Measurements of sandy bed scour processes in an oscillating flow by using structured light

In this paper an experimental investigation of the scour process that arises at the base of a vertical cylinder, placed in an erodible sandy bed, in the presence of an oscillating flow, is presented. The choice of the measurement strategy is crucial, as a highly non-invasive approach must be adopted in order to avoid perturbations of the sandy bed due to turbulence induced by the measurement equipment itself. A measurement strategy, based on image acquisition techniques and structured light, has been adopted in this work. In particular, the structured light was applied remotely to measure continuously the evolution of the scour at the base of the pile. The measurement technique has been applied under fixed bed conditions to determine the onset of the horseshoe vortex that arises from the interaction between the flow and the pile. Moreover, measured data gave experimental confirmation that an asymptotic value of the scour is reached and allowed some theoretical results regarding the behavior of the scour process to be assessed. The existence conditions of the horseshoe vortex finally have been derived as a function of the flow characteristics. (C) 2000 Elsevier Science Ltd. All rights reserved.