Investigation on the casing static pressure distribution and stall behaviors in a centrifugal compressor with volute

Obtaining the casing static pressure distribution of a centrifugal compressor with volute is beneficial in understanding the compressor stall mechanism and designing the corresponding asymmetric structures to improve the compressor performance and stability. The present study investigates the casing pressure evolution from the choke to stall operating conditions and focuses on the relationship between the casing pressure evolutions and stall behavior under different rotational speeds. A total of 72 steady static pressure sensors (6 sensors in circumferential direction and 12 in streamwise direction) were mounted around the compressor casing wall to measure the casing pressure. In the experiment, the steady pressure data were acquired by averaging the 50 values measured in 1 s. The results show that at the same rotational speed, from the near choke to near stall conditions, the casing pressure distribution patterns can be divided into two parts: the single-peak pressure pattern, from the choke point to maximum efficiency point (transition point), and the double-peak (peak and bulge) pressure pattern, from the transition point to near stall point. One interesting phenomenon is that the proportions of the flow rate range of the two casing pressure patterns at different rotational speeds are related to the surge line knee. The vast operating range contraction indicates that the double-peak pattern has more instability at a higher rotational speed, which is linked with the different stall behavior at different rotational speeds. Combined with unsteady full annulus simulations, the leading-edge spillage triggers the impeller long-lived stall earlier at a higher rotational speed, corresponding to the short-lived double-peak pressure pattern. However, at lower rotational speeds, short-lived diffuser stall occurs owing to the impeller outlet recirculation flow and diffuser inlet separated flow, corresponding to the long-lived double-peak pressure pattern. Furthermore, the circumferential non-uniform casing pressure distribution can indicate the circumferential position of the stall onset and provide a reason for the non-rotating stall in the impeller inlet and partly rotating stall in the diffuser, which is fundamental and beneficial to the compressor flow control system design.