沟槽面对湍流边界层流动特征影响的实验研究

An experimental study of turbulent boundary layer over the grooved-surface

利用二维激光多普勒测速仪对零压力梯度下光滑面和小尺度沟槽面的沟槽及峰上部区域中湍流边界层流场进行了对比测量。笔者着重考察了在相同流动条件下两位置的平均速度、流向速度脉动强度、高阶矩以及雷诺剪应力的分布特性。实验中发现:沟槽能够增加粘性底层的厚度,减小壁面剪切力,有减阻效应。而此处的流向速度脉动的强度、高阶矩以及雷诺剪应力在距离壁面的不同区域中均有减小或降低,说明沟槽具有削弱湍流湍动的功能;而峰上部的湍流统计平均量则表现出与槽相反的结果或趋势。还讨论了该沟槽面减阻的原因。

Measurements of fluid field by means of a two-component Laser Doppler Velocimetry are carried out in turbulent boundary layers over a micro-grooved surface's valley, peak and a smooth one in a zero pressure gradient. Much attention has been paid to the characteristics of the mean velocity, streamwise velocity fluctuation intensity, high-order moment and Reynold shear stress above the valley and peak. The present results clearly indicate that the valleys are able to increase the viscous sublayer thickness which implies a drag reduction. At the same time, other turbulent statistics such as turbulence intensity, high-order moment and Reynold shear stress decrease to different degree respectively, which demonstrates the valley takes a role of weakening turbulence. While the turbulent statistics of the boundary layer over the peak show a contrary tendency. And also the reason of drag reduction is discussed.