Investigation of transient flow characteristics inside a centrifugal compressor for design and off-design conditions

As the flow rate decreases from the design to the rotating stall condition, the enhanced impeller–diffuser interaction considerably deteriorates the flow condition at the diffuser inlet, which may trigger stall and blade vibration problems. In order to reveal the underlying mechanism and estimate the impact of the interaction within the impeller and diffuser passages, measurements using the wireless acquisition technique and high-frequency response system have been conducted on a 1.5 stage centrifugal compressor with the vaned diffuser. The details of its transient flow characteristics suggest that the effects of the impeller sweep extensively propagate in the diffuser passage. Distinctions of the shroud reversed vortex effect exist between the main and splitter blades at the impeller outlet, which initiates the predominant passage passing frequency at the diffuser inlet under small flow rate condition. In addition, the present study explains why the dominant disturbance shifts back and force between the passage passing frequency and blade passing frequency for different positions of the diffuser and flow rates. Through flow throttling, the diffuser reaction toward the impeller passage considerably strengthens due to the growing pressure potential near the convex surface of the diffuser vane, which is associated with the reversed flow.