Experimental Investigation of Surge and Stall in a High-Speed Centrifugal Compressor

Flow instability, known as surge and stall, limits the stable operating range of compressors. In this paper, a panoramic map of instability evolution across all typical operations is experimentally demonstrated for the first time in a high-speed centrifugal compressor with a maximum speed of 185; 000 r/min and a corresponding rotation velocity at the impeller outlet of 593 m/s. Twelve high-response Kulite pressure probes are mounted on the internal surface of the compressor's casing. The experimental results show that the instability phenomena are quite complex and diverse at different operations. At low speed (<70% of the maximum speed), high-frequency and low-frequency stall successively occurs at the impeller, and is followed by surge as mass flow rate reduced. The transient process of surge is a transient stall/unstall self-loop, with the "self-similarity" to the sustainable stall/unstall conditions. At 70% of the maximum speed, the system exhibits two types of surge, a minor-amplitude periodic surge with a frequency close to the Helmholtz system resonance frequency, and a deep surge. There is a non-surge region between them. Meanwhile the 70% of the maximum speed is a critical speed, beyond which the stable flow range narrows down abruptly. When the compressor operates at near of the maximum speed, surge suddenly sets in from stable state and there is no preceding stall. Finally, a new "mass-spring-damper" model is introduced for the first time to illustrate the diversity of surge/stall patterns across different operations.