Hi,

I have an unsteady velocity waveform that I want to hook up to Fluent. How do I set the criteria for the number of iterations per time step, the number of time steps, and the value of the time step? On what criteria are these based? Also, is it possible to hook the entire flow waveform from some data acquisition software like Windaq to Fluent?

I'm relatively new working with Fluent and so I would greatly appreciate it if someone could offer me a detailed explanation. I couldn't understand too much from the tutorials and hence I ask.

Thanks in advance.

Regards, Vidya

I do not think u shud worry abt such parameters, usually 500 iterations are chosen for the solution to converge. The value entirely depends on when the solution gets converged. Increase the number of iterations if solution does not converge in the given 500 iterations.

Yeah, but how do I set the value of the time step?

Vidya

In unsteady formulation size of time step and no of time stepes are important.it depends on what solution algorithm u have used like implicit or explicit,it also depends on the physical nature of ur problem like subsonic , supersonic, turbulance etc... The size of time step should be the one order less than ur minimum time scale in ur problem. size of time scale should be smaller for explicit than implicit. it will keep ur iteration stable. For no of time step u start with 100, i dont know ur problem so i cant tell the exact. try to get steady state solution. I hope this will help u,

Hi Balmiki,

Thanks a lot for the reply. I'm trying to model the blood flow in a human vein. So the flow is laminar and I'm using first order implicit formulation. I also want to try the secong order formulation.

So based on this information, how do I go about fixing the size of the time step and the number of time steps?

Thanks, once again. Vidya

If you know from experience or by another source the period of your wave T0, start with DT=T0/10...and see how your system behaves....

A second order formulation in space and in time might be necessary to get accurate results....