Flow Structure Over Uniform and Nonuniform Sand Bed Channel

Flow over sand bed occurs frequently in nature. Riverbeds are usually composed of non- uniform sediment mixtures and the respective particle size distribution of sediment in transport is generally finer than the distribution of bed material because of selective transport. The experimental study has been carried out to observe the turbulent characteristics of flow in an alluvial channel composing of uniform sediment and non-uniform sediment mixture. Instantaneous velocity measurements were taken at the centre line of flume by the Acoustic Doppler Velocimeter (ADV).The present study addresses on the flow zone in the vicinity of the bed surface. The variations of stream wise velocity with vertical distance in flows with non-uniform sediment in the near bed region are smaller than uniform sediment. This increase in stream wise velocities was sufficient for increased rate of sediment transport with uniform sand bed channel. The profiles of Reynolds shear stress is slightly scattered in general and decreased with non-uniform sediment which signifies the lower momentum transfer towards the boundary. The distribution of Reynolds shear stress undergoes a damping due to a decreasing level of turbulence fluctuation within the wall shear layer. . In presence of non-uniform sand bed channel, increased in stream wise and decreased in vertical turbulence intensities are observed than turbulence intensities in uniform sand bed channel.