[Techies]

Hi guys,
I'm finding under relaxation factor to make my solution converge.
I just have questions: Where is the under relaxation in CFX, how to specify it ? and what are the values that everyone often use ?

[Opaque]

May I ask why you need under relaxation factors to converge the solution?

The fact they are not obvious is an indication they are not "generally" needed, and likely the software uses a different approach to achieve converged solutions.

Mixing approaches could hide a setup issue, or make things worse in the long term.

Would you mind elaborating on your convergence problems?

[Techies]

Originally Posted by Opaque

May I ask why you need under relaxation factors to converge the solution?

The fact they are not obvious is an indication they are not "generally" needed, and likely the software uses a different approach to achieve converged solutions.

Mixing approaches could hide a setup issue, or make things worse in the long term.

Would you mind elaborating on your convergence problems?

I'm working with sst model with Reynolds from 5000 to 30000. But at Re 30000, RMS is unstable and results is not yet converge . So i want to modify the under relaxation

[Gert-Jan]

CFX does not use underrelaxation factors. It works using so-called false timesteps. Therefore you should reduce the timestep size which is 1 by default.

[Techies]

Originally Posted by Gert-Jan

CFX does not use underrelaxation factors. It works using so-called false timesteps. Therefore you should reduce the timestep size which is 1 by default.

Can u tell me where is it ?

[Gert-Jan]

In fluent, you can find these under Solver Controls.
CFX isn't very different. In CFX-Pre, it is called Solver Control.

Btw, I don't know which Fluent version you are used to work with, but lately ANSYS incorporated the CFX way of solving into Fluent. There it is called Pseudo Timestepping.

[Techies]

Originally Posted by Gert-Jan

In fluent, you can find these under Solver Controls.
CFX isn't very different. In CFX-Pre, it is called Solver Control.

Btw, I don't know which Fluent version you are used to work with, but lately ANSYS incorporated the CFX way of solving into Fluent. There it is called Pseudo Timestepping.

Sorry but i can't find Pseudo Timestepping Just see Timescale factor

[Gert-Jan]

That is what you need to reduce.

So, in CFX it is called Timescale Factor.
In Fluent it is called Time Scale Factor as well, but it is in the menu Pseudo Transient Settings.

BTW, don't use "local timescale factor", like in your picture. Use the default settings and use a timescale factor of 0.25, or 0.5.

[Techies]

Originally Posted by Gert-Jan

That is what you need to reduce.

So, in CFX it is called Timescale Factor.
In Fluent it is called Time Scale Factor as well, but it is in the menu Pseudo Transient Settings.

BTW, don't use "local timescale factor", like in your picture. Use the default settings and use a timescale factor of 0.25, or 0.5.

thanks for ur hepling me

[Techies]

Originally Posted by Gert-Jan

That is what you need to reduce.

So, in CFX it is called Timescale Factor.
In Fluent it is called Time Scale Factor as well, but it is in the menu Pseudo Transient Settings.

BTW, don't use "local timescale factor", like in your picture. Use the default settings and use a timescale factor of 0.25, or 0.5.

Why are my result using timescale factor different from normal result ?

[Gert-Jan]

https://www.cfd-online.com/Wiki/Ansy...ated_questions