Hi

I was wondering if anybody knew how I can stop backflow occuring at a pressure outlet? In my unsteady problem I have four ports that open one at a time and to simulate this I have a udf which changes the pressure at these pressure outlets. When a port is closed I set the pressure to be the same as the pressure inlet pressure as I do not know how to change the boundary condition to a wall. However, I get backflow from the "closed" ports which is completely messing up my results. How do I stop this from happening? Do I need to write a udf that changes the boundary condition from a pressure outlet to a wall and if so how do I do this?

Any help would be greatly appreciated. Dave

I have never done simulations during which the boundary conditions are varied. I guess backflow appears because the interior pressure based on last calculation is lower than the inlet pressure in the flow direction. Seting the outlet pressure=inlet pressure means the outlet pressure is higher than the interior too. That's why backflow appears.