中文摘要：

采用高时间分辨率粒子图像测速技术对沟槽壁面平板湍流边界层速度矢量场的时间序列及其统计量进行了实验测量，讨论了在同一来流速度下沟槽壁面对平均速度剖面、雷诺切应力及湍流强度的影响．用流向速度分量的多尺度空间局部平均结构函数辨识壁湍流多尺度相干结构，用条件采样和相位平均技术提取壁湍流多尺度相干结构喷射和扫掠事件的脉动速度、展向涡量的二维空间拓扑形态．结果表明，与同材料光滑壁面对比，沟槽壁面实现了10．73％的摩阻减小量；沟槽壁面湍流边界层湍流强度及雷诺切应力皆比光滑平板湍流边界层对应统计量小，说明沟槽壁面有效降低了湍流边界层内流体的脉动．通过比较壁湍流相干结构猝发事件各脉动速度分量与展向涡量的空间分布特征，肯定了沟槽壁面的减阻效果，发现沟槽壁面通过抑制相干结构猝发事件实现减阻．

英文摘要：

Time series of velocity vector field and statistics in the turbulent boundary layer（TBL） over the riblets surface and smooth one were measured utilizing the time-resolved particle image velocimetry （TRPIV） ; Several characteristic parameters in the TBL, such as the mean velocity profile, the Reynolds shear stress and the turbulent intensity, etc. were compared at the same free-stream velocity（0.19m/s） for the different surface plates. We firstly detected the coherent structures using multi-scale spatial locally-averaged structure function of the streamwise velocity component at different scales. Then, we utilized the conditional sampling and phase-average method to extract the spatial topologies of physical quantities, such as the velocity fluctuation and the spanwise vorticity, etc. based on the ejection or sweep events of coherent structures in the TBL. Results reveal that a drag-reduction of nearly 10.73 percent was acquired over the riblets surface when we compared the skin friction coefficient of such two Acrylic Plexiglas plates at the same free-stream velocity. In addition, that the streamwise turbulent intensity and the Reynolds shear stress of the TBL over riblets surface are both smaller than the ones over smooth surface at the same wall-normal position indicates riblets surface weaken the flow turbulence reducing the momentum exchange and energy loss in the flow. Lastly, we compared several statistic characteristics, mentioned above, based on the ejection and sweep events of coherent structures to clarify the effect of the drag-reduction over the riblets surface with triangle cross-section. More importantly, we find that the drag-reduction achieved by means of riblets surface suppressing the bursting events of coherent structures.