Optimization design of nozzle and analysis of flow field in fluid jet polishing

In this paper, the geometric structure of the nozzle in fluid jet polishing is optimized by computational fluid dynamics simulation. The design of small-diameter nozzle is carried out, the relationship between nozzle structure and fluid movement is analyzed, and the influence of machining error on nozzle to fluid stability is considered. Firstly, according to Bernoulli's Principle, the velocity at the nozzle outlet is theoretically calculated, and the holding length of the outlet velocity is defined. Based on computational fluid dynamics simulation, the ability to maintain fluid energy of different nozzle diameters with different length-diameter ratio is analyzed. The results show that the larger the nozzle diameter, the smaller the effect of the length-diameter ratio on the ability of maintain fluid energy. The divergence ratio is defined to explain the ability of constraining the divergence of the fluid. The larger the diameter, the smaller the influence of length-diameter ratio on the position of peak shear force. Then, aiming at the verticality of the cylindrical section in nozzle outlet caused by machining error is difficult to guarantee, the influence of inclination of cylindrical section on ability to maintain fluid energy and constraint the divergence of the fluid is analyzed. The shear force distribution on the workpiece surface still presents a circular shape within the inclination angle is small, and the acceptable error range of inclination angle is given. Finally, a fixed-point experiment of nanoparticle jet polishing is carried out on the surface of fused quartz, and the material removal profile is obtained.