Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session A01: Biological Fluid Dynamics: Infectious Disease I |
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Chair: Howard Stone, Princeton Room: North 120 AB |
Sunday, November 21, 2021 8:00AM - 8:13AM |
A01.00001: When fluid mechanics meets virology: a modeling framework for respiratory infection onset and projection of viral infectious dose Saikat Basu Synergizing airflow-induced inhaled particulate dynamics inside the nose, with clinical prognosis as well as virologic and epidemiologic data, can address questions like: (a) what are the hazardous particulate sizes predominantly responsible for a respiratory infection onset, or (b) what might be the minimum number of virions (i.e. the infectious dose) that can trigger an infection. This talk presents an extendable modeling framework to answer (a) and (b), in the context of SARS-CoV-2 transmission. The study combines computational fluid dynamics tracking of inhaled transport, with sputum assessments from hospitalized patients and prior measurements of speech ejecta sizes. To capture a variety of breathing conditions, four inhalation rates are simulated: 15, 30, 55, 85 L/min. The lower rate (i.e.15 L/min) replicates comfortable resting breathing with viscous-laminar steady-state physics; at higher rates, we apply Large Eddy Simulation. Regional deposition of virus-laden particulates at nasopharynx, which is the main initial infection site for SARS-CoV-2, peaks for the aerosol/droplet size range of 2.5–19 μm. Also, the infectious dose is projected at a remarkably low order of hundreds, underlining high viral transmissibility. See Basu, Scientific Reports, 11(1), 2021, for details. |
Sunday, November 21, 2021 8:13AM - 8:26AM |
A01.00002: Air Flows in an Orchestra Philippe Bourrianne, Paul R Kaneelil, Manouk Abkarian, Howard A Stone Infectious respiratory diseases spread through the release of droplets carrying pathogens from an infected person. During the COVID-19 pandemic, clusters of contaminations were identified during rehearsals within a choir or an orchestra. Activities like singing or playing wind instruments are indeed accompanied by an enhanced release of droplets, carried by expiratory flows, and so are able to contaminate other musicians of an orchestra, or perhaps members of the audience. One should expect that opera performance is at higher risk of infection due to the large number of wind instruments, and the spectacular loudness of opera singers. By working with members of the MET Orchestra in New York City, we have tracked the air exhaled by individual professional performers using an infrared camera and other flow visualization techniques. We measure the expiratory flow-rates, the flow velocities and the spatial extent of the exhaled air during the performance, and compare them with breathing or speaking. By describing the air flows in opera, we isolate situations where air flows from musicians might increase the risk of contamination within an orchestra. |
Sunday, November 21, 2021 8:26AM - 8:39AM |
A01.00003: Effects of turbulence and vortical structures on aerosolized droplets during speaking Apratim Dasgupta, Daniel Foti One of the main transmission routes of respiratory diseases is spread by the generation and aerosolization of virus-laden respiratory droplets. While the concentration of respiratory droplets is large for a cough or sneeze, talking—over time—can yield similar numbers of droplet nuclei but different droplet size distributions. Geometrically-resolving, large-eddy simulations incorporating a model geometry of the mouth and throat are undertaken to capture the expulsion of aerosolized droplets during speaking over a range of parameters, including Reynolds number, concentration, and size distribution. The trajectories of the droplets coupled with temperature and relative humidity are tracked. Simulation results are validated with experimental measurements of the concentration of droplets detected downwind of the mouth of a human, speaking. Statistics of droplet motion with respect to the background flow reveal that droplet trajectory is influenced by turbulent fluctuations and regions of high vorticity. This can affect the inertia and lifetime of expelled droplets. |
Sunday, November 21, 2021 8:39AM - 8:52AM |
A01.00004: Large-eddy simulation of human respiratory events with and without facial mask Ali Khosronejad, Wayne Oaks, Kevin Flora, Christian Santoni The Coronavirus disease outbreak of 2019 has been causing significant loss of life and unprecedented economic loss throughout the world. Social distancing and face masks are widely recommended around the globe in order to protect others and prevent the spread of the virus through breathing, coughing, and sneezing. To expand the scientific underpinnings of such recommendations, we carry out large-eddy simulations, along with Lagrangian and Eulerian particle transport approaches, of unprecedented resolution to elucidate the underlying physics of saliva particulate transport during human breathing and without facial masks. We elucidate the vortex dynamics of human breathing and show that saliva particulates could travel over 2.2 m away from the person without a mask. However, a non-medical grade face mask can drastically reduce saliva particulate propagation to 0.72 m away from the person. This study provides new quantitative evidence that facile masks can successfully suppress the spreading of saliva particulates due to normal breathing in indoor environments. |
Sunday, November 21, 2021 8:52AM - 9:05AM |
