Aerodynamic characteristics and surface flow structures of moderate aspect-ratio leading-edge tubercled wings

Abstract

Abstract Aerodynamic performance for NACA634-021 wings with different leading-edge (LE) tubercle configurations was tested under both finite- and infinite- wing conditions, and the general results show that larger tubercle amplitude A leads to gentler stall and smaller tubercle wavelength λ improve maximum lift. The ratios of tubercle amplitude and wavelength to wing chord, A/c and λ /c, as well as the A/ λ ratio should be considered together to determine the optimum design. Wings with smaller A and λ shows relatively better performance with lift-to-drag ratio significantly enhanced at lower pitch angles, which are also associated with their cruise condition. Surface flow structures for the tubercled wings under finite-wing condition were specially revealed by the fluorescent oil visualization technique. High quality nice fluorescent images reveal that wavy laminar separation bubbles (LSBs) are formed on pressure surface for the tubercled wings at lower pitch angles, with the waviness of LSBs strongly depending on those of wavy LE. Wavy LSB for the two wings with the largest tubercle A are even transited into small surface counter-rotating vortex-pairs (CRVPs). On the suction surface, separated flows behind the troughs also lead to surface CRVPs due to the spanwise pressure gradient. In addition, LSBs formed behind the tubercle peaks for the wings with smaller λ also resemble the surface CRVPs, possibly driven by the flow shearing arising from the narrower regions of upstream surface CRVPs. In the post-stall regime, except for the wing with larger tubercle λ andsmallest A, other tubercled wings are observed to induce drastically attached flows on suction surface, especially downstream of tubercle peaks.