Vapour cavities in liquid flows have long been associated with cavitation damage to nearby solid surfaces and it is thought that the final stage of collapse, when a highspeed liquid jet threads the cavity, plays a vital role in this process. The present study investigates this aspect of the motion of laser-generated cavities in a quiescent liquid when the distance (or stand-off) of the point of inception from a rigid boundary is between 0.8 and 1.2 times the maximum radius of the cavity. Numerical simulations using a boundary integral method with an incompressible liquid impact model provide a framework for the interpretation of the experimental results. It is observed that, within the given interval of the stand-off parameter, the peak pressures measured on the boundary at the first collapse of a cavity attain a local minimum, while at the same time there is an increase in the duration of the pressure pulse. This contrasts with a monotonic increase in the peak pressures as the stand-off is reduced, when the cavity inception point is outside the stated interval. This phenomenon is shown to be due to a splash effect which follows the impact of the liquid jet. Three cases are chosen to typify the splash interaction with the free surface of the collapsing cavity: (i) surface reconnection around the liquid jet; (ii) splash impact at the base of the liquid jet; (iii) thin film splash. Hydrodynamic pressures generated following splash impact are found to be much greater than those produced by the jet impact. The combination of splash impact and the emission of shock waves, together with the subsequent re-expansion, drives the flow around the toroidal cavity producing a distinctive double pressure peak.

In an attempt to shed more light on the complex process by which cavities interact destructively with rigid boundaries we consider experimentally the interaction of a laser-generated bubble with a nearby solid boundary. To determine the stresses the surface of the boundary experiences, particularly during the final stages of the first collapse phase, we present a series of pressure transducer traces observed when the laser-created cavity is produced close to the solid boundary. Through careful control of experimental parameters we record pressure increases for cavities created between 0.56 and 1.5 times the maximum bubble radius from the solid boundary. Previous studies have shown this to be a complex process which is particularly sensitive to the working parameters of the problem, which is borne out by our observations.

This paper reexamines the collapse of a cavity in water and its role in possible damage processes. Laser-generated cavities were formed near to a water–solid boundary and simultaneous observations made of the collapse processes and stresses on the solid surface. Using schlieren photography and a thin film transducer on the solid, the importance of fluid flow to induced material stress was determined. The stresses in the solid were also observed using dynamic photoelasticity. The cavity deformation in the collapse phase was observed with high spatial and temporal resolution. Two distinct surface stresses were observed associated with bubble collapse near the boundary. The results indicate that one was due to a shock wave. It is postulated that the second stress was associated with fluid flow through the bubble, set up by the so-called ‘‘liquid jet’’ as opposed to jet impact on its own.

In this paper new observations of a laser-generated cavitation bubble interacting with an inertial boundary are presented. Employing schlieren photography techniques and a thin film transducer placed on the surface of the boundary, the pressure stresses induced in the solid boundary and the surrounding fluid by collapsing bubbles, created very close to the solid surface, are experimentally measured. Liquid jet development, shock wave emission, and "splash" phenomena are identified. For different creation sites close to the boundary, the relevance of each of these phenomena with respect to potentially damaging pressure stresses in the boundary is speculated on.

In this work we consider the interaction of a laser-generated cavitation bubble with a solid boundary for the case of a cavity created very close to the wall. Using a combination of a thin-film transducer placed on the surface of the boundary and schlieren photography techniques we observe the induced pressure stresses on the solid boundary and in the surrounding fluid. By studying bubble shapes and identifying the formation of a liquid jet and shock wave emission, we speculate on the dominant pressures stresses induced by the bubble around the time of its first minimum volume for this chosen creation site of the cavity.