Author(s): Sjoerd Van Ballegooy; Bruce W. Melville; Stephen E. Coleman
Linked Author(s): Bruce W. Melville
Keywords: Particle tracking velocimetry; Bridge abutments; Flow fields
Abstract: The flow fields around spill-through abutments in compound channels were measured using a surface particle tracking velocimetry technique. The flow fields were seeded with 25mm fluorescentyellow, cube shaped wooden blocks that were scattered on the surface of the water, and illuminated under UV light so that the particles could be easily identified in the image processing. Surface plots of scalar velocity, vorticity, and normalised shear stress were produced from the measurements. By systematically altering the floodplain width and the abutment length, the velocity, vorticity, and normalised shear stress fields were determined for several different configurations. The results show that as the abutment length increases, the velocity and vorticity strength at the abutment tip also increase. However, when the abutment geometry is fixed and the compound channel geometry is altered, the velocity and vorticity strengths at the abutment tip decrease as the distance between the abutment tip and the main channel decreases. Values of normalised shear stress exceeding one are indicative of regions where scour will occur due to increased local velocities. Similarly, regions of high vorticity identify the area where scour is initiated.