Abstract
For centrifugal compressors used in automotive turbochargers, it becomes very important to suppress the compressor
surge because of a demand of higher boost at lower engine speed, i.e., smaller mass flow rate. In order to clarify the cause
of compressor surge, authors investigated two different compressors which have different surge characteristics by measur-
ing wall static pressures at diffuser exit. It was revealed that surge occurred in the diffuser for both compressors and the
scroll induce a positive pressure gradient locally. These may increase the compressor instability near the surgefor the
compressor which has larger surgemass flow rate. In this paper, oil flow visualizations and numerical simulations were
conducted to clarify the relationship between compressor instability and internal flow. Oil flow visualizations and CFD
results show reverse flow occurs near the tongue at small mass flow rate for the compressor which has larger surge mass
flow rate and the reverse flow induces positive pressure gradient locally.
