Outflow Bocos

Romuald Skoda

I am investigating the flow field through turbomachinery with complex geometry with an incompressible NS solver (pressure correction scheme). I have the problem, that the space between the trailing edge and the domain outflow border is quite narrow. This is due to a coupling algorithm which is applied to connect two stages of the machine in a stationary manner. So the distance between the leading edge of the first stage and the trailing edge of the second is narrow. The trailing edge has been cut off, that the flow sees a blunt body immediately in front of the outflow. Now the question arises what boundary conditions are suitable at the domain outflow. The narrow inflow area does not seem to be critical, but at the outflow the solver has serious problems. At the moment I have implemented two kinds of BoCos at the outflow: - dirlichet Pressure bocos (i.e. the pressure is precribed and the pressure correction is set to zero) - Neuman bocos (velocities are extrapolated and scaled in a way that they match the inflow mass flux. Prssure correction is extrapolated at the outflow.)

Both Bocos work well for a long area between trailing edge and outflow, but do not work at all for my problem. I am grateful for any hint! Thank you very much.