Jet-Surface Interaction Test: Far-Field Noise Results

Abstract

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet/Surface Interaction Test was intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. During phase one, the goal was to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet/surface interaction is creating additional noise, and (2) determine regions of interest for more detailed tests in phase two. To meet these phase one objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer (microphone array) and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface was moved through axial positions 2 ≤ xTE/Dj ≤ 20 (measured at the surface trailing edge, xTE, and normalized by the jet diameter, Dj) and radial positions 1 ≤ h/Dj ≤ 20. Far-field and phased array noise data were acquired at each combination of axial and radial surface location using two nozzles and at 8 different jet exit conditions across several flow regimes (subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic cold). The far-field noise results, discussed here, show where the surface shields some of the jet noise and, depending on the location of the surface and the observer, where scrubbing and trailing edge noise sources are created as a surface extends downstream and approaches the jet plume.

Non-homogeneous rapid distortion theory on transversely sheared mean flows

“…problems involving the interaction of turbulence with solid surfaces and other non-uniformities) by using them to calculate the sound radiation produced by the interaction of a two-dimensional jet with the trailing edge of a flat plate -a problem that is currently of considerable interest because of its relevance to understanding noise production in future aircraft configurations. Comparisons with recent experiments conducted at the NASA Glenn Research Center (Brown 2012;Zaman, Brown & Bridges 2013) are also presented in that section.…”

Noise measurements of high aspect ratio distributed exhaust systems

“…Note that the noise increase is greatest in the minor axis planes and is the same on both the long and short sides of the bevel. In [11] it is shown that the additional noise has a strong dipole behavior, which becomes more evident as the nozzle lip is extended. Thus the extra noise is a separate source from the jet mixing noise and scales differently with velocity, as demonstrated in Figure 7.…”

Noise Reduction with Fluidic Inserts in Supersonic Jets Exhausting Over a Simulated Aircraft Carrier Deck

“…Podboy [18] performed phased array measurements of a jet near a surface to localize the sound source and determine the jet surface interaction effects. Brown [19] also performed measurements with a near field phased array and additional far-field microphones. Measurements opposite to and below the surface with a focus on the shielding effects of simulated aircraft structures were obtained.…”