3d Numerical Modeling Of Flow And Local Scour Around A Vertical Pier Piercing A Free Surface

The flow around a vertical circular pile piercing a free surface exposed to a steady current and the local scour process are studied numerically. The numerical model is a three-dimensional flow model with sediment transport module included in it. The governing equation of the flow model is closed by a RNGk ? ? turbulence model. The horseshoe vortex and lee-wake vortex flow processes around the pier are simulated by the flow model. The influence of boundary layer thickness and Reynolds number on the horseshoe vortex is investigated. Ratio of boundary layer thickness to pile diameter ? / D ranges from 2 ? 10?2to 10 , and pile Reynolds number Re ranges from20 to 10 6. The amplification of the bed shear stress around the pile (including the location of the horseshoe vortex and the lee-wake region) is obtained for different values of the above parameters. Based on the numerical results of free surface elevation around the pier, the influence of Froude numbers on the rise of water surface elevation in front of the pier and the flow velocity distribution on the vertical plane around the pier is analysed. The model validation is achieved against the experimental data of others.The scour around a vertical pier exposed to a steady current is calculated for the case of non-cohesive sediment. The results show that the scour hole in the upstream of the peir has a slope being close to the respose angle (approximately 32°). The scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole at the initial stage of the scour,while that at the later stages is underpredicted. Discrepancy is observed at the downstream scour hole.