Effects of Oblique Swell on Turbulence Structure and Drag Forces on Wavy Walls

Abstract

Three-dimensional direct numerical simulations (DNS) are applied to turbulent boundary layers over the wavy walls, which imitate sheared air-water interfaces (wind-waves) with swells, and the effects of parallel and oblique swells on the turbulence structure and drag forces are investigated. The results show that the oblique swell increases the turbulence intensities and the Reynolds stress over the wavy wall, whose trends are similar to those of the parallel swell. The oblique swell also increases the pressure drag and decreases the friction drag on the wavy wall, and consequently increases total drag because of the remarkable increase of the pressure drag. These effects are smaller for the oblique swell than that for the parallel swell. The predictions suggest that the oblique swell supresses the mass transfer across the air-water interface, but the effect is weaker than that for the parallel swell.