Effects of breaking intensity on wave breaking dynamics

The breaking of ocean waves plays a fundamental role on momentum, energy and gas transfer between air and water. The phenomenon is characterized by a broad range of length scales. Moderate winds blowing over an otherwise flat sea surface give rise to waves of few centimeters wavelength. At such short scales the stabilizing action of gravity and surface tension dominate over the disrupting effect of the turbulence (Brocchini and Peregrine, 2001). The breaking is of the spilling type with essentially no air entrapped and vorticity is induced in water as a consequence of the viscous effects taking place beneath the bulge (Qiao and Duncan, 2001; Iafrati and Campana, 2005). In open ocean, where strong winds act over long fetches, the breaking is much more violent. Rather large jets develop about the wave crest and plunge onto the water surface entrapping large air cavities, with a strong turbulence field leading to a significant amount of drops, sprays and bubbles.In this paper the breaking of periodic wave trains with different initial steepnesses is simulated numerically. The numerical approach is based on a Navier-Stokes solver coupled with a Level-Set technique for the interface capturing. Results are discussed in terms of energy dissipation, induced circulation in water, momentum transfer, air entrapment and degassing.