point to an important difference with Solar Wind turbulence. New observations, particularly with the Very Long Baseline Array (VLBA) could yield much better measurements of the power spectrum of interstellar turbulence in the dissipation range. This research was supported at the University of Iowa by grants AST09-07911 and ATM09-56901 from the National Science Foundation.
Turbulence in simulated H II regions
NASA Astrophysics Data System (ADS)
Medina, S.-N. X.; Arthur, S. J.; Henney, W. J.; Mellema, G.; Gazol, A.
2014-12-01
We investigate the scale dependence of fluctuations inside a realistic model of an evolving turbulent H II region and to what extent these may be studied observationally. We find that the multiple scales of energy injection from champagne flows and the photoionization of clumps and filaments leads to a flatter spectrum of fluctuations than would be expected from top-down turbulence driven at the largest scales. The traditional structure function approach to the observational study of velocity fluctuations is shown to be incapable of reliably determining the velocity power spectrum of our simulation. We find that a more promising approach is the Velocity Channel Analysis technique of Lazarian & Pogosyan (2000), which, despite being intrinsically limited by thermal broadening, can successfully recover the logarithmic slope of the velocity power spectrum to a precision of ±0.1 from high-resolution optical emission-line spectroscopy.
Probing turbulence in the Coma galaxy cluster
NASA Astrophysics Data System (ADS)
Schuecker, P.; Finoguenov, A.; Miniati, F.; Böhringer, H.; Briel, U. G.
2004-11-01
Spatially-resolved gas pressure maps of the Coma galaxy cluster are obtained from a mosaic of XMM-Newton observations in the scale range between a resolution of 20 kpc and an extent of 2.8 Mpc. A Fourier analysis of the data reveals the presence of a scale-invariant pressure fluctuation spectrum in the range between 40 and 90 kpc and is found to be well described by a projected Kolmogorov/Oboukhov-type turbulence spectrum. Deprojection and integration of the spectrum yields the lower limit of ˜ 10 percent of the total intracluster medium pressure in turbulent form. The results also provide observational constraints on the viscosity of the gas. Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).
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.
Statistical theory of turbulent incompressible multimaterial flow
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.
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.
Distinguishing ichthyogenic turbulence from geophysical turbulence
NASA Astrophysics Data System (ADS)
Pujiana, Kandaga; Moum, James N.; Smyth, William D.; Warner, Sally J.
2015-05-01
Measurements of currents and turbulence beneath a geostationary ship in the equatorial Indian Ocean during a period of weak surface forcing revealed unexpectedly strong turbulence beneath the surface mixed layer. Coincident with the turbulence was a marked reduction of the current speeds registered by shipboard Doppler current profilers, and an increase in their variability. At a mooring 1 km away, measurements of turbulence and currents showed no such anomalies. Correlation with the shipboard echo sounder measurements indicate that these nighttime anomalies were associated with fish aggregations beneath the ship. The fish created turbulence by swimming against the strong zonal current in order to remain beneath the ship, and their presence affected the Doppler speed measurements. The principal characteristics of the resultant ichthyogenic turbulence are (i) low wave number roll-off of shear spectra in the inertial subrange relative to geophysical turbulence, (ii) Thorpe overturning scales that are small compared with the Ozmidov scale, and (iii) low mixing efficiency. These factors extend previous findings by Gregg and Horne (2009) to a very different biophysical regime and support the general conclusion that the biological contribution to mixing the ocean via turbulence is negligible.
Characterization of Turbulent Flows for Turbulence Modeling
NASA Astrophysics Data System (ADS)
Reynolds, W. C.; Haire, S. L.
1998-11-01
A diagram for the characterization of turbulent flows using the invariants of the mean velocity gradient tensor is introduced. All mean flows, from irrotationally strained flows to shearing flows, to purely rotational flows, can be identified on this diagram. Different flow fields which occupy the same region on the diagram are said to be comprised of the same topological features. The current state of turbulence modeling can be identified on the diagram based on the type of mean flow fields which can be accurately computed. Regions on the diagram can be shown for which current capabilities in turbulence modeling fail to accurately resolve the turbulent structures. Relevant mean field topology is identified for future work in turbulence modeling. Using this analysis, we suggest a number of flows to be computed by DNS or LES and used as testing cases for new models.
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.
Transient scattering from a thin arbitrary wire
NASA Astrophysics Data System (ADS)
Mohan, S. Ananda; Rao, Sadasiva M.
1988-08-01
The conjugate gradient (CG) method is applied to solve the problem of transient scattering from a thin arbitrary wire. The method is simple, efficient, and yields more accurate results than the marching-on-in-time procedure. Numerical examples for the case of a bent wire, a wire with discontinuous radii, and a circular loop are presented to highlight the advantages of this procedure. It is concluded that the occurrence of late-time oscillations may not be due to the accumulation of truncation of roundoff errors. These oscillations may be attributed to the insufficient sampling of the structure.
Gaussian quadrature formulae for arbitrary positive measures.
Fernandes, Andrew D; Atchley, William R
2006-01-01
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
Fluid distributions in random media - Arbitrary matrices
NASA Astrophysics Data System (ADS)
Madden, William G.
1992-04-01
The graphical theory of Madden and Glandt (1988) for a fluid adsorbed into a quenched medium is extended to situations in which the distribution of the immobile species has an arbitrary form, not necessarily arising from a thermal quench. The working equations of Madden and Glandt are shown to be applicable to this general case, and the approximations common in the theory of equilibrium mixtures are appropriate in this application as well. Extensions to mixtures are considered, and the connection with the graphical theory of small molecules is discussed.
Electron parallel closures for arbitrary collisionality
Ji, Jeong-Young Held, Eric D.
2014-12-15
Electron parallel closures for heat flow, viscosity, and friction force are expressed as kernel-weighted integrals of thermodynamic drives, the temperature gradient, relative electron-ion flow velocity, and flow-velocity gradient. Simple, fitted kernel functions are obtained for arbitrary collisionality from the 6400 moment solution and the asymptotic behavior in the collisionless limit. The fitted kernels circumvent having to solve higher order moment equations in order to close the electron fluid equations. For this reason, the electron parallel closures provide a useful and general tool for theoretical and computational models of astrophysical and laboratory plasmas.
Adding control to arbitrary unknown quantum operations
Zhou, Xiao-Qi; Ralph, Timothy C.; Kalasuwan, Pruet; Zhang, Mian; Peruzzo, Alberto; Lanyon, Benjamin P.; O'Brien, Jeremy L.
2011-01-01
Although quantum computers promise significant advantages, the complexity of quantum algorithms remains a major technological obstacle. We have developed and demonstrated an architecture-independent technique that simplifies adding control qubits to arbitrary quantum operations—a requirement in many quantum algorithms, simulations and metrology. The technique, which is independent of how the operation is done, does not require knowledge of what the operation is, and largely separates the problems of how to implement a quantum operation in the laboratory and how to add a control. Here, we demonstrate an entanglement-based version in a photonic system, realizing a range of different two-qubit gates with high fidelity. PMID:21811242
Arbitrary Lagrangian Eulerian Adaptive Mesh Refinement
Energy Science and Technology Software Center (ESTSC)
2009-09-29
This is a simulation code involving an ALE (arbitrary Lagrangian-Eulerian) hydrocode with AMR (adaptive mesh refinement) and pluggable physics packages for material strength, heat conduction, radiation diffusion, and laser ray tracing developed a LLNL, UCSD, and Berkeley Lab. The code is an extension of the open source SAMRAI (Structured Adaptive Mesh Refinement Application Interface) code/library. The code can be used in laser facilities such as the National Ignition Facility. The code is alsi being appliedmore » to slurry flow (landslides).« less
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}}++.
Multiboson Correlation Interferometry with Arbitrary Single-Photon Pure States.
Tamma, Vincenzo; Laibacher, Simon
2015-06-19
We provide a compact full description of multiboson correlation measurements of arbitrary order N in passive linear interferometers with arbitrary input single-photon pure states. This allows us to physically analyze the novel problem of multiboson correlation sampling at the output of random linear interferometers. Our results also describe general multiboson correlation landscapes for an arbitrary number of input single photons and arbitrary interferometers. In particular, we use two different schemes to demonstrate, respectively, arbitrary-order quantum beat interference and 100% visibility entanglement correlations even for input photons distinguishable in their frequencies. PMID:26196976
COLLISIONLESS DAMPING AT ELECTRON SCALES IN SOLAR WIND TURBULENCE
TenBarge, J. M.; Howes, G. G.; Dorland, W.
2013-09-10
The dissipation of turbulence in the weakly collisional solar wind plasma is governed by unknown kinetic mechanisms. Two candidates have been suggested to play an important role in the dissipation, collisionless damping via wave-particle interactions and dissipation in small-scale current sheets. High resolution spacecraft measurements of the turbulent magnetic energy spectrum provide important constraints on the dissipation mechanism. The limitations of popular fluid and hybrid numerical schemes for simulation of the dissipation of solar wind turbulence are discussed, and instead a three-dimensional kinetic approach is recommended. We present a three-dimensional nonlinear gyrokinetic simulation of solar wind turbulence at electron scales that quantitatively reproduces the exponential form of the turbulent magnetic energy spectrum measured in the solar wind. A weakened cascade model that accounts for nonlocal interactions and collisionless Landau damping also quantitatively agrees with the observed exponential form. These results establish that a turbulent cascade of kinetic Alfven waves that is terminated by collisionless Landau damping is sufficient to explain the observed magnetic energy spectrum in the dissipation range of solar wind turbulence.
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)
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.
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. PMID:26698490
Introduction to quantum turbulence.
Barenghi, Carlo F; Skrbek, Ladislav; Sreenivasan, Katepalli R
2014-03-25
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
Modeling Compressed Turbulence
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.
Introduction to quantum turbulence
Barenghi, Carlo F.; Skrbek, Ladislav; Sreenivasan, Katepalli R.
2014-01-01
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose–Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics. PMID:24704870
THE VIOLATION OF THE TAYLOR HYPOTHESIS IN MEASUREMENTS OF SOLAR WIND TURBULENCE
Klein, K. G.; Howes, G. G.; TenBarge, J. M.
2014-08-01
Motivated by the upcoming Solar Orbiter and Solar Probe Plus missions, qualitative and quantitative predictions are made for the effects of the violation of the Taylor hypothesis on the magnetic energy frequency spectrum measured in the near-Sun environment. The synthetic spacecraft data method is used to predict observational signatures of the violation for critically balanced Alfvénic turbulence or parallel fast/whistler turbulence. The violation of the Taylor hypothesis can occur in the slow flow regime, leading to a shift of the entire spectrum to higher frequencies, or in the dispersive regime, in which the dissipation range spectrum flattens at high frequencies. It is found that Alfvénic turbulence will not significantly violate the Taylor hypothesis, but whistler turbulence will. The flattening of the frequency spectrum is therefore a key observational signature for fast/whistler turbulence.
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.
Electron magnetohydrodynamics: dynamics and turbulence.
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 k(1)=k(2) 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 [proportionality]k(-2). The cascade remains weak (not critically balanced). The cascade is UV local, while the infrared locality is weakly (logarithmically) violated. PMID:24329368
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.
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
Spinor Structure and Matter Spectrum
NASA Astrophysics Data System (ADS)
Varlamov, V. V.
2016-08-01
Classification of relativistic wave equations is given on the ground of interlocking representations of the Lorentz group. A system of interlocking representations is associated with a system of eigenvector subspaces of the energy operator. Such a correspondence allows one to define matter spectrum, where the each level of this spectrum presents a some state of elementary particle. An elementary particle is understood as a superposition of state vectors in nonseparable Hilbert space. Classification of indecomposable systems of relativistic wave equations is produced for bosonic and fermionic fields on an equal footing (including Dirac and Maxwell equations). All these fields are equivalent levels of matter spectrum, which differ from each other by the value of mass and spin. It is shown that a spectrum of the energy operator, corresponding to a given matter level, is non-degenerate for the fields of type (l, 0) ⊕ (0, l), where l is a spin value, whereas for arbitrary spin chains we have degenerate spectrum. Energy spectra of the stability levels (electron and proton states) of the matter spectrum are studied in detail. It is shown that these stability levels have a nature of threshold scales of the fractal structure associated with the system of interlocking representations of the Lorentz group.
Rank-Ordered Multifractal Analysis of Probability Distributions in Fluid Turbulence
NASA Astrophysics Data System (ADS)
Wu, Cheng-Chin; Chang, Tien
2015-11-01
Rank-Ordered Multifractal Analysis (ROMA) was introduced by Chang and Wu (2008) to describe the multifractal characteristic of intermittent events. The procedure provides a natural connection between the rank-ordered spectrum and the idea of one-parameter scaling for monofractals. This technique has successfully been applied to MHD turbulence simulations and turbulence data observed in various space plasmas. In this paper, the technique is applied to the probability distributions in the inertial range of the turbulent fluid flow, as given in the vast Johns Hopkins University (JHU) turbulence database. In addition, a refined method of finding the continuous ROMA spectrum and the scaled probability distribution function (PDF) simultaneously is introduced.
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.
Spin filter for arbitrary spins by substrate engineering.
Pal, Biplab; Römer, Rudolf A; Chakrabarti, Arunava
2016-08-24
We design spin filters for particles with potentially arbitrary spin [Formula: see text] 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. PMID:27352129
Transmission spectrum of an optical cavity containing N atoms
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.
Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers
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
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.
NONLINEAR MULTISCALE SIMULATION OF TURBULENT FLUX TUBES
Ragot, B. R.
2011-10-20
A new method for the full nonlinear computation of sets of turbulent field lines has recently been introduced that allows inclusion of the equivalent of more than four decades of turbulent scales with a fully three-dimensional distribution of wavevectors. The integration scheme is here detailed, which, through transformation of the set of differential equations into mappings, compounds the efficiency and accuracy of the method. The potential of the method is then demonstrated with multiscale simulations of magnetic flux tubes ranging over nearly four decades of length scales both along and across the background field. Magnetic flux tubes of various sizes are computed for a turbulence spectrum typical of the quiet slow solar wind near 1 AU. Implications of the simulation results for the transport of energetic particles, and in particular, for the interpretation of impulsive solar-energetic-particle and upstream ion-event observations are discussed.
Acquired scaling relations in dark matter turbulence
NASA Astrophysics Data System (ADS)
Nakamichi, Akika; Morikawa, Masahiro
2010-01-01
Variety of scaling relations are observed in astronomical objects. We study a consistent understanding of them from a simple proposal that the collision-less dark matter fluid terns into a turbulent state, i.e. cosmic dark turbulence. This happens most likely when the density fluctuations cross the caustic surface toward the non-linear regime. Collision-less dark turbulence may not be eddy-dominant. We first derive Kolmogorov scaling laws from the gravitational Navier-Stokes equation by the method similar to the case in Smoluchowski coagulation equation. Then we apply this to several observations such as the scale-dependent velocity dispersion, mass-luminosity ratio, magnetic fields, and mass-angular momentum relation, power spectrum of density fluctuations. They all conclude a single value for a constant energy flow per mass: 0.3cm2/sec3. This value may deeply related with the speed of the hierarchical coalescence process in the cosmic structure formation.
Holographic vortex liquids and superfluid turbulence.
Chesler, Paul M; Liu, Hong; Adams, Allan
2013-07-26
Superfluid turbulence is a fascinating phenomenon for which a satisfactory theoretical framework is lacking. Holographic duality provides a systematic approach to studying such quantum turbulence by mapping the dynamics of a strongly interacting quantum liquid into the dynamics of classical gravity. We use this gravitational description to numerically construct turbulent flows in a holographic superfluid in two spatial dimensions. We find that the superfluid kinetic energy spectrum obeys the Kolmogorov -5/3 scaling law, with energy injected at long wavelengths undergoing a direct cascade to short wavelengths where dissipation by vortex annihilation and vortex drag becomes efficient. This dissipation has a simple gravitational interpretation as energy flux across a black hole event horizon. PMID:23888034
Intensity fluctuations of ultrasonic scattering in a highly turbulent flow.
Shen, C; Lemmin, U
2000-05-01
Aspects of ultrasound intensity fluctuations backscattered from additive microstructures in a turbulent flow have been investigated theoretically and experimentally for the conditions of a small insonified volume, a high sound frequency and strong turbulence. These conditions are typically found in high resolution Doppler sonar applications. An easily applicable expression for the auto-correlation of scattering intensity fluctuations is obtained by introducing open-channel turbulence theory, a semi-empirical scalar spectrum (including a Batchelor spectrum) and a Gaussian window function. Experiments carried out in a laboratory-clear water, open-channel flow for different turbulence levels verify the underlying assumptions. A good agreement is found with the predictions made with the above-derived expression. The feasibility of extracting flow information from the backscattered intensity fluctuations is discussed. PMID:10857575
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.
Triad interactions in multi-scale ITG/TEM/ETG turbulence
NASA Astrophysics Data System (ADS)
Maeyama, Shinya; Watanabe, Tomohiko; Idomura, Yasuhiro; Nakata, Motoki; Ishizawa, Akihiro; Nunami, Masanori
2015-11-01
Most of turbulent transport studies assume scale separation between electron- and ion-scale turbulence. However, latest massively parallel simulations based on gyrokinetics reveal that multi-scale interactions between electron- and ion-scale turbulence can influence turbulent transport [S. Maeyama, Phys. Rev. Lett. 114, 255002 (2015)]. The physical mechanism is investigated by applying triad transfer analysis. It is revealed that short-wave-length ITG turbulent eddies stabilize electron-scale streamers. Additionally, it is found that electron-scale turbulence has a damping effect on zonal flows. As a result, turbulent transport spectrum obtained from the multi-scale turbulence simulation differs from the sum of ones obtained from single-scale simulations. We will discuss gyrokinetic triad transfer analysis and the applicability of its fluid approximation, and explain the physical mechanism of multi-scale interactions by means of triad transfer analysis.
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
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
2015-07-01
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
Computing periodic orbits with arbitrary precision.
Abad, Alberto; Barrio, Roberto; Dena, Angeles
2011-07-01
This paper deals with the computation of periodic orbits of dynamical systems up to any arbitrary precision. These very high requirements are useful, for example, in the studies of complex pole location in many physical systems. The algorithm is based on an optimized shooting method combined with a numerical ordinary differential equation (ODE) solver, tides, that uses a Taylor-series method. Nowadays, this methodology is the only one capable of reaching precision up to thousands of digits for ODEs. The method is shown to be quadratically convergent. Some numerical tests for the paradigmatic Lorenz model and the Hénon-Heiles Hamiltonian are presented, giving periodic orbits up to 1000 digits. PMID:21867337
Two-Bounce Optical Arbitrary Permutation Network
NASA Astrophysics Data System (ADS)
Christensen, Marc P.; Haney, Michael W.
1998-05-01
The two-bounce free-space arbitrary interconnection architecture is presented. It results from a series of three-dimensional topological transformations to the Benes network, the minimum rearrangeable nonblocking network. Although functionally equivalent to the Benes network, it requires only two stages of global (spanning multiple chips) optical interconnections. The remaining stages of the modified Benes interconnection network are local and are implemented electronically (on individual chips). The two-bounce network is optimal in the sense that it retains the Benes minimum number of electronic switching resources yet also minimizes the number of optical links needed for global interconnection. Despite the use of higher-order k -shuffle ( k 2 ) global optical interconnects, the number of 2 2 switching elements is identical to the two-shuffle Benes network: there is no need for k k crossbar switches for local interconnection at each stage. An experimental validation of the two-bounce architecture is presented.
Electronic structure calculations in arbitrary electrostatic environments
NASA Astrophysics Data System (ADS)
Watson, Mark A.; Rappoport, Dmitrij; Lee, Elizabeth M. Y.; Olivares-Amaya, Roberto; Aspuru-Guzik, Alán
2012-01-01
Modeling of electronic structure of molecules in electrostatic environments is of considerable relevance for surface-enhanced spectroscopy and molecular electronics. We have developed and implemented a novel approach to the molecular electronic structure in arbitrary electrostatic environments that is compatible with standard quantum chemical methods and can be applied to medium-sized and large molecules. The scheme denoted CheESE (chemistry in electrostatic environments) is based on the description of molecular electronic structure subject to a boundary condition on the system/environment interface. Thus, it is particularly suited to study molecules on metallic surfaces. The proposed model is capable of describing both electrostatic effects near nanostructured metallic surfaces and image-charge effects. We present an implementation of the CheESE model as a library module and show example applications to neutral and negatively charged molecules.
Cloning quantum entanglement in arbitrary dimensions
Karpov, E.; Navez, P.; Cerf, N.J.
