基于湍流布朗效应的焊接气溶胶运动特征数值模拟研究

Numerical simulation of welding aerosol motion characteristics based on turbulence-Brownian effect

为了探究手工电弧焊接气溶胶颗粒的运动轨迹和扩散分布规律,根据气溶胶动力学、等离子体流动力学和计算流体力学原理,结合湍流流动和颗粒物布朗效应,建立了等离子体热空气颗粒物动量、能量耦合的焊接气溶胶颗粒扩散数学模型,并通过数值模拟探究了焊条夹角及颗粒物粒径对焊接气溶胶运动状态及水平、竖直分布特征的影响。研究结果表明:焊条夹角对于焊接颗粒物的初始位置分布及运动轨迹具有重要的影响,颗粒物产生的区域将向着背离焊条倾斜方向偏移,这一偏移将随着焊条与平面夹角的减小而增大;在焊接亚微米气溶胶颗粒的自由扩散过程中,颗粒的扩散分布与粒径密切相关,对于小粒径颗粒物,特别是0.1μm的超细颗粒物,在布朗力的作用下,颗粒物的水平距离原点矩D>75 mm,而对于粒径在0.5μm以上的较大颗粒物,其D<15 mm。说明粒径较小的颗粒物扩散性更强,分布更为广泛,由于分子滑移的作用,气流对超细颗粒物的拖曳效应下降,小粒径颗粒物的运动轨迹更易与气流方向发生偏离。

In order to explore the motion trajectory and diffusion distribution of aerosol particles in manual welding arc,a mathematical model of welding aerosol particle diffusion coupled with momentum and energy of plasma,hot air and particles is established according to aerosol dynamics,plasma flow mechanics and computational fluid dynamics,combined with turbulent flow and particle Brownian effect.The influences of electrode inclination angle and particle size on the movement characteristics,horizontal and vertical distribution of welding aerosol are investigated by numerical simulation.The results show that the electrode inclination angle has a great impact on the initial position distribution and motion trajectory of welding particles.The area where the particles are generated will be offset away from the electrode tilt,and this offset increases as the decrease of angle between the electrode and the plane.In the free diffusion process of welding submicron aerosol particles,the diffusion distribution of particles is closely related to the particle size.For small particles,especially for ultra-fine particles of 0.1μm,under the action of Brownian force,the horizontal distance origin moment of particles is more than 75 mm,while for larger particles with a particle size of more than 0.5μm,the horizontal distance origin moment is less than 15 mm.It indicates that the particles with smaller size have stronger dispersion and wider distribution.Due to the effect of molecular slip,the drag effect of airflow on ultra-fine particles decreases,and the movement trajectory of particles with smaller size is more likely to deviate from the direction of airflow.