Effects of Leading-edge Tubercles on the Aerodynamic Performance of Rectangular Blades for low-speed Wind Turbine Applications

Abstract

The rapid depletion of conventional energy resources like fossil fuels has harmed the environment. Hence, there is an urgent need to seek alternative and sustainable energy sources. Wind energy is considered one of the efficient sources of energy that can be converted to a useful form of electrical energy. Though the field of wind engineering has developed in recent years there is still scope for improvement in the effective utilization of energy. The turbine blades' aerodynamics and the turbulent fluid flow characteristics largely determine the wind turbine's energy efficiency. Hence, in the present studies, we investigated the improvement of small wind turbine blade design by incorporating bioinspired tubercles into blades. One of the issues of small wind turbines is the low-capacity factor in power. The wind in such circumstances under buildings and other adjacent obstructions for small turbines is normally weak, unstable, and turbulent in wind speed and direction. Thus, the design of small turbines needs to be improved to capture low wind speeds and to respond quickly to turbulent wind resource areas. Biomimetics is a science that helps us adapt designs from nature to solve modern problems. The wing-like flipper of the humpback whale (Megaptera novaeangliae) has a morphology with potential for aerodynamic applications. The humpback whale flipper has several sinusoidal rounded bumps, called tubercles which modify the flow over the blade surface, creating vortices between the tubercles. Therefore, we conducted an XFOIL analysis of symmetrical NACA airfoils and we observed that NACA0012 could produce the best lift/drag ratio. The airfoil was then validated using Computational Fluid Dynamics (CFD) analysis in which the results were found comparable to that of the published data. Finally, CFD analysis was conducted for tubercles with a different pitch-to-amplitude ratio (p/A) and the tubercled airfoil with p/A of 6 provided the best result.