Effects of tapered diffuser vane on the flow field and noise of a centrifugal compressor

The effects of a three-dimensional tapered diffuser vane on the flow field and noise radiated from a centrifugal compressor are investigated by both CFD analyses and experiments. Tapered diffuser vanes are very useful not only for the reduction of the interaction tone noise but also for the improvement of the pressure recovery characteristics within the diffuser passage. By using tapered diffuser vanes, the interaction area between the impeller-discharge flow and diffuser vanes becomes small, and then the noise level of the discrete tone can be reduced remarkably as a result. Furthermore, by utilizing the visualization technique of vortical structures based on the CFD results, the scale of vortex shedding leaving from the leading edge of the diffuser vanes is found to be contracted and a tendency for the turbulence level to decrease is observed. This may be the cause of the attenuation of broadband noise components. The secondary flow, which is considered to be an obstruction of diffuser pressure recovery, can also be suppressed by the tapered diffuser vanes, and the pressure decrease observed in the throat part of the diffuser passage is further reducible.