Spatial-Temporal evolution characteristics of pre-Stage-stall in a centrifugal compressor with a vaneless diffuser and a volute

The continuous throttling process is of great interest for compressor designers. Previous experimental studies mainly consider the temporal evolution characteristics of the pre-stage stall at the impeller inlet or outlet regions. In this study, we explore the spatial-temporal evolution characteristics of pre-stage-stall using a pressure array consisting of 15 high-response sensors. The dynamic evolution characteristics of the pressure signal on the time and frequency domains and the underlying unsteady flow structure evolution during the transition process were analyzed. We find that the evolution characteristics of pressure irregularity varied with the streamwise positions. The evolution process from the pre-stage stall point to the stage stall point can be divided into three stages based on the disturbance scale and pressure fluctuations, namely (I) the coexistence of the impeller RI, the mild impeller stall, and the mild diffuser stall, (II) the interaction of stall cell and RI disturbance, (III) a single large stall cell. In stage I, the streamwise influential regions of the stall cells are mainly confined in the impeller passage. In stage II, the stall cell expands upstream and gradually interacts with the RI disturbance. The wavelength of RI-related disturbance increases while the related pressure fluctuation decreases. In stage III, several stall cells merge into one large cell.