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-   -   Question about accelerating the convergence by changing the timestep (http://www.cfd-online.com/Forums/cfx/107033-question-about-accelerating-convergence-changing-timestep.html)

Anna Tian September 15, 2012 17:55

Question about accelerating the convergence by changing the timestep
 
Hi,

We often change the time step in the middle of the simulation running to accelerate the convergence. For example, according to the FAQ of this forum, we can set the time step to local time step with factor of 5 at the beginning. Then when the RMS does not decrease anymore, we can change the time step to let it continue to decrease.

But how do we know what time step should I change to?

ghorrocks September 16, 2012 07:50

The CFX documentation describes setting the time step - a good starting point is the fluid residence time in the domain. But note this is only a guide - if the simulation is converging well a larger time step is possible, if convergnce is difficult a smalle rtiem step will be required.


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