Subsonic fan noise

Barry, B.; Moore, C. J.

doi:10.1016/0022-460x(71)90455-x

Cited by 20 publications

(6 citation statements)

References 3 publications

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“…Further details on other types of scattering (such as modal scattering of noise, without frequency scattering) may be found elsewhere [26]. Barry and Moore [10], in a general discussion of subsonic rotor alone noise, studied the spectral content of the noise emitted from one or several rotor stages and how it is conceived of as having a pure tone content at the blade pass frequency and its harmonics superimposed on a broadband spectrum. Tones may also be present at sum and difference frequencies relative to the blade-pass frequency tone and its harmonics.…”

Section: Mechanism Of Interaction Between Incident Noise and Rotatingmentioning

confidence: 99%

“…For noise propagation problems in hard-walled cylindrical ducts of infinite length, the acoustic pressure in the duct can be considered as the linear superposition of modal amplitudes: (10) where A + m,n and A − m,n are the complex modal amplitudes, k + m,n and k − m,n are the axial wavenumbers, and m and n are the azimuthal and radial mode indices respectively. The + and − superscripts refer to the direction relative to the flow, with the convention that positive is in the direction of the mean flow.…”

Section: Modal Analysis Techniquesmentioning

confidence: 99%

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Spectral, modal and coherence analysis of sum and difference scattering of narrowband noise in turbomachinery

Davis

Bennett

2016

International Journal of Aeroacoustics

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The phenomenon of sum and difference frequency scattering of narrowband noise as it interacts with ducted rotating turbomachinery is studied experimentally in this article. This phenomenon will affect the spectral and modal distribution of the noise downstream of rotating turbomachinery, which must be considered in order to optimise any acoustic mitigation methods installed inside the engine. In the experimental set-up, narrowband noise is generated by a loudspeaker located at the upstream end of the test duct which then propagates through a rotor stage. A microphone array located downstream of the rotor is used to examine the spectral and modal distribution of the acoustic pressure field at a single axial location. The results from this analysis are compared with pre-existing theory which had not previously been experimentally validated in the literature. This theory may be used to predict the modal content of the scattered noise. A coherence analysis is also presented using microphones upstream and downstream of the rotor stage in order to assess whether sum and difference scattering is best predicted by a linear or non-linear model. The results from this study serve to enhance our current understanding of sum and difference scattering of narrowband noise through turbomachinery stages, and highlight interesting results from this interaction such as potential overlapping of incident and scattered noise which may otherwise be overlooked.

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Section: Mechanism Of Interaction Between Incident Noise and Rotatingmentioning

confidence: 99%

Section: Modal Analysis Techniquesmentioning

confidence: 99%

Spectral, modal and coherence analysis of sum and difference scattering of narrowband noise in turbomachinery

Davis

Bennett

2016

International Journal of Aeroacoustics

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“…An example of such an approach is outlined in some detail in Ref. 7. This concept will be briefly pursued in the following and some experimental data will be examined in light of the analytical work.…”

Section: It Has Been Shown In Ref I That the Bpf Amplitude Generatedmentioning

confidence: 98%

“…However, it can be shown that if the force applied by the flow on a rotating blade varies as its position in the duct varies, the pressure pattern will be spatially modulated. 7 A variation in the applied force F with the circumferential position 0 can be expressed as One can see that each circumferential mode n generated at the blade passing frequency will be modulated in such a way that it will break down into two modes of equal amplitude. The same process takes place also when a subharmonic tone generated by the rotor is modulated.…”

