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Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers
Institute for Materials, TU Braunschweig, Langer Kamp 8, Braunschweig D-38106, Germany
* Author to whom correspondence should be addressed.
Received: 30 November 2012; in revised form: 19 February 2013 / Accepted: 22 February 2013 / Published: 5 March 2013
Abstract: The growing noise exposure of residents, due to a rising number of flights, causes significant impacts on physical health. Therefore it is necessary to reduce the noise emission of aircrafts. During take-off, the noise generated by the jet engines is dominating. One way to lower the noise emission of jet engines is to build an absorption silencer by using porous liners. Because of the high thermic and corrosive attacks as well as high fatigue loads, conventional absorbers cannot be used. A promising material is sintered metal fibre felts. This study investigates the suitability of metal fibre felts for the use as absorption material in silencers. The influences of pore morphology, absorption coefficient, determined with perpendicular sound incidence, as well as geometric parameters of the silencer to the damping are identified. To characterise the material, the parameters fibre diameter, porosity and thickness are determined using three-dimensional computer tomography images. The damping potential of absorption silencers is measured using an impedance tube, which was modified for transmission measurements. The essential parameter to describe the acoustic characteristics of porous materials is the flow resistivity. It depends on the size, shape and number of open pores in the material. Finally a connection between pore morphology, flow resistivity of the metal fibre felts and damping potential of the absorption silencer is given.
Keywords: silencer; damping; porosity; pore size; impedance tube; CT scanner
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MDPI and ACS Style
Lippitz, N.; Rösler, J.; Hinze, B. Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers. Metals 2013, 3, 150-158.
Lippitz N, Rösler J, Hinze B. Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers. Metals. 2013; 3(1):150-158.
Lippitz, Nicolas; Rösler, Joachim; Hinze, Björn. 2013. "Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers." Metals 3, no. 1: 150-158.