I have noticed that for the first few time steps in my simulations, the results seem to be oscillating. When discussing the problem with someone from another CFD company, they suggested the following:
"Since the initial condition is essentially stagnant flow, a large number of iterations will be needed at the first time step to achieve complete convergence of the hydrodynamics, ie there is an instantaneous start up of the flow, and so many sweeps will be needed to establish a converged flow field. Thereafter, less iterations will be needed per time step because only the inlet values of H2S at the BOTTOM and FAN objects vary with time. I would also imagine that larger time steps can be tolerated in terms of temporal accuracy when the change in the inlet value of H2S changes slowly with time."
I think doing what is suggested above could help - is there a way to do this in Flow Simulation? I see in Calculation Control Options where I can change maximum iterations, but don't see a way to force the solver to do more at the beginning.