Dear friends my question is : "Is it correct to use relaxation parameters for unsteady flows ?" The Fluent users guide does not mention this topic and recommends about 20 iterations per time step with default relaxation parameters switched on. Could one obtain realistic solution ? Will this solution not be affected by relaxation when such low number of iterations is used ? Thanks a lot for your comments. Kim

Dear Kim

I think that everything is relative. 20 iteration is, sometimes very small number if the flow changes dramatically within your time increasement. But 20 iteration might be very large number when the change of the flow(and/or other dependent variables) is very slow within your prescribed time increasement.

So, I thinkt that it is the most important to know the characteristic time scale of your flow system. Then you can know reasonable time increasement and iteration number of each time increasement.

Sincerely, Jinwook