Hi All, I am modeling a simple problem, a baseball moving in a duct of air. I am imposing the flow on the ball (so the ball is stationary) and a rotational boundary condition on the ball (stationary but spinning). Was told to use an interface boundary condition on the ball, but Fluent spits out htat this condition is undefined. Any help? thanks

The ball itself is a wall... I think what they were telling you to do was to split a sphere from the main volume (connected option off) which was larger than the ball, add a spin to this volume, and then use an interface BC where the two volumes connect. An interface BC always needs a matching interface BC and then you need to tell Fluent to connect the two interfaces.

If you have split the volumes, then you must Define->Grid Interfaces (don't worry about coupled or periodic option, it's a straight forward interface).

The other option is to not bother with splitting the volume and define the wall of the ball as spinning.

Good luck, Jason