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 Tests are 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. The initial goal is 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 future, more detailed, tests. To meet these 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 and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface length was varied between 2 and 20 jet diameters downstream of the nozzle exit. Similarly, the radial distance from the jet centerline to the surface face was varied between 1 and 16 jet diameters. Far-field and phased array noise data were acquired at each combination of surface length and radial location using two nozzles operating at jet exit conditions across several flow regimes: subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic. The far-field noise results, discussed here, show where the jet noise is partially shielded by the surface and where jet-surface interaction noise dominates the low frequency spectrum as a surface extends downstream and approaches the jet plume.

Experimental validation of the hybrid scattering model of installed jet noise

“…The noise enhancement at 30 • , however, is virtually negligible. This is consistent with the earlier findings 2,8,9,13,18,27,28 and the edge-scattering mechanism proposed in the earlier paper 23 (at low frequencies, the scattered sound has a dipolar, rather than a cardioid directivity pattern). In the intermediate-and high-frequency range, jet noise is effectively shielded by the flat plate at angles close to 90 • to the jet axis, while these shielding effects diminish at lower observer angles.…”

Prediction of installed jet noise

“…However, examination of the acoustic properties of the low frequency installed noise and its dependence on the engine position, jet condition and flap position leads one to believe that the dominant effect is the trailing-edge noise. This is because the dipole characteristics are in agreement with the observed directivity pattern of trailing-edge noise at low frequencies (Head & Fisher 1976;Wang 1981;Mead & Strange 1998;Bondarenko et al 2012;Brown 2013;Amiet 1976b;Roger & Moreau 2005), decreasing L results in a reduced noise and a frequency shift toward high frequencies (Head & Fisher 1976;Way & Turner 1980;Stevens et al 1983;Wang 1981;Shearin 1983), there exists a high correlation between the pressure field near the trailing edge and the far-field sound (Head & Fisher 1976) and the dependence of sound intensity on the characteristic jet velocity is to the 5 to 6 power (Head & Fisher 1976;Brown 2013). These trailing-edge noise characteristics remind us the suitablity of Amiet's approach in modelling the low-frequency installed jet noise.…”

“…Many investigations followed and they fall roughly into three categories: identifying installed noise sources by studying the acoustic characteristics of an installed jet, the engine position, jet condition and flap position effects; developing installed jet noise prediction models; and investigating noise reduction techniques. The first category includes the experimental work of Head & Fisher (1976), Szewczyk (1979), Way & Turner (1980), Shearin (1983), Mead & Strange (1998) and Brown (2013). Through their experimental work, it was found that increasing H results in less noise at low frequencies and decreasing L follows the same trend and shifts the peak frequency to higher frequencies, the velocity dependence of the peak of the low frequency augmentation is to the five to sixth power.…”

Rapid distortion theory on transversely sheared mean flows of arbitrary cross-section

“…Measurements of the noise generated by the interaction of a circular jet with the trailing edge of a flatplate were carried out by Brown (2013Brown ( , 2015a in the Small Hot Jet Acoustic Rig (SHJAR) at the Aero-Acoustic Propulsion Laboratory (AAPL) at NASA Glenn Research Center (Bridges and Brown, 2005;Brown and Bridges, 2006). The experimental configuration along with the relevant geometric parameters are shown in figure 4.…”