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.

The noise emissions of a full-scale nose landing gear, measured in a wind tunnel and obtained from computational simulations, are compared with those of three regional aircraft types recorded in flyover measurements. The results from these three approaches are also compared with the predictions of two airframe noise models (Fink and Guo). The geometries of the nose landing gears in all cases were similar. Microphone arrays and acoustic imaging algorithms were employed to estimate 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. On the other hand, strong tonal peaks (at around 2200 Hz) were only found for the flyover tests and computational simulations and are not present in typical noise prediction models. As the frequencies of the tones did not depend on the flow velocity, they are likely 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. The noise emissions in the side direction did not present tonal peaks. The acoustic source maps showed that the dominant noise sources were located in the middle of the wheel axle, followed by the main strut and the bay doors. 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 with the use of cavity caps, for example.

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The noise emissions of a full-scale nose landing gear (NLG), measured in a wind tunnel and obtained from computational simulations, are compared with those of three regional aircraft types recorded in flyover measurements. A comparison is made with the noise prediction models of Fink, Guo, and DLR. A good agreement was found between all the spectra. The noise emissions up to 1.2 kHz were found to scale with the 6 th power of the flow velocity, as usual; however, the spectra at higher frequencies collapsed better when scaled to the 7 th power, confirming the fact that high-frequency noise is radiated from the turbulent flow surrounding small features of the NLG.

The reduction of noise generated by aircraft at take-off and approach is crucial in the design of new commercial aircraft. Landing gear noise is significant contribution to the total noise sources during approach. The noise is generated by the interaction between the non-aerodynamic components of the landing gear and the flow, which leads to turbulence generated noise. This research presents results from the European Clean Sky funded ALLEGRA project. The project investigated a fullscale Nose Landing Gear (NLG) model featuring the belly fuselage, bay cavity and hydraulic dressing. A number of low noise treatments were applied to the NLG model including a ramp door spoiler, a wheel axel wind shield, wheel hub caps and perforated fairings. Over 250 far field sensors were deployed in a number of microphone arrays. Since technologies were tested both in isolation and in combination the additive effects of the technologies can be assessed. This study describes the different techniques used to quantify the contribution of each technology to the global noise reduction. The noise reduction technologies will be assessed as a function of frequency range and through beamforming techniques such as source deletion.