Colliding respiratory jets as a mechanism of air exchange and pathogen transport during conversations

Arghyanir Giri (1) , Neelakash Biswas (1) , Danielle Chase (2) , Nan Xue (2) , Manouk Abkarian (3) , Simon Mendez (4) , Sandeep Saha (1) , Howard Stone (2)

1 IIT Kharagpur - Indian Institute of Technology Kharagpur
2 MAE - Department of Mechanical and Aerospace Engineering [Princeton]
3 CBS - Centre de Biochimie Structurale [Montpellier]
4 IMAG - Institut Montpelliérain Alexander Grothendieck

Air exchange between people has emerged in the COVID-19 pandemic as the important vector for transmission of the SARS-CoV-2 virus. We study the airflow and exchange between two unmasked individuals conversing face-to-face at short range, which can potentially transfer a high dose of a pathogen, because the dilution is small when compared to long-range airborne transmission. We conduct flow visualization experiments and direct numerical simulations of colliding respiratory jets mimicking the initial phase of a conversation. The evolution and dynamics of the jets are affected by the vertical offset between the mouths of the speakers. At low offsets the head-on collision of jets results in a 'blocking effect', temporarily shielding the susceptible speaker from the pathogen carrying jet, although, the lateral spread of the jets is enhanced. Sufficiently large offsets prevent the interaction of the jets. At intermediate offsets (8-10 cm for 1 m separation), jet entrainment and the inhaled breath assist the transport of the pathogen-loaded saliva droplets towards the susceptible speaker's mouth. Air exchange is expected, in spite of the blocking effect arising from the interaction of the respiratory jets from the two speakers.

Mots clés: jets; particle/fluid flow; turbulent mixing

Domaines: Mécanique des fluides [physics.class-ph]

Arghyanir Giri, Neelakash Biswas, Danielle Chase, Nan Xue, Manouk Abkarian, et al.. Colliding respiratory jets as a mechanism of air exchange and pathogen transport during conversations. Journal of Fluid Mechanics, 2021, 930, pp.R1. ⟨10.1017/jfm.2021.915⟩. ⟨hal-03795532⟩