Passive Flow Separation Control via Leading-Edge Tubercles: A Biomimetic Approach

Biomimetics, which is the imitation of nature to build innovative solutions, represents a fundamental multidisciplinary field. One exceptional biological adaptation are the protuberances on the Humphack whale pectoral flippers, called tubercles, which are considered to provide them incredible agility. Several studies were carried out on their effects on the leading edge of wings, generally showing a smoother stall occurrence and an improved post-stall lift. Nevertheless, no systematic review and meta-analysis exists to synthesize the results. In addition, inconsistencies emerged regarding tubercles impact on pre-stall performance, the effect of the geometrical parameters amplitude (A) and wavelength (λ), the sensitivity to Reynolds number (Re). Therefore, the objectives of this work are 1. to provide a state-of-art overview on the effects of tubercles and their most promising applications, 2. summarize the existing results on aerodynamic performance, and 3. highlight the discrepancies. It’s found that tubercles effectively improve post-stall lift, thanks to the creation of streamwise vortices that modify the pressure profile along span and cause local separation. This generally causes pre-stall lift degradation and drag increasing, but it prevents abrupt stall occurrence and allows improved post-stall efficiency. In some studies, a delayed stall angle and improved maximum lift coefficient are found. Tubercles efficiently work when applied on wind turbine blades, improving power production and torque, and are useful in noise reduction, but the A/λ ratio seems to have an opposite role in these two fields.