[jose_prime]

Hello!


I have a doubt about the need to use under-relaxation.


My currently project simulations consist in two steps:
1. Solve flow field.
2. Freeze the flow field and run the transport of a passive scalar (the passive scalar does not run during step 1). In this step, I monitor an average that should converge to a theoretical value.


In the first simulation, I set no under-relaxation to the passive scalar (factor = 1) and I was happy with the results. Here is why:
1. The passive scalar is running alone, so it does not affect anything else.
2. The passive scalar residual reduced smoothly without instabilities or oscillations.
3. The value that I monitor converged to the theoretical value smoothly without any instabilities or oscillations.


However, I was commanded to introduce under-relaxation in the passive scalar and the justification I was told was "not to rush the solution". I got sincerely puzzled by this, as do not understand this approach. So I have two questions:


1. Aren't my reasons enough to support the decision not to use any under-relaxation? What am I missing about this? Should I be looking into something else?

2. "not to rush the solution"... Shouldn't we try to rush the solutions as long as we do not introduce instabilities in the calculation?



Thank you.