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TURBULENT DRAG REDUCTION DUE TO LAMINAR WALL-JET FLOWS, SIMULATING EFFLUX FROM FISH GILLS

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 have carried out direct numerical simulation for turbulent flow with the injection of laminar wall jets in order to simulate efflux flow from the gills of swimming fish. The bulk-mean velocity of the jet is lower than the maximum velocity of main flow. It is found that a decrease in the turbulence intensity and the negative velocity gradient due to the jet flow lead to a decrease in the Reynolds shear stress, which causes a decrease in the turbulence intensities. A 3.3% reduction of spatiotemporal averaged value of wall shear stress is obtained in the case where the main-flow Reynolds number based on the friction velocity is 150 and the bulk-mean velocity of the jet is five times the friction velocity. This is due to fact that the jet flow weakens the sweep events in a wide region downstream from the place where the jet is located.