Noise Characteristics of a Tilted Forward and Fixed Aft Propeller on a 1/10th Scale Half-Model eVTOL Aircraft

An experimental investigation of the noise produced by propellers installed on a 10% scale half-model eVTOL aircraft is presented. The configuration consists of a tilting forward propeller and an aft propeller in a fixed orientation and installed on a pylon mounted on the scale model aircraft. This study investigates whether the wake from the forward propeller interacts with the aft propeller and how this interaction influences the far-field noise. The aircraft was installed in an aeroacoustic wind tunnel and far-field noise measurements were carried out at various wind speeds, propeller rotational speeds, forward propeller tilt angles, and aircraft pitch angles. Numerical simulations were also performed using a mid-fidelity aerodynamic solver based on the vortex particle method to visualise the trajectory of the forward propeller wake and assess whether it interacts with the aft propeller. Far-field noise spectra show that at low wind speeds and low forward propeller tilt angles, the turbulent wake from the forward propeller likely interacts with the aft propeller resulting in significantly higher broadband noise levels. At high wind speeds, the tonal noise measured at certain blade passing frequency harmonics exhibited increased levels when both propellers operated simultaneously compared with the aft propeller operating alone. Pitching the aircraft nose up had a negligible effect on the turbulent wake interaction between the forward and aft propellers as indicated by the small change in
broadband noise.