Author(s): M. Koken; G. Constantinescu
Linked Author(s): George Constantinescu
Keywords: Bridge abutment; Coherent structures; Large eddy simulation
Abstract: Results of eddy resolving numerical simulations are used to discuss the changes in the flow and turbulence structure around abutments of idealized shape (vertical wall) between channel Reynolds numbers of 18,000 and 240,000. The abutment is positioned at one of the sidewalls of a straight channel. A large scour hole is present around the abutment, corresponding to conditions at the end of the scour process. In both simulations the horseshoe vortex is subject to bimodal oscillations that amplify the turbulence within the upstream part of the scour hole. Results show that at Re=240,000 the region of the highest turbulence amplification within the horseshoe vortex region is not anymore situated around the flank of the obstacle, as was the case in the simulation conducted at Re=18,000. The study also investigates the changes in the flow structure between the case of a vertical-wall abutment and that of an abutment of more realistic geometry with sloped lateral walls (Re=240,000). We show that while the horseshoe vortex system induces a large amplification of the turbulence inside the scour hole in both geometries, the coherence of the horseshoe vortex system is lower in the case of an abutment with a sloped wall. This is mainly because of the larger deflection of the incoming flow toward the upstream face of the abutment with sloped walls and lower strength of the downflow.
Year: 2011