The Vortical Structure of Parasitic Capillary Waves

1995 ◽  
Vol 117 (3) ◽  
pp. 355-361 ◽  
Author(s):  
R. C. Y. Mui ◽  
D. G. Dommermuth
Keyword(s):  
Free Surface ◽  
Capillary Wave ◽  
Surface Current ◽  
Breaking Waves ◽  
Capillary Waves ◽  
Front Face ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Complex Boundary ◽  
Grid Points

A two-dimensional numerical simulation of the parasitic capillary waves that form on a 5 cm gravity-capillary wave is performed. A robust numerical algorithm is developed to simulate flows with complex boundary conditions and topologies. The free-surface boundary layer is resolved at the full-scale Reynolds, Froude, and Weber numbers. Seventeen million grid points are used to resolve the flow to within 6 × 10–4 cm. The numerical method is used to investigate the formation of parasitic capillary waves on the front face of a gravity-capillary wave. The parasitic capillary waves shed vorticity that induces surface currents that exceed twenty-five percent of the phase velocity of the gravity-capillary wave when the steepness of the parasitic capillary waves is approximately 0.8 and the total wave steepness is 1.1. A mean surface current develops in the direction of the wave’s propagation and is concentrated on the front face of the gravity-capillary wave. This current enhances mixing, and remnants of this surface current are probably present in post-breaking waves. Regions of high vorticity occur on the back sides of the troughs of the parasitic capillary waves. The vorticity separates from the free surface in regions where the wave-induced velocities exceed the vorticity-induced velocities. The rate of energy dissipation of the gravity-capillary wave with parasitic capillaries riding on top is twenty-two times greater than that of the gravity-capillary wave alone.

Novel free surface boundary conditions for spilling breaking waves

2020 ◽  
Vol 159 ◽  
pp. 103717
Author(s):  
Nikta Iravani ◽  
Peyman Badiei ◽  
Maurizio Brocchini
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Surface Boundary Conditions

Wind- and Wave-driven Ocean Surface Boundary Layer in a Frontal Zone: Roles of Submesoscale Eddies and Ekman-Stokes Transport

2021 ◽  
Author(s):  
Jianguo Yuan ◽  
Jun-Hong Liang
Keyword(s):  
Boundary Layer ◽  
Frontal Zone ◽  
Surface Current ◽  
Ocean Surface ◽  
Buoyancy Flux ◽  
Temperature Structure ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Horizontal Mixing ◽  
The Right

AbstractLarge-eddy simulations are used to investigate the influence of a horizontal frontal zone, represented by a stationary uniform background horizontal temperature gradient, on the wind- and wave-driven ocean surface boundary layers. In a frontal zone, the temperature structure, the ageostrophic mean horizontal current, and the turbulence in the ocean surface boundary layer all change with the relative angle among the wind and the front. The net heating and cooling of the boundary layer could be explained by the depth-integrated horizontal advective buoyancy flux, called the Ekman Buoyancy Flux (or the Ekman-Stokes Buoyancy Flux if wave effects are included). However, the detailed temperature profiles are also modulated by the depth-dependent advective buoyancy flux and submesoscale eddies. The surface current is deflected less (more) to the right of the wind and wave when the depth-integrated advective buoyancy flux cools (warms) the ocean surface boundary layer. Horizontal mixing is greatly enhanced by submesoscale eddies. The eddy-induced horizontal mixing is anisotropic and is stronger to the right of the wind direction. Vertical turbulent mixing depends on the superposition of the geostrophic and ageostrophic current, the depth-dependent advective buoyancy flux, and submesoscale eddies.

scholarly journals Measurements of Enhanced Near-Surface Turbulence under Windrows

2020 ◽  
Vol 50 (1) ◽  
pp. 197-215
Author(s):  
Seth F. Zippel ◽  
Ted Maksym ◽  
Malcolm Scully ◽  
Peter Sutherland ◽  
Dany Dumont
Keyword(s):  
Boundary Layer ◽  
Surface Flux ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Surface Turbulence ◽  
Order Of Magnitude ◽  
Convergence Zones ◽  
Shallow Bay

AbstractObservations of waves, winds, turbulence, and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of Rimouski, Québec. Water velocities measured from a forward-looking pulse-coherent ADCP mounted on a small zodiac show spanwise (cross-windrow) convergence, streamwise (downwind) velocity enhancement, and downwelling in the windrows, consistent with the view that windrows are the result of counterrotating pairs of wind-aligned vortices. The spacing of windrows, measured with acoustic backscatter and with surface imagery, was measured to be approximately twice the water depth, which suggests an aspect ratio of 1. The magnitude and vertical distribution of turbulence measured from the ADCP are consistent with a previous scaling and observations of near-surface turbulence under breaking waves, with dissipation rates larger and decaying faster vertically than what is expected from a shear-driven boundary layer. Measurements of dissipation rate are partitioned to within, and outside of the windrow convergence zones, and measurements inside the convergence zones are found to be nearly an order of magnitude larger than those outside with similar vertical structure. A ratio of time scales suggests that turbulence likely dissipates before it can be advected horizontally into convergences, but the advection of wave energy into convergences may elevate the surface flux of TKE and could explain the elevated turbulence in the windrows. These results add to a limited number of conflicting observations of turbulence variability due to windrows, which may modify gas flux, and heat and momentum transport in the surface boundary layer.

