Turbulent dispersion of breath by the wind
Florian Poydenot, Ismael Abdourahamane, Elsa Caplain, Samuel Der,, Antoine Jallon, In\'es Khoutami, Amir Loucif, Emil Marinov, Bruno Andreotti

TL;DR
This study experimentally investigates how aerosols disperse in turbulent airflow, revealing a ballistic-to-diffusive transition and non-diffusive decay of CO2, with implications for understanding pathogen transmission and educational approaches.
Contribution
It provides new experimental insights into aerosol dispersion at small source scales, challenging classical diffusion models, and demonstrates pedagogical and public health applications.
Findings
Aerosol dispersion exhibits a ballistic-to-diffusive transition.
CO2 concentration decays as inverse squared distance, not by classical diffusion law.
Experimental results inform public health policies for indoor air safety.
Abstract
The pioneering work of G.I. Taylor on the turbulent dispersion of aerosols is exactly one century old and provides an original way of introducing both diffusive processes and turbulence at an undergraduate level. Light enough particles transported by a turbulent flow exhibit a Brownian-like motion over time scales larger than the velocity correlation time. Aerosols are therefore subjected to an effective turbulent diffusion at large length scales. However, the case of a source of pollutant much smaller than the integral scale is not completely understood. Here, we present experimental results obtained by undergraduate students in the context of the COVID-19 pandemic. The dispersion of a smoke of oil droplets by a turbulent flow is studied in a wind tunnel designed for pedagogical purposes. It shows a ballistic-like regime at short distance, followed by Taylor's diffusive-like regime,…
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