Aerodynamic Performance and Flow Structure Analysis of a Swallow-Inspired NACA2415 Airfoil

This study investigates the aerodynamic characteristics of a swallow-inspired wing based on a NACA 2415 airfoil at Reynolds numbers of 7.5×10⁴and 1.25×10⁵using experimental force measurements and flow-visualization techniques. The bioinspired wing model was designed according to the top-view geometry of a swallow wing and tested in a low-speed open-suction wind tunnel together with a rectangular wing of identical planform area and airfoil profile to provide a baseline comparison. Aerodynamic measurements were conducted over an angle-of-attack range between -6oand 24oto determine lift, drag and moment coefficients as well as aerodynamic efficiency. In addition to force measurements, smoke-wire and TiO₂based flow visualization techniques were used to examine the flow topology around the test models. The results show that the swallow-inspired wing exhibits improved aerodynamic performance compared with the rectangular configuration under both Reynolds number conditions. At Re=1.25×10⁵, the bioinspired wing achieved a maximum lift coefficient of 0.694 at an angle of attack of 9o, while the minimum drag coefficient was approximately 7.48×10⁻³. The aerodynamic efficiency reached a maximum L/D ratio of 42.9 at an angle of attack of 2o. Similar aerodynamic trends were observed at Re=7.5×10⁴, although slightly reduced lift and aerodynamic efficiency were recorded due to stronger viscous effects at lower Reynolds numbers. The pitching moment coefficient varied approximately linearly with angle of attack, with a slope of -7.8×10⁻³per degree and a zero-lift moment value of -7.47×10⁻³, indicating stable longitudinal aerodynamic behavior. Flow visualization results revealed a gradual transition from attached laminar flow to separated turbulent flow, suggesting smoother stall development and improved flow stability for the bioinspired configuration. These findings highlight the aerodynamic advantages of swallow-inspired wing geometries and their potential to enhance aerodynamic efficiency in low Reynolds number flight.