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Drop-impact dynamics on solid surfaces : Evolution of impact force
In this talk, I will give an overview of our latest advances in understanding the dynamics of drop impacts on dry solid surfaces. By synchronizing high-speed photography with fast force sensing, we simultaneously measured the temporal evolution of the shape and impact force of impacting drops over a wide range of Reynolds numbers (Re). At high Re, the early-time evolution of impact force follows a square-root scaling. This observation provides direct evidence on the existence of upward propagating self-similar structures during the initial impact of liquid drops. At lower-Re impact, viscous forces gradually set in and the early-time scaling of the impact force of viscous drops changes. We used an analytical perturbation method to study this process that successfully predicts the quantitative increase of the maximum impact force with decreasing Re. This results provides a solid basis to understand the temporal evolution of impact forces across the inertial and viscous regimes and sheds new light on the self-similar dynamics during drop impact.