Detailed computations were made of energy transfer among the scales motion in incompressible turbulent fields at low Reynolds numbers generated by direct numerical simulations. It was observed that although resulted from triad interactions nonlocal k space, always transferred locally. The calculated eddy-damped quasinormal Markovian (EDQNM) theory turbulence is excellent agreement with results At high EDQNM predicts same mechanism inertial range numbers, i.e., predominantly local caused...

A new method for large eddy simulations is described and evaluated. In the proposed primary modeled quantity unfiltered velocity field appearing in definition of subgrid-scale stress tensor. An estimate obtained by expanding resolved large-scale to subgrid-scales two times smaller than grid scale. The estimation procedure consists steps. first step utilizes properties a filtering operation representation quantities terms basis functions such as Fourier polynomials. second step, phases...

Using a velocity field obtained in direct numerical simulation of isotropic turbulence at moderate Reynolds number the subgrid-scale energy transfer spectral and physical space representation is analyzed. The found to be composed forward an inverse component, both being significant dynamics resolved scales. Energy exchanges between unresolved scales from vicinity cutoff wave dominate processes energetics are unaffected by modes with numbers greater than twice number. Correlations large-scale...

We propose a method for computing effective numerical eddy viscosity acting in dissipative schemes used monotonically integrated large simulations of turbulence. The is evaluated on an example specific nonoscillatory finite volume scheme MPDATA developed geophysical flows.

Subgrid scale (SGS) models for large eddy simulations of turbulent flows fall into two general categories. One category consists the that provide expressions SGS terms such as a stress tensor or heat flux and usually employ viscosity concepts. The other unresolved primitive variables velocity temperature stresses are secondary quantities computed directly from definitions. We discuss fundamentals latter review several specific approaches, including defiltering deconvolution procedures...

Using velocity fields obtained in direct numerical simulations of turbulent convection and channel flow, the energy transfer process among lateral scales motion these low Reynolds number flows is analyzed. In all cases transferred most effectively between similar size. As a result, subgrid-scale caused almost exclusively by interactions resolved subgrid characterized wave numbers not greater than twice cutoff number. The scale dependence forward inverse transfers contributing to total eddy...

The mean velocity profile scaling and the vorticity structure of a stably stratified, initially turbulent wake towed sphere are studied numerically using high-accuracy spectral multi-domain penalty method model. A detailed initialization procedure allows smooth, minimum-transient transition into non-equilibrium (NEQ) regime evolution. broad range Reynolds numbers, Re = UD/ν ∈ [5 × 10 3 , 5 ] internal Froude Fr 2 U /( ND ) [4, 64] ( D characteristic length scales, N is buoyancy frequency)...

Direct numerical simulations of passive scalars, with Prandtl numbers Pr =3, 5, and 7, advected by turbulence at three low Reynolds were performed. The energy spectra are self-similar under the Kolmogorov scaling exhibit behaviour consistent many other investigations: a short inertial range for highest number universal exponential form spectrum all in dissipation range. In cases scalar collapse to single curve Batchelor k −1 followed an fall-off. We attribute applicability our...

Without resort to any modeling, subgrid-scale eddy viscosity is computed from the results of high-resolution (${64}^{3}$ and ${128}^{3}$ grid points) direct numerical simulations three-dimensional homogeneous, isotropic, decaying turbulence. In these peaks sharply at cutoff wave number, in rough agreement with Kraichnan. addition, low--wave-number range may be negative, contrary generally accepted concept a viscosity. Some possible explanations this behavior are discussed.

The subgrid-scale estimation procedure for large eddy simulations developed previously in the spectral (Fourier) representation is extended to physical space representation. provides an estimate of unfiltered velocity field appearing definition subgridscale stress tensor and consists two steps. In deconvolution step approximate inversion filtering operation performed. Subsequently, nonlinear used generate a range subgrid scales on mesh times smaller than employed discretization resolved...

Detailed transfer functions T(k‖p,q), which express turbulent energy rate to modes k caused by their nonlinear interactions with p and q, are analyzed using results of direct numerical simulations homogeneous turbulence. A previously found phenomenological scaling for the brings them into a self-similar form, is used deduce form spectrum in dissipation range proportional k−2 exp(−ak) exp(−ak). physical mechanism process consistent self-similarity proposed.

