Experimental study on bursting events around a bar in physical model of a braided channel

Abstract

Sediment particles entrainment from the channel bed is influenced by flow turbulence which creates fluctuating shear stress at the bed. Sweep quadrant event is considered to be most important for entrainment of sediment particles as it exerts forces in the flow direction resulting in rolling and sliding of sediment particle. Similarly, the ejection event has been considered important for sediment transport since these events maintain the sediment particles in suspension. In this paper, the nature of bursting events and in particular, the sweep events were studied in a model of braided river with a central island. The instantaneous velocities of flow were measured using the ADV. The turbulent stresses were determined from these instantaneous velocities. Box–Cox transformation is applied to transform the original data into a normally distributed data. The velocity measurements near the braided bar were made at 12 vertical sections using an ADV. The maximum value of turbulent kinetic energy and the Reynolds shear stress was found to occur near the bed level. These turbulent parameters have greater values for scouring points, this shows that these parameters are related with the scouring near the braided bar.

Keywords:

• Acoustic Doppler Velocimetry
• braided bar
• turbulence
• quadrant analysis
• turbulent kinetic energy