two phase model with CICSAM vof method

hilllike · September 9, 2011, 00:47

hi,
I wrote a 3d two phase model code based on a explicit projection method and there are some problems in my model.
In this model I didn't use surface tension model.

when I calculate the dam breaking case, there is velocity that is normal to the free surface and the stability is very bad.

Can anybody help me? I have tried many methods, (using 4 types of linear solver), but the result doesn't become better.

By the way,the most biggest residual locate at the corner.

Thank all.

HectorRedal · September 12, 2011, 16:07

One question.
Why are you not using surface tension?
From my point of view, you should consider surface tension between the two fluids. If no surface tension is considered, then no balance term for normal velocity will be present, and a lot of instabilities will appear.

You can give a try and see what happens when surface tension is consiered.

hilllike · September 15, 2011, 02:43

HectorRedal,
Thanks for your reply.
I think surface tension term can be ignored,if the water and air are treated as a whole domain, and maybe make the result inaccurate because of a smearing problem around the surface.
I am not sure that it can affect the stability of model.
HectorRedal,can you tell me more about that.

Ren

HectorRedal · September 15, 2011, 16:10

All the models I know for simulating the interface between two inmiscible fluids take into account the surface tension between them.
I don't know which could be the effect of not considering the surface tension on the stability of flow.
Maybe, you can try to reduce the time step, so as to eliminate any instability because of the CFL condition.
This may be help.

The VOF method is classified as an inmersed boundary method. And, as far as I know, this is a one-fluid aproach, that approximates the properties at the interface as a proportional value of the properties of the fluid in contact.
In this case, the VOF method uses the area / volume ocupied by each fluid.
I think that this reduces the smearing problem.
Maybe I am wrong, but this is what I have understood from the references I have consulted.

hilllike · September 16, 2011, 00:40

I check the CFL number in every time step.

I know some model you said about the one phase model, and they don't need to consider the surface tension instead of a boundary condition is added at the free surface according to the continuity equation.

I red some paper about IB and IMM methods, and both of those method is adding a boundary condition at the surface by a additional force, my problem is my professor told me we don't need to consider this at the free surface,because it is very small.

Thanks for your good advise, I will try to add surface tension model and see what will happen.

HectorRedal · September 16, 2011, 04:25

Hi again,

First of all, I would like to say that I am just a beginner in the field of multiphase flows.
So if you professor has advised you to not consider the surface tension in this case and model, then, maybe I am wrong.
I have adquire some knowledge on the multiphase flows, mainly in the VOF and Front Traking method, focusing in the interaction between two fluids.
I have not been involved in developent of multiphase flow code for free surface flow.
I had developed a code using the Front Tracking method. And, in this code, I am considering the surface tension effect.

I am sorry for not being able to provide you with more information / support.

chinaduck · February 21, 2014, 14:31

Hell,
I hope you are doing well. I am writing a VOF code now. It based on Simple method. I have met the similar problem. The solver can compute the low density ratio problem, but when I change the the materials to be water and air, the problem simialr to yours show up?
Did you solve your problem? If you have any suggestions, do let me know.
Thanks,waititng for your reply!

Quote:

Originally Posted by hilllike

hi,
I wrote a 3d two phase model code based on a explicit projection method and there are some problems in my model.
In this model I didn't use surface tension model.

when I calculate the dam breaking case, there is velocity that is normal to the free surface and the stability is very bad.

Can anybody help me? I have tried many methods, (using 4 types of linear solver), but the result doesn't become better.

By the way,the most biggest residual locate at the corner.

Thank all.

September 9, 2011, 00:47	two phase model with CICSAM vof method	#1
hilllike Member Ren/Xingyue Join Date: Jan 2010 Location: Nagoya , Japan Posts: 44 Rep Power: 16	hi, I wrote a 3d two phase model code based on a explicit projection method and there are some problems in my model. In this model I didn't use surface tension model. when I calculate the dam breaking case, there is velocity that is normal to the free surface and the stability is very bad. Can anybody help me? I have tried many methods, (using 4 types of linear solver), but the result doesn't become better. By the way,the most biggest residual locate at the corner. Thank all.

September 12, 2011, 16:07		#2
HectorRedal Senior Member Hector Redal Join Date: Aug 2010 Location: Madrid, Spain Posts: 243 Rep Power: 16	One question. Why are you not using surface tension? From my point of view, you should consider surface tension between the two fluids. If no surface tension is considered, then no balance term for normal velocity will be present, and a lot of instabilities will appear. You can give a try and see what happens when surface tension is consiered. hilllike likes this.

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September 15, 2011, 02:43		#3
hilllike Member Ren/Xingyue Join Date: Jan 2010 Location: Nagoya , Japan Posts: 44 Rep Power: 16	HectorRedal, Thanks for your reply. I think surface tension term can be ignored,if the water and air are treated as a whole domain, and maybe make the result inaccurate because of a smearing problem around the surface. I am not sure that it can affect the stability of model. HectorRedal,can you tell me more about that. Ren

September 15, 2011, 16:10		#4
HectorRedal Senior Member Hector Redal Join Date: Aug 2010 Location: Madrid, Spain Posts: 243 Rep Power: 16	All the models I know for simulating the interface between two inmiscible fluids take into account the surface tension between them. I don't know which could be the effect of not considering the surface tension on the stability of flow. Maybe, you can try to reduce the time step, so as to eliminate any instability because of the CFL condition. This may be help. The VOF method is classified as an inmersed boundary method. And, as far as I know, this is a one-fluid aproach, that approximates the properties at the interface as a proportional value of the properties of the fluid in contact. In this case, the VOF method uses the area / volume ocupied by each fluid. I think that this reduces the smearing problem. Maybe I am wrong, but this is what I have understood from the references I have consulted.

September 16, 2011, 00:40		#5
hilllike Member Ren/Xingyue Join Date: Jan 2010 Location: Nagoya , Japan Posts: 44 Rep Power: 16	I check the CFL number in every time step. I know some model you said about the one phase model, and they don't need to consider the surface tension instead of a boundary condition is added at the free surface according to the continuity equation. I red some paper about IB and IMM methods, and both of those method is adding a boundary condition at the surface by a additional force, my problem is my professor told me we don't need to consider this at the free surface,because it is very small. Thanks for your good advise, I will try to add surface tension model and see what will happen.

September 16, 2011, 04:25		#6
HectorRedal Senior Member Hector Redal Join Date: Aug 2010 Location: Madrid, Spain Posts: 243 Rep Power: 16	Hi again, First of all, I would like to say that I am just a beginner in the field of multiphase flows. So if you professor has advised you to not consider the surface tension in this case and model, then, maybe I am wrong. I have adquire some knowledge on the multiphase flows, mainly in the VOF and Front Traking method, focusing in the interaction between two fluids. I have not been involved in developent of multiphase flow code for free surface flow. I had developed a code using the Front Tracking method. And, in this code, I am considering the surface tension effect. I am sorry for not being able to provide you with more information / support.