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The flow within an oscillatory boundary layer, which approximates the flowgenerated by propagating sea waves of small amplitude close to the bottom, issimulated numerically by integrating Navier-Stokes and continuity equations.The bottom is made up of spherical particles, free to move, which mimicsediment grains. The approach allows to fully-resolve the flow around theparticles and to evaluate the forces and torques that the fluid exerts on theirsurface. Then, the dynamics of sediments is explicitly computed by means ofNewton-Euler equations. For the smallest value of the flow Reynolds numberpresently simulated, the flow regime turns out to fall in the intermittentlyturbulent regime such that turbulence appears when the free stream velocity isclose to its largest values but the flow recovers a laminar like behaviourduring the remaining phases of the cycle. For the largest value of the Reynoldsnumber turbulence is significant almost during the whole flow cycle. Theevaluation of the sediment transport rate allows to estimate the reliability ofthe empirical predictors commonly used to estimate the amount of sedimentstransported by the sea waves. For large values of the Shields parameter, thesediment flow rate during the accelerating phases does not differ from thatobserved during the decelerating phases. However, for relatively small valuesof the Shields parameter, the amount of moving particles depends not only onthe bottom shear stress but also on flow acceleration. Moreover, the numericalresults provide information on the role that turbulent eddies have on sedimentdynamics.

Interface-resolved direct numerical simulations of sediment transport in a turbulent oscillatory boundary layer