Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U07: Respiratory Flows II: Droplets and Disease Transmission |
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Chair: Arvind Santhanakrishnan, Oklahoma State University-Stillwater Room: 134 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U07.00001: A population-based study of the facemask fluid dynamics during talking activity Akshay Anand, Tso-Kang Wang, Tomas Solano, Kourosh Shoele Recent studies have shown that the flow generated during routine daily activities such as talking, breathing, and laughing has the potential to spread the SARS-CoV-2 virus. Droplets produced during everyday speech may act as a catalyst in the transmission of COVID-19. Here, we focus on understanding how some syllables may induce mouth movement and further may result in a poor fit of the mask during talking, resulting in modified leakages from the gaps. A novel analytical integral boundary layer solution is devised to quantify the flow in the interface region between the face and the mask. The mask is deployed on the face using the concept of minimum elastic energy to ensure a natural fit. The space between the face and the mask is mathematically modeled with a series of interconnected channels with the porous top boundary, wherein the compatibility conditions determine the channel flow distribution. The model is validated with a detailed flow simulation and employed to find the interconnected relation between fitness during talking, porosity, and leakage through the mask. We quantify the effectiveness of face masks during talking in a large cohort of faces and diverse probable talking scenarios to advise simple metrics that can quantify the leakage pattern and mask efficacy in talking activities. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U07.00002: Short-range exposure to airborne virus transmission and current guidelines Federico Dalla Barba, Jietuo Wang, Mobin Alipour, Giovanni Soligo, Alessio Roccon, Marco De Paoli, Francesco Picano, Alfredo Soldati After the Spanish flu pandemic, it was apparent that airborne transmission was crucial to spreading virus contagion, and research responded by producing several fundamental works like the experiments of Duguid and the model of Wells. These seminal works have been pillars of past and current guidelines published by health organizations. However, in about one century, understanding of turbulent aerosol transport by jets and plumes has enormously progressed, and it is now time to use this body of developed knowledge. In this work, we use experiments and simulations of droplet-laden turbulent puffs emitted during sneezes in different environmental conditions. We consider the same emission and we change temperature and humidity, and we observe strong variation in droplets' evaporation in accordance with their local temperature and humidity microenvironment. We assume that 3% of the initial droplet volume is made of nonvolatile matter. Our analysis confirms that droplets' lifetime is always about one order of magnitude larger compared to previous predictions. Finally, we have been able to produce original virus exposure maps, which can be a useful instrument for health scientists and practitioners to calibrate new guidelines to prevent short-range airborne disease transmission. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U07.00003: Coherent structures in the vocal tract and speaking jet: Simulation with anatomically accurate geometry Apratim Dasgupta, Saikat Basu, Daniel Foti Aerosolized particles emanating from the vocal tract are dispersed by a pulsed jet during speaking and breathing. The intricacies of the anatomically accurate vocal tract geometry and changes in flow rate create a wide range of turbulent scales both in the tract and jet. Geometrically-resolving large-eddy simulation with the curvilinear immersed boundary method is employed to capture the disparate internal flow and external speaking jet of a physically realistic vocal tract. We investigate the evolution of coherent structures of both steady and pulsating jets for breathing and speaking. We observe complex coherent structures and recirculation zones across disparate scales. Large structures are generated in the glottis and modified by the pharynx and oral cavity. The coherence and dominant structures are quantified with spectral analysis and proper orthogonal decomposition. Turbulent statistics of the speaking jet are compared to those of a canonical turbulent jet. The analysis reveals that the effects of geometry lead to various regions of high vorticity and the presence of coherent structures. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U07.00004: Interaction of physiological expiratory flow with gasper jets in an airliner cabin Jacqueline Esimike, Mitchell P Ford, Arvind Santhanakrishnan Airborne transmission of the SARS-CoV-2 virus has been identified as the dominant route for the spread of the COVID-19 pandemic. Transmission of airborne diseases is of particular concern in densely populated and highly confined indoor environments such as aircraft cabins. However, a detailed experimental characterization of flow within airliner cabins remains unavailable. We developed a respiratory flow phantom using a piston-cylinder apparatus and validated the setup against physiological expiratory flow rates of human coughing, sneezing and talking. This flow phantom was connected to a human dummy that was seated inside an MD-80 airliner cabin. Time-resolved 2D-2C PIV measurements were conducted in both flight and ground configurations. The interaction of airflow from the above expiratory activities with overhead gasper jets will be presented. