[Stephen Waite]

Hi everybody.

I need a bit of help with boundary conditions.

I am performing a 1-way fsi in fluent.

I have a balloon-like structure that contracts, expelling fluid out of an opening. This balloon then expands, drawing fluid back into the balloon through the same opening.

I am currently modelling this opening as a pressure-outlet boundary condition.

My model is converged but at the transition between contraction and expansion there is a discontinuity in the flow and pressure fields (i am assuming that the discontinuity in the flow is produced because of the pressure discontinuity).

I do not really understand how the pressure-outlet works I assumed it just set a 0 gauge pressure at the boundary and so was effectively and 'opening' condition like what is offered in CFX.

Does the pressure-outlet boundary have difficulty with revered flow? Can anyone think of a boundary condition that would be better for my model? I wanted to try pressure far-field but the option does not seems to be there. Any help is greatly appreciated.

I am using a coupled solver scheme, PRESTO! for the pressure interpolation and a second order upwind scheme for momentum.

Cheers
Stephen Waite