2005-10-15
We have found a quantum cloning machine that optimally duplicates the entanglement of a pair of d-dimensional quantum systems prepared in an arbitrary isotropic state. It maximizes the entanglement of formation contained in the two copies of any maximally entangled input state, while preserving the separability of unentangled input states. Moreover, it cannot increase the entanglement of formation of isotropic states. For large d, the entanglement of formation of each clone tends to one-half the entanglement of the input state, which corresponds to a classical behavior. Finally, we investigate a local entanglement cloner, which yields entangled clones with one-fourth the input entanglement in the large-d limit.
Scattering of Massless Particles in Arbitrary Dimensions
NASA Astrophysics Data System (ADS)
Cachazo, Freddy; He, Song; Yuan, Ellis Ye
2014-10-01
We present a compact formula for the complete tree-level S-matrix of pure Yang-Mills and gravity theories in arbitrary spacetime dimensions. The new formula for the scattering of n particles is given by an integral over the positions of n points on a sphere restricted to satisfy a dimension-independent set of equations. The integrand is constructed using the reduced Pfaffian of a 2n ×2n matrix, Ψ, that depends on momenta and polarization vectors. In its simplest form, the gravity integrand is a reduced determinant which is the square of the Pfaffian in the Yang-Mills integrand. Gauge invariance is completely manifest as it follows from a simple property of the Pfaffian.
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.
Toward the Theory of Turbulence in Magnetized Plasmas
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.
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.
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.
Perpendicular ion heating by anisotropic whistler turbulence at electron scales
NASA Astrophysics Data System (ADS)
Saito, S.; Nariyuki, Y.
2013-12-01
Magnetic energy spectrum in the solar wind turbulence is observed in very broad scale range, extending from Magnetohydrodynamic (MHD) scales to electron scales. The frequency spectrum observed at a position of spacecraft has a power-law feature, but its index is different depending on the frequency range. In low frequencies (< 0.1Hz) corresponding to the MHD scales in the solar wind at 1AU, where the Taylor hypothesis (scale size = solar wind speed / observed frequency) is assumed, the power-law index -5/3 is typically observed. This scale range is referred to as the inertial range. At higher frequencies, which correspond to the shorter scales, the power-law spectrum tends to be steeper than the inertial range. The steeper spectrum is considered to be due to the dissipation and/or dispersion effect of kinetic-wave turbulence. Many authors have discussed nonlinear properties and dissipation processes of the kinetic-wave turbulence at the ion and electron scales in theory, simulation, and observation. By using particle-in-cell simulation that includes kinetic effects of both ions and electrons, we study the ion heating by anisotropic whistler turbulence at electron scales that is of the order of electron inertial length. Whistler turbulence cascades their fluctuation energy in wavenumber space more preferentially to the perpendicular direction to the background magnetic field than parallel. The highly obliquely propagating whistler waves have electric fluctuations at wavenumbers perpendicular to the background magnetic field. By interacting with the perpendicular electric fluctuations, the ions are stochastically scattered into the perpendicular direction. Our simulation results show that whistler turbulence can transfer their fluctuation energy into not only electrons but also the perpendicular energy of ions. It suggests that whistler turbulence even at the electron scales contributes the perpendicular heating of protons in the solar wind. Whistler turbulence could
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.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2016-04-01
In this study, the modified anisotropic turbulence refractive-index fluctuations spectral model is derived based on the extended Rytov approximation theory for the theoretical investigations of optical plane and spherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. The anisotropic factor which parameterizes the asymmetry of turbulence cells or eddies in the horizontal and vertical directions is introduced. The general spectral power law in the range of 3-4 is also considered compared with the conventional classic value of 11/3 for Kolmogorov turbulence. Based on the modified anisotropic turbulence refractive-index fluctuations spectrum, the analytic expressions of the irradiance scintillation index are also derived for optical plane and spherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. They are applicable in a wide range of turbulence strengths and can reduce correctly to the previously published results in the special cases of weak anisotropic turbulence and moderate-to-strong isotropic turbulence. Calculations are performed to analyze the derived models. PMID:27140754
Wave turbulent diffusion due to the Doppler shift
NASA Astrophysics Data System (ADS)
Balk, A. M.
2006-08-01
Turbulent diffusion of a passive tracer caused by a random wavefield is believed to be quadratic with respect to the energy spectrum ɛk of the velocity field (i.e. proportional to epsi4, where epsi is the order of the wave amplitudes). So, the wave turbulent diffusion (say, on the ocean surface or in the air) is often believed to be dominated by the turbulent diffusion due to the incompressible flow. In this paper, we show that the wave turbulent diffusion can be associated with the Doppler shift and find that the wave turbulent diffusion can be more significant than previously thought. This mechanism works if the velocity field is compressible and statistically anisotropic, with the result that the wave system has a significant Stokes drift. The contribution of this mechanism has a lower order in epsi. We confirm our results with numerical simulations. To derive these results, we develop the statistical near-identity transformation.
Turbulence generation by waves
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.
NASA Astrophysics Data System (ADS)
Adhikari, L.; Zank, G. P.; Hunana, P.; Bruno, R.; Telloni, D.; Marino, R.
2016-03-01
Turbulence in the solar wind is ubiquitous. To understand the transport of low-frequency turbulence in the sub- and super-Alfvénic solar wind flow, Zank et al. 2012 developed an extensive turbulence transport model that describes the evolution of the energy in forward and backward propagating modes, the total turbulent energy, the cross-helicity, the residual energy, the correlation lengths corresponding to forward and backward propagating modes, and the correlation length of the residual energy. Adhikari et. al. 2015 presented the first detailed solution of Zank et al., and found good agreement between the Zank et al. model and observations. Here, we solve the 1D steady-state turbulence transport equations with and without sources of turbulence, and show that all the identified sources are required to reproduce the theoretical results to be consistent with the observations.
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.
The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence
NASA Astrophysics Data System (ADS)
Staebler, G. M.; Candy, J.; Howard, N. T.; Holland, C.
2016-06-01
The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. The zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ion-scale gyrokinetic simulations.
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.
Finite element method application for turbulent and transitional flow
NASA Astrophysics Data System (ADS)
Sváček, Petr
2016-03-01
This paper is interested in numerical simulations of the interaction of the fluid flow with an airfoil. Particularly, the problem of the turbulent flow around the airfoil with elastic support is considered. The main attention is paid to the numerical approximation of the flow problem using the finite element approximations. The laminar - turbulence transition of the flow on the surface airfoil is considered. The chois of the transition model is discussed. The transition model based on the two equation k-ω turbulence model is used. The structure motion is described with the aid of two degrees of freedom. The motion of the computational domain is treated with the aid of the arbitrary Lagrangian-Eulerian method. Numerical results are shown.
Direct computation of turbulence and noise
NASA Technical Reports Server (NTRS)
Berman, C.; Gordon, G.; Karniadakis, G.; Batcho, P.; Jackson, E.; Orszag, S.
1991-01-01
Jet exhaust turbulence noise is computed using a time dependent solution of the three dimensional Navier-Stokes equations to supply the source terms for an acoustic computation based on the Phillips convected wave equation. An extrapolation procedure is then used to determine the far field noise spectrum in terms of the near field sound. This will lay the groundwork for studies of more complex flows typical of noise suppression nozzles.
NASA Astrophysics Data System (ADS)
Bihlo, Alexander; Dos Santos Cardoso-Bihlo, Elsa Maria; Nave, Jean-Christophe; Popovych, Roman
2012-11-01
Various subgrid-scale closure models break the invariance of the Euler or Navier-Stokes equations and thus violate the geometric structure of these equations. A method is shown which allows one to systematically derive invariant turbulence models starting from non-invariant turbulence models and thus to correct artificial symmetry-breaking. The method is illustrated by finding invariant hyperdiffusion schemes to be applied in the two-dimensional turbulence problem.
Structures of the vorticity tube segment in turbulence
NASA Astrophysics Data System (ADS)
Wang, Lipo
2012-04-01
To address the geometrical properties of the turbulent velocity vector field, a new concept named streamtube segment has been developed recently [L. Wang, "On properties of fluid turbulence along streamlines," J. Fluid Mech. 648, 183-203 (2010), 10.1017/S0022112009993041]. According to the vectorial topology, the entire velocity field can be partitioned into the so-called streamtube segments, which are organized in a non-overlapping and space-filling manner. In principle, properties of turbulent fields can be reproduced from those of the decomposed geometrical units with relatively simple structures. A similar idea is implemented to study the turbulent vorticity vector field using the vorticity tube segment structure. Differently from the conventional vortex tubes, vorticity tube segments are space-filling and can be characterized by non-arbitrary parameters, which enables a more quantitative description rather than just an illustrative explanation of turbulence behaviors. From analyzing the direct numerical simulation data, the topological and dynamical properties of vorticity tube segments are explored. The characteristic parameters have strong influence on some conditional statistics, such as the enstrophy production and the probability density function of vorticity stretching. Consequently the common knowledge in turbulence dynamics that vorticity are more stretched than compressed need to be rectified in the vorticity tube segment context.
Kelvin waves cascade in superfluid turbulence.
Kivotides, D; Vassilicos, J C; Samuels, D C; Barenghi, C F
2001-04-01
We study numerically the interaction of four initial superfluid vortex rings in the absence of any dissipation or friction. We find evidence for a cascade of Kelvin waves generated by individual vortex reconnection events which transfers energy to higher and higher wave numbers k. After the vortex reconnections occur, the energy spectrum scales as k(-1) and the curvature spectrum becomes flat. These effects highlight the importance of Kelvin waves and reconnections in the transfer of energy within a turbulent vortex tangle. PMID:11290112
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.
Mutually independent cascades in anisotropic soap-film turbulence
NASA Astrophysics Data System (ADS)
Liu, Chien-Chia; Gioia, Gustavo; Chakraborty, Pinaki
2015-03-01
Computational, experimental and field data amassed to date indicate that in 2D turbulence the spectrum of longitudinal velocity fluctuations, E11 (k1) , and the spectrum of transverse velocity fluctuations, E22 (k1) , correspond always to the same cascade, consistent with isotropy, so that E11 (k1) ~k-α and E22 (k1) ~k-α , where the ``spectral exponent'' α is either 5/3 (for the inverse-energy cascade) or 3 (for the enstrophy cascade). Here, we carry out experiments on turbulent 2D soap-film flows in which E11 (k1) ~k - 5 / 3 and E22 (k1) ~k-3 , as if two mutually independent cascades were concurrently active within the same flow. To our knowledge, this species of spectrum has never been observed or predicted theoretically. Our finding might open up new vistas in the understanding of turbulence.
Laplace—Runge—Lentz vectors for arbitrary spin and arbitrary dimension
NASA Astrophysics Data System (ADS)
Nikitin, Anatoly G.
2015-06-01
Laplace-Runge-Lentz (LRL) vector is a cornerstone of celestial mechanics. It also plays an important role in quantum mechanics, being an integral of motion for the Hydrogen atom and some other systems. However, the majority of models of non-relativistic systems admitting LRL vector ignore the spin of orbital particles. In this survey a new collection of QM systems admitting LRL vector with spin is presented. It includes 2d and 3d systems with arbitrary spin, as well as systems of arbitrary dimension with spins 0, 1/2, and 1. All these systems are superintegrable and can be solved exactly. They emulate neutral particles with non-trivial multipole momenta (in particular, the neutron) interacting with a central external field.
Darrieus rotor aerodynamics in turbulent wind
Brahimi, M.T.; Paraschivoiu, I.
1995-05-01
The earlier aerodynamic models for studying vertical axis wind turbines (VAWT`s) are based on constant incident wind conditions and are thus capable of predicting only periodic variations in the loads. The purpose of the present study is to develop a model capable of predicting the aerodynamic loads on the Darrieus rotor in a turbulent wind. This model is based on the double-multiple streamtube method (DMS) and incorporates a stochastic wind model. The method used to simulate turbulent velocity fluctuations is based on the power spectral density. The problem consists in generating a region of turbulent flow with a relevant spectrum and spatial correlation. The first aerodynamic code developed is based on a one-dimensional turbulent wind model. However, since this model ignores the structure of the turbulence in the crossflow plane, an extension to three dimensions has been made. The computer code developed, CARDAAS, has been used to predict aerodynamic loads for the Sandia-17m rotor and compared to CARDAAV results and experimental data. Results have shown that the computed aerodynamic loads have been improved by including stochastic wind into the aerodynamic model.
Towed-Grid Studies of Quantum Turbulence
NASA Astrophysics Data System (ADS)
Liu, Shu-Chen; Labbe, Greg; Ihas, Gary G.
2006-11-01
We produce Homogeneous Isotropic Quantum Turbulence (HIQT) in liquid helium at 20 mK to compare with classical experiments and theories. Specifically, in the absence of viscosity, through what path does the turbulence decay? To produce HIQT we must quickly accelerate a grid to about 1 m/s in a channel of superfluid helium, tow it for 1 cm at a nearly constant speed, and then stop it equally quickly. To avoid joule and eddy current heating of the liquid helium, a magnetically shielded superconducting linear motor has been built, guided by simulations, along with the current pulses control program written in LabView with an embedded C compiler. The simulations, design process, and the experimental data demonstrating the functioning motor will be presented. We measure the HIQT energy decay mechanism using a calorimetric technique. Recent theory suggests the decay occurs through a Kelvin-wave cascade on the vortex lines which couples the initially large turbulent eddies to the short wavelength phonon spectrum of the liquid, yielding a characteristic rate of temperature rise. Doped germanium thermometers less than 300 μm diameter immersed in the turbulent helium allow fast calorimetric measurements to be made. The decay of turbulence is detected by the rate of temperature rise in the isolated cell after the grid is pulled.
Imbalanced relativistic force-free magnetohydrodynamic turbulence
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.
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.
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.
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.
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
Compressible Alfvenic Turbulence in One Dimension
NASA Astrophysics Data System (ADS)
Fleischer, J.; Diamond, P. H.
1997-11-01
Burgers' equation for 1-D compressible fluid dynamics is extended to a two-equation system which includes the effects of magnetic pressure. For the special case of equal fluid viscosity and magnetic diffusivity, the system reduces to two decoupled Burgers' equations in the characteristic (Elsasser) variables \\upsilon ± \\upsilon _A. Energy transfer, with and without external forcing, is examined for arbitrary molecular diffusivities. For forced turbulence, renormalized perturbation theory is used to calculate the effective transport coefficients. It is found that energy equi-dissipation, not equipartition, is fundamental to the turbulent state. In other words, the system dynamically self-adjusts to propagate disturbances along its characteristics. However, shock formation due to wave steepening is inhibited by the presence of small-scale forcing. Alternate large-scale structures, propagating ballistically, lead to asymmetry in the characteristic velocity pdf. These non-Gaussian tails, a hallmark of intermittency, are examined through the pdf generating functional. It is argued that the probability path integral may be approximated by the instanton contribution. Corresponding distribution functions for velocity and magnetic field fluctuations are given. Finally, implications for the spectra of turbulence and self-organization phenomena in MHD are discussed.
NASA Astrophysics Data System (ADS)
Kim, Daehwan; Heo, Seung; Cheong, Cheolung
2015-03-01
The present paper deals with development of the synthetic turbulence inflow boundary condition (STIBC) to predict inflow broadband noise generated by interaction between turbulence and an airfoil/a cascade of airfoils in the time-domain. The STIBC is derived by combining inflow boundary conditions that have been successfully applied in external and internal computational aeroacoustics (CAA) simulations with a synthetic turbulence model. The random particle mesh (RPM) method based on a digital filter is used as the synthetic turbulence model. Gaussian and Liepmann spectra are used to define the filters for turbulence energy spectra. The linearized Euler equations are used as governing equations to evaluate the suitability of the STIBC in time-domain CAA simulations. First, the velocity correlations and energy spectra of the synthesized turbulent velocities are compared with analytic ones. The comparison results reveal that the STIBC can reproduce a turbulent velocity field satisfying the required statistical characteristics of turbulence. Particularly, the Liepmann filter representing a non-Gaussian filter is shown to be effectively described by superposing the Gaussian filters. Each Gaussian filter has a different turbulent kinetic energy and integral length scale. Second, two inflow noise problems are numerically solved using the STIBC: the turbulence-airfoil interaction and the turbulence-a cascade of airfoils interaction problems. The power spectrum of noise due to an isolated flat plate airfoil interacting with incident turbulence is predicted, and its result is successfully validated against Amiet's analytic model (Amiet, 1975) [4]. The prediction results of the upstream and downstream acoustic power spectra from a cascade of flat plates are then compared with Cheong's analytic model (Cheong et al., 2006) [30]. These comparisons are also in excellent agreement. On the basis of these illustrative computation results, the STIBC is expected to be applied to
Development of anisotropy in incompressible magnetohydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Bigot, Barbara; Galtier, Sébastien; Politano, Hélène
2008-12-01
We present a set of three-dimensional direct numerical simulations of incompressible decaying magnetohydrodynamic turbulence in which we investigate the influence of an external uniform magnetic field B0 . A parametric study in terms of B0 intensity is made where, in particular, we distinguish the shear-from the pseudo-Alfvén waves dynamics. The initial kinetic and magnetic energies are equal with a negligible cross correlation. Both the temporal and spectral effects of B0 are discussed. A subcritical balance is found between the Alfvén and nonlinear times with both a global and a spectral definition. The nonlinear dynamics of strongly magnetized flows is characterized by a different k⊥ spectrum (where B0 defines the parallel direction) if it is plotted at a fixed k∥ (two-dimensional spectrum) or if it is integrated (averaged) over all k∥ (one-dimensional spectrum). In the former case a much wider inertial range is found with a steep power law, closer to the wave turbulence prediction than the Kolmogorov one such as in the latter case. It is believed that the averaging effect may be a source of difficulty to detect the transition towards wave turbulence in natural plasmas. Another important result of this paper is the formation of filaments reported within current and vorticity sheets in strongly magnetized flows, which modifies our classical picture of dissipative sheets in conductive flows.
Inhomogeneous turbulence in magnetic reconnection
NASA Astrophysics Data System (ADS)
Yokoi, Nobumitsu
2016-07-01
Turbulence is expected to play an essential role in enhancing magnetic reconnection. Turbulence associated with magnetic reconnection is highly inhomogeneous: it is generated by inhomogeneities of the field configuration such as the velocity shear, temperature gradient, density stratification, magnetic shear, etc. This self-generated turbulence affects the reconnection through the turbulent transport. In this reconnection--turbulence interaction, localization of turbulent transport due to dynamic balance between several turbulence effects plays an essential role. For investigating inhomogeneous turbulence in a strongly nonlinear regime, closure or turbulence modeling approaches provide a powerful tool. A turbulence modeling approach for the magnetic reconnection is introduced. In the model, the mean-field equations with turbulence effects incorporated are solved simultaneously with the equations of turbulent statistical quantities that represent spatiotemporal properties of turbulence under the effect of large-scale field inhomogeneities. Numerical simulations of this Reynolds-averaged turbulence model showed that self-generated turbulence enhances magnetic reconnection. It was pointed out that reconnection states may be divided into three category depending on the turbulence level: (i) laminar reconnection; (ii) turbulent reconnection, and (iii) turbulent diffusion. Recent developments in this direction are also briefly introduced, which includes the magnetic Prandtl number dependence, spectral evolution, and guide-field effects. Also relationship of this fully nonlinear turbulence approach with other important approaches such as plasmoid instability reconnection will be discussed.
NASA Astrophysics Data System (ADS)
Baluev, Roman V.; Shaidulin, Vakhit Sh.
2015-12-01
We present an attempt to improve models of the Rossiter-McLaughlin effect by relaxing several restrictive assumptions. We consider the entire multiline stellar spectrum rather than just a single line, use no assumptions about the shape of the lines profiles, and allow arbitrary size ratio for the star and its eclipser. However, we neglect the effect of macroturbulence and differential rotation. We construct our model as a power series in the stellar rotation velocity, V sin i, giving a closed set of analytic formulae for up to three terms, and assuming quadratic limb-darkening law. We consider three major approaches of determining the Doppler shift: cross-correlation with a predefined template, cross-correlation with an out-of-transit stellar spectrum, and parametric modelling of the spectrum. A numerical testcase revels that our model preserves good accuracy for the rotation velocity of up to the limit of two to three times the average linewidth in the spectrum. We also apply our approach to the Doppler data of HD 189733, for which we obtain an improved model of the Rossiter-McLaughlin effect with two correction terms, and derive a reduced value for V sin i.
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.
User's guide for a personal computer model of turbulence at a wind turbine rotor
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.
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.
