Acoustic emissions from a high-speed propeller

Abstract

This paper investigates the far-field noise signature of propellers rotating at a speed range of 2500-6000 rpm. The experiment is conducted on a two-bladed propeller with a tip to tip diameter of 25.4 cm and a pitch of 17.8 cm. The propeller is connected to a brushless DC stepper motor of 900 rpm/V capacity that helps in achieving the above-mentioned propeller speed. The experiments are conducted inside the anechoic chamber to simulate the free-field environment. The acoustic spectra showed that the propeller noise at higher rpm consists of both tonal and broadband frequency components. The tonal noise and its harmonics were found to be lower than Blade Passing Frequency. The tonal peaks are more pronounced in higher rpm when compared to the lower rpm. Acoustic measurements also revealed the distinct variations in the noise levels with rpm. The Overall Sound Pressure Level tends to increase as the speed of the propeller increases. The rate of increase in noise levels is dominant at higher rpm compared to that at lower rpm. The propeller noise is 7 dB higher than the brushless motor noise at higher speeds. The obtained results are compared with previous research papers.