Structural Design And Characteristics Research Of Self-excited Oscillation Pulse Water Jet Nozzl

The aerospace industry is closely related to human destiny.High-pressure water jet processing technology has the characteristics of strong processing capacity,many processing methods,small cutting force and no heat affected zone.It can be used for cutting,surface cleaning,polishing,milling and turning on metal,non-metal,composite materials and other materials.It holds a key place in the manufacturing of aerospace products.Scientific and technological workers prefer self-excited oscillation pulsed abrasive water jet technology because it has a higher destructive power than continuous water jet at the same system pressure.The oscillation of the jet is primarily caused by the continual effective feedback of the low-pressure vortex in the oscillating cavity and the turbulent disturbance at the oscillating cavity exit.The pulse effect near the nozzle area has a direct impact on the final processing quality.Aim of this work is to improve the nozzle’s pulse quality by adjusting the nozzle settings.The optimized design of the self-excited oscillation pulsed water jet nozzle mainly relies on numerical simulation and experimental assistance.To achieve the objective of maximizing the pulse quality close to the nozzle region,the multi-objective optimization design is optimized using the NSGA-II genetic algorithm and the grey correlation analysis method.The difficulty of numerical simulation and experimental engineering,as well as the tiny sample size,are to blame.The key research subjects discussed in this article are as follows:(1)A self-excited oscillation pulsed water jet nozzle with initial structural parameters is designed in accordance with the existing pressurization equipment and continuous jet nozzle design theory on the basis of an analysis of the research status of high pressure water jet technology and nozzle structure design both domestically and internationally.To increase modeling accuracy,large eddy simulation(LES)and other numerical simulation techniques appropriate for pulsed water jet are used.(2)The static cloud pressure diagram for a single pulse period was discussed,with a model applied to the first self-excited oscillation pulsed water jet nozzle.We studied the generation process and pressurization characteristics of the pulse.More research has been done on the characteristics of the self-excited oscillation nozzle,including the length,diameter,angle of the collision wall,and diameter of the lower nozzle.Analysis has been done on each parameter’s impacts and the process impacting the pulse characteristics of the self-excited oscillation pulsed water jet nozzle.(3)In this paper,the mathematical model and response surface diagram of the pulse effect of the central water jet at the outlet of the nozzle are obtained by designing four-factor and three-level response surface experiments.The oscillation cavity length Lc,oscillation cavity diameter Dc,collision wall angle α,and the key parameters of the lower nozzle diameter d2 of the self-excited oscillation nozzle are explored.According to the analysis,Lc > d2 > >> Dc is the order of the key parameters’ substantial influence on the average pulse peak,while Dc is the order of the key parameters’ significant influence on the proportion of pulse duration.Then,the average pulse peak value and the pulse market share pareto optimal solution set are determined using the NSGA-II genetic algorithm,and the nozzle structural parameters are optimized using grey correlation analysis.The chamber diameter Dc,the oscillation chamber length Lc,the lower nozzle diameter d2,and the collision wall angle of 1.24 mm,6 mm,3.5,150° make up the optimum nozzle construction parameters.The proportion of nozzle pulse duration and the peak value of average pulse velocity are 0.3592 and 401.4692 m/s,respectively,which are 134 %and 17.14 % higher than the original value.