Interaction between Impeller Stall and Vaneless Diffuser Stall in a Centrifugal Compressor

Abstract

The interaction between impeller stall and diffuser stall in a centrifugal compressor with a vaneless diffuser is investigated both experimentally and numerically. The numerical results showed that an impeller stall rotated at approximately 60% of the impeller rotational speed and diffuser stall cells rotated at approximately 25% of the impeller rotational speed. The experimental results showed that an impeller stall is generated intermittently, and one or two stall cells exists in the diffuser region and the number changes over time. In addition, it was found that the number of diffuser stall cells tended to be switched from one to two when an impeller stall was generated. This phenomenon was also observed by numerical analysis. Therefore, it is indicated that an impeller stall has effects on the formation of diffuser stalls. The low-velocity region discharged from impeller exit of the passage with impeller stall propagated in radial direction and merged into low-velocity region at diffuser exit. Thus, impeller stall effects diffuser stall.