<p>Rising sea levels are contributing to increasingly sever costal erosion. Areas where the sea bottom is made of loose sediments are particularly prone to erosion caused by the action of waves. The successful modeling of these effects requires an in depth understanding of the interaction between turbulent flow features and sediment grains. In this talk, we discuss the effects of oscillating pressure gradients caused by surface waves on the formation of bedforms and grain entrainment in a sandy seabed using high-fidelity Eulerian-Lagrangian simulations. In our approach, conservation equations for the fluid phase are solved on a Cartesian grid, while each individual sand grain is tracked and updated in a Lagrangian frame. The bed is created by allowing sand particles of size 460m&nbsp;to sediment onto a solid wall, forming a sediment layer of height approximately equal to 150 particle diameters. Three cases are considered where the period of oscillations is maintained constant at 9.72s and the magnitude of the pressure gradient is varied to yield the Reynolds numbers 474, 949 and 1790. The first two cases yield an oscillatory boundary layer in the disturbed laminar, whereas the third case falls under the intermittently turbulent regime. Statistics from the case at Reynolds 1790 are shown to agree with prior experimental observations, thus validating the numerical approach. The bedforms and particle transport statistics at the three different Reynolds numbers are compared and related to the varying turbulence intensities in the carrier fluid. Furthermore, to understand the role of the sediment grains in modifying flow features, auxiliary simulations with no particles, i.e., simulations of oscillatory boundary layers on a smooth flat wall, are conducted at the three same Reynolds numbers and compared with the simulations with sandy beds. These comparisons quantify the affect of particle dynamics upon the oscillating flow.</p>

Investigation of the Entrainment of Sediment Grains in an Oscillatory Boundary Layer at Increasing Reynolds Number Using High-Fidelity Eulerian-Lagrangian Simulations

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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