Double-tuning and experimental validation of rotated-offset inlet-outlet circular chamber muffler

Abstract

A muffler with extensions of the inlet pipe and outlet pipe of acoustic lengths of half and quarter of the chamber length (L) is known as double-tuned extended-tube expansion chamber (DTETEC). It has four times wider transmission loss (TL) periodic domes as compared to a simple expansion chamber (SEC) of the same chamber length, L. Moreover, a DTETEC with the same outer dimensions of an SEC has significantly higher values of TL as compared against the SEC TL values between the first and the fourth peaks of the TL spectrum of the SEC. In order to double-tune the extended inlet–outlet mufflers, the extended pipe lengths have to be shorter than L/2 and L/4 in order to account for the end corrections due to the generation of evanescent 3-D higher-order modes at the junctions of the extended pipes and the annular region. In the present study, end-corrections of the extended pipes of the rotated-offset inlet–outlet circular chamber (ROIOC) muffler are computed using the finite element analysis (FEA) with converged mesh size. In the present study, the effect of rotation angle on the end corrections for proper double-tuning is verified by experiments. Using multi-variate regression analysis with variation of all non-dimensional parameters relevant to the rotated-offset inlet–outlet circular chamber muffler, parametric expressions of end-corrections of the extended pipes are derived and validated against the 3-D FEM predictions. The resulting TL curve shows near-perfect double tuning. This study is perhaps the first known attempt at double-tuning of the ROIOC muffler. © 2022 Elsevier Ltd