[atmcfd]

Hi,

I have read many journals , which advocate implicit and explicit filtering.(Though implicit is almost always used). I'm yet to clearly understand how exactly the process of filtering works in the LES algorithm.This is my understanding of implicit filtering, Please correct it if I am wrong :

1) The LES governing equations containing the "filtered" terms and the subrid scale tensor are solved using some numerical scheme - e.g. SIMPLE.

2) The terms in the continuity and momentum equations - the velocity and pressure etc are solved for exactly the way normal Navier Stokes eqns are solved.i.e. Poisson;s eqn to solve for pressure, guessing the initial velocity field etc.

3) The subgrid tensor term is modeled using Smagorinsky or any other empirical model for EVERY cell in the mesh, where the LES equations are applied.i.e. the term is modeled in the equation for all mesh sizes, even when larger scales are being solved for.

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So basically, is it that the LES governing equations are solved just like the traditional NS equations, but the difference being that an extra subgrid tensor has to be included in the equation every time, to include the effect of the smaller scales? So in essence, we can thus use a coarser mesh so that the LES eqns resolve the larger scales, and the subgrid term in the eqn, models the smaller scales, which are not able to be resolved due to the mesh not being fine enough? I was just wondering where the actual "filtering" process takes place in the code....is it just a mathematical definition which is used to derive the LES eqns?Coz' all I can see here are a modified form of the NS eqns and a subgrid term which is modeled.
Hence, I guess the solution algorithm for a LES code would be almost same as the traditional incompressible NS solver, except for the fact that I would have to compute , and include it in the main NS eqns.

As I said, kindly correct me wherever I am wrong here.

I have gone through almost all the older threads relating to this in the forum, but I couldn't get this cleared.I have to start writing a LES code myself, and hence i feel I have to be very strong in these concepts before I embark on it.

I know this has been a long question., and I would really appreciate anyone offering their help .

Thanks in advance.