Abstract
The landing gear system is the dominant airframe noise source for most modern commercial aircraft during approach. This manuscript reports the results from the ALLEGRA (Advanced Low Noise Landing (Main and Nose) Gear for Regional Aircraft) project. This project assessed the performance of several highly realistic low–noise technologies (LNTs) applied to a detailed full–scale nose landing gear (NLG) model in aeroacoustic wind–tunnel experiments. Four individual low–noise concepts tested, namely a ramp door spoiler, a solid wheel axle fairing, wheel hub caps, and multiple perforated fairings. Combinations and small variations of some of these LNTs were also evaluated. The use of multiple planar microphone arrays allowed for the application of 2D and 3D acoustic imaging algorithms to assess the location and strength of the noise sources within the NLG system in different emission directions for each configuration. The wheel axle, the inner wheel hubs, the steering pinions and the torque link were identified as the noisiest NLG elements. The solid wheel axle fairing was the most effective individual LNT, and it improved its performance when applied in combination with the ramp door spoiler and wheel hub caps, reaching overall noise reductions of more than 4 dBA.
Highlights
Noise emissions generated by aircraft cause severe annoyance to tens of millions of people living in the vicinity of airports and pose environmental constraints for airport operations, with the consequence of revenue loss
With specific focus on the noise generated by the nose landing gear (NLG) wheels, a third set of conclusions found that the wheels generated noise in the 315 Hz, 630 Hz and 1.25 kHz one–third–octave bands, with the latter two frequency ranges being shown to result from inter–wheel noise sources
All the LNTs tested show an almost omnidirectional pattern in their noise reductions. This manuscript has investigated the acoustic performance of several low–noise technologies (LNTs) applied to a full–scale nose landing gear (NLG) in open–jet wind–tunnel measurements
Summary
Noise emissions generated by aircraft cause severe annoyance to tens of millions of people living in the vicinity of airports and pose environmental constraints for airport operations, with the consequence of revenue loss. The successful development of low– noise propulsion technologies has increased the significance of airframe noise in modern commercial aircraft [1]. In order to fulfil the ambitious aircraft noise reduction requirements set by governmental organisations, such as ACARE [2] (Advisory Council for Aviation Research and Innovation in Europe), and projects such as Flight Path 2050 [3], airframe noise levels need to be further reduced, as they set the threshold to aircraft noise in the future [4,5]. With respect to environmental noise, the landing gear (LG) system is often the dominant airframe noise source during approach and landing [6,7,8] depending on the aircraft. Because of its critical importance for the aircraft’s safety, this system has little aerodynamic and aeroacoustic refinement to ease its inspec-
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