Problems with boundary conditions - velocity and pressure not zero
 

Hello,
I have a problem with boundary conditions. I have four channels. In the inlet section, two of the channels have an inlet where gas enters, the other two channels are closed (it is a wall). In the outlet section the two channels with open inlets are closed (wall) and the channels with closed inlets are open. It this way the gas enters in the inlet section and then it is forced trough the wall between the channels and exits in the outlet section. A wall-flow system.

The problem is that in the outlet section in the channels that are closed the velocity of the gas should be zero, because I have the boundary condition "wall" here. However, it is not zero, but varies between 1-6 m/s depending on the temperature. What can I do to have zero velocity here?

In the channels in the outlet section that are opend the pressure should be zero since I have atmospheric pressure in the surrounding, and I have put Gauss pressure =0. Neither in this case the boundary conditions are correct. In the outlet channel I have a pressure of approx 700 Pa, in the beginning of the channel, and in the outlet (the end of the channel) I have approx 200 Pa, here it should be zero. What can I do to have a pressure that is zero here?

With kindest regards Mikaela