Experimental Flowfield And Aeroacoustic Investigation Of Twin Rotors In Hover Conditions

Abstract

The study examined the acoustic and aerodynamic properties of small rotors, considering the impact of rotor- rotor interactions. Two rotors equipped with three-bladed propellers, each with a diameter of 393.7 mm, were tested at a fixed rotational speed of 5200 RPM, with various configurations in terms of phase delay and mutual distance between the rotors. The aerodynamic loads, flow field velocity, and acoustic emissions were analysed using a six-component load cell, Particle Image Velocimetry, and microphone array measurements. The aerodynamic characteristics of the individual rotor were assessed across different rotational speeds. Additionally, the interaction between the rotor slipstreams for side-by-side rotors was investigated under co- rotating and counter-rotating configurations at distances between the rotor axes of 1.02D, 1.1D, and 1.2D. The findings indicated that the slipstreams of the side-by-side rotors deflect and change with the inter-axial distance, with the rotor-rotor interaction and acoustic emissions being influenced by the rotor distance. A noticeable decrease in thrust was observed at the closest distance of 1.02D. Regarding acoustic emissions, the overall sound pressure level increased when the rotors operated in counter-rotating verses compared to the co-rotating case.