Simplified mathematical models of Blade-Vortex Interaction (BVI) noise are developed to help gain insight and understanding of the BVI noise radiation process. These models highlight the importance of BVI phasing (acoustic waves coalescence), Doppler effects and dipole directivity. BVI noise radiation is found to have strong phase dependence. Measured BVI noise amplitudes and directivity are closely associated with the noise amplification due to in-phase accumulation of radiated BVI waves. Two major BVI events of the two-bladed Operational Load Survey (OLS) rotor are found to be capable of radiating large amount of energy from the rotor during normal descent-to-landing conditions: a supersonic decelerating (oblique) interaction and a broadside (parallel) interaction. Longitudinal and lateral directivity profiles are presented to illustrate the highly directional nature of acoustic waves radiating from these BVI interactions. Results show that the supersonic decelerating (oblique) interaction is a strong function of Mach number and radiates near in-plane BVI noise directly ahead of the helicopter's flight path.
Acoustic phasing, directionality and amplification effects of helicopter blade-vortex interactions
Akustische Phasen-, Richtungs- und Verstärkungseffekte von Hubschruber-Rotorblatt-Wirbel-Interaktionen
Journal of the American Helicopter Society ; 46 , 4 ; 273-282
2001
10 Seiten, 13 Bilder, 28 Quellen
Article (Journal)
English
Acoustic Phasing, Directionality and Amplification Effects of Helicopter Blade-Vortex Interactions
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