Acoustically treated turbomachine multi-duct exhaust device

A multi-duct diffusion exhaust device for an exhaust gas stream at an outlet of a turbomachine, comprising an annular inlet, an outer casing shaped symmetrically overall with respect to an axis, and at least one internal partition defining roughly concentric passages for the exhaust gas stream to flow through,

• wherein said at least one internal partition is provided, on at least one surface thereof, with an acoustic energy absorbent coating capable of absorbing some of the acoustic energy generated by the flow and entirely covering the at least one surface,
• wherein at least an interior surface of the outer casing is provided with an acoustic energy adsorbent coating capable of absorbing some of the acoustic energy generated by the flow, and
• wherein a thickness of the absorbent coating of said at least one internal partition and a thickness of the absorbent coating of said interior surface vary along a length of the exhaust device such that an overall cross-section of said passages continuously increases from said annular inlet to said outlet maintaining a low back pressure at the inlet of the exhaust.