Aerofoil geometry and in-flight effects on the interaction noise of co-axial contra-rotating rotors

Palleja-Cabre, Sergi, Paruchuri, Chaitanya and Joseph, Phillip (2023) Aerofoil geometry and in-flight effects on the interaction noise of co-axial contra-rotating rotors. In AIAA AVIATION Forum 2023 Proceedings. Aerospace Research Central.. (doi:10.2514/6.2023-4293).

Abstract

This paper presents an experimental investigation of the influence of propeller design parameters and in-flight effects on the interaction noise of co-axial contra-rotating rotors. A parametric study is performed to investigate the sensitivity of the radiated noise to the axial separation distance $z$ for different blade pitch angles and number of blades (even and odd) in hover conditions. It is found that the source balance in co-axial contra-rotating rotors can be significantly affected by the choice of propeller design parameters and therefore influence the optimum separation distance for minimum radiated noise. The noise radiation of isolated and co-axial contra-rotating rotors in forward flight is also investigated. The noise signature of isolated propellers in such in-flight configuration is found to be dominated by an increase of tonal noise at harmonics of the blade passing frequencies partly due to azimuthal variations of the blade loading. A simple analytical formulation is presented to estimate this effect with a good qualitative agreement with the measured data at the first blade passing frequency. It is also shown that the increased self noise due to inflow effects can dominate over the interaction noise sources in co-axial contra-rotating rotors in forward flight, which changes completely the source balance investigated previously for hover conditions.

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Contributors

Author: Sergi Palleja-Cabre

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