# simulate the cavity bottom of the offset

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April 11, 2013, 00:04
simulate the cavity bottom of the offset
#1
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Saeed
Join Date: Jan 2013
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I want to know can flow3d simulate the cavity bottom of the offset? with Increasing or decreasing the air rate into the ramp.
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April 12, 2013, 06:46
#2
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Saeed
Join Date: Jan 2013
Posts: 177
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I mean that can we inject secondary fluid like air into the working mesh in flow3d? ( defining second point for inlet fluid) see attached pic
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Last edited by flow_CH; April 14, 2013 at 05:46.

 April 23, 2013, 12:00 #3 Senior Member   Jeff Burnham Join Date: Apr 2010 Posts: 204 Rep Power: 10 Yes. You can do that. Create a new hole subcomponent so that the cavity is connected to the z-min boundary. Make the z-min and z-max boundaries pressure-type with fluid fraction = 0 (the pressure is for 'void', that is, air). Turn on bubble/phase-change physics (adiabatic bubbles). Set all pressures (boundary and initial) to absolute (that is, atmospheric pressure = 101325 Pa) and set the boundary above the flow (z-max) to be atmospheric. This is because the adiabatic bubble model uses ideal gas law and so pressure cannot be negative anywhere. Keep using air entrainment physics, preferably with a calibrated entrainment rate coefficient. Vary the pressure at the z-min boundary to change the supply rate to the jet. Good luck.

 April 26, 2013, 09:32 #4 Senior Member   Saeed Join Date: Jan 2013 Posts: 177 Rep Power: 6 thanks for your reply. 1- why hole subcomponent? i want to simulate all of the spillway in solid. 2- for calibrating the project i have to know negative pressure and the only reason for suction air into the air slot is negative pressure into the cavity and then can flow 3d show the negative pressure? because my friend said me it can't show negative pressure where the water is not exist. Last edited by flow_CH; April 30, 2013 at 10:35.

May 21, 2013, 06:45
thnx
#5
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Jarry Simon
Join Date: May 2013
Location: UK
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Quote:
 Originally Posted by JBurnham Yes. You can do that. Create a new hole subcomponent so that the cavity is connected to the z-min boundary. Make the z-min and z-max boundaries pressure-type with fluid fraction = 0 (the pressure is for 'void', that is, air). Turn on bubble/phase-change physics (adiabatic bubbles). Set all pressures (boundary and initial) to absolute (that is, atmospheric pressure = 101325 Pa) and set the boundary above the flow (z-max) to be atmospheric. This is because the adiabatic bubble model uses ideal gas law and so pressure cannot be negative anywhere. Keep using air entrainment physics, preferably with a calibrated entrainment rate coefficient. Vary the pressure at the z-min boundary to change the supply rate to the jet. Good luck.
thanx JBurnham

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