To run the case files, the mesh need not be imported. The polymesh is already contained of the mesh files in OpenFOAM readable format. Still if mesh needs to be imported, copy paste the appropriate mesh file from "meshFiles" folder into the caseFiles folder and use "fluent3DMeshToFoam" command to convert the fluent mesh to foam

Decompose the case appropriately using "decomposePar" command. 
To run the simulation, use "buoyantSimpleFoam" command.
To reconstruct the case after simulation, use "reconstructPar -latestTime" command.

Post-Process using paraView by opening the para.foam file. 