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Pressure inlet vs. Velocity inlet

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Old   October 31, 2018, 15:58
Default Pressure inlet vs. Velocity inlet
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Hamed Abdul Majeed
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Consider an incompressible pipe flow,

How can I ensure that these combinations give the same results:
1. Pressure inlet + Pressure outlet.
2. Velocity inlet + Pressure outlet.
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Old   October 31, 2018, 16:22
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Lucky
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They are much pretty guaranteed not to.

With a pressure inlet you impose a uniform stagnation pressure. The velocity profile is more or less guaranteed to be non-uniform except for very exceptional cases.

With a velocity inlet you impose a uniform velocity, and here you are pretty much guaranteed to get a non-uniform pressure profile. Again, except for very very exceptional cases.
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Old   November 2, 2018, 15:25
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Lee Strobel
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To add to what LuckyTran said:


A pressure-inlet is going to vary the velocity/mass flow to achieve the specified total pressure. A velocity-inlet is going to do the opposite and vary the total pressure to achieve the specified velocity.


If you do option #1; measure the average velocity on the inlet; and then apply that to the same geometry with option #2 (as a uniform velocity), you should get the same average total pressure on the inlet as in option #1, but, the distributions will be different (unless you save the velocity profile from case #1 and apply that in option #2, which would probably be the best way to achieve what you want).
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Old   November 4, 2018, 09:28
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It's possible (with other software) - you have to map the profile of the "other" boundary condition you want.
Run pressure inlet and write the velocity profile of the inlet and then map this profile to the velocity inlet condition to have the same pressure profile should work.

For quick simulations I prefer velocity inlet, for deep dive action the pressure inlet (to run a constant pressure difference).
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