Experimental study on microbubbles and their applicability to ships for skin friction reduction

Microbubble experiments were carried out using a circulating water tunnel specially designed for microbubble experiments. The tunnel has a long test section, which enables measurements on the persistence of the skin friction reduction effect by microbubbles in the streamwise direction. It also has a damp tank, which enables continuous testing of microbubbles. Skin friction was measured using a skin friction sensor, which is a force gauge type of 250 N/m(2) full scale, and skin friction reduction by microbubbles up to 40% was obtained. The local void ratio in the bubble condition was measured by putting a suction tube in the test section, and it was obtained that the local void ratio close to the wall has strong correlation with skin friction reduction. The scale effect and the applicability of microbubbles to full scale ships was discussed, based on experimental results using a long flat plate. (C) 2000 Begell House Inc. Published by Elsevier Science Inc. All rights reserved.