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 highspeed 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 JetSurface 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 jetsurface 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 twoaxis 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. Farfield 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 farfield noise results, discussed here, show where the jet noise is partially shielded by the surface and where jetsurface interaction noise dominates the low frequency spectrum as a surface extends downstream and approaches the jet plume.