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.

中文翻译：

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搏动性对呼气气流中颗粒扩散的作用。

诸如咳嗽之类的呼气事件通常在本质上具有搏动性，并导致输送呼吸颗粒的涡流结构。在这项工作中，进行了湍流脉动射流的直接数值模拟（DNS），并结合了拉格朗日对微米级液滴的粒子跟踪，以研究次生和三次生驱逐在粒子扩散和渗透中的作用。从湍流管道的DNS获得的充分发展的湍流位于喷孔处。根据阻尼正弦波及时调整孔口处的体积流速，从而可以控制脉冲数，持续时间和峰值幅度。忽略了诸如蒸发和浮力之类的热力学效应，以便隔离脉动对颗粒分散的作用。对于单脉冲，二脉冲和三脉冲射流，分析了所得的涡旋结构。然后将粒子云的演化与现有的单脉冲模型进行比较。发现颗粒的分散和整个云层的渗透受增加的脉动性的阻碍。然而，由于涡流结构向下游加速，因此二次或三次排出的颗粒的渗透性得以增强。