Numerical Investigation of Pneumatic Flap Based on Circulation Control Technology

Circulation control technique induces deflection of the airflow near the wing and changes the aerodynamic forces and moments to achieve the purpose of attitude control of the aircraft normally. It could generate virtual rudder surfaces through the Coanda effect caused by high-speed jets at the trailing edge of the wing. Since the monoplane geometry could not be optimal for all conditions encountered, circulation control technique, used at the trailing edge of the wing, replaces the existing high-lift flaps and control surfaces to modify the shape of the wing during takeoff and landing as well as cruise of the aircraft, so that the wing could be continuously deformed to its optimal pressure distribution state according to specific conditions. For this purpose, in this paper, numerical simulation of CC-E0020EJ, which is large thickness symmetric airfoil, and supercritical circulation control airfoil (GACC) has been carried out using CFD++. The flow field analysis of the two circulation control airfoils is performed by changing the jet momentum coefficient to determine the control ranges of the maximum lift coefficient and the maximum lift-to-drag ratio. In this paper, the aerodynamic shape optimization is accomplished by using the circulation control, and the virtual flaps formed by the high-speed jet provide a method to determine the optimal wing shape equivalent curvature in order to achieve the ideal control effect of pitching moment under different flight conditions. The high-speed jet separated from the trailing edge of the wing to form an aerodynamic flap can change the equivalent curvature of the wing, which makes the forward stationary point move backward and the trailing edge separation point move downward on the curved surface, forming a control effect similar to that of a variable curvature airfoil.