stream function boundary condition for cylinder with slots on it
 

Hi.
I have written a code for flow field around a square cylinder.
The base of my code is written in vorticity stream function approach.
For calculation of stream function on the cylinder I have used "single pressure magnitude" for multi-connected domains. now it works properly. but after I decided to insert two slot on the top and down edge of square it dose not work any more. the down slot sucks the fluid and the upper slot blow the fluid by constant velocity. I was wondering is there any one who know how i can determine the right magnitude of stream function on the cylinder?
thanks
http://i56.tinypic.com/k1p192.jpg


http://www.4shared.com/photo/D3bXq-sB/untitled.html

See if I understand your problem. You have a 2D box with two symmetrically placed slots in the downstream face. The velocity is high enough that the box is shedding vortices. If shedding vortices, you would expect pressure near the slots to oscillate, the two slots more or less out of phase. Similarly, you would expect out-of-phase flow in and out of the slots.

If this is correct, then you would expect the value of the stream function on the surface between the slots to oscillate. This value would not be fixed by a static boundary condition, but rather would have to be determined as a part of the calculation.