The acoustics of multirotor platforms for urban air mobility

Abstract

The sound field of hovering rotors has generated tremendous interest in recent years with the prospect of urban air mobility platforms comprising eVTOL type designs. In this presentation, we will review a number of key advancements that have been made with regard to an understanding of the sound field produced by multirotor systems in hover and how it relates to the aerodynamic performance of the rotor. Much of this work is based on laboratory-scale measurements of different configurations starting with multirotor drones comprising quad-copter, hexacopter, and even octocopter arrangements (Tinney and Sirohi, AIAA J., 2018) followed by stacked corotating rotors (Valdez and Tinney, AIAA J., 2022) where the trade-space based on stacking distance, index and angle and rotor speed are evaluated. Of particular interest is the constructive and destructive interference of sound waves from neighboring rotors which augment the first few fundamental rotor harmonics. Methods for characterizing the first few rotor harmonics based on POD-based Vold-Kalman order tracking filters (Tinney etal., Int. J. Aeroacoust., 2023) is presented as well as methods for collapsing the high frequency rotor broadband noise using a moving source model (Tinney et al., AIAA Paper 2023-3222).