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-   -   simulate the cavity bottom of the offset (http://www.cfd-online.com/Forums/flow-3d/116008-simulate-cavity-bottom-offset.html)

flow_CH April 11, 2013 00:04

simulate the cavity bottom of the offset
 
1 Attachment(s)
I want to know can flow3d simulate the cavity bottom of the offset? with Increasing or decreasing the air rate into the ramp.
see this pic.(immediately please)

flow_CH April 12, 2013 06:46

2 Attachment(s)
please help.
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

JBurnham April 23, 2013 12:00

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.

flow_CH April 26, 2013 09:32

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.

jarrysimon123 May 21, 2013 06:45

thnx
 
Quote:

Originally Posted by JBurnham (Post 422655)
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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