Author(s): Sofi Aamir Majid; Shivam Tripathi; Debopam Das

Linked Author(s):

Keywords: Vertical contraction; Pressure-flow scour; Particle image velocimetry; Velocity field

Abstract: A reliable estimate of scouring is a prerequisite for designing bridges. In extreme flood events, the water surface may rise above the bottom chord of the bridge, creating a pressure flow situation in the passage underneath. Contrary to the local and horizontal contraction scouring, which have been extensively studied, pressure-flow scour due to vertical contraction has received less attention. The transition of free surface flow to pressure flow due to the vertical contraction is accompanied by flow acceleration and increased velocity gradients resulting in the scouring in the contraction. However, in a recent experimental study, an anomaly has been observed in which scour hole has been reported to have formed downstream of the bridge where the flow transits back to free-surface flow. Due to the absence of the velocity field data, no plausible explanation for such an anomaly has been presented. The present study is an attempt to resolve this anomaly. In the present study, laboratory flume experiments are conducted to reproduce the anomalous pressure-flow scour due to vertical contraction. The mean velocity field inside and near the contraction is studied using particle image velocimetry (PIV) during the evolution of the scour hole. An increased vertical velocity component is observed downstream of the contraction. The scouring process is intermittent and is visible even after many hours from the start of the experiment. These results provide insights into the distribution of near-bed velocity components, which may help to explain the anomalous scouring behavior.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0326-cd

Year: 2023