Breakdown of propeller aircraft noise by applying conventional beamforming jointly with imaging using the rotating source identifier

Abstract

Full-scale propeller measurements are useful to study the total noise contribution of a propeller-driven aircraft, including installation effects. Full-scale measurements under operational conditions also provide an accurate validation opportunity for propeller noise prediction models. These studies are, therefore, necessary to quantify and reduce the noise annoyance of propeller-driven aircraft. For propeller aircraft, rotating sources need to be considered. In this research, propeller noise is studied for a full-scale propeller using an acoustic microphone array. The acoustic imaging techniques used are Conventional Frequency-Domain or Time-Domain Beamforming for the stationary noise sources and the ROtating Source Identifier for the rotating noise sources. By applying these two acoustic imaging methods simultaneously, in addition to filtering in the spatial and frequency domain, also filtering in the source velocity domain can be exploited. These methods were applied to an engine run-up of a Pipistrel Velis Electro, the first fully-electric certified aircraft.
This electric aircraft, placed on the ground, allows for an initial study on the present noise sources and their relative contributions. Ultimately, this information can be used to separate the measured spectrum into spectra of different noise components which in turn can be used for full-scale validation and improvement of propeller noise prediction models.