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A numerical investigation of wave‐breaking‐induced turbulent coherent structure under a solitary wave
Author(s) -
Zhou Zheyu,
Sangermano Jacob,
Hsu TianJian,
Ting Francis C. K.
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc009854
Subject(s) - turbulence , vortex , breaking wave , mechanics , eddy , volume of fluid method , particle image velocimetry , large eddy simulation , physics , intermittency , compressibility , classical mechanics , flow (mathematics) , optics , wave propagation
To better understand the effect of wave‐breaking‐induced turbulence on the bed, we report a 3 ‐ D large‐eddy simulation (LES) study of a breaking solitary wave in spilling condition. Using a turbulence‐resolving approach, we study the generation and the fate of wave‐breaking‐induced turbulent coherent structures, commonly known as obliquely descending eddies (ODEs). Specifically, we focus on how these eddies may impinge onto bed. The numerical model is implemented using an open‐source CFD library of solvers, called OpenFOAM, where the incompressible 3 ‐ D filtered Navier‐Stokes equations for the water and the air phases are solved with a finite volume scheme. The evolution of the water‐air interfaces is approximated with a volume of fluid method. Using the dynamic Smagorinsky closure, the numerical model has been validated with wave flume experiments of solitary wave breaking over a 1/50 sloping beach. Simulation results show that during the initial overturning of the breaking wave, 2 ‐ D horizontal rollers are generated, accelerated , and further evolve into a couple of 3 ‐ D hairpin vortices. Some of these vortices are sufficiently intense to impinge onto the bed. These hairpin vortices possess counter‐rotating and downburst features, which are key characteristics of ODEs observed by earlier laboratory studies using Particle Image Velocimetry. Model results also suggest that those ODEs that impinge onto bed can induce strong near‐bed turbulence and bottom stress. The intensity and locations of these near‐bed turbulent events could not be parameterized by near‐surface (or depth integrated) turbulence unless in very shallow depth.