External mean flow effect on sound transmission through composite sandwich structures filled with porous materials

A theoretical model is developed to investigate the influence of external mean flow on sound transmission loss (STL) through composite sandwich panels filled with porous materials. The equations of the motions for the composite laminate plates are established by adopting the first-order shear deformation theory. The porous materials in between the sandwich structures are characterized by an equivalent fluid model. Employing the fluid-structure coupling condition, the displacement continuity at fluid-structure interfaces is guaranteed. To validate the proposed theoretical model, a comparison among the present theoretical predictions, the existing theoretical and experimental results are executed, with overall agreements achieved. A systematical investigation is carried out to explore the influences of the external mean flow, incidence angle and laminate scheme on the coincidence frequency and sound transmission loss of the sandwich structures. This work provides a helpful guideline for the vibroacoustic design of composite sandwich structures.