Abstract
The flow within an oscillatory boundary layer, which approximates the flow generated by propagating sea waves of small amplitude close to the bottom, is simulated numerically by integrating Navier-Stokes and continuity equations. The bottom is made up of spherical particles, free to move, which mimic sediment grains. The approach allows to fully-resolve the flow around the particles and to evaluate the forces and torques that the fluid exerts on their surface. Then, the dynamics of sediments is explicitly computed by means of Newton-Euler equations. For the smallest value of the flow Reynolds number presently simulated, the flow regime turns out to fall in the intermittently turbulent regime such that turbulence appears when the free stream velocity is close to its largest values but the flow recovers a laminar like behaviour during the remaining phases of the cycle. For the largest value of the Reynolds number turbulence is significant almost during the whole flow cycle. The evaluation of the sediment transport rate allows to estimate the reliability of the empirical predictors commonly used to estimate the amount of sediments transported by the sea waves. For large values of the Shields parameter, the sediment flow rate during the accelerating phases does not differ from that observed during the decelerating phases. However, for relatively small values of the Shields parameter, the amount of moving particles depends not only on the bottom shear stress but also on flow acceleration. Moreover, the numerical results provide information on the role that turbulent eddies have on sediment dynamics.
Highlights
In nature, flows which involve the motion of solid particles coupled to that of a fluid are quite common and different models have been developed to predict phenomena involvingM
Only a few cases are considered in the following and attention is focused on values of the parameters such that sediment particles are set into motion and the Reynolds number is large enough to trigger turbulence appearance
The results are useful to quantify the bedload sediment transport outside the breaking and surf regions where higher values of the Reynolds number are usually found such that the Direct Numerical Simulations (DNSs) of the turbulent flow field within the bottom boundary layer are presently unaffordable
Summary
Flows which involve the motion of solid particles coupled to that of a fluid are quite common and different models have been developed to predict phenomena involving. Calantoni the motion of sediment particles and either air or water. The approaches employed to describe sediment and fluid motions are different depending on the spatial scale of interest which can range from a few millimetres to hundreds of kilometres, i.e. from the scale of the sediment grains to the scale of the largest morphological patterns observed on the
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