Variability in expiratory trajectory angles during consonant production by one human subject and from a physical mouth model: Application to respiratory droplet emission

摘要

The COVID-19pandemic has highlighted the need to improve understanding of droplettransport during expiratory emissions. While historical emphasis has been placedon violent events such as coughing and sneezing, the recognition of asymptomatic andpresymptomatic spread has identified the need to consider other modalities, such asspeaking. Accurate prediction of infection risk produced by speaking requires knowledgeof both the droplet size distributions that are produced, as well as the expiratoryflow fields that transport the droplets into the surroundings. This work demonstratesthat the expiratory flow field produced by consonant productions is highly unsteady,exhibiting extremely broad inter-andintra-consonantvariability, with mean ejectionangles varying from ≈+30° to −30°. Furthermore, implementation of a physical mouthmodel to quantify the expiratory flow fields for fricative pronunciation of [f] and [θ]demonstrates that flow velocities at the lips are higher than previously predicted,reaching 20–30m/s, and that the resultant trajectories are unstable. Because bothlarge and small droplet transport are directly influenced by the magnitude and trajectoryof the expirated air stream, these findings indicate that prior investigations ofthe flow dynamics during speech have largely underestimated the fluid penetrationdistances that can be achieved for particular consonant utterances.