Rotating Stall Acoustic Signature in a Low-Speed Centrifugal Compressor: Part 1—Vaneless Diffuser

An experimental study is performed to identify spatially coherent pressure waves, which would serve as precursors to the development of an instability in the Purdue Low-Speed Centrifugal Research Compressor when configured with a vaneless diffuser. To achieve this, sensitive electret microphones were uniformly distributed around the circumference in the inlet and diffuser sections of the compressor. Fourier analysis of simultaneously sampled data from these microphone arrays was employed to identify the development of dominant spatial modes in the pressure field in the compressor. The transition to stall was observed to be a gradual process, with the growth of the pressure waves into those corresponding to a large-scale stall condition occurring over a time span of 26 impeller revolutions. The excitation of the pressure waves, as indicated by spatial Fourier analysis, occurred 14 impeller revolutions before small changes were evident in the microphone signals, and 26 revolutions before the stall condition could be considered fully developed.