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outlet static pressure of a duct flow

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Old   December 17, 2007, 10:24
Default outlet static pressure of a duct flow
  #1
anhalimi
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Dear all,

Shld the outlet static pressure for a duct flow be zero?
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Old   December 17, 2007, 10:27
Default Re: outlet static pressure of a duct flow
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ag
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Only if you are flowing into a vacuum, or you have chosen a non-dimensionalization that results in zero non-dimensional pressure at that value of exit pressure.
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Old   December 17, 2007, 14:11
Default Re: outlet static pressure of a duct flow
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Barry
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Hi,

I have a similar question about the pressure BC. For an incompressible flow, can I arbitrarily set a static pressure value for the pressure outlet? Does the value I set affect the modelling result?

Regards,

Barry
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Old   December 18, 2007, 04:38
Default Re: outlet static pressure of a duct flow
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Mayur
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What is ur inlet condition? If it is vel. inlet then value of static pr. for incomp. flow will not have any effect on the flow(except for pr. values)
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Old   December 18, 2007, 06:07
Default Re: outlet static pressure of a duct flow
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anhalimi
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or you have chosen a non-dimensionalization that results in zero non-dimensional pressure at that value of exit pressure.

You mean taking the taking the absolute pressure as 0? as in just measuring the gauge pressure? or am i understanding this wrong

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Old   December 18, 2007, 09:59
Default Re: outlet static pressure of a duct flow
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ag
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If you are computing gage pressure then zero may be a valid value. Then your nondimensionalization would look something like

p_non = (p - p_baseline)/p_ref

where p_ref is the pressure used to non-dimensionalize the pressure variables and p_baseline is whatever baseline pressure you are computing gage pressure relative to. But absolute static pressure should not be zero, unless as noted above you are expanding into a perfect vacuum.
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Old   December 19, 2007, 01:32
Default Re: outlet static pressure of a duct flow
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Barry
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Could you please explain why the value of static pr. for incomp. flow will not have any effect on the flow if using velocity inlet BC?

Thanks,

Barry
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Old   December 19, 2007, 07:28
Default Re: outlet static pressure of a duct flow
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Mayur
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Is simple... for incomp. flows pr. enters the equation as only delta P ... so whatever be the absolute value the diffenence will remain the same and flow velocity will decide the pressure gradient... plz go through the analytical soultion of a pipe flow for a laminar case.
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