openFOAM RAS to LES

Question

I successfully ran a RANS simulation of industrial fan with all wall BCs, pimpleDyMFoam solver and spallart-almaras RAS model.

I got results upto some time, I would like to continue that simulation with LES instead of RAS, what are the options how I need to refine the mesh. (one parameter is way off the experimental value) specifically I would like to continue the simulation from where RAS ended say from 100s.

For instance if I am using one equation eddy model, how to accommodate nuSgs for the solution with RAS?

quick help would be appreciated

Answer 1

"pimple" is a good solver to work with, as it handles transient cases with RAS or LES turbulence. To change turbulence models, you'll need to specify this in your "turbulenceProperties" file by changing "simulationType" from "RASModel;" to "LESModel;" and providing an appropriate "lesProperties"file.

I'd suggest checking out the channel395 tutorial in tutorials\incompressible\pimpleFoam to see the usage of LES turbulence models. You'll also need the same boundary conditions for the solver (such as nuSgs, nuTilda, etc.)

That should be about it, and if you're missing something the error should point you toward something else to copy/modify.

For grid refinement, you'll want to have a much finer grid in regions with large gradients, because LES needs a finer resolution to resolve the turbulent kinetic energy accurately. It really depends on your flow conditions though. Try solving with your initial RAS mesh, then refine it in areas with sharp velocity gradients to improve your results.

I don't use "pimpleDyMFoam" for my research, but I am studying turbulent jets using "pimpleFoam" as a solver. pimpleDyM just uses a moving mesh.

Answer 2

I used 'mapFields' utility, which can be used to map field values from any arbitrary case to other, irrespective of turbulence model used, just the boundary patches need to be specified in one-to-one correspondence in 'mapFieldsDict' ins system/ directory.

for LES case set-up one can see any of the myriads of LES tutorials (in my case incompressible)

For more information,see this