Measurements of exhaled airflow velocity through human coughs using particle image velocimetry

Abstract

The sudden outbreak of coronavirus (COVID-19) has infected over 100 million people and led to over two million deaths (data in January 2021), posing a significant threat to global human health. As a potential carrier of the novel coronavirus, the exhaled airflow of infected individuals through coughs is significant in virus transmission. The research of detailed airflow characteristics and velocity distributions is insufficient because most previous studies utilize particle image velocimetry (PIV) with low frequency. This study measured the airflow velocity of human coughs in a chamber using PIV with high frequency (interval: 1/2986 s) to provide a detailed validation database for droplet propagation CFD simulation. Sixty cough cases for ten young healthy nonsmoking volunteers (five males and five females) were analyzed. Ensemble-average operations were conducted to eliminate individual variations. Vertical and horizontal velocity distributions were measured around the mouth area. Overall cough characteristics such as cough duration time (CDT), peak velocity time (PVT), maximum velocities, and cough spread angle were obtained. The CDT of the cough airflow was 520-560 m s, while PVT was 20 m s. The male/female averaged maximum velocities were 15.2/13.1 m/s. The average vertical/horizontal cough spread angle was 15.3°/13.3° for males and 15.6°/14.2° for females. In addition, the spatial and temporal distributions of ensemble-averaged velocity profiles were obtained in the vertical and horizontal directions. The experimental data can provide a detailed validation database the basis for further study on the influence of cough airflow on virus transmission using computational fluid dynamic simulations.

Keywords: Cough; Cough duration time; Cough spread angle; Particle image velocimetry; Peak velocity time; Velocity profile.

Fig. 1

Schematic of the chamber.

Fig. 2

Setups of the vertical and horizontal measurements using PIV.

Fig. 3

Experimental scene of cough and image acquired by PIV.

Fig. 4

Maximum velocity variation with time at $x/L_0=2.5$ of one cough case and definitions of PV, PVT, and CDT.

Fig. 5

Raw (upper) and dimensionless (lower) maximum velocity variations with time at $x/L_0=2.5$ for 15 male cough cases measured in vertical direction. Every single colorful curve represents the raw or dimensionless maximum velocity at $x/L_0=2.5$ varied with time in one cough case. Lower curves were obtained by scaling upper curves via nondimensionalization of velocity and time using PV and PVT, respectively. Colors are for the convenience of distinguishing and do not represent any meaning.

Fig. 6

Ensemble-averaged maximum velocity variation with time at $x/L_0=2.5$ in vertical and horizontal directions of all cases with fitted line.

Fig. 7

Instantaneous distribution of ensemble-averaged velocity vectors of males and females at time of $t/PVT=1.0,10.0,\text{ and }15.0$. The velocity was normalized by PV.

Fig. 8

Vertical (left) and horizontal (right) distributions of the instantaneous ensemble-averaged velocity near the mouth.

Fig. 9

Vertical distributions of ensemble-averaged velocity variations with time at various positions of 15 cough cases.

Fig. 10

Horizontal distributions of ensemble-averaged velocity variations with time at various positions of 15 cough cases. Solid line: averaged velocity; dashed line: one SD centered on averaged velocity.

Fig. 11

Vertical (left) and horizontal (right) distributions of the ensemble-averaged peak velocity at each position.

Fig. 12

Schematic of determination of cough airflow boundary edge and definition of cough spread angles ${\theta }_V,{\theta }_H$. Black solid curves represent velocity distribution at several positions; orange points represent feature points (maximum velocity and 1% of maximum velocity); solid orange lines were edge of cough airflow boundary fitted by feature points.

Fig. 13

Vertical spread angles ${\theta }_V$ (upper) and horizontal spread angles ${\theta }_H$ (lower) and their ensemble-averaged values of all cough cases.

Fig. A1

Comparison of measurement results obtained by the hotwire anemometer, PIV, and PIV with the particle supplement tube

Fig. A2

Circular tube for supplementing particles at the opening