Monroe K, Yao Y, Lattanzi A, Raghav V, Capecelatro J
Department of Aerospace Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Phys Fluids (1994). 2021 Apr;33(4):043311. doi: 10.1063/5.0048746. Epub 2021 Apr 12.
Expiratory events, such as coughs, are often pulsatile in nature and result in vortical flow structures that transport respiratory particles. In this work, direct numerical simulation (DNS) of turbulent pulsatile jets, coupled with Lagrangian particle tracking of micron-sized droplets, is performed to investigate the role of secondary and tertiary expulsions on particle dispersion and penetration. Fully developed turbulence obtained from DNS of a turbulent pipe flow is provided at the jet orifice. The volumetric flow rate at the orifice is modulated in time according to a damped sine wave, thereby allowing for control of the number of pulses, duration, and peak amplitude. Thermodynamic effects, such as evaporation and buoyancy, are neglected in order to isolate the role of pulsatility on particle dispersion. The resulting vortex structures are analyzed for single-, two-, and three-pulse jets. The evolution of the particle cloud is then compared to existing single-pulse models. Particle dispersion and penetration of the entire cloud are found to be hindered by increased pulsatility. However, the penetration of particles emanating from a secondary or tertiary expulsion is enhanced due to acceleration downstream by vortex structures.
呼气事件，如咳嗽，本质上通常是脉动性的，并会产生输送呼吸道颗粒的涡旋流动结构。在这项工作中，进行了湍流脉动射流的直接数值模拟（DNS），并结合微米级液滴的拉格朗日粒子追踪，以研究二次和三次喷射对颗粒扩散和穿透的作用。在射流孔口提供从湍流管道流动的DNS获得的充分发展的湍流。孔口处的体积流量根据阻尼正弦波随时间调制，从而可以控制脉冲数、持续时间和峰值幅度。为了分离脉动性对颗粒扩散的作用，忽略了诸如蒸发和浮力等热力学效应。对单脉冲、双脉冲和三脉冲射流的产生的涡旋结构进行了分析。然后将颗粒云的演化与现有的单脉冲模型进行比较。发现增加的脉动性会阻碍整个云团的颗粒扩散和穿透。然而，由于涡旋结构使下游加速，二次或三次喷射产生的颗粒的穿透得到增强。
