Changing the physical time

saisanthoshm88 · July 5, 2012, 02:40

I have a question on altering the physical time step. I just know that changing
( Increasing (or) decreasing) the physical time step in a steady state solution can aid convergence.

As a newbie to CFD I just have the following notions , please correct me if Iam wrong:

Provided that the convergence looks stable:

- The physical time step should be increased if the imbalances are high

- The physical time step should be decreased if the imbalances are low

If the convergence is not stable (or) if an oscillating trend is observed it is not a problem with the time step but a problem with the boundary conditions (or) some physical phenomenon like re circulation hence changing the time step will not help in that case.

ghorrocks · July 5, 2012, 06:01

This FAQ has some comments: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

If it diverges early - need smaller time steps
When it is converging nicely - can use bigger time steps to speed convergence.

July 5, 2012, 02:40	Changing the physical time	#1
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 17	I have a question on altering the physical time step. I just know that changing ( Increasing (or) decreasing) the physical time step in a steady state solution can aid convergence. As a newbie to CFD I just have the following notions , please correct me if Iam wrong: Provided that the convergence looks stable: - The physical time step should be increased if the imbalances are high - The physical time step should be decreased if the imbalances are low If the convergence is not stable (or) if an oscillating trend is observed it is not a problem with the time step but a problem with the boundary conditions (or) some physical phenomenon like re circulation hence changing the time step will not help in that case. __________________ Best regards, Santhosh.

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July 5, 2012, 06:01		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	This FAQ has some comments: http://www.cfd-online.com/Wiki/Ansys...gence_criteria If it diverges early - need smaller time steps When it is converging nicely - can use bigger time steps to speed convergence.