Transmission Loss Analyses on Different Angular Distributions of Periodic Inclusions in a Porous Layer

The scope of this paper is to investigate the sound transmission loss of an acoustic package of glass wool with embedded periodic inclusions, considering the possibility to improve a standard configuration and inserting the innovative package in a practical configuration used in the aeronautic field for noise suppression. Periodic inclusions are introduced to enhance the sound transmission loss performance of the acoustic package in the mid-high range of frequencies. The main interest of the present work, with respect to the state of the art, is represented by the arrangement of the inclusions one respect to the others, then creating an inclusion pattern that improves the performance of the periodicity peak. To reach this goal, a numerical model of the package is studied, and the effect of the patterns of periodic inclusions is simulated. The pattern behavior is evaluated for eight configurations, which are different from each other for the cubic dimensions and the inclusion radii. Furthermore, an optimized configuration for aeronautical applications is designed starting from the studied acoustic package; then, the results in terms of mass and performance are discussed. Results are presented in terms of tables and graphs, which may constitute a good basis to perform preliminary design consideration that could be interesting for further generalizations.