A study on rose-window instability in a dielectric droplet exposed to corona discharge

The rose-window instability (RWI) is an electrohydrodynamic instability occurring in a dielectric liquid subjected to an electric field. This instability leads to variations in the shape of the liquid and its spreading. Despite the significance of the RWI, there have been limited studies, especially concerning dielectric droplets. Thus, the aim of this study is to investigate the characteristic of rose-window instability in silicone oil droplets exposed to corona discharge. The study examines the effects of electrode gap, applied voltage, and viscosity on the formation of RWI. Increasing the electrode gap results in an enlarged rose-window lattice, accompanied by a decrease in the number of lattices. This can be attributed to a more diffusive ionic flow and a more pronounced inhomogeneity of charge distribution across the droplet surface. On the other hand, higher voltages, which enhances the ionic flow, accelerate the formation of RWI and lead to a larger inner diameter. Viscosity has little influence on the geometry of the lattice. However, droplets with low viscosity exhibit a more rapid development of instability. The observation suggests that the small Ohnesorge number (Oh), influenced by factors such as viscosity and surface tension, may play a role in the development of the rose-window instability. The influence of surface tension, although not the main focus of the study, cannot be completely disregarded as it is interconnected with the Oh and may contribute to the observed results.