Numerical modelling of thermal effects on the acoustic attenuation of dissipative mufflers

摘要

This work presents a finite element approach for the assessment of temperature effects on the acoustic performance of perforated dissipative mufflers. The main acoustic properties of the propagation media, air and absorbent material, are discussed considering the presence of a non-uniform temperature field. Thermal gradients lead to heterogeneous acoustic properties and their spatial variations are introduced through a suitable version of the wave equation. For a dissipative muffler, the absorbent material is modelled using its equivalent complex density and speed of sound. To account for the spatial variations of these properties, the temperature is related to the resistivity, the latter becoming also a coordinate-dependent function. The connection between the outer chamber and the central pipe is achieved by using the acoustic impedance of the perforated duct that relates the acoustic pressure jump and the velocity through the perforations. The impedance of the perforated duct depends on the properties of the absorbent material. The temperature-induced heterogeneity of the latter produces spatial variations of the perforated pipe impedance that are also taken into account in the finite element model. Finally, a study is presented to analyze the influence of the temperature on the acoustic behaviour of the dissipative muffler.