LES of Wall-Bounded Flows Using a New Subgrid Scale Model Based on Energy Spectrum Dissipation

2008 ◽  
Vol 75 (2) ◽  
Author(s):  
I. Veloudis ◽  
Z. Yang ◽  
J. J. McGuirk
Keyword(s):  
Energy Spectrum ◽  
Kinetic Energy ◽  
Transport Equation ◽  
Scale Effects ◽  
Energy Content ◽  
Scale Model ◽  
Length Scale ◽  
Subgrid Scale ◽  
New Approach ◽  
Accurate Representation

A new one-equation subgrid scale (SGS) model that makes use of the transport equation for the SGS kinetic energy (kSGS) to calculate a representative velocity scale for the SGS fluid motion is proposed. In the kSGS transport equation used, a novel approach is developed for the calculation of the rate of dissipation of the SGS kinetic energy (ε). This new approach leads to an analytical computation of ε via the assumption of a form for the energy spectrum. This introduces a more accurate representation of the dissipation term, which is then also used for the calculation of a representative length scale for the SGS based on their energy content. Therefore, the SG length scale is not associated simply with the grid resolution or the largest of the SGS but with a length scale representative of the overall SGS energy content. The formulation of the model is presented in detail, and the new approach is tested on a series of channel flow test cases with Reynolds number based on friction velocity varying from 180 to 1800. The model is compared with the Smagorinsky model (1963, “General Circulation Experiments With the Primitive Equations: 1. The Basic Experiment,” Mon. Weather Rev., 91, pp. 90–164) and the one-equation model of Yoshizawa and Horiuti (1985, “A Statistically-Derived Subgrid Scale Kinetic Energy Model for the Large Eddy Simulation of Turbulent Flows,” J. Phys. Soc. Jpn., 54(8), pp. 2834–2839). The results indicate that the proposed model can provide, on a given mesh, a more accurate representation of the SG scale effects.

Large Eddy Simulation of Rotating Channel Flows With and Without Heat Transfer

2000 ◽  
Author(s):  
Ning Meng ◽  
Richard H. Pletcher
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Channel Flow ◽  
Scale Effects ◽  
Scale Model ◽  
Finite Volume Scheme ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rotating Channel

Abstract Large eddy simulation of rotating channel flow with and without heat transfer is reported. The rotation axis is parallel to the spanwise direction of the parallel plate channel. An implicit finite-volume scheme was used to solve the preconditioned time-dependent filtered Navier-Stokes equations using a dynamic subgrid-scale model to account for the subgrid-scale effects. Comparisons are made with available results in the literature for isothermal rotating flows. The combined effects of rotation and heat transfer on the structure of turbulence channel flow is discussed.

scholarly journals Data-based stochastic subgrid-scale parametrization: an approach using cluster-weighted modelling

2012 ◽  
Vol 370 (1962) ◽  
pp. 1061-1086 ◽  
Author(s):  
Frank Kwasniok
Keyword(s):  
Clustering Algorithm ◽  
Prediction Models ◽  
Statistical Modelling ◽  
Scale Model ◽  
Ensemble Prediction ◽  
Subgrid Scale ◽  
New Approach ◽  
Lorenz 96 ◽  
The Impact

A new approach for data-based stochastic parametrization of unresolved scales and processes in numerical weather and climate prediction models is introduced. The subgrid-scale model is conditional on the state of the resolved scales, consisting of a collection of local models. A clustering algorithm in the space of the resolved variables is combined with statistical modelling of the impact of the unresolved variables. The clusters and the parameters of the associated subgrid models are estimated simultaneously from data. The method is implemented and explored in the framework of the Lorenz '96 model using discrete Markov processes as local statistical models. Performance of the cluster-weighted Markov chain scheme is investigated for long-term simulations as well as ensemble prediction. It clearly outperforms simple parametrization schemes and compares favourably with another recently proposed subgrid modelling scheme also based on conditional Markov chains.

