Comments

In my experience if you have to reduce RF's to very low values then it indicates meshing issues or the wrong model (i.e. turbulence model for laminar flow etc.). I agree that the normal procedure is to start the solution using the default values and allow the solution to evolve without trying to force convergence which can produce meaningless results.

However I have heard a user state that for very large models such as 10 million or 20 million fluid cells that you need to lower the URF's to very low values, but I totally disagree with this. The convergence should not depend on the model size, but for a given number of iterations required to converge with default URF's it will take more CPU time for a larger model, correct?

William