topic Re: Time step size in Rotating region and free surface simulation in CFD Forum

Time step size in Rotating region and free surface simulation

Anonymous — Mon, 11 Apr 2016 12:41:07 GMT

Hi,

I have a huge problem with a time step size whilst running the simulation: as suggested by Autodesk, I set 1 inner intervals and time step size of 0.05 (unchecked intelligent solution control) but when I see the results the difference in time between 2 steps are approx. 0.003 sec and only the firs step was 0.05 sec. So I changed it to 0.1 and it's a little bit faster but still not corresponding to 0.1. When I set 1 sec, a message like "solver exited unexpectably" pop up. Why thereare change in timing like that? I would like to reach a 1min simulation.

Best regards,

Marco

Re: Time step size in Rotating region and free surface simulation

Amal.C — Wed, 13 Apr 2016 10:28:26 GMT

Hi Marco,

To answer your question: Free Surface simulations use the time step as a maximum value and can then reduce it behind the scenes to maintain analysis stability

I advise you also to make sure that you have a good uniform mesh for the liquid.

Was that helpful for you?

Amal,

Re: Time step size in Rotating region and free surface simulation

Anonymous — Wed, 13 Apr 2016 12:17:13 GMT

Hi Amal,
that explains why the simulation took very long. Thanks!
My case is a bit off-norm. Close to the inlet of my water stream, I don't need very fine mesh, so I set coarse mesh; next to the outlet, there is a rotating region by which, together with a suitable geometry, generate a turbulence, so there I needed a fine mesh. Do you suggest to uniform the mesh anyway?
Best regards,
Marco

Re: Time step size in Rotating region and free surface simulation

Amal.C — Wed, 13 Apr 2016 14:49:42 GMT

Hi Marco,

The most important thing is to have a good uniform mesh wherever you have a free surface.

It would be better if you share with us your model

Thanks,

Amal