Fan Noise Source Diagnostic Test - Wall Measured Circumferential Array Mode Results

Premo, John; Joppa, Paul D.

doi:10.2514/6.2002-2429

Cited by 34 publications

(18 citation statements)

References 2 publications

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“…The range of n and m is set by the cut-off/cut-on boundary as described in Eq. (7). The ducted turbofan only produces sound waves at few values of m-order.…”

Section: Duct Modes Analysis At Bpf Harmonic Ordersmentioning

confidence: 99%

“…However, the higher the frequency, the higher the possible value of n as shown with Eq. (7). The number of possible modes can thus become large.…”

Section: Modal Decompositionmentioning

confidence: 99%

“…Significant overall broadband levels are radiated to the far field due to motion and stretching of turbulent flow eddies 1,2 . In addition, generally intense tonal noise at specific frequencies as a result of rotor-stator interaction coupled with duct mode propagation in the nacelle is observed [2][3][4][5][6][7][8][9] . In the past decade, an effort towards the development of efficient acoustics liner aiming to reduce mainly the tonal part of the noise has been carried out.…”

Section: Introductionmentioning

confidence: 99%

“…A method allowing accurate modal decomposition as well as a good estimation of overall broadband content is therefore required. The Advance Noise Control Fan (ANCF) geometry of the NASA Glenn Research Center was developed in the early 1990's to provide detailed measurements of a turbo fan flow and corresponding noise produced by the ducted rotor/stator [2][3][4][5][6][7][8][9]12,13 . The measurements provide a better understanding of the correlation between the flow and the propagation inside the duct as well as the radiation to the far field.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Advanced Noise Control Fan Direct Aeroacoustics Predictions Using a Lattice-Boltzmann Method

Mann¹,

Pérot²,

Kim³

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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A Lattice-Boltzmann Method (LBM) based approach is used to perform transient, explicit and compressible CFD/CAA simulations on the Advanced Noise Control Fan (ANCF) configuration. The complete 3-D ducted rotor/stator model including all the geometrical details and the truly rotating rotor is simulated. Detailed near and far-field measurements conducted at the NASA Glenn research center are used to validate the simulation results. The measured and predicted sound pressure levels at the far-field microphones are compared and both show the presence of broadband noise and sharp peaks which frequencies depend on the number of rotor blades and the angular velocity of the rotor. The 3-D duct acoustics modes observed in experiments are also captured in the 3-D transient CFD/CAA calculation and detailed analyses of the results are presented. The main circumferential modes predicted from the number of rotor blades and stator vanes are recovered in both experimental and simulation modal decompositions. Nomenclature M = Mach number f k = k -th BPF harmonic order c b = Rotor blade chord s b = Rotor blade span Δx tip = Tip clearance c v = Stator vane chord d h,up = Upstream hub diameter d h,do = Downstream hub diameter p = Static pressure r = Radial coordinate θ = Azimuthal coordinate x = Axis coordinate t = Time m = Circumferential mode order n = Radial mode order k = x-axis eigenvalue κ = radial eigenvalue J m = Bessel function of the first kind and order m B = Number of fan blades V = Number of stator vanes s = Fan shaft harmonic Ω = Rotation frequency of the fan c 0 2 R 0 = Fan radius ρ 0 = Air density C i = Discrete collision component in the i -th direction c i = Discrete velocity component in the i -th direction f i = Particle distribution function in the i -th direction T = Temperature τ = Relaxation time ν = Kinematic viscosity ∆t = Numerical time step

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“…The range of n and m is set by the cut-off/cut-on boundary as described in Eq. (7). The ducted turbofan only produces sound waves at few values of m-order.…”

Section: Duct Modes Analysis At Bpf Harmonic Ordersmentioning

confidence: 99%

“…However, the higher the frequency, the higher the possible value of n as shown with Eq. (7). The number of possible modes can thus become large.…”

Section: Modal Decompositionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Advanced Noise Control Fan Direct Aeroacoustics Predictions Using a Lattice-Boltzmann Method

Mann¹,

Pérot²,

Kim³

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

View full text Add to dashboard Cite

show abstract

“…Acoustic radiation from jet engine inlets has been studied experimentally [1][2][3][4][5][6][7][8][9] , analytically [10][11][12][13] and computationally [14][15][16][17][18][19][20][21][22][23][24][25][26] by a number of investigators in the past. These studies provide a variety of useful and interesting information.…”

Section: Introductionmentioning

confidence: 99%

Physics of Acoustic Radiation from Jet Engine Inlets

Tam

Parrish

Envia

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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Numerical simulations of acoustic radiation from a jet engine inlet are performed using advanced computational aeroacoustics (CAA) algorithms and high-quality numerical boundary treatments. As a model of modern commercial jet engine inlets, the inlet geometry of the NASA Source Diagnostic Test (SDT) is used. Fan noise consists of tones and broadband sound. This investigation considers the radiation of tones associated with upstream propagating duct modes. The primary objective is to identify the dominant physical processes that determine the directivity of the radiated sound. Two such processes have been identified. They are acoustic diffraction and refraction. Diffraction is the natural tendency for an acoustic wave to follow a curved solid surface as it propagates. Refraction is the turning of the direction of propagation of sound waves by mean flow gradients. Parametric studies on the changes in the directivity of radiated sound due to variations in forward flight Mach number and duct mode frequency, azimuthal mode number, and radial mode number are carried out. It is found there is a significant difference in directivity for the radiation of the same duct mode from an engine inlet when operating in static condition and in forward flight. It will be shown that the large change in directivity is the result of the combined effects of diffraction and refraction.

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Experimental investigation of a new two-microphone method for the determination of broadband noise radiation from ducts

2017

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This paper experimentally investigates a new technique for measuring the modal amplitude distribution, sound power transmission and radiation, and far field directivity of the broadband noise from hard walled ducts. The innovative aspect of this method is that it only requires the measurements of the two-point complex coherence function between the acoustic pressures at two closely spaced points on the duct wall. This method is therefore very useful when direct measurements of sound power and directivity are not possible. This paper describes detailed measurements of the sound power spectrum and coherence function from a hard walled circular duct excited at one end by a diffuse sound field. The other open end is terminated within an anechoic chamber with which to measure the radiated sound field at 11 microphones distributed over a polar arc. Measurements of the complex coherence were made at the duct and used to infer the sound power spectrum and far field directivity. This paper demonstrates generally good agreement between direct measurements of sound power and directivity and those inferred from the coherence function. The method is restricted to broadband noise in large ducts in the frequency range where many modes are able to propagate and the modal amplitudes are mutually uncorrelated. Nomenclature= Duct radius = Normalised mean square mode amplitude distribution for positive and negative propagating modes = Speed of sound = Schroeder frequency = Acoustic wavenumber = Acoustic pressure = Distance along duct of measurement = In-duct microphone separation distance = Duct area = Pressure amplitude of mode *Manuscript Click here to view linked References 2 3 4 5 6 7 8

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Fan Noise Source Diagnostic Test - Wall Measured Circumferential Array Mode Results

Cited by 34 publications

References 2 publications

Advanced Noise Control Fan Direct Aeroacoustics Predictions Using a Lattice-Boltzmann Method

Advanced Noise Control Fan Direct Aeroacoustics Predictions Using a Lattice-Boltzmann Method

Physics of Acoustic Radiation from Jet Engine Inlets

Experimental investigation of a new two-microphone method for the determination of broadband noise radiation from ducts

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