100-Billion-Atom Molecular Dynamics Simulation of Acoustic Cavitation in a Simple Liquid

TL;DR

This study presents a groundbreaking 100-billion-atom molecular dynamics simulation of acoustic cavitation, revealing detailed bubble dynamics and their effects on ultrasonic systems at an unprecedented scale.

Contribution

It is the first to simulate multi-bubble cavitation with such a large atom count, providing new molecular insights into bubble behavior and acoustic interactions.

Findings

Cavitation bubbles nucleate and form large clusters near the ultrasonic horn.

Bubble clusters periodically split and merge, synchronized with horn oscillation.

Pressure and temperature inside bubbles sharply increase during fragmentation.

Abstract

A large-scale molecular dynamics (MD) simulation of acoustic cavitation in a simple liquid was performed using the supercomputer Fugaku. The system, consisting of approximately 100 billion atoms, was subjected to ultrasonic irradiation. Direct observation of multi-bubble dynamics has been challenging in both experimental measurements and conventional numerical fluid mechanics simulations. Moreover, previous MD simulations involving only hundreds of millions of atoms were unable to generate multiple bubbles within a system. Our results reveal that cavitation bubbles nucleate and grow near the ultrasonic horn, forming a large bubble cluster that periodically splits into multiple small clusters and subsequently merges again. This cycle is synchronized with the oscillation period of the horn. Pressure and temperature inside the bubbles exhibit sharp increases during cluster fragmentation, and their oscillation amplitudes vary on a timescale longer than the driving period of the horn, indicating the presence of subharmonic behavior consistent with experimental observations. Despite bubble formation, the effect on the acoustic properties of the sound wave was almost negligible, indicating that cavitation near the horn surface has limited influence on bulk acoustic properties. These findings provide new insights into the molecular-scale mechanisms of cavitation and offer guidance for optimizing ultrasonic systems in chemical and biomedical applications. Future work will focus on quantifying long-period oscillations, analyzing attenuation effects, and extending simulations to complex fluids.