Stratified turbulence forced with columnar dipoles: numerical study

2015 ◽  
Vol 769 ◽  
pp. 403-443 ◽  
Author(s):  
Pierre Augier ◽  
Paul Billant ◽  
Jean-Marc Chomaz
Keyword(s):  
Reynolds Number ◽  
Energy Spectrum ◽  
Kinetic Energy ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Stationary Flow ◽  
Length Scale ◽  
Computational Domain ◽  
Stratified Turbulence ◽  
Kinetic Energy Spectrum

This paper builds upon the investigation of Augier et al. (Phys. Fluids, vol. 26 (4), 2014) in which a strongly stratified turbulent-like flow was forced by 12 generators of vertical columnar dipoles. In experiments, measurements start to provide evidence of the existence of a strongly stratified inertial range that has been predicted for large turbulent buoyancy Reynolds numbers $\mathscr{R}_{t}={\it\varepsilon}_{\!K}/({\it\nu}N^{2})$, where ${\it\varepsilon}_{\!K}$ is the mean dissipation rate of kinetic energy, ${\it\nu}$ the viscosity and $N$ the Brunt–Väisälä frequency. However, because of experimental constraints, the buoyancy Reynolds number could not be increased to sufficiently large values so that the inertial strongly stratified turbulent range is only incipient. In order to extend the experimental results toward higher buoyancy Reynolds number, we have performed numerical simulations of forced stratified flows. To reproduce the experimental vortex generators, columnar dipoles are periodically produced in spatial space using impulsive horizontal body force at the peripheries of the computational domain. For moderate buoyancy Reynolds number, these numerical simulations are able to reproduce the results obtained in the experiments, validating this particular forcing. For higher buoyancy Reynolds number, the simulations show that the flow becomes turbulent as observed in Brethouwer et al. (J. Fluid Mech., vol. 585, 2007, pp. 343–368). However, the statistically stationary flow is horizontally inhomogeneous because the dipoles are destabilized quite rapidly after their generation. In order to produce horizontally homogeneous turbulence, high-resolution simulations at high buoyancy Reynolds number have been carried out with a slightly modified forcing in which dipoles are forced at random locations in the computational domain. The unidimensional horizontal spectra of kinetic and potential energies scale like $C_{1}{\it\varepsilon}_{\!K}^{2/3}k_{h}^{-5/3}$ and $C_{2}{\it\varepsilon}_{\!K}^{2/3}k_{h}^{-5/3}({\it\varepsilon}_{\!P}/{\it\varepsilon}_{\!K})$, respectively, with $C_{1}=C_{2}\simeq 0.5$ as obtained by Lindborg (J. Fluid Mech., vol. 550, 2006, pp. 207–242). However, there is a depletion in the horizontal kinetic energy spectrum for scales between the integral length scale and the buoyancy length scale and an anomalous energy excess around the buoyancy length scale probably due to direct transfers from large horizontal scale to small scales resulting from the shear and gravitational instabilities. The horizontal buoyancy flux co-spectrum increases abruptly at the buoyancy scale corroborating the presence of overturnings. Remarkably, the vertical kinetic energy spectrum exhibits a transition at the Ozmidov length scale from a steep spectrum scaling like $N^{2}k_{z}^{-3}$ at large scales to a spectrum scaling like $C_{K}{\it\varepsilon}_{\!K}^{2/3}k_{z}^{-5/3}$, with $C_{K}=1$, the classical Kolmogorov constant.

scholarly journals Non-Repeatability, Scale- and Model Effects in Laboratory Measurement of Impact Loads Induced by an Overtopped Bore on a Dike Mounted Wall

2019 ◽  
Author(s):  
Maximilian Streicher ◽  
Andreas Kortenhaus ◽  
Corrado Altomare ◽  
Steven Hughes ◽  
Krasimir Marinov ◽  
...  
Keyword(s):  
Large Scale ◽  
Scale Effects ◽  
Vertical Wall ◽  
Scale Factor ◽  
Scale Model ◽  
Small Scale ◽  
Length Scale ◽  
Force Measurements ◽  
Impact Forces ◽  
Small Scale Model

Abstract Overtopping bore impact forces on a dike mounted vertical wall were measured in similar large-scale (Froude length scale factor 1-to-4.3) and small-scale (Froude length scale factor 1-to-25) models. The differences due to scale effects were studied, by comparing the up-scaled force measurements from both models in prototype. It was noted that if a minimum layer thickness, velocity of the overtopping flow and water depth at the dike toe were maintained in the small-scale model, the resulting differences in impact force due to scale effects are within the range of differences due to non-repeatability and model effects.

