Airframe Noise Component Interaction Studies

Abstract

Acoustic wind-tunnel tests were conducted to examine the noise-generating processes of an airframe during approach flight. The airframe model was a two-dimensional wing section, to which high-lift leading and trailing edge devices and landing gear were added. Far-field conventional microphones were utilized to determine component spectrum levels. An acoustic mirror directional microphone was utilized to examine differences in noise source distributions on airframe components extended separately and in combination. Measured spectra are compared with predictions inferred from aircraft flyover data. Aeroacoustic mechanisms for each airframe component are identified. Component interaction effects on total radiated noise generally were small (within about 2 dB). However, some interactions altered local flow velocities and turbulence levels, causing redistribution of local acoustic source strength. Possibilities for noise reduction exist if trailing edge flaps could be modified to decrease their noise radiation caused by incident turbulent flow.