On wind–wave interaction phenomena at low Reynolds numbers

Abstract

After decades of research efforts, wind–wave interaction mechanisms have been recognized as extremely elusive. The reason is the complex nature of the problem, which combines complex coupling mechanisms between turbulent wind and water waves with the presence of multiple governing parameters, such as the friction Reynolds number of the wind, the water depth and the wind fetch. As shown unequivocally here, the use of suitable flow settings allows us to reduce the complex problem of wind–wave interaction to its essential features, mainly as a function of the sole friction Reynolds number of the wind. The resulting numerical solution allows us to study the interactions between water and air layers with their own fluid properties, and to unveil very interesting features, such as an oblique wave pattern travelling upstream and a wave-induced Stokes sublayer. The latter is responsible for a drag reduction mechanism in the turbulent wind. Despite the simulated flow conditions being far from the intense events occurring at the ocean–atmosphere interface, the basic flow phenomena unveiled here may explain some experimental evidence in wind–wave problems. Among other things, the wave-induced Stokes sublayer may shed light on the large scatter of the drag coefficient data in field measurements where swell waves of arbitrary directions are often present. Hence the present results and the developed approach pave the way for the understanding and modelling of the surface fluxes at the ocean–atmosphere interface, which are of overwhelming importance for climate science.

Numerical experiments on scalar transport and mixing in turbulent boundary layers

“…In this preliminary work, we opted for low resolution simulations to test the potential of the method used. We verified that the classical statistics obtained with these settings are reliable when compared to those obtained from higher resolution simulations presented in [8].…”

“…The choice of addressing the scalar field evolution is crucial to decouple the effect of the two layers. More specifically, we analyse the evolution of passive scalars in the configuration of a temporally evolving boundary layer ( [6], [7] and [8]). The flow configuration of the boundary layer is chosen as it represents a canonical flow for the study of wall turbulence and additionally exhibits the presence of a Turbulent/Non-Turbulent Interface (TNTI).…”

The Effect of Surface Oil on Ocean Wind Stress

“…This study aims to produce a more realistic physical environment for examining the impact of surface oil on surface stress and surface oil transport using a two-way coupled modeling system. The two-way coupling allows different physical processes of the atmosphere, ocean, and waves to interact with each other [16][17][18]. To this end, a high-resolution two-way coupled-ocean-atmosphere-wave-sediment-transport (COAWST) modeling system [19] for the Gulf of Mexico region was utilized over the DWH oil spill period.…”