Spatial distribution of acoustic pressure and cavitation activity zones in a fluid system: numerical modelling and experiment

One of the areas of study of physicochemical processes occurring in liquids under the influence of high-frequency sound vibrations (ultrasound) is the determination of the role of acoustic cavitation. This phenomenon occurs due to the uneven distribution of acoustic pressure generated by an ultrasound source (emitter) inside the working chamber. The objective of this article is to study numerically the three-dimensional stationary distribution of acoustic pressure in a working cavity filled with a liquid with constant physicochemical properties using the COMSOL Multiphysics software. In addition to numerical modeling, we also conduct an experimental study in which a foil test technique is applied to determine the location of the areas where cavitation takes place; the results of the test are estimated by their comparison with the calculated acoustic field structure inside the working chamber. Within the framework of the developed numerical model, for simplicity we consider standing ultrasonic waves. Two geometrical configurations of a computational domain are used: a circular cylinder and a rectangular parallelepiped. The stationary distribution of acoustic pressure over a circular radiator is analyzed. It is assumed that ultrasonic standing waves propagate in a compressible medium with sound energy dissipation due to viscous friction or the formation of vapor-gas bubbles in the liquid being neglected. We set zero pressure or an impedance condition at the upper and lateral boundaries of the working cavity. We investigate the distribution of acoustic pressure in standing ultrasonic waves at resonant and non-resonant operating frequencies of the emitter. The acoustic pressure distribution in the central section of the working cavity is compared with photographs of the aluminum foil surface obtained in a full-scale experiment using the foil test method.