有什么区别LES-SGS模型和基于跑的湍流模型吗?- 江南体育网页版- - - - -地球科学堆江南电子竞技平台栈交换 最近30从www.hoelymoley.com 2023 - 04 - 11 - t12:18:44z //www.hoelymoley.com/feeds/question/2932 https://creativecommons.org/licenses/by-sa/4.0/rdf //www.hoelymoley.com/q/2932 17 有什么区别LES-SGS模型和基于跑的湍流模型吗? 朱利安·齐默尔曼 //www.hoelymoley.com/users/1228 2014 - 12 - 01 - t13:16:54z 2014 - 12 - 03 - t06:17:52z < p >我的新的世界大涡模拟(LES)模型,我想知道有什么区别LES次网格尺度模型Smagorinsky-Lilly模型和一个方程Reynolds-Averaged n - s Spalart-Allmaras(跑)的基础模型。他们都是基于布西涅斯克涡流粘度(\μ美元)假说,使用造型\μ美元的一个方程的方法。然而,没有人使用RAS Smagorinsky-Lilly模型或Spalart-Allmaras莱斯。< / p > < p >这两个模型之间的区别是什么,什么样的物理过程应用到吗? < / p > //www.hoelymoley.com/questions/2932/-/2939 # 2939 15 等密度线振荡回答的有什么区别LES-SGS模型和基于跑的湍流模型吗? 等密度线振荡 //www.hoelymoley.com/users/200 2014 - 12 - 02 - t20:40:43z 2014 - 12 - 03 - t06:17:52z < p >莱斯和跑的最大区别是,LES相反,跑假定美元\眉题{u ' _i} = 0美元(参见< a href = " https://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80%93Stokes_equations " rel = " noreferrer " > Reynolds-averaged n - s方程< / >)。在LES过滤器是基于空间和行为减少尺度运动的振幅,而在跑的时间过滤删除所有尺度运动与时间尺度小于滤波器的宽度。< / p > < p >我推荐阅读< em > < a href = " http://tu-dresden.de/die_tu_dresden/fakultaeten/fakultaet_maschinenwesen/ism/sm/mitarbeiter/froehlich/publications/Froehlich_vonTerzi_Hybrid-LES-RANS_PAS_08.pdf " rel = " noreferrer " > Frohlich, Jochen和多米尼克·冯·Terzi。“混合LES /跑的方法模拟湍流流动。”Progress in Aerospace Sciences 44.5 (2008): 349-377.

From that paper, specifically the section 'Structural similarity of LES and RANS equations', you can see that the equations being solved are essentially the same for LES and RANS, however, the physics are different. The main difference being that in RANS the unclosed term is a function of the turbulent kinetic energy and the turbulent dissipation rate whereas in LES the closure term is dependent on the length scale of the numerical grid. So in RANS the results are independent of the grid resolution!

A model qualifies as an LES model if it explicitly involves in one or the other way the step size of the computational grid. RANS models, in contrast, only depend on physical quantities, including geometric features like the wall distance.

As far as typical processes, this figure summarizes it pretty well. DNS resolves all scales of motion, all the way down to the Kolmogorov scale. LES is next up and resolves most of the scales, with the smallest eddies being modeled. RANS is on the other end of the spectrum from DNS, where only the large-scale eddies are resolved and the remaining scales are modeled.

DNS, LES, RANS The figure above is from André Bakker's lectures: http://www.bakker.org/dartmouth06/engs150/10-rans.pdf

DNS: Very small scale flow (ex:turbulent boundary layers). Currently computationally intractable for most problems.

LES: Aims to solve the computational cost that DNS poses and reveals the eddies hidden behind the mean in RANS. Good for coastal scale scale 2D simulations and possibly lab-scale 3D simulations with a highly optimized parallel code.

RANS: It is the least computationally expensive method that is used for turbulent modeling, but it is really not very good when certain phenomena cannot be averaged, such as instabilities. Acoustic waves are also incorrectly modeled because they are inherently unsteady processes which can't be averaged, so typically modelers will crank up the turbulent and numerical viscosity to remove acoustic waves from the system.

This shows the main difference between LES and RANS. LES vs RANS

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