The direct simulation of impellers with complex geometrical shapes has not yet been presented. The unstructured mesh with a multiple reference frame approach has to be used to model the system with complete fidelity. The ability of a new CFD unstructured package is investigated in a cylindrical baffled tank stirred by an industrial LUMPP LB propeller in turbulent flow. Different positions of the blade relative to the side-wall baffles have been computed to study the time-dependent flow fields. The computational results compared favourably with experimental LDA data, with pumping number and power number, but a great care should be put on the mesh quality since results are extremely sensitive. It is concluded that the multiple reference frame approach is suitable to design impeller optimized for a given application.