High-Resolution Large Eddy Simulations of Vortex Dynamics Over Ripple Defects Under Oscillatory Flow

We carried out high-resolution Large Eddy Simulations to study the three-dimensional hydrodynamic characteristics over regular and irregular wave-generated ripples. Two types of irregularities in ripple crestlines are considered, namely ripples with a termination defect and with a bifurcation defect. Over regular ripples, the flow and vortex structures vary in the spanwise direction, displaying evident three-dimensional vortex structures. Compared to regular ripples, the presence of a bifurcation or a termination defect implies local variations in ripple height and spacing. As a result, the maximum velocity, vortex strength and the position of the vortex center over ripples neighboring a defect are all affected by the presence of the defect. The maximum velocity at the ripple crest neighboring a defect is linearly related to the position of the vortex center. The presence of defects induces an asymmetric distribution of shear stress and sediment flux that will ultimately affect bedform evolution.