Nozzle Geometry and Forward Velocity Effects on Noise for CTOL Engine-Over-Wing Concept

Abstract

Acoustic shielding benefits for jet noise of engineover-the-wing for conventional aircraft (CTOL) application were studied with and without forward velocity for various small-scale nozzles. These latter included convergent, bypass and mixer, with and without forward ejector, nozzles. A 13-inch free jet was used to provide forward velocity. Farfield noise data were obtained for subsonic jet velocities from 650 to 980 ft/sec and forward velocities from zero to 260 ft/sec. The studies showed that although shielding benefits were obtained with all nozzles, the greatest benefits were obtained with mixer nozzles. The absolute magnitude of the jet noise shielding benefits with forward velocity was similar to the variation in nozzle-only noise with forward velocity.

Geometry considerations for jet noise shielding with CTOL engine-over-the-wing concept

“…The absolute value of SPL is then obtained for each noise source from equation (3) for which SPL is determined at the desired shielding length, L, from figure 19. The absolute SPLP values are plotted at the proper frequency, f , determined for each noise source by use of equation (1). The haystack or SPL versus 1/3-octave band frequency plots shown in figure 20 then are used to construct the lowfrequency noise source profiles beginning at the f -values ( fig.…”

“…With respect to the noise source, the distributed noise generation obtained with a jet near the surface increases the analysis complexity as compared with a "point" noise source normally assumed for ground applications. 1 iMember AIAA, Chief, Jet Acoustics Branch. 2 Aerospace Research Engineer.…”

Effects of Source Redistribution on Jet Noise Shielding

“…The focus here is jet noise, which is particularly challenging to shield because the noise source is extended and directional. Significant experimental research on the OTW concept for conventional and short-takeoff airplanes occurred in the 1970s [1][2][3] . Important trends were established for the changes in the spectrum of acoustic emission versus shield parameters.…”

Influence of mixer nozzle velocity decay characteristics on CTOL-OTWjet noise shielding

“…8-tube mixer nozzle, 5 an 8-lobed orifice nozzle, 8 ttAerospace Research Engineer. and a 7-lobed mixer nozzle.…”

“…The multi-element nozzles used in the present study consisted of: a 6-tube mixer nozzle, 5 an tMember AIAA; Chief, Jet Acoustics Branch.…”