The scale locality functions, originally introduced by Kraichnan, are computed from results of direct numerical simulations forced isotropic turbulence. It is found that a curve with the classical, asymptotic scaling exponent 4/3 provides lower bound for data in infrared limit and upper ultraviolet limit, i.e., nonlocality effects stronger weaker than theoretical result obtained an infinite inertial range. departures substantial fully resolved at Reynolds number but decrease impose −5/3...

The interaction between shear and buoyancy effects for Bénard convection in plane Couette flow is studied by performing direct numerical simulations. At moderate Rayleigh number (≈10000−50000), tends to organize the into quasi-two-dimensional rolls parallel mean can enhance heat transfer, while at higher (>150000), disrupt formation of convective plumes reduce transfer. A significant temporal oscillation local Nusselt was consistently observed high numbers, a factor that may contribute...

A numerical investigation of the near wake a sphere moving horizontally through linearly stratified fluid is presented. Simulations are first performed on flow with Reynolds number Re = 200 for range internal Froude number, 0.1 ≤ Fr ∞. The simulations capture buoyant characteristic behavior, presence vortex shedding at low Fr, and lee waves. higher 1000, 1 ∞ provide description parametrization wake, including density field. At effects utilizing two different averaging techniques in unsteady...

Using results of direct numerical simulations isotropic turbulence the subgrid-scale energy transfer in physical space is calculated exactly employing a spectral decomposition velocity field into large (resolved) and small (unresolved) scales. Comparisons with large-scale quantities reveal qualitative correlations between regions subgrid boundaries vorticity production. This suggests novel analysis nonlinear term, where it decomposed four components determined by combinations resolved...

Using the results of direct numerical simulations isotropic turbulence, we compute detailed energy exchanges between different scales motion and investigate how they contribute to global quantities such as transfer, spectral flux, subgrid-scale dissipation. The are defined by decomposing velocity fields using sharp smooth, tangent hyperbolic filters. analysis interactions reveals that individual nonlocal contributions large but significant cancellations lead asymptotically dominated local...

The scale-similarity model in large-eddy simulation (LES) leads to an attractive, functionally simple expression for the subgrid-scale (SGS) stress tensor. It is well known, however, that similarity fails accurately predict some of most fundamental quantities turbulent flows, perhaps important being global energy transfer and associated dissipation. To address this, additional dissipative terms are usually added improve its performance. In present paper, considerations interscale have been...

A previously developed method for large-eddy simulations (LES), based on spectral eddy-viscosity models, is generalised to the physical space representation. The estimates subgrid-scale (SGS) energy transfer using a similarity-type model expression SGS tensor obtained Gaussian filtering of velocity fields advanced in simulations. Following steps representation, used obtain spatially varying eddy viscosity at each time step LES. computed employed stress familiar Boussinesq form use tested LES...

Using direct numerical simulation techniques we investigate transition to turbulence in a boundary-layer flow containing two large-scale counter-rotating vortices with axes aligned the streamwise direction. The are assumed have been generated by Görtler instability mechanism operating flows over concave walls. Full, three-dimensional Navier–Stokes equations natural curvilinear coordinate system for wall solved pseudospectral method. simulations initialized most unstable mode of linear...

The amplitude equation for Taylor vortices with spatially varying in long but finite cylinders is derived arbitrary gap width. boundary condition to be satisfied by the at end of obtained a simple scaling argument. same argument also yields property boundary-layer flow cylinder ends. results conditions and correlation length are compared recent measurements Pfister Rehberg, excellent agreement obtained.

We examine and compare near-forward light scattering that is caused by turbulence typical particulate assemblages in the ocean. The particles was calculated using Mie theory for homogeneous spheres particle size distributions representative of natural Direct numerical simulations a passive scalar with Prandtl number 7 mixed were used to represent temperature fluctuations resulting inhomogeneities refractive index water. Light on simulated turbulent flow geometrical-optics approximation....