scholarly journals Large-eddy simulation of a mildly curved open-channel flow

2009 ◽  
Vol 630 ◽  
pp. 413-442 ◽  
Author(s):  
W. VAN BALEN ◽  
W. S. J. UIJTTEWAAL ◽  
K. BLANCKAERT
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Open Channel ◽  
Scale Model ◽  
Shear Stresses ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Outer Bank ◽  
Large Eddy ◽  
Subgrid Scale Model

After validation with experimental data, large-eddy simulation (LES) is used to study in detail the open-channel flow through a curved flume. Based on the LES results, the present paper addresses four issues. Firstly, features of the complex bicellular pattern of the secondary flow, occurring in curved open-channel flows, and its origin are investigated. Secondly, the turbulence characteristics of the flow are studied in detail, incorporating the anisotropy of the turbulence stresses, as well as the distribution of the kinetic energy and the turbulent kinetic energy. Moreover, the implications of the pattern of the production of turbulent kinetic energy is discussed within this context. Thirdly, the distribution of the wall shear stresses at the bottom and sidewalls is computed. Fourthly, the effects of changes in the subgrid-scale model and the boundary conditions are investigated. It turns out that the counter-rotating secondary flow cell near the outer bank is a result of the complex interaction between the spatial distribution of turbulence stresses and centrifugal effects. Moreover, it is found that this outer bank cell forms a region of a local increase of turbulent kinetic energy and of its production. Furthermore, it is shown that the bed shear stresses are amplified in the bend. The distribution of the wall shear stresses is deformed throughout the bend due to curvature. Finally, it is shown that changes in the subgrid-scale model, as well as changes in the boundary conditions, have no strong effect on the results.

Study of flow in a planar asymmetric diffuser using large-eddy simulation

1999 ◽  
Vol 390 ◽  
pp. 151-185 ◽  
Author(s):  
H.-J. KALTENBACH ◽  
M. FATICA ◽  
R. MITTAL ◽  
T. S. LUND ◽  
P. MOIN
Keyword(s):  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Scale Model ◽  
Subgrid Scale ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Unsteady Separation ◽  
Large Eddy ◽  
Rear Part ◽  
Subgrid Scale Model

Large-eddy simulation (LES) has been used to study the flow in a planar asymmetric diffuser. The wide range of spatial and temporal scales, the presence of an adverse pressure gradient, and the formation of an unsteady separation bubble in the rear part of the diffuser make this flow a challenging test case for assessing the predictive capability of LES. Simulation results for mean flow, pressure recovery and skin friction are in excellent agreement with data from two recent experiments. The inflow consists of a fully developed turbulent channel flow at a Reynolds number based on shear velocity, Reτ=500. It is found that accurate representation of the in flow velocity field is critical for accurate prediction of the flow in the diffuser. Although the simulation in the diffuser is well resolved, the subgrid-scale model plays a significant role for both mean momentum and turbulent kinetic energy balances. Subgrid-scale stresses contribute a maximum of 8% to the local value of the total shear stress with the maximum values found in the inlet duct and along the flat wall where the flow remains attached. The subgrid-scale model adapts to the enhanced turbulence levels in the rear part of the diffuser by providing more than 80% of the dissipation rate for turbulent kinetic energy. The unsteady separation excites large scales of motion which extend over the major part of the duct cross-section and penetrate deeply into the core of the flow. Instantaneous flow reversal is observed along both walls immediately behind the diffuser throat which is far upstream of the location of main separation. While the mean flow profile changes gradually as the flow enters the expansion, turbulent stresses undergo rapid changes over a short streamwise distance along the deflected wall. An explanation is offered which considers the strain field as well as the influence of geometry changes. The effect of grid resolution and spanwise domain size on the flow field prediction has been documented and this allows an assessment of the computational requirements for carrying out such simulations.

scholarly journals Large-Eddy Simulation of Stratified Turbulence. Part I: A Vortex-Based Subgrid-Scale Model

