MPPICFoam - Problems with Gravity
 

Hi All,

I'm experimenting at the moment with the MPPICFoam solver. I want to simulate the motion of particles in a fluid in a centrifuge.

This means i have about 100g as acceleration and only small density differences between the particles and the fluid.

As a start i just use Goldschmidt case of the MPPICFoam tutorial. there i remove most particles and set the inlet velocity to zero, gravity to 9810m/s^2 and run the simulation.

The problem i get is that the fluid phase has un-physical velocity-fluctuations, which depend on the acceleration. See the attached image: the air-phase has z-velocities up to 4.8e-4m/s for g=9810m/s^2. The fluctuations are very small, but the settling time of the particles is an order of magnitude smaller thus the settling is massively disturbed by the fluid-velocities.

Edit: might need to add that i still work with openfoam 3.0 --> did a lot change in the latest editions?

is this a limitation of the MPPIC solver? or is there a way to eliminate this unphysical behaviour? (on the incompressible fluid phase the gravity should not have any influence at all...)

thanks
alex