Performance Analysis of a Centrifugal Compressor Based on Circumferential Flow Distortion Induced by Volute

A volute is one of the key components in a centrifugal compressor. The aerodynamic stability of the compressor deteriorates remarkably when a volute is employed. This paper investigates the influence of volute-induced circumferential flow distortion on aerodynamic stability of a centrifugal compressor via experimentally validated three-dimensional (3D) numerical simulation method. First, the compressor performance is analyzed based on a newly developed stability parameter. The impeller is confirmed to be the main contributor to the instability of the investigated compressor. Next, the influence of volute on impeller performance is studied by circumferentially distorted boundary conditions at the impeller exit which are extracted from flow field at the volute inlet. Results show that the performance of an impeller passage is determined by not only the back pressure but also the local gradient of pressure distribution in the circumferential direction. Moreover, these passages confronted with pressure reduction in the rotational direction are most unstable, while those confronted with pressure rise have better performance. Consequently, the circumferentially distorted distribution at impeller exit results in a loop of passage performance encapsulating the performance of uniform case. The size of the loop is enhanced by the distortion amplitude. Moreover, the influence of volute-induced distortion on the impeller performance is concluded into two main reasons: the imbalance of the force on flow and the imbalance of tip clearance flow taken by passages. The force imbalance influences the accumulation of secondary flow, while the imbalance of the tip clearance flow results in discrepancies of the low momentum flow in passages.