Coughs are one of the primary means of transmission of diseases such as influenza and SARS-CoV-2 (COVID-19). Disease spreading occurs by the expulsion of pathogen containing aerosol droplets. Fine droplets can pass through layers of masks and are carried away by the exhaled airflow unlike larger droplets that settle down due to gravity. Hence, it is important to quantitatively assess the maximum distance of travel of typical human coughs with and without different types of masks. Even though near field data are available near the mouth, far field data are scarce. In this study, the schlieren method that is a highly sensitive, non-intrusive flow visualization technique is used. It can directly image weak density gradients produced by coughs. An assessment of different methods of covering the mouth while coughing is arrived at by using observations from high speed schlieren images. The effectiveness of coughing into the elbow is examined. The velocity of propagation of coughs and the distance of propagation with and without masks are quantified. It is also found that normalizing the distance-velocity profiles causes all the data to collapse onto a universal non-dimensional curve irrespective of the usage of different types of masks or test subjects. Visualization of cough flow fields and analysis of experimental data reveal that the flow physics is governed by the propagation of viscous vortex rings.

中文翻译：

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远距离人类咳嗽气流的普遍趋势

咳嗽是流感和 SARS-CoV-2 (COVID-19) 等疾病的主要传播途径之一。疾病传播通过含有气溶胶液滴的病原体的排出而发生。细小的飞沫可以穿过多层口罩，并被呼出的气流带走，而较大的飞沫则因重力而沉降。因此，重要的是定量评估使用和不使用不同类型口罩的典型人类咳嗽的最大传播距离。尽管在口附近可以获得近场数据，但远场数据很少。在这项研究中，使用了高度敏感、非侵入式流动可视化技术的纹影方法。它可以直接成像咳嗽产生的弱密度梯度。通过使用来自高速纹影图像的观察结果，对咳嗽时捂住嘴的不同方法进行了评估。检查咳嗽到肘部的有效性。咳嗽的传播速度和有和没有面具的传播距离被量化。还发现，无论使用不同类型的掩码或测试对象，对距离-速度曲线进行归一化都会导致所有数据折叠到通用无量纲曲线上。咳嗽流场的可视化和实验数据的分析表明，流动物理受粘性涡环的传播控制。咳嗽的传播速度和有和没有面具的传播距离被量化。还发现，无论使用不同类型的掩码或测试对象，对距离-速度曲线进行归一化都会导致所有数据折叠到通用无量纲曲线上。咳嗽流场的可视化和实验数据的分析表明，流动物理受粘性涡环的传播控制。咳嗽的传播速度和有和没有面具的传播距离被量化。还发现，无论使用不同类型的掩码或测试对象，对距离-速度曲线进行归一化都会导致所有数据折叠到通用无量纲曲线上。咳嗽流场的可视化和实验数据的分析表明，流动物理受粘性涡环的传播控制。