Abstract
The aerodynamic design requirements of the nozzle boattail for OTW configurations are different for cruise and powered lift. For cruise, a small nozzle boattail angle (<10°) is required to minimize drag; while for powered lift, a large angle (25°–30°) is needed to provide jet flow attachment to the lifting surfaces. A solution to these design requirements is to use an external flow-deflector downstream of the nozzle for powered lift and to store (retract) this deflector for cruise. For powered lift, however, the jet/deflector/wing noise transmitted to ground observers can be a problem. In the present paper, representative acoustic spectral data obtained from a model scale study of several OTW configurations with a 5:1 slot nozzle using various external deflectors are correlated in terms of deflector geometry and flow parameters. Variations in the deflector geometry include deflector size and deflector angle. In addition, geometry variations in flap setting and nozzle chordwise location are included. Three dominant noise sources are correlated: fluctuating lift noise, flap-trailing edge and deflector related noise, and jet mixing noise. Lift and thrust measurements obtained in the study for the various configurations are summarized.
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