Experimental Study on Internal Flow Field of a High-Speed Centrifugal Compressor at Different Altitudes

The alteration of altitude will affect the stability of centrifugal compressors. In this paper, the pressure field on the casing wall of a high-speed centrifugal compressor at two different altitudes (h = 0m and h = 4500m) was investigated by using 15 high-response pressure sensors. The operating condition of the centrifugal compressor ranged from choke condition to developed stall condition. The results show that the interaction of the shock wave and splitter-blade tip leakage flow occurs at 70% chord region near the choke condition, and the loss is more severe at the high altitudes. At the near-stall condition, the unstable disturbance at the low altitude is caused by the collapse of the horseshoe vortex, and the unstable disturbance at the high altitude is dominated by advanced breakdown of the main-blade tip leakage vortex. At the developed-stall condition, the stall mechanisms at the two altitudes are different, both of which are closely related to the main-blade tip leakage flow. With the decrease of flow rate, the unsteady disturbance caused by the volute tongue moves upstream from the diffuser to the impeller inlet. At the same time, the unsteady disturbance propagates along the opposite direction of the rotational direction in the partial impeller passage at the low altitude case. However, the circumferential propagation characteristics at the high altitudes case are not obvious.