Particle image velocimetry in the near-wake of a wing with leading edge tubercles

The results of particle image velocimetry in the near-wake of a rectangular wing section with the leading edge tubercles of various lengths and an airfoil, developed by the National Advisory Committee for Aeronautics (NACA 0012), are presented. The main attention is paid to the study of the influence of the tubercle length on the features of the formation of the flow in the near-wake of the wing model. Based on the reference case of a wing model with a chord of 100 mm and a span–chord ratio of 2, the influence of four tubercle lengths (5, 15, 25, and 35 mm) of tubercles, located symmetrically relative to the chord of the wing airfoil, was studied within the interval of chord-based Reynolds number Reb = 3.65 × 104–2.36 × 105 and for two angles of attack α = 0° (no separation case) and α = 9.5° (massive laminar stall). In order to understand the effect of the regular structure of counter-rotating vortex pairs, formed by the tubercles and its further interaction with the boundary layer of the wing, measurements were performed in two sections of the near-wake perpendicular to the wingspan: in the plane of symmetry of the tubercle and in the middle plane between the pair of neighbor tubercles. It has been experimentally confirmed that even at α = 0°, the tubercles are the source of additional drag, estimated at 3%–18%. It was also found that even the shortest tubercles of 5 mm are, apparently, the most rational in terms of their both aerodynamic and weight efficiency.