Lift Augmentation Potential of the Circulation Control Wing Driven by Sweeping Jets

Abstract

Circulation control (CC) is an airfoil lift augmentation technique that replaces mechanical structures by means of aerodynamic flaps generated by high-speed jets. In view of the high air consumption for the conventional steady jet to drive the circulation control wing (CCW), the emerging sweeping jet is proposed herein as an alternative excitation method and compared with continuous and discrete steady jets. Four dimensionless parameters characterizing the jet blowing intensity are used to comprehensively evaluate the lift augmentation capacity of the three types of jet. In terms of the velocity ratio and the momentum coefficient, the continuous steady jet is the most efficient to enhance the lift. On the other hand, with respect to the mass flow coefficient, the sweeping jet can reduce the air consumption by 48% compared to the continuous steady jet. Therefore, in the light of this contradiction, a more comprehensive indicator, namely, the energy coefficient, is used to quantify the energy expenditure. The accordingly plotted curves of the lift coefficient versus the energy coefficient for continuous steady jets and sweeping jets almost overlap each other, which indicates that the sweeping jets reduce the air consumption by virtue of higher jet velocities at the expense of higher pressure loss. Besides, compared to the discrete steady jets with the same jet spacing, the sweeping jets boast a notably higher lift generation performance, verifying that the unsteady lateral oscillation of the sweeping jet is also critical to the lift augmentation. Then, a new index, namely, the energy coefficient-based lift augmentation ratio, is proposed as the indicator to quantitatively compare the lift augmentation efficiencies of the CCWs driven by different jet actuators. The sweeping jet is proved to have a lift augmentation efficiency that is not at all inferior to that of the traditional steady slot jet.