柔性壁面湍流减阻机理与多尺度相干结构控制的实验研究

Experimental Investigation of Drag Reduction Mechanism over Compliant Wall and Multi-scale Coherent Structure Control in Turbulent Boundary Layer

用热膜测速仪以高于对应最小湍流时间尺度的分辨率，精细测量了水槽中刚性壁面和柔性壁面平板湍流边界层不同法向位置流向速度分量的时间序列信号，利用湍流边界层近壁区域的对数律平均速度剖面与壁面摩擦速度、流体粘性系数、壁面摩擦切应力等内尺度物理量的关系，在准确测量湍流边界层近壁区域对数律平均速度剖面的基础上，通过非线性迭代求解壁面摩擦速度以及湍流边界层壁面摩擦切应力。结果表明：柔性壁的湍流边界层速度分布在对数律层有所上移，缓冲层增厚，说明柔性壁面具有一定的减阻作用。 利用湍流多尺度局部平均结构函数的概念和多尺度局部平均结构函数的瞬时强度因子、平坦因子检测多尺度相干结构及其间歇性的方法，提取了湍流边界层多尺度相干结构的条件相位平均波形。对比研究了刚性壁面和柔性壁面平板湍流边界层近壁区域多尺度相干结构的条件相位平均波形及其间歇性的统计特征，分析了柔性壁面具有减阻作用的物理机理。

The hot film anemometer is used to precisely measure the longitudinal component of simultaneous velocity in the near wall region of turbulent boundary layer over rigid wall and compliant wall respectively in a water channel with fine resolution higher than Kolmogorov scale. With the relationship among the inner-scale physical quantities of logarithm average velocity profile, such as mean velocity, skin friction velocity and viscosity coefficient and the relationship between skin friction velocity and skin friction stress, the skin friction stress and skin friction coefficient are calculated using average velocity profile method. The result shows that the velocity profiles of logarithm law region over a compliant wall, compared with that of over a rigid wall, is extended further away from the wall and buffer region is becoming thicker. By means of the concept of intermittent factor and flatness factor of locally averaged velocity structure functions of turbulence, multi-scale coherent structures and their intermittency are detected and phase-averaged dynamics evolution waveforms of multirscale coherent structures are extracted. Phase-averaged dynamics evolution waveforms of multi-scale coherent structures and their intermittent statistics character in the near wall region of turbulent boundary layer are compared between rigid flat plate and compliant flat plate respectively. The physical mechanism of drag reduction is extendedly investigated for compliant wall.