Wave Breaking and Ocean Surface Layer Thermal Response

2004 ◽  
Vol 34 (3) ◽  
pp. 693-698 ◽  
Author(s):  
George Mellor ◽  
Alan Blumberg
Keyword(s):  
Surface Layer ◽  
Wave Breaking ◽  
Thermal Response ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Surface Temperatures ◽  
Charnock Constant ◽  
Ocean Surface Layer

Abstract The effect of breaking waves on ocean surface temperatures and surface boundary layer deepening is investigated. The modification of the Mellor–Yamada turbulence closure model by Craig and Banner and others to include surface wave breaking energetics reduces summertime surface temperatures when the surface layer is relatively shallow. The effect of the Charnock constant in the relevant drag coefficient relation is also studied.

Effects of soluble and insoluble surfactant on laminar interactions of vortical flows with a free surface

1995 ◽  
Vol 289 ◽  
pp. 315-349 ◽  
Author(s):  
Wu-Ting Tsai ◽  
Dick K. P. Yue
Keyword(s):  
Free Surface ◽  
Surface Concentration ◽  
Sorption Kinetics ◽  
Quantitative Model ◽  
Vortical Flow ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Vortical Flows ◽  
Slip Boundary ◽  
Surfactant Effects

We study the two-dimensional, laminar interactions between a contaminated free surface and a vortical flow below. Two canonical vortical flows are considered: a pair of vortex tubes impinging onto the free surface; and an unstable shear wake behind a body operating on the surface. A quantitative model for free-surface viscous flows in the presence of soluble or insoluble surfactants is developed. For the low to moderate Froude numbers considered here, for which weakly nonlinear free-surface boundary conditions are valid, the surface boundary layer and vorticity production are weak for clean water and the vortical flow evolution does not differ qualitatively from that under a free-slip boundary. When even a small amount of contamination is present, the flow can be dramatically affected. The vortical flow creates gradients in the surfactant surface concentration which leads to Marangoni stresses, strong surface vorticity generation, boundary layers, and even separation. These significantly influence the underlying flow which itself affects surfactant transport in a closed-loop interaction. The resulting flow features are intermediate between but qualitatively distinct from those under either a free- or no-slip boundary. Surfactant effects are most prominent for insoluble surface contamination with likely development of surfactant shocks and associated surface features such as Reynolds ridges. For soluble surfactant with initially uniform bulk concentration, surface concentration variations are moderated by sorption kinetics between the surface and bulk phases, and the overall effects are generally diminished. For initially stratified bulk concentrations, however, the evolution dynamics becomes more varied and surfactant effects may be amplified relative to the insoluble case. The dependence of these results on the properties of the contamination is studied.

scholarly journals Air Entrainment and Surface Fluctuations in a Turbulent Ship Hull Boundary Layer

2020 ◽  
Vol 64 (02) ◽  
pp. 185-201
Author(s):  
Naeem Masnadi ◽  
Martin A. Erinin ◽  
Nathan Washuta ◽  
Farshad Nasiri ◽  
Elias Balaras ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Outer Region ◽  
Surface Profile ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Quantitative Agreement ◽  
Surface Boundary ◽  
Moving Wall ◽  
Fluorescence Measurements

Air entrainment due to turbulence in a free-surface boundary layer shear flow created by a horizontally moving vertical surface-piercing wall is studied through experiments and direct numerical simulations (DNS). In the experiments, the moving wall is created by a laboratory-scale device composed of a surface-piercing stainless steel belt that travels in a loop around two vertical rollers; one length of the belt between the rollers simulates the moving wall. The belt accelerates suddenly from rest until reaching constant speed and creates a temporally evolving boundary layer analogous to the spatially evolving boundary layer that would exist along a surface-piercing towed flat plate. We report cinematic laser-induced fluorescence measurements of water surface profile histories, cinematic observations and measurements of air entrainment events, and air bubble size distributions and motions. To complement the experiments, DNS of the temporally evolving turbulent boundary layer were conducted, considering both the air and water phases. Because of cost considerations, only a portion of the belt was simulated at a lower Reynolds number, keeping the Froude number, however, at the same levels as in the experiments. The results of the experiments and DNS are found to be in qualitative agreement and are used synergistically to explore the physics of the air entrainment process; quantitative agreement is not to be expected given the differences in setup and Reynolds numbers. In the experiments and DNS, the free-surface motion is found to consist of a region near the belt with fast-moving uncorrelated large-amplitude ripples and an outer region of small-amplitude propagating waves. Entrainment events similar to plunging breaking waves are found in the experiments, and these and other entrainment mechanisms are examined in detail in the DNS. The spatial distributions of bubble numbers and velocities are reported along with their diameter distributions.

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