Bounds on the Spreading Radius in Droplet Impact: The Two-Dimensional Case

Abstract

We consider the problem of a cylindrical (quasi-two-dimensional) droplet impacting on a hard surface. Cylindrical droplet impact can be engineered in the laboratory, and a theoretical model of the system can also be used to shed light on various complex experiments involving the impact of liquid sheets. We formulate a rim-lamella model for the droplet-impact problem. Using Gronwall's Inequality, we establish theoretical bounds for the maximum spreading radius $\mathcal{R}_{max}$ in droplet impact, specifically $k_1 \mathrm{Re}^{1/3}-k_2(1-\cos\vartheta_{adv})^{1/2}(\mathrm{Re}/\mathrm{We})^{1/2}\leq \mathcal{R}_{max}/R_0\leq k_1\mathrm{Re}^{1/3}$, where $\mathrm{Re}$ and $\mathrm{We}$ are the Reynolds and Weber number based on the droplet's pre-impact velocity and radius $R_0$, $\vartheta_{adv}$ is the advancing contact angle (assumed constant in our simplified analysis), and $k_1$ and $k_2$ are constants. We perform several campaigns of simulations using the Volume of Fluid Method to model the droplet impact, and we find that the simulation results are consistent with the theoretical bounds.