Comparison between analog and digital phased microphone arrays for aeroacoustic measurements

25th AIAA/CEAS Aeroacoustics Conference

Vieira

Snellen

et al. 2019

Self Cite

Aircraft noise is an increasingly important issue that causes annoyance and complaints for the communities living in the vicinity of airports. The conventional sound metrics (such as the A-weighted sound pressure level) typically used for assessing the impact of aircraft noise often fail to conveniently represent the actual annoyance experienced. More sophisticated sound quality metrics (such as loudness, tonality and sharpness) can be used to determine the psychoacoustic annoyance perceived by the human ear. In this paper, an Airbus A320 landing flyover under operational conditions recorded with a microphone array is analyzed. The application of functional beamforming to the acoustic data allows for the separation of the emissions of different noise sources on board of the aircraft. For this case, the nose landing gear (NLG) and the turbofan engines were selected, due to their expected dominance during approach. It was found that, despite being more quiet than the turbofan engines, the NLG system emits a strong tonal sound that makes it overall more annoying than the noise of the engines. Airframe noise prediction models (Fink's and Guo's methods) do not consider this tone and considerably underpredict the noise levels and the annoyance of the NLG. Thus, it is highly recommended to employ these sound quality metrics to study aircraft noise and to evaluate the potential improvement in annoyance of future low-noise aircraft concepts, rather than just a difference in the sound pressure level in decibels.

Section: Acoustic Imaging Methods and Sound Propagationmentioning

confidence: 99%

Sound quality metrics applied to aircraft components under operational conditions using a microphone array

25th AIAA/CEAS Aeroacoustics Conference

Vieira

Snellen

et al. 2019

Self Cite

“…The results can be extended to different airfoil geometries, such as for the NACA 0018 case analyzed here. The higher thickness of the NACA 0018 airfoil with respect to the NACA 0012 one is expected to cause slightly higher noise emissions [63]. This model provides the predicted noise spectra in one-third-octave bands based on the given Reynolds number, effective angle of attack, airfoil's chord and span, and the observer's location.…”

Section: Frequency Spectramentioning

confidence: 99%

Assessment of the accuracy of microphone array methods for aeroacoustic measurements

Journal of Sound and Vibration

Luesutthiviboon

Zamponi

et al. 2020

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In this paper, the performance of four acoustic imaging methods: conventional frequency domain beamforming (CFDBF), functional beamforming (FUNBF), enhanced high resolution CLEAN-SC (EHR-CLEAN-SC) and generalized inverse beamforming (GIBF), is investigated in terms of accuracy and variability. Three experimental test cases are considered: 1) a single speaker emitting synthetic broadband noise, 2) two speakers emitting incoherent synthetic broadband noise, and 3) trailing-edge noise generated by a tripped NACA 0018 airfoil. All the measurements were performed in the anechoic wind tunnel of Delft University of Technology. Overall, GIBF and EHR-CLEAN-SC offer the most accurate results when point sources (speakers) are present. They even achieve super-resolution by separating sound sources beyond the Rayleigh resolution limit. Repeating the measurements indicates a standard deviation in the results of less than 1 dB. When analyzing distributed sound sources, such as trailing-edge noise, CFDBF and FUNBF provide the best performance. This indicates that the acoustic imaging method needs to be selected based on the expected sound source configuration.

“…However, the coherence length of a source is typically much smaller than the main lobe width, so the assumption of distributed incoherent monopoles is, in essence, valid. 43 This technique has already been applied to trailing-edge noise measurements in an openjet 14 and a closed-section wind tunnel 14,48 and a closed-section wind tunnel 16 with very satisfactory results.…”

Section: Source Power Integrationmentioning

confidence: 99%

Integration methods for distributed sound sources

International Journal of Aeroacoustics

Sijtsma

Carpio

et al. 2019

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Most acoustic imaging methods assume the presence of point sound sources and, hence, may fail to correctly estimate the sound emissions of distributed sound sources, such as trailing-edge noise. In this contribution, three integration techniques are suggested to overcome this issue based on models considering a single point source, a line source, and several line sources, respectively. Two simulated benchmark cases featuring distributed sound sources are employed to compare the performance of these integration techniques with respect to other well-known acoustic imaging methods. The considered integration methods provide the best performance in retrieving the source levels and require short computation times. In addition, the negative effects of the presence of unwanted noise sources, such as corner sources in wind-tunnel measurements, can be eliminated. A sensitivity analysis shows that the integration technique based on a line source is robust with respect to the choice of the integration area (shape, position, and mesh fineness). This technique is applied to a trailing-edge-noise experiment in an open-jet wind tunnel featuring a NACA 0018 airfoil. The location and far-field noise emissions of the trailing-edge line source were calculated.