Fundamental investigations of airframe noise

Abstract

An extensive numerical and experimental study of airframe noise mechanisms associated with a subsonic high-lift system has been performed at NASA Langley Research Center (LaRC). Investigations involving both steady and unsteady computations and experiments on a small-scale, part-span flap model are presented. Both surface (steady and unsteady pressure measurements, hot films, oil flows, pressure sensitive paint) and offsurface (5 hole-probe, particle-imaged velocimetry, laser velocimetry, laser light sheet measurements) were taken in the LaRC Quiet Flow Facility (QFF) and several hard-wall tunnels up to flight Reynolds number. Successful microphone array measurements were also taken providing both acoustic source maps on the model, and quantitative spectra. Critical directivity measurements were obtained in the QFF. NASA Langley unstructured and structured ReynoldsAveraged Navier-Stokes codes modeled the flap geometries excellent comparisons with surface and offsurface experimental data were obtained. Subsequently, these meanflow calculations were utilized in both linear stability and direct numerical simulations of the flap-edge flow field to calculate unsteady surface pressures and farfield acoustic spectra. Accurate calculations were critical in obtaining not only noise source characteristics, but shear layer correction data as well. Techniques utilized in these investigations as well as brief overviews of results will be given.

Novel approach for reducing rotor tip-clearance-induced noise in turbofan engines

“…The In particular, one may note the dramatic effectiveness of the porous-tip treatment at locations beyond the trailing edge (figs. [21][22].…”

Complex Landing Gear Noise Prediction Using a Simple Toolkit

“…To construct a time history of length T , the nondimensional loading spectrum, given by Eqn. (1), is sampled at 2 n values separated by dS = D/V n T . Each value, F i , i = 1, 2 n , is assigned a random phase and an inverse Fourier transform is used to generate a time history.…”

“…The goal of NASA's Advanced Subsonic Technology (AST) Program is a total aircraft noise reduction of 10 EPNdB relative to 1997 levels. 1 Previously, engine noise has been the major source of aircraft noise, but with the introduction of engine noise reduction technologies, it has been found that on approach the airframe noise is comparable with the engine noise and could well exceed it in the future. At take-off the major component of aircraft noise is still the engine noise since the engine is operating at full power.…”

Effect of Mictrotab on Reduction of Noise Due to Aircraft High-Lift Devices

“…Introduction D EFINED as the "nonpropulsive noise of an aircraft in flight" in [1], noise produced by airframe components becomes significant during the approach-to-land phase of aircraft operations. Research efforts on identifying and understanding the noise sources associated with the individual airframe components, in particular, high-lift systems, have been undertaken by many researchers [2]. It has been confirmed experimentally in [3][4][5], and analytically by using empirical methods [6], that both leading-edge slats and trailing-edge flap side edges are the most important noise contributors from the high-lift systems to overall noise levels of an aircraft in approach.…”