Resonance conditions of electrostatically levitated drops in microgravity

Abstract

The oscillation of electrostatically levitated droplets is a crucial technique for measuring thermophysical properties at high temperatures. However, notable disparities in resonance conditions have been observed between microgravity and ground experiments. In this study, a finite element method has been developed to investigate the oscillation process of charged droplets excited by an electric field in microgravity. The fluid dynamics is solved coupling with the electric field by using ALE method. It reveals that resonance conditions of electrostatically levitated drops strongly depend on the net surface charge of the droplet. When a drop possesses a substantial amount of net surface charge, it resonates as the excitation frequency approaches droplet’s natural frequency f2. Conversely, for drops with a small amount of net surface charge, the mode-2 oscillation can be excited only when the excitation frequency is half of the mode-2 resonance frequency f2/2. The simulation results demonstrate excellent agreement with experimental observations in microgravity. Understanding resonance dependence on net surface charge not only provides valuable information for improving accuracy in measuring thermophysical properties of electrostatically levitated drops, but also contribute significantly to understanding nonlinear oscillations behavior of charged drops in electrohydrodynamics.