Rans-Based Numerical Simulation of Wave-Induced Sheet-Flow Transport of Graded Sediments

An existing one-dimensional vertical (1DV) turbulence-closure flow model, coupled with sediment transport capabilities, is extended to incorporate graded sediment mixtures. The hydrodynamic model solves the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equations coupled with k–ω turbulence closure.

In addition to standard bed and suspended load descriptions, the sediment transport model incorporates so-called high-concentration effects (turbulence damping and hindered settling velocities). The sediment transport model treats the bed and suspended load individually for each grain fraction within a mixture, and includes effects associated with increased exposure of larger particles within a mixture.

The model also makes use of a modified reference concentration approach, with reference concentrations computed individually for each fraction, and then translated to a common level, which conveniently enables use of a single computational grid for the simulation of suspended sediments. Parametric study shows that these effects combine to help alleviate an otherwise systematic tendency towards over- and under- predicted transport rates for fine and coarse sand fractions, respectively.

The sediment transport model is validated against experimental sheet-flow measurements conducted in oscillatory tunnels beneath velocity-skewed wave signals, and demonstrates similar accuracy (predicted transport rates generally within a factor of two of measurements) for both graded mixtures and uniform sands.