Rotating stall characteristics in the vaned diffuser of a centrifugal pump

Rotating stall in centrifugal pumps takes place frequently under part-load conditions, along with high pressure pulsation. The major focus for studies is rotating stall inside the impeller, rarely paying attention to that in the vaned diffuser. In this study, rotating stall behavior in a vaned diffuser centrifugal pump has been numerically investigated, and the cross-power spectrum method is adopted to identify low-frequency pressure signals. The applied numerical method has been validated by experimental results including flow structures provided by PIV measurements. For the vaned diffuser pump, a hump region in head curve is observed between 0.25Q(d) and 0.5Q(d) conditions. Under 0.41Q(d) condition, rotating stall occurs in the vaned diffuser of the pump, with three stall cells rotating opposite to the direction of impeller rotation and the rotating frequency being 0.083 Hz equal to 1/600 of the impeller rotating frequency. Rotating stall takes place under 0.5Q(d) condition as well, whereas only a periodic process of stall cell from inception to disappearance appears in the diffuser channel under 0.35Q(d) condition. Furthermore, the effect of number of diffuser vanes on rotating stall characteristics has been analyzed in detail.