A detailed experimental study has been made to clarify the mechanism of impulsive pressure generation from a single bubble collapsing in a static fluid – this is the most essential and important research task concerned with cavitation damage. First, the general feature of impulsive pressure generation is discussed, and then the impulsive pressure directly contributing to damage is investigated by various means. As a result, it is found that the impulsive pressure causing plastic deformation of material is closely related, directly or indirectly, to the behaviour of a liquid jet. Further more, it is demonstrated that the interaction of a tiny bubble with a shock wave or a pressure wave must be an important effect in producing a local high pressure which causes damage to material. The damage pit caused by the bubble-shock-wave interaction essentially results from the impact pressure from a liquid microjet.
Laser-induced cavitation bubbles near a curved rigid boundary are observed experimentally using high-speed photography. An image theory is applied to obtain
information on global bubble motion while a boundary integral method is employed
to gain a more detailed understanding of the behaviour of a liquid jet that threads
a collapsing bubble, creating a toroidal bubble. Comparisons between the theory
and experiment show that when a comparable sized bubble is located near a rigid
boundary the bubble motion is significantly influenced by the surface curvature of
the boundary, which is characterized by a parameter ζ, giving convex walls for ζ < 1,
concave walls for ζ > 1 and a flat wall when ζ = 1. If a boundary is slightly concave,
the most pronounced migration occurs at the first bubble collapse. The velocity of
a liquid jet impacting on the far side of the bubble surface tends to increase with
decreasing parameter ζ. In the case of a convex boundary, the jet velocity is larger
than that generated in the flat boundary case. Although the situation considered
here is restricted to axisymmetric motion without mean flow, this result suggests that
higher pressures can occur when cavitation bubbles collapse near a non-flat boundary.
Bubble separation, including the pinch-off phenomenon, is observed in the final stage
of the collapse of a bubble, with the oblate shape at its maximum volume attached to
the surface of a convex boundary, followed by bubble splitting which is responsible
for further bubble proliferation.
The motion of single-and two-cavitation bubbles generated by laser beams directly beneath a free surface is studied experimentally, using high-speed photography, and theoretically using the highly accurate boundary integral method. Favorable comparisons of bubble shape history and centroid motion are observed while the numerical calculations provide information on the pressure field surrounding the bubbles. A range of responses, including the null impulse state, is obtained for the two bubbles depending on the bubble size ratio and the interbubble and bubble-free surface distances, although in all cases reported in this article, the bubble nearest the free surface yields a high-speed liquid jet directed away from the free surface. It is also found that when the free-surface-bubble interaction is strong, a fast free-surface spike is formed for both the single-and two-bubble cases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.