水平管内气液两相泡状流壁面切应力的研究

Investigation on Wall Shear Stress in Horizontal Air-Water Bubbly Flows

利用TSI-1268W热膜探针测量了内径为35 mm的水平管内气液两相泡状流的壁面切应力,得到了充分发展段同一截面上不同周向位置处的壁面切应力及其波动幅度数据.结果显示,管道顶部壁面切应力瞬时信号的功率谱密度没有明显的单一峰值,表明壁面切应力的变化具有非周期性特征.液相中加入气泡后,在管道下部的壁面切应力增大,在含气率较高的管道上部出现了壁面切应力减小的现象.随着气相流速的增加,管道上部的壁面切应力有较小幅度的降低,管道中下部的壁面切应力有较大幅度的增加;随着液相流速的增加,管道中下部的壁面切应力增加的幅度基本相同.低液流速度下,在管道上部,泡状流时的壁面切应力波动幅度要小于单相液流时的值,并随着气相流速的增加而减小,在管道下部,泡状流时的壁面切应力波动幅度与单相液流时的值接近.气泡的加入似乎对壁面切应力的波动有抑制作用,在高液流速度下,加入气泡对壁面切应力波动幅度的影响变小.

The circumferential distribution of the wall shear stress （WSS） in developed region of air-water bubbly flows in a horizontal tube with 35 mm I. D. was measured with TSI-1268W hotfilm probes. The results measured in the developed region show that the power density spectra of WSS at the top wall of the tube exhibit no single distinct peak, indicating an aperiodic nature of the WSS. As bubbles are introduced into the flow, the WSS increases at the bottom wall, and decreases at the top wall where the bubble population is high. With an increase of gas flow rate the amount of WSS reduction at the top wall is small, while the increase of WSS at the middle and bottom wall is obvious. An increase of liquid flow rate would result in approximately the same amount of increase of the WSS at the middle and bottom wall of the tube. When the liquid flow rate is low, the WSS fluctuation amplitude at the top wall of the tube is smaller than that of single-phase liquid flow and decreases with the increasing gas flow rate, and at the bottom wall of the tube the WSS fluctuation amplitude is nearly the same as that of single-phase liquid flow. The addition of gas into the flows seems to suppress the WSS fluctuations. When the liquid flow rate is high, the addition of gas into the flow would have less influence on the variation of WSS.