Analysis of landing gear noise during approach

Abstract

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.

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

“…This is especially the case for Aircraft Type C, for which a tone, more than 12 dB higher than the broadband noise around it, is found. This phenomenon was already observed for other full-scale aircraft types by Michel and Qiao [4], by Dedoussi et al [13] and by Merino-Martínez et al [9,18], and for full-scale landing gears of an Airbus A340 in wind-tunnel experiments by Dobrzynski et al [12]. In these publications, it was proposed that the cause for these tonal peaks was the presence of open pin-cavities in the NLG system.…”

“…Even if the MLG is typically larger than the NLG and has a more complex structure (and hence is expected to be noisier), the flow velocity impinging the MLG system is approximately 20% lower than that of the NLG due to the recirculation of the flow underneath the wings [8]. Therefore, the noise levels of both LG systems usually have comparable values [9]. A typical sound signal from a LG system is a combination of broadband noise, mainly caused by the interaction of the LG with the turbulent flow, and tonal noise, generated by noise due to cavities [10,11] and Aeolian tones due to flow separation and vortex shedding [12,13].…”

“…Several aircraft noise prediction models do not consider parasitic noise sources, such as cavity noise, in their calculations, which can lead to differences with the measured noise levels [9].…”

“…To obtain a better understanding of the actual noise emissions of LG systems, wind-tunnel [12,[14][15][16][17] and aircraft flyover experiments [4,9] are typically performed. Whereas the first case offers more controlled flow conditions, it requires the LG model being tested to have a high level of geometric detail to represent the small-scale sound generating mechanisms of the gear [4,5] and it is difficult to replicate the exact conditions present at an aircraft in flight.…”

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

“…Even though the MLG structure is typically larger and more complicated than the NLG (i.e., it is expected to be noisier), the flow velocity impinging the MLG system is approximately 20% lower than that of the NLG because of the recirculation of the flow underneath the wings [17]. 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]).…”