Noise reducing device having an obliquely pierced honeycomb structure

A method for manufacturing a noise reducing device for an aircraft turbine engine, said device having a structure in the form of a stack of layers such that a first and a second skin made of composite material form a first and a second outer layers, the first and second outer layers being substantially parallel to one another, the first and second outer layers enclosing a central layer having a honeycomb structure comprising partitions extending transversely from the first outer layer to the second outer layer, so as to form cavities,

• wherein the partitions of the honeycomb structure of the central layer are made of viscoelastic material, and in that said partitions form, with the first and second outer layers, an acute angle of inclination (α), all the partitions of the central layer being parallel to each other
• wherein each partition of the central layer has a thickness comprised between 3 mm and 7 mm,
• wherein the central layer has a thickness comprised between 20 and 30 mm, and
• wherein the cavities of the central layer have a depth of 40 mm, and
• wherein the viscoelastic material of the partitions of the honeycomb structure of the central layer comprise a polymer, the polymer being a polypropylene or a polymethacrylimide,
• wherein the method comprises the following steps:
• forming cavities in the central layer by piercing a solid panel of viscoelastic material which has two surfaces substantially parallel to one another, the piercings being made obliquely and all piercings being made parallel to each other, so that each cavity has a height forming part of a plane which is not perpendicular to the surfaces of the panel,
• fixing the first skin made of composite material to a first surface of the pierced viscoelastic material panel,
• fixing the second skin made of composite material to a second surface of the pierced viscoelastic material panel, and
• making perforation in the first skin made of composite material.