湍流数值模拟

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湍流数值模拟的经典文档,大涡模型和离散涡模型
2004 CFD SUMMIT What Is LES?-Basic Concepts (1) Turbulent flow consists of eddies(structures) with wide range of length and time scales In LES, large, energy-carrying eddies are directly computed(resolved), and the remaining smaller eddies are modeled FLUENT Thκ Rigt Answer in CH 2004 CFD SUMMIT What Is LES?-Basic Concepts (21 energy cascade injection (Richardson, 1922) of energy Dissipation of energy Dissipating Large-scale Fli ux of energv eddies eddies Ls=L/Re 3/4 Resolved DNS △ DNS Resolved Modeled LES LES M e adele FLUENT RANS Thκ Rit Answer in CH 2004 CFD SUMMIT What s lES? Filtering -Decomposition ux.t=ux.t)+ult resolved scale subgrid scale E Energy spectrum against the length scale u(X,t uX 2兀 2兀 FLUENT △ Thκ Rigt Answer in CH 2004 CFD SUMMIT hat s lES? Filtering of a variable A random variable, o(x), is filtered using a space filter function, P(x)=o (x)G(x, x,)dx D With the top-hat filter(among others) 1/v fo OX∈ G(x,x' otherwise The filtered variable becomes (x)=(x)dx,x'∈7 FLUENT Thκ Rigt Answer in CH 2004 CFD SUMMIT What s les? Filtered Navier-Stoke Equations Filtering the original Navier-Stokes equations gives filtered Navier-Stokes equations that are the governing equations in LES N-S OL equation at a Filte Filtered n-s 1,(n)0 equation Ox, Ox, O Needs modeling FLUENT Thκ Rigt Answer in CH Sub-grid scale(sGs) stress 2004 CFD SUMMIT Agenda What is LES? Why LEs? What about the cost? What does fluent offer? Best-practice LES With FLUENT Closing Remarks FLUENT Thκ Rigt Answer in CH 2004 CFD SUMMIT Why LES?-Rationales Large eddies are responsible for the transports of momentum, energy, and other scalars Large eddies are anisotropic, subjected to history effects, and are strongly dependent on boundary conditionS, which makes their modeling difficult Small eddies tend to be more isotropic and less flow-dependent (universal), which makes their modeling easier FLUENT Thκ Rigt Answer in CH 2004 CFD SUMMIT hy LES? Some applications need explicit computation of unsteady fields Bluff body aerodynamics Aerodynamically generated noise(sound) Fluid-structure interaction Combustion instability FLUENT Thκ Rigt Answer in CH

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