Recent advancements in the UAM (urban air mobility) sector pave the way for making urban eVTOL (electric vertical take-off and landing) flight a reality. Operating in urban environments, noise generated by aerial vehicles plays an imperative role in their certification. Urban flight is expected to subject aerial vehicles to a broad spectrum of large-scale turbulent structures generated by various sources such as flow around high-rise buildings, terrain-level obstacles, incoming ABL (atmospheric boundary layer)
characteristics, local windspeed variations, etc.. Unlike the well-documented effects of aerial vehicles flying under steady freestream or small-scale turbulence impingement, research on their performance when subjected to large-scale turbulence representative of an urban airspace is relatively scanty. This experimental work aims to generate large scale turbulence in the order of the rotor diameter and analyze its influence on propeller loading and noise emission.

Bluff body shedding from a cylinder is utilized to generate rotor scale turbulence in the inflow, with a variation in upstream cylinder placement tested to quantify the influence of it’s proximity to the propeller. The presence of an upstream obstruction results in severe penalties to the aerodynamic performance and thrust generation compared to an isolated propeller. An increase in rotor scale fluctuations in the inflow leads to an increased intensity of low-frequency loading fluctuations. The highly turbulent inflow has a severe impact on the noise emissions, with an overall increase in the broadband content and retention of discrete tones emitted at BPF (blade passing frequency) harmonics across all tested advance ratios; contrasting drastically with the emission of the isolated propeller. Further, with the cylinder obstruction placed closer to the propeller, the effect of haystacking is observed in the noise emissions, which dominates the high-frequency range and results in a spectrum comprising of purely broadband content above the 2nd
harmonic of the BPF. The findings highlight a strong influence of large-scale turbulence on propeller performance and noise emissions, while emphasizing the requirement for further investigation which isolates and analyzes each underlying effect to obtain a complete understanding of the identified influence.