Experimental investigations on the effects of divergent trailing edge and Gurney flaps on a supercritical airfoil

Wind tunnel experiments were conducted to investigate the effects of divergent trailing edges and Gurney flaps on a supercritical airfoil at a Mach number M = 0.7 and a Reynolds number Re = 3.15 × 10⁵ based on the airfoil chord length. The effects of Gurney flaps on a divergent trailing edge airfoil were also studied. Four Gurney flaps with heights h = 0.5 %, 1.0%, 1.5% and 2.0% chord length, respectively, were employed in this investigation. The results revealed that, in comparison with the divergent trailing edge, the Gurney flaps had significant effects on improving the aerodynamic characteristics of the tested supercritical airfoil, and even on the airfoil with divergent trailing edge. When the Gurney flaps were utilized, the lift coefficient, maximum lift coefficient and the maximum lift-to-drag ratio of both supercritical and divergent trailing edge airfoils were greatly increased. The lift-enhancing effects of Gurney flaps under high-speed circumstances mainly came from its ability of shifting backward the shock on the upper surface. Moreover, the installation of Gurney flaps will increase wave drag and base-pressure drag, but at the same time, the pressure on the lower surface of the airfoil was increased which led to an increased rear-body loading, and the position of the shock on the upper surface was greatly shifted backward, the supersonic region is thus enlarged, which led to an increased suction. Both the increments of pressure on the lower surface and suction on the upper surface resulted in a total lift increase. As the lift did not increase with the drag linearly, the lift-to-drag ratio increase and aerodynamic characteristics improvement were obtained under some circumstances.