Numerical Study of Nanosecond Pulsed Laser Impact on a Water Droplet

An integrated hydrodynamic model that involves a laser heat source, surface evaporation, and interfacial driving forces is developed to simulate the complex physical process of a nanosecond pulsed laser impacting on a water droplet. Droplet deformation tracked by the coupled level set and volume of fluid method is contrasted with the experimental results, and it is shown that the coupled model can be used to simulate the droplet expansion dynamics. From the simulation of droplet deformation, it can be found that, with increasing laser energy, the droplet becomes thinner. With the highest laser energy, the jet on the opposite side to laser impact is interpreted as the flow of high-speed fluid near the axis, which is also confirmed by the velocity field. The simulated temperature reaches or even exceeds the critical value, and the recoil pressure does not completely cover the whole hemispherical surface of the droplet. The liquid-removal depth, which represents the distance that the liquid-phase interface retreats during evaporation, is much shallower than the absorption depth. It can be concluded that propulsion is gained from the intense evaporation of the superheated layer.