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Old   January 26, 2015, 15:41
Default Negative volume cells
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Hi all,

I'm building a 2D simulation to analyze a vertical axis wind turbine. I'm trying to create an interface between a circular rotating region and an outer free-stream region. The meshing is good...when I run mesh diagnostics it has no negative volume cells. However, when I run the simulation, it gives an error that there are negative volume cells. I assume that this is from the interface initialization because the negative volume cells weren't there before. I've tried changing the intersection tolerance on the interface, but it only changes the number of negative volume cells created. Does anyone have any suggestions on how to fix this or information regarding creating intersections like this?

Much appreciated!
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Old   January 27, 2015, 02:57
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What type of mesh are you using? polyhedral or trimmed? If using poly, try to create a conformal mesh.
if using trimmed, then create same size mesh on either side of the interface to get a better interface. You could also try and align the mesh so that the mesh could be nearly conformal.
Hope that helps!!!
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Old   January 27, 2015, 13:18
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I'm using a trimmer mesh and I have specified the same mesh size on both of the boundaries. I tried aligning both of the meshes to the origin (center of the turbine) but it yielded the same result. What exactly is a conformal mesh?

Also, I've included pictures of the overall mesh of the two regions, the mis-aligned cells on the interface boundary, and the resulting negative-volume cells from the interface initialization. If you have any more suggestions from seeing the pictures, please let me know.

Attached Images
File Type: jpg trimmermesh.jpg (99.4 KB, 20 views)
File Type: jpg misalignedmesh.JPG (35.5 KB, 13 views)
File Type: jpg negative_volume_cells.jpg (79.8 KB, 16 views)
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interface, intersection tolerance, negative cell volume

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