Experimental Study on Cavitating Flow in Impeller of Axial-Flow Pump

Based on the external characteristic test, the performance of designed axial-flow model pump was determined. The cavitation performance of model pump at the best efficiency point was confirmed through the cavitation test. The cavitating flows in impeller at different NPSH values were shot by the high speed digital camera. MiVnt image analysis software was utilized to process the shooting images, track the cavitation region and outline of cavitation bubbles cluster. The experimental results show that the incipient cavitation regions are located in the inlet of blade suction surface near the tip and the leading edge of tip airfoil. With the decrease of NPSH values, the cavitation region at tip airfoil moves gradually from leading edge to trailing edge and the type of cavitation is vortex cavitation, its rotation axis direction is the same as circumferential direction. The cavitation region at blade suction surface indicates the same moving trend as at tip airfoil. The emerging of cloudy cavitation at the middle of blade suction surface indicates the beginning of pump cavitation. With the further increase of volume proportion of cavitation bubbles in impeller channel, the pump performance decreases severally. The experimental results reveal the preliminary laws of cavitating flow and provide an effective reference for the cavitation region and development process in impeller of axial-flow pump.