Under relaxation factors should not affect your solution. If they do, the solution did not converge.nincreasing URFs helps the solution to converge more quickly, but there is a risk of divergence. I am currently have no optimum criteria for the URFs, but I do change them between iterations using a UDF. I make them small in the first couple of iterations and increase them when the residuals decrease. Not sure if this is the optimum or not, but this decreases my solution time slightly. nRegarding your case, As you are interested in the transient solution, here is my advice. Decrease the time step and increase the number of iterations in the time step ... make sure that the residuals converge ... they should be almost straight lines before moving to the next time step.n