Experimental investigation of surge and stall in a turbocharger centrifugal compressor with a vaned diffuser

The stable flow range of a compressor is dominantly limited by flow instability, known as surge and stall. In this paper, surge and stall in a turbocharger centrifugal compressor with a vaned diffuser are investigated by experiments. The transitional process from stable to unstable conditions is quite different at different rotating speeds. With decreasing mass flow rate, the compressor successively experiences stable conditions and deep surge at low speed, while the compressor experiences stable conditions, mild surge and deep surge at high speed. During experiments, deep surge occurs at all tested rotating speeds with different characteristics and behavior, and a deep surge cycle includes three periods, named recovery period, oscillation period and breakdown period. The dynamic experimental signal shows that pressure behavior in the oscillation period differs at different rotating speeds: high frequency fluctuation occurs at low speed, while mild surge appears at high speed. Mild surge occurs independently or appears within a deep surge cycle with a frequency close to the Helmholtz resonant frequency of the compression system. The behavior of mild surge at the vaned diffuser inlet is different along the circumferential direction, which is a subversion of the conventional view that surge is an axisymmetric phenomenon. It is highly possible that the non-axisymmetric behavior of mild surge is induced by the volute. Because the volute affects the flow field structure significantly, a new volute design method considering the circumferential non-uniformity of the flow field may be established and developed to improve the compressor stability.