Study on Performance Characteristics near Surge of a Centrifugal Compressor

Abstract

For centrifugal compressors used in automotive turbochargers, it becomes very important to improve the compressor efficiency and to suppress the compressor surge because of a demand of high boosting at lower engine speed, i.e., smaller mass flow rate. In order to clarify the cause of compressor surge, two different compressors which have different surge characteristics were investigated by both experimental and numerical procedures. In the experimental approach, compressor performance characteristics beyond usual surge line were obtained by setting an orifice at the compressor exit, and wall static pressures were measured at impeller leading edge, trailing edge and diffuser exit respectively. As the numerical approach, compressor full-domain CFD analyses which include impeller and scroll were also conducted for above two compressors. Experimental and CFD results show circumferential pressure distributions in a diffuser and a scroll induce a positive pressure gradient locally and these may increase the compressor instability near the surge for the compressor which has larger surge mass flow rate.