Design,Manufacture Process And Thrust Performance Of Micro Nozzle

Micro Laval nozzle, as a key part to accelerate the gas and to obtain the supersonic gas flow, has been widely applied in various industrial fields such as micro thruster, metallurgical engineering, laser cutting, and cold spraying technology. However, compared to nozzles at normal scale, a lot of different challenges have been faced in design, simulation and manufacturing technology for micro scale nozzle. Thus, further detailed research on design rule, roughness effect, size effect, manufacturing technology and test technology will present great value for applications of Micro Laval nozzles. In this dissertation, fluid dynamic, numerical simulation and micro cutting technology are combined to perform integrated research on analysis of micro nozzle flow field as well as its manufacturing technology. The demonstration of roughness effect on the performance of micro nozzle and the establishment of nozzle performance prediction model based on air friction flow are investigated. The processing method to enhance the surface quality and accuracy is presented. The research of this dissertation will help to promote the development of integration technology of design, manufacturing and performance of micro nozzles.Firstly, CFD simulation is used to investigate the effect laws of the wall profile on nozzle performance. Optimized length of divergent section is obtained by the contrast of the nozzle performance under different lengthes. The research results show that straight line profile has less wall loss because of it has smallest inner surface area, which could reduce the maximum contact area between the air flow and the nozzle. Hence, the straight line profile should be used at both convergent section and divergent section for 1mm micro nozzles.Secondly, surface residual model, integrating various nozzle geometric models into CFD simulation model with different surface roughness has been proposed to demonstrate the change rule of flow field under different wall surface roughnesses, nozzle scale and total pressure of nozzle inlet. The nozzle performance prediction model is then presented with the error lower than 4% between prediction value and simulation value. The relationship among axial cutting depth, half cone angle and nozzle velocity performance is confirmed, which can be used to optimize the nozzle cutting parameters.Thirdly, cutting technology to obtain micro nozzles with higher processing quality is developed by the optimization of cutting tool, fixture, cutting parameters, tool path, machining route, and burrs control technology etc. The research result shows that burrs control method of coating with PMMA presents well restrain effect on burrs generated in ball end milling surface. Meanwhile, less burrs existed on nozzles machined surface with cone milling tool, which can further to use large axial cutting depth in machining process.Finally, the N level thrust inspection instrument is developed to evaluate the nozzle performance under different cutting parameters and tool paths. The test result shows that the nozzle thrust performance degrades with the increase of surface roughness, which gets more serious under the higher inlet total pressure. Nozzle with axial tool path presents better thrust performance than that with circular tool path. However, for nozzle with axial tool path under larger cutting depth, its performance still degrades obviously with the increase of surface roughness. Besides, the thrust performance differs among nozzles at different cutting depth becomes larger with the increase of total inlet pressure.