End corrections for double-tuning of the same-end inlet-outlet muffler

Abstract

Transmission loss spectrum of a simple expansion chamber (SEC) muffler is characterized by periodic domes. In recent years, it has been shown that by extending the inlet pipe and outlet pipe of the SEC inwards by nearly half and quarter lengths (L/2 and L/4) into the chamber, it is possible to raise three-fourths of all the TL-troughs, thereby ensuring a wide-band TL spectrum. This has been called Double-Tuning of the SEC. In practice, physical lengths of the extended inlet and extended outlet are made shorter than L/2 and L/4 by end correction in order to account for the higher-order evanescent modes at the two junctions.In this paper, making use of the three-dimensional (3-D) finite element method (FEM), general parametric expressions have been developed for the end corrections of the two junctions of the same-end inlet-outlet (SEIO) chamber, or flow-reversal chamber, in order to double-tune it on the lines of the co-axial opposite-ends inlet-outlet chamber muffler. The 3-D finite element mesh convergence has been validated against the available experimental TL spectra. This study is perhaps the first known attempt at double-tuning of the same-end inlet-outlet (SEIO) chamber muffler.