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Changing pressure at boundary conditions

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Old   February 1, 2021, 21:12
Default Changing pressure at boundary conditions
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Joseph
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Hello All,

I am running a simulation of water flowing through a pipe of small diameter (321 micrometers). The boundary conditions I am using for my inlet and outlet are a Stagnation Inlet of 4000 Pa and a Pressure Outlet of 0 Pa, respectively. As I run the simulation, my outlet pressure remains constant, but the inlet pressure dives from 4000 Pa to 2900 Pa (see attached picture). As I understand it (and I may be completely wrong), the boundary conditions should remain constant throughout the simulation. Does anyone have an explanation of why it may be dropping? Also, is there a better way to apply a constant pressure at the inlet? Thank you all so very much for your help!
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Old   February 2, 2021, 12:45
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Stagnation Inlet imposes Total Pressure, i.e. your 4000 Pa = Static Pressure + ρ·vē/2.
So as velocity develops at inlet - part of 4000 Pa is "stolen" for Dynamic Pressure (ρ·vē/2) and Pressure that you monitor is the remaining Static Pressure term in your case (it is actually piezometric pressure in general).
You can check that by monitoring Total Pressure function at the inlet the same way - it should be 4000 Pa.
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Old   February 3, 2021, 17:28
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Oh, I should have thought about that. Thank you for pointing that out!
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