使用二相歐拉-拉格朗日模式模擬泥沙在沙紋上的傳輸

Abstract

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Ripple indicators remain to be a major limitation of large-scale hydrodynamic modelling in coastal environments due to the lack of appropriate validation and direct measurement of near-bed dynamics. This limitation can be overcome with improved small-scale process models that can capture fluid-particle interactions and near-bed dynamics over the ripples. Here, we simulate the sediment transport over ripples induced by an oscillatory flow using a two-phase Euler-Lagrange model. The vortex ripple dimension, oscillatory flow condition, and sediment grain information are obtained from a wave-tunnel laboratory experiment. The two-phase model can well simulate the key patterns of observed oscillatory velocity flow field over a vortex ripple. Particularly, the weaker vortex can be found on the stoss side as compared to the stronger vortex on the lee side during reversals of the oscillatory flow that were ahead of the free-stream velocity. Sensitivity tests of three different sediment grain diameters (0.35mm, 0.44mm and 0.53 mm) are compared to examine the feedback of sediments particles with varying grain sizes. Our simulation results showed that finer sediment particles (0.35 mm and 0.44 mm) have higher particle motion and entrainment that enhanced the local vortex formation but neither high enough to alter the oscillatory flow nor enhance the turbulent kinetic energy. On the other hand, coarser sediment (0.53 mm) have lesser particle motion and entrainment but induced constant inter-phase drag that increasingly enhanced the turbulent kinetic energy of the oscillatory flow. Our results showed that different sediment grain size could have different drag contribution to the energy budget of an oscillatory flow.