同轴两个气泡融合特性的数值研究

Numerical Investigation on Coaxial Coalescence of Two Gas Bubbles

为了进一步研究气泡融合特性以及开发高效的界面追踪程序,以PLIC界面重构技术为基础,采用不分裂算法计算了目标网格向周围26个网格的输运流量;采用统一的表达式计算输运流量,大大降低了程序编写的难度。将PLIC算法与气液两相流动控制方程相结合,数值计算了直径为0.8～14mm的单个气泡的最终运动速度,模拟结果与文献中的实验结果吻合良好。研究了同轴两个气泡的融合过程,发现表面张力很大时,两个气泡近似独立运动,不发生融合;表面张力很小时,气泡容易发生破碎;气泡发生严重破碎时,尾部气泡会从顶部气泡的轴心穿过;液体黏度与表面张力对气泡融合时间的影响不是单调的。

To further study bubble coalescence and develop a highly efficient tracking interface program,an unsplit algorithm based on the PLIC interface reconstruction algorithm was applied to precisely calculate the fluid transport from one cell to its neighboring 26 cells,and the fluid transport of each cell was calculated using a unified expression which greatly reduces the programming difficulty and improves the calculation accuracy.The Navier-Stokes equations for gas-liquid two-phase flow were solved by combining an advection equation for liquid volume fraction to simulate the rise of the single bubble.The terminal velocities obtained by the numerical simulation for the single bubble with the diameter of 0.8-14 mm were in good agreement with the experimental data from literature.The co-axial coalescence of two gas bubbles in the initially quiescent liquid was then simulated by the unsplit algorithm.The numerical results show that when the surface tension is very high,the two bubbles rise and deform independently.The bubbles tend to break up when the surface tension is very small,and when the bubble breakup is serious,the following bubble would pass through the leading bubble.Additionally,the effect of liquid viscosity and surface tension on coalescence time is non-monotonous.