China
A numerical mode matching (NMM) approach is developed to predict the acoustic attenuation performance of expansion chambers with extended single inlet and double outlets, and validated by comparing the transmission loss predictions from the NMM, three-dimensional finite element method (FEM) and 1-D analytical method. Then theNMMmethod is used to investigate the effects of extended lengths of inlet and outlets as well as higher order modes on the acoustic attenuation performance.
The results demonstrated that the side-branch resonance may be produced only when the two extensions of outlets are nearly equal. Choosing the extensions of inlet and outlets reasonably may eliminate the pass frequencies and yield a broad band acoustic attenuation. The expansion chamber with symmetric outlets about the minor axis exhibits better acoustic attenuation performance than that with nonsymmetric outlets since the effects of some higher order modes may be eliminated by the symmetric outlets. © 2017 Institute of Noise Control Engineering.
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