Acoustic and aerodynamic performance of co-axial contra-rotating rotors with unequal diameters

Palleja-Cabre, Sergi, Paruchuri, Chaitanya C. and Joseph, Phillip (2024) Acoustic and aerodynamic performance of co-axial contra-rotating rotors with unequal diameters. In 30th AIAA/CEAS Aeroacoustics Conference, 2024. American Institute of Aeronautics and Astronautics.. (doi:10.2514/6.2024-3110).

Abstract

This short paper presents a preliminary experimental investigation of the influence of unequal diameters in co-axial contra-rotating rotors at hover conditions on their acoustic and aerodynamic performance. A parametric study is conducted to investigate the sensitivity of the radiated noise and performance metrics to the axial separation distance zfor different combinations of diameters of the upstream and downstream rotors operating at zero total torque conditions. The tested configurations include a reduction of the diameter of the downstream rotor, Dd, also known as clipping or cropping in the context of Contra Rotating Open Rotors, and a reduction of the upstream diameter, Du. Our preliminary findings suggest that, for a constant thrust setting, a reduction in the diameter of the upstream rotor proves more advantageous for acoustics than conventional cropping. This configuration can result in a reduction of up to 2 dB in OAPWL relative to equivalent cases with the same diameter. However, maintaining an equal diameter for both rotors results in a better aerodynamic performance. The influence of tip vortex meandering is hypothesised as the cause for tonal haystacking and a contributor to the increase in broadband noise at large (z/D > 0.25) axial separation distances.

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Contributors

Author: Sergi Palleja-Cabre

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