couples or not couples...
 

Hi.... I need a suggestion... My computational domain has an intersection between a round pipe and a box, they are mutually orthogonal... Whether I use the arbitrary couples at interface between the two solid, can I've problem in solution? Do you think is better, for the solution, to mesh the entire domain without couples? Thanks a lot...

Re: couples or not couples...
 

<font face = "Courier New">I am not sure if I understand your question right. If you are skeptical of creating couples, the best way will be to create a conformal mesh. And for interfaces like the ones you have mentioned, the best thing to do is to create a shell surface and extrude. In all my mesh creations, what I have ever used is the following stmt.

cpmatch all

It forms all new couples by itself. Do not try to match couples manually. STAR-CD does this coupling effectively automatically.

After you have created the couples do a geometry check. It should report no cracks. That would mean your mesh is good.

Murali

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Re: couples or not couples...
 

Make sure you use *partial* arbitrary coupling (create a new couple type or just modify the existing couple type 2).

I think also conservation is not as strongly enforced at the interfaces where there are couples as they are essentially interpolations of the fluxes. Also, phenomena like separation of flow at the joint may not be well represented. But then again, the loss in accuracy could be very minor compared to that from your mesh quality.

Re: couples or not couples...
 

Hi

A good way to form new couples are:

cpdel all cpma all save

This will delete any old couples and form new ones.

Hope this helps ..

Regards

Jens

Re: couples or not couples...
 

I don't think what you said is accurate. At couples, faces are split into subfaces and the fluxes are apportioned accordingly. They are not interpolated. There really should be no loss of accuracy.

Re: couples or not couples...
 

Oops. Typing hand quicker than brain...

Like steve says, fluxes are apporportioned appropriately for each face in a couple and conservation is enforced In fact, the couples split the mating faces into subfaces and the member cells then in effect become... polyhedral cells.

I made my original conclusion from this: "...care is taken, via appropriate interpolations in time and space, to preserve flux continuity across the interface and avoid introducing spurious perturbations to the flow field." Pg.13-5 of the methodology manual. Section on sliding boundaries.