Application of Tubercles in Wind Turbine Blades: A Review

Due to the rapid depletion of conventional energy resources like fossil fuels and their harmful effects on the environment, there is an urgent need to seek alternative and sustainable energy sources. Wind energy is considered as one of the efficient source of energy which can be converted to useful form of energy like electrical energy. Though the field of wind engineering has developed in the recent era there is still scope for improvement in the effective utilization of energy. Energy efficiency in wind turbine is largely determined by the aerodynamics of the turbine blades and the characteristics of the turbulent fluid flow. The objective of this paper is to have a review on the improvement of Horizontal Axis Wind Turbine (HAWT) blade design by incorporating biomimetics into blades. Biomimetics is the field of science in which we adapt designs from nature to solve modern problems. The morphology of the wing-like flipper of the humpback whale (Megaptera novaeangliae) has potential for aerodynamic applications. Instead of straight leading edges like that of conventional hydrofoils, the humpback whale flipper has a number of sinusoidal rounded bumps, called tubercles arranged periodically along the leading edge. The presence of tubercles modifies the flow over the blade surface, creating vortices between the tubercles. These vortices interact with the flow over the tubercle and accelerate that flow, helping to maintain a partially attached boundary layer. This aerodynamic effect can delay stall to higher angles of attack, increase lift and reduce drag compared to the post-stall condition of conventional airfoils. The modified airfoil is characterized by a superior lift/drag ratio (L/D ratio) due to greater boundary layer attachment from vortices energizing the boundary layer.