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-   -   About changing time step at the CFX-solver (http://www.cfd-online.com/Forums/cfx/106790-about-changing-time-step-cfx-solver.html)

Anna Tian September 8, 2012 09:35

About changing time step at the CFX-solver
 
Hi,

May I ask if there's any way to change the time step at the CFX-solver? So that when I want to change the time step to let the RMS converge I can stop the simulation and change it directly without going back to CFX-pre. Then start the running again with the result before changing the time step as the initial data.

Thank you very much.

cdegroot September 8, 2012 13:57

Yes there is a button to edit the run in progress.

ghorrocks September 9, 2012 06:22

For a stady state run use the edit run in progress option in the solver manager. For a transient state run use adaptive time stepping, converging on 3-5 coeff loops per iteration.

Anna Tian September 15, 2012 18:08

Quote:

Originally Posted by ghorrocks (Post 380921)
For a stady state run use the edit run in progress option in the solver manager. For a transient state run use adaptive time stepping, converging on 3-5 coeff loops per iteration.

Thanks! But is there a way that I can set the change in advance and change it automatically during the running? Like I can set when the convergence stop, it changes its time step to another value. Or when it reaches a time step number (for example, like 500), it changes to another.

cdegroot September 15, 2012 18:23

Yes you can give multiple timesteps. See the section of the CFX manual entitled "Transient Timestep Control". You can give a comma separated list, but in your case it's probably better to write an expression that gives the timestep.

Anna Tian September 16, 2012 04:50

Quote:

Originally Posted by cdegroot (Post 381954)
Yes you can give multiple timesteps. See the section of the CFX manual entitled "Transient Timestep Control". You can give a comma separated list, but in your case it's probably better to write an expression that gives the timestep.

Thanks. But I work on the steady-state flow. And I always would like to change my time step from local time step of factor 5 to physical time step of 10^-4 in the middle of the simulation (when RMS doesn't decrease any more). How to make it changes automatically?

ghorrocks September 16, 2012 07:47

Set it up as two runs, one which does the local time step bit and a second which uses that as an initial condition for a physical time step run. The automate is by using a batch/script file so you can run it all from a single command.


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