Unsteady response of performance for centrifugal compressor under pulsating backpressure condition

Abstract

The intermittent throttling effects of intake valves of internal combustion engine generate pulsations at compressor exit, which has a great impact on the compressor performance. In this paper, the influence of pulsation on the compressor is studied via unsteady 3-D numerical method validated by experiments. Results show that the cycle-average efficiency is lower than the quasi-steady value. The impeller is confirmed as the main reason for efficiency deterioration according to entropy generation analysis, due to the difference of secondary flow patterns. The tip leakage vortex at impeller inlet is alleviated at pulsating condition because of inertia effect, resulting in a lower velocity thus higher incidence angle near splitter. The stronger separation and tip leakage flow at splitter leading edge lead to the wake with higher losses. Moreover, the circumferential distortion at the impeller exit is found to be weaker under pulsation. It is caused by two reasons: the flow field, which is closer to the quasi-steady one with a higher mass flow rate due to the lagging effect; the additional pressure gradient in volute caused by propagation of pulse. It results in an evener flow field and improves impeller stability. Specifically, the recirculation region at impeller inlet shrinks 5% under pulsation.