Time step
 

Hi all how should we decide the time step in an unsteady flow?

Re: Time step
 

You should set a Time Step Size so that the number of iterations necessary to get convergence at each time step is 5-10. If converce at each time step requires more than 5-10 iterations then reduce the Time Step Size. If converce at each time step requires less than 5-10 iterations then you can increase the Time Step Size.

Re: Time step
 

You should set a Time Step Size so that the number of iterations necessary to get convergence at each time step is 5-10. If convergence at each time step requires more than 5-10 iterations then reduce the Time Step Size. If convergence at each time step requires less than 5-10 iterations then you can increase the Time Step Size.

Re: Time step
 

The advise above is acceptable only for small cases when time is not a critical issue.

Your timestep has to be at least 2-5 times less than a period of smallest disturbance in your flow.