Fly-over source localization on civil aircrafts

Simons

2017

Journal of Aircraft

Enforcing noise control environmental laws around airports is a difficult task due to the large variability in the noise levels observed for flyovers of the same aircraft type under similar conditions. These variations are not properly considered by the current models, such as the Noise-Power-Distance tables. In this research, noise measurements of aircraft flyovers are used to assess this variability and investigate its causes. 115 flyovers of landing aircraft were recorded using a 32 microphone phased array. It was assumed that the main cause of this variability is the change of the emitted aircraft noise, as previous studies showed that the effect of the variable atmosphere (for the distances considered) is negligible. The noise level variability for the Boeing 737 and Fokker 70 cases was approximately 7 dB. The fan rotational speed of each flyover was determined by analyzing the spectrograms. Functional beamforming was applied to the acoustic data. For the Boeing 737 case it was found that the engines are the dominant noise source for all flyovers and that over 75% of the variation of the noise levels can be explained by variations in the engine settings. The Fokker 70 flyovers were dominated by airframe noise sources. Differences in the aircraft velocity explain almost 70% of the noise level variability in this case.

Section: B Functional Beamformingmentioning

confidence: 99%

Assessment of Noise Variability of Landing Aircraft Using Phased Microphone Array

Snellen

Simons

2017

Journal of Aircraft

“…The de-Dopplerized acoustic signals were employed and the movement of the source was taken into account in the beamforming formulation [18,24,36]. Removing the main diagonal of the CSM for this algorithm is prone to significant errors, since the method relies on the eigenvalue decomposition of the CSM [37].…”

Section: Iiib Methods For the Flyover Measurementsmentioning

confidence: 99%

Comparing flyover noise measurements to full-scale nose landing gear wind tunnel experiments for regional aircraft

23rd AIAA/CEAS Aeroacoustics Conference

Neri

Snellen

et al. 2017

The noise emissions of the nose landing gear of a full-scale model tested in a wind tunnel, and of three regional aircraft types in flyover measurements are compared in this contribution. The geometries of the nose landing gears in all cases were similar. Microphone arrays and beamforming algorithms were used to determine the sound emissions of the nose landing gears. A good agreement was found between the overall trends of the frequency spectra in all cases. Moreover, the expected 6 th power law with the flow velocity was confirmed for both experiments. On the other hand, strong tonal peaks (at around 2200 Hz) were only found for the flyover tests. As the frequencies of the tones do not depend on the aircraft velocity, they are thought to be caused by cavities found in structural components of the nose landing gear. Removing these tones would cause overall noise reductions up to 2 dB in the frequency range examined. It is, therefore, recommended to further investigate this phenomenon, to include cavity-noise estimations in the current noise prediction models, and to eliminate such cavities where possible.

“…This method is based on the conventional frequency domain beamforming (CFDBF) algorithm, also known as delay-andsum, which is the most widely used method for aeroacoustic experiments [6,[13][14][15][16][17][18]. The performance of functional beamforming depends on an exponent parameter ν which needs to be set by the user.…”

Section: B Functional Beamformingmentioning

confidence: 99%

Analysis of landing gear noise during approach

22nd AIAA/CEAS Aeroacoustics Conference

Bertsch

Simons

et al. 2016

Airframe noise is becoming increasingly important during approach, even reaching higher noise levels than the engines in some cases. More people are affected due to low flight altitudes and fixed traffic routing associated with typical approaches. For most aircraft types, the landing gear system is a dominant airframe noise source. However, this element can only be modeled in an approximate manner in wind tunnel experiments. In this research, flyovers of landing aircraft were recorded using a 32 microphone array.Functional beamforming was applied to analyze the noise emissions from the landing gear system. It was confirmed that for some aircraft types, such as the Airbus A320 and the Fokker 70, the nose landing gear is a dominant noise source during approach. The correlation between the noise levels generated by the landing gear and the aircraft velocity was found to be significant, explaining about 70% of the variability found in the noise levels, which is in good agreement with all known theory. Moreover, the experimental results for the Airbus A320 measurements were compared with those obtained using the DLR system noise prediction tool PANAM. Whereas the total aircraft noise levels were in good agreement, the measurements indicate a higher contribution from the nose landing gear noise compared to the predictions.