沟槽面湍流边界层近壁区拟序结构实验研究

 应用氢气泡流动显示技术,对沟槽面湍流边界层近壁区带条结构进行了研究。通过分析流动显示结果,发现沟槽面的带条比较平坦,低速带条有较好的直线性,说明沟槽限制了流体的横向流动,增强了流动的稳定性。通过统计分析发现沟槽板湍流边界层中无量纲低速带条间距及无量纲高速带条间距均符合对数正态分布。对同种沟槽板而言,两种带条的分布特性无明显差别。沟槽板的平均无量纲低速带条间距比光滑板的要小,最多小30%,且沟槽尺寸对平均无量纲低速带条间距亦有影响。对同一种沟槽板同一位置而言,平均无量纲低速带条间距随离开壁面的无量纲距离的减小而减小,但最可几概率增大,表明沟槽板对近壁流动影响最为强烈。另外,还对低速带条与减阻特性的关系做了初步探讨,得到的沟槽无量纲高度和间距为15～18的沟槽板有较好的减阻效果。

EXPERIMENTAL STUDIES ON THE NEAR WALL TURBULENT COHERENT STRUCTURES OVER RIBLETS SURFACES

The hydrogen bubble flow visualization technique was used to study the low speed streaks in the near wall region for the turbulent boundary layer flow over riblets surfaces. By analyzing the flow visualization results, it is found that the low speed streaks appear to be flat and linear. This means that the streamwise riblets limit the flow motion in the spanwise direction, and the flow stability is enhanced. The statistical analysis indicates that, for the turbulent boundary layer flow over riblets surfaces, both the non dimensional low speed streaks and the non dimensional high speed streaks obey the normal log distribution. For the same riblets plate, there is no obvious difference for the distributions of the low and high speed streaks. The average of the non dimensiond low speed streaks is influenced by the scale of riblets surfaces, and its value is less than the smooth wall results. In this experiments, the maximum decrement of the awerage of the non dimensional low speed streaks is about 30% less than the smooth wall value. For the same riblets plate at a fixed position, the awerage of the non dimensional low speed streaks decreases as the non dimensiond distramce decreases, and the most probability increases. This implies that the riblets plate strongly influences flow in the near wall region. In addition, the relation between the low speed structures and the drag reduction property was also investigated, and it was obtained that the optimum design of the riblets plate is its non dimensional spacing and height of 15~18.