# Coupled VOF and Multiphase Segregated Flow for a gas bubble problem??

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December 4, 2013, 13:27
Coupled VOF and Multiphase Segregated Flow for a gas bubble problem??
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Hi all,

I urgently need your help to overcome this problem. Thank you all in advance!!

Here, I need to simulate a single gas bubble moving from the bottom of a rectangular tank which is containing water, oil and air. I've already used Eulerian multiphase method to specify the volume fractions and positions of gas bubble, water, oil, and air by applying field functions. Since the surface of this gas bubble can be treated as no-slip wall and the gas bubble is deformable, that ensures the water will encapsulate the gas bubble when it starts to move upwards. Then I selected the "Wang curve fit" as the model of drag coefficient in the multiphase interaction. I have checked the user guide which says the "Wang curve fit" model is suitable for the deformable gas bubbles in multiphase fluid.

However, when I tried to initialize the simulation, an error happened to appear that "Uninitialized wall shear force on Boundary XXX(the boundary of the tank). Please initialize the solution or solve an iteration/time step." I never met this problem before and already tried to clear the solution. It didn't work though. Have anyone solved this problem before? Any ideas are welcomed!!

My goal of this analysis is to obtain the drag coefficient and the deformed diameter of the gas bubble until the gas bubble is rupture. That's why I focused on the drag coefficient of the gas bubble. Originally, I was just using VOF model in this analysis and modified the surface tension coefficient. I finally found out the gas bubble is over deformed and the water was mixing with the gas bubble instead of encapsulating it.

So, guys, please give me some ideas on how to realize this simulation. All opinions are appreciated!! I really need your helps!!

P.S: The picture of the initialized conditions of the analysis with VOF method is attached.

Many thanks!!
Enron
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 December 19, 2013, 09:41 #2 Senior Member     siamak rahimi ardkapan Join Date: Jul 2010 Location: Copenhagen, Denmark Posts: 218 Rep Power: 10 If you consider slip condition then STAR-CCM knows that wall shear force is zero. Since you have considered no-slip condition, then you need to give a number for wall shear force. __________________ Good luck Siamak

 Tags gas bubble, segregated flow, vof

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