A:Inquiry of boundary conditions for rotating wall
 

I am working on a flow meter model which is in cyllindrial shape. The gears are mounted inside the casing. They are free to rotate. The mass flow rate at the inlet is known quantity. Due to this mass flow the gears rotate with certain rpm. I want to determine the rpm of the gear. what would be my boundary condition for the gears so that it will rotate freely due to the fluid flowing accross it. Please tell me the best possible approach for my case. Thanks. I appriciate yourtime. Gaurav S Ranzekar