吹吸扰动对壁湍流边界层摩擦阻力的影响

对风洞中平板湍流边界层施加局部周期性吹吸扰动,并用IFA-300热线风速仪测量了其近壁区域不同法向位置瞬时速度的时间序列信号.利用湍流边界层对数律平均速度剖面,计算湍流的壁面摩擦阻力.对平板湍流脉动速度信号用子波分析进行多尺度分解,通过条件采样以及相位平均的方法获得不同尺度下的相干结构波形和能量分布,来研究吹吸扰动对平板湍流边界层的摩擦阻力的影响.结果表明,扰动使得窄缝附近流动阻力增加,而下游区域流动阻力减小.

Effect of blowing and suction on friction drag of wall turbulent boundary layer

An experimental study was carried out to investigate the effect of local forcing on the friction drag of a turbulent boundary layer. The local forcing was given to the boundary layer flow by means of a sinusoidally oscillating jet issuing from a thin spanwise slot at the wall. The relationship among some inner-scales physical parameters, e.g. the mean-velocity profile, skin friction velocity and fluid dynamics viscosity, and the rela-tionship between skin friction velocity and skin friction shear stress were taken advantage of accurately calcu-lating skin friction drag. The velocity signals were decomposed into multi-scale eddy structures by wavelet transform. A conditional sampling technique for multi-scale coherent structures detection from simultaneous turbulent field was introduced using multi-scale instantaneous intensity factor of wavelet coefficients. Coherent structures for different scales were extracted by this technique and the effect of blowing and suction on friction drag was investigated in flat-plate turbulent boundary layer .The results reveal that friction drag is increased by the local forcing near the thin slot and decreased at downstream region.