Experimental and Computational Aeroacoustic Investigation of Small Rotor Interactions in Hover

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.

Numerical and Experimental Characterization of an Isolated Low-Reynolds Rotor in Pusher Configuration

“…The results of this analysis are reported in Tab. 1, which shows the target thrust [24] and the additional collective pitch that guarantees the match between the numerical and the experimental thrust with a maximum error of 0.1 N. Once the collective blade pitch is evaluated, the aerodynamic solver is applied to evaluate the flow-field to be compared with the experimental PIV measurements. The instantaneous velocity fields, in this case, were acquired on the wake side immediately downstream of the propeller, imaging an area of about 120x90 mm.…”

Numerical characterisation of noise generated by a distributed-propulsion propeller

“…This can be expected to be caused by omission of test stand, load cells, spinners and motors from the numerical model along with the surrounding walls which are shown to increase overall noise levels due to recirculation effects [36,38]. Furthermore, the coarser frequency resolution of the numerical signal relative to measured signal also leads to the under-prediction of tonal peaks [39].…”

Influence of fuselage arm cross-section on the aerodynamic and aeroacoustic performance of quadcopter unmanned aerial vehicles: A numerical investigation

“…It would also encounter challenges from the communities as the goods delivery drones represent a unique community noise source. 10 To characterize the aeroacoustic noise of drones, a series of experimental and numerical studies has been conducted with different rotor blade designs, 11,12 varying speed of rotations, 13,14 varying rotor numbers 15 etc. To reduce the noise level of drones, noise reduction methods, such as propeller trailing edge serration, 16,17 wavy rotor blade, 18 rotor phase synchronization, 19 have been investigated for quadcopter UAVs showing a potential reduction of aeroacoustic noise level.…”

“…Figure13. Comparison of the thrust forces for the elliptical cross-section and the circular cross-section, (a) @ 6000 rpm, (b) @ 9000 rpm.…”