Multi-approach study of nose landing gear noise

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 German Aerospace Center (DLR). A good agreement was found between all the spectra. The noise emissions up to 1.2 kHz were found to scale with the sixth power of the flow velocity, as usual; however, the spectra at higher frequencies collapsed better when scaled to the seventh power, confirming the fact that high-frequency noise is radiated from the turbulent flow surrounding small features of the NLG. Microphone arrays showed that the main noise sources were located in the middle of the wheel axle. For the flyovers and computational simulations, strong tonal peaks (at around 2200 Hz) were found, which are likely to be caused by open cavities in the NLG. This phenomenon is not accounted for in prediction models. Removing these tones would result in noise reductions of up to 2 dB. Thus, it is highly recommended to include cavity-noise estimations in the current prediction models, or to simply eliminate such cavities where possible with the use of cavity caps.