Hello,

I try to solve a problem using CFX4.1/4.2. The problem consists of multi-region which using different equations. Any experiences and advices for creating multi-region mesh using CFX-build are wellcom. How can I put the different equation in each region?

Any insights and suggestions are appreciated. Thanks in advance.

Qing zhang

Hello,

I am working on a pressure driven problem and have difficult for setting the pressure boundaries. Any advices will be help especially for the packedge of FASTFLO. Thanks.

qing Zhang

Hello,

What kinds of regions do you want to use (porous, solid, solid conducting, etc)? Could you explain what you mean by different equations? Does this mean that you want every region to have a different set of governing equations?

David Creech CFX User Subroutine Archive

Hi, David

The regions I needed are: a central pipe with porous wall and a shell. For example, liquid flows through the pipe and the porous wall which exit through the shell. The governing equations in this three regions should be: N-S equations (in pipe) and Darcy equation (in porous medium) and N-S equations (in shell).

Thanks.

Qing Zhang

Qing,

Making the geometry for your problem shouldnt be too difficult. The basic technique is to divide your geometry up into blocks. You need to use Build or Meshbuild to first make the central pipe. I am going to give you directions in Meshbuild because I am most familiar with it, but the technique should be similar with Build.

I usually make pipes with five blocks to get a good mesh. Think of a circle with a square in it, and then draw lines from the corners of the square to the circle. This gives you a circle divided into 5 pieces. Make this shape and create the faces.

The porous wall and shell are created similarly. Make a circle around your pipe and divide it into 4 faces. Then do the same for the shell. You should get something that looks like this, except not in bad ASCII art:

<code> ****_________ ***/\_______/\ **/*/\_____/\*\ */*/*/\*__/\*\*\ (*(*(**|__|*)*)*) *\*\*\*/__\/*/*/ **\*\/_____\/*/ ***\/_______\/ </code>

Now extrude the faces along the length of your pipe to create blocks. You then need to set the block types. This is similar to setting boundary conditions. There is an option to set 3D block types instead of 2D face types. Use this to set the porous region. Then set your bc types as usual.

Everything else you need to do is in CFX. I dont have much experience using porous regions, so I dont know if CFX uses the Darcy equations by default. You can check this in the manual. The other regions will use the NS equations by default.

If CFX doesnt use the Darcy equations, the only way to do this would be with user subroutines.

David CFX User Subroutine Archive

David,

Thanks indeed. It would help.

Qing

Dear Qing,

Please let us know if you are OK with your responses with CFX 4.1/4.2.

Many thanks

John Brookes

Qing, David was right. You most likely need to mess around with two subroutines: USRSRC and USRPOR. You may need to assign patch group numbers for 3-D porous patches if you set porosities in command file. In general, the Darcy law shows a linear function between the pressure drop and the velocity, You may as well need to consider a quadratic form of correlation equation if the fluid flows fast enough. I have been doing some CFD work using CFX 4.2 in modeling fluid flow over the tube bundle (bank). The region was modeled as a porous medium (3-D patch). The results look reasonable. If you need any further information, please feel free to contact me.

Michael