Abstract
The addition of protuberances, inspired by the humpback whale flipper, on the leading edge of lift producing foils has been shown to improve hydrodynamic performance under a certain range of flow conditions. Specifically, finite wing models have displayed delayed stall characteristics at higher angles of attack and increased maximum lift coefficients without significant hydrodynamic penalties. The objective of this project was to investigate the impact that leading edge protuberances (i.e. tubercles) have on the effectiveness of marine tidal turbine blades, especially at lower tidal flow speeds. The experimental results obtained utilizing three different blade designs (baseline and two tubercle modified) are compared. All blades were designed with a 3-D computer aided design software package and manufactured utilizing rapid prototype techniques. The tests were conducted in the 120 ft tow tank at the U.S. Naval Academy using an experimental apparatus that measured flow speed and electrical power generated. Results for power coefficients are presented for a range of tip speed ratios. Cut-in velocity was also used to evaluated the blade designs. For all test criteria, the tubercle modified blades outperformed the smooth leading edge baseline design blades at the lower test velocities, and did not show degraded performance at the higher velocities tested.