Wei Jianjian, Li Yuguo
Department of Mechanical Engineering, The University of Hong Kong, Hong Kong.
Shenzhen Institute of Research and Innovation, Shenzhen, China.
PLoS One. 2017 Jan 3;12(1):e0169235. doi: 10.1371/journal.pone.0169235. eCollection 2017.
The human cough is a significant vector in the transmission of respiratory diseases in indoor environments. The cough flow is characterized as a two-stage jet; specifically, the starting jet (when the cough starts and flow is released) and interrupted jet (after the source supply is terminated). During the starting-jet stage, the flow rate is a function of time; three temporal profiles of the exit velocity (pulsation, sinusoidal and real-cough) were investigated in this study, and our results showed that the cough flow's maximum penetration distance was in the range of a 50.6-85.5 opening diameter (D) under our experimental conditions. The real-cough and sinusoidal cases exhibited greater penetration ability than the pulsation cases under the same characteristic Reynolds number (Rec) and normalized cough expired volume (Q/AD, with Q as the cough expired volume and A as the opening area). However, the effects of Rec and Q/AD on the maximum penetration distances proved to be more significant; larger values of Rec and Q/AD reflected cough flows with greater penetration distances. A protocol was developed to scale the particle experiments between the prototype in air, and the model in water. The water tank experiments revealed that although medium and large particles deposit readily, their maximum spread distance is similar to that of small particles. Moreover, the leading vortex plays an important role in enhancing particle transport.
人类咳嗽是室内环境中呼吸道疾病传播的一个重要媒介。咳嗽气流的特征是呈两阶段射流；具体而言，起始射流（咳嗽开始且气流释放时）和中断射流（源供应终止后）。在起始射流阶段，流速是时间的函数；本研究考察了出口速度的三种时间分布（脉动、正弦和真实咳嗽），我们的结果表明，在我们的实验条件下，咳嗽气流的最大穿透距离在50.6 - 85.5个开口直径（D）的范围内。在相同的特征雷诺数（Rec）和归一化咳嗽呼出体积（Q/AD，其中Q为咳嗽呼出体积，A为开口面积）下，真实咳嗽和正弦情况比脉动情况表现出更强的穿透能力。然而，Rec和Q/AD对最大穿透距离的影响更为显著；Rec和Q/AD的值越大，反映出咳嗽气流的穿透距离越大。制定了一个方案来对空气中原型和水中模型之间的颗粒实验进行缩放。水槽实验表明，尽管中大型颗粒容易沉积，但其最大扩散距离与小颗粒相似。此外，主导涡在增强颗粒传输方面起着重要作用。
