[bastil]

Hello all,

I have a case that is running fine in chtMultiRegionSimpleFoam in steady-state. Now I am trying to run the same case (with steady-state BCs) in transient using chtMultiRegionFoam (I will switch to transient BCs later on). So far this is a desaster. What I did:

1. Use the case without any changes but run "chtMultiRegionFoam" instead of "chtMultiRegionSimpleFoam". This gives me mass conservation for time 1. However, as expected courant numbers are way to high for PISO and the simulation is crashing after a few time steps.

2. Next step was to reduce time-stepping to 1e-4. This gives me max. courant of 0.43. However, this calculation gives significant mass inconsistency between my in- and outlet and massively to high pressure drop after the first time step. It ends up with unphysical high velocities after a few time-steps. I realized that reducing time step further (1e-6) makes everything even worse which I don't really understand. However, larger time steps (1e-2) gives better but not perfect behavior.

Has anybody observed similar effects? I have no explanation for this nor an idea what can be done to overcome this to get a stable solution.

Regards bastil