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-   -   Negative Volume in Mesh by Gridgen (http://www.cfd-online.com/Forums/fluent/38258-negative-volume-mesh-gridgen.html)

James October 16, 2005 13:59

Negative Volume in Mesh by Gridgen
 
Dear All,

I was wondering if any one can help me with a little problem I am here. I have generated a 2D mesh using Gridgen and when I examine the blocks, it shows negative volumes. I dont know how to fix it and the elliptical solver here doesn't seem to help either.

I have read the file in Fluent 2D and it produces reversed flow since it has got negative volumes!

If any one can suggest a way on how to fix the mesh and which attributes to set while smoothing for positive volume then it would be greatly appreciated.

Many Thanks in advance.

James

P.S. I dont want to remesh since the mesh I have generated is very complicated!

John Chawner October 16, 2005 16:21

Re: Negative Volume in Mesh by Gridgen
 
Hi James,

Are all the volumes negative or only a few? If all the volumes are negative it may simply be a left-handed coordinate system that's causing all the problems. If only a few cells have negative volumes, you can probably use the elliptic PDE solver along with subgrids to fix the grid (by making a subgrid around the region with bad cells and then using something like the LaPlace background control function with a very low relaxation factor to step through solution one iteration at a time).

I suggest that you contact our Tech Support staff at support@pointwise.com or 888-GRIDGEN. They can take a look at your grid and prescribe a more precise solution.

James October 16, 2005 17:24

Re: Negative Volume in Mesh by Gridgen
 
Hello John,

Many thanks for the reply. In answer to your question I would like to say that yes all the volumes are negative. I have re-specified the normal directions which in turn gets rid of the negative volume, however when I export the grid to Fluent, it starts to complain about cell coordinates being in appropriate.

Yes, I will contact support if I could not sort this out my self, however it is worth having a go at it my self first.

Kind Regards,

James

John Chawner October 16, 2005 19:00

Re: Negative Volume in Mesh by Gridgen
 
For the purpose of export to Fluent, Gridgen assumes that 2D grids are in the x-y plane. Could that be the problem?

James October 16, 2005 20:30

Re: Negative Volume in Mesh by Gridgen
 
Hello John,

Just to let you know that I have managed to fix the problem. My eyes hurt now, however it did pay off!

Many Thanks,

James

Jonny February 3, 2010 08:34

Re: Negative Volume in Mesh by Gridgen
 
It was very nice to hear the problem was fixed but exactly how you did this would have been more useful. I've just had the same problem.

The handedness of the faces in Gridgen is changed through Blocks/Modify/ and clicking reorient faces.


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