Investigation of the Effects of Nasal Flow and Dynamic Mouth Opening on Cough-Induced Airflow and Particle Dispersion: A Large-Eddy Simulation Study

Airborne transmission of respiratory pathogens remains a major public-health concern, as highlighted by the COVID-19 pandemic. Coughing is especially important because it is both a common symptom of airborne diseases and an efficient mechanism for generating and transporting pathogen-laden aerosols.

To better understand cough-driven transport, researchers have traditionally relied on experiments to measure cough flow and particle behavior. These studies have provided valuable flow-rate data and insight into jet development, but they can be resource-intensive and constrained by experimental complexity and ethical considerations. Computational fluid dynamics (CFD), particularly large-eddy simulation (LES), has therefore become an increasingly useful tool for resolving transient cough airflow and aerosol transport. In most CFD studies, however, cough boundary conditions are simplified by prescribing a time-varying volumetric flow-rate waveform together with a constant mouth opening area, while often neglecting the nasal pathway and assuming a mouth-only cough.
In reality, mouth opening can change during a cough, which can alter the local exit velocity even when the overall flow-rate waveform is fixed. In addition, any nasal outflow may modify jet directionality, entrainment, and particle trajectories near the source. As a result, previous studies may underrepresent the sensitivity of cough dispersion to physiologically realistic boundary-condition assumptions.

In the present study, we investigate how dynamic mouth opening area and nasal–oral flow partitioning affect near-field cough airflow and particle dispersion using LES. Time-varying mouth area is measured from camera images using image-processing methods and combined with a prescribed cough volumetric flow-rate waveform to define a time-dependent inlet velocity. Four nasal-to-oral flow-rate ratios are then simulated to isolate the effect of nasal exhalation. Preliminary results show that dynamic mouth opening increases mouth-exit velocity and shifts peak flow earlier, while nasal outflow can increase the spread angle of aerosol. These findings support more physiologically realistic cough modeling and improve prediction of airborne exposure.