Direct numerical simulation of a turbulent wind over a wavy water surface

Abstract

Parameterization of the wind‐water‐waves interaction is a key problem of the air‐sea system modeling. Of most importance are water waves with sufficiently large steepness, when nonlinear effects related to the boundary layer separation and vortex generation in the wind flow are well pronounced. Known experimental techniques (contact methods and particle image velocimetry) are not yet able to provide a full, detailed understanding of the wind flow in the viscous sublayer and the buffer region. As an alternative, we consider direct numerical simulations (DNS). In the present paper we discuss numerical algorithm and results of DNS of a turbulent wind flow over a wavy water surface. Waves with maximum steepness of ka = 0.2, wave age 0 < c/u* < 10, and Reynolds number Re = 15,000 are considered. Full, 3‐D Navier‐Stokes equations are solved in curvilinear coordinates in a reference frame moving with the wave phase speed c. DNS results show that an instantaneous velocity field is characterized by the presence of well‐pronounced separation zones in the vicinity of the wave crests whereas the average velocity field is nonseparating. We also perform a comparison of the DNS results with the predictions of a theoretical quasi‐linear model of the wind‐wave interaction.