Learning Forum

[acukrov]

Dear all,

with this message I would like to ask how one could stabilize the interface behavior (velocity field) in an water entry simulation using Multi-fluid VOF (ANSYS Fluent 2020 R2) since the divergence occurs (Fig. below)?

I would need very fine time step (1e-6 s was found as an appropriate); however, the simulation would be very lengthly.

Any suggestion how to make the simulation with higher time step, because Multi-fluid VOF is used, would be appreciated.

Best regards,

Alen

[Rob]

You often do need a small time step for multiphase models, but if that's very small relative to the flow passing through one cell you may find you can increase it once the initial instabilities settle down. 

[Nikhil N]

In addition, you can have a look at the VOF solution stability controls. 

Refer to this section of the Fluent User's Guide: 22.8. Solution Strategies for Multiphase Modeling (ansys.com)  

If you are not able to access the link, please refer to this forum discussion: Using Help with links (ansys.com)

[Amine Ben Hadj Ali]

VOF Stability Controls won't work for Eulerian.

Try assessing smaller time steps and try to have a nice decent size jump free mesh. 

[acukrov]

 

Dear Dr. Ben Hadj Ali,

thank you very much for your answer.

Seems to be working now (time step 1e-5 s); however, more time needed to be absolutely sure.

Best regards,

Alen

 

[Amine Ben Hadj Ali]

Super.