Direct Numerical Simulations of Oscillatory Boundary Layers Over Moving Spherical Particles*

     Oscillating turbulent flows contribute to the coastal erosion that affects natural and human-made structures located in the coastal regions of the ocean. To study this phenomenon, Direct Numerical Simulations of the oscillating turbulent boundary layer were performed. As an initial benchmark, a first set of simulations were completed where the oscillatory flow was studied over a bed composed of fixed spherical particles. With increasing Reynolds number, it was observed that the turbulent stresses reached their maximum values at different phases of the oscillation. At the same time, at each given Reynolds number, a phase delay was present between the maximum stress and wall oscillation. As a consequence, imbalances in the turbulent kinetic energy budgets were generated during the oscillation. 

     In the second set of simulations, the motion of the particles was computed by solving the rigid body equation using the hydrodynamic forces of the flow. These forces were calculated from the flow velocity and pressure acting around the particles. The effect of particles on the near wall velocity field will be discussed at the conference presentation.