雨滴表面惯性粒子捕集的湍流效应数值分析

Numerical analysis of turbulent effect on the collection of inertial aerosols by raindrops

雨滴对气溶胶粒子的清除系数与捕集效率密切相关,并依赖于雨滴附近的气流型式.考虑到实际大气背景均为湍流状态,分别对层流和湍流状态下大尺寸雨滴表面上惯性粒子的捕集过程进行了数值模拟,讨论了湍流脉动对不同粒子轨迹的畸变和扰动.结果表明,层流条件下的模拟结果与已有的实验结果具有很好的一致性.若对雨滴的绕流附加一个湍流强度,则雨滴附近流动速度的随机变化将对粒子的运动轨迹产生明显的影响,导致惯性粒子在湍流状态下被雨滴捕获的效率大于层流捕集效率,湍流脉动效应对粒子捕集效率的提高幅度随粒子尺度的增大而减弱.

The scavenging coefficient of aerosols by raindrops depends on the collection efficiency and the flow pattern around the raindrops. Considering the turbulent features of the ambient atmosphere, the collecting processes of inertial aerosols on large raindrops for both laminar and turbulent flows are estimated by employing numerical simulation. The distortion of particle trajectories caused by turbulent fluctuation are discussed and analyzed. The numerical results show that the collection efficiency for laminar flow agrees well with the experimental data of previous studies. When a turbulent intensity exists in the incoming air, particle trajectories are strongly affected by the stochastic variations of the flow, the collection efficiency of the inertial particles are higher for turbulent flow than the case of laminar, and the enhancement of efficiency decreases with the increase of particle size.