An investigation on finite wings with leading-edge protuberances

Abstract

The ability of humpback whales to perform tight manoeuvres underwater drew the attention of researches to the protuberances on their pectoral flippers. Numerous studies were conducted on wings with leading-edge protuberance and to date, the mechanics behind them have been fair well explored and understood. These protuberances were found to suppress flow separation and soften the negative impacts of stall, opening up a whole new expanse of applications, especially in fields of low Reynolds number. Many studies have focused on symmetrical wings but little are the research on asymmetrical wings, which remains to be the aerofoil type of choice in most applications. Hence, the present study sought to explore the flow behaviour in low Reynolds number for asymmetrical wings with leading-edge protuberances in order to expand upon the understanding already established. SD7032 and FX63-137 aerofoils with large amplitude protuberances but varying amplitude-to-wavelength ratios were the subject of study. Water tunnel experiments were conducted with Particle Streak Photography and Particle Image Velocimetry techniques at Re = 1.4 × 10^4 to analyse the flow behaviour while wind tunnel experiments were conducted at three different Reynolds number to measure lift, drag, and moment coefficients. Results showed that flow suppression largely existed behind the peak of the protuberances while larger amplitude-to-wavelength ratios generally displayed poorer flow behaviour and less lift. The effects of camber were also discussed and initial findings suggested that the camber size typically affects the effectiveness of flow suppression only at small angle-of-attack. The modified wings displayed relatively constant performances at varying Reynolds number, which justifies their use in low Reynolds number applications. Additionally, preliminary studies were also conducted in the water tunnel with Particle Image Velocimetry for dynamic flows with the SD7032 Baseline wing oscillating at a reduced frequency of k = 1.15 and a(mean) = 0°. PIV vorticity results presented interaction between the flow separation bubble and the trailing-edge vortex but failed to show the presence of dynamic stall vortex.