The present study investigates aerosol transport and surface deposition in a realistic
classroom environment using computational fluid-particle dynamics simulations. Effects of
particle size, aerosol source location, glass barriers, and windows are explored. While
aerosol transport in air exhibits some stochasticity, it is found that a significant
fraction (24%–50%) of particles smaller than 15
µ
m exit the system within
15 min through the air conditioning system. Particles larger than 20
µ
m
almost entirely deposit on the ground, desks, and nearby surfaces in the room. Source
location strongly influences the trajectory and deposition distribution of the exhaled
aerosol particles and affects the effectiveness of mitigation measures such as glass
barriers. Glass barriers are found to reduce the aerosol transmission of 1
µ
m particles from the source individual to others separated by at least
2.4 m by ∼92%. By opening windows, the particle exit fraction can be increased by ∼38%
compared to the case with closed windows and reduces aerosol deposition on people in the
room. On average, ∼69% of 1
µ
m particles exit the system when the windows
are open.
Identifying economically viable intervention measures to reduce COVID-19 transmission on aircraft is of critical importance especially as new SARS-CoV2 variants emerge. Computational fluid-particle dynamic simulations are employed to investigate aerosol transmission and intervention measures on a Boeing 737 cabin zone. The present study compares aerosol transmission in three models: (a) a model at full passenger capacity (60 passengers), (b) a model at reduced capacity (40 passengers), and (c) a model at full capacity with sneeze guards/shields between passengers. Lagrangian simulations are used to model aerosol transport using particle sizes in the 1–50
μ
m range, which spans aerosols emitted during breathing, speech, and coughing. Sneeze shields placed between passengers redirect the local air flow and transfer part of the lateral momentum of the air to longitudinal momentum. This mechanism is exploited to direct more particles to the back of the seats in front of the index patient (aerosol source) and reduce lateral transfer of aerosol particles to other passengers. It is demonstrated that using sneeze shields on full capacity flights can reduce aerosol transmission to levels below that of reduced capacity flights without sneeze shields.
Background
Human snores are caused by vibrating anatomical structures in the upper airway. The glottis is a highly variable structure and a critical organ regulating inhaled flows. However, the effects of the glottis motion on airflow and breathing sound are not well understood, while static glottises have been implemented in most previous in silico studies. The objective of this study is to develop a computational acoustic model of human airways with a dynamic glottis and quantify the effects of glottis motion and tidal breathing on airflow and sound generation.
Methods
Large eddy simulation and FW-H models were adopted to compute airflows and respiratory sounds in an image-based mouth-lung model. User-defined functions were developed that governed the glottis kinematics. Varying breathing scenarios (static vs. dynamic glottis; constant vs. sinusoidal inhalations) were simulated to understand the effects of glottis motion and inhalation pattern on sound generation. Pressure distributions were measured in airway casts with different glottal openings for model validation purpose.
Results
Significant flow fluctuations were predicted in the upper airways at peak inhalation rates or during glottal constriction. The inhalation speed through the glottis was the predominating factor in the sound generation while the transient effects were less important. For all frequencies considered (20–2500 Hz), the static glottis substantially underestimated the intensity of the generated sounds, which was most pronounced in the range of 100–500 Hz. Adopting an equivalent steady flow rather than a tidal breathing further underestimated the sound intensity. An increase of 25 dB in average was observed for the life condition (sine-dynamic) compared to the idealized condition (constant-rigid) for the broadband frequencies, with the largest increase of approximately 40 dB at the frequency around 250 Hz.
Conclusion
Results show that a severely narrowing glottis during inhalation, as well as flow fluctuations in the downstream trachea, can generate audible sound levels.
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