Computational fluid dynamics simulations of single-bubble evolution under synergy of ultrasound and an electrostatic field

In the study reported here, a two-phase flow model was developed for the evolution of a single bubble under ultrasonic irradiation coupled with an electrostatic force. We started with the following assumptions: (I) the liquid is incompressible, (II) the effect of gravity is negligible in the liquid, (III) the bubble is insulating, and no free charges are distributed on the liquid–gas interface, and (IV) the liquid contains only one bubble. Using computational fluid dynamics, we analyzed how the bubble shape evolves under various conditions, and the main findings are as follows: (1) With increasing electric field strength, the bubble reaches a larger maximum area and a smaller minimum area. Furthermore, during the positive phase of ultrasound, a higher electric field strength leads to faster compression and a more slender bubble. (2) As the initial bubble radius is increased from 3 to 5 μm, the cavitation becomes significantly stronger, but when the initial bubble radius reaches 10 μm, the cavitation intensity decreases instead because of greater compression resistance caused by there being more gas in the bubble. (3) Cavitation cannot be triggered under an excessively low acoustic pressure amplitude, and an excessively high acoustic pressure amplitude results in weaker cavitation; the appropriate acoustic pressure amplitude is considered to be 1.35 atm.