Development of the experimental apparatus for a cluster of oscillating cavitation bubbles in pressure fields

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1. Focussing pressure wave generators and plane pressure wave generators are developed. The focussing pressure wave generator is constituted by two circular piezoelectric ceramics, an acoustic lens and a rod. Adequate choices of the voltage and wave form applied to the ceramics make it possible to create a bubble cluster near the focus of the lens. The dynamics of the bubble cluster in oscillatory pressure fields are observed through high speed photographs and laser and pressure measurements. The following results are obtained: (1) Individual bubbles oscillate with surface deformation; (2) Transmitted light scattered by the bubble takes a chaotic behavior; (3) The pressure variation near the bubbles takes a period-doubling bifurcation and comes to chaos. The correlation dimension in the chaotic state is less than three.2. Governing equations of a cluster of bubbles in an incompressible and viscous liquid are obtained by taking account of the translational motion and the deformation of … More each bubble which are induced by the interactions of the bubbles. Governing equations of a cluster of interacting spherical bubbles in a compressible liquid are also obtained. It is shown that the bubbles in oscillatory pressure fields take a period-doubling bifurcation and come to chaos with the increase of the pressure amplitude. The bubble interactions suppress the independent motions of the individual bubbles, and thereby the correlation dimension of the oscillations of the bubbles is less than three. These results support the experimental ones.3. The Arbitrary-Lagrangian-Eulerian (ALE) method is used to simulate the interaction between a bubble and an incident shock wave. The numerical results are obtained as follows: (1) When the pressure of the incident shock wave, p_0, is high, a liquid micro-jet occurs the early stage of the collapse; (2) Although the velocity of the liquid micro-jet increases with the increase of p_0, the jet velocity saturates at about p_0=10MPA; (3) The state of the gas inside the bubble is regarded as uniform when p_0 is litter than about 1MPa. However, a shock wave is found inside the bubble when p_0 is greater than about 100MPa. Less