Numerical study of micro–sized bubble deformation and shape oscillation in ultrasonic standing wave fields

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To promote the development of science and technology such as underwater explosions, water cleaning, and medical treatment, it is necessary to understand the mechanism of the influence of ultrasonic fields on bubble dynamics. The authors investigated in depth the effects of the dimensionless sound pressure amplitude pa*, the dimensionless wave number k* and the liquid–gas viscosity ratio μl/μg on the micro–sized bubble deformation and shape oscillation using the volume of fluid (VOF) method. It was found that the bubble deformation and oscillation types can be classified into four categories: volume oscillation, shape oscillation, splitting oscillation and other types of oscillation. Both the dimensionless sound pressure amplitude pa* and the dimensionless wave number k* determine the bubble oscillation types. The regime map of predicting the micro–sized bubble deformation and shape oscillation was drawn based on pa* and k*. If the shape oscillation occurs in a micro–sized bubble, the dimensionless time τ*, when the micro–sized bubble experiences the shape oscillation, decreases with an increase in pa*, but increases with an increase in k* and μl/μg. The mode number n of shape oscillation increases with an increase in k* but decreases with an increase in μl/μg, and it is irrelevant to pa*. If the splitting oscillation happens to a micro–sized bubble, τ*, when a micro–sized bubble experiences splitting, decreases with an increase in pa* and increases with an increase in k*, while the liquid–gas viscosity ratio μl/μg has a negligible effect on this phenomenon.