Effects of Nonaxisymmetric Volute on Rotating Stall in the Vaneless Diffuser of Centrifugal Compressors

Abstract

Rotating stall is an important unstable flow phenomenon that leads to performance degradation and limits the stability boundary in centrifugal compressors. The volute is one of the sources inducing nonaxisymmetric flows in centrifugal compressors, which has an important effect on compressors' aerodynamic performance. However, the influence of volute on rotating stall is not clear. Therefore, the effects of volute on rotating stall behavior have been explored in this paper by experiments and numerical simulations. The frequency of the rotating stall captured by the experiments is 43.9% of the impeller passing frequency (IPF), while it is 44.7% of IPF calculated from the numerical results, which proves the accuracy and capability of the numerical method in this work to study the rotating stall behavior. The flow fields from computational fluid dynamics (CFD) simulations further reveal that one stall cell initializing in a particular location deforms into several stall cells while rotating along the circumferential direction and becomes much smaller in a specific location during the evolution process, and finally, it is suppressed in another specific location as a result of the distorted flow field caused by the volute. Moreover, stall cells' behavior, including shrinking and enlarging along the spanwise direction during rotation, is closely related to the circumferentially nonaxisymmetric pressure distribution caused by the volute. The existence of volute makes rotating stall incept in the flow rate 32% larger than that of the centrifugal compressor without volute. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that the rotating stall can be weakened or suppressed, which is helpful to extend the stable operating range of centrifugal compressors.