An internal structure of a primary exhaust duct of a turbomachine. The internal structure comprises a primary wall comprising a surface of revolution, allowing air to pass through the orifices and forming an internal surface of the primary exhaust duct, an interior skin, comprising a surface of revolution, arranged inside the primary wall and extending between an upstream flank for facing toward the front of the turbomachine and a downstream flank for facing toward the rear of the turbomachine, and a plurality of spacers angularly distributed around a periphery of the interior skin and fixed between the primary wall and the interior skin. The particular way in which the interior wall is fixed makes the internal structure easier to construct and allows attenuation of noise at chosen frequencies.