P. M. Radavich
Dept. of Mech. Eng. and Appl. Mech., 120 W. E. Lay Automotive Lab., Univ. of Mich., Ann Arbor, MI 48109-2121
Following an earlier analytical and computational work of Sahasrabudhe et al. [Noise Control Eng. J. 38(1), 27--38 (1992)], the present study investigate the effect of the length on the acoustic attenuation performance of concentric expansion chambers. Three approaches are employed here to determine the transmission loss: (1) a two-dimensional, axisymmetric analytical solution; (2) a three-dimensional computational solution based on the boundary element method; and (3) experiments on an extended impedance tube setup with nine expansion chambers fabricated with the fixed inlet and outlet duct, and chamber diameters, and varying chamber length to diameter ratios from l/d=0.2--3.5. The results from all three approaches are shown to agree well. The effect of multidimensional propagation is discussed in comparison with the classical treatment for the breakdown of planar waves. The study also provides a simple relation between the l/d ratio of the expansion chamber and the number of repeating attenuation domes prior to the domination of higher-order modes.