# Degassing Boundary Condition

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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 OpenFoam-2.1.1. Since OF-2.2 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
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Jigar Parekh
Join Date: Jul 2015
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Quote:
 Originally Posted by Aurelien Thinat 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 OpenFoam-2.1.1. Since OF-2.2 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.
Hi Aurelien,

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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