Convergence with reduced under relaxation and time scale factors

saisanthoshm88 · March 19, 2013, 10:02

In a steady state simulation if a reduction of under relaxation factor (for continuity) and a reduction of time scale factor (auto time scale) gives convergence with the monitor points then -

Is it fine to relay on such convergence (or) is it always a must in general to
run a few more iterations by revoking the default under relaxation factor
and with a time scale factor = 1 ?

SST turbulence model is used

ghorrocks · March 19, 2013, 17:31

I have never had to use relaxation factors in CFX, so it is highly unlikely you need to use them. If you have convergence difficulties there are better approaches.

There is no need to run time scale factor=1 at the end. As long as you are using physical time stepping, any time step size is fine providing it converges.

saisanthoshm88 · March 19, 2013, 20:57

Many thanks for the clarification Glenn.

Actually I'm using Fluent to solve this case and my question indeed takes fluent as the reference.

I thought of gaining also a general insight so I also posted the question on this forum.

The information you provided is of help because the application of time scale factor in fluent is similar to that of cfx.

Fluent is ofcourse more driven by under relaxation factors too.

ghorrocks · March 20, 2013, 06:04

So would this post have been better placed on the Fluent forum?

For SIMPLE based solvers, like Fluent's default solver URF are important and it is normal to adjust them. Also I have no idea what Fluent's time scale factor =1 means.

March 19, 2013, 10:02	Convergence with reduced under relaxation and time scale factors	#1
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 17	In a *steady state* simulation if a reduction of under relaxation factor (for continuity) and a reduction of time scale factor (auto time scale) gives convergence with the monitor points then - Is it fine to relay on such convergence (or) is it always a must in general to run a few more iterations by revoking the default under relaxation factor and with a time scale factor = 1 ? *SST turbulence model is used* __________________ Best regards, Santhosh.

March 19, 2013, 20:57		#3
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 17	Many thanks for the clarification Glenn. Actually I'm using Fluent to solve this case and my question indeed takes fluent as the reference. I thought of gaining also a general insight so I also posted the question on this forum. The information you provided is of help because the application of time scale factor in fluent is similar to that of cfx. Fluent is ofcourse more driven by under relaxation factors too. __________________ Best regards, Santhosh.

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March 19, 2013, 17:31		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I have never had to use relaxation factors in CFX, so it is highly unlikely you need to use them. If you have convergence difficulties there are better approaches. There is no need to run time scale factor=1 at the end. As long as you are using physical time stepping, any time step size is fine providing it converges.

March 20, 2013, 06:04		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	So would this post have been better placed on the Fluent forum? For SIMPLE based solvers, like Fluent's default solver URF are important and it is normal to adjust them. Also I have no idea what Fluent's time scale factor =1 means.