CFD Simulation Calculation On High Velocity Oxygen Fuel (HVOF) Thermal Spray Process

Due to the high velocity and relatively low temperatures of flame flow, HighVelocity Oxygen Fuel (HVOF) thermal spraying technology shows a significantadvantage in spraying metal carbides and metal alloy powders and has become animportant processing method. HVOF thermal spray process is very complex andinvolves many physical and chemical processes such as the combustion of fuel,turbulence phenomena, compressible flow, two-phase flow (gas and solid particles) oreven three-phase flow (gas, fuel droplet and solid particles), subsonic/supersonic flowtransitions and many other physical and chemical processes. In HVOF sprayingprocess, many process parameters affect coating performance and mutually influenceeach other. With the aid of numerical modeling of HVOF spraying process, it mightbe done to analyze gas and particle dynamics in HVOF spraying process and providesome theoretical guidance for improving the coating performance.In this thesis, the computational fluid dynamics software Fluent is used tosimulate the JP-5000HVOF thermal spray process, which consumes liquid keroseneianncdl uodxey greeanl iaModel (EDMzn)ad,b wlesh prikac-h y s sttouhlrevb euWsl eCan c-se1i7ngmColeo-dpseotel,wp ddrieesracscr.e Ititnoen t,ph heaa nsrdee seEmadorcdydh e,Dl,t hisEe sdaipdpaypt lioDienid s Csmioponadctieeolpnst(EDC) model which solves an8-step reaction. In this study, it was analyzed for thevariation of the gas temperature, velocity, Mach number, pressure, and the gascomponent. By adding the discrete phase model, the particle in-fight trajectory,particle velocity and temperature of WC-17Co powders were studied under differentcombustion models, particle diameters, particle shapes and particle injection rates.Some guidance is to be provided for optimizing process parameters in HVOF.The computational results show that combustion models affect the distribution ofthe gas flow field and, thus influence the spray particles’ dynamics in the gas flowfield. When the oxygen and liquid kerosene mass flow rates are0.022kg/s and0.007kg/s, the maximum temperature and pressure are located in the combustionchamber and respectively about3250K and9.65atm predicted by the EDM. The gasvelocity is about2260m/s at gun exit after acceleration by the gun. While, in the eddydissipation conceptual model (EDC), the maximum temperature and pressure of the combustion chamber is respectively3280K and6.56atm. The gas velocity at gun exitis about2550m/s after acceleration of the gun. In the comprehensive consideration ofeffects of particle diameters on the in-flight trajectory, particle velocity andtemperature, it is suggested that particle diameter range is10-40μm.In this research,particle injection velocity10-15m/s is a suitable range and the injection rate15m/s isthe optimum for small particles and10m/s is the optimum for large particles.