Competitive epidemic spreading over arbitrary multilayer networks
NASA Astrophysics Data System (ADS)
Darabi Sahneh, Faryad; Scoglio, Caterina
2014-06-01
This study extends the Susceptible-Infected-Susceptible (SIS) epidemic model for single-virus propagation over an arbitrary graph to an Susceptible-Infected by virus 1-Susceptible-Infected by virus 2-Susceptible (SI1SI2S) epidemic model of two exclusive, competitive viruses over a two-layer network with generic structure, where network layers represent the distinct transmission routes of the viruses. We find analytical expressions determining extinction, coexistence, and absolute dominance of the viruses after we introduce the concepts of survival threshold and absolute-dominance threshold. The main outcome of our analysis is the discovery and proof of a region for long-term coexistence of competitive viruses in nontrivial multilayer networks. We show coexistence is impossible if network layers are identical yet possible if network layers are distinct. Not only do we rigorously prove a region of coexistence, but we can quantitate it via interrelation of central nodes across the network layers. Little to no overlapping of the layers' central nodes is the key determinant of coexistence. For example, we show both analytically and numerically that positive correlation of network layers makes it difficult for a virus to survive, while in a network with negatively correlated layers, survival is easier, but total removal of the other virus is more difficult.
Electron plasma oscillations at arbitrary Debye lengths
NASA Astrophysics Data System (ADS)
Lehnert, B.
1991-06-01
A solution is presented for electron plasma oscillations in a thermalized plasma, at arbitrary ratios of the Debye length AλD and the perturbation wavelength λ. The limit λDλ corresponds to the conventional fluid-like theory of small particle excursions, whereas λDλ corresponds to the free-streaming limit of strong kinetic phase mixing due to large particle excursions. A strong large-Debye-distance (LDD) effect already appears when λD λ. The initial amplitude of the fluid-like contribution to the macroscopic density perturbation then becomes small compared with the contribution from the free-streaming part. As a consequence, only a small fraction of the density perturbation remains after a limited number of kinetic damping times of the free-streaming part. The present analysis can be considered as a first exercise in an attempt to tackle the far more difficult problem of large-Larmor-radius (LLR) effects in a magnetized plasma. The analysis further shows that a representation in terms of normal modes of the form exp (— iωt) leads to amplitude factors of these modes that are related to each other and that depend on the combined free-streaming and fluid behaviour of the plasma. Consequently, these modes are coupled and cannot be treated as independent of each other.
Arbitrary-resolution global sensitivity kernels
NASA Astrophysics Data System (ADS)
Nissen-Meyer, T.; Fournier, A.; Dahlen, F.
2007-12-01
Extracting observables out of any part of a seismogram (e.g. including diffracted phases such as Pdiff) necessitates the knowledge of 3-D time-space wavefields for the Green functions that form the backbone of Fréchet sensitivity kernels. While known for a while, this idea is still computationally intractable in 3-D, facing major simulation and storage issues when high-frequency wavefields are considered at the global scale. We recently developed a new "collapsed-dimension" spectral-element method that solves the 3-D system of elastodynamic equations in a 2-D space, based on exploring symmetry considerations of the seismic-wave radiation patterns. We will present the technical background on the computation of waveform kernels, various examples of time- and frequency-dependent sensitivity kernels and subsequently extracted time-window kernels (e.g. banana- doughnuts). Given the computationally light-weighted 2-D nature, we will explore some crucial parameters such as excitation type, source time functions, frequency, azimuth, discontinuity locations, and phase type, i.e. an a priori view into how, when, and where seismograms carry 3-D Earth signature. A once-and-for-all database of 2-D waveforms for various source depths shall then serve as a complete set of global time-space sensitivity for a given spherically symmetric background model, thereby allowing for tomographic inversions with arbitrary frequencies, observables, and phases.
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.
Damage from pulses with arbitrary temporal shapes
Trenholme, J.B.
1994-06-06
In fusion laser designs, the laser pulse has a complicated temporal shape which undergoes significant change as it passes through the laser. Our damage data, however, was taken with pulses whose temporal shapes were (more or less) Gaussian. We want to determine the damage propensity of a material exposed to a pulse of arbitrary temporal shape , given data taken with Gaussian pulses of different pulse widths. To do so, we must adopt a physical model of damage. This model will contain some number of parameters that depend on material properties, geometry, and so forth. We determine the parameters of the model appropriate to each material by fitting the model to the Gaussian data for that material. The resulting normalized model is then applied, using the appropriate pulse shape, to find the damage level for a specific material subjected to a specific pulse. The model we shall assume is related to diffusion, although (as we shall see) the experimental results do not fit any simple diffusion model. Initially, we will discuss simple diffusion models. We then examine some experimental data, and then develop a modified diffusive model from that data. That modified model is then used to predict damage levels in various portions of the NIF laser design.
Supernova-driven interstellar turbulence
NASA Astrophysics Data System (ADS)
Joung, M. K. Ryan
To study how supernova feedback structures the turbulent interstellar medium, we construct 3D models of vertically stratified gas stirred by discrete supernova explosions, including vertical gravitational field and parametrized heating and cooling. The models reproduce many observed characteristics of the Galaxy such as global circulation of gas (i.e., galactic fountain) and the existence of cold dense clouds in the galactic disk. Global quantities of the model such as warm and hot gas filling factors in the midplane, mass fraction of thermally unstable gas, and the averaged vertical density profile are compared directly with existing observations, and shown to be broadly consistent. We find that energy injection occurs over a broad range of scales. There is no single effective driving scale, unlike the usual assumption for idealized models of incompressible turbulence. However, >90% of the total kinetic energy is contained in wavelengths shortward of 200 pc. The shape of the kinetic energy spectrum differs substantially from that of the velocity power spectrum, which implies that the velocity structure varies with the gas density. Velocity structure functions demonstrate that the phenomenological theory proposed by Boldyrev is applicable to the medium. We show that it can be misleading to predict physical properties such as the stellar initial mass junction based on numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. Supernova-driven turbulence inhibits star formation globally rather than triggering it. Feedback from massive stars is perhaps the least understood aspect of the current scenario of large-scale structure formation. Many recent observations on both galactic and cosmological scales require
Turbulence compensation: an overview
NASA Astrophysics Data System (ADS)
van Eekeren, Adam W. M.; Schutte, Klamer; Dijk, Judith; Schwering, Piet B. W.; van Iersel, Miranda; Doelman, Niek J.
2012-06-01
In general, long range visual detection, recognition and identification are hampered by turbulence caused by atmospheric conditions. Much research has been devoted to the field of turbulence compensation. One of the main advantages of turbulence compensation is that it enables visual identification over larger distances. In many (military) scenarios this is of crucial importance. In this paper we give an overview of several software and hardware approaches to compensate for the visual artifacts caused by turbulence. These approaches are very diverse and range from the use of dedicated hardware, such as adaptive optics, to the use of software methods, such as deconvolution and lucky imaging. For each approach the pros and cons are given and it is indicated for which scenario this approach is useful. In more detail we describe the turbulence compensation methods TNO has developed in the last years and place them in the context of the different turbulence compensation approaches and TNO's turbulence compensation roadmap. Furthermore we look forward and indicate the upcoming challenges in the field of turbulence compensation.
CHEMICALLY REACTING TURBULENT JETS
The paper reports additional experimental evidence supporting a new description of the mechanism of turbulent entrainment, mixing, and chemical reactions that is emerging from experiments in the last few years which reveal the presence of large scale structures in turbulent shear...
Superstatistics and atmospheric turbulence
NASA Astrophysics Data System (ADS)
Rizzo, S.; Rapisarda, A.
2005-08-01
In this very short contribution we summarize some recent results on wind velocity data recorded at Florence airport. In particular we show that one can describe this example of atmospheric turbulence by means of the superstatistics approach proposed by Beck and Cohen (2003). The latter justifies the successful application of Tsallis generalized statistics in different fields, and more specifically in turbulence experiments.
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.
Investigation of the effect of inlet turbulence length scale on fan discrete tone noise
NASA Technical Reports Server (NTRS)
Hodder, B. K.
1973-01-01
Results of an experimental investigation at the Ames 40- by 80-Foot Wind Tunnel of fan rotor alone discrete tone noise is presented. The investigation examines rotor interaction with fan inlet turbulence. The importance of turbulence length scale is shown by comparing the fan radiated acoustic spectrum with and without modified turbulence length scales. A small-scale low pressure ratio fan was used for the experiment.
Origin of Perpendicular Scales in Solar Wind Turbulence
NASA Astrophysics Data System (ADS)
Galinsky, V. L.
2015-10-01
Results of a study of dispersive Alfvén modes propagating outward from the Sun in streaming inhomogeneous plasma are presented for the inner heliosphere (≲1 AU) region. The results clearly show that a combination of nonlinear wave-particle and wave-wave interactions of outward-only Alfvén modes initially propagating along the local background magnetic field is perfectly capable of explaining the prevalence of turbulent energy in perpendicular ({k}\\perp ) scales over energy contained in scales propagating parallel ({k}\\parallel ) to the local magnetic field perturbations observed in the solar wind. The currently agreed on explanation for this anisotropy, as well as for the scale dependence of wave energy spectra, involves various nonlinear models of imbalanced incompressible MHD turbulence that require a mixture of inward and outward propagating waves to fuel a nonlinear cascade of energy into the {k}\\perp spectrum. The presented approach, for the first time, bridges a gap between week and strong turbulence theories—the interplay of wave-particle and wave-wave processes allows us to obtain strong turbulence scalings from seemingly week turbulence wave resonances. The reported results have a major implication on the current theories of solar wind turbulence and may require a complete overhaul of the state-of-the-art turbulence paradigm, including reassessment and reevaluation of the magnitude and directions (outward \\rightleftarrows inward; {k}\\perp \\rightleftarrows {k}\\parallel ) of the turbulent cascades that are necessary to explain the observations.
Helicopter rotor noise due to ingestion of atmospheric turbulence
NASA Astrophysics Data System (ADS)
Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.
1986-05-01
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.
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.
Stochastic superparameterization in quasigeostrophic turbulence
Grooms, Ian; Majda, Andrew J.
2014-08-15
In this article we expand and develop the authors' recent proposed methodology for efficient stochastic superparameterization algorithms for geophysical turbulence. Geophysical turbulence is characterized by significant intermittent cascades of energy from the unresolved to the resolved scales resulting in complex patterns of waves, jets, and vortices. Conventional superparameterization simulates large scale dynamics on a coarse grid in a physical domain, and couples these dynamics to high-resolution simulations on periodic domains embedded in the coarse grid. Stochastic superparameterization replaces the nonlinear, deterministic eddy equations on periodic embedded domains by quasilinear stochastic approximations on formally infinite embedded domains. The result is a seamless algorithm which never uses a small scale grid and is far cheaper than conventional SP, but with significant success in difficult test problems. Various design choices in the algorithm are investigated in detail here, including decoupling the timescale of evolution on the embedded domains from the length of the time step used on the coarse grid, and sensitivity to certain assumed properties of the eddies (e.g. the shape of the assumed eddy energy spectrum). We present four closures based on stochastic superparameterization which elucidate the properties of the underlying framework: a ‘null hypothesis’ stochastic closure that uncouples the eddies from the mean, a stochastic closure with nonlinearly coupled eddies and mean, a nonlinear deterministic closure, and a stochastic closure based on energy conservation. The different algorithms are compared and contrasted on a stringent test suite for quasigeostrophic turbulence involving two-layer dynamics on a β-plane forced by an imposed background shear. The success of the algorithms developed here suggests that they may be fruitfully applied to more realistic situations. They are expected to be particularly useful in providing accurate and
Samanta, Devranjan; Dubief, Yves; Holzner, Markus; Schäfer, Christof; Morozov, Alexander N; Wagner, Christian; Hof, Björn
2013-06-25
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
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
NASA Astrophysics Data System (ADS)
Gemmrich, J.; Farmer, D.
2003-04-01
Breaking surface waves are believed to provide a major pathway for the energy input from the atmosphere to the ocean and are a source of enhanced turbulent kinetic energy levels in the near-surface layer. Increased turbulence levels relate to enhanced air-sea exchange processes. The ocean surface is a complex system with a wide range of relevant scales. We use direct measurement of the small-scale velocity field as a first step to evaluate near-surface turbulence. At wind speed up to 14 m/s, velocity profiles were obtained with pulse-to-pulse coherent acoustic Doppler profilers. Based on wavenumber spectra calculated with the empirical mode decomposition, dissipation of turbulent kinetic energy at ~1m beneath the free surface and 1 Hz sampling rate is estimated. In addition, bubble size distributions were obtained from acoustic resonator measurements and whitecap occurrence was monitored with video cameras. High turbulence levels with dissipation rates more than four orders larger than the background dissipation are linked to wave breaking. The decay and depth-dependence of the wave-induced turbulence are examined and implications for turbulence models are discussed. In individual breaking waves, the onset of enhanced dissipation occurs up to a quarter wave period prior to the air entrainment. Magnitude and occurrence of the pre-breaking turbulence are consistent with wave-turbulence interaction in a rotational wave field. The detailed structure of the turbulence and bubble field associated with breaking waves will be presented. Implications for air-sea exchange processes will be discussed.
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.
Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence
Nevins, W M; Parker, S E; Chen, Y; Candy, J; Dimits, A; Dorland, W; Hammett, G W; Jenko, F
2007-05-07
The GEM gyrokinetic {delta}f simulation code [Chen, 2003] [Chen, 2007] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [Nevins, 2006]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.
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.
Simulating system dynamics with arbitrary time step
NASA Astrophysics Data System (ADS)
Kantorovich, L.
2007-02-01
We suggest a dynamic simulation method that allows efficient and realistic modeling of kinetic processes, such as atomic diffusion, in which time has its actual meaning. Our method is similar in spirit to widely used kinetic Monte Carlo (KMC) techniques; however, in our approach, the time step can be chosen arbitrarily. This has an advantage in some cases, e.g., when the transition rates change with time sufficiently fast over the period of the KMC time step (e.g., due to time dependence of some external factors influencing kinetics such as moving scanning probe microscopy tip or external time-dependent field) or when the clock time is set by some external conditions, and it is convenient to use equal time steps instead of the random choice of the KMC algorithm in order to build up probability distribution functions. We show that an arbitrary choice of the time step can be afforded by building up the complete list of events including the “residence site” and multihop transitions. The idea of the method is illustrated in a simple “toy” model of a finite one-dimensional lattice of potential wells with unequal jump rates to either side, which can be studied analytically. We show that for any choice of the time step, our general kinetics method reproduces exactly the solution of the corresponding master equations for any choice of the time steps. The final kinetics also matches the standard KMC, and this allows better understanding of this algorithm, in which the time step is chosen in a certain way and the system always advances by a single hop.
Turbulence Effect of the Intergalactic Medium
NASA Astrophysics Data System (ADS)
Zhu, W. S.
2013-07-01
The turbulence in the intergalactic medium (IGM) and its impact on the clustering of baryonic matter are investigated with the cosmological hydrodynamic simulation in the ΛCDM framework. The observational tools that may be used to verify the possibility of the turbulence in the IGM are also discussed. A brief review of modern cosmology is given in chapter 1, mainly focusing on the dynamical equation of the scale factor -- Friedmann equation, and the theory background of the structure formation. Then the method of cosmological numerical simulation is introduced, as well as the cosmological hydrodynamic code WIGEON. After a short review of the turbulence in classic fluid mechanics, the IGM turbulence on large scales is investigated with simulations in chapter 2. The vorticity in the IGM velocity field significantly increases with time, as it can be effectively generated by shocks and complex structures. The vorticity field shows highly non-Gaussian and intermittent features. Its power spectrum is then used to measure the development of turbulence. The relation between the power spectra of vorticity and velocity indicates that the cosmic baryonic and velocity fields are in the state of fully developed turbulence within the scale range of 0.2h^{-1}˜ 3.0h^{-1} Mpc at z≈0. The dynamical effect of the IGM turbulence on the baryon clustering is studied in chapter 3. The random motion of the turbulent fluid yields non-thermal turbulent pressure, which would enlarge the Jeans length, and hence delay and partly prevent the IGM from falling into the gravitational well of dark matter halos. Consequently, the baryon fraction f_{b} will deviate from its cosmic mean f_{b}^{cosmic}, and become highly nonuniform on the scales from a few hundred kpc to several Mpc, varying from as low as 1% to a few times of f_{b}^{cosmic}. The turbulence pressure in the IGM is weakly scale-dependent, and comparable to the gravitational energy density of the halos with masses of approximate 10
Anisotropy in turbulent flows and in turbulent transport
NASA Astrophysics Data System (ADS)
Biferale, Luca; Procaccia, Itamar
2005-07-01
The problem of anisotropy and its effects on the statistical theory of high Reynolds number (Re) turbulence (and turbulent transport) is intimately related and intermingled with the problem of the universality of the (anomalous) scaling exponents of structure functions. Both problems had seen tremendous progress in the last 5 years. In this review we present a detailed description of the new tools that allow effective data analysis and systematic theoretical studies such as to separate isotropic from anisotropic aspects of turbulent statistical fluctuations. Employing the invariance of the equations of fluid mechanics to all rotations, we show how to decompose the (tensorial) statistical objects in terms of the irreducible representation of the SO(d) symmetry group (with d being the dimension, d=2 or 3). This device allows a discussion of the scaling properties of the statistical objects in well-defined sectors of the symmetry group, each of which is determined by the “angular momenta” sector numbers (j,m). For the case of turbulent advection of passive scalar or vector fields, this decomposition allows rigorous statements to be made: (i) the scaling exponents are universal, (ii) the isotropic scaling exponents are always leading, (iii) the anisotropic scaling exponents form a discrete spectrum which is strictly increasing as a function of j. This emerging picture offers a complete understanding of the decay of anisotropy upon going to smaller and smaller scales. Next, we explain how to apply the SO(3) decomposition to the statistical Navier-Stokes theory. We show how to extract information about the scaling behavior in the isotropic sector. Doing so furnishes a systematic way to assess the universality of the scaling exponents in this sector, clarifying the anisotropic origin of the many measurements that claimed the opposite. A systematic analysis of direct numerical simulations (DNS) of the Navier-Stokes equations and of experiments provides a strong support
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.
Jeans criterion in a turbulent medium
NASA Technical Reports Server (NTRS)
Bonazzola, S.; Falgarone, E.; Heyvaerts, J.; Perault, M.; Puget, J. L.
1986-01-01
According to the classical Jeans analysis, all the molecular clouds of mass larger than a few 100 M(solar), size larger than about 1pc and kinetic temperature Tk less than 30K are gravitationally unstable. We have shown that in clouds supported by internal supersonic motions, local gravitational instabilities may appear within molecular clouds which are globally stable. The argument is threefold: (1) when the turbulent kinetic energy is included into the internal energy term, the virial equilibrium condition shows that molecular clouds such as those observed, which are gravitationally unstable according to the Jeans criterion, are indeed globally stable if supported by a turbulent velocity field of power spectrum steeper than 3; (2) 2D compressible hydrodynamical simulations show that a supersonic turbulent velocity field generates a turbulent pressure within clouds, the gradients of which stabilize the unstable scales (i.e., the largest scales and the cloud itself) against gravitational collapse; (3) an analysis similar to the Jeans approach but including the turbulent pressure gradient term, gives basically the same results as those given in (1). Clouds of mean density lower than a critical value are found to be stable even though more massive than their Jeans mass. In clouds of mean density larger than that critical value, the gravitational instability appears only over a range of scales smaller than the cloud size, the largest scales being stable. In practice, the observed mean densities are lower than this critical value: the observation of a small number of cores and stars of a few solar masses embedded in clouds of several hundred solar masses can only be understood in terms of small scale density fluctuations of large amplitude generated by the supersonic turbulence which would occasionally overtake the limit of gravitational stability.
Jeans criterion in a turbulent medium
NASA Astrophysics Data System (ADS)
Bonazzola, S.; Falgarone, E.; Heyvaerts, J.; Perault, M.; Puget, J. L.
1986-10-01
According to the classical Jeans analysis, all the molecular clouds of mass larger than a few 100 M(solar), size larger than about 1pc and kinetic temperature Tk less than 30K are gravitationally unstable. We have shown that in clouds supported by internal supersonic motions, local gravitational instabilities may appear within molecular clouds which are globally stable. The argument is threefold: (1) when the turbulent kinetic energy is included into the internal energy term, the virial equilibrium condition shows that molecular clouds such as those observed, which are gravitationally unstable according to the Jeans criterion, are indeed globally stable if supported by a turbulent velocity field of power spectrum steeper than 3; (2) 2D compressible hydrodynamical simulations show that a supersonic turbulent velocity field generates a turbulent pressure within clouds, the gradients of which stabilize the unstable scales (i.e., the largest scales and the cloud itself) against gravitational collapse; (3) an analysis similar to the Jeans approach but including the turbulent pressure gradient term, gives basically the same results as those given in (1). Clouds of mean density lower than a critical value are found to be stable even though more massive than their Jeans mass. In clouds of mean density larger than that critical value, the gravitational instability appears only over a range of scales smaller than the cloud size, the largest scales being stable. In practice, the observed mean densities are lower than this critical value: the observation of a small number of cores and stars of a few solar masses embedded in clouds of several hundred solar masses can only be understood in terms of small scale density fluctuations of large amplitude generated by the supersonic turbulence which would occasionally overtake the limit of gravitational stability.
