Numerical Simulation Of Supersonic Fluid Flow For De-laval Nozzle With Rectangular Cross Section

Cold spraying （CS） is a new type of coating technology which has beendeveloping recently. It works by accelerating the spray particles to300m/s-1200m/s bya supersonic gas flow to hit the substrate, resulting in the formation of the dense coatinglayer on the substrate surface. Since being carried out at low temperature, the coldspraying has a clear advantage in preparing and developing the new materials coatingssuch as the heat-sensitive ones nano-materials and amorphous materials, so on and soforth.The spray particles accelerated by carrier gas to obtain high velocity is the key tocold spraying technology. Therefore the converging-diverging nozzle which is thedevice speed up the carrier gas from subsonic to supersonic becomes one of thehighlights of the research on cold spraying technology. Due to the disadvantages ofconventional De-Laval nozzle for cold gas dynamic spray process, a novel structure ofDe-Laval nozzle was proposed in this paper. The numerical simulations of supersonicfluid flow within this nozzle and spraying particles accelerated by carrier gas have beenconducted by commercial CFD software Fluent. This paper also explores the effect ofthe convergent-divergent nozzle with rectangle cross section, different nozzle inletparameters and different ratio of length to width of the nozzle inlet cross section on thesupersonic gas flow field and particle acceleration behavior. Furthermore, therelationships between the performance of particle acceleration and the locations ofreleased particles are thoroughly studied for this new De-Laval nozzle. The majorcontributions are summarized as follows:1．In the same condition, the supersonic flow in both circular cross sectionDe-Laval nozzle and rectangular cross section De-Laval nozzle are similar. Due to theturbulence exist in the four corners in the rectangular cross section De-Laval nozzle; thevelocity of carrier gas circular cross section nozzle is slightly higher than that throughrectangular section De-Laval nozzle. On the nozzle exist, the flow velocity inrectangular section De-Laval nozzle is more uniformity than that in circular crosssection De-Laval nozzle. This advantage of rectangular cross section De-Laval nozzle isgood for spraying the work piece with small diameters in engineering application.2. Due to the maximum velocity of carrier gas in circular cross section De-Lavalnozzle is larger than that in rectangular section De-Laval nozzle, the velocity of particle in circular cross section De-Laval nozzle is larger than that in rectangular sectionDe-Laval nozzle.3. When the spray particle diameter less than5microns or larger than50microns,the spray particle can not obtain high speed to deposit on the substrate.4. Spray particles can obtain maximum velocity by releasing from the center of thenozzle inlet section through studying the influence between spray particle releasepositions and performance of the particle acceleration.Therefore, the research results of this thesis could provide some constructive datato product superior performance, simple structure and low manufacture cost ofrectangular section De-Laval nozzle.