Suppression of Rayleigh-Bénard secondary instability in dielectric fluids by unipolar charge injection

In this study, the strong unipolar charge injection induced by a uniform electric field was found to have a suppressing effect on Rayleigh-Bénard secondary instability, regardless of the charge injection direction. The liquid was modeled as a perfect dielectric, and the charge injection was assumed to be autonomous and homogeneous. Direct numerical simulations were performed using a newly developed unified lattice Boltzmann model for electrothermohydrodynamics (ETHD). The electric field was applied only when the flow is in a stable oscillation state of the secondary instability. Two different cases representing charge injection from above and below were considered. The results show that periodic temperature fluctuations can be fully suppressed by a sufficiently strong electric field and that the charge injection direction has a significant impact on the flow patterns. For even stronger electric field strength, the system turns into periodic oscillatory flow again and the fundamental frequency is two orders of magnitude higher than the original ones. Besides, the effects of charge injection direction on the flow intensity and heat transfer rate of ETHD are also investigated.