ring 121 and the distributor more precisely upstream the ring presses via a seal 104 a against a radial flange 123 a of the hp turbine casing 123 that is close to the edge of the ring 121 or as here in the same transverse plane as the latter downstream the ring 104 is held by a tongue and groove fastener 104 d fixedly attached to the hp casing 123 an axial flange 102 d forms a bearing surface 104 e for the ring 104 the ring 104 comprises radial openings 104 b communicating with the cavities 102 b of the first wall by means of fitted connecting tubes 106 these cylindrical tubes have at their ends surfaces with an axial section in the arc of a circle interacting with the walls of the openings 104 b on the one hand and of the cavities 102 b the diameters are adjusted so as to form a sealed contact between the tubes and the cylindrical walls of the openings 104 b and the cavities 102 b the gaseous fluid is guided through the connecting tube with no leak a limited rotary movement of the tubes in their housings is therefore allowed so as not to immobilize the first wall relative to the ring the ring 104 arranges an annular space 110 with the wall of the turbine casing 123 downstream of the radial flange 123 a a seal 104 c provides the seal downstream between the ring 104 and the wall 123 of the casing orifices 123 b arranged in the wall of the turbine casing 123 place the space 110 in communication with a fluid supply.