Aerodynamic and acoustic interactional effects for small commercial propellers in co-axial counter-rotating arrangements

Abstract

The study examines the acoustic and aerodynamic properties of small propeller configurations, particularly focusing on propeller-propeller interactions. Two 330.2 mm diameter propellers were tested at a constant speed of 10120 RPM in both isolated and coaxial configurations under hover conditions, with relative spacings of half and a full blade radius. The study evaluated aerodynamic loads, flow field velocity, tip vortex behaviour, and acoustic emissions using a six-component load cell, Particle Image Velocimetry, and microphone measurements. PIV measurements were synchronised across the propeller azimuth angle at 30◦ intervals to track tip vortex paths for up to 3.5 revolutions. Results showed that each tip vortex travels vertically over two propeller radii and curls up in the second revolution. The impact of the support pylon on the isolated propeller’s performance was assessed and compared to coaxial interactions, revealing that the pylon affects performance, with the pusher propeller being more effective. The lower propeller experiences a thrust loss of about 20% in coaxial configurations. The interaction of tip vortices alters tonal emissions, with increased noise levels observed in coaxial setups, especially with larger propeller spacings. Turbulent kinetic energy and vortex meandering align with the acoustic findings.