Pressure recovery in a turbocharger compressor volute

The diffusion and pressure recovery in a centrifugal compressor stage is normally accomplished in the diffuser (vaned or vaneless) downstream of the impeller and, at the design flowrate, the volute is designed to collect the gas flow without further diffusion. It is, however, well established that at high flowrates the gas accelerates around the volute and as a consequence the pressure decreases, while at flowrates less than that at design the gas decelerates and a pressure rise occurs. There is little published material with respect to the detailed design of volutes, and the procedure is largely one of experience based on previous designs and tests. This investigation describes the performance of the volute with both a vaneless diffuser and a series of low solidity vaned diffusers upstream. It is shown that the volute provides a significant pressure rise at the best efficiency point and at flowrates down to full surge. It is shown that the volute performance is a function of inlet flow angle and that it plays a significant role in setting both the best efficiency flowrate and the operating range of the compressor.