If you are new to CFD then I suggest you first review "Overview: Geometry To Results" and then try a basic Caedium RANS Flow tutorial.

For your specific example you will need a flow domain and physics similar to the tutorial "Flow Over a Rotating Wheel with Moving Ground", minus the wheel and moving ground. Within your box you will need to subtract the geometry for your 'hollow structures' and at the base of each assign Conditions->Inlet from the Physics Tool Palette. For each plume inlet you will need to set the specific inlet velocity - Physics:Inlet->Type:Default->U = Surface Normal, Speed = the speed perpendicular to the plume inlet faces.