Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Direct Numerical Simulation of Surface Tension Dominated and Non-Dominated Breaking Waves
Direct Numerical Simulation of Surface Tension Dominated and Non-Dominated Breaking Waves
Pages 254-267
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From page 254... ...
INTRODUCTION In the present paper, attention is drawn to two aspects of the wave breaking process: the role of the surface tension on breakers of progressively smaller length scale and the effects of viscosity on short waves producing micro-breakers. Among the large body of works on breaking waves, many papers have been studying surface tension effects theoretically, experimentally or numerically.
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From page 255... ...
On the basis of the above considerations, an unsteady heterogeneous domain decomposition approach has been developed to tackle the wave breaking flow induced by a submerged hydrofoil moving beneath the free surface (Iafrati & Campana, 20021. In the free surface region, a viscous flow model with an interface capturing technique is adopted, while, in the body region, a potential
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From page 256... ...
Is the volume flux normal to the (m iso-surface and J-i is the inverse of the Jacobian. According to the smooth variation of fluid properties through the interface, surface tension effects are included by using a continuum model, as suggested by Brackbill et al.
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From page 257... ...
and in literature cited therein. In the above equations, for the sake of clarity, a compact notation is used to represent the convective, diffusive and surface tension contributions: C(ui)
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From page 258... ...
, wave breaking conditions are recovered by setting the depth of the hydrofoil to be 0.783 times the chord. In order to investigate the role of surface tension onto the wave breaking dynamics, repeated numerical simulations have been carried out progressively reducing the test scale, starting from a length scale comparable to the one used by Duncan (1983)
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From page 259... ...
Effects of surface tension on the wave breaking de- o velopment The unsteady process that results into the breaking wave formation and establishment is numerically computed for three different length scale at the same Froude num ber, thus varying the role of surface tension effects onto the free surface dynamics, compared to inertial and grav ity terms. To clearly describe how deeply surface tension af fects the wave breaking establishment in the three cases A,B,C, pictures of the resulting free surface shape and of the vorticity field are shown in Figs.
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From page 260... ...
To produce test conditions in which surface tension has a dominant effect on the evolution of the breaking wave, a further reduction of the length scale is finally used (case C)
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From page 261... ...
After an initial acceleration, the toe reaches an almost constant speed. As this motion continues, flow separates due to the sudden change in the free surface slope at the toe, thus originating an intense shear layer that propagates downstream, remaining closely beneath to the free surface.
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From page 262... ...
(1994) , by using a wave focusing technique to induce breaking, argued that the ripples are generated by the instability of the shear layer, produced between the gravity induced downslope flow and the incoming upslope flow, which separates at the toe.
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From page 263... ...
During this time, the bulge front moves from x = 1.30 up to x = 0.95 and free surface ripples are established. The instantaneous vorticity fields illustrate the initial growth of the instabilities of the shear layer formed at the toe.
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From page 264... ...
Maximum backward position 230 Table 2: Ratio between total velocity defect and the thickness of the shear layer at different stages of the bulge motion for case D (Fig.
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From page 265... ...
CONCLUSIONS In this paper the effects of surface tension on the wave breaking dynamics and the effects of viscosity on micro-breakers have been numerically addressed. By using a domain decomposition approach, an accurate description of the breaking and post-breaking evolution has been obtained by solving the Navier-Stokes equations only in a narrow region encompassing the free surface.
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From page 266... ...
15-53. Rosenfeld, M., Kwak, D., and Vinokur, M., "A fractional step solution method for the unsteady Incompressible Navier-Stokes equations in generalized coordinate system," Journal of Computational Physics, Vol.
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From page 267... ...
As to the second question the authors are thinking of taking advantage from the two-phase formulation used to solve this problem and move toward the analysis of the small-scale wave-wind interaction, being a very important generation mechanisms for short surface tension dominated breaking waves. This point has been studied experimentally, for instance by Tulin (1996)
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