Three-Dimensional Numerical Investigations of the Flow Pattern and Evolution of the Horseshoe Vortex at a Circular Pier during the Development of a Scour Hole

Featured Application The (k-omega) turbulence model showed good results in capturing the flow structure at the wake zone downstream of the pier, with continuous oscillation matching the pier downstream turbulence pattern. Personal computer computational and storage resources were sufficient to run the computational fluid dynamics (CFD) simulations for the case in hand with the selected turbulence model. The required computational resources are cheap and affordable compared to those required for the Large Eddy Simulation (LES) and Detached Eddy Simulation (DES). This will lead to significant savings in time and resources in future CFD modeling for similar cases. In the current study, a three-dimensional CFD model is utilized to investigate the variation of the flow structure and bed shear stress at a single cylindrical pier during scour development. The scour development is presented by seven solidified geometries of the scour hole, collected during previous experimental work at different scour stages. Different turbulence models are evaluated and the (k-omega) model is chosen due to its relative accuracy in capturing the flow oscillation and vortex shedding at the pier downstream side with personal computer computational and storage resources. The numerical results are verified against dimensionless parameters from different previous experimental works. This research describes in detail the flow structure and bed shear stress variations through seven stages of the scour hole development. The dimensionless area-averaged circulation coefficient (psi(i)) is developed to evaluate the changes in the vortex strength through the scouring process by eliminating the calculation area effect. It was concluded that the circulation in the (Y) direction is the main driving factor in the development of the scour hole more than the circulation in the (X) direction. The ratio between the horseshoe vortex (HV) mean size and the scouring depth (D-V/d(S)) in addition to the location of the maximum bed shear stress are investigated during different stages of the scour development.