System for ventilating a downstream cavity of an impellor of a centrifugal compressor

1. A system for ventilating a downstream cavity of an impellor of a centrifugal compressor in a turbomachine, this cavity being delimited by a downstream face of the impellor and by an annular downstream end-piece of an annular diffuser arranged at the output of the compressor and being ventilated by taking air from the outlet of the centrifugal compressor, which comprises diversion means mounted fixedly in the downstream cavity of the impellor in order, on the one hand, to divert, along the annular end-piece of the diffuser, the air taken from the outlet of the compressor to its inlet in the downstream cavity of the impellor, and in order, on the other hand, to divert the ventilation air from the downstream portion of the downstream cavity and cause it to flow radially from the inside to the outside along the downstream face of the impellor.

2. The system as claimed in claim 1 , wherein the diversion means comprise an annular metal sheet mounted fixedly in the downstream cavity of the impellor on means of attaching the downstream end of the annular end-piece of the diffuser, this metal sheet extending upstream from these attachment means along the downstream face of the impellor and terminating in the vicinity of the means for taking air from the outlet of the compressor.

3. The system as claimed in claim 2 , wherein the diversion means include a second annular metal sheet mounted fixedly on means for attaching the downstream end of the annular end-piece of the diffuser, this second metal sheet extending upstream from these attachment means substantially parallel to the annular end-piece of the diffuser and terminating in the vicinity of the means for taking air from the outlet of the compressor.

4. The system as claimed in claim 3 , wherein the upstream end of the second annular metal sheet is situated radially outside the upstream end of the first annular metal sheet.

5. The system as claimed in claim 4 , wherein the downstream face of the impellor supports an annular flow diversion element that extends as a protrusion into the downstream cavity between the upstream ends of the two annular metal sheets.

6. The system as claimed in claim 3 , wherein the first annular metal sheet forms, with the downstream face of the impellor, an annular ventilation air passageway that communicates at its downstream end with an annular ventilation air passageway formed between the second annular metal sheet and the end-piece of the diffuser.

7. The system as claimed in claim 6 , wherein the second annular metal sheet is inside the downstream cavity and the annular passageway that it forms with the annular end-piece of the diffuser is supplied with air taken from the outlet of the compressor.

8. The system as claimed in claim 6 , wherein the second annular metal sheet is outside the downstream cavity and annular passageway that it forms with the annular end-piece of the diffuser is supplied with air coming out of the diffuser.

9. The system as claimed in claim 3 , which comprises means for injecting ventilation air onto the downstream face of the impellor, the flow of air coming out of these injection means being oriented in the direction of rotation of the impellor, the injection means being supported by the second annular metal sheet and/or by the annular end-piece of the diffuser.

10. The system as claimed in claim 2 , wherein the annular metal sheet defines, with the downstream face of the impellor, an annular passageway supplied at its downstream end with air taken from a ventilation air injection circuit.

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