The flow field around the vertical-wall abutments is investigated through detailed three-dimensional velocity measurements performed after reaching equilibrium scour bed for non cohesive soil as well as cohesive soil. Velocity measurements are taken upstream, downstream and on the side of the abutment by using the Acoustic velocity Doppler (ADV). The stagnation pressure gradient leads to downward deflection of the flow to form the downward flow at the upstream side of the abutment. The primary vortex formed at the upstream side of the abutment near the bottom rotates in downstream direction adjacent to the side of the abutment in a spiral motion. The primary vortex and secondary vortex created at the side of the abutment by flow separation extend around the abutment from side in downstream direction to form wake vortices. The flow field is used to explain the scour pattern at the vertical-wall abutments. The velocity measurements are useful for the development and validation of future flow field numerical models, which can be incorporated with scour model to estimate scour depth at bridge abutments. |
