Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers are discussed by experiments, numerical simulation as well as visualization techniques using oil-film method. The focus of the research is concentrated on the pressure recovery characteristics within a vaned diffuser passage which is deeply influenced by diffuser vane geometries. By using the presented tapered diffuser vanes, a decrement of the pressure recovery characteristics occurred in the vicinity of the throat part of the diffuser passage can be successfully avoided, and also pressure drop due to the secondary flow recognized near the trailing edge of the diffuser vanes can also be suppressed. Furthermore, not only the sound pressure level of the interaction tone noise but also that of the broadband components can be attenuated effectively by using the tapered diffuser vanes.
