Abnormally large acceleration of bubbles in flows of bubbly liquid

1. 建立了一种可变形气泡在不可压缩粘性流体中上升时绕流的数值计算公式。求解算法是一种改进的MAC算法。测定了不同雷诺数和韦伯数下的气泡形状和阻力系数。对气泡流动特性进行了理论和实验研究。首先提出了一种新的控制分散气泡相的运动模型方程。其次，详细研究了气泡流控制方程组的斜曲性。利用所提出的模型方程组，在富士通VP-2600型超级计算机上进行了气泡流动的数值模拟。数值计算结果与水氮排污装置的实验结果进行了比较。结果表明，数值计算结果与实验结果吻合较好。利用频闪闪光灯的瞬时照片对气泡云的流动行为进行了研究。在喷嘴喉部下游区域观察到一些有趣的现象。例如，其中之一是泡沫阶段的“膨胀冲击”。至少目前还不能从理论上解释这一现象。杂质或表面活性剂对气泡流动行为的影响有待进一步研究。

1. A numerical sckeme was developed for flow around a deformable bubble rising through an incompressible viscous fluid. The solution algorithm is a modified MAC method. The bubble shape and the drag coefficient were determined for various Reynolds and the Weber numbers.2. Characteristics of bubbly flows were investigated theoretically and experimentally. First a new model equation of motion governing a dispersed bubble phase was proposed. Next, herperbolicity of the resultant system of governing equations for the bubbly flow was investigated in detail. Numerical simulations of bubbly flows through a converging- diverging nozzle were carried out on a supercomputer Fujitsu VP-2600 by using the propsed system of model equations. The numerical results were compared with the experiments in a water-nitrogen blow-down facility. It was confirmed that the numerical results agrees well with the experiments.3. Flow visualization by instantaneous photographs with a stroboscopic flash was performed to investigate the flow behavor of bubble clouds. A few interesting phenomena were observed in the downstream region of the nozzle throat. One of them, for example, is an "expansion-shock" of the bubble phase. This phenomenon cannot be explained theoretically at least for the present.4. The effects of impurity or surfactant on the flow behavior of bubbles remained for future study.