Effects of simulated flight on fan noise suppression

Heidmann, M. F.; Dietrich, D. A.

doi:10.2514/6.1977-1334

Cited by 4 publications

(1 citation statement)

References 6 publications

(4 reference statements)

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“…An alternative to ICD's are anechoic wind from the prominent residual peaks. tunnels (24)(25)(26) which also have been found to eliminate the bulk of the extraneous inlet disturbances.…”

Section: Mechanism Identificationmentioning

confidence: 99%

Aircraft Turbofan Noise

Groeneweg

Rice

1983

Volume 5: Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; Process Industries

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Recent advances in the understanding of turbofan noise generation and suppression in aircraft engines are reviewed with particular emphasis on NASA research. The review addresses each link in the chain of physical processes which connect unsteady flow interactions with fan blades to far field noise. Mechanism identification and description, duct propagation, radiation and acoustic suppression are discussed. Recent advances in the experimental technique of fan inflow control assure that in-flight generation mechanisms are not ma.,ked by extraneous sources in static tests. Rotor blade surface pressure and wake velocity measurements aid the determination of the types and strengths of the generation mechanisms. Approaches to predicting or measuring acoustic mode content, optimizing treatment impedance to maximize attenuation, translating impedance into porous wall structure and interpreting far field directivity patterns are illustrated by comparisons of analytical and experimental results. A persistent theme of the review is the interdependence of source and acoustic treatment design to minimize far field noise. Areas requiring further research are discussed and the relevance of aircraft turbofan results to quieting other turbomachinery installations is addressed.

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“…An alternative to ICD's are anechoic wind from the prominent residual peaks. tunnels (24)(25)(26) which also have been found to eliminate the bulk of the extraneous inlet disturbances.…”

Section: Mechanism Identificationmentioning

confidence: 99%

Aircraft Turbofan Noise

Groeneweg

Rice

1983

Volume 5: Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; Process Industries

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Flight effects on predicted fan flyby noise

Heidmann

Clark

1977

The Journal of the Acoustical Society of America

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A paper study was made of the impact on PNLT (Perceived Noise Level, Tone corrected) and flyby EPNL (Effective Perceived Noise Level) when forward motion reduces the noise generated by the bypass fan of an aircraft engine. Blade passage frequency (BPF) of a typical subsonic tip-speed fan with BPF tone cutoff design features was systematically varied from 0.5 to 8 kHz. Two cases of predicted flight effects on fan source noise were considered: (1) reduced BPF tone level of 8 dB and (2) reduced broadband noise levels of about 2 dB in addition to reduced tone level. The fan source noise attained its maximum perceived noise reduction due to flight effects at a BPF of 4 kHz. The PNLT was reduced 7.6 and 10.0 dB for cases (1) and (2), respectively. The maximum reduction in 500-ft sideline flyby noise occurred at a BPF of 2.5 kHz. The EPNL was reduced 5.0 and 7.8 dB for cases (1) and (2), respectively. A factor of 2 change in tone frequency gave about one-half the maximum EPNL reduction.

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