Droplet bounce simulations and air pressure effects on the deformation of pre-impact droplets, using a boundary element method

An inviscid axisymmetric model capable of predicting both droplet bounce and the detailed pre-impact motion that is influenced by ambient pressure has been developed using a boundary element method (BEM). Previous simulations could not accurately describe the effect of the gas compressed between a falling droplet and the impacting substrate because most droplet impact simulations assumed that the droplet was already in contact with the impacting substrate at the beginning of the simulation. To properly account for the surrounding gas, the simulation must begin when the droplet is released from a certain height. High pressures are computed in the gas phase in the region between the droplet and the impact surface at instances just prior to impact. This simulation shows that the droplet retains its spherical shape when the surface tension energy is dominant over the dissipative energy. When the Weber number is increased, the droplet's surface structure is highly deformed due to the presence of capillary waves and, consequently, a pyramidal surface structure is formed. This phenomenon was verified experimentally. Parametric studies using our model include the pre-impact behavior that varies as a function of the Weber number and the surrounding gas pressure.