Aerodynamic and aeroacoustics investigation of tandem propellers in hover for eVTOL configurations

The present study investigates the aerodynamic interactions and the aeroacoustic footprint of a tandem propellers configuration typical of a multi-rotor eVTOL aircraft in hover conditions. In particular, an experimental campaign was conducted to collect a comprehensive aerodynamic and aeroacoustic database over two scaled propellers models in tandem. Aerodynamic loads and acoustic measurements were performed in an anechoic test chamber. Measurements also included flow field surveys using stereoscopic PIV technique. The configurations tested included twin propellers in side-by-side and staggered configurations with partial overlap between rotor disks. The activity was completed by numerical simulations performed with the mid-fidelity aerodynamic solver DUST. The analysis of experimental and numerical results enabled to provide a robust comprehension of the different flow mechanisms that characterise aerodynamic interaction between propellers wakes by changing longitudinal and lateral distances as well as blades sense of rotation. In particular, the effects of these interactions on both the aerodynamic performance and aeroacoustic footprint was investigated. Specifically, the partial overlap between propellers disks leads to a conspicuous reduction of aerodynamic performance of the propeller invested by front propeller slipstream as well as an increase of the acoustic emission of the dual propeller system.