Abstract
This paper investigates the aeroacoustic interactions of small hovering rotors, using both experiments and computations. The experiments were conducted in an anechoic chamber with arrays of microphones setup to evaluate the azimuthal and polar directivity. The computational methodology consists of high fidelity detached eddy simulations coupled to the Ffowcs-Williams and Hawkings equation, supplemented by a trailing edge broadband noise code. The aerodynamics and aeroacoustics of a single rotor are investigated first. The simulations capture a Reynolds number effect seen in the performance parameters that results in the coefficient of thrust changing with the RPM. The acoustic analysis enables the identification of self-induced noise sources. Next, dual side-by-side rotors are studied in both counter-rotating and co-rotating configurations to quantify the impact of their interactions. Higher harmonics appear due to the interactions and it is verified that the counter-rotating case leads to more noise and a less uniform azimuthal directivity. Difficulties that arise when trying to validate small rotor calculations against experiments are discussed. Comparisons of computational and experimental results yield further insight into the noise mechanisms that are captured by each methodology.
Highlights
Accepted: 23 October 2021The rapid progress in the electric vertical takeoff and landing industry warrants the need for fundamental understanding of flight-enabling technology
Aircraft from the scale of unmanned aerial vehicles (UAVs) for drone delivery to urban air mobility (UAM) transport vehicles rely on multiple rotors to attain controlled flight
The advanced precision composite (APC) 8x4.5MR rotor was tested in both single and dual rotor hover configurations to quantify the effect of self-induced interactions as well as rotor–rotor interactions
Summary
Accepted: 23 October 2021The rapid progress in the electric vertical takeoff and landing (eVTOL) industry warrants the need for fundamental understanding of flight-enabling technology. Aircraft from the scale of unmanned aerial vehicles (UAVs) for drone delivery to urban air mobility (UAM) transport vehicles rely on multiple rotors to attain controlled flight These rotors will experience significant aerodynamic interactions that have implications on performance and noise. They tested five versions of the same rotor made of plastic and had a wide range of measured tip twist deflections across the entire RPM range tested Both the manufacturing discrepancies and the blade material properties had an impact on the experimental results. They showed that incorporation of an elasticity model in the computations shows better agreement with the experimental measurements. The rotor structure is an important contributor to the performance and noise, but it is often difficult to quantify the effects in a way that can be integrated into the computations
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