Aeroacoustic Measurements

Allen, Christopher S.; Blake, William K.; Dougherty, Robert P.; Lynch, Denis A.; Soderman, P. T.; Underbrink, James R.

doi:10.1007/978-3-662-05058-3

Cited by 52 publications

(46 citation statements)

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“…To compute source maps, shown in Fig. 5 (a) and (b) for the baseline and the perforated insert with l h = 3 mm case respectively, Conventional Frequency Domain Beamforming (CFDBF) [33] is applied to a square grid ranging between -2 < X/c < 2 and -2 < Z/c < 2 with 1 cm distance between grid points. The minimum distance at which the array can distinguish two sources R c is given by the Rayleigh criterion [34] as R c = d tan(1.22c 0 /( f D)), where c 0 refers to the speed of sound.…”

Section: Fig 4 Distribution Of the Microphones Within The Array Thementioning

confidence: 99%

3D-printed Perforated Trailing Edges for Broadband Noise Abatement

Carpio

Avallone

Ragni

et al. 2019

25th AIAA/CEAS Aeroacoustics Conference

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Turbulent boundary layer trailing-edge noise scattered by a NACA0018 airfoil equipped with 3D printed perforated trailing-edge inserts, i.e. with straight cylindrical channels connecting the two sides of the airfoil, is investigated. The inserts have different permeability in order to assess the effect of this property on broadband noise generation. Far-field noise is measured with a phased microphone array. The experiments are performed at free-stream velocities of 26 and 41 m/s, corresponding to chord-based Reynolds numbers of 3.4×10 5 and 5.4×10 5 , and at angles of attack of 0 and 4.8 •. The inserts, with permeability values of 1.5×10 −9 and 5.4×10 −9 m 2 , attenuate respectively up to 5 and 9.5 dB at 0 • and up to 4 and 7.5 dB at 4.8 • incidence. The noise abatement of inserts with straight passages is compared with that of inserts manufactured using metallic foams with a random pore distribution but similar permeability. It is found that to achieve similar overall noise attenuation levels, the perforated inserts require at least 3 times higher permeability than the metal foam inserts. From this we conclude that in order to maximize the noise attenuation potential of permeable inserts, the inner structure of the permeable trailing-edge insert must be considered.

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Section: Fig 4 Distribution Of the Microphones Within The Array Thementioning

confidence: 99%

3D-printed Perforated Trailing Edges for Broadband Noise Abatement

Carpio

Avallone

Ragni

et al. 2019

25th AIAA/CEAS Aeroacoustics Conference

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“…Two measurement sets were made for each angle of incidence, with and without the airfoil, in order to estimate the background noise. With the finality to isolate the TE noise, a cross-spectral analysis of Sound Pressure Level (SPL) measurements was employed using the microphone pair [25]. Additionally, as TE noise must be significantly higher than background noise in order to be considered, a criterion for rejection was established.…”

Section: Acoustic Measurementsmentioning

confidence: 99%

LES-based numerical prediction of the trailing edge noise in a small wind turbine airfoil at different angles of attack

et al. 2018

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In this paper, the aerodynamic field around a FX 63-137 airfoil for four angles of attack and low Reynolds numbers was simulated with a Large Eddy Simulation (LES). Following, an acoustic analogy method was employed to calculate the airfoil trailing edge (TE) noise. In this second scheme step, the far-field acoustic pressure was predicted from the LES source terms using two different methods based on Lighthill's analogy: Curle's surface approach and Ffowcs-Williams and Hall's volumetric analogy (FW-Hall). Numerical results have been validated with hot-wire anemometry for the aerodynamic fields, thus verifying the accuracy of the CFD simulation for the prediction of noise propagation to the far field. Additionally, aeroacoustic results were validated with experimental measurements carried out in an anechoic wind tunnel using a frequency analyzer. The FW-Hall formulation shows a better agreement with the experiments, especially in the range of frequencies corresponding to the trailing edge, whereas Curle's analogy overpredicts airfoil sound. An exhaustive analysis of the aerodynamic flow field has been performed in order to better understand the generation mechanisms of the TE noise. The aeroacoustic calculations presented in this work contribute to develop a more reliable and efficient prediction methodology based on the Computational Aeroacoustics Approach (CAA).

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“…The effective aperture radius accounts for the propagation direction of the incident waves 19 . For a point on the scan plane located at a radial distance of r s from the origin and for a horizontal distance between the scan plane and the array of z s (Fig.…”

Section: Approximation Of Psf For Rotating Source Beamformingmentioning

confidence: 99%

“…For a point on the scan plane located at a radial distance of r s from the origin and for a horizontal distance between the scan plane and the array of z s (Fig. 1), the nearfield effective aperture radius is given by (Allen et al 19 ),…”

Section: Approximation Of Psf For Rotating Source Beamformingmentioning

confidence: 99%

Airy pattern approximation of a phased microphone array response to a rotating point source

Debrouwere

Angland

2017

The Journal of the Acoustical Society of America

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Deconvolution of phased microphone array source maps is a commonly applied technique in order to improve the dynamic range and resolution of beamforming. Most deconvolution algorithms require a Point Spread Function (PSF). In this work, it is shown that the conventional definition of the PSF, based on steering vectors, is changed when the source is rotating. The effect of rotation results in an increase in the resolution and aperture of the array. The concept of virtual array positions created by source rotation is used to derive an approximation of the PSF based on an Airy pattern. The Airy pattern approximation is suitable for use in deconvolution of rotating source maps as it is more accurate and is computationally less expensive than the conventional PSF definition. The proposed Airy pattern approximation was tested with both CLEAN and DAMAS deconvolution algorithms. On the same hardware, it was significantly faster when compared to the conventional definition. The limitations of the Airy pattern approximation are shown in a synthesized broadband test case with a high dynamic range. However, in most practical beamforming applications, the proposed Airy pattern approximated PSF for deconvolution is a suitable option considering its accuracy and speed.

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Aeroacoustic Measurements

Cited by 52 publications

References 0 publications

3D-printed Perforated Trailing Edges for Broadband Noise Abatement

3D-printed Perforated Trailing Edges for Broadband Noise Abatement

LES-based numerical prediction of the trailing edge noise in a small wind turbine airfoil at different angles of attack

Airy pattern approximation of a phased microphone array response to a rotating point source

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