
[Sponsors] 
change boundary conditions on interface in VOF model 

LinkBack  Thread Tools  Search this Thread  Display Modes 
June 30, 2014, 08:07 
change boundary conditions on interface in VOF model

#1 
New Member
Mayank Jain
Join Date: Jun 2014
Posts: 3
Rep Power: 11 
Hi
How can i apply boundary conditions at the interface(moving) between fluids in VOF model. for ex. the interface should always have certain value of a scalar 

April 29, 2020, 06:00 

#2  
Member
James
Join Date: Jan 2014
Posts: 38
Rep Power: 12 
Quote:
Hi Mayank, It has been quite sometime but if you recall this, were you able to implement the BC on the interface? Could you please suggest? Thanks. 

April 29, 2020, 11:58 
Free Surface

#3 
Senior Member

Usually, no boundary condition is required to be applied at the free surface or interface between two fluids in VOF. All the fluxes are conserved at the interface and boundary specification could lead to conservation issues. However, if this needs to be done, then it has to be applied either as a source term or as flux since the interface is not a real boundary.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. 

April 29, 2020, 15:40 

#4 
Member
James
Join Date: Jan 2014
Posts: 38
Rep Power: 12 
Hi Venerm,
Thanks for your reply. And I agree with you. I have applied BC on the interface as a source term in the past. e.g. heat source on the metal surface as a surface heat flux. But in this particular case, I can't implement it as a flux on the surface. And in order to solve this equation, I know the condition that should be satidfied on the interface. Well, in literature people have computed by applying this BC on top of the domain but it gives very small magnitude of the forces on the interface. I have detailed my issue with graphics, equation and BC on this post (at the end). Would you please have a look at it? Interface boundary conditions in chtMultiRegionFoam Thanks! 

April 29, 2020, 15:52 
Interface

#5 
Senior Member

It appears that the meaning of the interface is different for both of us. In my post, interface implies fluidfluid interface, such as, free surface of water in a partially filled vessel. In your post, you seem to be talking about FluidSolid Interface, which is a real wall, a real physical boundary for the flow. It is easier to apply condition for a scalar on physical boundary than on fluidfluid interface. I do not know how OpenFOAM handles it but in Fluent you can apply value for a scalar at the fluidsolid interface.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. 

April 29, 2020, 17:25 

#6 
Member
James
Join Date: Jan 2014
Posts: 38
Rep Power: 12 
Hi Vinerm again,
Well, It is indeed free surface interface. But at the initial condition, the metal in my case is treated as a fluid with very high viscosity. As temperature increases upto melting temperature and phase change occurs, then we will get real fluiffluid free surface interface. Ideally, the condition should satisfy on the free surface interface at each time step. But meanwhile my assumption is that the free surface deformation is not large enough to cause significant change in the term I am interested in. That's why I only need to initialize the force and use it as a constant body force in my momentum equation. Thanks! 

April 30, 2020, 05:44 
Body Force

#7 
Senior Member

I am afraid I could not understand what do you mean by body force at the interface. Which body force are you talking about?
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. 

April 30, 2020, 05:55 

#8 
Member
James
Join Date: Jan 2014
Posts: 38
Rep Power: 12 
Sorry for I was not very clear in my earlier post.
In my other post, when I solve the equation of electric potential with the BC on the interface. It eventually generates electromagnetic body force. The concern for now is to solve the equation of electric potential only as the other term to generate electromagnetic force depends on the electric potential. 

April 30, 2020, 06:00 
BC at Interface

#9 
Senior Member

Let me rephrase to be clear
You want to apply an electric potential at a fluidfluid interface. Is that correct?
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. 

April 30, 2020, 06:03 

#10 
Member
James
Join Date: Jan 2014
Posts: 38
Rep Power: 12 
Yes, that's correct. The gradient of electric potential at the fluidfluid interface is a known value that I want to apply.
regards, 

April 30, 2020, 06:19 
Gradient

#11 
Senior Member

Well, gradient implies flux. Now, there are two possible scenarios
1. In one of the phases, say, solid phase, the electric potential field is more or less constant. Then, the life becomes easier. You can simply apply a constant value in whole of that phase. The gradient will be calculated automatically and field calculated. 2. If that is not the case, then you will have to determine value using the gradient since directly apply the value of gradient could cause issues. So, determine the field values from the gradient and then apply the values in each phase around the interface. Or, using divergence theorem, similar to what is done for surface tension force model, convert this into volumetric force and apply source value.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. 

May 4, 2020, 11:17 

#12 
Member
James
Join Date: Jan 2014
Posts: 38
Rep Power: 12 
Hi,
Electric potential is not constant in thw whole domain. Electrical conductivity is. Electrical conductivity is needed to calculate electric potential. The latter option using the divergence theorem seems to be doing the trick. I am exploring into it. Thanks. 

Tags 
vof model 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
mass flow in is not equal to mass flow out  saii  CFX  12  March 19, 2018 05:21 
Multiphase simulation of bubble rising  Niru  CFX  5  November 25, 2014 13:57 
Low Mixing time Problem  Mavier  CFX  5  April 29, 2013 00:00 
VOF Model Boundary Conditions  Blue  FLUENT  2  March 6, 2013 13:42 
Water vapour condensation in CFX5.7.1  hdj  CFX  1  November 27, 2005 07:15 