A drag reduction for 3-dimensional body is attempted by microbubble injection. Two models with different lengths are used for experiments to distinguish the resistance due to on microbubble injection itself and the skin friction affected by microbubble covering. A reformed Wigley model is used to investigate the effect of microbubble injection on wave making. Measurements of the resistance and the longitudinal wave profiles are performed. The covering by microbubbles is realized by injected air through a porous pipe with pore size of 15 μm. The flow of microbubbles is obsered and the bubble sizes are estimated based on the rising velocity of a bubble in still water.
The results show that it is possible to reduce the resistance of a 3-dimensional body by use of microbubbles if the body is well covered by microbubbles. Although the resistance increases where microbubbles are injected, the local frictional resistance is reduced more than 20 % where microbubbles cover the body. The total resistance is reduced more than 5 %. Based on a wave analysis, it is found that injecting microbubbles into water does not affect on wave making resistance.