A dynamic procedure based on the scale-similarity hypotheses for large-eddy simulation

2007 ◽  
Vol 1 (4) ◽  
pp. 468-472
Author(s):  
Bing Zhou ◽  
Guixiang Cui ◽  
Naixiang Chen
Keyword(s):  
Large Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Scale Similarity

Large-eddy simulation of free-surface turbulence

2001 ◽  
Vol 440 ◽  
pp. 75-116 ◽  
Author(s):  
LIAN SHEN ◽  
DICK K. P. YUE
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Large Eddy Simulation ◽  
Surface Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Similarity Model ◽  
Scale Similarity ◽  
Surface Turbulence ◽  
Free Surface Turbulence

In this paper we investigate the large-eddy simulation (LES) of the interaction between a turbulent shear flow and a free surface at low Froude numbers. The benchmark flow field is first solved by using direct numerical simulations (DNS) of the Navier–Stokes equations at fine (1282 × 192 grid) resolution, while the LES is performed at coarse resolution. Analysis of the ensemble of 25 DNS datasets shows that the amount of energy transferred from the grid scales to the subgrid scales (SGS) reduces significantly as the free surface is approached. This is a result of energy backscatter associated with the fluid vertical motions. Conditional averaging reveals that the energy backscatter occurs at the splat regions of coherent hairpin vortex structures as they connect to the free surface. The free-surface region is highly anisotropic at all length scales while the energy backscatter is carried out by the horizontal components of the SGS stress only. The physical insights obtained here are essential to the efficacious SGS modelling of LES for free-surface turbulence. In the LES, the SGS contribution to the Dirichlet pressure free-surface boundary condition is modelled with a dynamic form of the Yoshizawa (1986) expression, while the SGS flux that appears in the kinematic boundary condition is modelled by a dynamic scale-similarity model. For the SGS stress, we first examine the existing dynamic Smagorinsky model (DSM), which is found to capture the free-surface turbulence structure only roughly. Based on the special physics of free-surface turbulence, we propose two new SGS models: a dynamic free-surface function model (DFFM) and a dynamic anisotropic selective model (DASM). The DFFM correctly represents the reduction of the Smagorinsky coefficient near the surface and is found to capture the surface layer more accurately. The DASM takes into account both the anisotropy nature of free-surface turbulence and the dependence of energy backscatter on specific coherent vorticity mechanisms, and is found to produce substantially better surface signature statistics. Finally, we show that the combination of the new DFFM and DASM with a dynamic scale-similarity model further improves the results.

Regularized, parameter free scale similarity type models for Large Eddy Simulation

2020 ◽  
Vol 81 ◽  
pp. 108496 ◽  
Author(s):  
Markus Klein ◽  
S. Ketterl ◽  
L. Engelmann ◽  
A. Kempf ◽  
H. Kobayashi
Keyword(s):  
Large Eddy Simulation ◽  
Similarity Type ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Scale Similarity

Hybrid LES–RANS: back scatter from a scale-similarity model used as forcing

2009 ◽  
Vol 367 (1899) ◽  
pp. 2905-2915 ◽  
Author(s):  
Lars Davidson
Keyword(s):  
Large Eddy Simulation ◽  
Transition Region ◽  
Navier Stokes ◽  
Viscous Term ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Similarity Model ◽  
Scale Similarity ◽  
Reynolds Averaged Navier Stokes ◽  
Subgrid Stress

A dissipative scale-similarity subgrid model was recently proposed in which only the dissipative part of the subgrid stresses was added to the momentum equations. This was achieved by adding the gradient of a subgrid stress only when its sign agreed with that of the corresponding viscous term. In the present work, this idea is used the other way around as forcing in hybrid large eddy simulation–Reynolds-averaged Navier–Stokes: only the part of a subgrid stress term that corresponds to back scatter is added to the momentum equations. The forcing triggers resolved turbulence in the transition region between the unsteady Reynolds-averaged Navier–Stokes and large eddy simulation regions. The new approach is evaluated for fully developed channel flow at Re τ =4000. It is found that the forcing indeed does increase the resolved turbulence in the transition region. The magnitude of the production (i.e. back scatter) due to forcing in the equation for resolved kinetic energy is of the order of that due to the usual strain-rate production term. The present approach of using back scatter from a scale-similarity model can also probably be useful for triggering transition.

