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Old   January 10, 2008, 06:09
Default Negative Volume in CFX
  #1
Barbara
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Hello

I will simulate film cooling effectivness on a plate. My mesh is 2.2 mill nodes big and in some areas very fine. I convert the ICEM CFD file into a cfx5-file and start the simulation in Ansys CFX 11.0. But CFX gets/computates a negative Volume and doesn´t start the the simulation.

Has someone an idea, how I could solve the problem? Thank you.
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Old   January 10, 2008, 06:19
Default Re: Negative Volume in CFX
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Subha
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Hai Barbara,

Negative volume indicates that your mesh does not fit the volume. Just got to ICEM and check for elements with Quality lesser than 0 (negative values). Try to fix the mesh within your geometry. It is always better to handle the mesh with a minimum quality of 0.2 or higher.

Hope you will find it easily.

Regards,

Subha.
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Old   January 10, 2008, 11:19
Default Re: Negative Volume in CFX
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CycLone
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Hi Barbara,

Note the error message carefully. A negative element volume is easily detectable in ICEM CFD, but the solver may be reporting a negative element sector volume, which may not show up. If you're running v11, the solver will write element quality variables to the res or res.err file which you can view in Post. Use Post to find the regions of low quality and return to ICEM CFD to improve the mesh in these regions.

I don't recommend using the mesh manipulation tools to fix these regions. Although smoothing should be done, you may find yourself endlessly smoothing and pushing nodes to fix the problem. It is much better to improve your mesh controls (local refinement, expansion) or switch to a different volume mesher (Delauney or Advancing Front) and remesh. It is also easier to repeat.

-CycLone
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