Wave reflection and vortex evolution in Bragg scattering in real fluids

Abstract

The vortex generation and dissipation accompanying Bragg scattering of water waves propagating over a series of submerged rectangular breakwaters are investigated both numerically and experimentally. The present model, which takes effects of non-linearity, viscosity and turbulence into consideration, is applied to simulate the entire vortex evolution process as water waves pass over a series of artificial rectangular bars. Particle image velocimetry is used to measure the velocity field in the vicinity of the bars. The numerical model is validated via a comparison with measured water surface elevations and velocity fields; the results show good agreement. The mechanism of vortex evolution and its influence on the interaction of water waves with submerged structures for cases with and without resonance are studied. The corresponding wave reflection coefficients for both cases are calculated and compared with experimental data and solutions based on linear wave theory. Examination of the turbulence properties shows that the turbulent intensity decreases on the weather side but increases on the lee side under the Bragg scattering conditions.