Biomimetic improvement of hydrodynamic performance of horizontal axis tidal turbines

Abstract

This study explored the potential of further improving the hydrodynamic performance of tidal turbines by applying leading-edge tubercles to the blades inspired by the humpback whales. Within this framework, a wide variety of experimental investigations, supported by numerical studies, has been conducted. The study first focused on the design of the leading edge tubercles for a tidal turbine blade. Numerical simulation has been conducted for various designs and the best candidate was then applied onto a representative tidal turbine blade, a 3D hydrofoil can be fitted with various leading-edge designs. Experimental test was conducted in a cavitation tunnel and demonstrated significant benefits in terms of improving the lift coefficient and lift-to-drag ratio especially after stall. The results were then validated and complemented by numerical simulations for further detailed analysis. This simulation explicitly showed that the contra-rotating vortices generated by the tubercles formed a vortex fence prevented the tip vortex from inducing the spanwise flow, which meanwhile energized the flow and maintained more attached. Following that, a set of tidal turbine models with different leading-edge profiles was manufactured and were tested to evaluate the efficiency, cavitation, underwater noise and detailed flow characteristics in the cavitation tunnel. These experimental investigations confirmed that the leading-edge tubercles could: improve the hydrodynamic performance in the low Tip Speed Ratio (TSR) region without lowering the maximum power coefficient; maintain the power coefficient in the low Reynolds number; constrain the cavitation development to within the troughs of the tubercles; hence mitigate the underwater noise levels.