time step vs convergence
 

Hi! this is the problem...
I need to perform unsteady state study to get info about how a system behaves during 60 seconds.
If I use a time step of 0.00001 it converges perfect and the results seem to be right. But it will take weeks of running calculations... so it doesn't work

If I use another time step... it diverges.
If I use a coarsen mesh, it diverges because of the poor mesh.

I am working with density-based , implicit time advancement , courant number 0.1

any suggestion???

thanks

I think it is just the way how CFD works... You have to choose a good time step according to your mesh and the phenomenon that you would like to simulate. There is no good way of making the time step larger...

That is my experience...