Efficient prediction of propeller noise in non-axial uniform inflow conditions

This paper investigates the prediction accuracy and time efficiency of two distinct low-fidelity methods for predicting the tonal and broadband noise of a drone rotor in axial and non-axial inflow conditions. These are both derived from an aerodynamic rotor model based on the blade element momentum theory, respectively coupled with a time- and a frequency-domain solution of the Ffowcs Williams-Hawkings integral equation applied to a radial distribution of acoustically compact and non-compact sources. Experimental data and scale-resolving lattice-Boltzmann/very-large eddy simulation results for a two-bladed small unmanned aerial system in transitional boundary layer conditions are used to validate the low-fidelity approaches. Comparison between low-fidelity, high-fidelity and experimental results reveal that the underlying sound generation mechanisms are accurately modeled by the low-fidelity methods, which therefore constitute a valid tool for the preliminary design of quiet drone rotors and for the estimation of the community noise impact of drone operations. • Efficient, accurate methods are needed to predict propeller noise in non-axial inflow, common in takeoff and landing flights. • Efficient tools are vital for evaluating low-noise flight procedures and optimizing trajectories. • Blade-element-momentum theory with 2D unsteady models, like Sears' function, reliably predicts loads in non-axial inflows. • Low-order models predict propeller noise in non-axial inflow, matching high-fidelity simulations and measurements.