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Large eddy simulation of the turbulent flow field around a submerged pile within a scour hole under current condition

ABSTRACT Coastal finite structures, bridge piers, and bank protection structures may become submerged during storm surges. In the present study, a turbulent flow field around a submerged pile within a scour hole is numerically simulated considering a very fine mesh in the order of 50 million cells distributed within a relatively small computational domain. Necklace vortices, including two horseshoe vortices (HVs) and a junction vortex (JV), are detected upstream from the cylinder. In many snapshots, the tails of the HVs stretch in the flow direction, while their size and length change considerably over time. Downstream of the cylinder, the influence of the trailing vortex from the cylinder roof is mainly limited to a zone near the cylinder top, whereas the effect of the separated shear layers (SSLs) from the cylinder sides is dominant within a larger region. The strength of vorticity associated with the trailing vortex is mainly notable within the “very near wake” area, where the strength of the upward velocity component of the wake vortices generated from the cylinder sides mitigates. This paper describes the distribution and origin of streaks and rollers on the scoured bed, i.e. the main cause of sediment transported downstream of the cylinder.