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

Abstract

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.

Noise Characterization of a Full-Scale Nose Landing Gear

“…The theory of Curle [5] shows that, in such instances, the acoustic intensity or pressure squared term is proportional to V 6 . For the ALLEGRA data, V 6 proportionality was confirmed when beamforming analysis from the top (flyover) array was compared to outdoor flyover beamforming analysis of real aircraft of similar design [14]. Figure 7c shows a very satisfactory collapse of sound levels when scaled in this manner.…”

“…Such measurements enable relative magnitudes to be determined and unexpected tones to be localized to landing gear as the source region [13,14]. However, these measurement campaigns are extremely expensive to conduct, and although they are satisfactory for the verification of final design improvements, they are not cost-effective for the execution of parametric analysis.…”

Analysis of nose landing gear noise comparing numerical computations, prediction models and flyover and wind-tunnel measurements

“…Therefore, due to the strong dependence between the LG noise levels and the flow velocity [18], both LG systems usually emit comparable noise levels [19]. The object of study of this paper is the NLG system of regional aircraft, which represent a considerable share of the total flights in Europe (about 30% of the flights recorded in the campaign used in [20]).…”

“…According to Dobrzynski [4], noise prediction models based solely on wind-tunnel tests featuring scale models are prone to underestimate airframe noise levels compared to full-scale flight tests. In this paper, wind tunnel measurements [20] of the full-scale NLG model within the ALLEGRA project are considered.…”

“…2. Flyover measurements [10,19,20,23] with aircraft under operational conditions present different challenges, such as the inability to control the aircraft position, larger distances between the sound source and the observer, and less-controlled flow and atmospheric characteristics, but they fully represent the actual conditions experienced in reality [24][25][26], such as crosswind. Hence, a comparison between the results of both experiments is of great interest [16].…”