Acoustic response of non-concentric perforated duct filters

摘要

The presence of perforated surfaces provides stiffness to acoustic filters and prevents that any absorbent material can be detached. Due to the interaction of flow with the perforations, their acoustic response is partly dissipative so that the total attenuation of the muffler is improved. In addition, they induce low pressure loss in the flow thus having little impact on engine performance. By means of non-concentric layouts, interferential systems may be configured inside mufflers which, depending on the geometrical definition, may give rise to acceptable attenuation levels for broad-band noise abatement. Since cost-effective and reliable calculation tools are still required for the optimum design of such non-concentric perforated duct mufflers, a calculation model able to reproduce both the resistive and reactive effects of the perforated duct is proposed in this paper. With this purpose, a finite volume scheme has been used for the description of tridimensional acoustic cavities, and the dissipative effect of the perforations has been implemented through the introduction of a resistive term in the linearized flow equations, which is obtained assuming a local mean flow in the vicinity of the holes. The accuracy of the model has been verified against measurements performed in a modified impulse test rig.