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

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.

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.

[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

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

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

In expert parameters set:

solve fluids = f
solve turbulence = f

f is false, t is true.