Evolution of Scour and Velocity Fluctuations Due to Turbulence Around Cylinders

Abstract

The study is aimed at investigating the turbulence characteristics in scour geometry developed near a circular cylinder placed over the sand bed transverse to the flow. An obstacle of length 10 cm, placed on a sand bed develops a crescent-shaped scour mark on the bed. The scour is caused by generation of vortex developed on the upstream side of the obstacle. The turbulent flow field within the scour mark was measured using an acoustic Doppler velocimeter (ADV). We estimate the joint probability density function of fluctuating velocity components (u ′, w ′) applying the cumulant-discard method to the Gram–Charlier series at different locations over the scour mark. The scour marks named as current crescents preserved in geological record are traditionally used as indicators of palaeo-current direction. We further study the evolution of scour width till a state of equilibrium is attained. The scour-width growth curve is estimated by lowess nonparametric regression and smoothing spline techniques. Scour geometry is an indicator of velocity of past waterflow, preservation of fossils in ancient riverbed, etc. With an application of a robust nonparametric method (Dasgupta, 2013, Non uniform Rates of Convergence to Normality for Two sample U-statistics in Non IID Case with Applications, appearing in this volume as chapter 4) we estimate the first and higher order derivatives of growth curve in the present context and interpret the results.KeywordsCylinder DiameterJoint Probability Density FunctionAcoustic Doppler VelocimeterFlume ExperimentJoint Density FunctionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.