Recent advances in flow separation control of airfoils through surface grooves

Flow separation control is one of the burning questions in the field of aerodynamics. The performance of an airplane or any other aerial vehicle is greatly influenced by this phenomenon. The cross section of an airplane’s wing is termed an airfoil. When air flows past an airfoil, the aerodynamic characteristics of that airfoil are largely influenced by its boundary layer separation or flow separation. Continuous effort is being made by many researchers worldwide to improve the aerodynamic characteristics of airfoils by controlling flow separation phenomena. Among numerous active and passive flow control strategies, the application of surface grooves on the airfoil surface is gaining more attention nowadays due to its design simplicity. A very slight modification is required when surface grooves are employed on the airfoil surfaces to modify the airfoils. Surface grooves act as flow deflectors, creating turbulence to disturb the streamlined flow and result in an early conversion from laminar to turbulent flow, thereby delaying flow separation and improving the aerodynamic performance of airfoils. Surface grooves having various geometries and dimensions can be employed at variable locations along the chord length and wing span, depending on the performance requirement. Together with the groove’s specific geometry and placement, some other factors such as groove spacing and number, recess depth ratio (groove’s depth to the local boundary layer thickness), and groove aspect ratio (ratio of the groove’s depth to its width) greatly influence the performance of a grooved airfoil. To access the performance of a grooved airfoil in comparison with the baseline airfoil, several numerical investigations and a number of wind tunnel experimentations have already been done adopting various groove geometries, which include bionic, semicircular, rectangular, arc, V shape, and L shape grooves. To execute the URANS and LES simulations, ANSYS Fluent, ICEM CFD, and CATIA V5R20 software were used. The findings from the simulations establish that surface grooves can effectively alter the flow dynamics around an airfoil by mitigating local separation zones and boundary layer transitions. Various surface groove geometries and placement locations significantly influence airfoil aerodynamics by enhancing lift, reducing drag, and delaying stall. Studies also show that optimized groove shapes, such as semicircular, rectangular, L-shaped, and triangular, can improve lift-to-drag ratios by up to 52%, reduce drag by nearly 17%, and increase stall angles, demonstrating their strong potential for aerodynamic performance enhancement. As surface grooves are found to be effective for both the symmetric and asymmetric airfoils, they can be employed with confidence to modify the airfoils for better maneuverability.