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 Kjetil W July 19, 2006 06:06

Symmetryplanes

Hi. I have a problem with a flow throug a system that is symmetric. It starts as a regular piping. At the middle of the system the flow divides into two symmetrical ducts before it returns into one piping at the end. I have defined a symmetry boundary condition to the planes before and after the part where the piping is devided, but this gives me an error when i start the solver:

" The symmetry boundary condition requires that the boundary patch mesh faces form a plane or axis. However, face set 5 in the symmetry boundary batch Symmetry is not in a strict plane, which means that at least one of its faces is not parallel to the others. "

One of the suggestions i get is that I should change the "vector parallel tolerance". But I dont understand why i should do this since the two symmetryplanes are parallell. How will the vector parallell tolerance affect results?

 Joe July 19, 2006 07:13

Re: Symmetryplanes

There are two possibilities here:

(a) One of the patches you have specified as symmetric is in fact not planar. Look very carefully at the mesh set you defined as symmetric, edge on, and make sure its planar.

(b) Your patches are nominally planar but there is at least one mesh element that is more then 5 degrees (default toletance) off-planar.

Its probably (a) ... if you are 100% sure its not (a) then increase the vector parrallel tolerance ... its an expert parameter.

Inflation perpendicular to a symmetry plane cam sometimes trigger (b).

 Robin July 19, 2006 08:48

Re: Symmetryplanes

If it is (b) and you generated your mesh in ICEM CFD, check that ICEM didn't associate an element face to the symmetry plane that is slightly off the plane at the edge.

An easy way to look for the bad elements is to plot each of the normal components in post using the local range (or plot X, Y, or Z, if it is aligned with an axis). You should find that all the values are constant, except for the problem face.

Regards, Robin

 nicolas July 19, 2006 08:51

Re: Symmetryplanes

I had this problem, 1 month ago. Maybe, it can help you, to know my problem. I made a plane of symetry, and some points, to attach the blocking(i used an hexa mesh), in order to be sure that the mesh will be on this plane. I made 1 mistake: -1 vertice of blocking wasn't linked to the point of the plane (so the vertex wasn't on the plane)