Aeroacoustics of Unconventional Drone Rotors - From Leonardo da Vinci's Designs to Toroidal Loops

Unmanned Aerial Vehicles (UAVs) are transforming everything from agriculture to product delivery, environmental monitoring, and disaster relief. Delivery drones have a lower environmental footprint compared to other modes of delivery, but the noise generated by traditional rotary drones hinders their widespread use. As the demand for drones grows, the need for a quieter propeller becomes paramount. da Vinci envisioned an aerial screw long before the first flying machine was built. While propeller with loops were designed way back in the 1890s for steamships (C Myers' screw propeller), recently a novel design of a toroidal rotor has emerged for UAVs which aims to reduce broadband noise compared to traditional propellers. In our study, we explore the aerodynamics and aeroacoustics of da Vinci's aerial screw and the toroidal propeller via simulations. Since the unsteady surface pressure on the rotor blade, which is the source of aeroacoustic noise, is simultaneously affected by all the structures in the flow, we use the Force Partitioning Method (FPM) to calculate the pressure forces induced by various vortex structures. We then employ the Ffowcs Williams–Hawkings based acoustic partitioning method to get the corresponding far-field noise due to these propellers and quantify the effectiveness of these designs.