When combining different mesh files from different mesh cells into one Ansys Fluent cell, Ansys Fluent assigns 'solid' type to all cell zones even though these were designated as 'fluid' in meshing.
Too keep Ansys Fluent from assigning a 'solid' type to all cell zones, use Named Selections in meshing and give the fluid zone names a prefix such as 'fluid_' to these named selections.
One this is done, Ansys Fluent will assign 'Fluid' type to cell zones.