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.