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A technique is proposed that uses a multi-scale approach to calculatetransport properties of compressed felts using only image analysis andnumerical calculations. From the image analysis fiber diameter distribution andfiber orientation are determined. From a known porosity and the latter twocharacteristics, two representative elementary volumes (REV) are constructed:one based on the volume-weighted average diameter and one on an inversevolume-weighted average diameter. Numerical calculations on the former showedthat it correctly estimates viscous and thermal permeabilities, while thelatter correctly estimates tortuosity and viscous and thermal characteristiclengths. From these calculations, micro-macro analytical expressions aredeveloped to estimate the transport properties of polydisperse composite feltsbased solely on open porosity, fiber diameter polydiversity, and fiberorientation. Good agreements are obtained between analytical predictions andmeasurements of transport properties. The predicted transport properties arealso used in the Johnson-Champoux-Allard-Lafarge (JCAL) equivalent fluid modelto predict the sound absorption coefficient of the felts. Excellent agreementsare obtained with impedance tube measurements.

Effect of polydispersity on the transport and sound absorbing properties of three-dimensional random fibrous structures