Re: Turbulence Models

[takamori67]

Thanks a lot, Patrick and Matthias! Your input was very insightful.

For the time being, I decided to first get my simulation set up and going with an under resolved mesh and a Smagorinsky turbulence model, in order to limit computation time. Then I will move on to scaling the mesh.

While setting up and testing the case, a few questions have come up:
-when applying a velocity boundary condition (Poiseuille velocity profile) at the pipe inflow and pressure boundary condition at the outlet, the results look a lot like a free jet, with a distinct velocity profile at the beginning that breaks down towards the end, with velocities close to zero at the outlet. Have I set up my boundary conditions incorrectly? Or should I just increse the Smulation time to let the flow build up.
– I have considered using a pressure boundary condition at the inlet, since this is often used in RANS based solvers. Would that be appropiate for LBM? And how do I set up the pressure boundary value, since I can only use defineRho?
-I have noticed, that the value of charU has a huge impact on computaion speed. When playing with the values of charU and charNu to reach a high Re, computaion time was almost proportional to charU, with unchanged number of voxels. Is there a reason behind this?
-can I expoit the symmetry of the pipe by just simualting a wedge (e.g. a quarter of the circle) and using periodic boundaries for the planes neighboring the outer flow field?

Thanks in advance for your kind support.

Best, Sumit