System for ventilating a combustion chamber wall

1. A system for ventilating a combustion chamber wall in a turbomachine comprising:

a centrifugal compressor including an impeller;

a diffuser including an annular end-piece with a substantially L-shaped section that extends downstream and along the impeller of the centrifugal compressor so as to present a radial annular passageway for communicating a flow of air between a radially external end of the diffuser and an outlet of the compressor;

an annular combustion chamber; and

an annular case arranged radially between the combustion chamber and the end-piece of the diffuser and extending axially from the diffuser to the vicinity of the outlet of the combustion chamber and of the downstream end of the end-piece of the diffuser, the case including a radially external wall of revolution which cooperates with a radially internal wall of the combustion chamber to guide an air flow coming out of the diffuser, and a radially internal wall of revolution which cooperates with the end-piece of the diffuser so as to provide an annular channel therebetween for air coming out of the diffuser to pass through,

wherein the end-piece of the diffuser includes an upstream radial portion which extends radially inward from an inlet of the diffuser and a cylindrical downstream portion which extends downstream from the upstream radial portion, and

wherein the internal wall of revolution of the case includes an upstream annular portion which extends radially inward and substantially parallel to the upstream radial portion of the end-piece of the diffuser, an intermediate cylindrical portion which extends axially, and a frustoconical downstream annular portion which extends downstream and radially outward.

2. The system as claimed in claim 1 , wherein the case is formed of two half-shells assembled transversely together.

3. The system as claimed in claim 1 , wherein the radially external wall of revolution of the case extends substantially parallel to the radially internal wall of the combustion chamber.

4. The system as claimed in claim 1 , wherein the radially internal wall of revolution of the case extends substantially parallel to the end-piece of the diffuser.

5. The system as claimed in claim 1 , wherein the walls of revolution of the case include pressure-balancing orifices.

6. The system as claimed in claim 1 , wherein the case includes an upstream cylindrical rim centered and supported on the diffuser and a downstream cylindrical rim centered and supported on an annular ring of the internal wall of the combustion chamber.

7. The system as claimed in claim 6 , wherein the upstream rim of the case is attached by shrink-fitting to the diffuser and the downstream rim of the case is attached by shrink-fitting to the annular ring of the internal wall of the combustion chamber.

8. The system as claimed in claim 6 , wherein the upstream cylindrical rim of the case is crenellated and forms orifices which supply, with air coming out of the diffuser, the air passageway channel along the end-piece of the diffuser.

9. The system as claimed in claim 6 , wherein the case is attached by a cylindrical ring engaged axially and attached to the downstream cylindrical rim of the case.

10. A turbomachine, which comprises a ventilation system as claimed in claim 1 .

11. An annular case for a ventilation system according to claim 1 , comprising two coaxial walls of revolution extending one inside the other, the upstream ends of these walls being connected to one another by an axial cylindrical rim oriented upstream, and the downstream ends of these walls being connected to one another by an axial cylindrical rim oriented downstream.

12. The case as claimed in claim 11 , wherein the radially external wall is substantially frustoconical, and the radially internal wall has a substantially U-shaped section.

13. The case as claimed in claim 11 , wherein the walls of revolution comprise orifices.

14. The case as claimed in claim 1 , which is formed of two half-shells juxtaposed transversely.

15. The system as claimed in claim 1 , further comprising an air injection unit which injects air to components disposed downstream of the combustion chamber, the air injection unit including an annular duct disposed between a downstream flange of the annular end-piece of the diffuser and an attachment flange of the combustion chamber.