Human response to the noise emissions of an isolated propeller under turbulent inflow conditions

Psychoacoustic listening experiments were conducted to investigate the human response to propeller noise under turbulent inflow conditions. The sound stimuli considered were recorded in aeroacoustic wind tunnel experiments featuring an isolated six-bladed propeller. The propeller operated under different isotropic inflow turbulence conditions and collective blade pitch angles. Higher inflow turbulence intensity levels caused a growth in the broadband noise emissions of the propeller, increasing the overall loudness levels. On the other hand, sharpness and tonality consistently decreased due to the increase in low-frequency noise and the tone-masking effect by the aforementioned broadband noise, respectively. The listening experiments aimed to elucidate the effect of these contradicting trends on sound perception. It was observed that lower noise annoyance ratings were reported for higher inflow turbulence intensity levels and lower collective blade pitch angles. Overall, only the tonality metric provided a statistically significant correlation with the annoyance ratings, indicating the importance of this perceptual aspect in propeller noise, in combination with loudness and sharpness. Other energy-based sound metrics, like the effective perceived noise level, failed to correctly describe the results of the listening experiment. In general, this analysis is valuable for the perception-influenced design of devices equipped with propellers.