2014 ◽  
Vol 71 (5) ◽  
pp. 1863-1879 ◽  
Author(s):  
Daniel Chung ◽  
Georgios Matheou
Keyword(s):  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Similarity Theory ◽  
Scale Model ◽  
Extended Model ◽  
Subgrid Scale ◽  
Stratified Turbulence ◽  
Vortex Model ◽  
Eddy Simulation ◽  
Large Eddy

Abstract The stretched-vortex subgrid-scale (SGS) model is extended to enable large-eddy simulation of buoyancy-stratified turbulence. Both stable and unstable stratifications are considered. The extended model retains the anisotropic form of the original stretched-vortex model, but the SGS kinetic energy and the characteristic SGS eddy size are modified by buoyancy subject to two constraints: first, the SGS kinetic energy dynamics is determined by stationary and homogeneous conditions, and second, the SGS eddy size obeys a scaling analogous to the Monin–Obukhov similarity theory. The SGS model construction, comprising an ensemble of subgrid stretched-vortical structures, naturally limits vertical mixing but allows horizontal mixing provided the alignment of the SGS vortex ensemble is favorable, even at high nominal gradient Richardson numbers. In very stable stratification, the model recovers the z-less limit, in which a vortex-based Obukhov length controls the SGS dynamics, while in very unstable stratification, the model recovers the free-convection limit, in which a vortex-based Deardorff velocity controls the SGS dynamics. The efficacy of the present SGS model is demonstrated by simulating the canonical stationary and homogeneous, stratified sheared turbulence at high Reynolds numbers and moderately high Richardson numbers. In the postprocessing, the SGS dynamics of the stretched-vortex model is further interrogated to yield predictions of buoyancy-adjusted one-dimensional SGS spectra and SGS root-mean-square velocity-derivative fluctuations.

Characteristics of Turbulence in a Turbofan Stage

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Jeremy Maunus ◽  
Sheryl Grace ◽  
Douglas Sondak ◽  
Victor Yakhot
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Turbulence Models ◽  
Energy Dissipation Rate ◽  
Scale Model ◽  
Length Scale ◽  
Experimental Measurements ◽  
Hot Wire ◽  
Turbofan Engine

Two-equation turbulence models are commonly used in the simulation of turbomachinery flow fields, but there are limited experimental data available to validate the resulting turbulence quantities. Experimental measurements are available from NASA’s Source Diagnostic Test (SDT), a 1/5th scale model representation of the bypass stage of a turbofan engine. Detailed unsteady hot-wire anemometer data were taken at two axial locations between the rotor and fan exit guide vanes (FEGVs). Here, an accurate and consistent procedure is used to obtain the turbulent kinetic energy, dissipation rate, and integral length scale from structure functions calculated using the SDT data. These results are compared to the solutions provided by four proprietary CFD codes that employ two-equation turbulence models. The simulations are shown to predict the turbulent kinetic energy and length scale reasonably well as well as the trend in mean dissipation. The actual mean dissipation rates differ by nearly two orders of magnitude due to a difference in interpretation between the classical definition and what is used in CFD.

One-Equation Subgrid Scale Model Using Dynamic Procedure for the Energy Production

2005 ◽  
Vol 73 (3) ◽  
pp. 368-373 ◽  
Author(s):  
Takeo Kajishima ◽  
Takayuki Nomachi
Keyword(s):  
Transport Equation ◽  
Plane Channel ◽  
Suction Side ◽  
Scale Model ◽  
Subgrid Scale ◽  
Production Term ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Fully Developed Turbulent Flow ◽  
Subgrid Scale Model

The transport equation of subgrid scale (SGS) kinetic energy, KSGS, is used for the large-eddy simulation (LES), considering its consistency with dynamic procedure. The dynamically determined parameter is suitable for describing the energy transfer from resolved turbulence to SGS portion. Thus the procedure is applied to the production term in the transport equation of KSGS, while the eddy viscosity in the filtered equation of motion is determined indirectly through KSGS. The statistically derived model for KSGS equation is adopted for the basis of our improvement. Computational examination has been conducted for fully developed turbulent flow in a plane channel. Agreement with DNS database was satisfactory. Moreover, in a channel on solid body rotation, our model reasonably reproduced the decay of SGS turbulence in the vicinity of the suction side.

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