Improved performance on highly swept wings by suction boundary-layer control

Abstract

A wind-tunnel experiment was conducted to investigate the use of suction boundary-layer control (BLC-suction) on the leading edge of a highly swept cranked-delta wing as a means to improve performance at a nominal take-off lift coefficient. Highly swept wings are paramount for efficient supersonic cruise but in the absence of any leading or trailing edge treatment have poor low-speed performance. The poor performance is caused by flow separation at the leading-edge that occurs at the take-off angle of attack. With the flow separated at the leading edge, a loss in leading-edge thrust occurs. A number of leading-edge devices have been investigated to retain the leading-edge thrust term, e.g., attached-flow flaps and vortex flaps are two of these devices. The BLC-suction method prevents leading-edge separation by forcing the boundary layer to remain thin and the velocity profiles full. The wind-tunnel test was conducted in the NASA Langley 30X 60-Foot Tunnel at a dynamic pressure of 10 lb/ft, Mach number of 0.1 and Reynolds number of 2.1 million. Integrated static force and moment data along with wing-surface pressures and suction plenum pressures were measured. In addition to L/D, the leading edge suction parameter, S, was used as a performance metric. The on-surface and off-surface flow fields were mapped with florescent mini-tufts and laser light sheet, respectively. Results from the wind-tunnel test showed that the BLC-suction method improved L/D by 21% and S by 32% over the suction-off configuration. Symbols AR aspect ratio, b/ Sref b wing span BL butt line Cq suction coefficient, poVo/pooVoo Cref reference wing chord (mean geometric chord) Cp pressure coefficient, P0 P_/q * Graduate Student, Student Member AIAA t Professor, Mechanical and Aerospace Engineering Dept., Associate Fellow AIAA Copyright © by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. FS fuselage station IB inboard LE leading edge L/D lift to drag ratio LS lower surface M Mach number OB outboard P0 local pressure P. freestream pressure q freestream dynamic pressure, l/2p«,V.. Re Reynolds number, p-V-Cref/ji. S leading-edge suction parameter 8, wing reference area SCFM standard cubic feet per minute US upper surface TE trailing edge o local velocity V., freestream velocity a angle of attack P angle of sideslip 8 flap deflection angle measured normal to the hinge-line A, taper ratio |J~ freestream viscosity