Introducing the concept of anisotropy at different scales for modeling optical turbulence.
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. PMID:25121545
NASA Technical Reports Server (NTRS)
Baldwin, B. S.; Maccormack, R. W.; Deiwert, G. S.
1975-01-01
The time-splitting explicit numerical method of MacCormack is applied to separated turbulent boundary layer flow problems. Modifications of this basic method are developed to counter difficulties associated with complicated geometry and severe numerical resolution requirements of turbulence model equations. The accuracy of solutions is investigated by comparison with exact solutions for several simple cases. Procedures are developed for modifying the basic method to improve the accuracy. Numerical solutions of high-Reynolds-number separated flows over an airfoil and shock-separated flows over a flat plate are obtained. A simple mixing length model of turbulence is used for the transonic flow past an airfoil. A nonorthogonal mesh of arbitrary configuration facilitates the description of the flow field. For the simpler geometry associated with the flat plate, a rectangular mesh is used, and solutions are obtained based on a two-equation differential model of turbulence.
Modeling turbulent flame propagation
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.
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.
BER of Gaussian beam propagation in non-Kolmogorov turbulent atmosphere on slant path
NASA Astrophysics Data System (ADS)
Yang, Rui-ke; Chen, Yuan; Hou, Jie; Chen, Hui
2013-08-01
The propagation characteristic of a Gaussian beam through turbulent atmosphere have been studied in the past several years. The main advantage of Gaussian beam wave model is that the infinite plant wave and a spherical wave are being included. Non-Kolmogorov spectrum can describe generalized turbulent atmosphere environment. The propagation properties of Gaussian beam propagating through the turbulent atmosphere described by non-Kolmogorov spectrum are studied on slant path. The scintillation index is analyzed with the Gaussian beam of different turbulent strength, zenith angle, φ , and the spectral exponent, α, of non-Kolmogorov, respectively. The effect of the turbulent structure constant on the ground on sicntillation is notable. The scintillation index reduces remarkably with zenith angle and structure parameter decrease. At weak turbulenc, scintillation index increases as spectral exponent decreases. The bit error rate (BER) of a Gaussian beam propagating in non-Kolmogorov atmospheric turbulence channel is estimated on Earth-space slant path. By comparing the effect of the spectral power with the structure constant on BER at moderate and strong turbulence, the effect of the spectral power change on BER is small. With turbulence weakening , at the order of 10-15m-2/3 , the relative effect of the spectral power on BER is gradually increase. Hence, at the small structure constant on the ground, or weak turbulence, the effect of the turbulent spectral power on BER is required to take into account.
Quasi-geostrophic turbulence and generalized scale invariance, a theoretical reply
NASA Astrophysics Data System (ADS)
Schertzer, D.; Tchiguirinskaia, I.; Lovejoy, S.; Tuck, A. F.
2012-01-01
Lindborg et al. (2010) claim that the apparent spectrum power law E(k) ≈ k-3 on scales ≥600 km obtained with the help of commercial jetliner trajectory deviations (GASP and Mozaic databases) could not be brought into question (Lovejoy et al., 2009a), because this spectrum corresponds to "a well known theory of quasi-geostrophic turbulence developed by Charney (1971)". Lindborg et al. (2010) also claim that "limitations [of this theory] have been relaxed in many of the modern models of atmospheric turbulence". We show that both claims are irrelevant and that generalized scale invariance (GSI) is indispensable to go beyond the quasi-geostrophic limitations, to go in fact from scale analysis to scaling analysis in order to derive better analytical models. In this direction, we derive vorticity equations in a space of (fractal) dimension D=2+Hz (0 ≤ Hz ≤ 1), which corresponds to a first step in the derivation of a dynamical alternative to the quasi-geostrophic approximation and turbulence. The corresponding precise definition of fractional dimensional turbulence already demonstrates that the classical 2-D and 3-D turbulence are not the main options to understand atmospheric dynamics. Although (2 + Hz)-D turbulence (with 0 < Hz < 1) has more common features with 3-D turbulence than with 2-D turbulence, it has nevertheless very distinctive features: its scaling anisotropy is in agreement with the layered pancake structure, which is typical of rotating and stratified turbulence but not of the classical 3-D turbulence.
Analogy between the electromagnetic and hydrodynamic equations: Application to turbulence
NASA Astrophysics Data System (ADS)
Marmanis, Haralabos
In this thesis we have accomplished the following tasks: (1) A new theory of turbulence is initiated, for the purpose of describing the dynamical behavior of averaged flow quantities in incompressible fluid flows of high Reynolds numbers. It is based on a new analogy between electromagnetism and turbulent hydrodynamics. The central idea of the theory is the presentation of turbulent dynamics as an interplay between the vorticity field ( w = ∇ x u) and the Lamb vector (l = w x u). Two important concepts are introduced: (a) the turbulent charge and (b) the turbulent current. This leads to a closed linear system of equations for the averaged vorticity and the averaged Lamb vector. The averaged distributions of the turbulent charge and the turbulent current appear as source terms in this system. The premise of the theory is that the averaged distributions of the sources are the most natural choice of turbulent quantities to be modeled. The general framework of the theory is presented. (2) The case of homogeneous turbulence is studied next. Direct numerical simulations of decaying homogeneous turbulence in a periodic box are conducted. The Fourier coefficients of the vorticity field are recorded as functions of time, while turbulence decays. These functions are projected onto the temporal eigenfunctions provided by the theory. Three eigenfunctions suffice to reproduce the time evolution of a Fourier coefficient, for nearly all the period of decay. The eigenvalues of the vorticity are discrete, which suggests that the phenomenon of intermittency arises naturally in this context. The statistical properties of turbulent waves are inquired and shown to result in a Kolmogorov type of spectrum. (3) Two cases of inhomogeneous turbulence are studied: Flow in a channel, and flow in a circular pipe. Direct numerical simulations are used to calculate the distribution of the turbulent sources. The partial universality of the averaged velocity profile, from the center of the duct
Turbulence Detection and Mitigation Element
NASA Technical Reports Server (NTRS)
Bogue, Rod
2003-01-01
This paper presents viewgraphs on turbulence detection and mitigation technologies in weather accident prevention. The topics include: 1) Organization; 2) Scope of Turbulence Effort; 3) Background; 4) Turbulence Detection and Mitigation Program Metrics; 5) Approach; 6) Turbulence Team Relationships; 7) WBS Structure; 8) Deliverables; 9) TDAM Changes; 10) FY-01 Results/Accomplishments; 11) Out-year Plans; and 12) Element Status.
Energy Science and Technology Software Center (ESTSC)
2008-01-25
BOUT is a parallelized 3D nonlocal electromagnetic turbulence code. The principal calculations are the boundary plasma turbulence in a realistic magnetic geometry. BOUT uses fluid Braginskii equations for plasma vorticity, density, electron and ion temperature and Parallel mementum. With sources added in the core-edge region and sinks in the scrape-off-layer (SOL), BOUT follows the self-consistent profile evolution together with turbulence. BOUT also includes coupling to a magnetohyfrodynamic equlibrium (EFIT package) and a two-dimensional hydrodynamic edgemore » transport model (UEDGE package).« less
Periodically kicked turbulence
Lohse
2000-10-01
Periodically kicked turbulence is theoretically analyzed within a mean-field theory. For large enough kicking strength A and kicking frequency f the Reynolds number grows exponentially and then runs into some saturation. The saturation level Re(sat) can be calculated analytically; different regimes can be observed. For large enough Re we find Re(sat) approximately Af, but intermittency can modify this scaling law. We suggest an experimental realization of periodically kicked turbulence to study the different regimes we theoretically predict and thus to better understand the effect of forcing on fully developed turbulence. PMID:11089041
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.
Fourth-order mutual coherence function in oceanic turbulence.
Baykal, Yahya
2016-04-10
We have recently expressed the structure constant of atmospheric turbulence in terms of the oceanic turbulence parameters, which are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of the mean-squared temperature, wavelength, Kolmogorov microscale, and link length. In this paper, utilizing this recently found structure constant and the fourth-order mutual coherence function of atmospheric turbulence, we present the fourth-order mutual coherence function to be used in oceanic turbulence evaluations. Thus, the found fourth-order mutual coherence function of oceanic turbulence is evaluated for the special case of a point source located at the transmitter origin and at a single receiver point. The variations of this special case of the fourth-order mutual coherence function of oceanic turbulence against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of the mean-squared temperature, the wavelength, and the Kolmogorov microscale at various link lengths are presented. PMID:27139862
Analysis of low altitude atmospheric turbulence data measured in flight
NASA Technical Reports Server (NTRS)
Ganzer, V. M.; Joppa, R. G.; Vanderwees, G.
1977-01-01
All three components of turbulence were measured simultaneously in flight at each wing tip of a Beech D-18 aircraft. The flights were conducted at low altitude, 30.5 - 61.0 meters (100-200 ft.), over water in the presence of wind driven turbulence. Statistical properties of flight measured turbulence were compared with Gaussian and non-Gaussian turbulence models. Spatial characteristics of the turbulence were analyzed using the data from flight perpendicular and parallel to the wind. The probability density distributions of the vertical gusts show distinctly non-Gaussian characteristics. The distributions of the longitudinal and lateral gusts are generally Gaussian. The power spectra compare in the inertial subrange at some points better with the Dryden spectrum, while at other points the von Karman spectrum is a better approximation. In the low frequency range the data show peaks or dips in the power spectral density. The cross between vertical gusts in the direction of the mean wind were compared with a matched non-Gaussian model. The real component of the cross spectrum is in general close to the non-Gaussian model. The imaginary component, however, indicated a larger phase shift between these two gust components than was found in previous research.
Implementation and Validation of the BHR Turbulence Model in the FLAG Hydrocode
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.
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.
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.
Teleportation of an arbitrary mixture of diagonal states of multiqudit
NASA Astrophysics Data System (ADS)
Du, Qian-Hua; Lin, Xiu-Min; Chen, Zhi-Hua; Lin, Gong-Wei; Chen, Li-Bo; Gu, Yong-Jian
2008-03-01
This paper proposes a scheme to teleport an arbitrary mixture of diagonal states of multiqutrit via classical correlation and classical communication. To teleport an arbitrary mixture of diagonal states of N qutrits, N classically correlated pairs of two qutrits are used as channel. The sender (Alice) makes Fourier transform and conditional gate (i.e., XOR(3) gate) on her qutrits and does measurement in appropriate computation bases. Then she sends N ctrits to the receiver (Bob). Based on the received information, Bob performs the corresponding unitary transformation on his qutrits and obtains the teleported state. Teleportation of an arbitrary mixture of diagonal states of multiqudit is also discussed.
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. PMID:26298671
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
Decaying Turbulence in the Generalised Burgers Equation
NASA Astrophysics Data System (ADS)
Boritchev, Alexandre
2014-10-01
We consider the generalised Burgers equation where f is strongly convex and ν is small and positive. We obtain sharp estimates for Sobolev norms of u (upper and lower bounds differ only by a multiplicative constant). Then, we obtain sharp estimates for the dissipation length scale and the small-scale quantities which characterise the decaying Burgers turbulence, i.e., the structure functions and the energy spectrum. The proof uses a quantitative version of an argument by Aurell et al. (J Fluid Mech 238:467-486, 1992). Note that we are dealing with decaying, as opposed to stationary turbulence. Thus, our estimates are not uniform in time. However, they hold on a time interval [ T 1, T 2], where T 1 and T 2 depend only on f and the initial condition, and do not depend on the viscosity. These results allow us to obtain a rigorous theory of the one-dimensional Burgers turbulence in the spirit of Kolmogorov's 1941 theory. In particular, we obtain two results which hold in the inertial range. On one hand, we explain the bifractal behaviour of the moments of increments, or structure functions. On the other hand, we obtain an energy spectrum of the form k -2. These results remain valid in the inviscid limit.
A Heliosphere Buffeted by Interstellar Turbulence?
NASA Astrophysics Data System (ADS)
Jokipii, J. R.; Giacalone, J.
2014-12-01
Recent observations from IBEX combined with previous measurements from other sources suggest new, local, effects of interstellar turbulence. Observations of various interstellar parameters such as the magnetic field, fluid velocity and electron density, over large spatial scales, have revealed a broadband Kolmogorov spectrum of interstellar turbulence which pervades most of interstellar space. The outer scale (or coherence scale of this turbulence) is found to be approximately 10^19 cm and the inner cutoff scale is less than 1000 km. The root-mean-square relative fluctuation in the fluid and the magnetic-field parameters is of order unity. If this turbulence exists at the heliosphere, the root-mean-square relative fluctuations at 100 (heliospheric) AU scales is approximately 0.1. The recently published value for the change In observed velocity direction for the interstellar flow relative to the heliosphere (Frisch, etal, 2014)is consistent with this. Similarly, interpreting the width of the IBEX ribbon in terms of a fluctuating magnetic field also is in agreement with this picture. Observations of TeV cosmic rays can also be explained. Potential effects of these fluctuations in the interstellar medium on the heliosphere will be discussed. Reference: Frisch, etal, Science, 341, 480
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.
Observational evidence of big bang turbulence
NASA Astrophysics Data System (ADS)
Gibson, Carl
2003-11-01
Turbulence is proposed as the driving force behind the formation of the universe in a hot big bang model of quantum gravitational dynamics at Planck scales. Space, time, energy, and entropy of the expanding universe are produced by inertial-vortex Planck-Kerr forces matching gravity. Planck particle pairs permitted by the uncertainty principle emerge from the vacuum as extreme Schwarzschild black holes that form spinning extreme Kerr black holes. Prograde particle accretions to minimum-radius stable orbits release up to 42% of the rest mass energy to create an expanding, rotating, turbulent Planck gas with 10^6 Reynolds number after cooling to the (GUT) strong force freeze out temperature 10^28 K = 10-4 T_P. Inflation occurs and stretches the Corrsin-Obukhov temperature spectrum to length scales larger than the 3x10-25 m scale of causal connection ct, where c is the light speed and t the time. These fossil-temperature-turbulence patterns trigger patterns in the nucleosynthesis of the light elements that trigger the formation of gravitational plasma structures at 10^12 to 10^13 seconds. Patterns found in cosmic microwave background temperature anomalies by Bershadskii and Sreenivasan 2002 precisely match Kolmogorovian patterns for high Reynolds number turbulent mixing.
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
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.
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
Information content of turbulence
NASA Astrophysics Data System (ADS)
Cerbus, R. T.; Goldburg, W. I.
2013-11-01
We treat a turbulent velocity field as a message in the same way as a book or a picture. All messages can be described by their entropy per symbol h, defined as in Shannon's theory of communication. In a turbulent flow, as the Reynolds number Re increases, more correlated degrees of freedom are excited and participate in the turbulent cascade. Experiments in a turbulent soap film suggest that the spatial entropy density h is a decreasing function of Re, namely h∝-logRe + const. In the logistic map, also analyzed here, increasing the control parameter r increases h. A modified logistic map with additional coupling to past iterations suggests the significance of correlations.
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.
RF wave propagation and scattering in turbulent tokamak plasmas
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.
Test particle study of ion transport in drift type turbulence
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.
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.
RF wave propagation and scattering in turbulent tokamak plasmas
NASA Astrophysics Data System (ADS)
Horton, W.; Michoski, C.; Peysson, Y.; Decker, J.
2015-12-01
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.
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.
Polymers in 2D Turbulence: Suppression of Large Scale Fluctuations
NASA Astrophysics Data System (ADS)
Amarouchene, Y.; Kellay, H.
2002-08-01
Small quantities of a long chain molecule or polymer affect two-dimensional turbulence in unexpected ways. Their presence inhibits the transfers of energy to large scales causing their suppression in the energy density spectrum. This also leads to the change of the spectral properties of a passive scalar which turns out to be highly sensitive to the presence of energy transfers.
Turbulent Flames in Supernovae
NASA Astrophysics Data System (ADS)
Khokhlov, A. M.
1994-05-01
First results of three-dimensional simulations of a thermonuclear flame in Type Ia supernovae are obtained using a new flame-capturing algorithm, and a PPM hydrodynamical code. In the absence of gravity, the flame is stabilized with respect to the Landau (1944) instability due to the difference in the behaviour of convex and concave portions of the perturbed flame front. The transition to turbulence in supernovae occurs on scales =~ 0.1 - 10 km in agreement with the non-linear estimate lambda =~ 2pi D(2_l/geff) based on the Zeldovich (1966) model for a perturbed flame when the gravity acceleration increases; D_l is the normal speed of the laminar flame, and geff is the effective acceleration. The turbulent flame is mainly spread by large scale motions driven by the Rayleigh-Taylor instability. Small scale turbulence facilitates rapid incineration of the fuel left behind the front. The turbulent flame speed D_t approaches D_t =~ U', where U' is the root mean square velocity of turbulent motions, when the turbulent flame forgets initial conditions and reaches a steady state. The results indicate that in a steady state the turbulent flame speed should be independent of the normal laminar flame speed D_l. The three-dimensional results are in sharp contrast with the results of previous two-dimensional simulations which underestimate flame speed due to the lack of turbulent cascade directed in three dimensions from big to small spatial scales. The work was supported by the NSF grants AST 92-18035 and AST 93-005P.
Measurements of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murrow, Harold N.
1987-01-01
Various types of atmospheric turbulence measurements are addressed for the purpose of stimulating discussion relative to available data. An outline of these various types of measurements are discussed. Some specific results of detailed characterization studies made at NASA Langley are emphasized. The most recent reports on statistics of turbulence encounters for various types of aircraft operations are summarized. Special severe encounter studies and reference to remote sensing are also included. Wind shear is considered to be a special topic and is not covered.
Flavor evolution of supernova neutrinos in turbulent matter
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.
Light Front Wave Function for Hadrons with Arbitrary Twist
NASA Astrophysics Data System (ADS)
Vega, Alfredo; Schmidt, Ivan; Gutsche, Thomas; Lyubovitskij, Valery E.
2016-07-01
We present a phenomenological light-front wave function for hadrons with arbitrary twist dimension (mesons, baryons and multiquark states), which gives the correct scaling behavior of structure functions and form factors. Some examples of his uses are presented.
Light Front Wave Function for Hadrons with Arbitrary Twist
NASA Astrophysics Data System (ADS)
Vega, Alfredo; Schmidt, Ivan; Gutsche, Thomas; Lyubovitskij, Valery E.
2016-05-01
We present a phenomenological light-front wave function for hadrons with arbitrary twist dimension (mesons, baryons and multiquark states), which gives the correct scaling behavior of structure functions and form factors. Some examples of his uses are presented.
A general theory of turbulent fragmentation
NASA Astrophysics Data System (ADS)
Hopkins, Philip F.
2013-04-01
We develop an analytic framework to understand fragmentation in turbulent, self-gravitating media. In previous work, we showed how some properties of turbulence can be predicted by application of the excursion-set formalism. Here, we generalize this to understand fully time-dependent gravo-turbulent fragmentation and collapse. We show that turbulent systems are always gravitationally unstable in a probabilistic sense. The fragmentation mass spectrum, size-mass-density-linewidth relations of collapsing objects, their correlation functions and clustering, the range of spatial scales over which fragmentation occurs, and the time-dependent rate of collapse/fragmentation (as a function of size/mass) are analytically predictable. We show how these depend on bulk properties of turbulence; fragmentation is promoted at higher Mach numbers and shallower power spectra. We also generalize the model to properly include rotation, complicated gas equations of state, collapsing/expanding backgrounds, magnetic fields, intermittency and non-normal statistics (with inherently correlated fluctuations). This allows us to formally derive how fragmentation is suppressed with `stiffer' equations of state (e.g. higher polytropic index γ) or differently driven turbulence (solenoidal versus compressive). The suppression appears at an `effective sonic scale' where b {M}(R_s, ρ _crit[R_s])≈ 1, with ρcrit being the (scale-dependent) critical density for fragmentation. Gas becomes stable against collapse below this scale for γ > 4/3; however, fragmentation still occurs on larger scales. We show that the scale-free nature of turbulence and gravity generically drives mass spectra and correlation functions towards universal shapes (observed in a wide variety of astrophysical phenomena), with weak residual dependence on many properties of the media. We find that correlated fluctuations on different scales, non-Gaussian density distributions and intermittency have surprisingly small effects on
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
Nonlinear Flow Generation By Electrostatic Turbulence In Tokamaks
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.
