High-Performance Airfoil Using Coflow Jet Flow Control

Abstract

T O ACHIEVE revolutionary aircraft performance, advanced technologies should be pursued to drastically reduce the weight of aircraft and fuel consumption and significantly increase aircraft mission payload and maneuverability. Both the military and commercial aircraft will benefit from the same technology. Flow control is a promising technology to break through the limits of the conventional aerodynamic concepts. Recently, a novel active airfoil flow control concept with zero-net mass flux, the coflow jet (CFJ) airfoil, has been developed by Zha et al. [1–5]. The CFJ airfoil achieves three effects simultaneously in a dramatic fashion: lift augmentation, stall margin increase, and drag reduction. The energy expenditure of the CFJ airfoil is low [1], and the CFJ airfoil concept is straightforward to implement. The CFJ airfoil may create a new concept of an “engineless” airplane, which uses the CFJ to generate both lift and thrust without conventional propulsion systems of propellers or jet engines [6]. A CFJ airfoil [1–5] uses an injection slot near the leading edge (LE) and a suction slot near the trailing edge (TE) on the airfoil suction surface. Similar to tangential blowing, the LE jet is in the same direction of the main flow, but the same amount of mass flow that is injected is removed via suction near the TE, resulting in zeronet mass-flux flow control. A proposed fundamental mechanism [2] is that the severe adverse pressure gradient on the suction surface strongly augments turbulent mixing between the main flow and the jet [7]. The mixing then creates the lateral transport of energy from the jet to the main flow and enables the main flow to overcome the large adverse pressure gradient and remain attached at high angle of attack (AOA). The stall margin is hence significantly increased. At the same time, the high-momentum jet drastically increases the circulation, which significantly augments lift, reduces drag, or even generates thrust (negative drag). The objective of this paper is to demonstrate the high performance of the CFJ airfoil with the windtunnel test results.