Spatiotemporal Changes In Bed Elevations With Turbulence Around Submerged Cylinders Embedded In Sand Beds

This paper studies the spatial and temporal bed changes due to submerged cylindrical piers at a constant flow discharge. Experiments were carried out with three cylinder diameters of 4, 5 and 6 cm placed vertically at the centerline of the flume separately, possessing a common submergence ratio of 0.6. Instantaneous sand bed elevations at selected locations around the cylinders were recorded with time using a SeaTek 5 MHz Ultrasonic Ranging System (URS) composed of 24 transducers. Clearwater experimental conditions were maintained with a constant flow discharge at a Reynolds number Re-h similar or equal to 63700. Near-bed velocity data were collected over the stable deformed bed topography generated by the cylindrical piers using 3-D Micro-Acoustic Doppler Velocimeter (ADV) to study the bottom Reynolds shear stresses along three different planes. A stable bed condition was achieved more rapidly for the smaller cylinder diameters, whereas the largest scour-depth and areas were observed for larger cylinder diameters. As cylinder diameter increases, more positive value of tau(uv) was observed at right side just downstream of the cylinder and more negative value of tau(uv) was observed at left side of the cylinder base. However, the tau(uw) component showed smaller negative values at just upstream of the cylinder due to the return flow, whose magnitude increased as cylinder size increases. This work provides an experimental database for numerical simulation of loose sediment dynamics around submerged cylindrical piers-like obstacles.