SPECTRA OF STRONG MAGNETOHYDRODYNAMIC TURBULENCE FROM HIGH-RESOLUTION SIMULATIONS
Beresnyak, Andrey
2014-04-01
Magnetohydrodynamic (MHD) turbulence is present in a variety of solar and astrophysical environments. Solar wind fluctuations with frequencies lower than 0.1 Hz are believed to be mostly governed by Alfvénic turbulence with particle transport depending on the power spectrum and the anisotropy of such turbulence. Recently, conflicting spectral slopes for the inertial range of MHD turbulence have been reported by different groups. Spectral shapes from earlier simulations showed that MHD turbulence is less scale-local compared with hydrodynamic turbulence. This is why higher-resolution simulations, and careful and rigorous numerical analysis is especially needed for the MHD case. In this Letter, we present two groups of simulations with resolution up to 4096{sup 3}, which are numerically well-resolved and have been analyzed with an exact and well-tested method of scaling study. Our results from both simulation groups indicate that the asymptotic power spectral slope for all energy-related quantities, such as total energy and residual energy, is around –1.7, close to Kolmogorov's –5/3. This suggests that residual energy is a constant fraction of the total energy and that in the asymptotic regime of Alfvénic turbulence magnetic and kinetic spectra have the same scaling. The –1.5 slope for energy and the –2 slope for residual energy, which have been suggested earlier, are incompatible with our numerics.
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.
Spectra of Strong Magnetohydrodynamic Turbulence from High-resolution Simulations
NASA Astrophysics Data System (ADS)
Beresnyak, Andrey
2014-04-01
Magnetohydrodynamic (MHD) turbulence is present in a variety of solar and astrophysical environments. Solar wind fluctuations with frequencies lower than 0.1 Hz are believed to be mostly governed by Alfvénic turbulence with particle transport depending on the power spectrum and the anisotropy of such turbulence. Recently, conflicting spectral slopes for the inertial range of MHD turbulence have been reported by different groups. Spectral shapes from earlier simulations showed that MHD turbulence is less scale-local compared with hydrodynamic turbulence. This is why higher-resolution simulations, and careful and rigorous numerical analysis is especially needed for the MHD case. In this Letter, we present two groups of simulations with resolution up to 40963, which are numerically well-resolved and have been analyzed with an exact and well-tested method of scaling study. Our results from both simulation groups indicate that the asymptotic power spectral slope for all energy-related quantities, such as total energy and residual energy, is around -1.7, close to Kolmogorov's -5/3. This suggests that residual energy is a constant fraction of the total energy and that in the asymptotic regime of Alfvénic turbulence magnetic and kinetic spectra have the same scaling. The -1.5 slope for energy and the -2 slope for residual energy, which have been suggested earlier, are incompatible with our numerics.
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.
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.
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.
The dynamics of interacting nonlinearities governing long wavelength driftwave turbulence
Newman, D.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 {times} 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.
Wind speed power spectrum analysis for Bushland, Texas
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.
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.
Optical rogue waves in integrable turbulence.
Walczak, Pierre; Randoux, Stéphane; Suret, Pierre
2015-04-10
We report optical experiments allowing us to investigate integrable turbulence in the focusing regime of the one-dimensional nonlinear Schrödinger equation (1D NLSE). In analogy with broad spectrum excitation of a one-dimensional water tank, we launch random initial waves in a single mode optical fiber. Using an original optical sampling setup, we measure precisely the probability density function of optical power of the partially coherent waves rapidly fluctuating with time. The probability density function is found to evolve from the normal law to a strong heavy-tailed distribution, thus revealing the formation of rogue waves in integrable turbulence. Numerical simulations of 1D NLSE with stochastic initial conditions quantitatively reproduce the experiments. Our numerical investigations suggest that the statistical features experimentally observed rely on the stochastic generation of coherent analytic solutions of 1D NLSE. PMID:25910126
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.
Toward the assessment of the role of cloud turbulence in warm-rain processes
NASA Astrophysics Data System (ADS)
Grabowski, W. W.; Wyszogrodzki, A.; Wang, L.-P.; Ayala, O.
2012-04-01
Cloud turbulence has been argued to play a significant role in the development of precipitation through the warm-rain (collision/coalescence) processes. In recent years, we developed collision kernels that include effects of cloud turbulence on collisions between cloud droplets. The kernels apply the theoretical model of the turbulent droplet collisions verified by direct numerical simulation (DNS) of droplet-laden turbulent flows. The impact of cloud turbulence on the collision efficiency was also included and it was assessed using a novel DNS methodology that includes hydrodynamic interactions between droplets carried by the turbulent flow. In general, the turbulent collision kernel depends on the characteristics of the small-scale turbulence, the turbulent dissipation rate in particular. We quantified the impact of turbulent collisions in simulations with increasingly complex setups, from the evolution of the initial droplet spectrum with collision/coalescence alone; through rising adiabatic parcel simulations that included droplet activation, diffusional growth and growth by collision/coalescence; and in idealized rising thermal simulations mimicking processes within a single cloud. The latter simulations show that cloud turbulence not only leads to earlier rain formation, but can also result in higher precipitation efficiency of a single cloud. The next logical step is to apply the new kernel in realistic cloud field simulations to include feedbacks between clouds and their environment. Such simulations are underway and will be discussed at the conference.
NASA Astrophysics Data System (ADS)
Skaugen, Audun; Angheluta, Luiza
The relationship between vortex dynamics and the turbulent energy spectrum is an active research topic in quantum turbulence of superfluids and Bose-Einstein condensates. The energy spectra in quantum turbulence exhibit a Kolmogorov -5/3 scaling law, analogous to classical turbulence. Recent developments show that in two-dimensional quantum flows, this energy spectrum corresponds to an inverse energy cascade, which is realized by clustering of like-signed quantized vortices. We investigate numerically the statistics of quantized vortices in two-dimensional quantum turbulence using the Gross-Pitaevskii equation. We find that a universal -5/3 scaling law in the turbulent energy spectrum is intimately connected with the vortex statistics, such as number fluctuations and velocity, which also show a similar scaling behavior. The -5/3 scaling law appearing in the power spectrum of the vortex number is consistent with a scenario of isolated vortices passively advected by a turbulent superfluid velocity, which is again generated by like-signed vortex clusters. The velocity probability distribution of clustered vortices is also sensitive to spatial correlations, and exhibits a power-law tail with a -5/3 exponent that we can predict analytically from the point vortex model.
NASA Astrophysics Data System (ADS)
Lee, Gyung Su.
This thesis is devoted to two studies of low-frequency turbulence in toroidally confined plasma. Low-frequency turbulence is believed to play an important role in anomalous transport in toroidal confinement devices. The first study pertains the the development of an analytic theory of ion-temperature-gradient-driven turbulence in tokamaks. Energy-conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra of stationary ion-temperature-gradient-driven turbulence. Corrections to mixing-length estimates are calculated explicitly. The resulting anomalous ion thermal diffusivity is derived and is found to be consistent with experimentally-deduced ion thermal diffusivities. The associated electron thermal diffusivity, particle and heat-pinch velocities are also calculated. The effects of impurity gradients on saturated ion-temperature-gradient-driven turbulence are discussed and a related explanation of density profile steepening during Z-mode operation is proposed. The second study is devoted to the role of multiple helicity nonlinear interactions of tearing modes and dynamics of magnetic relaxation in a high-temperature current-carrying plasma. To extend the resistive MHD theory of magnetic fluctuations and dynamo activity observed in the reversed field pinch, the fluid equations for high-temperature regime are derived and basic nonlinear interaction mechanism and the effects of diamagnetic corrections to the MHD turbulence theory are studied for the case of fully developed, densely packed turbulence. Modifications to the MHD dynamo theory and anomalous thermal transport and confinement scaling predictions are examined.
The performance of heterodyne detection system for partially coherent beams in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Chengqiang, Li; Tingfeng, Wang; Heyong, Zhang; Jingjiang, Xie; Lisheng, Liu; Shuai, Zhao; Jin, Guo
2015-12-01
The performance of heterodyne system is discussed for partially coherent beams in turbulent atmosphere by introducing turbulence spectrum of refractive-index fluctuations. Several analytic formulae for the heterodyne detection system using the partially coherent Gaussian Schell-model beam are presented. Based on Tatarskii spectrum model, some numerical results are given for the variation in the heterodyne efficiency with the misalignment angle, detector diameter, turbulence conditions, and parameters of the overlapping beams. According to the numerical results, we find that the turbulent atmosphere degrades the heterodyne efficiency significantly, and the variation in heterodyne efficiency is even slower against the misalignment angle in turbulence. For the deterministic received signal and the detector, the performance of the heterodyne detection can be adjusted by controlling the local oscillator signal parameters.
Temporal-frequency spectra for optical wave propagating through non-Kolmogorov turbulence.
Du, Wenhe; Tan, Liying; Ma, Jing; Jiang, Yijun
2010-03-15
Nowadays it has been accepted that the Kolmogorov model is not the only possible turbulent one in the atmosphere, which has been confirmed by the increasing experimental evidences and some results of theoretical investigation. This has prompted the scientist community to study optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, using a non-Kolmogorov power spectrum which has a more general power law instead of standard Kolmogorov power law value 11/3 and a more general amplitude factor instead of constant value 0.033, the temporal power spectra of the presentative amplitude and phase effects, irradiance and angle of arrival fluctuations, have been derived for horizontal link in weak turbulence. And then the influence of spectral power-law variations on the temporal power spectrum has been analyzed. It is anticipated that this work is helpful to the investigations of atmospheric turbulence and optical wave propagation in the atmospheric turbulence. PMID:20389593
Wave turbulence in shallow water models.
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 2048{2} 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. PMID:25019897
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.
Repeated cascade theory of homogeneous turbulence.
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1973-01-01
The problem of turbulent spectrum engenders two coupled hierarchies: one originates from the development of stress, leading to a transfer function, and the other from the development of an eddy viscosity. In order to incorporate physical roles among scales, the turbulent velocity fluctuation is decomposed into a series of ranks in the increasing order of randomness, contributing successively to energy or stress, eddy viscosity, relaxation frequency, and higher-rank frequencies in the memory chain. As a result, the first hierarchy mentioned above becomes closed at the quadrupole correlation. The second hierarchy governs the eddy viscosities of different ranks, related to relaxation frequencies of such ranks, in the form of a memory chain. It is cut off by an implicit viscous mechanism. For zero wind gradient, the spectrum in the inertial subrange recovers the Kolmogoroff k to the minus 5/3 law with a numerical constant 1.58, in good agreement with experiments. For a strong wind gradient, the spectrum in the production subrange has a k to the minus 1 law.
Scaling of turbulence and turbulent mixing using Terascale numerical simulations
NASA Astrophysics Data System (ADS)
Donzis, Diego A.
, suggesting a universal scaling of small scales. Simulations at Rlambda ≈ 650 on 2048 3 grids with scalars at Sc = 1/8 and 1 have allowed us to obtain the clearest evidence of attainment of k -5/3 inertial-convective scaling in the scalar spectrum (as function of wavenumber k) in numerical simulations to date. In addition, results at high Sc appear to support k -1 viscous-convective scaling. Intermittency for scalars as measured by the tail of the PDF of scalar dissipation and moments of scalar gradient fluctuations is found to saturate at high Sc. This asymptotic state is reached at lower Sc when R lambda is high. Statistics of scalar gradients in different directions are used to address the scaling of anisotropy due to the imposed mean scalar gradient. Persistent departures from isotropy are observed as R lambda increases. However, results suggest a return to isotropy at high Schmidt numbers, a tendency that appears to be stronger at high Reynolds numbers. The effects of the Coriolis force on turbulence under solid-body rotation are investigated using simulations at 10243 resolution on enlarged solution domains which reduce the effects of periodic boundary conditions due to the growth of integral scales. Anisotropy at all scales is observed, and is strongest at intermediate rotation rates. Spectra, structure functions and different alignments show strong departures from classical scaling. At high rotation rates the nonlinear terms are damped which help explain the observed decrease in intermittency. The basic property of enstrophy production through vortex stretching in non-rotating flows is also reduced at high rotation rates. Results from DNS do not appear to support some of the assumptions leading to the classical form of the Taylor-Proudman theorem. A mechanism for mixing and a scaling for structure functions is proposed for rapidly rotating flows.
Noise produced by turbulent flow into a rotor: Theory manual for noise calculation
NASA Technical Reports Server (NTRS)
Amiet, R. K.
1989-01-01
An analysis is presented for the calculation of noise produced by turbulent flow into a helicopter rotor. The method is based on the analysis of Amiet for the sound produced by an airfoil moving in rectilinear motion through a turbulent flow field. The rectilinear motion results are used in a quasi-steady manner to calculate the instantaneous spectrum of the rotor noise at any given rotor position; the overall spectrum is then found by averaging the instantaneous spectrum over all rotor azimuth angles. Account is taken of the fact that the rotor spends different amounts of retarded time at different rotor positions. Blade to blade correlation is included in the analysis, leading to harmonics of blade passing frequency. The spectrum of the turbulence entering the rotor is calculated by applying rapid distortion theory to an isotropic turbulence spectrum, assuming that the turbulence is stretched as it is pulled into the rotor. The inputs to the program are obtained from the atmospheric turbulence model and mean flow distortion calculation, described in another volume of this set of reports. The analytical basis is provided for a module which was incorporated in NASA's ROTONET helicopter noise prediction program.
Recent advances in turbulence prediction
NASA Astrophysics Data System (ADS)
Bhattacharya, Atreyee
2012-08-01
Turbulence in the upper troposphere and the lower stratosphere (8-14 kilometers in altitude) is a well-known aviation hazard; it is the major cause of injuries and occasional fatalities to passengers and crew members on commercial aircraft. Jet streams, thunderstorms, flow over mountains, and even the passage of other aircraft cause turbulence. However, the lack of precise observational data (which is still mainly from pilots reporting turbulence) and a clear understanding of the processes that cause turbulence make it difficult to accurately forecast aviation-scale turbulence. Hence, upper troposphere and lower stratosphere turbulence forecasting is an area of active research.
Impact of collisionality on fluctuation characteristics of micro-turbulence
Vermare, L.; Hennequin, P.; Guercan, Oe. D.; Bourdelle, C.; Clairet, F.; Garbet, X.; Sabot, R.
2011-01-15
The influence of changing collisionality on density fluctuation characteristics is studied during dedicated {nu}* scaling experiments, using Doppler backscattering system. First, the repartition of fluctuation energy over different spatial scales, as represented by the wavenumber spectrum, is investigated and a modification of the shape of the perpendicular wavenumber spectrum in the low wavenumber part of the spectrum is observed when changing collisionality. In addition, a new procedure to evaluate the dispersion relation of micro-turbulence is presented. From the behavior of the perpendicular mean velocity of density fluctuations with the perpendicular wavenumber, different dispersion relations are obtained between low and high collisionality cases.
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.
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
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.
Swirl flow turbulence modeling
NASA Technical Reports Server (NTRS)
Abujelala, M. T.; Jackson, T. W.; Lilley, D. G.
1984-01-01
Confined turbulent swirling flow data obtained from a single hot-wire using a six-orientation technique are analyzed numerically. The effects of swirl strength and the presence of a strong contraction nozzle further downstream on deduced parameters is also presented and discussed for the case of chamber-to-inlet diameter ratio D/d = 2. Three swirl strengths are considered with inlet swirl vane angles of 0, 45 and 70 deg. A strong contraction nozzle with an area ratio of 4 is located two chamber-diameters downstream of the inlet to the flowfield. It is found that both the swirl strength and the contraction have strong effects on the turbulence parameters. Generally, the most dramatic effect of increase of swirl strength is the considerable increase in values of all the parameters considered, (rx-viscosity, kinetic energy of turbulence, length scales, and degree of nonisotropy). The presence of a strong contraction nozzle tends to increase the turbulence parameter values in regions of acceleration and to reduce them in deceleration regions. Based on similarity of viscosity and length scale profiles, a C sub mu formulation is deduced which is shown to improve the predictive capability of the standard k-epsilon turbulence model in swirling recirculating flows.
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.
A new approach to the study of the turbulence layer
NASA Technical Reports Server (NTRS)
Levenson, Ruth A.
1993-01-01
Turbulent thermal convection is of considerable importance in fluid dynamical transport phenomena occurring, for example, in the planetary boundary layer of the Earth, the interiors of stars, and accretion disks. In particular, during a significant portion of the evolutionary phase of many stars having convectively unstable cores or outer envelopes, a substantial fraction of energy is transported from the central layers to the outer layers by thermal convection. Moreover, as much of the interior of a star is in highly turbulent motion, a complete theory of stellar structure and evolution requires the explicit consideration of turbulence in order to have expressions for the turbulent quantities arising in the stellar structure equations, and particularly, the turbulent fluxes that appear in the total flux conservation equation, such as the convective flux, kinetic energy flux, etc. A reliable quantification of these fluxes continues to present a challenge in astrophysical fluid dynamics, primarily because astrophysical turbulence is almost always fully-developed and nearly inviscid, and therefore governed by strong nonlinear interactions that distribute the energy among a very wide spectrum of eddies with scales ranging from the characteristic dimension of the flow to those sufficiently small to be affected by viscous dissipation. Furthermore, astrophysical flows are invariably compressible, anisotropic, and inhomogeneous, which requires the consideration of the dynamics of longitudinal modes and their interaction with the transverse modes, as well as complicated boundary conditions. In order to reach a compromise between analytical and numerical tractability and the basic physics of turbulent convection, we have constructed a model of stationary turbulent convection that yields various turbulence statistics, including the convective flux, that are required in stellar evolution models.
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.
Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow.
Hawkins, Christopher; Angheluta, Luiza; Krotkiewski, Marcin; Jamtveit, Bjørn
2016-04-01
In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity K_{L}, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of K_{L}(Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the K_{L}(Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method. PMID:27176402
Neutrino oscillations in a turbulent plasma
Mendonça, J. T.; Haas, F.
2013-07-15
A new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both time-invariant and time-dependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicates the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.
Stellarator Turbulence: Subdominant Eigenmodes and Quasilinear Modeling
NASA Astrophysics Data System (ADS)
Pueschel, M. J.; Faber, B. J.; Citrin, J.; Hegna, C. C.; Terry, P. W.; Hatch, D. R.
2016-02-01
Owing to complex geometry, gyrokinetic simulations in stellarator geometry produce large numbers of subdominant unstable and stable, near-orthogonal eigenmodes. Here, results based on the full eigenmode spectrum in stellarator geometry are presented for the first time. In the nonlinear state of a low-magnetic-shear ion-temperature-gradient-driven case, a multitude of these modes are active and imprint the system. Turbulent frequency spectra are broadband as a consequence, in addition to a nonlinear, narrow signature at electron frequencies. It is shown that successful quasilinear, mixing-length transport modeling is possible in stellarators, where it is essential to account for all subdominant unstable modes.
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.
A numerical investigation of relativistic turbulence
NASA Astrophysics Data System (ADS)
Zrake, Jonathan J.
We present a program of numerical simulations designed to investigate the fundamental properties and phenomenological consequences of relativistic hydrodynamic and magnetohydrodynamic (MHD) turbulence. For the hydrodynamic case, we simulate a relativistically warm gas in a cubic periodic domain continuously driven at large scales with Lorentz factor of about 3. We employ a fifth-order accurate conservative finite-difference scheme on a uniform mesh with resolution up to 20483. The power spectrum of four-velocity scales with the -5/3 power of the wave-number, although deviations from strict scale similarity are evident. A Lorentz-covariant generalization of the longitudinal structure function is introduced, and found to be consistent with existing intermittency models. One-point statistics of the density field Gammarho are approximately log-normal, with skewness toward low densities being well modeled by recent advances in the compressible turbulence literature. Fundamental properties of driven, trans-relativistic, trans-Alfvenic MHD turbulence are studied on uniform meshes up to $10243. Classical predictions from the non-relativistic turbulence literature, such as the scale dependence of anisotropy with respect to the local magnetic field, are verified to hold in trans-relativistic conditions. Detailed studies of the small-scale turbulent dynamo for the conditions of merging neutron star binaries have been conducted. The dynamo is studied at a range of resolutions between 163 and 10243, from the kinematic through non-linear and saturation phases. Good agreement is found with classical predictions of the kinematic phase, and comparisons are made with recent measurements of non-linear dynamo efficiency. We find that very robustly, seed fields are amplified to magnetar strength (4 x1016 Gauss) within the ˜1 ms merger time-scale over 1 km turbulent volumes. The global magnetic energy budget is controlled by the prevalence and vigor of the turbulent volumes, with
Soliton turbulence in shallow water ocean surface waves.
