Turbulent Flow around Fully Submerged Circular and Square Cylinders Over Plane and Scoured Beds Subjected to Change of Alignment Angle

Abstract

Local scour around submerged structures is a frequently occurring phenomenon which, usually, is observed in the turbulent flow near submerged piers, well foundations and offshore structures during extreme climatic conditions like floods, heavy water release, high tides, etc. Also, clusters of different shapes, which are built inside the streams, perform as fish habitat structures as well as help in the restoration of aquatic life. In the present study, the quadrant analysis technique is employed for studying the turbulent flow around submerged circular and square cylinders with varying angle of alignments over plane and scoured beds, with an attempt to establish correlation between the bursting events and the resulting coherent turbulent structures. An experimental investigation was carried out using Acoustic Doppler Velocimeter at various sections along different radial directions around the submerged cylinders over plane and scoured bed conditions, which are subsequently used for the quadrant analysis. The study investigates the flow field and the effect of the turbulent burst sweep events on the Reynolds stress around the vertical submerged cylinders over plane and scoured beds. The contour of higher magnitude of resultant velocity are evident near the free surface due to the acceleration of the flow over the top of the cylinder over plane bed, whereas, for scoured beds, the higher velocity contours are observed inside the scour hole due to the diving nature of the flow within the hole. 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. Evidently, the bed shear stress is maximum in the transverse direction for all shapes of the cylinders. The bed shear stress is higher for the square cylinder with different angular alignments than the circular cylinder.