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Definition of pressure

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Old   August 15, 2001, 13:31
Default Definition of pressure
  #1
Ola Nordblom
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Hi,

I found the information given in the Fluent manual about pressure boundary conditions rather confusing. Can someone try to explain how the calculated pressure in FLUENT is defined, and how the hydrostatic pressure comes into the picture? I assume that my flow problem is incompressible.

Usually the hydrostatic pressure field is subtracted from the N.S. Equations in order to include the hydrostatic head into the body force term. The new pressure variable will then be equal to the basic one minus the hydrostatic pressure (based on some reference density). However, from the FLUENT manuals I get the impression that FLUENT adds the hydrostatic pressure, and that the solved pressure field will include the hydrostatic head. The manuals then say that the inputs of pressure at the boundary should not include hydrostatic pressure differences, which is confusing. Se the chapter about pressure boundary conditions.

Any information related to pressure definitions and pressure boundary conditions would be very helpful.

Thanks in advance,

Ola Nordblom
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Old   August 16, 2001, 15:58
Default Re: Definition of pressure
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Mary
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You define what your reference pressure is in the system. I always leave it at atmospheric. FLUENT does all its calcs with total absolute pressures. BUT, the inlet and outlet boundary conditions simply are the gage pressures relative to the reference. The manual is just letting you know that the software is programmed to assume you are entering gage pressure. As long as you enter in the correct reference pressure and boundary conditions, it will do the calcs from there.

good luck

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