Noise Characteristics of Aircraft High Lift Systems

Abstract

The characteristics of far-field noise from aircraft high lift systems are discussed. Analyses are made of the data from an airframe noise test conducted in the 40 by 80 ft wind tunnel at NASA Ames Research Center, using a 4.7% DC-10 aircraft model. Discussions are given on both far-field free microphone data and measurements from a phased microphone array. Major trends are revealed and discussed from the free microphone data, which include far-field frequency characteristics, dependence of the acoustic radiation on flow Mach numbers, effects of flap and/or slat deployment, and far-field directivity. Data from the phased microphone array are used to identify locations of major noise sources. Four subregions on the wing are identified as important source locations, namely, the leading-edge slat region, the inboard and outboard side edges of the outboard flap, and the inboard flap region close to the hub of the wing. The source strength distributions in these subregions are integrated to reveal dependencies of various noise sources on flow conditions and high lift system configurations. The effects of flap side edge fences on far-field noise are also discussed, which shows a reduction of a few decibels in flap-related noise.