Experimental investigation of characteristics of instability evolution in a centrifugal compressor

The stable range of operation for the centrifugal compressor significantly influences the dynamic, economic, and environment-friendly characteristics of power systems. A deep understanding of the characteristics of instability evolution is necessary to improve the compressor stability. A centrifugal compressor equipped with a vaneless diffuser is experimentally investigated using high-response static-pressure measurements. The results obtained indicate that three typical rotational-speed ranges exist based on the different instability evolution characteristics, which reveals the various impeller–diffuser matching behaviors over the entire speed range. At low-speed ranges ((40%–75%)Nmax, Nmax is the maximum rotational speed), the compressor exhibits stable, Rotating Instability (RI), impeller stall (diffuser stall), and surge modes. The impeller stall mode is induced by RI and propagates downstream, resulting in the diffuser stall and compressor surge modes. In the medium-speed range ((75%–85%)Nmax), the compressor exhibits stable, diffuser stall, RI, and surge modes. In the high-speed range ((85%–100%)Nmax), the compressor exhibits stable, diffuser stall, and surge modes. The dominant instability position is shifted from the impeller to the diffuser as the rotational speed increases. Both the impeller and diffuser stall present an irregular sawtooth static-pressure wave and exhibit broadband frequency spectrum patterns.