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kjetil November 24, 2009 20:44

Major differences between Comsol and OpenFOAM, steady state diffuser singlephase flow
 
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Dear OpenFOAM community,

I just finished a simulation case in Comsol to verify the separation limits for diffusers. As a reference I used the characteristics in White's Fluid Dynamics.

Comsol returned pretty plausible results, having backflow at the outlet when the diffuser angle was set too large. On the other hand, creating a similar case in OpenFOAM using simpleFoam, still using water and 4m/s as inlet condition, the solution turns out very different; separation occurs almost immediately after diffuser inlet - at this angle (7 deg half angle) the flow "should" be uniform. What may be wrong? Wall functions are enabled for k and epsilon ...

Illustrations attached.


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