Implementation of tonal cavity noise estimations in landing gear noise prediction models

Landing gear noise is considered the dominant airframe noise source on aircraft during approach. Previous studies indicated the presence of a strong tonal sound on flyovers of several commercial aircraft types, and suggested that it was caused by the interaction of open cavities in the nose landing gear (NLG) system with the flow. Airframe noise prediction models, however, do not account for parasitic noise sources, such as cavities, which can lead to severe underpredictions of the noise levels generated by NLG systems. In this paper, a method to improve the well–known landing gear noise prediction methods of Fink and Guo is suggested. The study is based on aircraft flyover measurements performed with a microphone array which, together with acoustic imaging techniques, allows for the separation of the noise emissions coming from the NLG. Flyover recordings from several Airbus A320 aircraft under operational conditions are analyzed and, based on the tonal frequency observed, potential cavity dimensions are suggested. The sound pressure levels of the narrowband tones were found to scale with approximately the 9^th power of the airspeed. A simple correction formula for accounting for this type of cavity noise in the prediction models, depending on the aircraft velocity, is proposed. By applying this correction, the overall noise level predictions of the updated noise models become more accurate, reducing their average difference with the experimental data from 5 dB to just 1 dB.