Costa, Andrea; Osborne, Alfred R; Resio, Donald T; Alessio, Silvia; Chrivì, Elisabetta; Saggese, Enrica; Bellomo, Katinka; Long, Chuck E
2014-09-01
We analyze shallow water wind waves in Currituck Sound, North Carolina and experimentally confirm, for the first time, the presence of soliton turbulence in ocean waves. Soliton turbulence is an exotic form of nonlinear wave motion where low frequency energy may also be viewed as a dense soliton gas, described theoretically by the soliton limit of the Korteweg-deVries equation, a completely integrable soliton system: Hence the phrase "soliton turbulence" is synonymous with "integrable soliton turbulence." For periodic-quasiperiodic boundary conditions the ergodic solutions of Korteweg-deVries are exactly solvable by finite gap theory (FGT), the basis of our data analysis. We find that large amplitude measured wave trains near the energetic peak of a storm have low frequency power spectra that behave as ∼ω-1. We use the linear Fourier transform to estimate this power law from the power spectrum and to filter densely packed soliton wave trains from the data. We apply FGT to determine the soliton spectrum and find that the low frequency ∼ω-1 region is soliton dominated. The solitons have random FGT phases, a soliton random phase approximation, which supports our interpretation of the data as soliton turbulence. From the probability density of the solitons we are able to demonstrate that the solitons are dense in time and highly non-Gaussian. PMID:25238388
Nonhelical inverse transfer of a decaying turbulent magnetic field.
Brandenburg, Axel; Kahniashvili, Tina; Tevzadze, Alexander G
2015-02-20
In the presence of magnetic helicity, inverse transfer from small to large scales is well known in magnetohydrodynamic (MHD) turbulence and has applications in astrophysics, cosmology, and fusion plasmas. Using high resolution direct numerical simulations of magnetically dominated self-similarly decaying MHD turbulence, we report a similar inverse transfer even in the absence of magnetic helicity. We compute for the first time spectral energy transfer rates to show that this inverse transfer is about half as strong as with helicity, but in both cases the magnetic gain at large scales results from velocity at similar scales interacting with smaller-scale magnetic fields. This suggests that both inverse transfers are a consequence of universal mechanisms for magnetically dominated turbulence. Possible explanations include inverse cascading of the mean squared vector potential associated with local near two dimensionality and the shallower k^{2} subinertial range spectrum of kinetic energy forcing the magnetic field with a k^{4} subinertial range to attain larger-scale coherence. The inertial range shows a clear k^{-2} spectrum and is the first example of fully isotropic magnetically dominated MHD turbulence exhibiting weak turbulence scaling. PMID:25763960
Turbulent magnetic dynamo excitation at low magnetic Prandtl number
Mininni, Pablo D.
2006-05-15
Planetary and stellar dynamos likely result from turbulent motions in magnetofluids with kinematic viscosities that are small compared to their magnetic diffusivities. Laboratory experiments are in progress to produce similar dynamos in liquid metals. This work reviews recent computations of thresholds in critical magnetic Reynolds number above which dynamo amplification can be expected for mechanically forced turbulence (helical and nonhelical, short wavelength and long wavelength) as a function of the magnetic Prandtl number P{sub M}. New results for helical forcing are discussed, for which a dynamo is obtained at P{sub M}=5x10{sup -3}. The fact that the kinetic turbulent spectrum is much broader in wave-number space than the magnetic spectrum leads to numerical difficulties that are bridged by a combination of overlapping direct numerical simulations and subgrid models of magnetohydrodynamic turbulence. Typically, the critical magnetic Reynolds number increases steeply as the magnetic Prandtl number decreases, and then reaches an asymptotic plateau at values of at most a few hundred. In the turbulent regime and for magnetic Reynolds numbers large enough, both small- and large-scale magnetic fields are excited. The interactions between different scales in the flow are also discussed.
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.
Heating and acceleration of ions in nonresonant Alfvenic turbulence
Nariyuki, Y.; Hada, T.; Tsubouchi, K.
2010-07-15
Nonlinear scattering of protons and alpha particles during the dissipation of the finite amplitude, low-frequency Alfvenic turbulence is studied. The process discussed here is not the coherent scattering and acceleration, as those often treated in the past studies, but is an incoherent process in which it is essential that the Alfvenic turbulence has a broadband spectrum. The presence of such an Alfvenic turbulence is widely recognized observationally both in the solar corona and in the solar wind. Numerical results suggest that, although there is no apparent sign of the occurrence of any parametric instabilities, the ions are heated efficiently by the nonlinear Landau damping, i.e., trapping and phase mixing by Alfven wave packets which are generated by beating of finite amplitude Alfven waves. The heating occurs both in the parallel and in the perpendicular directions, and the ion distribution function which is asymmetric with respect to the parallel velocity is produced. Eventual perpendicular energy of ions is much influenced by the spectrum and polarization of the given Alfvenic turbulence since the turbulence initially possess transverse energy as specified by Walen's relation.
Soliton Turbulence in Shallow Water Ocean Surface Waves
NASA Astrophysics Data System (ADS)
Costa, Andrea; Osborne, Alfred R.; Resio, Donald T.; Alessio, Silvia; Chrivı, Elisabetta; Saggese, Enrica; Bellomo, Katinka; Long, Chuck E.
2014-09-01
We analyze shallow water wind waves in Currituck Sound, North Carolina and experimentally confirm, for the first time, the presence of soliton turbulence in ocean waves. Soliton turbulence is an exotic form of nonlinear wave motion where low frequency energy may also be viewed as a dense soliton gas, described theoretically by the soliton limit of the Korteweg-deVries equation, a completely integrable soliton system: Hence the phrase "soliton turbulence" is synonymous with "integrable soliton turbulence." For periodic-quasiperiodic boundary conditions the ergodic solutions of Korteweg-deVries are exactly solvable by finite gap theory (FGT), the basis of our data analysis. We find that large amplitude measured wave trains near the energetic peak of a storm have low frequency power spectra that behave as ˜ω-1. We use the linear Fourier transform to estimate this power law from the power spectrum and to filter densely packed soliton wave trains from the data. We apply FGT to determine the soliton spectrum and find that the low frequency ˜ω-1 region is soliton dominated. The solitons have random FGT phases, a soliton random phase approximation, which supports our interpretation of the data as soliton turbulence. From the probability density of the solitons we are able to demonstrate that the solitons are dense in time and highly non-Gaussian.
NASA Astrophysics Data System (ADS)
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-01
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.
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. PMID:25768746
Abarzhi, S I; Sreenivasan, K R
2010-04-13
Turbulence is a supermixer. Turbulent mixing has immense consequences for physical phenomena spanning astrophysical to atomistic scales under both high- and low-energy-density conditions. It influences thermonuclear fusion in inertial and magnetic confinement systems; governs dynamics of supernovae, accretion disks and explosions; dominates stellar convection, planetary interiors and mantle-lithosphere tectonics; affects premixed and non-premixed combustion; controls standard turbulent flows (wall-bounded and free-subsonic, supersonic as well as hypersonic); as well as atmospheric and oceanic phenomena (which themselves have important effects on climate). In most of these circumstances, the mixing phenomena are driven by non-equilibrium dynamics. While each article in this collection dwells on a specific problem, the purpose here is to seek a few unified themes amongst diverse phenomena. PMID:20211872
Turbulence Modeling: A NASA Perspective
NASA Technical Reports Server (NTRS)
Gatski, T. B.
2001-01-01
This paper presents turbulence modeling from NASA's perspective. The topics include: 1) Hierarchy of Solution Methods; 2) Turbulence Modeling Focus; 3) Linear Eddy Viscosity Models; and 4) Nonlinear Eddy Viscosity Algebraic Stress Models.
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.
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.
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.
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. PMID:19037366
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.
Spectrum of classes of point emitters of electromagnetic wave fields.
Castañeda, Román
2016-09-01
The spectrum of classes of point emitters has been introduced as a numerical tool suitable for the design, analysis, and synthesis of non-paraxial optical fields in arbitrary states of spatial coherence. In this paper, the polarization state of planar electromagnetic wave fields is included in the spectrum of classes, thus increasing its modeling capabilities. In this context, optical processing is realized as a filtering on the spectrum of classes of point emitters, performed by the complex degree of spatial coherence and the two-point correlation of polarization, which could be implemented dynamically by using programmable optical devices. PMID:27607498
Turbulence in pure superfluid flow
Ashton, R.A.; Opatowsky, L.B.; Tough, J.T.
1981-03-09
A series of experiments is described which provide an unambiguous description of the steady-state properties of turbulence in pure superfluid flow. The turbulence is qualitatively different from that observed in counterflow but comparable to the homogeneous turbulence described by theory.
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Klein, R I; Li, P S; McKee, C F; Fisher, R
2008-04-10
Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256{sup 3} and 512{sup 3} simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li et al. (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.
A computer-based simulator of the atmospheric turbulence
NASA Astrophysics Data System (ADS)
Konyaev, Petr A.
2015-11-01
Computer software for modeling the atmospheric turbulence is developed on the basis of a time-varying random medium simulation algorithm and a split-step Fourier transform method for solving a wave propagation equation. A judicious choice of the simulator parameters, like the velocity of the evolution and motion of the medium, turbulence spectrum and scales, enables different effects of a random medium on the optical wavefront to be simulated. The implementation of the simulation software is shown to be simple and efficient due to parallel programming functions from the MKL Intel ® Parallel Studio libraries.
Freely Decaying Weak Turbulence for Sea Surface Gravity Waves
NASA Astrophysics Data System (ADS)
Onorato, M.; Osborne, A. R.; Serio, M.; Resio, D.; Pushkarev, A.; Zakharov, V. E.; Brandini, C.
2002-09-01
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.
Freely decaying weak turbulence for sea surface gravity waves.
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. PMID:12366050
A non-isotropic multiple-scale turbulence model
NASA Technical Reports Server (NTRS)
Chen, C. P.
1990-01-01
A newly developed non-isotropic multiple scale turbulence model (MS/ASM) is described for complex flow calculations. This model focuses on the direct modeling of Reynolds stresses and utilizes split-spectrum concepts for modeling multiple scale effects in turbulence. Validation studies on free shear flows, rotating flows and recirculating flows show that the current model perform significantly better than the single scale k-epsilon model. The present model is relatively inexpensive in terms of CPU time which makes it suitable for broad engineering flow applications.
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.
Energy dynamics in a simulation of LAPD turbulence
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.
Numerical calculation of two-phase turbulent jets
Saif, A.A.
1995-05-01
Two-phase turbulent round jets were numerically simulated using a multidimensional two-phase CFD code based on the two-fluid model. The turbulence phenomena were treated with the standard k-{epsilon} model. It was modified to take into account the additional dissipation of turbulent kinetic energy by the dispersed phase. Within the context of the two-fluid model it is more appropriate and physically justified to treat the diffusion by an interfacial force in the momentum equation. In this work, the diffusion force and the additional dissipation effect by the dispersed phase were modeled starting from the classical turbulent energy spectrum analysis. A cut-off frequency was proposed to decrease the dissipation effect by the dispersed phase when large size particles are introduced in the flow. The cut-off frequency combined with the bubble-induced turbulence effect allows for an increase in turbulence for large particles. Additional care was taken in choosing the right kind of experimental data from the literature so that a good separate effect test was possible for their models. The models predicted the experimental data very closely and they were general enough to predict extreme limit cases: water-bubble and air-droplet jets.
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.
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.
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.
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.
Resampling of data between arbitrary grids using convolution interpolation.
Rasche, V; Proksa, R; Sinkus, R; Börnert, P; Eggers, H
1999-05-01
For certain medical applications resampling of data is required. In magnetic resonance tomography (MRT) or computer tomography (CT), e.g., data may be sampled on nonrectilinear grids in the Fourier domain. For the image reconstruction a convolution-interpolation algorithm, often called gridding, can be applied for resampling of the data onto a rectilinear grid. Resampling of data from a rectilinear onto a nonrectilinear grid are needed, e.g., if projections of a given rectilinear data set are to be obtained. In this paper we introduce the application of the convolution interpolation for resampling of data from one arbitrary grid onto another. The basic algorithm can be split into two steps. First, the data are resampled from the arbitrary input grid onto a rectilinear grid and second, the rectilinear data is resampled onto the arbitrary output grid. Furthermore, we like to introduce a new technique to derive the sampling density function needed for the first step of our algorithm. For fast, sampling-pattern-independent determination of the sampling density function the Voronoi diagram of the sample distribution is calculated. The volume of the Voronoi cell around each sample is used as a measure for the sampling density. It is shown that the introduced resampling technique allows fast resampling of data between arbitrary grids. Furthermore, it is shown that the suggested approach to derive the sampling density function is suitable even for arbitrary sampling patterns. Examples are given in which the proposed technique has been applied for the reconstruction of data acquired along spiral, radial, and arbitrary trajectories and for the fast calculation of projections of a given rectilinearly sampled image. PMID:10416800
NASA Astrophysics Data System (ADS)
Niccoli, Giuliano; Terras, Véronique
2015-07-01
Generic inhomogeneous integrable XXZ chains with arbitrary spins are studied by means of the quantum separation of variables (SOV) method. Within this framework, a complete description of the spectrum (eigenvalues and eigenstates) of the antiperiodic transfer matrix is derived in terms of discrete systems of equations involving the inhomogeneity parameters of the model. We show here that one can reformulate this discrete SOV characterization of the spectrum in terms of functional T - Q equations of Baxter's type, hence proving the completeness of the solutions to the associated systems of Bethe-type equations. More precisely, we consider here two such reformulations. The first one is given in terms of Q-solutions, in the form of trigonometric polynomials of a given degree , of a one-parameter family of T - Q functional equations with an extra inhomogeneous term. The second one is given in terms of Q-solutions, again in the form of trigonometric polynomials of degree but with double period, of Baxter's usual (i.e., without extra term) T - Q functional equation. In both cases, we prove the precise equivalence of the discrete SOV characterization of the transfer matrix spectrum with the characterization following from the consideration of the particular class of Q-solutions of the functional T - Q equation: to each transfer matrix eigenvalue corresponds exactly one such Q-solution and vice versa, and this Q-solution can be used to construct the corresponding eigenstate.
An analysis of the vertical structure equation for arbitrary thermal profiles
NASA Technical Reports Server (NTRS)
Cohn, Stephen E.; Dee, Dick P.
1989-01-01
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.
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.
Nonrelativistic equations of motion for particles with arbitrary spin
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.
Hypersonic Arbitrary-Body Aerodynamics (HABA) for conceptual design
Salguero, D.E.
1990-03-15
The Hypersonic Arbitrary-Body Aerodynamics (HABA) computer program predicts static and dynamic aerodynamic derivatives at hypersonic speeds for any vehicle geometry. It is intended to be used during conceptual design studies where fast computational speed is required. It uses the same geometry and hypersonic aerodynamic methods as the Mark IV Supersonic/Hypersonic Arbitrary-Body Program (SHABP) developed under sponsorship of the Air Force Flight Dynamics Laboratory; however, the input and output formats have been improved to make it easier to use. This program is available as part of the Department 9140 CAE software.
Generation of Electromagnetic Waves with Arbitrary Orbital Angular Momentum Modes
NASA Astrophysics Data System (ADS)
Cheng, Li; Hong, Wei; Hao, Zhang-Cheng
2014-04-01
Recently, much attention has been focused on beams carrying orbital angular momentum (OAM) for radio communication. Here we experimentally demonstrate a planar-spiral phase plate (planar-SPP) for generating arbitrary mixed OAM beams. This proposed planar-SPP uses the concept of transmit array antenna having a perforated substrate to control the outputting phase for generating beams carrying OAM with arbitrary modes. As demonstrations, three planar-SPPs with a single OAM mode and two mixed OAM modes around 94 GHz have been investigated with design and experiments in this paper, respectively. The typical experimental intensity and phase patterns show that the proposed method of generating OAM beams really works.
Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating
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.
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.
Turbulence in the harassed galaxy NGC4254
NASA Astrophysics Data System (ADS)
Dutta, Prasun; Begum, Ayesha; Bharadwaj, Somnath; Chengalur, Jayaram N.
2010-06-01
Galaxy harassment is an important mechanism for the morphological evolution of galaxies in clusters. The spiral galaxy NGC4254 in the Virgo cluster is believed to be a harassed galaxy. We have analysed the power spectrum of HI emission fluctuations from NGC4254 to investigate whether it carries any imprint of galaxy harassment. The power spectrum, as determined using the 16 central channels which contain most of the HI emission, is found to be well fitted by a power law P(U) = AUα with α = -1.7 +/- 0.2 at length-scales 1.7 to 8.4kpc. This is similar to other normal spiral galaxies which have a slope of ~ -1.5 and is interpreted as arising from two-dimensional turbulence at length-scales larger than the galaxy's scaleheight. NGC4254 is hence yet another example of a spiral galaxy that exhibits scale-invariant density fluctuations out to length-scales comparable to the diameter of the HI disc. While a large variety of possible energy sources like protostellar winds, supernovae, shocks, etc. have been proposed to produce turbulence, it is still to be seen whether these are effective on length-scales comparable to that of the entire HI disc. On separately analysing the HI power spectrum in different parts of NGC4254, we find that the outer parts have a different slope (α = -2.0 +/- 0.3) compared to the central part of the galaxy (α = -1.5 +/- 0.2). Such a change in slope is not seen in other, undisturbed galaxies. We suggest that, in addition to changing the overall morphology, galaxy harassment also affects the fine scale structure of the interstellar medium, causing the power spectrum to have a steeper slope in the outer parts.
NASA Astrophysics Data System (ADS)
Xu, G. S.; Wan, B. N.; Wang, H. Q.; Guo, H. Y.; Naulin, V.; Rasmussen, J. Juul; Nielsen, A. H.; Wu, X. Q.; Yan, N.; Chen, L.; Shao, L. M.; Chen, R.; Wang, L.; Zhang, W.
2016-03-01
A new model for the low-to-high (L -H ) confinement transition has been developed based on a new paradigm for turbulence suppression by velocity shear [G. M. Staebler et al., Phys. Rev. Lett. 110, 055003 (2013)]. The model indicates that the L -H transition can be mediated by a shift in the radial wave number spectrum of turbulence, as evidenced here, for the first time, by the direct observation of a turbulence radial wave number spectral shift and turbulence structure tilting prior to the L -H transition at tokamak edge by direct probing. This new mechanism does not require a pretransition overshoot in the turbulent Reynolds stress, shunting turbulence energy to zonal flows for turbulence suppression as demonstrated in the experiment.
Xu, G S; Wan, B N; Wang, H Q; Guo, H Y; Naulin, V; Rasmussen, J Juul; Nielsen, A H; Wu, X Q; Yan, N; Chen, L; Shao, L M; Chen, R; Wang, L; Zhang, W
2016-03-01
A new model for the low-to-high (L-H) confinement transition has been developed based on a new paradigm for turbulence suppression by velocity shear [G. M. Staebler et al., Phys. Rev. Lett. 110, 055003 (2013)]. The model indicates that the L-H transition can be mediated by a shift in the radial wave number spectrum of turbulence, as evidenced here, for the first time, by the direct observation of a turbulence radial wave number spectral shift and turbulence structure tilting prior to the L-H transition at tokamak edge by direct probing. This new mechanism does not require a pretransition overshoot in the turbulent Reynolds stress, shunting turbulence energy to zonal flows for turbulence suppression as demonstrated in the experiment. PMID:26991181
Intermittency growth in 3D turbulence
NASA Astrophysics Data System (ADS)
Kimura, Y.
1991-07-01
Recently increasing attention has been paid to the non-Gaussian properties of small scales in turbulent flows as a manifestation of intermittency. Past numerical studies were, however, almost always restricted to simulations with external forces or to results after several eddy-turn-over times. This is because the equilibrium shapes of the Probability Density Functions (PDFs) of velocity and velocity gradients were the main concern. As a theoretical tool to analyze non-Gaussianity, Kraichnan and his co-workers developed a systematic technique called mapping closure. The working hypothesis of the technique is that the shape of PDF is determined by a balance between advection which produces active small eddies and dissipation which wipes them out. At these processes have different time scales, different shapes of PDF are possible as a result of combinations of the processes. Accurate statistical calculations for decaying turbulence with the initial Gaussian distribution is vital, in the examination of the hypothesis. In this article, we shall present numerical results on the development of the shape of PDFs of the velocity components and transverse velocity gradients of Navier-Stokes turbulence. The possibility of controlling intermittency will be discussed. We used three-dimensional pseudospectral simulations with 64(sup 3) periodic grid points. To get clean statistical information, averages over a large number of ensembles of different initial conditions satisfying the same energy spectrum were taken.
