Experimental study on flow evolution and pressure fluctuation characteristics of the underwater suction vortex of water jet propulsion pump unit in shallow water

The occurrence of the underwater suction vortex will cause the ship to vibrate violently and even lose thrust. The evolution process of the underwater suction vortex was obtained by high-speed photography. According to the characteristics of vortex in different phases, its diachronic process can be divided into five phases: premonitory, nascent, developing, weakening, and disappearing. The underwater suction vortex is a vertical axis vortex below the intake, and its shape is similar to a tornado, showing a form of thick at the top and thin at the bottom. The pressure fluctuation test studied the time-frequency characteristics of pressure fluctuation induced by the underwater suction vortex. The results show that the underwater suction vortex can cause the pressure fluctuation amplitude to recover after a sudden drop. The frequency of characteristic low frequency induced by the underwater suction vortex is 0.28 Hz, which is easy to be ignored. The corresponding amplitude of this frequency is much larger than that of other frequencies, and the low-frequency pressure fluctuation induced by the underwater suction vortex is dominant. The results can provide a theoretical basis for the mechanism and prevention of suction vortex of water jet propulsion pump unit. © 2022 Elsevier Ltd