Eulerian two-phase modeling of wave orbital ripples: a sensitivity study on closure models

Abstract

A two-dimensional simulation of sediment transport over wave orbital ripples driven by onshore velocity-skewed oscillatory flow using a Eulerian two-phase flow model, SedFoam, is presented to investigate the sensitivity of the turbulence closure models with respect to sediment transport and ripple migration. The comparison of simulation results between k-ɛ model and k-ω SST model at equilibrium stage confirms that the k-ω SST model predicts a significantly weaker vortices evolution in orbital ripple field, which causes less suspended sediment transport during a wave period. The resulting equilibrium ripple steepness is also under-predicted. An in-depth analysis reveals that the negative component of cross-diffusion term neglected in k-ω SST model results in weaker turbulence and lower turbulent suspension. Hence, a larger onshore near-bed sediment transport and a smaller offshore suspended load transport are obtained. Consequently, the model with k-ω SST closure over-predicts the onshore ripple migration rate. The root cause of which the neglected negative cross-diffusion term leads to the under-prediction of primary vortices on the ripple flanks under oscillatory flows is worth of further investigation.