Numerical Simulation of Buoyant Bubble Dynamics in Dielectric Liquid Under Uniform Electric Fields

In oil-paper insulation, bubbles are often generated under the joint action of temperature, moisture, and vibration. Bubble defects seriously weaken the insulation strength, and their motion and accumulation are related to the insulation weakness locations. In this work, bubble deformation and motion patterns under uniform vertical electric field and gravity are numerically studied by the volume of fluid (VOF) interface capture method. Based on electrohydrodynamic (EHD) theory, electric stress perpendicularly acts on the interface of a bubble in a uniform electric field, stretching the bubble along the electric field direction, and changing its deformation and motion under gravity. Bubble deformation and rising velocity are quantitatively analyzed using dimensionless numbers, and an empirical formula estimating the deformation of bubbles of different sizes under different electric field intensities is summarized. Buoyant bubbles' transverse deformation is reduced and rising velocity is also affected by the vertical elongation and downward resultant electrical field force. In a power frequency ac field, bubbles' deformation and rising velocity fluctuate in a period of 0. 01s, and phase differences exist. This research is helpful to provide a reference for further study of bubble accumulation and insulation weakness prediction.