Atomisation, or aerosolisation as it is known in Covid studies, is a striking example of the huge complexity of multiphase flow turbulence. The theory of atomisation starts with the consideration of Kelvin-Helmholtz instabilities. To make these theories predictive of the length scales and frequencies observed in experiments is a surprisingly difficult task and is still being investigated in some aspects in full three-dimensional simulations.
In recent years numerical simulations and experiments have illustrated the important role played by thin liquid sheets and ligaments. Moreover the importance of aerosolisation phenomena in respiratory disease transmission has motivated specific experiments such as those of the “cough machine”. In that setup the impulsive air flow over a thin liquid layer can be investigated. This allows to study the influence of the liquid viscosity on sheet thickness and droplet sizes.