Acoustic liner

Liners are applied on the internal walls of the engine nacelle, both in the intake and by-pass ducts, and use Helmholtz resonance principle for the dissipation of incident acoustic energy.

An acoustic liner is a sandwich panel made by: The lower half of a liner features dedicated internal slots to allow liquid drainage in order to prevent ice formation or fire hazards.

[1] Acoustic liners can be distinguished by their internal configuration on the base of the number of honeycomb cell layers: Porous layers (e.g. the septum and the face-sheet) can be for example a perforate plate, a wire mesh or a felt-metal.

In order to have a cylindrical barrel, panel parts are structurally joined together leading to a partial loss of the acoustic area known as splice.

[5] Moreover, the in-situ method is the only one able to measure the impedance directly on full scale acoustic liners.