Prediction of potential interaction noise in a generic rotor–strut arrangement

Abstract

The growing demand for quiet unmanned aerial vehicles (UAVs) calls for noise prediction tools capable of capturing the complex aerodynamic interactions occurring in rotor-airframe integrations at low computational cost. This paper presents an analytical framework to predict the potential-interaction tonal noise generated by a propeller operating upstream of its supporting strut, a dominant contributor to the acoustic signature of small UAVs. Aerodynamic sources of loading noise from the propeller and strut are modelled using potential-flow solutions, while a hypotrochoidal conformal mapping is employed to represent the inflow distortion induced by struts with arbitrary non-circular cross-sections. The method requires as input the spanwise distribution of steady loads from an isolated propeller, estimated through an unsteady panel solver that offers a favourable trade-off between computational efficiency and simulation fidelity. Analytical predictions are validated against experimental data for struts of varying cross-section diameters and shapes, different blade numbers, and multiple far-field observer locations. The results confirm that the models accurately capture the dominant physics of propeller-strut potential interaction, predicting sound pressure levels within 3 dB for most observer angles and blade-passing-frequency harmonics. The potential of the proposed methodology to support UAV noise optimisation is demonstrated by addressing the sound radiated by propellers with struts featuring spanwise-varying cross-sections.