How to calculate time step size , number of time step and max iteration ?

- April 30, 2021 at 5:02 am
  
  johnny02
  Subscriber
  
  Hello guys,
  This is Johnny here. I am doing a CFD simulation on a mixing tank with different liquid heights. And I am using VOF multiphase model and SST k- omega model and I just want to know how can I calculate the time step size, number of time steps, and maximum iteration for the transient case?
  Thank you
- April 30, 2021 at 1:57 pm
  
  Karthik Remella
  Administrator
  
  Hello Your time-step size is dependent on the CFL number calculations (min cell length, velocity scale, and Courant number = 1, if explicit VOF [might be able to use a larger value if using Implicit]).
  Once you fix the time-step size, the number of time-steps gives you the total physical time you are modeling.
  Fluent will attempt to iterate based on the specified value of a Maximum number of iterations every single time step. This number comes into play if Fluent is unable to converge the model every single time step, which is not recommended. You want to select your time-step size such that the model converges before the maximum number of iterations is reached. It is an optimization game to ensure that your model is running sufficiently fast.
  Karthik
- April 30, 2021 at 7:15 pm
  
  johnny02
  Subscriber
  
  Thank you karthik