Aerodynamic and surface pressure characteristics of quasi two-dimensional wings featuring leading-edge flags: An experimental and statistical approach

The present study explores a passive flow control technique utilizing leading-edge flags (with and without serrations) over the airfoil to improve the performance of the airfoil. These flags are attached to the leading-edge of the airfoil that oscillates naturally in response to the oncoming airflow thereby promoting favorable pressure conditions and optimizing the flow over the airfoil. NACA 63(4)-021 airfoil was modified by incorporating flags at leading-edge with different GSM (75G, 85G, 100G) and length (0.3C, 0.2C). Experimental tests were conducted in the low-speed subsonic wind tunnel at Reynolds number 1.71 × 10 5 featuring leading-edge flags with and without serrations. Surface pressure data were acquired over all the test cases with the help of MPS4264 miniature pressure scanner of Scanivalve make at 700 Hz across 46 pressure taps distributed over pressure and suction surfaces. Aerodynamic forces and force coefficients for all the test cases were calculated by applying pressure integration technique to the surface pressure data acquired across angles of attack between 0° and 70° (in 5° increments). The study observed lift augmentation and a significant delay in stall resulting from the leading-edge flag’s motion. Maximum lift was increased by 8.61% and a stall delay of 5° was observed. At post-stall angles, the modified models enhance the lift by 57.7% when compared with the baseline configuration. Additionally, surface pressure distribution over the airfoil induced by leading-edge flags (with and without serrations) were also evaluated. Coefficient of pressure distributions (C p ) confirmed that leading-edge flags with lower GSM and longer length configuration (both with and without serrations) generated wider suction regions, rendering delayed flow separation. These findings confirm the aerodynamic viability of passive leading-edge devices for flow control.