Influence of Leading-Edge Tubercle with Amplitude Modulation on NACA 0015 Airfoil

Flow around a NACA0015 airfoil with leading-edge tubercles was investigated using force measurements and flow visualization at 0 deg <= alpha <= 30 deg. The experiments were carried out at a low Reynolds number of Re = 6.3 x 10(4), where the transition to turbulent flow still occurred on the suction side of the airfoil. The leading-edge patterns of the models were produced by using only either one wave function or one superposition of two wave functions. Two tubercle models with uniform distribution and nine more realistic biomimicked airfoil models with amplitude modulation in tubercle geometry were tested in experiments. Force measurements showed that when compared to the baseline model, models with tubercles did not experience a sudden loss of lift and have higher lift coefficients in the poststall regime, irrespective of the model. It was found that the W15 model performs best in terms of maximum lift coefficient, stall angle, aerodynamic performance (C-L/C-D) in the poststall regime; as well as in terms of the minimum fluctuating lift coefficient C-L' in both pre- and poststall regimes. Enhancement of aerodynamic performance is due to the presence of stall cell formation with the counter-rotating vortex pairs and three-dimensional spanwise flow pattern initiated by leading-edge tubercles at the poststall regime.