Estimation and experiment for sound absorption coefficient of cross-sectional shape of clearance by concentric cylinder

Double cylinder structures (Yamamoto, et al., 2014), (Tamura, et al., 1999) are frequently used as machine elements and tube elements of equipments such as reactors (Fujiwara, et al., 2000), catalysts, heat exchangers (Alkan and Al-Nimr, 1999), and thermal insulators. A clearance exists between double cylinders of annular cross-section. This has engineering benefits if we can predict the acoustic properties such as the sound absorption coefficient of a sound incident on the clearance of such an annular cross-section based on the geometric dimensions of the tubes and the physical properties of the gas. With respect to the propagation of a sound wave in a narrow tubule structures, several studies have been performed on the propagation constant and particle velocity distribution (Tijdeman, 1975), complex density and complex compressibility (Stinson, 1991), complex density and complex bulk modulus (Allard and Atalla, 2009) in a circular hole, in an equilateral-triangular tube, or in between two planes (Stinson and Champou, 1992). Further, analysis using the finite element method of the vibration of the air in a rectangular tube (Beltman, et al., 1998), and on the propagation of a sound wave in the clearance created by the close packing of cylinders has also been conducted (Matsuzawa, 1963). With respect to naturally derived narrow tubes, studies have been performed on the acoustic absorption properties of straw (McGinnes, et al., 2005) and rice straw (Sakamoto, et al., 2011). The authors experimentally clarified that acoustic absorption effect in the clearance of an annular cross-section of a rice straw was useful (Sakamoto, et al., 2-8050 Ikarashi, Nishi-ku, Niigata, 950-2181, Japan