Acoustic Characterization of Shallow Flow Reversal Chambers

Flow reversal chambers are common design elements in mufflers. Here an idealized flow reversal chamber with large cross-section but small depth has been studied. The inlet and outlet ducts as well as the cross-sectional area are fixed while the depth of the chamber can be varied. The resulting systems are then characterized experimentally using the two-microphone wave decomposition method and compared with results from both finite element modeling and various approaches using two-port elements. The finite element modeling results are in excellent agreement with the measurements over the whole frequency range studied, while two-port modeling can be used with engineering precision in the low frequency range. The influence of mean flow was studied experimentally and was shown to have relatively small influence, mainly adding some additional losses at low frequencies. This study yields an insight into the modeling approach necessary to capture the acoustical behavior of a flow reversal chamber. For initial studies of the performance the recommendation is to model the flow reversal as a straight duct two-port element connecting the inlet and outlet. For more in depth studies finite element modeling should be used to construct a two-port element for inclusion in a network model.