Airfoil Trailing Edge Noise Measurements in an Open-jet, Hard-wall and Kevlar-wall Test Section: a Benchmark Exercise.

Sanders, Martinus P.J.; Koenjer, C. F. J.; Bolivar, Laura Botero; Santos, Fernanda L. dos; Venner, Cornelis H.; Santana, Leandro D. de

doi:10.2514/6.2021-2253

Cited by 3 publications

(6 citation statements)

References 11 publications

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“…The calibration follows the procedure described by Mish [42], where a GRAS 40PH microphone served as reference. Further specifications about the calibration device used and a measured frequency response can be found in the work of Sanders et al [39]. We analyze the wall-pressure measurement spectra by taking a window size of 1024 samples and applying a Hanning window to each block with a 50% overlap.…”

Section: Calibration Methods For the Wall-pressure Microphonesmentioning

confidence: 99%

“…Frequencies larger than 5 kHz are not included because the trailing-edge noise becomes less distinguishable at these frequencies due to a low signal-to-noise ratio. All integrated spectra are normalized to a reference distance of 1 m and airfoil span of 1 m. Note that the integrated levels from the CTS measurements are higher than those shown by Sanders et al [39]. This is because a mistake in the source power integration method was corrected here.…”

Section: Comparability Of the Far-field Noise 1 Absolute Noise Levelsmentioning

confidence: 99%

“…The array has a diameter of 1 m and is placed at a distance of 1.5 m from the centerline of the wind tunnel. All microphones were mounted on an open aluminum structure for minimal sound field interference (see [39]). In the HTS, the same microphone phased array is used at the same distance from the wind tunnel centerline.…”

Section: Open-jet and Hybrid Test Section Arraymentioning

confidence: 99%

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Trailing-Edge Noise Comparability in Open, Closed, and Hybrid Wind Tunnel Test Sections

et al. 2022

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Open-jet, hard-wall, and hybrid test section configurations are typically used in wind tunnel tests, aiming to represent the ideal free-flight condition. Each test section type requires special adaptations of the experimental hardware and specific correction methodologies that account for systematic measurement errors. Differently from previous research, this paper investigates the comparability of measurements performed in three test section configurations in the same wind tunnel. With this approach, systematic errors related to the facility or boundarylayer tripping methodology are minimized. Basic 2D aerodynamic boundary corrections are evaluated using a DU97W300 airfoil. The corrected lift curve collapsed well while differences in stall behavior and C p distribution at larger angles of attack are nonnegligible. The trailing-edge noise produced by a NACA-0012, NACA-0018, and NACA-63018 served as reference aeroacoustic sources in this comparability analysis. Moreover, the noise reduction from trailing-edge serrations served as an additional reference for the comparability of relative noise levels. The chord-based Reynolds number of the experiments ranged from 260,000 to 660,000. Unsteady wall pressure measurements performed near the trailing-edge provided a reference for the aeroacoustic noise source terms, demonstrating a negligible change between the different test section types. The applied experimental hardware and acoustic corrections yielded aeroacoustic sources of comparable absolute far-field noise level in the three test section types within 1 − 3 dB. The relative noise levels are comparable within 1 − 3 dB. These results show that aeroacoustic measurements of trailing-edge noise performed in different test section configurations are equivalent, provided that adequate experimental and postprocessing methodologies are systematically implemented.

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Section: Calibration Methods For the Wall-pressure Microphonesmentioning

confidence: 99%

Section: Comparability Of the Far-field Noise 1 Absolute Noise Levelsmentioning

confidence: 99%

Section: Open-jet and Hybrid Test Section Arraymentioning

confidence: 99%

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Trailing-Edge Noise Comparability in Open, Closed, and Hybrid Wind Tunnel Test Sections

et al. 2022

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“…4.1b). All microphones were mounted on an open aluminum structure for minimal sound field interference (see [Sanders et al, 2021a]). In the hybrid test section, the same microphone phased array is used at the same distance from the wind tunnel centerline (see Fig.…”

Section: Open-jet and Hybrid Test Section Arraymentioning

confidence: 99%

“…Frequencies larger than 5 kHz are not included because the trailing-edge noise becomes less distinguishable at these frequencies due to a low signal-to-noise ratio. All integrated spectra are normalized to a reference distance of 1 m and airfoil span of 1 m. Note that the integrated levels from the CTS measurements are higher than those shown in [Sanders et al, 2021a]. This is because a mistake in the source power integration method was corrected here.…”

