Spanwise stall-cell organisation of an aerofoil with leading-edge tubercles

The stall of a NACA0021 aerofoil with leading-edge tubercles is investigated experimentally in this work. Time resolved three-dimensional flow field on the suction side of the aerofoil is captured using shake-the-box (STB) particle tracking velocimetry (PTV). Pairs of counter-rotating streamwise vortices generated at each tubercle enhances the mixing of the low-speed fluid at the wall and high-speed fluid in the free stream. At 15° angle-of-attack (AoA), stable stall-cell structures are observed to originate from the trough between tubercles, spanning approximately 4 tubercle wavelengths (equivalently 1 mean chord length). For AoAs larger than 20°, the stall cells are not fixed at certain troughs, but wander along the spanwise direction.