4 Replies Latest reply on Jan 27, 2016 9:57 AM by Amit Katz

# Delta P vs Flowrate pipe flow problem.

I am trying to simulate pipe flow through a 5” Sch 10 pipe running vertically about ~14 feet as shown in attachments. I would like to first benchmark my Flow Simulation model against the same model in BOSFluids.  For a delta P of 2psi I expect to get an average flowrate of ~22 ft^3/s and an average velocity ~144 ft/s.  When I apply a boundary condition of 5 psi at the inlet surface and 3 psi at the outlet surface in Flow Simulation I get a an average velocity ~1000 ft/s.  Conversely, if I apply a flowrate of 22 ft^3/s at the inlet and 3psi at the outlet, the velocity is close to 144 ft/s but the delta P between the outlet and inlet surfaces is ~0.01 psi.  Can someone help with what I could be doing wrong with my Flow Simulation model?  My mesh is set at level 5 with ‘minimum gap size’ equal to 0.5*inside pipe radius and ‘minimum wall thickness’ equal to 0.5*pipe wall thickness with narrow channel refinement checked. Goals are selected for Av Velocity, Av Static and Av Total Pressure.

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Just to verify, you do have gravity turned on and in the correct direction?

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Yes, gravity is turned on in the -Y direction.

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Looking again, are you really interested in setting the Total Pressure at both ends?  I usually work in gauge so I'd have to think on that...

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Total pressure = pressure + dynamic pressure, so I don't think you'd be wanting to use that in this case.

Doing some quick back of the envelope your numbers are pretty confusing. I'm assuming you're using water. The hydrostatic pressure required to raise water to a  height of 14 ft is approximately 6.1 psi (http://www.wolframalpha.com/input/?i=density+of+water+*+9.81+m%2Fs%2Fs+*+14+ft+to+psi ), so where does that leave head for moving your flow?

On the other hand, if your fluid is air then the head loss is less than 0.008 psi, which means nearly all of your 2 psi difference is dynamic. If that's the case, then for air the expected velocity at the outlet would be around 480 ft/s (sqrt(2*2psi/density of air) - Wolfram|Alpha )