送粉气流对冷喷涂流场及粒子速度影响的数值模拟

通过建立二维数值模型,利用计算流体力学软件进行数值模拟,研究了送粉气流压力和温度对冷喷涂过程中流场及粒子速度的影响.结果表明:喷涂中不可忽略送粉气流对流场及粒子速度的影响；为将粉末注入喷管,送粉气流的出口压力不能小于出口处的主气流压力,但增大送粉气流压力会使得进入喷管渐缩段的送粉冷气体流量增大,从而排挤高温主气流,同时也降低喷管气体流动的滞止焓,导致喷管喉部声速减小,不利于粒子加速；增加主气流温度对粒子加速效果不明显,而增加送粉气流温度可有效提高粒子撞击基板的速度,进而提高粉末粒子的沉积效率.

Numerical Simulation for Effect of Powder Carrier Gas on Flow Field and Particle Impact Velocity in Cold Spraying

A two-dimensional numerical model is established and numerical simulation with computational fluid dynamics(CFD) software FLUENT is conducted to investigate the effect of the powder deliver gas on flow field and particle velocity inside and outside supersonic nozzle in cold spraying process.It is found that the powder deliver gas with higher pressure and lower temperature than main stream gas exerts significant effects on the flow field and the particle velocity.The inlet pressure of the powder deliver gas must be higher than that of the main stream gas to inject the particles into the nozzle.However,increasing the pressure of the powder deliver gas will result in the increase in the flow rate of the cold powder deliver gas to squeeze out the high temperature main gas.Then the stagnation enthalpy of the gas in the nozzle also decreases,which leads to the reduction in the speed of sound at the nozzle throat and impedes the acceleration of particles.At this time,the increase in the main gas temperature does not significantly affect the acceleration of particles,while the increase in the temperature of powder deliver gas effectively improves the particles’ impact velocity and deposition efficiency.