On development of rational design guidelines for large side-inlet side-outlet perforated element mufflers

Logistics of an acoustic enclosure for a diesel generator (DG) set require mounting of the exhaust muffler on the top of the enclosure with side inlet and side outlet. In this article, four different, yet somewhat similar, side-inlet side-outlet (SISO) perforated element muffler configurations have been investigated. It has been shown that the 1-D plane wave analysis is adequate for the first few harmonics of the engine speed order that are of prime interest for muffler designers. This simplified analysis throws light on the significant role of the resistive part of the perforate impedance and thence the bias flow Mach number. In particular, the effect of bias flow in raising the troughs is suitably exploited while limiting the overall backpressure of the muffler. The 1-D plane wave analysis, however, becomes too approximate at higher frequencies, and for that reason, one has to rely on the 3-D FEA for evaluation of the overall four-pole parameters of the muffler. A convergence study has been performed on one of the four configurations in order to arrive at an average mesh size that can capture the transmission loss (TL) values correctly up to 1000 Hz, and thereby economize on the RAM as well as the computational time for analysis of all four configurations. The backpressure for all the four muffler configurations is kept approximately the same. Finally, some design guidelines for similar mufflers are discussed.