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Old   September 26, 2008, 05:42
Default compressor problem.
  #1
john
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Hi friends,

I ran a case of centifugal compressor rotating at 1,00,000 rpm. I specified mass flow at inlet and pressure at outlet (2.5 bar). but I am really shocked wht i got. I got 2.7 bar inlet pressure (instead 1.012bar.) Was I wrong to put mass flow at inlet? Should I use pressure at inlet and pressure at outlet.But if I am using pressure bcs, how can I achieve mass flow rate??? pls clarify. thanks a lot.
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Old   September 26, 2008, 08:52
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Andrea
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Hi
I don't know if you really need to use 2 pressure boundaries, but I know that you can specify a "target mass flow rate" at a pressure boundary...you can try to run your sim with this setup and specify in the target mass flow rate your desider mass flow.
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Old   September 26, 2008, 09:02
Default Re: compressor problem.
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john
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hi andrea, thanks a lot for suggetion you are right. but by specifying "target mass flow", solver keeps mass flow but adjusts pressure according to that mass flow. is it right. while my pressure at outlet is fixed.
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Old   September 27, 2008, 02:59
Default Re: compressor problem.
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Anton Lyaskin
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If you know the inlet pressure in advance, have you checked that this value and density and temperature you've specified at inlet are consistent with state equation?
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Old   September 29, 2008, 04:15
Default Re: compressor problem.
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Andrea
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yes John you're right also, but as Anton said have you checked your equation of state? Because it sounds strange that you get an inlet pressure 1.5 bar higher than expected...with the desider mass flow rate and the exact outlet pressure. Have you checked the moving mesh? It's all ok with the fluid motion in the mesh also? (I suppose you use a moving mesh...)
Bye
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