Free-stream characteristics of bio-inspired marine rudders with different leading-edge configurations

The use of leading-edge tubercles has been reported to provide superior lifting characteristics in the post-stall regime for three-dimensional foils. In this paper, different configurations of leading-edge protuberances are investigated for a marine rudder, the most widely used manoeuvring device for marine propulsion. Two modification strategies are considered-a rudder with a uniform distribution of tubercles, and an actual bio-mimicked rudder inspired by the humpback whale configuration. Numerical investigations of lift and drag characteristics are performed using CFD computations with the RANS approach to find the suitable geometry. Experiments with the selected designs are performed in the circulating water tank to investigate rudder forces. Velocity profiles are measured using Acoustic-Doppler Velocimetry. The bio-mimicked rudder shows a lesser extent of flow separation over the suction side at angles of attack greater than 15 degrees. The influence of tubercles is more prominent in the lower Reynolds number ranges. The most significant outcome of this study is the development of a bio-inspired foil and its modified configurations which has a potential for better performance compared to uniform wavy leading-edge configurations under certain conditions. Such bio-inspired designs can be employed in flow control devices for efficiency improvement over specific operation regimes.