Behaviour of cavitation characteristics for various vane leading edge shapes of radial flow pump impeller

Abstract Cavitation is a dynamic phenomenon that degrades hydraulic machines performance. In a pump, the lowest static pressure occurs near the leading edge of the vane, which causes cavitation when it falls below the vapour pressure of the fluid at that prevailing temperature. For the cavitation studies, three different leading-edge profiles of the vane of a low specific speed pump are chosen. Plain, ellipse with semi-minor axis along vane course, and circular are the three leading edge profiles. The radial flow pump impeller was designed through point by point method to obtain the vane course from leading to trailing edge instead of single arc and double arc methods. In this method, smooth transitions of relative and meridional velocities were insisted from inlet to outlet radius. The leading edges of vanes as well as the vane course are cross verified through the coordinate measuring machine for its accuracy. Cavitation tests were performed at various constant flow rates and constant speeds by lowering the water level in the sump (which as 10 m deep from pump centre line) so that the pump transitioned from a non-cavitating to a cavitating state. Cavitation studies revealed that the leading edge has a significant impact on pump performance because the incidence flow angle is disturbed at the inlet. Although the leading-edge profile had little effect on overall performance, but it had a significant effect on cavitation. Detailed cavitation characteristics were arrived for different flow rates, speeds, and the leading edge profiles. It is reconfirmed that affinity law will not hold good for a pump with cavitation. Development of cavitation in impeller channel from the inception were visualised and compared for different leading edge profiles with reference net positive suction head. For all tested flow rates, the pump with a circular leading-edge impeller has a lower Net Positive Suction Head requirement than the pump with an ellipse or plain leading-edge impeller.