Acoustic Shielding and Scattering Effects of a Propeller Mounted Above a Flat Plate

Abstract

To reduce the overall noise pollution generated by aircraft, design choices often attempt to incorporate acoustic shielding often using aircraft wings to minimise the noise generated by engines and propellers. By mounting a propeller above a wing, increasing the noise shielding, acoustic scattering effects can be introduced which change the directivity and magnitude of the noise generated. Experiments were carried out to investigate the acoustic shielding and scattering effects of a propeller mounted above a flat plate trailing edge. Two propellers were tested at constant rotational rates of 5000 RPM and 7000 RPM respectively. The tests were conducted within an anechoic wind tunnel facility with loading and far-field noise data collected by microphone arrays at a parametric set of propeller locations relative to the flat plate trailing edge. Analysis of the spectral content of the noise along with the tonal content of the signals are presented. The levels of coherence and cross spectrum phase are considered to give greater insights into the levels of noise attenuation due to shielding and scattering effects. Analysis of the acoustic data shows locations with notable levels of noise attenuation for both the tonal and broadband noise content.