Abstract
We have invented a novel bubble generator with a vented hydrofoil for ship drag reduction. The hydrofoil has an air outlet on the top surface, and small air bubbles are generated by the negative pressure above the hydrofoil as the device moves forward. In order to understand the relationship between the local shear stress and the local projection void fraction under the ship hull, towing tank (100m) experiments using a 4m-long model ship made by transparent acrylic resin were conducted at Hiroshima University. The void imaging data obtained by a high-speed video camera revealed that the characteristics of the entrained bubbles (bubble size, bubble volume flux, etc.) depend on the towing velocity, angle of attack, and the arrangement of the vented hydrofoil. A large amount of air was introduced by this device when the hydrofoil was mounted at the non-inverted position with the angle of attack from 10 to 15 deg. On the other hand, the local drag reduction rate of the inverted hydrofoil setting was higher than that of the non-inverted one.