Section: Comparability Of the Far-field Noisementioning

confidence: 99%

Aeroacoustic measurements of airframe components: in an open-jet, a hard-wall and a hybrid wind tunnel test section

Sanders

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Aircraft noise is a major source of environmental noise that negatively affects human health. Stakeholders and policymakers are nowadays increasingly confronted with protests from residents exposed to high aircraft noise levels, forcing them to change their noise policies. A solution to the aircraft noise problem is the further development and validation of more accurate noise prediction tools and noise reduction technologies. These tools and technologies are crucial to aircraft manufacturers because they help reduce uncertainties arising during the design process of a new aircraft. Wind tunnel measurements play an essential role in the development of noise prediction tools and noise reduction technologies because they provide valuable physics-based data in a controlled environment in a cost-efficient way. This data is then be used to develop or validate new (semi-)analytical noise prediction models or extend existing semi-empirical noise prediction models for new or even disruptive aircraft designs. Moreover, computational aeroacoustic (CAA) simulation tools still rely heavily on wind tunnel data for validation.Aeroacoustic measurements in wind tunnels nowadays commonly use the microphone phased array technique for the localization and quantification of sound sources. However, this type of measurement is subject to considerable uncertainty. This is mainly due to a lack of: (1) an understanding of how the wind tunnel affects the aeroacoustic measurements, (2) a general framework to correct aeroacoustic measurement to a standard free-field condition and (3) an identification and reduction of systematic errors. The work in this thesis aims at understanding and reducing the uncertainty in wind tunnel testing, thereby facilitating the development of more accurate noise prediction tools and noise reduction technologies.A literature review of the theoretical principles and basic concepts of aerodynamic noise is first presented, and airframe noise prediction models are described. Aeroacoustic measurements in wind tunnels are discussed, and a review of comparability studies found v xi keuze te maken in het selecteren van een windtunnel testsectieconfiguratie voor een specifiek doeleind. Ten slotte zullen de meetgegevens beschikbaar worden gesteld in een open database voor validatiedoeleinden, waarbij een vergelijking met metingen in andere windtunnelfaciliteiten kan worden gedaan. Met name de datsets van de NACA-63018 en 30P30N zijn beschikbaar als maatstaaf in de Hybrid Anechoic Wind Tunnel Workshop. Bovendien kunnen de 30P30N gegevens worden gebruikt in de workshop Bechmark for Airframe Noise Computations om numerieke simulaties te valideren.

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The Influence of Low-Frequency Oscillations on Trailing-Edge Tonal Noise with Symmetry Spanwise Source Regions

Song,

Liu,

Guo

et al. 2024

Symmetry

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For noise reduction at a low-to-moderate Reynolds number, airfoil trailing-edge tonal noise has multiple prominent tones. Among these tones, secondary tones are greatly influenced by external disturbances such as oscillations commonly in the environment. In previous experiments, the spatial movement of sources was found to be related to an inherent high-frequency oscillation. Therefore, the spatial influence of external low-frequency oscillations was investigated in this study. By using tripping tapes to construct different symmetry source regions on the pressure side with side secondary tones, a transient spatial analysis of an NACA0012 airfoil at 2 degrees was performed by microphone arrays when a 10 Hz pressure oscillation was significant at 24 m/s. Temporally, this 10 Hz periodic strength change became more intense at a broader frequency bandwidth for a longer source region. Furthermore, a substantial time delay, significantly larger than the sound propagating time difference between microphones, was observed exclusively along the spanwise direction. This delay led to a periodic directivity pattern, particularly when two 0.2 m source regions were separated by a 0.2 m or 0.4 m tripping region. This low-frequency oscillation introduces an asymmetric transient switching pattern for symmetric spanwise source regions. Consequently, the response of airfoils to external oscillations in field tests should be considered.

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Airfoil Trailing Edge Noise Measurements in an Open-jet, Hard-wall and Kevlar-wall Test Section: a Benchmark Exercise.

Cited by 3 publications

References 11 publications

Trailing-Edge Noise Comparability in Open, Closed, and Hybrid Wind Tunnel Test Sections

Trailing-Edge Noise Comparability in Open, Closed, and Hybrid Wind Tunnel Test Sections

Aeroacoustic measurements of airframe components: in an open-jet, a hard-wall and a hybrid wind tunnel test section

The Influence of Low-Frequency Oscillations on Trailing-Edge Tonal Noise with Symmetry Spanwise Source Regions

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