Study On Cavitation And Tip Leakage Vortex Characteristics Of Axial Water Jet Propulsion Pump

The water jet propulsion pump is the core component of the water jet propulsion device,which uses the water thrust generated at the outlet of the propulsion pump to propel the ship’s instruments forward.The water jet propulsion pump is very easy to operate under cavitation conditions,producing cavitation bubbles that block the impeller flow path and interacting with the tip leakage vortex structure to accelerate the deterioration of the internal flow pattern of the water jet propulsion pump.This paper investigates the cavitation and tip leakage vortex characteristics of water jet propulsion pumps based on numerical simulation techniques,and the main work and findings are as follows.(1)For the different flow conditions of the water jet propulsion pump to carry out the cavitation characteristics of the impeller flow path and internal flow characteristics analysis,to obtain the cavitation characteristics curve of the propulsion pump,the results of the study show that cavitation first appears in the blade suction front edge near the top of the blade,the reduction of the inlet pressure will lead to cavitation to the hub,trailing edge of the two directions,respectively,and will lead to the position of the impeller blade suction surface lateral jet to the outlet position.The formation,development and collapse of shear layer cavitation at the head,cloud-like cavitation and trailing edge of lamellar cavitation can be clearly observed in the impeller runner during the critical cavitation period,and the formation,development and collapse of cloud-like cavitation are the main reasons for the formation of the peaks and valleys of the bubble volume and bubble area curves,and the appearance of cloud-like cavitation will lead to a decrease in the bubble area in the impeller.(2)The tip leakage vortex for different inlet conditions of water jet propulsion pump is studied,and the vortex intensity and relative vortex transport equations of different cross-sections are analyzed.The vortex structure of the tip leakage vortex structure in the blade area has a larger vortex structure generation term,and the vortex structure dissipation term in the trailing edge area is larger;the tip shear vortex,vertical cavitation vortex and trailing edge shedding vortex are easy to occur vortex line stretching and distortion,the Koch force is an important factor driving the leakage flow at the top of the impeller,the oblique pressure moment term on the vortex volume is mainly located in the collapse area of the cavitation cloud,and the role of the viscous dissipation term on the vortex flow and cavitation is negligible compared with other terms.can be ignored.(3)Analysis of the pressure pulsation in different parts of the impeller runner under different inlet conditions shows that the frequencies of the pressure pulsation in different parts of the impeller runner are mainly the impeller blade frequency,guide vane frequency and their multiples during the incipient cavitation period;during the critical cavitation period,the turbulence of the flow pattern in the impeller runner intensifies,resulting in abnormal pressure pulsation at different locations of the impeller outlet section,which is mainly influenced by the top leakage vortex and the trailing edge The pressure pulsation at the impeller top clearance area is mainly affected by the top leakage vortex,vertical cavitation vortex and trailing edge shedding vortex structure;the pressure pulsation at the blade pressure surface is mainly affected by the top leakage vortex,while the trailing edge at the suction surface is mainly affected by the trailing edge shedding vortex and vertical cavitation vortex.