Dynamics of drop impact on solid surfaces: evolution of impact force and self-similar spreading

Abstract

We investigate the dynamics of drop impacts on dry solid surfaces. By synchronising high-speed photography with fast force sensing, we simultaneously measure the temporal evolution of the shape and impact force of impacting drops over a wide range of Reynolds numbers (Re). At high Re, when inertia dominates the impact processes, we show that the early-time evolution of impact force follows a square-root scaling, quantitatively agreeing with a recent self-similar theory. This observation provides direct experimental evidence on the existence of upward propagating self-similar pressure fields during the initial impact of liquid drops at high Re. When viscous forces gradually set in with decreasing Re, we analyse the early-time scaling of the impact force of viscous drops using a perturbation method. The analysis quantitatively matches our experiments and successfully predicts the trends of the maximum impact force and the associated peak time with decreasing Re. Furthermore, we discuss the influence of viscoelasticity on the temporal signature of impact forces. Last but not least, we also investigate the spreading of liquid drops at high Re following the initial impact. Particularly, we find an exact parameter-free self-similar solution for the inertia-driven drop spreading, which quantitatively predicts the height of spreading drops at high Re. The limit of the selfsimilar approach for drop spreading is also discussed. As such, our study provides a quantitative understanding of the temporal evolution of impact forces across the inertial, viscous and viscoelastic regimes and sheds new light on the self-similar dynamics of drop impact processes.

Onset of rebound suppression in non-Newtonian droplets post-impact on superhydrophobic surfaces

“…In addition, the temporal evolution of drops during retraction and rebound will be challenging phenomena for numerical simulations. Further, force measurement during impacts of non-Newtonian droplets can lead to greater insight [25]. Our studies maybe beneficial in deciding the optimum amount of non-Newtonian additives and release height for maximizing the droplet depositions on hydrophobic substrates.…”

Vibration Control Performance Analysis and Shake-Table Test of a Pounding Tuned Rotary Mass Damper under the Earthquake

“…T , contains n entries for the n-DOF structure and one entry for the tuned mass; M, C and K are the (n + 1) × (n + 1) mass, damping, and stiffness matrices, respectively; F(t) denotes the vector of the external excitation; f c (t) is the interaction force between the main structure and the ball, which can be calculated using equation (12) [12,[19][20][21].…”

Slamming Liquid Impact and the Mediating Role of Air

“…Impacts of a liquid against a solid are found to occur in a variety of scenarios in nature and industry. At small scales, the knowledge of the force due to the impact of a drop on a solid substrate is useful in industrial processes such as spraying, coating and printing [1,2]. The same is also useful to understand natural processes such as the erosion of soil due to rain [3,4] (see figure 1(a)), how insects survive in the rain [5] (figure 1(b)), the forces that are generated when birds dive into water to catch their prey [6,7] (figure 1(c)), locomotion of lizards on water [8] (figure 1(d)), and in the sport of diving [9].…”

“…Finally we discuss how this gradient information is integrated in a least-squares sense to obtain a fully reconstructed FS profile from the imaged snapshot at a given instant. We finish by discussing the specifics of the setup, and the reconstruction process as they are implemented in later chapters (2)(3)(4)(5) of this thesis to obtain the results therein.…”

“…TIR-D setup (see chapters[1][2][3][4] used to see how the free surface of water appears at different stages of time during the impact of a cone. At t = 0 ms, the cone makes the first contact with the water surface.…”