Turbulence-resolving Two-Phase Flow Simulations of Wave-induced Boundary Layer over Sloped Bed: Evaluation of Wave-supported Gravity Flow Dynamics and Off-shore Sediment Transport

Over the last three decades, the ubiquity of current-and wave-enhanced gravity flows have been extensively reported in many modern fluvial marine dispersive systems. The significance of such flows on geomorphic changes, such as clinoform dynamics in muddy continental shelves, has been observed with growing evidence. Wave-supported gravity flows (WSGFs) are particular types of such flows when along-or cross-shore currents are insignificant. Due to small scales involved in WSGF, O(10 cm), the hydrodynamic details are limited with the current state-of-the-art sensors deployed in the field. Therefore, turbulence-resolving two-phase flow simulations serve as invaluable tools to unravel the details of the particle and turbulent flow interaction and their implications to off-shore sediment transport through WSGF. In this presentation, we show the results of turbulence-resolving two-phase flow simulations of fine sediment loaded wave boundary layer for variable slope values, 0 to 1 m/km, and fine sediment concentration, 10 to 50 g/l, where typical WSGFs take place. Our results show that: (i) maximum off-shore sediment transport occurs when the flow exhibits transitional flow characteristics, i.e., when the flow switches between laminar to turbulent states. We also observe that when the flow is transitional the magnitude of the slope-induced steady sediment flow, U_g is three times the one of its turbulent counterpart, (ii) when the flow is turbulent the off-shore sediment transport increases with the sediment load but shows a decrease when it is marginally turbulent, i.e. just before becoming transitional, and (iii) when the flow is laminar, the value of U_g attains large values within a very thin layer in the boundary, however this does not lead to significant off-shore sediment transport. We shall also compare our results with the prior field and numerical observations and the relevant analysis of how fine sediments alter the drag coefficient and its estimate is warranted.