Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session ZC05: Respiratory Flows II |
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Chair: Saikat Basu, South Dakota State University Room: Ballroom E |
Tuesday, November 26, 2024 12:50PM - 1:03PM |
ZC05.00001: EVAPORATION OF LEVITATED BACTERIA-LADEN DROPLETS AT DIFFERENT STAGES AND RELATIVE HUMIDITY Amey Nitin Agharkar, Dipasree Hajra, Kush Kumar Dewangan, Dipshikha Chakravortty, Saptarshi Basu A droplet is the main component of aerosols responsible for transmitting many respiratory diseases. Therefore, understanding the desiccation dynamics of the droplet in conjunction with infection studies is a comprehensive research study. Such studies are rarely attempted due to the complexity of experimenting with bacteria/viruses. Our study experimentally compared the levitated samples at two different relative humidity conditions and three stages of diameter-based evaporation. Our study demonstrates the role of the differential relative humidity-based precipitation in conferring virulence to infectious pathogens. For the same initial diameter of the droplet, the average mass evaporation rate for the droplet at low RH is one to two orders higher than the droplet at high RH conditions. Therefore, more evaporative stress is experienced by the bacteria in the low RH case. The bacterial survival is higher in the high RH case than in the low RH case. Also, the bacteria survive more at the early stage of the diameter-based evaporation than the final precipitate stage for both RH conditions. Therefore, the high RH samples exhibited increased virulence properties compared to the low RH samples. |
Tuesday, November 26, 2024 1:03PM - 1:16PM |
ZC05.00002: Integrating Machine Learning and Physics-Based Flow Models for Population-Level Respiratory Disease Simulation Akshay Anand, Kourosh Shoele This study presents a novel framework for simulating respiratory disease transmission across diverse populations using advanced machine learning and fluid-based reduced-order modeling. Our approach leverages computational efficiency to integrate a wide range of facial shapes, mask sizes, and fluid dynamics, modeling the intricate interactions between facial movement, mask fit, and varying dynamic conditions. We represent the space between the face and mask as interconnected channels with porous boundaries and imposed compatibility conditions to accurately predict airflow leakage patterns. By incorporating facial deformations linked to specific phonemes, we analyze how different speech scenarios affect mask efficacy, providing a nuanced understanding of how verbal communication impacts leakage. We will then compare these results with our breathing simulations inside a large cohort of subjects, quantifying the differential impact of these two distinct respiratory events on mask leakage patterns. Finally, we discuss how this methodology contributes to the identification of more effective mitigation strategies for respiratory disease transmission. |
Tuesday, November 26, 2024 1:16PM - 1:29PM |
ZC05.00003: Pulmonary Edema, Reabsorption, and Clearance James Bernard Grotberg, Francesco Romano', John Grotberg We present a 2D flow model of the alveolar interstitium as a long, thin rectangle, 0≤x≤L, -d≤y’≤d where d/L<<1. The capillary membrane at y’=-d follows a Starling equation with kc the hydraulic conductivity. The alveolar membrane at y’=d also employs a Starling equation with kA the hydraulic conductivity, but we include an additional velocity term, -vab, for active fluid reabsorption. Interstitial pressures are imposed at the ends, pi = piB at x=0,L. Lubrication theory is applied to the capillary blood flow while the alveolus has a static liquid lining with surface tension, σ. The interstitium is treated as a porous media using the Brinkman equation and the coupled system solved with Fourier series. The resulting flow can be from the alveoli to the capillary (clearance), from the capillary to the alveoli (pulmonary edema), or both. Fluid originating from both capillary and alveolus exits the ends to the lymphatics. Model predictions correlate well with clinical criteria of pulmonary edema and therapies such as reducing σ, positive end expiratory pressure (PEEP) for the alveolar gas, and reducing blood pressure. There is good correlation to animal experiments that measure pulmonary lymphatic flows which increase linearly with blood pressure, but only account for ~10% of edema recovery flows with ~90% crossing directly to the capillary. vab increases reabsorption flow rates in the central region and shifts streamlines in the end regions to enhance alveolar fluid exit. Wall shear stress levels on the membranes are found to be in the biologically stimulating range. |
Tuesday, November 26, 2024 1:29PM - 1:42PM |
