Different surface flow values - Incompressible case

kornickel · October 18, 2013, 07:16

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 m³/s) is also more realistic than the outlet value (0.0532 m³/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

kornickel · October 20, 2013, 07:54

Does anybody have an idea? How to correctly read out the surface flow or why I have different flow values?

vinz · October 21, 2013, 05:47

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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October 20, 2013, 07:54		#2
kornickel Member Frank Ubber Join Date: Aug 2013 Posts: 32 Rep Power: 13	Does anybody have an idea? How to correctly read out the surface flow or why I have different flow values?

October 21, 2013, 05:47		#3
vinz Senior Member Vincent RIVOLA Join Date: Mar 2009 Location: France Posts: 283 Rep Power: 18	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.