[ALLEN_Wang]

The 2D picture below showing what I am trying to do:the circle represents a viscous tolune sphere fixed in the water fluid zone,and water runs past the sphere at a certain velocity. Due to viscous force, the fluid inside the sphere will have a certain velocity, but how could I fix the sphere in the moving fluid without defineing the interface as wall boundary condition? Because WALL boundary doesen't transform the viscous force across the interface, hence there would not be internal circulation inside the sphere.