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Aeroacoustic Characteristic Analyses of Coaxial Rotors in Hover and Forward Flight

Aeroacoustic Characteristic Analyses of Coaxial Rotors in Hover and Forward Flight A numerical method combining computational fluid dynamics (CFD) method and Ffowcs Williams–Hawkings (FW–H) equations is established for predicting acoustic characteristics of the coaxial rigid rotor in hovering and forward flight. The unsteady Reynolds-averaged Navier–Stokes (URANS) solver coupled with the moving-embedded grid technique is established to obtain sound source information in the flowfield with high accuracy. On the basis of the accurate solution for the coaxial rotor flowfield, the blade–vortex interaction (BVI) noise in hovering state and the high-speed impulsive (HSI) noise in high-speed forward flight are estimated by the Farassat 1A formula and the FW–H equation with a penetrable data surface (FW–Hpds), respectively. Then the sound pressure distribution characteristics and sound radiation pattern for the coaxial rotor in a hovering state and in a forward flight are obtained through the comparative analysis of the sound pressure time histories and the distribution of sound pressure levels of the upper rotor, lower rotor, and coaxial rotor. The simulation results indicate that significant unsteady characteristics appear in blade aerodynamic loading due to the Venturi effect, blade–vortex interaction phenomenon, and action of the downwash existing in the coaxial rotor flowfield, causing the loading noise of the coaxial rotor to occupy the dominant position in hovering state; the counter-rotating characteristics of the upper and lower rotors cause a significant phase difference between their respective sound pressure waveforms, and the phase difference is determined by the angle between the observation point and the intersection position of the upper and lower blades; the difference with the single rotor in terms of the severe HSI noise generated in the high-speed forward flight is that the noise radiation intensity of the coaxial rotor along both sides in the forward direction exhibits an approximately symmetrical distribution. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Aeronautical & Space Sciences Springer Journals

Aeroacoustic Characteristic Analyses of Coaxial Rotors in Hover and Forward Flight

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References (25)

Publisher
Springer Journals
Copyright
Copyright © The Korean Society for Aeronautical & Space Sciences 2021
ISSN
2093-274X
eISSN
2093-2480
DOI
10.1007/s42405-021-00408-5
Publisher site
See Article on Publisher Site

Abstract

A numerical method combining computational fluid dynamics (CFD) method and Ffowcs Williams–Hawkings (FW–H) equations is established for predicting acoustic characteristics of the coaxial rigid rotor in hovering and forward flight. The unsteady Reynolds-averaged Navier–Stokes (URANS) solver coupled with the moving-embedded grid technique is established to obtain sound source information in the flowfield with high accuracy. On the basis of the accurate solution for the coaxial rotor flowfield, the blade–vortex interaction (BVI) noise in hovering state and the high-speed impulsive (HSI) noise in high-speed forward flight are estimated by the Farassat 1A formula and the FW–H equation with a penetrable data surface (FW–Hpds), respectively. Then the sound pressure distribution characteristics and sound radiation pattern for the coaxial rotor in a hovering state and in a forward flight are obtained through the comparative analysis of the sound pressure time histories and the distribution of sound pressure levels of the upper rotor, lower rotor, and coaxial rotor. The simulation results indicate that significant unsteady characteristics appear in blade aerodynamic loading due to the Venturi effect, blade–vortex interaction phenomenon, and action of the downwash existing in the coaxial rotor flowfield, causing the loading noise of the coaxial rotor to occupy the dominant position in hovering state; the counter-rotating characteristics of the upper and lower rotors cause a significant phase difference between their respective sound pressure waveforms, and the phase difference is determined by the angle between the observation point and the intersection position of the upper and lower blades; the difference with the single rotor in terms of the severe HSI noise generated in the high-speed forward flight is that the noise radiation intensity of the coaxial rotor along both sides in the forward direction exhibits an approximately symmetrical distribution.

Journal

International Journal of Aeronautical & Space SciencesSpringer Journals

Published: Dec 1, 2021

Keywords: Helicopter; Rigid coaxial rotor; Aerodynamic noise; Navier–Stokes equation; Farassat 1A formula; FW–Hpds equation

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