Experimental Study On Sand Ripple Evolution And Corresponding Turbulent Characteristics

As the minimum scale of bed forms in open channel, sandripple is the group effect of bed load traveling and plays animportant role in river friction formulation and sanddischarging. They are the footprint of open channel turbulentflow on erodible bed in long time effect. The steady shape ofsand ripple reflects the interaction between water and sand,which is complex in micro scale while regular in overall macroview. The formation and development of sand ripples is theresult of coordination between river bed and flow over it. In this paper the characteristics of flow in open channelwith different beds under different disturbs are measuredsystematically in laboratory flume with Acoustic DopplerVelocitimeter (ADV) and flow visualization device of waterdyeing. Based on the high frequency turbulence signal collected,statistic parameters of open channel flow are calculated,compared and analysed, including fluctuating intensity,Reynolds stress, turbulent kinetic, velocity probabilitydensity, spectrum density, skewness coefficient and kurtosiscoefficient etc. Besides, quasi-ordering structures inturbulent flow were also studied with correlation analysis andwavelet analysis. As the emphasis of our experimental study, the turbulentstructure over sand ripples was carefully studied, includingthe strong bursting phenomenon on the front face etc.Photography at a fixed point and topographic measurement werealso applied to study the evaluation of sand ripples and sandtransportation over it, on which the micro dynamiccharacteristic were also analysed. Besides, we also studied therelationship between sand starting velocity and turbulentcharacteristic, the effect of bed coarseness and form onturbulent characteristic, the influence of disturbs on thestability of bed etc.