An Investigation on Plunging Breaking Waves over a Slope with a CFD based Numerical Wave Tank.

Mayilvahanan Alagan Chella, Hans Bihs, Dag Myrhaug

Thursday 2 july 2015

17:15 - 17:30h at Oceania (level 0)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 13E. Engineering - Computational

In the present investigation, the CFD based numerical wave tank REEF3D is utilized to simulate plunging breaking waves over a slope. The numerical model solves the incompressible Reynolds Averaged Navier-Stokes (RANS) equations over a Cartesian grid. This model uses staggered configuration for the location of the velocity and the pressure, which is important to describe the distinct density jumps across the water-air interface accurately. The main feature of breaking waves is the complex motion of the free surface. The flow problem is solved as a two-phase flow of water and air, with the free surface being represented by the level set method. A large amount of energy is dissipated through the action of turbulence during the wave breaking process, and the turbulence is described by the k-_ model. The 5-th order Weighted Essentially Non-Oscillatory (WENO) scheme is employed for the convective discretization. A comprehensive examination of breaking process is essential for the understanding of the mechanisms of wave breaking over slopes. The main focus of the present numerical study is to investigate the breaking process of plunging breaker over a sloping bed. The numerical experiments are performed with the 5-th order cnoidal waves over a sloping bed with a slope of 1:35. The present numerical model is validated by comparing the numerical results with experimental results by Ting and Kirby, (1994). The study further investigates the variations in the free surface elevation, horizontal velocity, wave envelope and wave profile in different regions during wave breaking process. The simulated horizontal velocities, free surface elevations and wave envelope are in good agreement with the experimental measurements. Moreover, the present model can describe the key flow features during the breaking process such as the motion of air pockets in the water, formation of a forward moving jet, the splash-up phenomenon and the mixing of air and water in the breaking region.