hi, i am working on LES chanel flow. i have set my first grid around y+=2 and took 5-6 points within y+=11.

i am getting friction velocity right...but my mean velocity is overprectied by 30%. AS, my case , it should be 1.0 , but i am getting 1.36. So, every result is overeprected by some margin.

Could, you face this type of situation. Please, tell what is the remedy?

LES channel simulation is challenge. Result stongly depends on subgrid model. For example, classic Smagorinsky model is not good for this simulation. Usually dynamic model a la Germano is used.

I use this more simple model

E.Leveque, F.Toschi, L.Shao and J.-P. Bertoglio. Shear-improved Smagorinsky model for large-eddy simulation of wall-bounded turbulent flows, J. Fluid Mech, (2007) vol. 570, pp. 491-502.

It gives good result.

Hi,

Rule of thumb: first grid point at y+=1 and three grid points within y+=5. This is at least the requirement for DNS. What kind of subgrid model are using? Is the subgrid viscosity correctly zero at the wall?

i am using dynamic model. and cs behaves correctly near the wall. only thing is that , my mean flow increases ...

can u tell, what is the reason?

Did you validate your code against some tests? For example, lid-driven cavity laminar problem?

If you are overpredicting at the center, you must be underpredicting somewhere else, even if your wall profile is correct. I suspect it is your LES model. This can be tested easily. Just increase your grid resolution in the y-direction and see if it alleviates your problem. If it does, you should look at your LES model to see if it is ok.

hi,

I have validate my LES model, with square cylinder case and lid-driven case.

As, agg, i will increase the resolution to check it.

One more thing, i am using carseian rectangular grid and no tarnofrmation. so, i am using no-uniform grid in computational calculation.

i am using hybdid scheme----3rd order upwind biased of kuwamura and 2nd order cd. with wt factor 0.15 and 0.85 respectively.

is the problem is coming from scheme??

can anyone tell--what should the variation of instantaneous w velocity above 0.0.

my case, i am getting (-0.1to 0.1) is it too large, because my time history shows, it very dense signal. so, i doubt, whethere, numerical oscullation comes into solution or not?

Have your looked at your urms vrms and wrms plots? How do they compare with DNS results?

Hi,

The combination of upwind (biased) schemes and LES hasn't been very successful I think. These schemes can introduce quite a lot of numerical viscosity. The combination of LES and CD appears to perform better.