Geometry effects on STOL engine-over-the-wing acoustics with 5:1 slot nozzle

Abstract

The effect of nozzle roof (kickdown) angle and nozzle location relative to the wing trailing edge on noise was determined at model scale with a 5:1 slow nozzle (equivalent diameter, 5.1 cm) for several OTW configurations. Nozzle roof angles of 10° to 40°, with and without cutback at the nozzle sides were tested. Also included, for comparison, was a 5:1 slot nozzle with external deflector. Three wing chord sizes were used: standard (33 cm), 23-standard, and 32-standard. Flap deflection angles used were 20° and 60°. The nozzle was located at 20% and 35% of chord. In addition, velocity maps were obtained at the trailing edge of the wings. With increasing wing size, representing a variety of airframe/engine installations, low-frequency noise was increasingly attenuated and shielding benefits increased directly with wing size. With increasing nozzle roof angle, the jet velocity at the trailing edge was decreased, causing a decrease in trailing-edge noise; however, the jet impingement noise on the wing increased. Cutback of the nozzle sides improved flow attachment and reduced the trailing-edge velocity and noise. The best flow attachment and least trailing-edge noise was obtained with the external deflector configuration.