Author: Keshav Basnet

Publisher:

Published: 2010

Total Pages: 73

ISBN-13: 9781124454139

It is often necessary to determine the flow field and velocity vectors associated with flow around hydraulic structures, such as bridge piers and abutments. Large-scale particle image velocimetry (LSPIV) holds promise for use as a means to obtain this information. However, there are no prior studies focused on the use of LSPIV to delineate unsteady flow fields dominated by large-scale turbulence structures as occur in the wake region immediately downstream of a structure. The present study comprised laboratory flume experiments to assess how LSPIV can be applied for resolving unsteady flow features in the wake region behind a vertical cylinder and a square prism in an open-channel flow. Several circular cylinders were tested, including half cylinders and square-section prisms, which simulated a pier. Also investigated was a half cylinder that approximated a caisson structure located at the channel side. The use of optimized parameters, obtained by slight adjustment on estimated parameters, enabled the LSPIV method to produce expected velocity vector fields, including the vortex-shedding in the wake of a cylinder. The LSPIV-derived wake vortices and their frequency of shedding agreed with the estimated values obtained from the Strouhal number. It is concluded that, with optimal adjustment of parameters used for LSPIV technique, the technique can be used to successfully estimate the actual shedding frequencies. An important aspect of LSPIV considered in the experiments is the size of seed-particle needed for LSPIV use. The experiments led to a recommendation in this regard. They also demonstrate the usefulness of small soap bubbles as seed particles for the range of cylinder diameters the study considered.