Research on the contact time of a bouncing microdroplet with lattice Boltzmann method

Abstract

The bouncing dynamics of microdroplets with various viscosities on a superhydrophobic surface is numerically investigated. An axisymmetric lattice Boltzmann method is developed on the basis of Zheng et al. capable of handling multiphase flows with a large density ratio, which is implemented to simulate the impact. It is shown that in the low-viscosity regime, the contact time tc remains constant over a wide Weber number range (10 < We < 120), which is consistent with macro-scale bouncing. Nevertheless, in the high-viscosity regime, tc increases with impact velocity. A contact number T≡WeRe−1/2=ρD0 ηU03/σ21/2 is proposed to describe the viscosity effect; meanwhile, a new scaling τ ∼ D0/U0T=ρηD03U0/σ21/2 is deduced to characterize the contact time for this regime, and the simulated results for such droplets agree well with the new scaling. To find out the internal physical mechanism, the evolution of kinetic energy, dissipated energy, and velocity vector fields is studied, which quantifies the impact dynamics. Also, simulation data demonstrate that viscous dissipation is not negligible even for relatively low-viscosity fluids. These findings are highly useful for fundamental understanding of microdroplet dynamics with various viscosities, and it can be used to precisely control the contact time.