In Workbench you can use ICEM CFD (.cfx5) meshes for FLUENT, or .msh files (from gambit or TGrid) for CFX. When run in standalone mode, Fluent can also import meshes from a CFX setup (.def) or solution (.res) file. Meshes imported from CFX .def or .res files will inherit the region names created during CFX boundary condition definition. Please keep in mind that a default mesh created for CFX may be too coarse or otherwise inappropriate for FLUENT simulation. Check the mesh quality including skewness before conducting your runs.