Question about accelerating the convergence by changing the timestep

Anna Tian · September 15, 2012, 17:55

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.

September 15, 2012, 17:55	Question about accelerating the convergence by changing the timestep	#1
Anna Tian Senior Member Meimei Wang Join Date: Jul 2012 Posts: 494 Rep Power: 16	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? __________________ Best regards, Meimei

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September 16, 2012, 07:50		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	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.