Study on the key influencing factors and vortex characteristics of the water jet propulsion pump underwater suction vortex

The formation and development of the underwater suction vortex in water jet propulsion pump systems lead to energy loss, reduced propulsion efficiency, and vibrations in the system. This study investigates the flow field characteristics under various operating conditions by combining numerical simulations with visualization experiments. The tested parameters include under-keel clearance ranging from 0.83D0 to 7.5D0 (D0 represents inlet diameter of the water jet propulsion pump, with a value of 120 mm), inlet suction flow rates from 4 to 28 L/s, and pump rotational speeds between 300 and 800 r/min. When the clearance is less than 2.5D0, the velocity gradient near the riverbed cross section increases sharply with decreasing clearance. The vorticity significantly intensifies, the low-pressure region becomes more concentrated, and the risk of suction vortex-induced disturbances increases. An increase in inlet flow rate causes the region of concentrated velocity gradients to shift toward the inlet lip, disrupting the symmetry of the pressure field. The absolute vorticity shows a linear increase, significantly raising the likelihood of vortex formation. As pump speed increases, the velocity gradient shifts toward the lip side, with proportional vorticity growth, expanding the low-pressure region and enhancing shear effects.