Stop-and-go locomotion of superwalking droplets

TL;DR

This study uses numerical simulations to predict and analyze the stop-and-go motion of superwalking droplets driven by two-frequency vibrations with a linearly varying phase difference, revealing diverse dynamic behaviors.

Contribution

It introduces a numerical investigation of superwalking droplets with detuned two-frequency driving, predicting complex stop-and-go motions and classifying different droplet behaviors.

Findings

Identification of three distinct droplet motion types

Prediction of stop-and-go motion consistent with experiments

Mapping of motion regimes in parameter space

Abstract

Vertically vibrating a liquid bath at two frequencies, $f$ and $f/2$, having a relative phase difference $\Delta\phi_0$ can give rise to self-propelled superwalking droplets on the liquid surface. We have numerically investigated such superwalking droplets with the two driving frequencies slightly detuned, resulting in the phase difference $\Delta\phi(t)$ varying linearly with time. We predict the emergence of stop-and-go motion of droplets, consistent with experimental observations [Valani et al. Phys. Rev. Lett. {\bf 123}, 024503 (2019)]. Our simulations in the parameter space spanned by the droplet size and the rate of traversal of the phase difference uncover three different types of droplet motion: back-and-forth, forth-and-forth, and irregular stop-and-go motion. Our findings lay a foundation for further studies of dynamically driven droplets, whereby the droplet's motion may be guided by engineering arbitrary time-dependent functions $\Delta\phi(t)$.