Section: It Has Been Shown In Ref I That the Bpf Amplitude Generatedmentioning

confidence: 99%

Research on Fan Noise Generation

Benzakein

1972

The Journal of the Acoustical Society of America

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Different aspects of multiple-pure-tone (MPT) "broadband" noise generation in high-speed fans are discussed. An analytical model for multiple-pure-tone generation is presented. Experimental evidence indicates that the MPT generation does not seem to be a function of the presence of shock waves. It is also shown that fan "broadband" noise is not broadband in character and could be attributed to the modulation of the blade-passing-frequency tones, their sub-and higher harmonics. INTRODUCTIONThe subject of fan noise has received a lot of attention since the advent of high-bypass turbofans. A considerable amount of theoretical and experimental research has been carried out with the dual purpose of defining the fan noise-generation mechanisms and developing adequate means to suppress fan radiated noise. This effort has led to a relative satisfactory understanding of the generating mechanisms of blade-passing-frequency (BPF) tones and their higher harmonics (see, for example, Ref. 1). It is evident, however, that as the BPF noise is brought under control, more attention should be directed to understanding the rest of the spectrum. Subharmonic tones (sometimes called multiple pure tones) as well as broadband noise components of the fan spectrum can no longer be ignored if further fan noise reductions at the source are required. This paper will therefore present the results of some analytical and experimental work on the definition of multiple pure tones and broadband noise-generation mechanisms in high-speed fans. I. MULTIPLE PURE TONESThe presence of discrete tones other than harmonics of the blade passing frequency has been noted in the inlet spectra of turbofan engines since the advent of high-tip-speed fans and compressors. The main research effort was directed towards the understanding and reduction of the BPF noise and little work was directed to subharmonic tones. It is now evident that the importance of low-frequency tones can no longer be ignored.A good understanding of the multiple-pure-tone (MPT) phenomena is therefore required if greater progress is to be achieved in the noise control of transonic fans. Two questions should eventually be answered: (1) What phenomena are responsible for the MPT generation? (2) Under what circumstances do the MPTs propagate to the farfield? Physical observations of high-speed-fan data indicate that MPTs have the following characteristics.(1) They are detected only in the inlet duct.(2) They propagate only when the rotor-tip Mach number is greater than 1.(3) The strongest MPTs exist in general at frequencies below the rotor blade passing frequency and occur at integral multiples of engine shaft revolution frequency.(4) The higher-frequency MPTs are the first ones to appear as the fan speed is increased. Figs. 1 and 2, which represent probe measurements taken respectively in the inlet and exhaust duct of a fan at a supersonic tip speed. While Fig. 1 indicates the presence of MPTs in the inlet, Fig. 2 shows only the blade passing frequency superimposed on a broadband noise backg...

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“…Many studies can be found in the literature investigating these mechanisms, including overviews of the aerodynamic sound mechanisms as in Morfey (1972Morfey ( , 1973 and Barry and Moore (1971), as well as an introduction to the physics and basic analysis by Roger (2000). There are several sources of aerodynamic noise in such systems, such as that from inflow turbulence, steady and unsteady blade loading, turbulent or laminar boundary layers on the blade, etc.…”

Section: Introductionmentioning

confidence: 99%

Design and evaluation of an aeroacoustic wind tunnel for measurement of axial flow fans

Bilka

Anthoine²,

Schram³

2011

The Journal of the Acoustical Society of America

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An anechoic wind tunnel dedicated to fan self-noise studies has been designed and constructed at the von Karman Institute The multi-chamber, mass flow driven design allows for all fan performance characteristics, aerodynamic quantities (e.g., wake turbulence measurements), and acoustic properties to be assessed in the same facility with the same conditions. The acoustic chamber performance is assessed using the optimum reference method and found to be within the ISO 3745 standards down to 150 Hz for pure tone and broadband source mechanisms. The additional influence of installation effects of an aerodynamic inlet was found to create a scattered sound field only near the source location, while still providing good anechoic results at more distant sound pressure measurement positions. It was found to have inflow properties, span-wise uniformity, and low turbulence intensity, consistent with those desired for fan self-noise studies.

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Subsonic fan noise

Cited by 20 publications

References 3 publications

Spectral, modal and coherence analysis of sum and difference scattering of narrowband noise in turbomachinery

Spectral, modal and coherence analysis of sum and difference scattering of narrowband noise in turbomachinery

Research on Fan Noise Generation

Design and evaluation of an aeroacoustic wind tunnel for measurement of axial flow fans

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