Langmuir circulations and enhanced turbulence beneath wind-waves

Abstract

This paper presents a set of experiments which describes the mutual influences between wind-wave enhanced turbulence and secondary motions like Langmuir circulations (LCs). Different external driven forces were produced in laboratory wind-wave flumes, and mean and turbulent fields were measured for each experimental situation. A ( k– ε) model coupled to momentum equations are numerically integrated to investigate the influences of a diffusion–dissipation (Diff= ε) equilibrium of turbulent kinetic energy (TKE) to represent surface boundary conditions under wind-waves. A new formulation for estimating surface energy is obtained from wave and wind stress parameters, expressed in non-dimensional grounds as k S =0.12(σa/u ∗) 2+C μ −1/2 . The close fit between measurements and numerical results suggests that Craik–Leibovich's equations associated with ( k– ε) turbulence model provides a good description of flow characteristics. Model issues confirm that secondary motions have remarkable influences over the distribution of momentum and turbulence, indicating that wind-wavy boundary conditions resulting from a balance between diffusion and dissipation of TKE is capable of reproducing the realistic scales of phenomena.