KochHillDrag model: how to set-up scaleDrag coeff

Submitted by gabrieleDOF on Fri, 02/05/2016 - 20:03

Dear all,

I have some doubt about how to set the "KochHillDrag" model.
My case treats a cloud of solid particles that flows through a high viscosity liquid.
I found that the simulation blows up due to the drag force values, which arise almost immediately.
On the other side I found that, setting the "scaleDrag" parameter to a value much lower than 1 (between 0.3 and 0.5),
the simulation becomes stable and runs well.

So my question is: which is exactly the function of "scaleDrag" coefficient?
How does it affect the simulation results from a physical point of view?

I thank you a lot in advance.

Bye

Forums:

cgoniva's picture

cgoniva | Mon, 02/15/2016 - 17:41

Hello,

the scaleDrag parameter is nothing physical or model related.
It is a pure (brute force) parameter to scale your drag.

Higly viscous fluids can be tricky to handle especially if the particle volume fraction is high.

Limiting the maximum drag or volume fraction is a possible solution, but take care that you do not "chop-off" parts of the physics.

Best regards,
Chris

gabrieleDOF | Wed, 02/17/2016 - 11:40

Dear Chris,

thanks a lot for the answer.
My aim is to reproduce the interaction between a highly viscous fluid and steel spheres.
I finally managed to avoid the blow up of the simulation not limiting the Koch Hill Drag force,
but decreasing the coupling interval between CFD and DEM.
What I found however is not completely correct: the velocity of both fluid and spheres seems
qualitatively realistic, but the pressure field absolutely not.
Do you think that the scale drag parameter could help to capture the pressure field correctly?

I thank you a lot again for your help.

Best regards,