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Noise mitigation strategies
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
Acoustic treatment (also called “acoustic liner”) is routinely used in turbofan engines to absorb fan noise as it propagates through the inlet and bypass duct. Liners are locally reactive resonators that are tuned to absorb one or more frequencies of sound. They consist of a face sheet that can be porous metal or wire mesh, a honeycomb structure, and a backing plate (Fig. 4.6). The depth of the honeycomb, D, and the cell diameter, d, are varied to control the tuning frequencies. The acoustic impedance of the face sheet, which is a measure of the resistance of the liner to the incident acoustic pressure, is selected to permit acoustic waves to penetrate into the liner core in the presence of grazing flow on the liner. Sometimes multiple layers are used to increase the number of absorption target frequencies and provide better broadband attenuation. Acoustic treatment is added to the inner surface of the nacelle upstream and downstream of the fan (Fig. 4.5). It is also added to the inner bypass duct if space permits. The construction of the liner can affect its performance. Seams resulting from splicing liners together in the circumferential direction can create noise due to impedance discontinuities. Newer liners minimize the extent of the seams and have been found to reduce the extraneous noise created by the seam.
Impact properties of thermoplastic composites
Published in Textile Progress, 2018
Ganesh Jogur, Ashraf Nawaz Khan, Apurba Das, Puneet Mahajan, R. Alagirusamy
TP composites made from carbon/PEI are used as the acoustic liners in several major turbofan engines. Brackets, supporting hoses, cables, and printed circuits are the parts made from carbon/PEEK TPC and have found their applications in jet engines of many civil and military aircraft. TPC engine seals, shielding components, trusses, and other structures are also being made and planned for future engine families. The cargo floors of the CH-53K heavy–lift helicopter of US marine demonstrate effective, low-cost manufacturing and assembling of TPC. Gulfstream’s G450, G550, and G650 business jets adopted TPC floor panels and Airbus Military’s A400M cockpit flooring is also made from a variety of TPC profiles. The G650 aircraft features the first welded TPC rudder and elevator tail section, which was developed by Fokker.