CFX steady simulation

gharek · April 7, 2010, 09:24

Hi CFD users,

I am rather confused by the steady simulation in CFX. I'm using CFX 12.1. As far as I know, when assuming steady conditions, all the D(phi)/Dt terms are set to be equal to zero. Why is there a time step in CFX steady simulation?

So, if I am solving an unsteady and/or turbulent flow by assuming steady, would I get my residuals as fluctuating or divergent?

As far as I know from Fluent, there is no such timestep used for steady calculations.

Thanks for any advice.

ghorrocks · April 7, 2010, 19:41

This is all explained in the documentation. The solver takes a psuedo-time stepping approach to convergence. Many other solvers take a under-relaxation approach to convergence and hence no time step is required - but you need to set under relaxation factors instead.

In CFX it is psuedo-time stepping as not all the transient terms are included and different equations can be advanced at different rates.

April 7, 2010, 09:24	CFX steady simulation	#1
gharek New Member Gareth Join Date: Apr 2010 Location: Sydney Aus Posts: 14 Rep Power: 16	Hi CFD users, I am rather confused by the steady simulation in CFX. I'm using CFX 12.1. As far as I know, when assuming steady conditions, all the D(phi)/Dt terms are set to be equal to zero. Why is there a time step in CFX steady simulation? So, if I am solving an unsteady and/or turbulent flow by assuming steady, would I get my residuals as fluctuating or divergent? As far as I know from Fluent, there is no such timestep used for steady calculations. Thanks for any advice.

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April 7, 2010, 19:41		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	This is all explained in the documentation. The solver takes a psuedo-time stepping approach to convergence. Many other solvers take a under-relaxation approach to convergence and hence no time step is required - but you need to set under relaxation factors instead. In CFX it is psuedo-time stepping as not all the transient terms are included and different equations can be advanced at different rates.