Noise from a circulation control wing with upper surface blowing

Abstract

The work presented in this paper represents a first step in understanding and evaluating the noise characteristics of a circulation control wing (CCW) with upper surface blowing (USB). It was found that high frequency noise was dominated by the effects of the circulation control jet and that low frequency noise was dominated by the effects of the upper surface blowing. The individual effects of the CCW and USB can be superimposed to yield a good approximation of the resultant effect in a combined CCW/USB configuration. basic aerodynamics of the circulation control wing concept involve the adherence of a thin, tangentially ejected jet sheet to the rounded trailing edge of an otherwise conventional airfoil. This phenomenon, called the Coanda effect, is produced by a balance within the jet sheet between centrifugal force and the low static pressure lifting force, generated by the jet velocity Vs (Fig. la). This device initially provides a blow- ing-type boundary-layer control, but achieves its high-lift capability by controlling the airfoil stagnation points to in- crease the circulation around the wing. Due to the absence of a long mechanical flap, this circulation control is achieved at considerably lower momentum coefficients than those needed in the somewhat similar tangentially blown flap systems.3'5 The primary mechanism of the CCW lift augmentation is the increased streamline deflection, which accompanies movement of the stagnation points; the overall result is to produce an effective camber which is considerably greater than the geometric value. Further, by combining the circulation control (CC) and with upper surface blowing (USB) in a CCW/USB con- figuration, as shown in Fig. Ib, some very significant benefits are obtained from the ability of circulation control phenomenon to entrain and control the engine thrust direc- tion.6'7 The rather complex and heavy USB mechanical flap system and its supporting structure and actuators can be eliminated and replaced by the stationary circulation control (CC) round trailing edge and internal blowing plenum. For the CCW/USB system, the thrust deflection angle depends on the CC plenum pressure, slot mass flow, and the geometry of the CC trailing edge. The CCW thrust deflec- tion angle is changed nearly instantly by a control valve or pressure regulator which modulates the slot mass flow. The thrust can be deflected pneumatically up to 160 deg, thereby providing high lift, the possibility of vertical flight, and thrust reversal, all without complex mechanisms. The near- instantaneous thrust deflection variation provides quick- responding direct lift and flight path control.8