Collaborative Research: Effect of Pulsatility on Expiratory Droplet-Laden Flows

预测打喷嚏、咳嗽或说话等呼气过程中产生的飞沫和气溶胶的扩散，是了解传染病传播和制定有效对策以控制疫情的关键一步。工业和学术界使用的现有开源和商业工具，用于预测液滴和气溶胶的分散，依赖于简单的模型，无法捕捉潜在湍流物理的细节。在这个项目中，通过实验和计算相结合的方法，在开发改进模型方面取得了进展，这些模型可以通过直接实施到现有工具中来轻松接受。该项目还包括重要的教育和外联活动。研究人员将扩大他们正在进行的努力，采用基于虚拟现实的成像技术，使充满液滴的呼气流的沉浸式三维表示成为一种教育工具。这些教育工具将用于奥本大学和密歇根大学的外展活动和研讨会。这个合作实验和计算项目的总体目标是量化在脉动呼气流中控制液滴运输和分散的基本流动物理。利用离体咳嗽模拟器和人体实验结合直接数值模拟，我们将量化脉动呼气流产生的流动相互作用对气溶胶分散的作用，并评估二次排出物的穿透长度。通过将时间分辨速度法与广泛验证的流体颗粒模拟方法相结合，这项工作将在揭示流动相互作用对液滴夹带和分散影响的新流动物理学方面取得突破性进展。一些预期的结果包括：(1)一个广泛的实验测量和高分辨率模拟数据库；(2)为紊流分散两相流的建模提供了良好的理论基础。这种流动物理的改进量化和降阶模型的发展将能够更好地预测液滴的分散，这是了解病毒感染传播的关键一步。所开发的方法将用于研究含液滴的呼气射流与气流屏障（例如面罩）的相互作用，并评估其减轻撞击呼气气流分散的功效。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Predicting the dispersion of droplets and aerosols generated during expiratory events like sneezing, coughing, or speech is a key step towards understanding the spread of infectious diseases and to develop effective countermeasures to contain outbreaks. Existing open-source and commercial tools used in industry and academia, to predict dispersion of droplets and aerosols, rely on simplistic models that fail to capture details of the underlying turbulent flow physics. In this project, through a combined experimental and computational approach, advancements are made towards the development of improved models that could be easily embraced through direct implementation into existing tools. This project also encompasses significant education and outreach activities. The investigators will expand their ongoing efforts to adopt Virtual Reality based imaging to enable immersive three-dimensional representations of droplet-laden expiratory flow as an educational tool. These educational tools will be used for outreach events and workshops at both Auburn University and the University of Michigan.The overall goal of this collaborative experimental and computational project is to quantify the fundamental flow physics that govern the transport and dispersion of droplets in a pulsatile expiratory flow. Using an ex-vivo cough simulator and human subject experiments combined with direct numerical simulations we will quantify the role of flow interactions, generated by pulsatile expiratory flow, on aerosol dispersion and assess the penetration length of secondary expulsions. By combining time-resolved velocimetry with an extensively validated fluid-particle simulation methodology, this effort will break ground in uncovering new flow physics relating the influence of flow interactions on the entrainment and dispersion of droplets. Some of the anticipated outcomes include: (1) an extensive database of experimental measurements and high-resolution simulations; and (2) a sound theoretical foundation for modeling turbulent disperse two-phase flows. Such improved quantification of flow physics and development of reduced-order models will enable better prediction of droplet dispersion, a key step towards understanding the spread of viral infections. The methods developed will be used to study the interaction of droplet-laden expiratory jets with flow barriers (for example face shields) and evaluate their efficacy to mitigate the dispersion of impinging expiratory flows.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.