ACOUSTIC ATTENUATION PERFORMANCE OF CIRCULAR EXPANSION CHAMBERS WITH EXTENDED INLET/OUTLET

The acoustic attenuation performance of circular expansion chambers with extended inlet/outlet is investigated. Three approaches are employed to determine the transmission loss: (1) a two-dimensional, axisymmetric analytical solution for the concentric configuration; (2) a three-dimensional computational solution based on the substructure boundary element–transfer impedance matrix technique; and (3) experiments on an extended impedance tube set-up with expansion chambers fabricated with fixed inlet, outlet, and chamber diameters, and varying lengths for the extended ducts and the chamber, and varying offset locations of the inlet and outlet. The transmission loss results from all three approaches are shown to agree well for the concentric configurations. The computational approach is also applied to determine the acoustic attenuation performance of asymmetric expansion chambers with extended inlet/outlet, which also compares well with the experiments. The effect of geometry (lengths of the extended ducts and expansion chamber, and the offset angles of the asymmetric configuration) on the multidimensional wave propagation and acoustic attenuation performance is discussed in detail.