Boundary Conditions problem
 

I have developed a code to solve 2D Navier stokes equation in a channel.
I have used Immersed boundary method to simulate the vibration of a cantilever beam in the channel.
The problem is that i do not know the direction of flow.
So i can not specifiy which boundary to be inlet and which boundary to be outlet.
Thus, i have to set both of the boundary to be Open Boundary.
My question is:
Waht should be the pressure and velocity boundary conditions on both boundaries ???
Please Help me.

I assume that any flow created is going to be due to the vibration of the beam -- hence the open channel.

In that case,

jj = 1:ny
u(1,jj) = u(2,jj)
u(nx,jj) = u(nx-1,jj)

You get the idea.

i applied neumann boundary conditions for velocity
Dirichlet boundary conditions for pressure
P_inlet=0
p_outlet=0
The code works very well.

However, when i change the P_outlet to have a value for example 2 Pascal
the code fails and blow up.

Do you have any suggestions ??