Electrostatic field can be effectively used to control the transport process in different types of fluids, which provides the foundation for various innovative applications, such as the active control of heat and fluid flow based on the electric field (EF), electrohydrodynamic pumping, and electro-spraying. These applications depend on a deep understanding of the mutual coupling between EFs, charges, and flow fields (FFs). In this study, we experimentally investigated the flow and voltage–current characteristics of a dielectric liquid subjected to high voltage DC field in a needle–plate configuration. The experimental results show that for the needle electrode with a curvature around 0.1 mm, when the needle–plate distance is 30 mm and the absolute value of the applied voltage is 5–6 kV, liquid is in a stable state of convection, flow direction originates from the needle electrode toward the plate electrode, and flow pattern is similar to the typical submerged jet. The flow is driven by the Coulomb force due to the EF acting on the injected ions from the needle–liquid interface. Through the analysis of axial velocity, longitudinal velocity, and plume width, we observed that the maximum velocity in the FF is located on the horizontal axis. In the steady-state flow range, the flow pattern remains unchanged, but the flow intensity increases along the voltage. In addition, experimental comparison revealed that the current value and flow intensity are larger when we applied the negative voltage under the same amplitude, and the core position of the plume was farther away from the needle electrode.

Experiments on the electrohydrodynamic (EHD) flow characteristics of a dielectric liquid in a sharp needle-plate configuration under direct current (DC) and alternating current (AC) electric field are carried out. The current-voltage characteristics and the velocity field are simultaneously recorded for understanding the flow behavior and its mechanism. For the DC case, a critical voltage separating the conduction and injection regimes and the corresponding flow reverse is observed. Results indicate the polarity of voltage only influences the flow's intensity in the injection regime. For the AC case, two types of signals with the same 50% duty cycle are considered. For the pulsed voltage (−2.0kV to 0), the flow generally keeps the plume structure and shows weaker strength than the corresponding DC case. For the AC signal (-2.0kV–+2.0kV), the velocity amplitude first decreases and then tends to be constant with the increase of frequency. The weak flow motion with high frequency AC field is due to conduction.