[rorymcd98]

I've spent a really long time trying to figure out why my turbulent viscosity is orders of magnitude too small. I was going to write a post about all the things I've tried but I think most of it is irrelevant. I'm using the Smagorisnky-Lilly model for 2D LES (it's for an assignment, I have to use these).

My questions:

1) For 2D LES (in fluent), should I make the domain one cell thick? I think Fluent is having issues calculating length scales. I think it assumes all cells have 1 meter of thickness in the z direction.

2) I'm unfamiliar with 3D LES, when I give my domain thickness, will I have to define a boundary condition on the 'top' and 'bottom' face? Which should I use?

3) As a criteria for LES I'm comparing the resolved to the total (resolved + modelled) kinetic energy. My equation for modelled tke is (Mu_sgs/rho*L_sgs)^2 where Mu_sgs is the turbulent viscosity, and L_sgs is the subgrid length scale. I don't have a good source for my modelled tke, does anyone know where this equation originates from?

4) My criteria failed, it said that 99.999% of my flow's TKE was resolved. I suspect the issue is that Mu_sgs is way too small as my viscosity ratio ranged from about 20-200 in most of the flow. I used a custom function to calculate Mu_sgs from the Wikipedia article on turbulence modelling. This gave me good results, the tke was now about 70% resolved which is what I was expecting. But I'm 95% sure this equation is wrong, I think it should be 1/100th of what it actually is as there is no C_s constant included. Opinions?