Noise breakdown of landing aircraft using a microphone array and an airframe noise model

摘要

For current generation aircraft, airframe noise is considered to have a significant contribution to the aircraft noise levels, especially during the landing phase. In this paper, a noise breakdown of landing aircraft is presented to investigate this airframe noise contribution. Use is made of data acquired with an acoustic array. The flyover measurements have been taken for a number of aircraft types in the landing phase. In addition, a model for predicting airframe noise is employed. Conventional beamforming is applied for two frequency bands separately, i.e., 1500-4500 Hz and 4500-9500 Hz. From the resulting beamform source maps, and also from the spectrograms of the flyover data, engine noise is found to be clearly present in both frequency bands. Additionally, by comparing the measured overall sound pressure levels with the airframe noise model predictions, the engine noise is found to be dominant. In agreement with the model predictions, the source plots reveal airframe noise to be present only in the lower frequency band. From the source plots it is found that there are clear differences between the different components (main landing gear, nose landing gear, flaps, slats) contributing to the airframe noise for the different aircraft types. These differences are partly in agreement with the model predictions, but discrepancies between model and data exist. Especially the nose landing gear is often clearly visible in the source plots, which is not expected from the model predictions. These differences can be considered to be a source of input to efforts for the further improvement of aircraft noise source models.