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THE EFFECTS OF SWELLS ON TURBULENCE STRUCTURE OVER WAVY WALLS

Takanori Imashiro
Department of Mechanical Engineering and Science, Kyoto University Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan

Toshiyuki Yamamoto
Department of Mechanical Engineering and Science, Kyoto University Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan

Ryoichi Kurose
Department of Mechanical Engineering and Science, and Advanced Research Institute of Fluid Science and Engineering, Kyoto University, Kyoto daigaku-Katsura, Nishikyo-ku, Kyoto 615–8540, Japan

Satoru Komori
Department of Mechanical Engineering and Science Kyoto University Kyoto daigaku-Katsura, Nishikyo-ku, Kyoto, 615-8140, Japan

Abstract

Three-dimensional direct numerical simulations (DNS) are applied to turbulent boundary layers over the wavy walls, which imitate air-water interfaces with pure wind-wave and swells, and the effects of parallel and oblique swells on the turbulence structure and drag forces are investigated. The results show that both parallel and oblique swells increase the turbulence intensities and the Reynolds stress over the wavy walls. The swells also increase the pressure drag and decrease the friction drag on the wavy walls, and consequently increase 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. This suggests that the swells suppress the mass transfer across the air-water interface, but the effect becomes weak by their obliqueness.