Numerical investigation of laminar separation bubble induced stall loss in high lift coefficient S1223 airfoil with passive flow control

Natural and man-made flying vehicles are used in a wide range of applications. Today, interest in mini–Unmanned Aerial Vehicles (UAVs) is constantly growing. Wings are the most crucial component affecting the performance of UAVs. Therefore, they have been and continue to be the focus of numerous research and experiments from past to present. Thanks to scientific and technological advancements, it has become possible to examine and analyze the physical principles governing the behavior of airborne objects, paving the way for the development of highly efficient wings for various aviation applications. The topic of wings with high lift at low Re numbers has been received and continues to receive intense attention in numerous academic research and studies for years. In this study, the aerodynamic performance of the S1223 airfoil, which offers high lift at low Re numbers and is proposed for use in mini unmanned aerial vehicles, was analyzed and verified. Furthermore, the focus was on developing a modified wing with a higher lift-to-drag ratio. For this purpose, the Laminar Separation Bubbles (LSB) regions that form on the upper surface of the S1223 airfoil and cause vibrations and turbulence that negatively affect performance were identified. To increase wing efficiency and reduce the effects of LSBs, two modifications were made to the wing surface: one with a curved surface and the other with slots varying in width, length, and depth. The resulting airfoils were examined for changes in the 𝐶𝑙 coefficient, 𝐶𝑑 coefficient, 𝐶𝑙/𝐶𝑑 ratio, 𝐶𝑝 distribution, and velocity and pressure contours, with increases of 2° from 0° angle of attack to the stall angle, and for Re numbers of 200,000, 300,000, and 400,000. Aerodynamic coefficients of performance were determined for each case. Analyses revealed that the use of a flat, curved surface on the upper wing surface improved performance, while the use of a circularly slotted surface decreased performance. However, the use of a circularly slotted surface on the upper wing surface resulted in the elimination of LSB regions. Instead of using the S1223 airfoil in low Re number aircraft, the use of the airfoil with the code O-S1223_4, which has a 4° pitch angle and provides improvement in all angles of attack and Re numbers, increases the aerodynamic performance.