Noise measurements of generic small-scale propellers

Abstract

The geometric profiles of several commercial propellers were studied to guide the design of thirteen generic and fully-defined propellers. The generic propellers applied a NACA 0010 profile entirely across the span, and the propeller shape was defined in terms of the diameter, as well as the chord lengths and pitch angles at the 20% span and propeller tip positions. The propellers were machined out of an aluminum alloy and fitted onto a test rig. The noise from each propeller was measured by twenty free-field microphones placed at least 1.5 m away from the propeller hub. The rotational speed of the propellers was varied between 3600 and 7800 revolutions per minute. The changes in the tonal and broadband noise levels caused by variations in the aspect ratio, taper ratio, pitch angle and twist angle were observed. The tonal analysis was performed using the noise levels at the blade passage frequency, acquired by a microphone placed along the rotor plane. The power spectral density of the data acquired by the microphone downstream of the rotor plane, was processed by a locally weighted regression smoothing method. This process provided an estimate of the broadband noise levels. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.