A01.00005: Effect of coughing pulsatility on the effectiveness of a surgical mask Sarah E Morris, Will McAtee, Jesse S Capecelatro, Vrishank Raghav It is well established that diseases such as COVID-19 are spread by airborne transmission, as infectious particles are generated in respiratory events like talking and coughing. Although coughing is a multi-pulsed event, the pulsatile nature of coughs on the dispersion of droplets is not well understood. One strategy to reduce disease transmission via expiration is the use of face coverings. In this work, the effectiveness of a surgical mask is studied for single- and double-pulsed coughs. Three cases are considered: a single-pulse (S1), a double-pulse (D1) comprising two S1 pulses and a single-pulse (S2) with the same cough expired volume as D1. Using a custom-built pulsatile coughing simulator, the flow leakage around the mask is quantified via flow visualization and PIV. The flow velocity profiles at the side and top of the mask take the form of a jet and a wall jet, respectively. Preliminary results show that the leakage volume expelled in a D1 event is greater than for S1 and S2. The leakage penetration distance at the side and top of the mask both appear to scale with t1/2 in the starting jet stage and t1/4 in the interrupted jet stage. |
Sunday, November 21, 2021 9:05AM - 9:18AM |
A01.00006: Simple Models of Face Mask Aerodynamics to Quantify Effects of Peripheral Leaks on Mask Effectiveness Chuanxin Ni, Tomas Solano, Tso-Kang Wang, Jung-Hee Seo, Kourosh Shoele, Kenny Breuer, Rajat Mittal Face masks continue to be at the front lines of our defense against COVID-19. Studies have shown that the filtration effectiveness (fractional blockage of respiratory droplets) depends not only on the cloth/fabric/material employed in the face mask but also the "fit" of the mask on the face. Most of the face masks worn by people have peripheral leaks, which can significantly diminish the filtration effectiveness of the masks. In the current study, we combine a simple lumped-element model of face mask aerodynamics with (a) numerical data from computational models of face mask deployment on realistic faces, and (b) experimental data on permeability and filtration efficiency of various cloths/fabrics, to quantify the filtration effectiveness of various masks. Results show that even with small peripheral gaps, the leaks through the periphery can reach a considerable proportion of the total respiratory volume flow rate, resulting in reduced filtration effectiveness. It is also found that the permeability of the mask material plays a significant role in determining the overall filtration effectiveness of face masks. The implications of these findings for the design of more effective face masks are discussed. |
Sunday, November 21, 2021 9:18AM - 9:31AM |
A01.00007: Estimation of Infectious Respiratory Droplets Spread and Size Distribution Evolution with CFD Simulations Jhon Quinones, Lucy T Zhang, Ali Doosttalab, James Cassidy, Ethan Wilens, Richard M Voyles, Victor Castano, Luciano Castillo With the development of new vaccines against the COVID-19, the reopening phase of public spaces such as schools, universities, restaurants, offices, among others, is a reality. However, there is a global concern that the number of cases may increase because of new virus variants and future pandemics. We employ unsteady Reynolds-Averaged Navier-Stokes (URANS) with the Euler-Lagrange approach to predicts the spread of the infectious saliva droplets contained on a single cough or sneeze. We fitted the discrete phase data from the CFD results with probability density functions (PDFs) to estimate the droplet size distribution as a function of time. The results indicate that the suggested social distancing protocol is not enough to avoid the transmission of COVID-19 since small saliva droplets (≤ 12μm) can travel in the streamwise direction up to 4 m when an infected person coughs, and more than 7 m when sneezes. The number of droplets in locations close to the respiratory system of a healthy person increases when the relative humidity of the room is low. The URANS simulations performed agree with previous experiments and LES simulations. Also, we developed particle-based CFD simulations for quasi-real-time predictions of the droplet spread. |
Sunday, November 21, 2021 9:31AM - 9:44AM |
A01.00008: Short-range exposure to airborne virus transmission and current guidelines Alfredo Soldati, Jietuo WANG, Mobin Alipour, Giovanni Soligo, Alessio Roccon, Marco De Paoli, Francesco Picano 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 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 detailed experiments and accurate computationally-intensive numerical simulations of droplet-laden turbulent puffs emitted during sneezes. We consider the same emission and we consider different temperatures and humidities. We observe strong variation in droplets evaporation or condensation in accordance with their local temperature and humidity microenvironment. Our systematic analysis confirms that droplets lifetime is always one order of magnitude larger compared to previous predictions, in some cases up to 200 times. Finally, we 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. |
Sunday, November 21, 2021 9:44AM - 9:57AM |
A01.00009: Effects of temperature and humidity on the spread of COVID-19 via respiratory droplet transport Han June Park, Sung-Gwang Lee, Jeong Suk Oh, Steven Barrett, Wontae Hwang Ever since the World Health Organization proclaimed Severe Acute Respiratory Syndrome-2 (SARS-CoV-2) as a pandemic in 2020, several research groups have investigated the correlation between temperature and humidity on COVID-19 spread. As respiratory droplets are expired into the ambient environment, they evaporate as they travel. Thus, most studies incorporate a droplet evaporation model. However, most models have not been thoroughly validated in terms of temperature and humidity. Herein, we first validated an evaporation model by imaging a droplet suspended in air using an acoustic levitator, placed within a constant temperature and humidity environmental chamber. Next, simulations were conducted using this model, to assess trajectories of cough droplets ejected from the mouth. Our results suggest that temperature does not have a significant effect on droplet trajectories, while humidity does. For larger droplets, higher humidity causes them to fall quicker to the floor and travel less. On the contrary, for smaller droplets, higher humidity causes the droplets to travel farther and end up at a lower height before evaporating, reducing the concentration of small aerosols near the respiratory tract. Therefore, we conclude that higher humidity helps in suppressing virus spread. |
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