The Experimental Study of Matching Between Centrifugal Compressor Impellers and Vaneless Diffusers for Turbochargers

The operating range of centrifugal compressors for turbochargers using vaneless diffuser is considered from measurements of the separate pressure rise of the impeller and the diffuser. In some cases, the peak pressure rise of the stage corresponds to the peak pressure rise of the impeller (which is considered to correspond to inducer stall). From these measurements a new correlation for the onset of inducer stall is proposed. In other cases the stability of the vaneless diffuser (defined as positive slope of the pressure rise versus flow characteristic) determines the stability of the stage. A 1D analysis of the pressure rise versus flow rate in a vaneless diffuser captures the main physical effects due to friction and provides a guide to the effect of design changes for increasing the range. Subsequent tests confirm that reduction of diffuser height is the most effective measure for reducing the surge flow rate.