Experimental study on unsteady flow field in a centrifugal compressor at pulsating backpressure conditions

Abstract

Centrifugal compressor is confronted by pulsating backpressure when coupled with turbocharged internal combustion engine. Few studies have been reported on the understanding of pulsating flow field in the compressor although its performance is notably influenced by the strongly pulsating condition. This paper experimentally studies unsteady flow field in a centrifugal compressor at pulsating backpressure conditions. Experimental facilities and methodology are introduced firstly, followed by detailed discussions on experimental results of unsteady flow at different pulsating conditions. Results show that the pulses of pressure and mass flow rate are alleviated as the pulses propagate from compressor exit to the impeller, but then are enhanced remarkably in the impeller inducer. Flow field at compressor inlet manifests that the axial velocity and the incidence angle are evidently distorted in both circumferential and radial directions induced by the volute at both steady and pulsating conditions. Specifically, the incidence angle is higher in the region upstream the volute tongue than the values downstream the configuration. The patterns of distortions vary periodically with the pulsating backpressure. In particular, comparing with the variation near hub region, the incidence angle varies with the magnitude as about 10 degrees near 85% blade height, implying that the flow in spanwise direction responses to the pulsating backpressure with different sensitivity. The study experimentally demonstrates the clear evidence of the unsteadiness of the flow field in the compressor at pulsating backpressure conditions.