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Different surface flow values - Incompressible case

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Old   October 18, 2013, 06:16
Default Different surface flow values - Incompressible case
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Frank Ubber
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Hi everyone,

I have an incompressible (simpleFoam) MRF case with an axial fan in a tube (see screenshots). I also got realistic solutions but if I ask paraview to give me the surface flow I get different flows at the outlet and at the middle of the outlet tube. The value at the middle of the outlet tube (0.05437 m/s) is also more realistic than the outlet value (0.0532 m/s). Why that? Shouldn't it be the same values since it's an incompressible case?
I made a slice at both positions and got the flow value via the "Surface Flow" filter.

I also enclosed two screenshots of the glyphs mid-tube (glyph_mid.png) and at the outlet (glyph_out.png).

Does anyone know what's going on here?


Best regards,

Frank Ubber
Attached Images
File Type: jpg glyph_mid.jpg (30.8 KB, 5 views)
File Type: png glyph_out.png (95.6 KB, 3 views)
File Type: png screen_full.png (23.6 KB, 3 views)
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Old   October 20, 2013, 06:54
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Frank Ubber
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Does anybody have an idea? How to correctly read out the surface flow or why I have different flow values?
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Old   October 21, 2013, 04:47
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Vincent RIVOLA
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Dear Frank,

There could be few reasons:
- either your case is not fully converged
- either your mesh is not good enough and you get some mass loss
- either your farfield (cylinder tube) is not a wall boundary condition and you get some inflow/outflow there as well.
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