The particle image velocimetry of vortical electrohydrodynamic flows of oil near a high-voltage electrode tip

A dual-domain particle image velocimetry (PIV) is employed to characterize the electrohydrodynamic flows arising in an oil bath with a grounded bottom near a high-voltage pin electrode with its tip close to the bottom. The applied voltage is varied to explore its effect on the arising flow field. Spatially, PIV observations are conducted using a dual-domain approach by synchronizing two cameras on the sampling plane. One camera is focused on the electrode tip and the second one on the fluid bulk. By capturing these synchronized domains, the velocity field is explored in its entirety, demonstrating a broad scope of morphology spanning the domain with the high velocity within the inter-electrode gap to the slow eddies in the fluid bulk. At high applied voltages, a transitional regime is observed in which the flow field bifurcates into toroidal Moffatt-like eddies. The experimental technique employed has its limitations. For example, at high applied voltages, the peak velocity domain could not be adequately resolved in every trial due to the deposition of fatty acids on the electrodes. Accordingly, the peak velocity has been measured only in the trials where fatty acid build-up did not interfere. Additionally, due to the axisymmetric geometry, reflections interfere with the observations of the near-surface velocity field.