Performance and Acoustic Modulation Response of a UAM Rotor Under Harmonic Gust Excitation

Abstract:
Urban Air Mobility (UAM) vehicles will operate in complex atmospheric environments where unsteady inflow conditions can significantly influence rotor performance and acoustic emissions. This study investigates the impact of an axially oscillating time-harmonic gust (i.e., a single mode of an impinging turbulence spectrum) on the aerodynamics and acoustics of a subscale UAM rotor in edgewise flight. Both mid-fidelity and high-fidelity analysis methods are employed to capture the unsteady rotor response and provide cross-validation of predictions. The results highlight a frequency modulation mechanism, wherein the gust excitation introduces sideband content around the blade-passing frequency (BPF), located at BPF ± the gust frequency and higher harmonics. This modulation alters both the tonal structure and overall acoustic signature of the rotor, with corresponding implications for performance metrics. A novel analytical method, employing a spatio-temporal modal representation of the gust field, is used to predict the unsteady rotor response.

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