Development and Testing of a Novel Acoustic Wind Tunnel Concept

Smith, Benjamin S.; Camargo, Hugo E.; Burdisso, Ricardo A.; Devenport, William J.

doi:10.2514/6.2005-3053

Cited by 19 publications

(9 citation statements)

References 5 publications

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“…Microphones recessed in a cavity are offered commercially too [50]. A more radical solution for the TBL issues is to replace the wind-tunnel walls by Kevlar sheets, as in the stability tunnel of the Virginia Polytechnic Institute and State University [51]. In addition, acoustic measurements are hampered by reflections by the test section walls [19,20].…”

Section: Closed-test Sectionsmentioning

confidence: 99%

A review of acoustic imaging methods using phased microphone arrays

et al. 2019

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Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most wellknown and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

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Section: Closed-test Sectionsmentioning

confidence: 99%

A review of acoustic imaging methods using phased microphone arrays

et al. 2019

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“…A compromise solution is a hybrid wind tunnel configuration, which consists in replacing the hard windtunnel walls of the closed-section configuration with acoustically transparent walls, such as tensioned Kevlar sheets [34], like in the stability tunnel of the Virginia Polytechnic Institute and State University [35,36] or the Poul la Cour wind tunnel of the Technical University of Denmark. This hybrid configuration has the advantages of both closed-section (better controlled aerodynamic properties) and open-jet wind tunnels (placement of the microphones and instrumentation outside the flow), but the conversion of currently existing facilities into hybrid wind tunnels can become a challenging and costly process.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of advanced acoustic imaging methods for microphone--array measurements in closed--section wind tunnels

Martinez

VanDercreek

Snellen

2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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Aeroacoustic measurements with microphones in closed-section wind tunnels are typically hampered by the pressure fluctuations of the turbulent boundary layer (TBL) on the tunnel's walls, ceiling, or floor, where phased microphone arrays are usually mounted. This paper evaluates the performance of several advanced acoustic imaging methods that aim at overcoming this limitation for localizing and quantifying sound sources in closed-section wind-tunnel measurements. The acoustic data employed was obtained using a phased microphone array installed in two different configurations: flush-mounted on the wind-tunnel wall and recessed within cavities behind an acoustically transparent covering. The acoustic imaging methods considered are conventional frequency domain beamforming (CFDBF, as a baseline), functional (projection) beamforming (FUNBF), orthogonal beamforming (OB), CLEAN-SC, and the deconvolution approach for the mapping of acoustic sources (DAMAS). Two sound sources are analyzed: (1) a single speaker emitting broadband sound as a reference signal, and (2) a flat plate inside of the flow as a distributed aeroacoustic source. In general, it is observed that the array with cavities provides considerably better results as it benefits from a higher signal-to-noise ratio. In addition, removing the main diagonal from the cross-spectral matrix also helps obtaining clearer acoustic source maps and more accurate quantitative sound spectra estimations. Overall, DAMAS and OB are the best performing methods for the case with a single speaker. CFDBF and FUNBF are the most suitable methods for the case with the distributed sound source of the trailing edge of the flat plate, whereas the other techniques fail to properly identify it.

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“…The pores directly connect regions of the suction and the pressure sides, allowing a point-to-point communication between both sides. On the other hand, a stretched Kevlar fabric, which has widely been used in aeroacoustic applications to replace hard walls of closed-section wind tunnels to allow for acoustic measurements [32][33][34][35][36] due to their ability to be acoustically transparent while being aerodynamically impermeable, 33,34 is used to cover the surface of the 3D-printed perforated structure. There are two main purposes; first, the relatively smooth texture of the Kevlar fabric is expected to mitigate the roughness noise; second, the flow-impermeable Kevlar fabric is used to cover the regular highly permeable 3D-printed pattern to prevent the tonal noise generation.…”

Section: Introductionmentioning

confidence: 99%

An alternative permeable topology design space for trailing-edge noise attenuation

Luesutthiviboon

Ragni

Avallone

et al. 2021

International Journal of Aeroacoustics

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This study focuses upon a new permeable topology design concept as an alternative to porous metal foams, for turbulent boundary layer trailing-edge (TBL-TE) noise attenuation. The present permeable topology has unconventional characteristics with respect to the metal foams: a combination of low flow resistivity r and high form drag coefficient C. The unconventional characteristics are realized by a Kevlar-covered 3D-printed perforated structure. An experimental study featuring a NACA 0018 airfoil model with a Kevlar-covered 3D-printed TE insert at chord-based Reynolds numbers up to [Formula: see text] is carried out. The airfoil with this TE insert gives a broadband TBL-TE noise reduction up to approximately 5 dB, compared to a solid TE. This reduction varies only slightly with airfoil loading (lower than 1 dB variation), in contrast to the porous metal foams (up to 3 dB variation). When comparing the variation of noise attenuation given by all the permeable materials considered, the variation is found to decrease with the increasing C. This is because C specifies the permeable material's ability to withstand the increasing pressure difference, which causes cross flow that might interfere with the noise attenuation mechanism. Additionally, the drag coefficients as well as the roughness noise of the airfoil equipped with the present TE insert are also significantly lower than those of the metal-foam TE, and are mostly negligible compared to the fully solid airfoil. Based on the findings, design guidelines for permeable TE are proposed: the permeable material shall have a combination of a low flow resistivity and a high form drag coefficient as well as a negligible surface roughness.

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Development and Testing of a Novel Acoustic Wind Tunnel Concept

Cited by 19 publications

References 5 publications

A review of acoustic imaging methods using phased microphone arrays

A review of acoustic imaging methods using phased microphone arrays

Evaluation of advanced acoustic imaging methods for microphone--array measurements in closed--section wind tunnels

An alternative permeable topology design space for trailing-edge noise attenuation

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