Measurement and control of aircraft landing gear broadband noise

Noise generated by aircraft landing gear is a major contributor to the overall airframe noise during landing approach of a commercial aircraft. Fairings covering geometrically complex areas of the gears have proved to be very effective in noise reduction, but in tests on an A340 main landing gear the overall benefits of the fairings were offset by an increase in low-frequency noise. In this study the measurement and control of broadband noise throughout the frequency range have been investigated using a 1/4 scale A340 main landing gear model that has been tested using a range of different measurement methods and wind facilities. Experiments were firstly conducted in a conventional closed-section wind tunnel using two phased microphone arrays mounted on the ceiling and sidewall of the tunnel respectively, and noise control strategies with modified fairings were developed. Noise tests were then performed in an open-jet aeroacoustic facility using far-field microphones to verify the wind-tunnel test results. Comparison between the two tests showed that the relatively smaller noise-reduction potential of the fairings measured in wind tunnel was due to the higher flow blockage of the tunnel. Nevertheless, the experiments indicated that the phased microphone arrays could be applied to measure the noise reductions achieved by noise control treatments with reasonable accuracy, especially in mid- and high-frequency range. The aeroacoustic facility test results were finally projected to full scale and compared to the full-scale model wind-tunnel test. Both results were shown to agree over a wide frequency range, indicating the validity of the tests on the 1/4 scale model.