Effect of coherent structures on particle transport and deposition from a cough

Abstract

The transport of droplets expelled when coughing is of critical importance for understanding and preventing airborne disease transmission. However, the cough flow structure is complex, and numerous simplifications are often made to the initial flow condition in laboratory and numerical studies. We aim to challenge some of these assumptions, through particle transport experiments from a highly repeatable cough generator with a realistic oral cavity. In the present study the simultaneous transport and deposition of 22–27 μm, 45–53 μm, and 180–212 μm particles was investigated. Hot-wire measurements of the flow field showed the formation of two parallel jets on either side of the tongue, which produced a free shear layer downstream. Quantitative deposition measurements show that particle deposition patterns are strongly dependent on the formed shear layer for the smaller particles but not the largest size. The effect of circulation was characterized using a modified Stokes number of the form given by Davila and Hunt (2001). The scaling analysis and quantitative data both support the conclusion that while the 180–212 μm particles are not strongly affected, the transport and deposition of the smaller particles are influenced by orifice geometry. These results demonstrate that particle transport from a cough, for which most released droplets are below 22 μm, is a strong function of coherent flow structures present in the 3D flow field.