Coherent Structures on Sand Wave Bed in Turbulent Flow

点击翻译按钮获取中文摘要

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.