Experimental investigation of far-field human cough airflows from healthy and influenza-infected subjects

Abstract

Seasonal influenza epidemics have been responsible for causing increased economic expenditures and many deaths worldwide. Evidence exists to support the claim that the virus can be spread through the air, but the relative significance of airborne transmission has not been well defined. Particle image velocimetry (PIV) and hot-wire anemometry (HWA) measurements were conducted at 1 m away from the mouth of human subjects to develop a model for cough flow behavior at greater distances from the mouth than were studied previously. Biological aerosol sampling was conducted to assess the risk of exposure to airborne viruses. Throughout the investigation, 77 experiments were conducted from 58 different subjects. From these subjects, 21 presented with influenza-like illness. Of these, 12 subjects had laboratory-confirmed respiratory infections. A model was developed for the cough centerline velocity magnitude time history. The experimental results were also used to validate computational fluid dynamics (CFD) models. The peak velocity observed at the cough jet center, averaged across all trials, was 1.2 m/s, and an average jet spread angle of θ = 24° was measured, similar to that of a steady free jet. No differences were observed in the velocity or turbulence characteristics between coughs from sick, convalescent, or healthy participants.

Keywords: aerosol sampling; biological sampling; cough airflow; particle image velocimetry; virus transmission.

Figure 1

Schematic diagram of experimental facility

Figure 2

PIV field of view on cough chamber center plane

Figure 3

Instantaneous 2D velocity magnitude contour with overlaid vector arrows

Figure 4

Example instantaneous velocity time history at cough jet center with key quantities labeled

Figure 5

Cough inlet velocity time history (CFD) calculated from volume flow rate and mouth diameter measured by Gupta et al (2009)

Figure 6

Cough jet angles, θ ₁ = 15 ± 5°, θ ₂ = 40 ± 4°, θ = 25 ± 9° (adapted from Gupta et al 2009)

Figure 7

Mathematical modeling of the average normalized instantaneous velocity magnitude time history, at cough center (x = 1.0 m)

Figure 8

Variation of peak velocity with time of peak at cough center (x = 1.0 m, y location varies)

Figure 9

Normalized PSD of residual velocity fluctuations about the moving average

Figure 10

Normalized moving‐averaged velocity time histories (CFD) compared with average PIV instantaneous velocity time history and experimental modeling function V _fit(τ) at x = 1.0 m, on cough jet centerline (y = z = 0)

Figure 11

Variation of normalized peak velocity and distance from the inlet (CFD)

Figure 12

Normalized velocity magnitude time histories (A) for x = 0.0‐0.3 m, on cough jet centerline (y = z=0) (LES and ensemble‐averaged PIV), (B) for x = 0.0‐0.3 m, on cough jet centerline (y = z=0) (URANS and ensemble‐averaged PIV), (C) for x = 0.4‐1.5 m, on cough jet centerline (y = z=0) (LES and ensemble‐averaged PIV), and (D) for x = 0.3‐1.5 m, on cough jet centerline (y = z=0) (URANS and ensemble‐averaged PIV)