[nikos_]

Good Evening. I study a case of a film of fluid (oil) that is being squeezing and rotated simultaneously by 2 disks (top and bottom). In the attached files there is my geometry and mesh. The 2 disks move both in z direction ( in the presence of an axial velocity) and in theta direction ( in the presence of an circumferential velocity u_theta=angular_velocity * radius). Therefore I have a combination of couette and hagen poiseuille flow. The thickness of the film is 1.5 mm and the outflow of fluid ( squeeze out) is happening at inner and outer radius.

The boundary conditions I insert to Ansys are the following :

Top Disk: Moving wall- Components : Constant u_z and velocity field u_x and u_y which has been occurred by analyzing circumferential velocity to Cartesian coordinates (Ansys doesn’t allow giving a combination of moving and rotational wall, neither giving velocity components in polar coordinates).

Bottom Disk: Moving wall- Components : Constant u_z and velocity field u_x and u_y which has been occurred by analyzing circumferential velocity to Cartesian coordinates (reverse direction of circumferuntial velocity of the Top Disk ).

Inner Radius : Pressure outlet at 101325 Pa

Outer Radius : Pressure outlet at 101325 Pa

The main problem is that Ansys can’t solve the case because continuity equation can’t be converged. There is reversed flow in both Pressure Outlets and I can’t understand why.

Do you have any idea why this is happening and how to overcome it ? I have try many combinations of finite elements focusing mainly in the elements near outlets but still problem can't be solved.

Thank you a lot in advance!

Ps: I import the x,y velocity field in ansys top and bot disks by a point type profile. In a script I generate N random points and calculate the velocity components, then print them to a file.profile which I import to ansys.