Simultaneous 3-D PTV and micro-pressure sensor equipment for flow analysis in a subsurface gravel layer

摘要

An experimental setup for the simultaneous analysis of flow, pressure and sediment movement within and above a gravel layer covering a sand base layer in an open-channel flow is presented. A multi-camera setup is used to acquire digital image sequences from various locations of the flow field. Optical access to the gravel layer is provided by endoscopic imaging. The image sequences are analysed by a 3-D Particle-Tracking Velocimetry algorithm and optical flow techniques to calculate 3-D Lagrangian trajectories of seeding particles resp. 2-D displacement vector fields of sand particles. Special micro-pressure sensors based on the piezoelectric effect have been developed, which can be inserted into the gravel layer at arbitrary locations. The system is used to perform extensive measurements in an experimental flume under a wide range of flow conditions, including surface waves. The goal of the experiments is to gain new insight into the physical flow processes inside the gravel layer and to quantify the influence of turbulent fluctuations on the stability of both the gravel and the sand grains. This paper focuses on the description of the measurement system. A detailed analysis of the results will be given in a later publication.