Coherent Structures on Sand Wave Bed in Turbulent Flow

湍流中沙波床面的固有结构尚不清楚，也不完全清楚。本研究分为两部分，一部分是研究Uroko粗糙床和沙波床在湍流中的拟序结构特征。另一部分是基本部分，旨在阐明明渠紊流光滑平面壁上形成的内层拟序结构。利用多种流动显示技术，得到了两个重要的拟序结构，即沿法向排列的流向涡结构，以及沿展向周期性振荡的结构。这些事件依赖于雷诺数，对大尺度螺旋流的形成起着重要作用。扫掠事件是由流向涡的相互作用形成的。对沿流方向涡随雷诺数变化的特性进行了深入研究。

Ooherent sturucture on sand wave bed in turbulent flow has not been clarified and fully understood yet. The study consists of two parts.The one is to find out of the characteristics of the coherent structures on Uroko roughness bed and sand ripple bed in turbulent flow. The other is a fundamental part which aims at clarify-ing the coherent structures in inner layer formed on smooth plane wall in turbulent open channel flow.With several flow visualization techniques, two important coherent events which the structure that streamwise vortices are arrenged in normal direction exsists and oscillates periodicly in spanwise direction. These events depend on Reynolds number and play a important role to form large scale-spiral flow. The characteristic coherent structures are formed by three dimensional roughness of sand ripple.By combined simultaneous flow visualization/LDV measurement, one to one correspondence bet-ween a time series of velocity signal and a spanwise pattern of streamwise vortices was found out. Sweep events are formed by the interaction of streamwise vortices. The characteristics of stream-wise vortices changing with Reynolds number are examined thoroughly.