Timestep size & Max Stagger Iterations

Nazrin

Hello everyone,

1. For vortex shedding simulation (transient), how should I know if my max stagger iterations value is 'enough' or not? what is the good starting value of max stagger iterations.

2. For example: my timestep size is 0.002 + max stagger iterations = 10, if i want to decrease my timestep size to 0.001, should I decrease my max stag iterations? or should i keep it at 10?

3. Does value of max stagger iteration really give big difference compared to timestep size in accuracy?

*Case details: transient sim, flow over cylinder, subcritical regime (re 20k-100k), SST.

acupro

My rule of thumb - if I need more than 6 stagger iterations to reach the per-time-step convergence level I desire, then I reduce the time increment. Each time step of the transient is essentially a mini steady-state run, so we need enough stagger iterations to reach convergence for each time step, to get a time-accurate solution.

A good rule of thumb is to have at least 30 to 50 time steps (or so) for each dominant 'cycle' to be captured in the flow behavior. For unknown solutions, various runs would be completed to determine the solution sensitivity to the time increment.