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中文核心期刊

低雷诺数沟槽表面湍流/非湍流界面特性的实验研究

EXPERIMENTAL STUDY ON PROPERTIES OF TURBULENT/NON-TURBULENT INTERFACE OVER RIBLETS SURFACES AT LOW REYNOLDS NUMBERS

  • 摘要: 湍流/非湍流界面是流动中湍流和无旋流的边界,其相关研究在加深对湍流与无旋流之间的物质、动量和能量交换的理解有重要意义.本文采用时间解析的二维粒子图像测速技术,分别对零压梯度光滑、顺流向锯齿形沟槽表面平板在不同雷诺数下对湍流/非湍流界面的几何特征及动力学特性进行了实验研究.实验雷诺数为Re_\tau =400\sim1000.本文采用了湍动能准则对湍流/非湍流界面进行了识别,并分析界面高度分布、分形特征及界面附近的条件平均速度和涡量.结果表明在不同雷诺数下, 无论是光滑壁面还是沟槽壁面,界面平均高度在0.8 \sim 0.9\delta_99 附近. 对于沟槽壁面而言,减阻时对应的界面高度的概率密度分布与光滑壁面基本一致, 均遵循正态分布,而当阻力增大时, 界面高度分布偏离正态分布出现正的偏度. 在本实验情况下,界面分形维度、跨界面速度跳变均会随着雷诺数增大而增大. 此外,不同壁面情况下无量纲条件平均涡量在界面附近的分布相近,而界面附近无量纲速度梯度最大值近似为常数.

     

    Abstract: The turbulent/non-turbulent(T/NT) interface usually refers to the thin layer that separates turbulent flow from irrotational flow. The research of T/NT interface is of great importance to deepen the understanding of matter, momentum and energy transfer between the turbulent and irrotational flow. The geometrical and dynamical properties of the T/NT interface at different Reynolds numbers over smooth and riblets surfaces with zero-pressure-gradient at different Reynolds numbers are experimentally investigated using two-dimensional time-resolved particle image velocimetry (2D-TRPIV). The Reynolds number range is about Re_\tau \approx 400 \sim 1000 in the present experiment. The T/NT interface is detected with the turbulent kinetic energy criterion. The probability density function of the interface position, fractal characteristics and the conditional averaged velocity and vorticity near the interface are analyzed. It is shown that the mean heights of the interfaces are around 0.8 \sim 0.9\delta_99 under different Reynolds numbers for both smooth and riblets surfaces. The probability density function of the interface position over drag reduction riblets surface is kept the same with the smooth surface, whose distribution agrees well with normal distribution. While for the drag increment riblets surface, the distribution of interface position deviates from the normal distribution and presents positive skewness. The fractal dimension of the interface and the velocity jump across the interface will gradually increase with the Reynolds number under the present experiment condition. Moreover, the dimensionless conditional averaged vorticities have similar distributions in the vicinity of the interface over both smooth and riblets surfaces when Re_\tau is less than 1000, correspondingly, the maximum gradient of dimensionless conditional average streamwise velocity is approximately constant.

     

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