[fivos]

Hi to all,

I am currently trying to implement a LES model (simple Smagorinsky to begin with, later we shall see) in a CFD code. The code has capability of 3D and transient runs, of course and in its current state it is a pressure based RANS code (both compressible & incompressible).

First of all, it is my understanding that the algorithm should be more or less the same as it was in the former RANS form, with the main modification being the calculation of the subgrid turbulent viscosity; in other words it would be like a laminar solver with the viscosity increased by the subgrid viscosity. Is this true?

The main question I have is what is the treatment of the so called trace term of the SGS stress (the one mentioned as tkk in http://www.cfd-online.com/Wiki/Large...imulation_(LES)).

What exactly is this term (I mean what is the equation of this term)? In a work (http://croccolab.umd.edu/publication...FD00_vol13.pdf) it is mentioned that tkk is:

tkk = Ci * 2 * rho * Delta^2 * |S|^2

where Ci is a constant (0.09)
rho the density
Delta is the cell volume ^ (1/3)
and |S| = Sqrt(2*Sij:Sij), with Sij the element of the subgrid stress tensor.

Is the above correct?

I have seen also in several works and books (including Pope, Lesieur) that the tkk term is added to pressure. In others (including the Fluent manual, see also http://www.cfd-online.com/Forums/ope...pressible.html ), it is said that the term is omitted. What is your opinion on the treatment of this term?

Finally, do you have any book/reference to suggest for practical, application oriented LES implementation (I do not want another book pilling a ton pages on how LES is derived and when it comes to the implementation details of the LES equations it presents them in just 10 lines)?

Any comments are welcome
Thank you in advance