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Frustrating puzzles on compressor modeling

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Old   August 30, 2008, 07:52
Default Frustrating puzzles on compressor modeling
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I am modeling a compressor, the inlet total pressure and outlet mass folw rate are set. But the results I got is frustrating me very much.

First, the pressure decreases throught the wheel instead of increasing. It is a compressor, not a turbine. How strange! I am sure that the flow direction is right. And the rotation direction is specified based on right hand rule.

Second, the inlet mass is not equal to the outlet mass. Maybe it caused by the mesh quality. I have the mesh completed by Tetra. But I think it is not the only reason.

What can I do now? Is it possible that the inducer angle of the blade is not well designed?

Wish help from you can help me to overcome this. Thanks in advance!

If you have experienced in this, pls show me some tricks. You are very appreciated. ^_^

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Old   August 31, 2008, 02:25
Default Re: Frustrating puzzles on compressor modeling
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Dear Rikio, whatt type of compressor you r modelling and how you have defined physics must be mentioned when you want somebody to answer your question.

So pls be specific,to get some clue.

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Old   August 31, 2008, 02:49
Default Re: Frustrating puzzles on compressor modeling
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Thanks for your reply, Pankaj.

The compressor is an air compressor, so the fluid is air ideal gas.The inlet total pressure is 1 bar, and mass flow rate is 1 kg/s.

The rotation speed is 42000 RPM. And I defined the rotor as rotating, while others as stationary. Wall velocity of Shroud is defined as Conuter Rotating Wall because it did not move with the wheel.

In addition, this condition point lies just at the center line of the compressor map. IT SHOULD BE A VERY STABLE CONDITION.

Expecting replys. Many thanks to all of you!

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Old   September 2, 2008, 06:44
Default Re: Frustrating puzzles on compressor modeling
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Dear Rikio,

I was asking abt centrifugal or any other type? As it is Centrifugal one,velocity will increase in passage but at the cost of RPM and respective dia.

So velocity will increase and pressure will also rise but that is design dependent,otherwise it will rise in Diffuser and volute.

You increase your RPm step by step,means first try with low speeds,if getting results,then go ahead. What ref pressure you r using? if its 1 atm then Static pressure at suction is Total-ref-(rho*vel^2/2) in Pa.

Otherwise it may be a surging condition,try with 25% additional flowrate,or more.

There may be too many issues with design,physics or modelling.Try one by one to get results.

Hope u solve it.

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