自由场空泡溃灭过程能量转化机制研究

综合应用实验与数值模拟方法, 深入讨论了自由场空泡溃灭过程中的能量转化机制. 在实验研究中, 应用纹影法记录了空泡溃灭的演变过程, 提取了空泡在溃灭过程中的半径, 溃灭速度等数据, 结合空泡势能和动能方程, 描述了空泡能量的转化过程. 在开展数值模拟分析时, 运用弱可压缩流体质量守恒方程和动量方程, 建立了三维数值模型用以模拟空泡在自由场中的溃灭过程, 并且由结果中获取了空泡溃灭过程中的压力及速度变化规律, 揭示了空泡在溃灭过程中能量转化机制. 研究结果表明: (1) 自由场空泡在溃灭过程中, 空泡势能与空泡半径具有相同的演化趋势, 空泡动能与势能变化趋势相反; 当空泡达到最大半径处时, 空泡势能最大, 流场动能为零. (2) 溃灭后期在空泡周围会形成高压区域, 该区域的压力梯度与速度梯度较高, 随着空泡收缩, 高压区域面积逐渐减小. (3) 空泡在自由场中发生溃灭时, 空泡势能不断转化为流场动能, 在溃灭时刻可以明显观察到冲击波现象, 空泡的大部分能量会在此时转化为冲击波的波能. 

ENERGY TRANSFORMATION MECHANISM OF A GAS BUBBLE COLLAPSE IN THE FREE-FIELD

Both the experiment method and numerical simulation method are applied in this paper to investigate the energy transformation mechanism of a gas bubble collapseing in the free field. The bubble radius, velocity and acceleration of the bubble evolution process are obtained according to the experimental results via the schlieren method. These parameters are substituted~into the bubble potential energy and kinetic energy equation to explain the energy changing. By using the CFD simulation method, a three-dimensional model with reformulated mass conservation equation and momentum equation considering the weakly compressibility, is introduced to discuss the bubble collapse process. The pressure and velocity distribution around the bubble are extracted from the simulation results in order to analyze the energy transformation mechanism. The results show that (i) the relation between the potential energy and bubble radius maintains the positive correlation, with the increasing of the potential energy, the kinetic energy decreases significantly. The value of potential energy is maximum at the end of the bubble expanding, and the kinetic energy of free field returns to zero at the same time. (ii) During the shrinking stage, a high-pressure area appears around the bubble, and gradients of velocity and pressure are higher than the other area in the free field. The high-pressure area is shrinking gradually when the bubble is collapsing. (iii) The potential energy transforms into kinetic energy during the whole process of the bubble evolution, and the kinetic energy is form of wave energy. A shock wave is captured when the bubble collapse, and the most of bubble energy transform into wave energy of the shock wave at this time.