Coherent Structures on Sand Wave Bed in Turbulent Flow

沙波床在紊流中的内部结构至今尚未被阐明和充分认识。本研究分为两部分，一是探讨在紊流条件下，Uroko粗糙床与沙涟漪床的拟序结构特性。另一部分是基础部分，旨在阐明明渠湍流光滑壁面上形成的内层拟序结构，通过多种流动显示技术，发现了两个重要的拟序事件，即流向涡沿法向排列的拟序结构的存在和沿展向的拟序振荡。这些事件依赖于雷诺数，对形成大尺度螺旋流起着重要作用。沙涟漪的三维粗糙度形成特征相干结构，通过流动显示/LDV同步测量，发现速度信号的时间序列与流向涡的展向分布有一一对应的关系。后掠事件由流向涡的相互作用形成。深入研究了流向涡随雷诺数变化的特性。

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.