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

Extensive research on centrifugal compressors has been planned. The main task of the research is to improve present prediction criteria coming from the literature with particular attention to low flow coefficient impellers (low width to radius ratios) where they are no more valid. Very little data has been published for this kind of stages, especially for the last stage configuration (with discharge volute). Many experimental tests have been planned to investigate different configurations. 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 configuration. Several diffuser types with different widths, pinch shapes and diffusion ratios were tested. The effect of geometric parameters on stage stability has been discussed inside part I of the present work; the purpose of this part of the work is to illustrate the effect of the same geometric parameters on stage performance and to quantify the impact of stability improvements on stage losses.