气泡在横流中的几何及动力学特性

为研究横流中气泡的几何特征和动力学特征,采用向循环水洞中通气的方法形成气泡,利用高速摄像技术对气泡的形态及演化过程进行采集,并基于MATLAB软件编写特定算法,对获得图像中的气泡特征参数进行提取.对气泡的初生形态、受力分析、运动轨迹、上升角度、尺寸与脱离频率进行分析,并获得了气泡终速度和当量直径的线性关系,通过量纲一数的分析,将气泡纵横比与韦伯数相关联,得到以下结论:随着雷诺数的增加,气泡脱离尺寸减小,脱离角度增加并且脱离频率呈线性增加趋势;气泡运动轨迹与静水环境中相似,分为直线段和振荡段,上升角度变化呈正弦规律且随雷诺数增加而逐渐稳定.轨迹随着水流速度的上升逐渐倾斜接近于直线,振荡段摆幅降低;气泡的终速度随着当量直径的增加迅速减小,小气泡的速度上升速度较快;高雷诺数下气泡形变与表面张力的关联可以忽略.

Geometric and dynamic characteristics of bubbles in cross-flow

To study the geometric and dynamic characteristics of bubbles in cross-flow, air was injected into the circulating water tunnel to produce bubbles. The high-speed photography was used to record the shape and evolution of bubbles. An algorithm was developed based on MATLAB to extract characteristic bubble parameters from the acquired images. The trajectory, stress analysis,rising angle, bubble shape, bubble size and shedding frequency were analyzed. The linear relationship between the bubble terminal velocity and the equivalent bubble diameter was described. Based on a non-dimensional analysis, the bubble aspect ratio was associated with Weber number. The results show that the bubble movement tra-jectory is similar to that in the hydrostatic environment, which is divided into straight line segment and oscillation segment. The rising angle changes sinusoically and becomes gradually stable with the increase of Reynolds number.With the rise of water flow velocity, the trajectory gradually inclines to a straight line and the oscillation amplitude decreases. The final velocity of the bubble decreases rapidly with the increase of the equivalent diameter and the velocity of the small bubble rises rapidly. The correlation between bubble deformation and surface tension at high Reynolds number can be ignored.