Aeroacoustic metastructure: Toroidal propeller with enhanced acoustic and aerodynamic performance

Propeller noise has become a major constraint in the development of high-efficiency and low-disturbance unmanned aerial vehicles (UAVs). This study proposes and investigates a novel toroidal propeller configuration, whose closed-loop structure fundamentally modifies the flow behaviour and acoustic characteristics. A computational fluid dynamics (CFD)-based numerical prediction model, a sound pressure level (SPL) characteristic function model, and an integrated aeroacoustic testing platform were established to analyse its aerodynamic performance and noise behaviour. Through simulations and experiments comparing between the toroidal and benchmarking propellers, the underlying noise reduction mechanism of the toroidal configuration was revealed. The results indicate that, under equal thrust conditions, the figure of merit (FM) of the toroidal propeller increases by 4.6%, whereas the horizontal and longitudinal sound pressure levels (SPLs) decrease by 4.9 dBA and 16.9 dBA, respectively. In addition, SPL attenuation rates of the toroidal propeller significantly increase with distance, increasing by 32.9% in the horizontal plane of the disk and by 29.6% in the longitudinal plane of the hub. Compared with the streamlined propeller, the unique closed-loop configuration of the toroidal design markedly reduces surface pressure fluctuations, effectively suppresses tip–vortex shedding, and mitigates blade–vortex interactions (BVIs), thereby attenuating high-frequency broadband noise and aerodynamic sound radiation while eliminating the typical dipole directivity pattern of streamlined propellers. These findings provide a theoretical and experimental foundation for the aerodynamic and acoustic optimization of toroidal propeller configurations and offer a promising solution for reducing noise in aircraft.