[avdagde]

I am performing a Transient CHT analysis problem for cooling of structural steel weighing around 10MT by atmospheric air.My aim is to find optimum air velocity to have a temperature drop from 1000C to 500C in 35 mins.And domain size is 4.5(m) X 3.5 (m) X 2(m).

I am running the simulation in fluent with around 2.9M cells with symmetry option and hardware is 6 cores and 16GB RAM.

I am having a problem with increasing the Time step size and continuity convergence.Initially, I have used the 1e-4s time step and increased it to 0.02s in a span of 37000 iterations and 2500 timestep (around a week calculation) and total flow time is 11s only.

Now at 0.02s timestep, I am getting convergence in 30 iterations (Max iterations are 40)and all the residuals except continuity get converged in 5 iterations but continuity convergence is delaying the solution at every time step.

For continuity convergence, I have checked the net mass flux report at inlet and outlet and it is well below the 0.2%.

Should I increase the continuity convergence or else??
What will be correct max time step