Recent insights in solar wind MHD turbulence
Bruno, R.; D'Amicis, R.; Bavassano, B.; Carbone, V.; Marino, R.; Sorriso-Valvo, L.; Noullez, A.; Pietropaolo, E.
2008-08-25
In this short review we report about recent findings related to two fundamental points in the study of solar wind turbulence: a) the verification of the equivalent of the -4/5 law in the solar wind and b) the estimate of the energy cascade along the spectrum and its comparison with the heating rate necessary to heat the solar wind during its expansion as deduced from in-situ measurements. As a matter of fact, a Yaglom-like scaling relation has recently been found in both high-latitude and in-ecliptic data samples. However, analogous scaling law, suitably modified to take into account compressible fluctuations, has been observed in a much more extended fraction of the same data set recorded at high latitude. Thus, it seems that large scale density fluctuations, despite their low amplitude, play a major role in the basic scaling properties of turbulence. The compressive turbulent cascade, moreover, seems to be able to supply the energy needed to account for the local heating of the non-adiabatic solar wind.
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.
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. PMID:24215748
Multilevel turbulence simulations
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.
Turbulence compressibility corrections
NASA Technical Reports Server (NTRS)
Coakley, T. J.; Horstman, C. C.; Marvin, J. G.; Viegas, J. R.; Bardina, J. E.; Huang, P. G.; Kussoy, M. I.
1994-01-01
The basic objective of this research was to identify, develop and recommend turbulence models which could be incorporated into CFD codes used in the design of the National AeroSpace Plane vehicles. To accomplish this goal, a combined effort consisting of experimental and theoretical phases was undertaken. The experimental phase consisted of a literature survey to collect and assess a database of well documented experimental flows, with emphasis on high speed or hypersonic flows, which could be used to validate turbulence models. Since it was anticipated that this database would be incomplete and would need supplementing, additional experiments in the NASA Ames 3.5-Foot Hypersonic Wind Tunnel (HWT) were also undertaken. The theoretical phase consisted of identifying promising turbulence models through applications to simple flows, and then investigating more promising models in applications to complex flows. The complex flows were selected from the database developed in the first phase of the study. For these flows it was anticipated that model performance would not be entirely satisfactory, so that model improvements or corrections would be required. The primary goals of the investigation were essentially achieved. A large database of flows was collected and assessed, a number of additional hypersonic experiments were conducted in the Ames HWT, and two turbulence models (kappa-epsilon and kappa-omega models with corrections) were determined which gave superior performance for most of the flows studied and are now recommended for NASP applications.
One-dimensional wave turbulence
NASA Astrophysics Data System (ADS)
Zakharov, Vladimir; Dias, Frédéric; Pushkarev, Andrei
2004-08-01
The problem of turbulence is one of the central problems in theoretical physics. While the theory of fully developed turbulence has been widely studied, the theory of wave turbulence has been less studied, partly because it developed later. Wave turbulence takes place in physical systems of nonlinear dispersive waves. In most applications nonlinearity is small and dispersive wave interactions are weak. The weak turbulence theory is a method for a statistical description of weakly nonlinear interacting waves with random phases. It is not surprising that the theory of weak wave turbulence began to develop in connection with some problems of plasma physics as well as of wind waves. The present review is restricted to one-dimensional wave turbulence, essentially because finer computational grids can be used in numerical computations. Most of the review is devoted to wave turbulence in various wave equations, and in particular in a simple one-dimensional model of wave turbulence introduced by Majda, McLaughlin and Tabak in 1997. All the considered equations are model equations, but consequences on physical systems such as ocean waves are discussed as well. The main conclusion is that the range in which the theory of pure weak turbulence is valid is narrow. In general, wave turbulence is not completely weak. Together with the weak turbulence component, it can include coherent structures, such as solitons, quasisolitons, collapses or broad collapses. As a result, weak and strong turbulence coexist. In situations where coherent structures cannot develop, weak turbulence dominates. Even though this is primarily a review paper, new results are presented as well, especially on self-organized criticality and on quasisolitonic turbulence.
Magneto-optical response in the arbitrary-Chern number topological phase on square lattice
NASA Astrophysics Data System (ADS)
Wang, Yi-Xiang
2016-07-01
In this work, we investigate the magneto-optical response in the arbitrary-Chern number topological phase. Based on the Dirac theory, we derive the analytic expressions for the magneto-optical response. More importantly, we construct the model on the possible square lattice and make the numerical calculations with the exact diagonalization method. We find the analytical and numerical results are in good agreement with each other. For the optical absorption spectrum, the low-energy absorptive peaks and the corresponding hopping processes are distinct in different Chern number phases, heavily depending on the filling factor of the system. While for the optical Hall conductivities, the physical mechanisms are revealed for the dichroism of the absorption peaks in response to the right- and left-circularly polarized light. We discuss the feasibility of these results in experiment.
Renormalized perturbation theory - Vlasov-Poisson system, weak turbulence limit, and gyrokinetics
NASA Astrophysics Data System (ADS)
Zhang, Y. Z.; Mahadjan, S. M.
1988-10-01
The self-consistency of the renormalized perturbation theory of Zhang and Mahajan (1985) is demonstrated by applying it to the Vlasov-Poisson system and showing that the theory has the correct weak turbulence limit. Energy conservation is proved to arbitrary high order for the electrostatic drift waves. The theory is applied to derive renormalized equations for a low-beta gyrokinetic system. Comparison of this theory with other current theories is presented.
Workshop on Computational Turbulence Modeling
Not Available
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. Separate abstracts have been prepared for articles from this report.
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.
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.
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.
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.
Stellar Turbulent Convection: A Self-consistent Model
NASA Astrophysics Data System (ADS)
Canuto, V. M.; Goldman, I.; Mazzitelli, I.
1996-12-01
We present a self-consistent model for stellar turbulent convection that is similar in spirit to the CM model (Canuto & Mazzitelli 1991) since it accounts for the full spectrum of the turbulent eddies rather than only one eddy, as done in the mixing length theory (MLT). The model differs from the CM model in the treatment of the rate of energy input nS(k) from the source that generates the turbulence. In the present model, nS(k) is controlled by both the source and the turbulence it ultimately generates, thus ensuring a self-consistent modeling of the turbulence. This improves the CM model in which nS(k) was taken to be equal to the growth rate of the linear unstable convective modes. However, since the formulation of a self-consistent treatment is far from simple, we were forced to use a representation of the nonlinear interactions less complete than the one in the CM model. The ensuing equations were solved numerically for a wide range of convective efficiencies. The results are the convective flux, the mean square turbulent velocity, the root mean squared turbulent pressure and the turbulent viscosity. We implemented the model in the ATON stellar structure code and computed the evolution of a solar model. The results are generally similar to those of the CM model and thus quite different from the MLT. The present model requires a smaller overshoot into the upper radiative zone than does the CM model, in accord with recent empirical estimates. Application to Population II stars and comparison with the very metal-poor globular cluster M68 yields an age in the range 11-12 Gyr. This is somewhat younger than the CM age, which in turn is younger than the corresponding MLT age, a result of possible cosmological interest
Radio Wave Scintillations and Models of Interstellar Turbulence
NASA Astrophysics Data System (ADS)
Spangler, Steven R.
1998-05-01
There are a number of well-established observational results from radio scintillations which have implications for the nature of interstellar turbulence. Among such results are evidence for anisotropy and a Kolmogorov spectrum for the density irregularities. It is probable the galactic magnetic field organizes these irregularities so that spatial gradients along the field are much less than those perpendicular to the field. Such a behavior for turbulence is predicted by theories of magnetohydrodynamic turbulence in which the amplitude is small. The turbulence is then described by a theory termed reduced magnetohydrodynamics. A limiting case of reduced magnetohydrodynamics is two dimensional magnetohydrodynamics, in which the direction of the large scale magnetic field z defines the ignorable coordinate. Two dimensional magnetohydrodynamics consists of a pair of coupled nonlinear partial differential equations for the velocity stream function psi and the z component of the magnetic vector potential A_z. A number of observed features of interstellar turbulence can be identified with solutions to the equations of two dimensional magnetohydrodynamics. Examples are the development of Kolmogorov-like spectra for the velocity and magnetic field from a wide class (although not totally general) initial conditions, a natural explanation for the formation of intermittancy in turbulence, and the rapid development of small scale, large spatial wavenumber fluctuations, in contrast to the eddy cascade of hydrodynamic turbulence. The equations of two dimensional magnetohydrodynamics may serve as a simple but tractable model of interstellar plasma turbulence that may complement and be superior to the traditional model of an ensemble of magnetohydrodynamic waves.
NASA Astrophysics Data System (ADS)
Huang, Y. X.; Schmitt, F. G.; Lu, Z. M.; Liu, Y. L.
2009-04-01
In this work, we present the analysis of two long time series of daily river flow data, 32 years recorded in the Seine river (France), and 25 years recorded in the Wimereux river (Wimereux, France). We apply a scale based decomposition method, namely Empirical Mode Decomposition (EMD), on these time series. The data are decomposed into several Intrinsic Mode Function (IMF). The mean frequency of each mode indicates that the EMD method acts as a filter bank. Furthermore, the cross-correlation between these IMF modes from the Seine river and the Wimereux river demonstrates strong correlation among the large scale IMF modes, which indicates that both rivers are influenced by the same events. We also find that the large scale parts have the same evolution trend. We finally apply arbitrary order Hilbert spectral analysis (Huang et al. EPL, 2008), a new technique coming from turbulence studies and time series analysis, on the flow of the Seine river. This new method provides on amplitude-frequency representation of the original time series, giving a joint pdf p(ω,A). When marginal moments of the amplitude are computed, one obtains an intermittency study in the frequency space. Applied to river flow discharge data from the Seine river, this shows the scaling range and characterizes the intermittent fluctuations over the range of scales from 4.5 day to 60 days. Reference Huang Y.X., Schmitt F. G., Lu Z.M. And Liu Y.L. An amplitude-frequency study of turbulent scaling intermittency using Hilbert spectral analysis Europhys. Lett. 2008, 84: 40010
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.
Energy transfer in stably stratified turbulence
NASA Astrophysics Data System (ADS)
Kimura, Yoshifumi; Herring, Jackson
2015-11-01
Energy transfer in forced stable stratified turbulence is investigated using pseudo-spectral DNS of the Navier-Stokes equations under the Boussinesq approximation with 10243 grid points. Making use of the Craya-Herring decomposition, the velocity field is decomposed into vortex (Φ1) and wave (Φ2) modes. To understand the anisotropy of stably stratified turbulence, the energy flues in terms of the spherical, the horizontal and the vertical wave numbers, are investigated for the total kinetic, Φ1, Φ2 energies, respectively. Among the three fluxes, the spherical and the horizontal look similar for strong stratification, and Φ1 flux shows a wave number region of constant value, which implies Kolmogorov's inertial range. The corresponding spectral power are, however, k - 5 / 2 for the spherical and k⊥- 5 / 3 for the horizontal cases. In contrast to these, the vertical energy fluxes show completely different features. We have observed the saturation spectrum E (kz) ~ CN2kz-3 for strong stratification as before, but the mechanism to produce this spectrum seems different from the Kolmogorov picture.
Mathematical model of bisubject qualimetric arbitrary objects evaluation
NASA Astrophysics Data System (ADS)
Morozova, A.
2016-04-01
An analytical basis and the process of formalization of arbitrary objects bisubject qualimetric evaluation mathematical model information spaces are developed. The model is applicable in solving problems of control over both technical and socio-economic systems for objects evaluation using systems of parameters generated by different subjects taking into account their performance and priorities of decision-making.
Optimal Fisher Discriminant Ratio for an Arbitrary Spatial Light Modulator
NASA Technical Reports Server (NTRS)
Juday, Richard D.
1999-01-01
Optimizing the Fisher ratio is well established in statistical pattern recognition as a means of discriminating between classes. I show how to optimize that ratio for optical correlation intensity by choice of filter on an arbitrary spatial light modulator (SLM). I include the case of additive noise of known power spectral density.
Information balance in quantum teleportation with an arbitrary pure state
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.
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.
Kull ALE: II. Grid Motion on Unstructured Arbitrary Polyhedral Meshes
Anninos, P
2002-02-11
Several classes of mesh motion algorithms are presented for the remap phase of unstructured mesh ALE codes. The methods range from local shape optimization procedures to more complex variational minimization methods applied to arbitrary unstructured polyhedral meshes necessary for the Kull code.
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…
Analytical solutions of the Rayleigh equation for arbitrary polytropic exponent
NASA Astrophysics Data System (ADS)
Kudryashov, Nikolay A.; Sinelshchikov, Dmitry I.
2016-06-01
The Rayleigh equation for the description of spherical gas-filled bubbles dynamics is considered. It is shown that this equation can be transformed into an equation for the elliptic function for arbitrary values of the polytropic exponent. General analytical solutions of the Rayleigh equation are studied for some particular cases, such as the isothermal case.
Arbitrary unitary transformations on optical states using a quantum memory
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.
Criterion for faithful teleportation with an arbitrary multiparticle channel
NASA Astrophysics Data System (ADS)
Cheung, Chi-Yee; Zhang, Zhan-Jun
2009-08-01
We present a general criterion which allows one to judge if an arbitrary multiparticle entanglement channel can be used to teleport faithfully an unknown quantum state of a given dimension. We also present a general multiparticle teleportation protocol which is applicable for all channel states satisfying this criterion.
Acquisition of arbitrary conditional discriminations by young normally developing children.
Pilgrim, C; Jackson, J; Galizio, M
2000-01-01
Three experiments investigated conditions designed to facilitate acquisition of arbitrary conditional discriminations in 3- to 6-year-old normally developing children. In Experiment 1, 6 subjects failed to master the arbitrary match-to-sample task under conditions of differential reinforcement alone, but 7 subjects did so when instructions or instructions and sample naming were added. In Experiment 2, sample naming introduced in a blocked-trial arrangement resulted in acquisition, but only when the sample name was a nonsense syllable provided by the experimenter (5 of 7 subjects) and not when the sample name was generated by the subject (0 of 5 subjects). Experiment 3 demonstrated the effectiveness of a training sequence involving thematically related stimuli as an intermediate step facilitating the transition from identity to novel arbitrary relations. The difficulties in mastering arbitrary conditional discriminations shown here imply that further analyses with young children will be particularly important in efforts to investigate the development of theoretically important stimulus relations. PMID:10784008
A scalable, fast, and multichannel arbitrary waveform generator
NASA Astrophysics Data System (ADS)
Baig, M. T.; Johanning, M.; Wiese, A.; Heidbrink, S.; Ziolkowski, M.; Wunderlich, C.
2013-12-01
This article reports on the development of a multichannel arbitrary waveform generator that simultaneously generates arbitrary voltage waveforms on 24 independent channels with a dynamic update rate of up to 25 Msps. A real-time execution of a single waveform and/or sequence of multiple waveforms in succession, with a user programmable arbitrary sequence order is provided under the control of a stand-alone sequencer circuit implemented using a field programmable gate array. The device is operated using an internal clock and can be synced to other devices by means of transistor-transistor logic (TTL) pulses. The device can provide up to 24 independent voltages in the range of up to ± 9 V with a dynamic update-rate of up to 25 Msps and a power consumption of less than 35 W. Every channel can be programmed for 16 independent arbitrary waveforms that can be accessed during run time with a minimum switching delay of 160 ns. The device has a low-noise of 250 μVrms and provides a stable long-term operation with a drift rate below 10 μV/min and a maximum deviation less than ± 300 μVpp over a period of 2 h.
Rainbows in the grass. II. Arbitrary diagonal incidence.
Adler, Charles L; Lock, James A; Fleet, Richard W
2008-12-01
We consider external reflection rainbow caustics due to the reflection of light from a pendant droplet where the light rays are at an arbitrary angle with respect to the horizontal. We compare this theory to observation of glare spots from pendant drops on grass; we also consider the potential application of this theory to the determination of liquid surface tension. PMID:19037345
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.
Geostrophic turbulence in CZ silicon crucible
NASA Astrophysics Data System (ADS)
Kishida, Yutaka; Okazawa, Kensuke
1999-03-01
In the CZ silicon process, silicon melt convection is affected by the Coriolis force as a rotating fluid system. As a result, a special fluid motion called baroclinic instability appears and disturbs the single crystal growth. Since the Coriolis force will increase the curvature of the fluid particle paths, when the curvature exceeds the crucible size, another unstable fluid motion, the so-called geostrophic turbulence, is expected to occur at higher Taylor numbers. This study investigates the geostrophic turbulence by numerical flow simulation and experimental observations in an actual CZ crucible. In the numerical flow simulation, we solved 3D differential equations on a cylindrical lattice of 80×60×65 points, where the Rayleigh number of the system was fixed to be 2.7×10 7. With the Taylor number higher than 1×10 11, the calculated fluid motion and temperature structure produce a polka-dot pattern, which continues from the melt surface to the bottom. When the Taylor number is increased, the vertical vorticity component increases extremely. In the actual CZ crucible, temperature profiles on the melt surface were recorded by video camera thermometer in the same conditions as in the numerical simulation. The thermal images of the melt surface also show a fluctuating polka-dot pattern consisting of high temperature areas as seen in the numerical simulation results. The size and amplitude of the high temperature areas decrease with increase of the Taylor number, thus thermal clusters will relax the radial gradient and fluctuations. The Fourier power spectrum of the time dependent fluctuations has an f-4 behavior, which statistically indicates 2D turbulence. These facts observed both in numerical simulations and the actual experiment are completely consistent with the characteristics of geostrophic turbulence.
Dynamical Field Line Connectivity in Magnetic Turbulence
NASA Astrophysics Data System (ADS)
Ruffolo, D. J.; Matthaeus, W. H.
2014-12-01
Point-to-point magnetic connectivity has a stochastic character whenever magnetic fluctuations cause a field line random walk, with observable manifestations such as dropouts of solar energetic particles and upstream events at Earth's bow shock. This can also change due to dynamical activity. Comparing the instantaneous magnetic connectivity to the same point at two different times, we provide a nonperturbative analytic theory for the ensemble average perpendicular displacement of the magnetic field line, given the power spectrum of magnetic fluctuations. For simplicity, the theory is developed in the context of transverse turbulence, and is numerically evaluated for two specific models: reduced magnetohydrodynanmics (RMHD), a quasi-two dimensional model of anisotropic turbulence that is applicable to low-beta plasmas, and two-dimensional (2D) plus slab turbulence, which is a good parameterization for solar wind turbulence. We take into account the dynamical decorrelation of magnetic fluctuations due to wave propagation, nonlinear distortion, random sweeping, and convection by a bulk wind flow relative to the observer. The mean squared time-differenced displacement increases with time and with parallel distance, becoming twice the field line random walk displacement at long distances and/or times, corresponding to a pair of uncorrelated random walks. These results are relevant to a variety of astrophysical processes, such as electron transport and heating patterns in coronal loops and the solar transition region, changing magnetic connection to particle sources near the Sun or at a planetary bow shock, and thickening of coronal hole boundaries. Partially supported by the Thailand Research Fund, the US NSF (AGS-1063439 and SHINE AGS-1156094), NASA (Heliophysics Theory NNX11AJ44G), and by the Solar Probe Plus Project through the ISIS Theory team.
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.
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Trapped electron mode turbulence driven intrinsic rotation in Tokamak plasmas.
Wang, W X; Hahm, T S; Ethier, S; Zakharov, L E; Diamond, P H
2011-02-25
Progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported. The turbulence-driven intrinsic torque associated with nonlinear residual stress generation due to zonal flow shear induced asymmetry in the parallel wave number spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing experimental empirical scalings of intrinsic rotation. The origin of current scaling is found to be enhanced k(∥) symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The intrinsic torque is proportional to the pressure gradient because both turbulence intensity and zonal flow shear, which are two key ingredients for driving residual stress, increase with turbulence drive, which is R/L(T(e)) and R/L(n(e)) for the trapped electron mode. PMID:21405577
Statistical acceleration of electrons by lower-hybrid turbulence
NASA Technical Reports Server (NTRS)
Wu, C. S.; Gaffey, J. D., Jr.; Liberman, B.
