Turbulent drag reduction realized by hydrogen microbubbles was investigated experimentally. A method of generating microbubbles of 10–60μm diameter by water electrolysis was established. Experiments were performed using a water circulating tunnel. Microbubbles generated by electrolysis can achieve the same drag reduction as the injected air bubbles at a much lower void fraction. The present experimental results suggest that microbubbles produced by electrolysis are 10∼100 times more effective in terms of drag reduction than large bubbles generated by air injection. Thus, it is considered that the diameters of microbubbles play an important role in drag reduction.

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