Experimental investigation and characterization of the rotating stall in a high pressure centrifugal compressor. Part I: Influence of diffuser geometry on stall inception

Extensive research on centrifugal compressors has been planned to define diffuser stall limits for a group of stages characterized by low blade-outlet-width-to-impeller-radius-ratio. Very little data is available on this centrifugal compressor family, especially for the last stage configuration. In addition, the most important stall diffuser prediction criteria barely cover this machine type. Many experimental tests have been planned to investigate several geometry variations. A simulated stage with a backward channel upstream, a 2D impeller with a vaneless diffuser and a constant cross section volute downstream constitute the basic geometry. Several diffuser geometries with different widths, pinch shapes, diffusion ratios were tested. Test results and conclusions are shown in the paper in terms of critical diffuser inlet flow angles, flow coefficients at stall inception and stage working ranges. The main task of the present work is to increase the knowledge and the amount of available data to characterize rotating stall phenomena, in particular for very narrow stages.