1981-01-01
The statistical acceleration of electrons along an ambient magnetic field by large-amplitude lower-hybrid turbulence is discussed. Perturbations driven by a crossfield current and propagating nearly perpendicular to the applied magnetic field are considered. It is assumed that the instability saturates rapidly and that the fluctuating electric field is predominantly electrostatic. If the turbulence is characterized by a spectrum of small parallel wavenumbers, such that the parallel phase velocity of the waves is greater than the electron thermal velocity, then the turbulence can only accelerate electrons moving with large velocities along the magnetic field. The quasi-linear diffusion equation is solved using a Green's function technique, assuming a power law spectral energy density. The time evolution of an initial Maxwellian distribution is given and the time rate of change of the mean electron energy is calculated for various cases.
Cosmic-Ray Anisotropy as a Probe of Interstellar Turbulence
NASA Astrophysics Data System (ADS)
Giacinti, Gwenael; Kirk, John
2016-07-01
IceTop and IceCube have observed a mysterious cold spot in the angular distribution of high energy (≳ 100 TeV) cosmic rays, thereby placing interesting constraints on their transport properties. In this paper we examine these constraints by comparing the observations with the predictions of pitch-angle diffusion in various kinds of turbulence. In the case of incompressible Alfvénic turbulence with a Goldreich-Sridhar power-spectrum, we show that pseudo-Alfvén modes produce a signature that is compatible with the observations, although they fail to provide enough scattering to confine cosmic rays in the galaxy. We confirm that adding fast magnetosonic modes can alleviate this problem, and further show that for physically relevant values of the turbulence parameters, this model can still match the observations. Finally, we study the imprint on the cosmic-ray anistropy of anistropic damping of the fast modes.
Microelectrokinetic turbulence in microfluidics at low Reynolds number
NASA Astrophysics Data System (ADS)
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.
Spatiotemporal detection of Kelvin waves in quantum turbulence simulations
NASA Astrophysics Data System (ADS)
Clark di Leoni, P.; Mininni, P. D.; Brachet, M. E.
2015-12-01
We present evidence of Kelvin excitations in space-time resolved spectra of numerical simulations of quantum turbulence. Kelvin waves are transverse and circularly polarized waves that propagate along quantized vortices, for which the restitutive force is the tension of the vortex line, and which play an important role in theories of superfluid turbulence. We use the Gross-Pitaevskii equation to model quantum flows, letting an initial array of well-organized vortices develop into a turbulent bundle of intertwined vortex filaments. By achieving high spatial and temporal resolution we are able to calculate space-time resolved mass density and kinetic energy spectra. Evidence of Kelvin and sound waves is clear in both spectra. Identification of the waves allows us to extract the spatial spectrum of Kelvin waves, clarifying their role in the transfer of energy.
Microelectrokinetic turbulence in microfluidics at low Reynolds number.
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. PMID:26871154
Space-time resolved wave turbulence in a vibrating plate.
Cobelli, Pablo; Petitjeans, Philippe; Maurel, Agnès; Pagneux, Vincent; Mordant, Nicolas
2009-11-13
Wave turbulence in a thin elastic plate is experimentally investigated. By using a Fourier transform profilometry technique, the deformation field of the plate surface is measured simultaneously in time and space. This enables us to compute the wave-vector-frequency (k, omega) Fourier spectrum of the full space-time deformation velocity. In the 3D (k, omega) space, we show that the energy of the motion is concentrated on a 2D surface that represents a nonlinear dispersion relation. This nonlinear dispersion relation is close to the linear dispersion relation. This validates the usual wave-number-frequency change of variables used in many experimental studies of wave turbulence. The deviation from the linear dispersion, which increases with the input power of the forcing, is attributed to weak nonlinear effects. Our technique opens the way for many new extensive quantitative comparisons between theory and experiments of wave turbulence. PMID:20365984
NASA Astrophysics Data System (ADS)
Zhang, Min-Cang
2013-11-01
The arbitrary l-wave solutions to the Schrödinger equation for the deformed hyperbolic Eckart potential is investigated analytically by using the Nikiforov—Uvarov method. The centrifugal term is treated with the improved Greene and Aldrich approximation scheme. The wave functions are expressed in terms of the Jacobi polynomial or the hypergeometric function. The discrete spectrum is obtained and it is shown that the deformed hyperbolic Eckart potential is a shape-invariant potential and the bound state energy is independent of the deformation parameter q.
Solar Wind Turbulence and the Role of Ion Instabilities
NASA Astrophysics Data System (ADS)
Alexandrova, O.; Chen, C. H. K.; Sorriso-Valvo, L.; Horbury, T. S.; Bale, S. D.
Solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of magnetic field, the differences with neutral fluid isotropic turbulence are: (i) weakness of collisional dissipation and (ii) presence of several characteristic space and time scales. In this paper we discuss observational properties of solar wind turbulence in a large range from the MHD to the electron scales. At MHD scales, within the inertial range, turbulence cascade of magnetic fluctuations develops mostly in the plane perpendicular to the mean field, with the Kolmogorov scaling k_{perp}^{-5/3} for the perpendicular cascade and k_⊥^{-2} for the parallel one. Solar wind turbulence is compressible in nature: density fluctuations at MHD scales have the Kolmogorov spectrum. Velocity fluctuations do not follow magnetic field ones: their spectrum is a power-law with a -3/2 spectral index. Probability distribution functions of different plasma parameters are not Gaussian, indicating presence of intermittency. At the moment there is no global model taking into account all these observed properties of the inertial range. At ion scales, turbulent spectra have a break, compressibility increases and the density fluctuation spectrum has a local flattening. Around ion scales, magnetic spectra are variable and ion instabilities occur as a function of the local plasma parameters. Between ion and electron scales, a small scale turbulent cascade seems to be established. It is characterized by a well defined power-law spectrum in magnetic and density fluctuations with a spectral index close to -2.8. Approaching electron scales, the fluctuations are no more self-similar: an exponential cut-off is usually observed (for time intervals without quasi-parallel whistlers) indicating an onset of dissipation. The small scale inertial range between ion and electron scales and the electron dissipation range can be together described by ˜ k
Solar Wind Turbulence and the Role of Ion Instabilities
NASA Astrophysics Data System (ADS)
Alexandrova, O.; Chen, C. H. K.; Sorriso-Valvo, L.; Horbury, T. S.; Bale, S. D.
2013-10-01
Solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of magnetic field, the differences with neutral fluid isotropic turbulence are: (i) weakness of collisional dissipation and (ii) presence of several characteristic space and time scales. In this paper we discuss observational properties of solar wind turbulence in a large range from the MHD to the electron scales. At MHD scales, within the inertial range, turbulence cascade of magnetic fluctuations develops mostly in the plane perpendicular to the mean field, with the Kolmogorov scaling for the perpendicular cascade and for the parallel one. Solar wind turbulence is compressible in nature: density fluctuations at MHD scales have the Kolmogorov spectrum. Velocity fluctuations do not follow magnetic field ones: their spectrum is a power-law with a -3/2 spectral index. Probability distribution functions of different plasma parameters are not Gaussian, indicating presence of intermittency. At the moment there is no global model taking into account all these observed properties of the inertial range. At ion scales, turbulent spectra have a break, compressibility increases and the density fluctuation spectrum has a local flattening. Around ion scales, magnetic spectra are variable and ion instabilities occur as a function of the local plasma parameters. Between ion and electron scales, a small scale turbulent cascade seems to be established. It is characterized by a well defined power-law spectrum in magnetic and density fluctuations with a spectral index close to -2.8. Approaching electron scales, the fluctuations are no more self-similar: an exponential cut-off is usually observed (for time intervals without quasi-parallel whistlers) indicating an onset of dissipation. The small scale inertial range between ion and electron scales and the electron dissipation range can be together described by , with α≃8/3 and the dissipation scale ℓ d close to the
Compressible turbulence with slow-mode waves observed in the bursty bulk flow of plasma sheet
NASA Astrophysics Data System (ADS)
Wang, Tieyan; Cao, Jinbin; Fu, Huishan; Meng, Xuejie; Dunlop, M.
2016-03-01
In this paper, we report the evidence of compressible turbulence with slow-mode waves in a bursty bulk flow of plasma sheet. This compressible turbulence is characterized by a multiscale (1-60 s) anticorrelation between plasma density and magnetic field strength. Besides, the magnetic compressibility spectrum stays nearly constant at all the measured frequencies. Furthermore, the turbulence energy distributions are anisotropic with k⊥ > k//, and the dispersion relation is consistent with slow-mode prediction. The fluctuations of density and magnetic field have similar double slope spectrum and kurtosis. These results suggest that the slow waves are involved in the intermittent turbulence cascade from MHD to ion kinetic scales, which may have significant implications for the energy transfer in the plasma sheet.
Experimental observation of steady inertial wave turbulence in deep rotating flows
NASA Astrophysics Data System (ADS)
Yarom, Ehud; Sharon, Eran
2015-11-01
We present experimental evidence of inertial wave turbulence in deep rotating fluid. Experiments were performed in a rotating cylindrical water tank, where previous work showed statistics similar to 2D turbulence (specifically an inverse energy cascade). Using Fourier analysis of high resolution data in both space (3D) and time we show that most of the energy of a steady state flow is contained around the inertial wave dispersion relation. The nonlinear interaction between the waves is manifested by the widening of the time spectrum around the dispersion relation. We show that as the Rossby number increases so does the spectrum width, with a strong dependence on wave number. Our results suggest that in some parameters range, rotating turbulence velocity field can be represented as a field of interacting waves (wave turbulence). Such formalism may provide a better understanding of the flow statistics. This work was supported by the Israel Science Foundation, Grant No. 81/12.
Fossils of big bang turbulence
NASA Astrophysics Data System (ADS)
Gibson, C. H.
2004-12-01
A model is proposed connecting turbulence, fossil turbulence, and the big bang origin of the universe. While details are incomplete, the model is consistent with our knowledge of these processes and is supported by observations. Turbulence arises in a hot-big-bang quantum-gravitational-dynamics scenario at Planck scales. Chaotic, eddy-like-motions produce an exothermic Planck particle cascade from 10-35 m at 1032 K to 108 larger, 104 cooler, quark-gluon scales. A Planck-Kerr instability gives high-Reynolds-number (Re 106) turbulent combustion, space-time-energy-entropy and turbulent mixing. Batchelor-Obukhov-Corrsin turbulent-temperature fluctuations are preserved as the first fossil-turbulence by inflation stretching the patterns beyond the horizon ct of causal connection faster than light speed c in time t 10-33 seconds. Fossil-big-bang-temperature-turbulence re-enters the horizon and imprints nucleosynthesis of H-He densities that seed fragmentation by gravity at 1012 s in the low Reynolds number plasma before its transition to gas at t 1013 s and T 3000 K. Multi-scaling coefficients of the cosmic-microwave-background (CMB) temperature anisotropies closely match those for high Reynolds number turbulence, Bershadskii and Sreenivasan 2002, 2003. CMB spectra support the interpretation that big-bang-turbulence-fossils triggered fragmentation of the viscous plasma at supercluster to galaxy mass scales from 1046 to 1042 kg, Gibson 1996, 2000, 2004ab.
NASA Technical Reports Server (NTRS)
Faeth, G. M.
1989-01-01
Measurements and predictions of the structure of several multiphase flows are considered. The properties of dense sprays near the exits of pressure-atomizing injectors and of noncombusting and combusting dilute dispersed flows in round-jet configurations are addressed. It is found that the properties of dense sprays exhibit structure and mixing properties similar to variable-density single-phase flows at high Reynolds numbers within the atomization regime. The degree of development and turbulence levels at the injector exit have a surprisingly large effect on the structure and mixing properties of pressure-atomized sprays, particularly when the phase densities are large. Contemporary stochastic analysis of dilute multiphase flows provides encouraging predictions of turbulent dispersion for a wide variety of jetlike flows, particle-laden jets in gases and liquids, noncondensing and condensing bubbly jets, and nonevaporating, evaporating, and combusting sprays.
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.
NASA Astrophysics Data System (ADS)
O'dell, C. R.
1986-10-01
It has been known for many decades that the Reynolds number in HII regions must be very high and that the corresponding fine scale flow must be turbulent. Even though the theoretical relation between turbulent element separation and random velocity was derived by Kolmogoroff over forty years ago, there have been only a few attempts to test this theory and its corresponding assumptions. An attempt by Munch for M42 with marginal velocity resolution lead to ambiguous results, although more recent studies by Jean Rene Roy and his colleagues have been more credible. The internal velocities of a number of HII regions were systematically studied and the theory was tested with considerable certainty. The results should be important for the determination of the energy balance of HII regions and the relation of small scale motion to the process of star formation.
Homogeneous quantum electrodynamic turbulence
Shebalin, J.V.
1992-10-01
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.
Effects of small scale energy injection on large scales in turbulent reaction flows
NASA Astrophysics Data System (ADS)
Xuan, Yuan
2014-11-01
Turbulence causes the generation of eddies of various length scales. In turbulent non-reacting flows, most of the kinetic energy is contained in large scale turbulent structures and dissipated at small scales. This energy cascade process from large scales to small scales provides the foundation of a lot of turbulence models, especially for Large Eddy Simulations. However, in turbulent reacting flows, chemical energy is converted locally to heat and therefore deploys energy at the smallest scales. As such, effects of small scale energy injection due to combustion on large scale turbulent motion may become important. These effects are investigated in the case of auto-ignition under homogeneous isotropic turbulence. Impact of small scale heat release is examined by comparing various turbulent statistics (e.g. energy spectrum, two-point correlation functions, and structure functions) in the reacting case to the non-reacting case. Emphasis is placed on the identification of the most relevant turbulent quantities in reflecting such small-large scale interactions.
Multi-scale grid generated turbulence in an internal flow application
NASA Astrophysics Data System (ADS)
Ranade, Piyush; Morris, Scott
2013-11-01
Turbulence generation using multi-scale, or fractal grids, is a method of creating high turbulence intensity flows passively by utilizing the intrinsic scales associated with the grid. This has become the topic of research in many external flow applications. In turbomachinery, the flow at the exit of the combustor and into the first nozzle stage is highly turbulent. In order to create high turbulence intensities in a lab setting passively, multi-scale turbulence generation grids are proposed. The presence of multiple length scales in the grid geometry innately gives rise to turbulent motions of a wide spectrum being shed immediately downstream of the grid, leading to high turbulence intensity flow. The biggest challenge with using such a grid in an internal flow, however, is to achieve spatial uniformity. In this research, three grid geometries commonly found in literature were tested in an experimental set-up consisting of flow between two flat plates. In addition, several other fractal grid geometries were created and tested in an attempt to maximize turbulence intensity while maintaining spatial homogeneity. This research hopes to begin giving insight into the development of turbulence downstream of a multi-scale grid in an internal flow setting.
Stability, transition and turbulence
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.
1987-01-01
A glimpse is provided of the research program in stability, transition and turbulence based on numerical simulations. This program includes both the so-called abrupt and the restrained transition processes. Attention is confined to the prototype problems of channel flow and the parallel boundary layer in the former category and the Taylor-Couette flow in the latter category. It covers both incompressible flows and supersonic flows. Some representative results are presented.
Stability, transition and turbulence
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.
1987-01-01
A glimpse is provided of the research program in stability, transition, and turbulence based on numerical simulations. This program includes both the so-called abrupt and the restrained transition processes. Attention is confined to the prototype problems of channel flow and the parallel boundary layer in the former category and the Taylor-Couette flow in the latter category. It covers both incompressible flows and supersonic flows. Some representative results are presented.
Turbulent General Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Eyink, G. L.
2015-07-01
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.
NASA Astrophysics Data System (ADS)
Huang, Yongxiang; Schmitt, François G.; Lu, Zhiming.; Liu, Yulu
2009-06-01
SummaryIn this paper we presented the analysis of two long time series of daily river flow data, 32 years recorded in the Seine river (France), and 25 years recorded in the Wimereux river (Wimereux, France). We applied a scale based decomposition method, namely Empirical Mode Decomposition (EMD), on these time series. The data were decomposed into several Intrinsic Mode Functions (IMF). The mean frequency of each IMF mode indicated that the EMD method acts as a filter bank. Furthermore, the cross-correlation between these IMF modes from the Seine river and Wimereux river demonstrated correlation among the large scale IMF modes, which indicates that both rivers are likely to be influenced by the same maritime climate event of Northern France. As a confirmation we found that the large scale parts have the same evolution trend. We finally applied arbitrary order Hilbert spectral analysis, a new technique coming from turbulence studies and time series analysis, on the flow discharge of the Seine river. This new method provides an amplitude-frequency representation of the original time series, giving a joint pdf p(ω,A). When marginal moments of the amplitude are computed, one obtains an intermittency study in the frequency space. Applied to river flow discharge data from the Seine river, this shows the scaling range and characterizes the intermittent fluctuations over the range of scales from 4.5 to 60 days, between synoptic and intraseasonal scales.
A mesh partitioning algorithm for preserving spatial locality in arbitrary geometries
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.
NASA Astrophysics Data System (ADS)
van den Berg, Thomas H.; Luther, Stefan; Mazzitelli, Irene M.; Rensen, Judith M.; Toschi, Federico; Lohse, Detlef
The effect of bubbles on fully developed turbulent flow is investigated numerically and experimentally, summarizing the results of our previous papers (Mazzitelli et al., 2003, Physics of Fluids15, L5. and Journal of Fluid Mechanics488, 283; Rensen, J. et al. 2005, Journal of Fluid Mechanics538, 153). On the numerical side, we simulate Navier Stokes turbulence with a Taylor Reynolds number of Re?˜60, a large large-scale forcing, and periodic boundary conditions. The point-like bubbles follow their Lagrangian paths and act as point forces on the flow. As a consequence, the spectral slope is less steep as compared to the Kolmogorov case. The slope decrease is identified as a lift force effect. On the experimental side, we do hot-film anemometry in a turbulent water channel with Re? ˜ 200 in which we have injected small bubbles up to a volume percentage of 3%. Here the challenge is to disentangle the bubble spikes from the hot-film velocity signal. To achieve this goal, we have developed a pattern recognition scheme. Furthermore, we injected microbubbles up to a volume percentage of 0.3%. Both in the counter flowing situation with small bubbles and in the co-flow situation with microbubbles, we obtain a less spectral slope, in agreement with the numerical result.
Is Saturn's Magnetosphere Turbulent?
NASA Astrophysics Data System (ADS)
Walker, Raymond; Fukazawa, Keiichiro; Eriksson, Stefan; Weygand, James
2016-04-01
On February 12, 2008 the Cassini spacecraft passed through Saturn's dayside bow shock and spent 16 hours in the solar wind. The interval in the solar wind was characterized by a series of dynamic pressure pulses and a rotation of the interplanetary magnetic field from southward to northward. We have used these Cassini solar observations to drive our global magnetohydrodynamic simulation of the interaction of solar wind with Saturn's magnetosphere and ionosphere. We found that large amplitude waves formed at the magnetopause in response to the changes in the dynamic pressure. The vorticity (both parallel and perpendicular) increased within the outer magnetosphere. The vorticity was mostly driven by pressure variations and not reconnection. The vortices frequently were nested with smaller vortices within the large scale vortices. This cascade in vorticity is suggestive of turbulent flows. In this presentation we will evaluate vorticity in our Saturn simulation to determine if the flows are turbulent. With Cassini in the solar wind there were no simultaneous observations within Saturn's magnetosphere. However we will examine the Cassini observations at other times to look for evidence of turbulence.
Zooplankton intermittency and turbulence
NASA Astrophysics Data System (ADS)
Schmitt, François G.
2010-05-01
Planktonic organisms usually live in a turbulent world. Since marine turbulence is characterized by very high Reynolds numbers, it possesses very intermittent fluctuations which in turn affect marine life. We consider here such influence on zooplankton on 2 aspects. First we consider zooplankton motion in the lab. Many copepods display swimming abilities. More and more species have been recently recorded using normal or high speed cameras, and many trajectories have been extracted from these movies and are now available for analysis. These trajectories can be complex, stochastic, with random switching from low velocity to high velocity events and even jumps. These complex trajectories show that an adequate modeling is necessary to understand and characterize them. Here we review the results published in the literature on copepod trajectories. We discuss the random walk, Levy walk modeling and introduce also multifractal random walks. We discuss the way to discriminate between these different walks using experimental data. Stochastic simulations will be performed to illustrate the different families. Second, we consider zooplankton contact rates in the framework of intermittent turbulence. Intermittency may have influence on plankton contact rates. We consider the Particle Stokes number of copepods, in a intermediate dissipation range affected by intermittent fluctuations. We show that they may display preferential concentration effects, and we consider the influence on contact rates of this effect in the intermediate dissipation range.
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.
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. PMID:24580684