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oringo March 1, 2013 05:41

Bad pressure distribution in pump
Hello everyone,
I use CFD to calculate radial force in cetrifugal pump. I made geometry of old "test stand" used to calculate radial force. I have data from scientific research (capacity, static pressure in inlet and outlet). I want to confront them with CFD results. My problem is I get bad results, which are not connected with scientific data, eg. force decreases with capacity lower than in BEP (0,5*Qn), so it's not physical. It looks that I get bad pressure distribution.
see the pictures of model:
Blue colour are interfaces, red are rotating walls in stationary domain, purple - LE and TE. Volute geometry is very simple-similar to rectangle.
When I print forces in Fluent when residuals are about 2e-3 I get eg 200N, but when my residuals are about 1e-3 the force can be twice lower. It looks that pressure distribution is not stable(?), but residuals are quite stable. Usually I can't get converge lower than 1,5e-3 for second order upwind. I used k-e, k-e realizable, k-w SST but it not helped. In inlet I use BC mass flow inlet and in outlet outflow. I tried also use pressure BC in outlet and inlet, but I didn't get capacity which I should get.
I've meshed impeller domain in TurboGrid. Minimum orthogonal quality is 0,15. I made volute grid in ICEM (hexa) and it has min quality 0,45. So mesh is acceptable. Hub and inlet_and_shroud domain were made in Ansys Meshing. I tried 2 grids, bigger has about 4,5 mln nodes and it not helped.
I don't know what am I supposed to do?
Are my interfaces in bad position (see the pictures)? Should I place them in other place or way? Impeller diameter is 268 trailing edge diameter is 264 and tongue diameter in volute is about 290.
Why I get pressure distribution completety not connected with scientific data.
I'd be very grateful for help because I don't know what should I do....


mix_mentzos March 1, 2013 16:42

I think that concerning the BC it is better for inlet Velocity or mass (the same) and for outer Pressure.

oringo March 2, 2013 11:38

Thanks for advice. I've moved interface of impeller farther into volute and now it looks better even with low quality mesh

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