[Jacob Jensen]

Has anyone come across boundary conditions in OpenFoam that impose anti-symmetric periodicity …

An anti-symmetric periodic boundary condition is just like periodic boundary conditions only swapped or mirrored … i.e.

u(x, y)=u(x+L, ymax-y)
v(x, y)=-v(x+L, ymax-y)
p(x, y)=p(x+L, ymax-y)

rather then (pure periodicity):

u(x, y)=u(x+L, y)
v(x, y)=v(x+L, y)
p(x, y)=p(x+L, y)

here u =velocity in x, v = velocity in y, p=pressure, x and y coordinates where y[0, ymax].

The boundary condition is described in “ON THE IMPLEMENTATION OF SYMMETRIC AND ANTISYMMETRIC PERIODIC BOUNDARY CONDITIONS
FOR INCOMPRESSIBLE FLOW” by GUUS SEGAL, KEES VUIK AND KEES KASSELS.

[olegrog]

Cyclic boundary conditions can be used in this case.

[Fredo]

Originally Posted by olegrog

Cyclic boundary conditions can be used in this case.

Hello,

yes they can, but then you need a cyclic geometry.

Let me explain my case :
I have a cubic domain which describe a porous media (liquid and solid). Only the liquid phase is meshed. Since the media is pretty random, the faces of my cube do not have the same mesh.
To apply a cyclic boundary conditions (because that's what I want), I mirror the mesh in the x, y and finally z directions.
I have then a cube 8 times bigger than my initial cube with all the same faces.
I can then use cyclic boundary.

But, I compute 7 times something I am not really interessted in.
If I could apply antisymmetric periodicity, that would save a lot a time.

Do you have any suggestions ?

Fred.

[Cyp]

Hi Fredo,

What I do in this case: I had a thin layer of cells surrounding my domain. Like that I can impose cyclic boundary conditions.

The two main problems when mirroring the domain: 1) it significantly increases the number of cells, 2) it biases the anisotropy (primordial for permeability estimation!).

[Fredo]

Hi Cyp,

thank you for this quick reply. Your solution seems very relevant ! Did you quantify the errors induced by this thin layer. My media is not very percolating so I fear that all the fluid goes through this thin layer.

I will try and keep you updated.

Fred.