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

1. 研制了聚焦压力波发生器和平面压力波发生器。聚焦压力波发生器由两个圆形压电陶瓷、一个声透镜和一根棒组成。适当选择施加到陶瓷上的电压和波形，可以在透镜焦点附近产生气泡簇。通过高速摄影、激光和压力测量，观察了振荡压力场中气泡团簇的动力学特性。结果表明：(1)单个气泡随表面变形而振荡；(2)经气泡散射的透射光呈现混沌行为；(3)气泡附近的压力变化呈倍周期分岔，出现混沌。混沌状态下的相关维数小于3。考虑了不可压缩粘性液体中气泡群的平移运动和每个气泡之间的相互作用引起的变形，得到了不可压缩粘性液体中气泡群的控制方程。得到了可压缩液体中球形气泡簇相互作用的控制方程。结果表明，随着压力幅值的增大，振荡压力场中的气泡呈倍周期分岔，并进入混沌状态。气泡相互作用抑制了单个气泡的独立运动，因此气泡振荡的相关维数小于3。这些结果支持了实验结果。采用任意-拉格朗日-欧拉（ALE）方法模拟了气泡与入射激波的相互作用。数值计算结果表明：(1)当入射激波压力p_0较大时，在坍塌初期出现液体微射流；(2)尽管液体微射流的速度随着p_0的增大而增大，但射流速度在p_0=10MPA左右达到饱和；(3)当p_0小于1MPa时，气泡内气体状态为均匀状态。然而，当p_0大于约100MPa时，气泡内部出现激波。少

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