Numerical Assessment of a High‐Lift Configuration with Circulation Control and flexible Droop Nose

Abstract

The use of active flow control in high-lift systems is a promising solution to improve aircraft low-speed capabilities and reduce noise emissions during landing. To date, however, the system power requirements have been too high in relation to the achieved lift gains, to allow a large use of these technologies in the aeronautical industry. The present work addresses this problem by developing and testing a leading-edge device to increase the efficiency of an internally-blown Coanda-flap configuration. The main objectives are the increase of the stall angle of attack and the reduction of the jet momentum requirements. A 2D sensitivity analysis is performed to explore the effects of varying the airfoil camber and thickness in the first 20% of the airfoil chord. The resulting droop-nose configuration yields a reduction of 32% of the jet momentum required to achieve a target maximum lift coefficient of 5.0, while improving the stall angle by 10°. As the modified leading edge geometry presents different stall mechanisms, the aerodynamic response to variations of jet momentum is also different. In particular, for a jet momentum coefficient above 0.035 the stall angle of attack increases with jet momentum, in contrast to the behavior observed with the baseline leading-edge configuration. Subsequent to the 2D study, the results are tested on a wing-body configuration with a circulation controlled plain flap, which is deflected by 65°. Therefore, calculations at an identical blowing coefficient are performed on the clean-nose and droop-nose configurations. The comparison of the 3D results verifies the stall delay observed in 2D. The outboard leading edge stall seen on the clean-nose configuration is successfully suppressed. In contrast, the maximum lift of the droop-nose configuration is limited due to fuselage-wing integration effects. As a result, the increase of the maximum lift coefficient is limited to 3%, whereas the maximum angle of attack is raised by 10°.