I want to allow a fluid to flow in a closed circular loop at a particular flow rate or velocity. The closed loop will not have any inlet or outlet. One way of doing this problem is by MHD pumping. Is there any other way? Is it possible to assign a flow rate or velocity at the interfaces? I am using CFD-ACE+. Apparently CFD-ACE+ does not allow me to assign velocity or pressure or flow rate at the interfaces. Instead it allows only at inlets and outlets. Please inform me if any package allows to set flow rate or pressure at the interfaces.

Thanks John

I think what you need is a "periodic boundary condition" in which the conditions at your exit plane become the conditions at your inlet plane. This logically connects control volumes on opposite sides of the mesh. One way to force motion is to prescribe the body force (gravity, EMF, etc) on the fluid. If you need a particular flow rate, you can adjust the strength of the body force until the flow meets your requirements.

I'm aware that at least one commercial code allows these kinds of specifications.

Hope this helps.

It is possible to apply volume forces to the flow using user coding.

So no interfaces/bc are required at all.