Poblem with Unsteady for Natural Convection
 

Hi, everyone. I am simulating natural convection heat transfer from horizontal cylinder.I solve with time unsteady, but i think it's wrong results. Anybody know how to set the right solutions in fluent to get a good results. I know PISO is good for unsteady, but when i set PISO it's always diverged. In time step size i set 3600 sec, number of time step is 36 to get 36 hrs. I think solution control in fluent is an important factor to get a good results.

Thank you all.

TK