On the Impact of Large-Scale Vortical Gusts on the Aeroacoustics of a Propeller at Low Reynolds Numbers

This study investigates the aeroacoustic behavior of a low-Reynolds-number propeller in forward flight subjected to large-scale inflow disturbances. The incoming flow is modeled as single-frequency sinusoidal vortical gusts, enabling a systematic assessment of the effects of gust frequency, initial phase, and direction on aerodynamic performance and noise generation. The numerical setup is first validated against experimental data under steady inflow conditions. The results show that the loading fluctuations caused by the incoming gust result in discrete tonal components in the acoustic spectrum at frequencies determined by the combination of the gust frequency and multiples of the rotational frequency. These components arise from a double modulation mechanism, and their amplitude is further shaped by inter-blade interference effects. The phase of the gust with respect to the rotor primarily affects the phase of the blade response, thereby modifying the noise directivity, particularly at low frequencies. When the gust is inclined relative to the mean flow, the interaction becomes more complex, leading to a richer tonal spectrum with high intensity tones extending up to the 10th harmonic of the blade passing frequency. Overall, the results provide a physical interpretation of the coupling between rotating blades and large-scale inflow disturbances, supporting the development of improved models for unsteady tonal noise prediction.