Hi all,

I am using cfx5.7 to model multiple domains, say [fluid - solid - fluid]. the solid domain seperates the fluid domains completely and the air temperature at the two seperate fluid domains is different. I need to activate buoyancy and at either side the buoyancy reference temperature should be different. But it seems cfx-pre automatically updates this 'buoyancy reference temperature', I mean if I set the buoyancy reference temperature for one fluid domain, it will overwrite the other domain. Is it a must for different fluid domains using 'one' buoyancy reference temperature only?

I can change it after the definition file is written, but I am not sure if I am messing up with the solver because the convergence doesn't look good. Anyone came cross this before? Thank you for your comments.

Regards, Forrest

It is legal to have different reference temperatures in different disconnected fluid domains. You can have Pre respect these different settings if you turn off the 'constant physics check'. To do this, set the environment variable CFX5_NO_CONSTANT_PHYSICS prior to running Pre. This is very useful... you can even have (for example) laminar flow inside the pipe and turbulent flow outside; or single phase flow inside and multiphase flow outside.

Thank you very much, Phil.

Really helpful comments! Never tried to do this, and had a look with the manual, couldn't figure out where I set this environment variable. Could you please let me how you do this?

Thanks a lot

Regards, Forrest

This is a beta feature, which is probably why its not well-documented. How to set environment variables depends on architecture. With unix/linux 'setenv' does the trick. On Windows, you need to set it through the Control Panel (can't quite remember the details...)

This environment variable can be set in cfx5rc.txt file. The content of this file is: CFX5_NO_CONSTANT_PHYSICS=1 export CFX5_NO_CONSTANT_PHYSICS

On Windows machine, you can put this file at: C:\Documents and Settings\userA\.cfx\10.0\cfx5rc.txt. Here "userA" is the username on that machine.

Hi longbow,

Thank you for your comments. I tried to find the file (cfx5rc.txt) you mentioned but I couldn't find it there. I am using cfx5.7.1. I also checked another machine which got cfx10, at the location you suggested, I couldn't find the file. I tried to search it under Documents and Settings. Not sure if I should make the file on my own. Any comments?

Thanks a lot

Regards, Forrest

The purpose of that file is to modify defualt setup of CFX. When you install CFX, there is no such a file in that directory. More information about "cfx5rc.txt" can be found in installation section of CFX mannual.

You need to create a file named as "cfx5rc.txt". There should be two lines in this file. The first line is: "CFX5_NO_CONSTANT_PHYSICS=1", and second one is: "export CFX5_NO_CONSTANT_PHYSICS". By the way, since you are using CFX-5.7.1, the file directory on your machine should be: C:\Documents and Settings\userA\.cfx\5.7.1\cfx5rc.txt.

Thank you very much indeed, longbow. I will do this as your suggested.

Cheers, Forrest

Hi everyone,

I did what you suggested, and it worked well. But, when I put the simulation file to start, it didnt go well. An error occour. Can someone help plz?? Thanks!!