超音速火焰喷涂焰流和粒子流的数值模拟研究

Numerical Modeling of HVOF Flame and in-flight Particle

本文采用FLUENT流体力学数值模拟软件,以自行研发的TJ-9000型喷涂系统为基础,基于有限体积法,根据流体力学建立数学模型,对采用该系统喷涂制备WC-12Co涂层过程中的焰流及粒子流飞行传热过程进行了仿真模拟。TJ-9000型HVOF系统以氧气为助燃气体,丙烷为燃料。氧气与丙烷的总质量流速Q一定时,其质量比n与焰流的温度和速度呈抛物线的变化关系。当Q=16g/s,n=3.0时,焰流温度能达到3000K以上,焰流速度1800m/s左右;并且在自由射流阶段的前半段和靠近基体的位置存在较大的径向焰流速度。研究发现小粒径的粒子温度和速度的变化对焰流都具有很强的跟随性,表现为升得快也降得快。由于焰流的湍流特性和径向速度的存在,粒径小于20μm的粒子会随焰流一起沿径向飞行而不能到达基体。粒径太大则熔化程度太低从而降低涂层的结合强度。本文选用的WC-12Co颗粒的最适宜粒径分布范围为20～40μm。

In this study,a CFD （Computational Fluid Dynamics） software FLUENT was used to simulate the HVOF （High Velocity Oxygen Fuel） spraying process for the home-made TJ-9000 spray system,in which oxygen and propane were applied as combustion-support gas and fuel respectively,and WC-12Co was taken as feedstock powders. The mass flow ratio of the oxygen and propane （n） has a significant impact to the flame temperature and velocity,and shows a kind of parabolic relationship. When the total mass flow rate of oxygen and propane was 16g/s and the mass flow rate of them was 3.0,the temperature of the flame jet can reach over 3000K,the velocity is 1800m/s or so,and the free jet has an obvious radial velocity at the first part and near the substrate. When the particle is small,the temperature and velocity have a strong following tendency to the flame jet,and it rise and drop quickly. As the flame turbulence properties and the existence of radial velocity,when the WC-12Co particle size is smaller than 20μm,the particles will fly along the radial direction and can＇t impact onto the substrate. And also the too larger particle size will lead to decrease the bonding strength because of the low particle melting degree. In this study,the optimal particle size distribution of the WC-12Co powder is 20-40μm.