Analytical modelling of acoustic transmission across double-wall sandwich shells: Effect of an air gap flow

This paper presents an analytical modelling on the effect of an internal air gap flow on acoustic transmission across double-wall sandwich shells lined with poroelastic materials. The shell motions are described by Love's theory, and the poroelastic lining is modelled as an equivalent fluid by considering only the energetically most dominant wave. The vibroacoustic problem with the boundary conditions is formulated in a transfer matrix equation and solved simultaneously. The random incidence transmission loss in a diffuse field and the limiting angle of incidence due to total internal reflection are calculated numerically and analysed in detail. It is shown that the air gap flow enhances the transmission loss in the mid-high frequency range near the critical frequency but has no influence on the thin-shell characteristic frequencies. The gap flow effect is dependent on the flow velocity, flow direction, gap depth, air pressure and shell configuration. Despite the marginal effect in the presence of an external flow, the air gap flow has great potential for tuning the sound insulation performance of double-wall sandwich shells through the enlarged design space.