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U07.00005: Droplet Formation and Transport during Exhalation and Aspiration of Bottlenose Dolphins Subhamoy Gupta, OMRI RAM, Lisa Dipinto, Yuhui Lu, Deepan Sharma, Sylvia Rickett, Elizabeth Stratton, Joseph Katz Advancement in understanding of exposure of marine mammals to surface crude oil after a spill is necessary for evaluating risks and responses. In this study, we characterize the airflow and airborne water droplets generated by trained bottlenose dolphins during exhalation and inhalation. Data is obtained for various dolphins’ size, sex, levels of prior activities, chuffs, and normal breaths. Test performed in the National Aquarium involve acquisition of high-speed holograms of a sample volume with a cross section of 68x68 mm2 covering the exit from the dolphins’ blowhole at a resolution of 33 μm/pixel. Upon reconstruction, we obtain a record of the droplet generated by the breathing. In some cases, the air is also seeded by externally generated mist for evaluating the velocity field after accounting for the settling velocity of the droplets. The evolution of the droplets size and spatial distributions are processed using a machine learning algorithm. Cross-correlation based analysis is used for mapping the velocity distributions in a series of volume slabs. Ongoing data analysis shows that for normal breathing events the exhalation occurs for 200-300 ms with speeds exceeding 5 m/s, and that the most probable droplet diameter is about 130 μm. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U07.00006: On asymmetric and incomplete bronchial trees Debjit Kundu, Mahesh Panchagnula Multiple forms of life depend on branched flow networks for physiological transport processes. Human airways are one among them and is a brilliant example of how evolution has developed optimal designs for biological systems. Existing body of research on anatomy of bronchial trees and air-flow physics within them has discovered the existence as well as benefits of asymmetry in branch divisions. The present study builds morphometric parameter-based mathematical models of the bronchial trees to study the effects of asymmetry and incompleteness due to anatomical limitations of the body on the area available for gas exchange, resistance to fluid flow, volume occupied the bronchial tree and particle deposition within the bronchial tree. We observe that maximum surface area for gas exchange, minimum resistance and minimum volume are obtained at either symmetry or very small asymmetry. But with increasing asymmetry, deposition of inhaled foreign particles in the non-terminal airways is enhanced. This aids in self-defence of the host against virus laden aerosols as well. Thus, we can appreciate how natural asymmetry present in human lungs provides an optimal design taking care of maximising gas exchange and protection while minimising resistance and volume. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U07.00007: A statistical framework for assessing the effectiveness of filtration and ventilation in preventing indoor airborne viral transmission using high-fidelity simulations Krishnaprasad Kalivelampatti Arumugam, Nadim Zgheib, S Balachandar, Jorge Salinas The risk of airborne viral contagion in indoor spaces can be greatly mitigated or aggravated by the quality of the ventilation system. Theoretical models have been used extensively to predict the spread of infectious diseases in such settings. However, it is reasonable to expect that a perfectly well-mixed state predicted by those models cannot be achieved at any realistic level of ventilation. This work evaluates the theory with results from large eddy simulations of flow in a canonical room of dimensions 10m × 3.2m × 10m with an overhead air conditioning unit. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U07.00008: Onto Understanding the Mitigation of Airborne Pathogen Transmission Michael P Kinzel, Jonathan Reyes, Douglas Fontes, Aaron Foster, Bernhard Stiehl, Steven Schroeder, Rajendra Shrestha, Juanpablo Delgado, kareem ahmed This effort summarizes ongoing efforts at the University of Central Florida focused on understanding the fluid dynamics of transmission processes associated with airborne pathogens and the COVID-19 pandemic. The effort uses a combination of experiments, computational fluid dynamics (CFD), and Wells-Riley transmission probability models. These studies indicate the efficacy of common approaches such as masks, ventilation system design, and social distancing. In general, we find that all these methods show benefit, however, perhaps the least impactful and most harmful to societal function is social distancing. The effort expands well beyond these established methods and develops novel understanding and methods for control. A few unexpected findings are the relationship between age, health, and transmission. This includes that transmission in children is reduced through their lower emission rate and pulmonary rates. But we also find that the elderly, ill, and women may be less likely to transmit pathogen-carrying droplets/aerosols. In addition, we found unexpected relationships between transmission and the ingestion of foods, which can promote or inhibit the formation of droplets. These processes will be discussed in relation to underlying fluid dynamic processes. These factors are all critical to passive control of the transmission events. Results from these studies will be summarized in the presentation. |
