Microjet in nonspherical bubble collapsing under modulated water-hammer shocks

Bubble collapse is a high-energy process in fluid dynamics with broad relevance to industrial, medical, and environmental applications. While shock-induced bubble collapse has been extensively studied, most existing work is restricted to planar shock–bubble interactions, leaving the role of shock characteristics in governing jet dynamics insufficiently explored. In this study, a simple topology based on collision to generate modulated shock waves is presented, where the considered collision velocities are ranging from 20 to 100 m/s. The high-resolution numerical simulations are conducted to investigate four distinct shock types—planar, converging, planar–planar, and planar-converging, and their interactions with bubbles. The collapse behavior is quantitatively examined in terms of collapse time, maximum jet velocity, and jet morphology. Results show that converging shocks significantly intensify microjets through focused pressure amplification, whereas sequential dual-shock interactions modulate jet structure and prolong collapse duration, enabling regulation of energy accumulation. By integrating the Rayleigh collapse framework with pressure distributions along the axis of symmetry, a semi-empirical models are further established to capture the evolution of jet velocity and collapse dynamics, demonstrating good agreement with numerical predictions. These findings elucidate the mechanisms of asymmetric bubble collapse under different shock characteristics and advance the theoretical understanding of shock–bubble interactions. The outcomes also offer guidance for the controlled exploitation of microjets in precision material processing, ultrasonic medicine, and environmental remediation.