A Two-Phase Turbulent Flow Model And Its Application To Coastal Sediment Transport

It is of current significance to develop an advanced two-phase turbulent model forsediment-laden flow with important theoretical and practical background. With unifiedsediment transport description and specifically revealed general laws of sedimentmovement for both suspended and bedload sediments, the theory about near-shoresediment transport mechanics can be further enriched and perfected. Thus such avertical-horizontal2D numerical model is developed based on Euler-Euler approach oftwo-phase turbulence theory for the nearshore sediment-laden flow under a wide rangeof validation. The fluid phase and the sediment phase are coupled according to theirinteraction forces containing drag force, inertia force and lift force. The traditional k-model is applied for turbulence closure of the fluid phase, while an algebraic particleturbulence model is taken for the sediment phase.By modeling conventional particles and light particles sediment transport underunidirectional flow conditions, it reveals the two-phase velocity distribution,concentration distribution, two-phase interaction, different boundary conditions andsediment diffusion coefficient distribution under different flow and sediment conditions.Further more, the model is applied for non-equilibrium sediment transport problem forbetter understanding of variation of concentration, diffusion coefficient, fall velocity,and their relationships.Under oscillatory sheet flow conditions, the results reveal the temporal and specialvariation of the sediment concentration, horizontal velocities, thickness of the sheetflow layer, horizontal and vertical fluxes of the sediment, and net sediment transportrate under a wide range of conditions. Base on the discussion, it explores the perioddynamic phase response together with turbulence and sediment movement undernearshore period dynamic conditions.Furthermore, it reveals horizontal and vertical sediment fluxes systematicallyunder nonlinear oscillatory flows conditions according to difficulty in traditionalresearch, also explains the effects of flow period, shape, velocity and sedimentdiameters. Model reveals the detail of sediment transport process accompanying withvelocity skewness and acceleration skewness, especially the difference between onshore and offshore durations, according to the illustrating of sediment transport rate andsediment flux. Additionally, it illustrates the vertical sediment flux characteristics at thereference height, near immobile bed and at low concentration area, and explains totalsuspended sediment amount of different sediment sizes under the same flow conditions.Finally, the model is applied for general description of the hydrodynamic andsediment movement near vortex ripples regions under oscillatory flow conditions.Model reconstructs the strong interaction and phase exchange between two phases, andreveals the detail characteristics of formation ejection and dissipation of flow vortexaccompanying with the sediment entrainment and transport process over vortex ripples.