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

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 t(c) remains constant over a wide Weber number range (10 < We< 120), which is consistent with macro-scale bouncing. Nevertheless, in the high-viscosity regime, t(c) increases with impact velocity. A contact number T equivalent to WeRe(-1/2) = (rho D-0 eta U-0(3)/sigma(2))(1/2) is proposed to describe the viscosity effect; meanwhile, a new scaling tau similar to (D-0/U-0)T = (rho eta(D0U0)-U-3/sigma(2))(1/2) 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. Published under exclusive license by AIP Publishing.

Automated summary

The bouncing dynamics of microdroplets with varying viscosities on a superhydrophobic surface were investigated through numerical simulations. It was found that the contact time of the droplets remains constant over a wide Weber number range in the low-viscosity regime, but increases with impact velocity in the high-viscosity regime. New scaling parameters were proposed to describe the viscosity effect and characterize the contact time in different viscosity regimes. The study also revealed that viscous dissipation is significant even for relatively low-viscosity fluids, providing valuable insights for understanding and controlling microdroplet dynamics.