  Human respiratory events, such as coughing and sneezing, play an important
role in the host-to-host airborne transmission of diseases. Thus, there has
been a substantial effort in understanding these processes: various analytical
or numerical models have been developed to describe them, but their validity
has not been fully assessed due to the difficulty of a direct comparison with
real human exhalations. In this study, we report a unique comparison between
datasets that have both detailed measurements of a real human cough using
spirometer and particle tracking velocimetry, and direct numerical simulation
at similar conditions. By examining the experimental data, we find that the
injection velocity at the mouth is not uni-directional. Instead, the droplets
are injected into various directions, with their trajectories forming a cone
shape in space. Furthermore, we find that the period of droplet emissions is
much shorter than that of the cough: experimental results indicate that the
droplets with an initial diameter $\gtrsim 10\mu$m are emitted within the first
0.05 s, whereas the cough duration is closer to 1 s. These two features (the
spread in the direction of injection velocity and the short duration of droplet
emission) are incorporated into our direct numerical simulation, leading to an
improved agreement with the experimental measurements. Thus, to have accurate
representations of human expulsions in respiratory models, it is imperative to
include parametrisation of these two features.
