Under Relaxation Factors(URF) in unsteady problem
 

Dear all,
I am using Fluent calculating unsteady flow field. At first all the URF are set as 0.1 by me, or it is hard to continue. then, when the residual reduces steady, I increase the URF to 0.5, it can also continue fluently. I set Max Iterations/Time Step as 20. The problem is how can I make myself belive that the unsteady flow is the one I want. In other words, how to prove the calculation is convergenced in every time step? also by Residual? I think there must be relationship between URF and Max Iterations/Time Step. But if the Max Iterations/Time Step are set too large, it will be very hard to get a wanted unsteady solution if the cash is big.,Right? Thank you very much and looking forward to your reply.
Best
Maxmum