A numerical and experimental study of local hydrodynamics due to interactions between a solitary wave and an impervious structure

A series of experiments and numerical simulations on the interactions between a solitary wave and an impervious structure of square cross-section (block) in relatively shallow water were conducted to shed light on the physical processes of origination and evolution of coherent structures induced during such events. The block was placed at two different positions in a laboratory flume and was exposed to a solitary wave. The flow fields around the block were measured spatially and temporally for the validation of a three-dimensional (3D) computational fluid dynamics (CFD) numerical model results. The numerical model results were, then, used to further understand the generation and propagation of turbulent coherent structures around the block. The results show that two-dimensional (2D) spanwise vortices attributed to surface wave can evolve into coupled 3D turbulent coherent structures that penetrate into the water column at the sharp corners of the block. As the incident wave approaches the block, flow accelerates resulting in positive pressure gradients near the leading and trailing edges of the block. This leads to flow separation and, thus, the formation of vortices near the sharp corners. The vortices are extended through the water column, from the surface to the bottom. This is accompanied by a streamwise return flow that has a velocity of 25-50% of the incident flow velocity at the block. This flow carries the vortex tubes away from the block in the upwave direction. The one-dimensional power spectral density of the streamwise velocity demonstrates the production range and inertial subrange, following slopes of -1 and -5/3, respectively. The production range indicates the production of turbulence kinetic energy as a result of low frequency coherent structures. The inertial subrange marks the transfer of energy from the low to high frequency coherent structures, which correspond to high and low energy eddies, respectively. It is noted that the number of the initial vortices formed at the block corresponds to the number of sharp corners exposed to the incident wave.