LES,Periodic Boundary Conditions
Hi,
I'm conducing a study to insert in an existing CFD code developed in my department a computational model based on LES. Specifically, this is the " Combined LES and time dependent RANS" proposed by Speziale in 1997 (a reference: "A combined LargeEddies Simulation and TimeDependent RANS Capability for HighSpeed Compressible Flows",C.G.Speziale,Journal of Scientific Computing, Vol 13,No3 ,1998). Briefly: subgrid scale models are dimensionless functions of the computational mesh size times a Reynolds stress model based on a two equations model. A LES go continuously to a RANS computation as the mesh becomes successively more coarse or the Reynolds number becomes much larger ; the level of dicretization is parameterised by the nondimensional ratio of the mesh size to the Kolmogorov length scale. I have to write a new FORTRAN algorithm to insert in the old code, than to test it in the classic backward facing step. Have you got any experience of this model ? Furthermore, I have some doubt about the lateral boundary conditions in the channel: I must apply periodic boundary conditions, but does this simply mean that the variables (velocity,pressure,ecc.,) are identical but unknowed in the two opposite walls ? And in LES should I make any particular adaptations to impose this conditions? Thanks for Your help. 
Re: LES,Periodic Boundary Conditions
hello,I'm a beginer in LES,and i wrote my code using fortran language.now my code does not work well :( furthermore,i didn't read the paper Combined LES and time dependent RANS?proposed by Speziale in 1997. i use the periodic boundary in my code in spanwise, and set the velocity(pressure,etc) of front as the same as the behind,that is to say the first grid==the lastest grid. Perhaps it's not real! you can read the book "Turbulence:the legacy of Komogrove".

Re: LES,Periodic Boundary Conditions
Hi ,Tom I think that the method of Speziale is not the best for a beginner, to understand the LES. I'm also beginner,but i have before studied the theory of the LES,and now i begin the applications. I use periodic conditions in spanwise, but i think that this mean , for example in a channel, that the lateral wall are identical. If the first grid = lastest grid, we have a streamwise periodic condition.
Thanks 
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