著者

田中 泰爾 大石 義彦 朴 炫珍 田坂 裕司 村井 祐一 川北 千春

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.88, no.907, pp.21-00297, 2022 (Released:2022-03-25)

参考文献数

24

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Drag reduction by bubble injection in turbulent boundary layers was investigated using a 36-m-long flat-bottom model ship. The model ship was towed at 8.0 m/s, resulting in a downstream-distance-based Reynolds number as high as 2.9 × 108. The total resistance exerting on the model ship was reduced, and the resistance reduction increased with the air flow rate for the bubble injection. The local wall shear stress on the bottom plate was measured at multiple locations to clarify the streamwise transition of the drag reduction. The local drag reduction observed at the upstream measurement locations was increased with the air flow rate. The higher gas flow rate, moreover, produced the longer streamwise persistence of the drag-reduction effect. These multiple factors improved the efficiency of the total resistance reduction against the power consumption for the bubble injection. We provide the estimation of total frictional drag reduction for the full-scale ships using the equation of the local friction coefficient obtained experimentally. The results of the model ship experiment and the full-scale estimation consistently indicated that the downstream persistence of the local drag-reduction effect strongly affect the total drag reduction of such the long hulls.

著者

児玉 良明 角川 明 高橋 孝仁 石川 暁 川北 千春 金川 健 戸田 保幸 加藤 洋治 地本 晶彦 山下 和春 永松 哲朗

出版者

The Japan Society of Naval Architects and Ocean Engineers

雑誌

日本造船学会論文集 (ISSN:05148499)

巻号頁・発行日

vol.2002, no.192, pp.1-13, 2002 (Released:2007-05-30)

参考文献数

17

被引用文献数

5 2

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This paper is the first half of the report on the study on microbubbles carried out by the SR239 project of the Shipbuilding Research Association of Japan, and describes the preparatory study for the full-scale experiment using a 116m-long ship. In the present study, first the skin friction reduction effect by microbubbles was investigated including the use of an array-of-holes plate for bubble generation, the effects of streamwise pressure gradient, surface curvature, and vertical plate, the sea-water effect, and the effect of bubble size. Bubble generators for the full-scale experiment were designed and built, and a preliminary injection experiment was carried out. Two new measuring devices for the full-scale experiment were developed; they are skin friction sensors and local void ratio sensors. Microbubble experiments were carried out in a 400m-long towing tank using a 50m-long flat plate ship, in order to obtain the scale effect data and to confirm the validity of the new devices for the full-scale experiment. The use of adhesives to fix measurement devices and cables on the hull surface was tested and established. The hydrodynamic fairing of the cables was also tested and established. Finally, a preliminary microbubble experiment using a small ship was carried out and the bubble behavior was observed.