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April 25, 2013, 10:21 
Degassing Boundary Condition

#1 
Senior Member
Aurelien Thinat
Join Date: Jul 2010
Posts: 165
Rep Power: 8 
Hello everyone,
I'm looking for a way to model a degassing boundary condition for twoPhaseEulerFoam solver. The case : Air bubbles are injected at the bottom of a water tank, free surface at the top. As far as I know I have three options : 1) Compute the interface of the free surface. 2) Slip wall at the BC and add a negative source term in the alpha equation and pressure equation at the last cell before the BC. Something like : S =  alpha/time_step. How should I modify the momentum equation ? I guess I have to include a source term in the momentum equation too. 3) Find a boundary condition setup as there is on Fluent or CFX. But I could'nt find any litterature on this subject. I have already tested a setup and I'm not really happy with the result: p : fixedValue alpha : inletOutlet Ua : zeroGradient Ub : surfaceNormalFixedValue : 0 Do you have any tips on how to manage this kind of problem ? 

October 29, 2013, 06:15 
degassing BC

#2 
Member
Jeong Kim
Join Date: Feb 2010
Posts: 42
Rep Power: 8 
I'm also looking for this BC available for twoPhaseEulerFoam.
That'd be very appreciated if you give me some idea on how to implement this BC or share a source code with me.^^ Thanks in advance for your big help. 

October 31, 2013, 04:39 

#3 
Senior Member
Aurelien Thinat
Join Date: Jul 2010
Posts: 165
Rep Power: 8 
Hi Enoch,
There are 2 ways of dealing with that as far as I know :  slip wall for the continuous phase and free stream for the dispersed one. I had few problems with this in OpenFoam2.1.1. Since OF2.2 release, it seems ok.  source term applied at the first cells near your degassing BC. At each time step you extract the mass of the dispersed phase (something like : alpha 1 * rho1 / DT). You'll have to modify the pressure equation and add source terms in the momentum equations. I'm not fond of this but well...it does the trick. 

April 21, 2016, 10:25 

#4  
New Member

Quote:
About the first option  Slip wall for the continuous phase is understood, but why free stream for the dispersed phase? I mean one can use pressureInletOutletVelocity or inletOutlet too. About the second option  Do you have any reference for this option? I haven't found much about making changes in the source code to implement degassing BC (except for the CFX Tutorial on UDFs, which does something similar to what you mentioned above). 

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