Features of Air Flow in the Trough-Crest Zone of Wind Waves

TL;DR

This study analyzes the vertical profiles of wind and wave-induced momentum flux over wind waves, revealing deviations from typical turbulence profiles and indicating complex, anisotropic dynamics in the trough-crest zone.

Contribution

It provides detailed numerical calculations of wind and wave-induced fluxes and spectra, highlighting deviations from classical turbulence laws in the trough-crest zone of wind waves.

Findings

Wind-velocity profiles deviate from logarithmic law

Wave-induced momentum flux changes sign near surface

Spectral analysis indicates nonlinear, anisotropic dynamics

Abstract

Vertical profiles for mean wind, standard deviations of velocity fluctuations, and wave-induced part of the momentum flux over a wavy fluid surface are calculated in the Cartesian coordinates on the basis of recent numerical results by Chalikov and Rainchik. Besides, calculations of spectra for surface elevation and wave-induced velocity components at this surface are carried out. Unlike the profiles typical to the near-wall turbulence, the calculated wind-velocity profiles deviate significantly from the logarithmic law throughout the entire trough-crest zone of wind waves, and the wave-induced part of the momentum flux changes its sign in close vicinity of the mean surface level. Vertical scales of the profiles features are estimated. Spectral analysis of the water-surface oscillations and wind-velocity components suggests nonlinear and strongly anisotropic dynamics of the system under consideration. Points of application of the results obtained are discussed.