Scale-Similarity Subgrid-Scale Turbulence Closure for Supercell Simulations at Kilometer-Scale Resolutions: Comparison Against a Large Eddy Simulation

2020 ◽  
Author(s):  
Shiwei Sun ◽  
Bowen Zhou ◽  
Ming Xue ◽  
Kefeng Zhu
Keyword(s):  
Large Eddy Simulation ◽  
Deep Convection ◽  
Eddy Diffusivity ◽  
Turbulent Fluxes ◽  
Subgrid Scale ◽  
Diffusion Type ◽  
Eddy Simulation ◽  
Gradient Diffusion ◽  
Large Eddy ◽  
Scale Similarity

AbstractIn numerical simulations of deep convection at kilometer-scale horizontal resolutions, in-cloud subgrid-scale (SGS) turbulence plays an important role in the transport of heat, moisture and other scalars. By coarse-graining a 50 m high-resolution large-eddy simulation (LES) of an idealized supercell storm to kilometer-scale grid spacings ranging from 250 m to 4 km, the SGS fluxes of heat, moisture, cloud and precipitating water contents are diagnosed a priori. The kilometer-scale simulations are shown to be within the “gray zone” as in-cloud SGS turbulent fluxes are comparable in magnitude to the resolved fluxes at 4 km spacing, and do not become negligible until ~500 m spacing. Vertical and horizontal SGS fluxes are of comparable magnitudes, both exhibit non-local characteristics associated with deep convection as opposed to local gradient-diffusion type of turbulent mixing. As such, they are poorly parameterized by eddy-diffusivity-based closures. To improve the SGS representation of turbulent fluxes in deep convective storms, a scale-similarity LES closure is adapted to kilometer-scale simulations. The model exhibits good correlations with LES-diagnosed SGS fluxes, and is capable of representing counter-gradient fluxes. In a posteriori tests, supercell storms simulated with the refined similarity closure model at kilometer-scale resolutions show better agreement with the LES benchmark in terms of SGS fluxes than those with a turbulent-kinetic-energy-based gradient-diffusion scheme. However, it underestimates the strength of updraft, which is suggested to be a consequence of the model effective resolution being lower than the native grid resolution.

scholarly journals Dynamic Nonlinear Algebraic Models With Scale-Similarity Dynamic Procedure For Large-Eddy Simulation of Turbulence

2021 ◽  
Author(s):  
Zelong Yuan ◽  
Yunpeng Wang ◽  
Chenyue Xie ◽  
Jianchun Wang
Keyword(s):  
Large Eddy Simulation ◽  
Mixed Model ◽  
A Priori ◽  
Correlation Coefficients ◽  
Algebraic Model ◽  
Algebraic Models ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Scale Similarity

Abstract A dynamic nonlinear algebraic model with scale-similarity dynamic procedure (DNAM-SSD) is proposed for subgrid-scale (SGS) stress in large-eddy simulation of turbulence. The model coefficients of the DNAM-SSD model are adaptively calculated through the scale-similarity relation, which greatly simplifies the conventional Germano-identity based dynamic procedure (GID). The a priori study shows that the DNAM-SSD model predicts the SGS stress considerably better than the conventional velocity gradient model (VGM), dynamic Smagorinsky model (DSM), dynamic mixed model (DMM) and DNAM-GID model at a variety of filter widths ranging from inertial to viscous ranges. The correlation coefficients of the SGS stress predicted by the DNAM-SSD model can be larger than 95% with the relative errors lower than 30%. In the a posteriori testings of LES, the DNAM-SSD model outperforms the implicit LES (ILES), DSM, DMM and DNAM-GID models without increasing computational costs, which only takes up half the time of the DNAM-GID model. The DNAM-SSD model accurately predicts plenty of turbulent statistics and instantaneous spatial structures in reasonable agreement with the filtered DNS data. These results indicate that the current DNAM-SSD model is attractive for the development of highly accurate SGS models for LES of turbulence.

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