time step size
 

Hello, I am using sliding mesh model for a 3D turbine (36 stators and 54 rotors). I am modeling 2 stators and 3 rotors (periodic angle of 20 degrees). Rotor speed is 2700 rpm. Kindly suggest how to calculate passing period of rotor blade, time step size and number of time steps for unsteady simulation. Many Thanks,

Re: time step size
 

It'll really depend based on your model. When I'm running simulations I usually start off at a very small time step size, around .0005s. As each time step begins to converge faster and faster (meaning less iterations required) and things look good, I gradually increase the time step size.

As for the number of iterations, again its different for every sample. Give 100 a try. You might not necesserily converge the first time, but a few more time steps might converge under 100.

And as for the number of time steps, I like to start out with 1 and have a plot of the residuals going to make sure they are headed in the right direction. Then you can move up to 5, then groups of larger numbers say 25, and if they're moving along fine, either increase the time-step size or just set it for a high number, and enable the autosave so in case it does crash you still have data.