leflix 
August 13, 2012 11:51 
Quote:
Originally Posted by landa
(Post 376765)
I have a question about setting under relaxation factor.
is changing the relaxation factor supposed to change the final answer?!
when i changed it in a problem, the final solution that i was expected wasn't gained and when i decreased it again, the final solution changed again

If the choice of your relaxation factor change your solution, so there is a bugg in your code.
With an improper value of relaxation factor your solution can blow up. with a good one the solution will converge. But there are plenty values for which the solution will converge. For all theses values the solution should be the same (especially for steady cases) and the only difference will be the rate of convergence.
As an example it is often recommended to underlax the pressure for incompressible flow. Underlaxation factor over 0.7 may blow up your code,it is really problem dependent. For UF =0.6 it may converge, but for UF=0.5 also and for UF=0.2 too. For all theses values between 0.2 and 0.6 you will obtain the same solution. But there is an optimal value for which your code will converge faster. Generally it is the highest value for which the code still converge just over this limit it diverges.
Some authors have prescribed that UF_velocity+ UF_p = 1
