Fluid Dynamics of Speech and the Spatial-Temporal Distribution of Aerosols

新冠肺炎的传播突显出，在没有疫苗的情况下，缺乏减少传染性病毒影响的指导方针和缓解策略。事实上，包括无症状个体在内的随意互动，如说话，被认为在病毒传播中发挥了重要作用。然而，关于语音特征对呼出流空间范围的影响的定量研究很少，也没有人知道一对说话人之间相应的气流。这类研究在流体力学和运输现象文献中基本没有，甚至在公共卫生的定量研究中更普遍地缺乏。要解决病原体在个体尺度上的“局部运输”这一主题，一种方法是使用代表语音中气流的模型实验以及基于相应流体运动方程的数值模拟来表征气流的空间和时间特征，并通过融入语言学知识来关注英语口语的语音特征。这项研究将填补文献中的这一重要空白，并允许人们对病原体在人与动物之间传播的流体动力学进行更广泛的思考，因为动物对食物供应至关重要。它还将提供必要的洞察力，以评估随意互动模型中的感染风险。外展工作包括突出研究人员与未来研究科学家接触、教学和指导的方法，包括继续自2002年以来每年一次的“假期”讲座。该项目的目标是为对话中典型的气流提供新的定性见解和定量特征，因为现在人们更好地认识到，在许多情况下，空中运输即使不是病毒/病原体传播的主要机制，也可以是主要的。事实上，尽管自1918年新冠肺炎大流行以来，对公共卫生的研究已有百年历史，但疾病预防控制与预防中心和世卫组织几个月来一直对通过空气传播的新冠肺炎构成的危险的认识令疾控中心和世卫组织感到惊讶。为了应对这一挑战，将要开展的研究将在三个系统目标中整合实验和数值模拟。首先，语音流的发展将通过测量声音和单词的压力和流率信号来量化，包括元音、辅音和塞音的签名。实验中将使用粒子图像测速仪和激光照射下扬声器周围的雾滴薄片以及相应的图像处理来研究流动的物理性质，直接的数值模拟将用与实验一致的初始和边界条件求解Navier-Stokes方程。然后，将通过实验和数值模拟来研究面对面对话中的流动，包括源流之间的垂直偏移所起的关键作用，以及相应的呼出物质的传播。最后，实验和数值模拟将表征附近水平边界的影响，例如桌子，它影响呼出物质的水平传播。结果将提供给其他研究人员，然后他们也可以利用这个数据库。这些研究主题将促进对病原体传播的理解，这些病原体可能会伴随着随意互动的流言流。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The spread of COVID-19 highlights the lack of guidelines and mitigation strategies for reducing the impact of a contagious virus in the absence of a vaccine. In fact, casual interactions, such as speaking, involving asymptomatic individuals are believed to play a significant role in virus transmission. Nevertheless, there are few quantitative studies of the influence of the phonetic features of speech on the spatial extent of the exhaled flows, nor are the corresponding airflows between a pair of speakers known. Such studies have largely been absent from the fluid mechanics and transport phenomena literatures, and even absent more generally from quantitative studies of public health. One approach for tackling this theme of “localized transport” of pathogen at the scale of individuals is to use model experiments representative of the airflows in speech along with numerical simulations based on the corresponding equations of fluid motion to characterize the spatial and temporal features of the airflows, with attention given, by incorporating knowledge in linguistics, to the phonetic-features characteristic of spoken English. This study will fill this important gap in the literature and allow broader thinking about the fluid dynamics of pathogen transmission between people, as well as animals which are important to the food supply. It will also provide insights necessary to assess risk of infection in models of casual interactions. The outreach efforts included characterize the investigator’s approaches to engaging with, teaching, and mentoring future research scientists, including continuing an annual “holiday” lecture that has been delivered since 2002. The goal of this project is to provide new qualitative insights and quantitative characterization of the airflows typical of conversations, as it is now better appreciated that airborne transport can, in many cases, be a major, if not the dominant, mechanism of viral/pathogen transmission. In fact, the realization of dangers posed by airborne spread of COVID-19 surprised the CDC and WHO for many months despite 100 years of research in public health since the 1918 pandemic. To address this challenge the research to be performed will integrate experiments and numerical simulations in three systematic aims. First, the development of flows in speech will be quantified by measuring pressure and flow rate signals characteristic of sounds and words, including the signatures of vowels, consonants, and plosives. The physics of the flow will be investigated in experiments using particle-image velocimetry and a laser-illuminated sheet of fog droplets around a speaker and corresponding image processing, and direct numerical simulations will solve the Navier-Stokes equations with initial and boundary conditions consistent with the experiments. Then, experiments and numerical simulations will be used to study flows in face-to-face conversations, including the key role played by the vertical offset between the source flows, and the corresponding spread of exhaled material. Finally, experiments and numerical simulations will characterize the influence of a nearby horizontal boundary, such as a table, which influences horizontal propagation of exhaled material. The results will be made available to other researchers who can then also take advantage of this database. The research themes will advance the understanding of pathogen transport that may accompany fluid flows of speech that are characteristic of casual interactions.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.