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 well-known 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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A review of acoustic imaging methods using phased microphone arrays

Functional beamforming is a state-of-the-art nonlinear algorithm based on the conventional frequency domain beamformer. In general, it is found to provide improved array spatial resolution and dynamic range. The computational time required for the functional beamforming is approximately the same as that for the conventional frequency domain beamformer and, in general, notably shorter than those of the deconvolution methods. In this paper, several simulations are presented comparing the performance of this algorithm with other imaging methods. Moreover, this beamforming technique is applied to 115 flyover measurements performed with a 32 microphone array on landing aircraft. The simulated and experimental results show good agreement. It is found that, for both synthetic and experimental data, functional beamforming offers better quality acoustic images, with a dynamic range (i.e., the difference in decibels between the main lobe and the highest sidelobe) approximately 30 times larger and an array spatial r...

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Functional Beamforming Applied to Imaging of Flyover Noise on Landing Aircraft

/pdf/comparing-flyover-noise-measurements-to-full-scale-nose-2q3ta8x2z1.pdf

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

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. Formost air- craft 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. Fun ctional beamforming was
applied to analyze the noise emissions from the landing gear system. lt 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 du ring approach.
The correlation between the noise levels generated by the landing gear and the aircraft velocity was found to be
significant, explai ning about 70% of the varia bility found in the noise levels, which is in good agreement with all
known theory. Moreover, the experimental resu lts 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.

/pdf/analysis-of-landing-gear-noise-during-approach-3jjb5qto31.pdf

Analysis of landing gear noise during approach

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 conditi...

Assessment of Noise Variability of Landing Aircraft Using Phased Microphone Array

In June 2012, fly-over measurements were performed on landing aircraft at P.-E. Trudeau Montreal airport. A custom-made measurement system developed by GAUS (Groupe d’Acoustique de l’Universite de Sherbrooke) including a 95-microphone array with its related audio pre-amplifying and recording system have been used to acquire a comprehensive data set of over 300 flyovers during a five-day period. A particular focus has been made on Bombardier CRJ200 aircraft for which several flight conditions have been measured. Trajectories of aircraft were tracked by a synchronized 2-camera system. Precise localizations of landing gear, flaps and engine have been obtained as preliminary results. The article details source identification results as well as the complete experimental set-up and the algorithms used in de-dopplerization and Beamforming computations.

M. Patenaude-Dufour

Papers

Fly-over source localization on civil aircraft