Airframe Noise Reduction Technologies applied to High-Lift Devices of Future Green Regional Aircraft

Paper in proceeding, 2014

Regional aircraft typically operate over airports located in the neighbourhood of densely populated areas, with high frequency of take-off / landing events and, hence, they strongly contribute to community noise and gaseous emissions. These issues currently limit further growth of traffic operated by regional airliners which, in the next future, will have to face even more stringent environmental constraints worldwide as prescribed by the civil aviation certification normative and local regulations as well. Therefore, in accordance with ACARE Vision 2020 toward a drastic reduction of air transport environmental impact over next decades, several mainstream technologies have been considered in the frame of Clean Sky JTI – Green Regional Aircraft (GRA) ITD project for application to next-generation regional aircraft. Such technologies are concerning: i) advanced aerodynamics and load control to maximise lift-to-drag ratio in both design and off-design conditions of the whole flight mission profile, thus reducing fuel consumption/ air pollutants emission and also allowing for steeper/ noise-abatement initial climb paths; ii) load alleviation to avoid loads from gust encounter and manoeuvre exceeding given limits, thus optimising the wing structural design for weight saving; iii) low airframe noise to reduce aircraft acoustic impact in approach flight condition. High-Lift-Devices (HLD) in fully-deployed settings represents one of the main sources of aircraft community noise during the approach flight phase and of consequent annoyance perceived by the resident population in the vicinity of airports. Therefore, in the overall scenario as above outlined, several HLD architectures, integrating either matured or more advanced low-noise concepts/technical solutions still preserving high-lift performances, have been investigated in the frame of the GRA ITD project. These HLD have been tailored to different classes/ configurations of future regional aircraft, ranging from high-wing 90-seat Turboprop to low-wing 130-seat Turbofan with different power-plant and engine installation. Technological studies of High-Lift Low-Noise devices carried out in the framework of the GRA ITD project have been presented. Both computational analyses and wind tunnel tests have been described in detail. Some passive acoustic devices have been firstly analysed with different numerical approaches. First of all, the use of conventional liners, as acoustic treatments carefully integrated with the wing, have revealed to be effective in noise detection for a wide range of frequencies. Also side-edge fences have demonstrated a promising aptitude in suppression of the turbulent vortex occurring around the flap side-edge. These encouraging results have been also confirmed during an extensive WT test campaign. Finally, multi-objective optimizations and the numerical assessment of several configurations have been performed by applying both aerodynamic and aeroacoustic methodologies. These studies have showed the successfully design of high-lift technologies with a low noise impact. The most promising among the addressed HLD technologies will be brought to the final demonstration phase within the GRA ITD work programme, in order to assess in a realistic experimental environment (TRL 5) the aircraft low-speed aerodynamic and aero-acoustic performances through WT tests on large-scale (say 1:6) complete A/C powered models.