Modelling wind-induced changes to overturning wave shape

• Published in: Journal of fluid mechanics 2024-11, Vol.1000
• Main Authors: Feddersen, Falk, Hanson, Kentaro, Mostert, Wouter, Fincham, Adam
• Format: Article
• Language: English
• Subjects: Aspect ratio; Bathymeters; Bathymetry; Bond number; Boundary conditions; Direct numerical simulation; Fluid flow; Inertia; JFM Papers; Overturn; Partial differential equations; Potential energy; Pressure; Pressure dependence; Pressure effects; Reynolds number; Shape; Shape effects; Shoaling; Shoaling waves; Simulation; Solitary waves; Surface tension; Turbulence; Turbulent flow; Velocity; Velocity potential; Water depth; Water waves; Wave energy; Wave propagation; Wind; Wind effects
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2024.1012

Depth-limited overturning wave shape affects water turbulence and sediment suspension. Experiments have shown that wind affects shoaling and overturning wave shape, with uncertain mechanism. Here, we study wind effects (given by the wind Reynolds number) on solitary wave shoaling and overturning with the two-phase direct numerical simulations model Basilisk run in two dimensions on steep bathymetry for fixed wave Reynolds number and Bond number. For all wind, the propagating solitary wave sheds a two-dimensional turbulent air wake and has nearly uniform speed with minimal wave energy changes over the rapidly varying bathymetry. Wave-face slope is influenced by wind, and shoaling wave shape changes are consistent with previous studies. As overturning jet impacts, wind-dependent differences in overturn shape are quantified. The non-dimensional breakpoint location and overturn area have similar wind dependence as previous experience, whereas the overturn aspect ratio has opposite wind dependence. During shoaling, the surface viscous stresses are negligible relative to pressure. Surface tension effects are also small but grow rapidly near overturning. In a wave frame of reference, surface pressure is low in the lee and contributes 2–5 % to the velocity potential rate of change in the surface dynamic boundary condition, which, integrated over time, changes the wave shape. Reasons why the overturn aspect ratio is different than in experiment and why a stronger simulated wind is required are explored. The dramatic wind effects on overturning jet area, and thus to the available overturn potential energy, make concrete the implications of wind-induced changes to wave shape.