Cavitating flow investigation in low specific speed axial flow waterjet pumps

Abstract

Abstract In this paper, the cavitating flow in low specific speed axial flow waterjet pumps are treated at different cavitation conditions. In order to analyze the cavitating turbulent flow comprehensively, three axial flow waterjet pumps with the specific speed less than 650 min-1·m3s-1·m are chosen to compare the internal flow phenomenon. The investigations are conducted by numerical simulation, where RANS method is applied with k-ω SST turbulence model and homogeneous cavitation model. The results show that there are several types of cavitation such as tip leakage vortex cavitation, sheet cavitation attached on blade suction surface, and shedding cavity in the pumps. The vortex structure in the low specific speed waterjet pump contains tip leakage vortex, shedding vortex downstream of the sheet cavitation and perpendicular cavitation vortex. It is noted that the cavity firstly occurs at the leading edge near blade tip, and the sheet cavity covering the blade suction surface extends from leading edge to the middle part, while the tip leakage vortex cavitation develops with the decreasing cavitation number. Further analysis using relative vortex transport equation depicts that the vortex stretching term is the main contributor for the vorticity production in the pump, and the vortex dilation and baroclinic torque occur at the interface between cavity and water.