NUMERICAL INVESTIGATION OF THE EFFECT OF THE SPANWISE GROOVE ON THE AERODYNAMIC CHARACTERISTIC OF A NACA 0012 AIRFOIL USING ?-RE?t TRANSITION TURBULENCE MODEL

Time-accurate numerical simulations are conducted to investigate the effect of a semi-circular groove on the unsteady aerodynamic characteristics of a NACA 0012 airfoil at a Reynolds number of 50,000. A semi-circular groove of depth 0.025c or 0.05c, measured normal to the surface of the airfoil, is placed at various discrete locations on the suction surface of the airfoil. The two-dimensional unsteady Reynolds averaged Navier-Stokes equations are solved using a pressure-based finite volume solver wherein the effect of turbulence is captured with a four-equation transition gamma-Re theta t turbulence model. The numerical results suggests that a semi-circular groove at 0.1c can improve the aerodynamic efficiency [lift-to-drag (L/D) ratio], by up to 110% in the pre-stall regime, with a corresponding reduction of 42% in profile drag. The grooves at other locations also enhance the aerodynamic efficiency in the pre-stall regime, primarily due to their drag reduction ability. The drag reduction ability of these grooves is a result of an earlier transition of the boundary layer thereby favoring an attached flow with reduced pressure drag. An earlier transition of the boundary layer diminishes the vortex shedding and flow unsteadiness. The current finding indicates that aerodynamic perfor-mance of micro aerial vehicles and unmanned aerial vehicles can be significantly improved through suitable design of grooves.