ZC05.00004: Mechanical Reproduction of Aerosols during Respiration of Bottlenose Dolphins Subhamoy Gupta, Yulong Liang, Aryan Unnikrishnan, Lisa Dipinto, Daniel Levine, Joseph Katz To characterize the evolution of airborne droplets and flow field during exhalation and inhalation of bottlenose dolphins, we recorded and analyzed high-speed holograms for multiple breaths of trained dolphins at the National Aquarium in Baltimore. These results are being used as a reference for the design and calibration of a mechanism that mimics the dolphin breaths, for use in laboratory tests aimed at understanding the exposure and risk posed to marine mammals during and after an oil spill. The exhalation plume is reproduced by opening a high-speed valve at the exit of a 20L pressurized volume representing the lungs, and placing two aerosol generators, consisting of porous cylinders having pressurized liquid on their outer side, along the path of the air outflow. These generators are the primary source of small droplets and high-speed ejecta. The source of larger droplets and non-spherical blobs is the liquid on top of the exhalation valve, representing water in the dimple of a dolphin's blowhole after surfacing. The inhalation is simulated by opening another high-speed valve at the entrance of a second chamber in partial vacuum. The droplet statistics are recorded using high-speed holography, and the flow-field is resolved using PIV. The inhaled liquid is collected and monitored. Ongoing calibration tests involving clean water aim at reproducing the airflow and droplet statistics recorded in the aquarium. Subsequent tests will involve different oil and oil-dispersant mixtures. |
Tuesday, November 26, 2024 1:42PM - 1:55PM |
ZC05.00005: Respiratory airflow driven by propagative collapse in insect tracheae Saadbin Khan, John J Socha, Khaled Adjerid, Anne E Staples Insect respiratory systems are highly effective at transporting respiratory gases at the microscale, but their mechanisms of flow production are not well understood. Rhythmic tracheal compression (RTC), a gas exchange pattern that has been identified in multiple insect taxa, is characterized by the periodic compression and reinflation of parts of the tracheal system, creating advective flows that enhance transport. Synchrotron X-ray imaging has provided the precise kinematics of tracheal compression during RTC in several insects. Two types of tube collapse have been observed in tracheal pathways: propagating, with the collapse partially directed along the tracheal axis, and non-propagating. While multi-site, non-propagating collapse phenomena have been studied and modeled extensively, propagative collapse is less explored. Here, building on a previous theoretical model (Aboelkassem, Phys. Fluids, 2019) we study propagative collapse using three-dimensional finite volume simulations in idealized and in realistic tracheal geometries, with physiological collapse kinematics obtained from synchrotron X-ray imaging. The simulation results suggest that propagative collapses alone can induce net unidirectional flows in insect tracheae. Mimicking propagative collapse and other robust, decentralized insect respiratory actuation and control mechanisms in microfluidic devices may lead to improved performance. |
Tuesday, November 26, 2024 1:55PM - 2:08PM |
ZC05.00006: A mechanics-based model for inhalation-driven transmission of smallpox Mohammad Yeasin, Mohammad Mehedi Hasan Akash, Saikat Basu This study models human inhalation during normal breathing, replicated through high-fidelity Large Eddy Simulations of 15 and 30 L/min airflow rates. Inhaled transport of pathogenic particulates against the ambient airflow is then monitored using an inert discrete phase model. The anatomically realistic airway geometries used in the simulations are clinically healthy, developed from high-resolution medical scans from two subjects. The results, with cross-disciplinary inputs, can help quantify infection onset parameters in the airway. Smallpox from the Poxviridae family, with infection trigger sites at the oropharynx and in the lower airway, is picked as a sample pathogen capable of airborne transmission. The simulated findings on inhaled transmission to such infective sites are integrated with virological and epidemiological parameters for smallpox, namely the virion concentration in host ejecta material and the typical exposure durations for confirmed infection. This integration helps estimate the infectious dose, or the number of virions sufficient to infect an exposed individual. Our findings also confirm that a precise consideration of vortex-dominated effects on respiratory transport is crucial for a reliable mechanistic model of infection onset. |
Tuesday, November 26, 2024 2:08PM - 2:21PM |
ZC05.00007: Numerical simulations of a diagnostic ultrasound-induced deformation of a pulmonary alveolus interface Nazarii Koval, Emma Slaght, Avery Trevino, Mauro Rodriguez Diagnostic ultrasound (DUS) of the lung uses high-frequency acoustic waves that interact with tissue. These waves reflect, allowing visualization of internal structures, such as air-filled alveoli and blood vessels. Due to misalignment between the gradient of the acoustic wave and material interface, baroclinic vorticity may be deposited at the tissue-air interface (air-filled alveoli). It is hypothesized that vorticity can distort the interface, potentially leading to harmful bioeffects such as hemorrhage. We conduct 3D numerical simulations of the DUS-induced deformation of an alveoli interface using the open-source Multicomponent Flow Code (MFC) [Radhakrishnan & Le Berre et al. Comp. Phys. Comm. (2024)]. MFC solves compressible flow equations using a six-equation multiphase model and, for the lung tissue, a hyperelastic material model. We present the deformation of the air-filled alveoli material interface and characterize the principal stresses within the lung tissue as a function of elastic properties, initial acoustic wave parameters, and interface geometry. Additionally, we will show elasticity inhibiting the growth of the material interface and compare with theoretical results. |
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