Performance of a Hydrofoil Travelling Near a Water Surface

Abstract

Performance tests of a fully submerged hydrofoil travelling near a water surface are carried out. The lift and drag forces are measured by a load cell in the towing tank of Kobe University of Mercantile Marine(KUMM). The flow characteristics around the hydrofoil are observed in both of the towing tank and the circulating water channel of KUMM. The examined hydrofoil is made by author's own hands with FRP materials. The type of wing section is NACA2410. Test variables are attack angle, immersion depth and advance speed. The immersion depth and advance speeds are varied extensively in order to examine the relation between the performance of hydrofoil and the flow characteristics in detail. The obtained results are summarized as follows. (1)In a low Froude number region, the performance of hydrofoil changes drastically. (2)In case of little immersion depth, the lift performance remarkably declines in the region of Froude number defined with immersion depth Fr-I=1.0-1.3. In the nighborhood of Fr-I=1.1, the lift takes a minimum value. (3)In this neighborhood, a wave-breaking phenomenon is observed just over the hydrofoil. The location of a wave breaking moves backward with advance speed. (3)Wadlin's estimation method is applicable in case of large immersion depth or large Fr-I. However, in the region where the water surface effects are remarkable on the hydrofoil performance, the estimation method is not applicable.