Tuesday, November 22, 2022 9:44AM - 9:57AM Author not Attending |
U07.00009: Importance of inhomogeneous mixing in governing exposure to indoor airborne contaminants Markus J Schmidt, Xiaoyi Hu, Reid Kovacs, Abbas Ghasemi, James Lynch, Naijian Shen, Jonathan Jilesen, Thomas Heldt, Lydia Bourouiba Airborne contaminant concentration and transport in closed indoor spaces play a crucial role in exposure of occupants to respiratory pathogen transmission and public health outcomes in time of pandemics. One key assumption often invoked in indoor transmission risk modelling is that of homogeneous air mixing. Yet indoor spaces, including both mixing or displacement ventilation, are seldom homogeneously mixed. Yet there are little to no direct quantification and prediction of heterogeneity for such spaces. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U07.00010: Quantifying Covid-19 Transmission Risk Indoors using GPU Accelerated Spectrally Accurate Simulations of Aerosol Transport Som Dutta, Neil Lindquist, Misun Min, Paul Fischer, Rao Kotamarthi One of the primary modes of transmission of the SARS-CoV-2 virus has been identified to be airborne, with human generated respiratory aerosols and droplets being the main carrier of the virus. This is not only applicable for SARS-CoV-2, but for all airborne diseases. The respiratory aerosols/droplets are generated during various expiratory events, like speaking and coughing; and understanding their dispersion will help design effective transmission mitigation strategies. To quantify this phenomena we conducted high-fidelity turbulence resolved multiphase simulations, where the aerosols were modeled using the Lagrangian particle tracking method. The model was implemented in the NekRS, the GPU accelerated version of the high-order spectral element based incompressible Navier-Stokes solver Nek5000 [1]. A fast and robust GPU-enabled interpolation utility for NekRS was utilized [2]. |
Tuesday, November 22, 2022 10:10AM - 10:23AM |
U07.00011: Optimization of air purifier placement for mitigation of airborne contamination Fuqian Yin, George Love, Yves C Dubief The best approach to avoid airborne contamination in confined space is (1) to clean the air and (2) to mask. This study focuses on air purification, an affordable mtigation method used with success gainast COVID and air pollution. Using state of the art large eddy simulation and a multi-objective optimization platform, we investigate the optimal placement of air purifiers in a modeled conference room and classroom. Emissions are either modeled as individual aerosols using Lagrangian transport, or concentration of contaminants using Eulerian transport equations. Realistic room turbulence is produced via natural convection and HVAC systems when applicable. The potential, limitations and uncertainties of the approach will be discussed as a tool to design solutions aiming at lowering the risk of contaminations in schools and common areas in the workplace. |
Tuesday, November 22, 2022 10:23AM - 10:36AM |
U07.00012: Estimation of viral load and infection probability for a "mild" cough using direct numerical simulation Sourabh S Diwan, Shashank S Reddy, Rohit Singhal, S Ravichandran The transmission of virus-laden droplets from one person to another for COVID-19-type diseases is a fluid dynamical problem. Here we present results from direct numerical simulation of a "mild" cough flow using an Eulerian approximation for liquid droplets, which is valid for small droplet Stokes numbers. The Boussinesq-Navier-Stokes equations are solved numerically using a closure model for the droplet evaporation time scale. We estimate the viral exposure on an imaginary susceptible person by computing the liquid droplet flux through a circular region (approximating human face) at different distances from the infected speaker and using values of the number of virions per unit volume of cough liquid from the literature. We consider the inhalation of virions through the nose as well as exposure through the eyes and the mouth while determining the total viral load. The associated infection probability is then determined based on a characteristic infection dose. The resulting map of infection probability as a function of space and time can serve as an important input to epidemiological modelling. Moreover, the present scheme, being computationally inexpensive, can be used for determining long-range transmission of infectious droplets and the resulting spread of airborne diseases. |
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