Stochastic analysis of a single-rotor to quantify the effect of RPS variation on noise of hovering multirotors

Abstract

Multirotor drone generally controls its attitude and position through the variation of the angular speed of each rotor, which makes the sound signature from it considerably different from the one of single-rotor flight vehicle. Specifically, the sound spectrum of single-rotor vehicles is dominated by the blade passing frequency (BPF) components, determined by the angular speed of the rotor. In contrast, the variation in the angular speed in the multirotor makes it challenging to predict the effects of the multirotor noise. In this study, the effects of the variation in the angular speed of each rotor on the noise of a hovering multirotor were quantified and predicted through uncertainty quantification and single-rotor stochastic analysis. Multirotor experimental results indicated that the Revolution per second (RPS) uncertainty of the multirotor is sensitive to maximum tilt angle and payload. The experimentally quantified angular speed variation is used as input to single-rotor stochastic analysis, and the measured aerodynamic and acoustics results show good agreement with the analytically/numerically predicted results. On comparing multirotor noise, the single-rotor noise with RPS uncertainty results exhibit similar spectral characteristics, especially near the BPF harmonics. Furthermore, the results reveal that the single-rotor stochastic simulation with angular speed uncertainty can predict angular speed variation effects on the multirotor noise in the hovering condition. This study concludes that the sound characteristics of a hovering multirotor can be predicted by considering a single-rotor case with RPS uncertainty.