Acoustic attenuation analysis of expansion chamber mufflers with non-uniform cold and hot flow

Abstract

In the presence of flow, the acoustic field and the flow field inside mufflers will interact with each other. In order to capture this phenomenon, the frequency-domain linearized Navier–Stokes equations (LNSEs) are employed to investigate the vortex-sound interaction inside expansion chamber mufflers. The calculations are performed in three steps: (1) to obtain the background mean flow variables by using the steady-state CFD simulation, (2) to map CFD results to acoustic meshes, and (3) to calculate the acoustic perturbation by using the finite element method based on LNSEs. Primarily, the transmission loss of single expansion chamber with inlet/outlet extensions is predicted in the presence of cold flow and the numerical predictions of LNSEs showed consistent agreements with measurements published in the literature. With the increase of inlet flow velocity, transmission loss in the low frequency range is obviously influenced by the vortex-sound interaction, which is attributed to the energy transfer between the fluidic and acoustic scales inside the muffler. Further, the acoustic attenuation performance of dual-chamber mufflers with flow is investigated numerically and experimentally, and the LNSEs predictions agree well with measurements. In the presence of cold flow, the transmission loss curves of the mufflers in the low frequency range is disturbed by the acoustic dissipation and amplification, while the effect of hot flow on the acoustic attenuation behavior of the mufflers is almost the same as that of cold flow, except that the non-coaxial mufflers with side-inlet is remarkably influenced by temperature. The studies demonstrated that the background mean velocity gradient is the most important impact factor for acoustic attenuation performance of the dual-chamber mufflers in low frequency range, whether in the presence of cold or hot flow.