STUDY ON TYPICAL COLLAPSE PATTERNS OF SINGLE CAVITATION BUBBLES NEAR COMPOSITE BOUNDARIES

Cavitation phenomena are involved in various industrial fields such as hydraulic engineering, shipbuilding, underwater blasting, and oral healthcare. When cavitation bubbles collapse, multiple flow patterns emerge under strong impact, multi-scale, and highly transient loading conditions, including bubble pulsation, high-speed jets, and shock waves. Replacing traditional metals and alloys with composite materials—characterized by high specific stiffness, high specific strength, and strong designability—to manufacture blades has become an important improvement direction for hydraulic machinery. Based on existing research on the interaction between composite materials and cavitation bubbles, high-speed schlieren imaging technology was employed to observe the schlieren images of single bubble collapse at varying distances from composite boundaries, and the collapse patterns and their characteristics were discussed. The results indicate that the distance between the single bubble and the composite boundary is the main factor influencing the bubble collapse pattern, and the thickness of the composite boundary is also a significant factor. During the expansion, contraction, and collapse processes of the bubble, as the dimensionless distance γ between the bubble and the composite boundary increases, the bubble shape transitions from a "mushroom-like" form to a "spherical" form, and the contraction rate approaches 1. In the collapse stage, depending on the range of γ, multiple annular shock waves, asymmetric shock waves, or complete spherical shock waves are formed, mainly presenting four typical collapse modes: When the material thickness δ is less than 2.0 mm., a Segmented Double Collapse (SDC) mode occurs at γ = 0.8–1.2; a Jet Impact Collapse (JIC) or Single Complete Collapse mode(SCC) occurs at γ = 1.4–2.0; and when δ = 2.0 mm, a Jet Oscillation Collapse (JOC) mode occurs at γ = 0.8.