Impeller Stalling as Influenced by Diffusion Limitations

Abstract

Relatively small stable flow ranges experienced on some high Mach number centrifugal compressors, triggered by the inability of stationary vaned diffusers to operate at flows below their maximum recovery point, have focused considerable research effort on the diffuser component. With improved impeller stability, vaned diffusers can be assisted to operate to lower flows where impeller stalling becomes predominant. The results of tests on a small high Mach number centrifugal compressor are presented to suggest that in certain applications the primary factor affecting compressor surge could be the impeller inlet-to-exit velocity diffusion ratio, with specific diffuser types, Mach numbers, and incidence considerations becoming secondary in importance.