Pressure boundary conditions in cyclic geometery
 

Hello,

I am trying to solve a simple laminar flow problem using icoFoam. The physical problem is flow through an axi-symmetric tube with walls represented in a periodic fashion (eg cosine function). In other words, this is a 2D flow problem with the radius of the tube varying in a periodic fashion as a function of z, the distance along the tube. Also, the flow is driven by a constant pressure drop between the ends of the tube.

I would have thought that I could solve this problem by studying flow in the tube over one period in the z direction. Also, I could scale the problem so that there is a unit pressure drop over that period.

I have created a mesh in a wedge shape using gmsh, as described in the tutorial on axi-symmetric flows. I have used wedge patches in the theta direction, inlet and outlet patches in the z direction and a wall patch in the r direction. Also, I have used cyclicAMI conditions in the boundary file for the inlet and outlet patches and this presents no problem.

I assumed that it was reasonable to apply cyclicAMI boundary conditions on the velocity U on the inlet and outlet patches. However, I am not sure what to use for the pressure boundary condition on these patches. I have tried to use fixedjumpAMI, but I am not not sure if I am doing it correctly. Although the simulation runs, nothing happens.

I realise this is a rather wordy description of my problem, but at this stage I am not sure what is the most relevant further information to provide. I can provide mesh pictures and/or various input files.

I also realise that there are many posts on cyclic boundary conditions, but I cannot seem to see how they apply to my problem. I have looked at the channel345 (not sure of the correct number) problem, but cannot see the relevance to my problem.

I would be grateful for any advice and can provide further relevant information upon request.

Thanks very much,

Peter.