Cavitation bubble structures below a soft boundary in an ultrasonic field

Area of Science:

• Fluid dynamics
• Acoustics
• Interface science

Background:

• Bubble layer structures form at liquid interfaces.
• Understanding these structures is crucial for various applications, including sonochemistry and material processing.
• The influence of acoustic fields on bubble collective behavior at interfaces requires further investigation.

Purpose of the Study:

• To investigate the layer structure of bubbles below water/air and water/EPE interfaces.
• To understand the mechanisms of bubble structure formation and the role of acoustic fields.
• To develop a model describing bubble interactions and structure formation.

Main Methods:

• High-speed photography to capture bubble layer structures.
• Analysis of bubble source mechanisms (nuclei attachment, bulk flotation, transducer generation).
• Development of a simplified model involving bubble columns and chains.

Main Results:

• Bubble layer structures exhibit similar profiles below water/air and water/EPE interfaces.
• The resonant frequency of bubbles in structures is lower than that of isolated bubbles.
• Acoustic frequency and pressure influence the distance between the structure and the interface.
• Low-frequency intense cavitation (28, 40 kHz) favors hat-like structures; higher frequency (80 kHz) favors discrete clusters.

Conclusions:

• Acoustic fields are critical in generating bubble layer structures.
• Bubble collective behavior and resonant frequencies differ from isolated bubbles.
• The findings align with theoretical predictions and offer insights into cavitation dynamics.