An internal structure of a primary exhaust duct of a turbomachine, the internal structure comprising a primary wall comprising a surface of revolution about a longitudinal axis, allowing the air to pass through orifices and forming an internal surface of the primary exhaust duct, an interior skin comprising a surface of revolution about the longitudinal axis, arranged inside the primary wall, an upstream flange and a downstream flange which attach the interior skin to the interior of the primary wall, at least one separator which is attached to the interior skin and which extends from the interior skin towards the primary wall, the, or each, separator extends in a plane generally parallel to the longitudinal axis, between the two flanges, and the, or each, separator is not attached to the primary wall.