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 -6° and 24° to 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. AtRe= 1.25 × 10⁵, the bioinspired wing achieved a maximum lift coefficient of 0.694 at an angle of attack of 9°, while the minimum drag coefficient was approximately 7.48 × 10^-3. The aerodynamic efficiency reached a maximumL/Dratio of 42.9 at an angle of attack of 2°. Similar aerodynamic trends were observed atRe= 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.