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TURBULENCE STRUCTURE, FRICTION DRAG AND PRESSURE DRAG DUE TO TURBULENT FLOW OVER ANGLED WAVY SURFACES

Hideto Fujii
Department of Mechanical and System Engineering, Kyoto Institute of Technology, Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Katsutoshi Sakurai
Department of Mechanical and System Engineering Kyoto Institute of Technology Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Tadashi Nakano
Department of Mechanical and System Engineering Kyoto Institute of Technology Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Yoshimichi Hagiwara
Department of Mechanical and System Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Аннотация

We carried out direct numerical simulation for turbulent flow over angled wavy walls. The walls are models of the folded areas of skin which appear on the abdominal parts of fast swimming dolphins. The angles between the streamwise direction and the ridgelines of the wavy walls were 90, 63.4 and 45 degrees. The ratio of amplitude to wavelength in the streamwise direction of the wavy wall was 0.0064. The computational results show that the mean velocity in the transverse direction becomes predominant as the angle decreases. This is due to the occurrence of secondary flow along the ridgelines of the wavy walls. It is also found that the wall-shear stress tensor decreases with the decrease in the angle. This is because the contribution of the Reynolds-shear-stress component ρu'w' becomes more noticeable with the decrease in the angle. The local modification of coherent structure caused by the secondary flow along the ridgelines leads to the decrease in the Reynolds shear stress.