Liquid BC wall no-slip, gas BC wall slip
 

Dear all,

I am carrying out a two phases VOF simulation and I would like to set a no-slip boundary condition for the liquid and a slip wall boundary condition for the air. Is it possible in FLUENT? I haven’t found how to do it…

Thanks a lot!

I do not think so, since the momentum equation is shared between the fluids (well not without udf anyway - with a udf you may be able to couple shear and volume fraction)

I'm curious to why you would like to do this however; since you resolve the bubbles, and any lubrication layer that may exist between them and the wall, what is the point of having different shearing behavior for one fluid than for another?

I want to do this because I'm doing something similar to the paper "Simulating injection moulding of microfeatured components T. Tofteberg1* and E. Andreassen1" and it says:

"At the walls we have applied no-slip conditions for the

polymer and free slip for the air." This was done using CFX.

Moreover, I have found in another thread (http://www.cfd-online.com/Forums/cfx...p-no-slip.html):

"Almost certainly you want the water phase to be no slip, but for some simulations you may wish the air phase to be free slip so you don't get wall function problems if the air drag is insignificant in the simulation. I think the CFX tutorials talk about this issue."

and they used VOF as well? When I do Euler-Euler, I indeed set the b.c. for air to no-shear, but that is because there in reality is a lubricating water layer and the air itself is not in contact with the wall. For free surface, a no-shear boundary also works because there is little shear between the water and free-flowing air.

But for VOF, when the air is directly in contact with the wall, the fact that there is little shear is already accounted by the low viscosity. But there is still direct contact, so there is still interaction. I don't see why you would want to change that. If there is a lubricating water layer between the droplet and the wall, it seems to me that that should be resolved.

The paper only says that they use "multiphase model", I assumed it was VOF...

You can download it here:

http://www.google.es/url?sa=t&rct=j&...HbYVnchyWdRUFQ

I doubt that it is, although the type of flow they are looking at calls for VoF. Anyway, I do not think a no-shear b.c. for the gas is in order here, considering the air phase is in contact with the wall and should interact with it if it is truly a wall. But if you do think it is, you will have to go for a UDF.

I have created a new thread with a doubt arised from what we talked here:

http://www.cfd-online.com/Forums/flu...-transfer.html