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 Ongoing project research efforts are focused on reducing noise produced by the engines and airframe of subsonic fixed-wing aircraft.
Technologies for engine noise reduction include Ultra-High-Bypass (UHB) engines, such as the geared turbofan engine; soft vane, over-the-rotor foam metal liners; distortion-tolerant fans with active noise control; and variable area fan nozzles. Multifunctional materials and structures containing metallic and polyimide foams and aerogel materials are being developed for application in long ducts and fan containment systems to simultaneously carry load and reduce noise.
Airframe noise reduction research includes continuous mold-line wing structures; drooped leading edge; active flow control; adaptive and flexible wing structure; smart chevrons; and toboggan fairing for landing gear noise reduction.
Novel Hybrid Wing Body (HWB) configurations are now in development and testing that integrate airframe and propulsion systems. The HWB dramatically reduces noise and will help to achieve N+2 goals for the 2020 timeframe. One example is the Blended Wing Body (BWB) configuration that can achieve significant noise reduction through airframe shielding of engine noise.
Computational tools with improved noise prediction capability are being developed to identify promising noise reduction technologies. Advanced flow and noise diagnostic techniques are helping researchers to better understand the sources of airframe, fan, and jet noise, with a focus on detailed spatial and temporal characterization of noise generation mechanisms. Prediction capabilities are focused on rotor-stator interaction noise, slat and landing gear airframes noise, flow interaction and acoustic scattering for integrated propulsion-airframe systems, and the integration of various tools into the Aircraft Noise Prediction Program (ANOPP).
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