I don't want to solve some equation to save time

yhddd · April 5, 2022, 06:54

Now， I am currently using CFX, additional variable is used to calculate the RTD curve, I firstly calculates the steady state, then the steady state flow field results as the initial conditions of the transient simulation, hope to get the RTD curves, but transient calculation takes too long.
I have used Fluent before, and this software has a function that after obtaining steady-state results, It can no longer solve the flow equation, momentum equation, etc., which can save the time of transient calculation. I wonder if CFX has a similar function, which can not calculate some equations.

ghorrocks · April 5, 2022, 07:19

Yes. In expert parameters have a look at the solver over-rides. You can choose to turn equations off to save simulation time. It means that variable will not get updated and will stay at the values in the initial condition.

yhddd · April 5, 2022, 07:27

[QUOTE=ghorrocks;825522]Yes. In expert parameters have a look at the solver over-rides. You can choose to turn equations off to save simulation time. It means that variable will not get updated and will stay at the values in the initial condition.[/Q
I don't know how to close some equations, can you tell me

ghorrocks · April 5, 2022, 07:30

What do you mean by "close some equations"?

Do you mean turn them off? If so, then my previous post explains that.

If you mean something else please explain what you mean.

yhddd · April 5, 2022, 07:33

Quote:

Originally Posted by ghorrocks

What do you mean by "close some equations"?

Do you mean turn them off? If so, then my previous post explains that.

If you mean something else please explain what you mean.

A: I see. Thank you. I will study the method carefully

Opaque · April 5, 2022, 08:16

just be careful, turning off equations is a dangerous thing unless you are aware of ALL dependencies between the equations.

The flow equations are decoupled from the energy equation ONLY for constant properties single component material; otherwise, they are fully coupled and they cannot be turned off from one another.

If your additional variable interacts with other equations, those equations cannot be turned off either.

It can be done, but carefully

Gert-Jan · April 5, 2022, 11:30

In expert parameters set:

solve fluids = f
solve turbulence = f

f is false, t is true.

April 5, 2022, 06:54	I don't want to solve some equation to save time	#1
yhddd New Member hang yang Join Date: Apr 2022 Posts: 17 Rep Power: 4	Now， I am currently using CFX, additional variable is used to calculate the RTD curve, I firstly calculates the steady state, then the steady state flow field results as the initial conditions of the transient simulation, hope to get the RTD curves, but transient calculation takes too long. I have used Fluent before, and this software has a function that after obtaining steady-state results, It can no longer solve the flow equation, momentum equation, etc., which can save the time of transient calculation. I wonder if CFX has a similar function, which can not calculate some equations.

April 5, 2022, 07:19		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,705 Rep Power: 143	Yes. In expert parameters have a look at the solver over-rides. You can choose to turn equations off to save simulation time. It means that variable will not get updated and will stay at the values in the initial condition. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

April 5, 2022, 07:30		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,705 Rep Power: 143	What do you mean by "close some equations"? Do you mean turn them off? If so, then my previous post explains that. If you mean something else please explain what you mean. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

April 5, 2022, 08:16		#6
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	just be careful, turning off equations is a dangerous thing unless you are aware of ALL dependencies between the equations. The flow equations are decoupled from the energy equation ONLY for constant properties single component material; otherwise, they are fully coupled and they cannot be turned off from one another. If your additional variable interacts with other equations, those equations cannot be turned off either. It can be done, but carefully __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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April 5, 2022, 07:27		#3
yhddd New Member hang yang Join Date: Apr 2022 Posts: 17 Rep Power: 4	[QUOTE=ghorrocks;825522]Yes. In expert parameters have a look at the solver over-rides. You can choose to turn equations off to save simulation time. It means that variable will not get updated and will stay at the values in the initial condition.[/Q I don't know how to close some equations, can you tell me

April 5, 2022, 11:30		#7
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,827 Rep Power: 27	In expert parameters set: solve fluids = f solve turbulence = f f is false, t is true.