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THE DEGREE AND THE MECHANISM OF SKIN FRICTION REDUCTION BY MICROBUBBLES

Yoshiaki Kodama
Ship Performance Division, National Maritime Research Institute 6-38-1 Shinkawa, Mitaka, Tokyo 181-0004, Japan

Kazuyasu Sugiyama
Graduate School of Engineering Science, Osaka University

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

Masahiko Makino
Center for Smart Control of Turbulence, National Maritime Research Institute Shinkawa, Mitaka, Tokyo 181-0004, Japan

Takahito Takahashi
Center for Smart Control of Turbulence, National Maritime Research Institute Shinkawa, Mitaka, Tokyo 181-0004, Japan

Koichi Hishida
Department of System Design Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522

Shu Takagi
Department of Bioengineering, School of Engineering, University of Tokyo 7 Chome-3-1 Hongo, Bunkyo, Tokyo 113-8654, Japan

Resumo

First the applicability of microbubbles to ships as a skin friction reduction device is reviewed on their efficiency and from the environmental viewpoint, based on some experimental results including full scale. The review result is mostly favorable, but it is commented that the skin friction reduction mechanism is still unclear. Then two results of the most recent research on the skin friction reduction mechanism are shown in detail. One is an experimental one, in which microbubble flow was optically measured and the reduction of the Reynolds stress by microbubbles was obtained. The other is a numerical one, in which bubble injection into a turbulent channel flow was simulated and skin friction reduction was obtained. Finally some discussions on the skin friction reduction mechanism are given.