Propeller–strut interaction tone noise

Abstract

This paper presents a detailed investigation into the tonal noise produced by an unmanned aerial vehicle (UAV) propeller operating with a circular strut mounted just downstream. Experimental measurements of the acoustic pressure in the near- and far-fields are presented and it is observed that the measured pressure signals contain a strong impulse caused by the propeller-strut interaction. The magnitude and shape of this impulse varies significantly with observer location. It was also observed that the magnitude of these impulses was reduced by increasing the distance between the propeller and the strut. In order to investigate the physics of the noise generation mechanism, a number of computational fluid dynamics (CFD) simulations were performed and a numerical method was developed to predict the radiated acoustic tones using the CFD data. This analysis showed that the unsteady loading sources on the strut and the propeller both made significant contributions to the total impulse and that the directivity of the sound radiated from the strut was different to that radiated from the propeller. Therefore, the addition of the signals from the propeller and the strut produced a pressure impulse which had a complex directivity. Analytical models were also developed to estimate the unsteady loading on the propeller and strut from which estimates of the radiated noise field could be made. Predictions made using these models are compared with CFD predictions and experimental measurements of the unsteady loading on the strut and also the total radiated noise field and show reasonable agreement.

Numerical study on interactional aerodynamics of a quadcopter in hover with overset mesh in OpenFOAM

“…The close proximity of rotors and fuselage in multicopter configurations leads to complex aerodynamic interaction, which generates unsteady airloads. Unsteady aerodynamic loads can reduce the overall performance of a vehicle [1,2,3,4], potentially cause vibration and sectional loading in rotors [5,6,7,8], and degrade the control authority [9]. With increasing demand for more compact configurations in recent multirotor aircraft, stronger interactional aerodynamics is anticipated among distributed rotors and an airframe.…”