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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脉动对呼气气流中颗粒分散的作用。


呼气事件（例如咳嗽）本质上通常是脉动的，并导致输送呼吸颗粒的涡流结构。在这项工作中，对湍流脉动射流进行直接数值模拟（DNS），结合微米级液滴的拉格朗日粒子跟踪，研究二次和三次喷射对粒子分散和渗透的作用。在喷射孔处提供从湍流管流的 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进行及时调制，从而可以控制脉冲数量、持续时间和峰值幅度。为了分离脉动对颗粒分散的作用，忽略了热力学效应，例如蒸发和浮力。对单脉冲、二脉冲和三脉冲射流产生的涡流结构进行分析。然后将粒子云的演化与现有的单脉冲模型进行比较。发现粒子的分散和整个云的渗透受到脉动增加的阻碍。然而，由于涡流结构对下游的加速，二次或三次排出所发出的颗粒的渗透性得到增强。