Numerical simulations of oscillating turbulent boundary layer flow over a spherical bed*

Erosion, transport and deposition of sediments within a turbulent flow is a key problem which arises in several engineering applications and natural environments, such as fluvial or coastal beds. To date, a complete understanding of the fluid-particle interaction is still lacking, which hinders reliable predictions of the morphological evolution of the sediment bed. The flow dynamics plays a primary role in the initiation of sediment motion and affects the trajectory of suspended particles. In coastal environments, this problem is further compounded by the presence of the oscillating coastal bottom boundary layer generated by sea waves. In this work, we study an oscillating boundary layer over a bed of spherical particles through direct-numerical simulations. Spherical particles are an abstraction for sediments in non-cohesive silica sands encountered in many littoral zones. In the simulations, the sediments are treated with the immersed boundary method, which allows to explicitly resolve frictional and pressure forces due to the flow around the particle. The objective of this study is to investigate the effect of the oscillating boundary layer over the rough bed towards an improved understanding of sediment transport dynamics.