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Old   October 6, 2005, 00:48
Default Negative Pressure
S Christopher
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I am simulating the entire pump model using CFX. In post processing results, there is a negative pressure around -4 bar (approx.). But Head delivered by the pump is correct.

The Inlet condition are Inlet dynamic pressure and outlet are velocity. Reference pressure is atmospheric. But still there is negative pressure. please give the reason?

If i want to know to exact magnitude of staic or absolute pressure near the blade surface, can i use the same value or some other method is used to find, if so please inform.

Since all pressure are measured from zero absolute pressure.
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Old   October 6, 2005, 08:43
Default Re: Negative Pressure
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With incompressible fluids the pressure is always relative. Unless your fluid properties change with pressure or you model cavitation, the reference pressure will have no effect on your solution. It is entirely possible to have very low pressures in this case.

If you were to activate cavitation, I think you would find that your pump is cavitating in the area where the pressure is low. If cavitation is turned on, the reference pressure will have an effect.

Regards, Robin
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Old   October 6, 2005, 18:14
Default Re: Negative Pressure
Glenn Horrocks
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I agree with Robin, your pump is probably cavitating in reality. However if your pump simulation without cavitation is accurate then it is likely the cavitation is localised to a small region of the flow, and not having a major effect on the overall flow.

Regards, Glenn
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