Zero gradient pressure
 

Hi all,

I have a geometry of two paralell plates with a whole in the middle (like two paralell CDs). One of these plates is rotating, and the axis of rotation is in the middle of the geometry. The figure can be seen here: https://drive.google.com/open?id=1DB...dp8UQurfpQ67Fz.

I would like to use a zero pressure gradient as boundary condition. Consider that the inlet BC is the small space between the parallel plates closer to the middle of the geometry (the inner radius). The outlet is the space between the parallel plates at the far end of the geometry (the outer diameter).

I have used an Inlet Pressure BC equal to zero (gauge total pressure) and at the outlet I have used an Outlet Pressure BC equal to zero (gauge pressure).

However, I am getting a very weird result: when I check the mass flow rate at the inlet, I get a negative value and at the outlet, a positive value. It is like fluid is going to the outer radius from the inner radius. The radial velocity component also confirms this behaviour.

Does anyone know why this is happening?

Thanks in advance for any help!