Turbulent burst-sweep events around fully submerged vertical square cylinder over plane bed

Abstract

The subtle variations of the turbulent shear stress affect the entrainment of bed sediments into the flow as well as sediment transport around submerged obstructions. The present study investigates the turbulent flow field and the effect of the turbulent burst sweep events on the Reynolds stress around a vertical submerged square cylinder over a plane bed. Three dimensional point velocity measurements were carried out using Acoustic Doppler Velocimeter at various sections along different radial directions around the submerged square cylinder. Higher resultant velocity magnitude contours are evident near the free surface due to the acceleration of the flow over the top of the cylinder. The profiles of the turbulence intensity shows the evolution of high secondary currents in the downstream of the square cylinder. The bed shear stress as calculated from the Reynolds stress decreases away from the outer edge of the cylinder and is maximum at the downstream of the cylinder. Quadrant analysis suggest that the outward and inward interactions are dominant near the bed, whereas ejections and sweep are dominant towards the top of the cylinder. It also reveals that the fractional contributions due to the sweep and ejection events to the Reynolds shear stress increase with the height above the bed of the channel. Further, analysis of the third order correlations shows streamwise acceleration of the flow due to the increase in downstream flux and increased upward advection.