Cooling circuit for gas turbine fixed ring

1. A stationary ring surrounding a hot gas passage of a gas turbine, the ring being surrounded by a stationary annular housing so as to co-operate therewith to define an annular cooling chamber into which there opens out at least one cooling air feed orifice, the ring comprising:

a plurality of ring segments, wherein each ring segment includes a top internal cooling circuit and a bottom internal cooling circuit, the bottom cooling circuit being independent of the top cooling circuit, and being radially offset relative to the top cooling circuit, and the bottom cooling circuit including at least one cooling air feed orifice leading from the cooling chamber,

wherein said top cooling circuit includes at least one cooling air feed orifice leading from said cooling chamber.

2. A ring according to claim 1 , wherein the top cooling circuit of each ring segment comprises:

at least one first internal cavity extending circumferentially between first and second longitudinal walls of the ring segment;

at least one second internal cavity extending circumferentially between the longitudinal walls of the ring segment and disposed axially upstream from the first cavity;

at least one cooling air feed orifice leading from the cooling chamber and into the first cavity to feed the first cavity;

a plurality of emission holes leading from the first cavity into the second cavity so as to cool the second cavity by air impact; and

a plurality of outlet holes leading from the second cavity and into the hot gas passage at an upstream end of the ring segment.

3. A ring according to claim 1 , wherein the bottom cooling circuit of each ring segment comprises:

at least one first internal cavity extending circumferentially between first and second longitudinal walls of the ring segment and disposed at a downstream end of the ring segment;

at least one second internal cavity extending circumferentially between the longitudinal walls of the ring segment and disposed axially upstream from the first cavity;

at least one third internal cavity extending circumferentially between the longitudinal walls of the ring segment and disposed axially upstream from the second cavity;

at least first and second passages respectively putting the first cavity into communication with the second cavity, and putting the second cavity into communication with the third cavity; and

a plurality of outlet holes leading from the third cavity into the hot gas passage at an upstream end of the ring segment, the cooling air feed orifice leading into the first cavity to feed it with air.

4. A ring according to claim 3 , wherein the second internal cavity of the bottom cooling circuit includes baffles to increase heat transfer.

5. A ring according to claim 3 , wherein the air feed orifice and the second passage of the bottom cooling circuit are formed beside the first longitudinal wall of the ring segment, and the first passage of the bottom cooling circuit is formed beside the second longitudinal wall of the ring segment so as to increase the cooling air flow path length.

6. A ring according to claim 1 , wherein the top cooling circuit of each ring segment comprises a portion of a top internal cavity such that said top internal cavity extends circumferentially around a longitudinal axis of said gas turbine, and

wherein the bottom cooling circuit of each ring segment comprises a portion of a bottom internal cavity such that said bottom internal cavity extends circumferentially around said longitudinal axis of the gas turbine, wherein said top and bottom internal cavities are radially offset with respect to each other.

7. A ring according to claim 6 , wherein the entirety of said bottom internal cavity is disposed between said top internal cavity and an internal annular surface of the ring segment, wherein said internal annular surface defines said hot gas passage of the gas turbine.

8. A ring according to claim 1 , wherein said at least one cooling air feed orifice that opens out into said annular cooling chamber feeds said annular cooling chamber with cooling air, and wherein said annular cooling chamber feeds both said top and bottom internal cooling circuits with said cooling air.

9. A ring according to claim 8 , wherein said cooling air fed to both said top and bottom internal cooling circuits includes a fraction of outside air passing through a fan of a turbomachine that includes the gas turbine and flowing around a combustion chamber of the turbomachine.

10. A ring according to claim 1 , wherein said top cooling circuit primarily cools an upstream end of the ring segment, and wherein the bottom circuit primarily cools an inside surface of the ring segment.

11. A stationary ring surrounding a hot gas passage of a gas turbine, the ring being surrounded by a stationary annular housing so as to co-operate therewith to define an annular cooling chamber into which there opens out at least one cooling air feed orifice, the ring comprising:

a plurality of ring segments, wherein each ring segment includes a top internal cooling circuit and a bottom internal cooling circuit, the bottom cooling circuit being independent of the top cooling circuit, and being radially offset relative to the top cooling circuit, and the bottom cooling circuit including at least one cooling air feed orifice leading from the cooling chamber,

wherein the bottom circuit cooling of each ring segment comprises:

at least one first internal cavity extending axially between upstream and downstream transverse walls of the ring segment and disposed besides one of first and second longitudinal walls of the ring segment;

at least one second internal cavity extending axially between the upstream and downstream transverse walls of the ring segment and being circumferentially offset relative to the first cavity;

at least one third internal cavity extending axially between the upstream and downstream transverse walls of the ring segment and being circumferentially offset relative to the second cavity;

at least one fourth internal cavity extending axially between the upstream and downstream transverse walls of the ring segment and being circumferentially offset relative to the third cavity;

at least first and second cooling air feed orifices leading from the cooling chamber into the second and third cavities respectively to feed the second and third cavities;

at least first and second passages putting respectively the second cavity into communication with the first cavity, and putting the third cavity into communication with the fourth cavity;

a plurality of first outlet holes leading from the first cavity into the hot gas passage through the first longitudinal wall of the ring segment beside which the first internal cavity is disposed; and

a plurality of second outlet holes leading from the fourth cavity into the hot gas passage through the second longitudinal wall of the ring segment.

12. A ring according to claim 11 , wherein each of the second and third internal cavities of the bottom cooling circuit includes baffles for increasing heat transfer.

13. A ring according to claim 11 , wherein the first and second feed orifices of the bottom cooling circuit are formed beside the first transverse wall of the ring segment and the first and second passages of the bottom cooling circuit are formed beside the second transverse wall of the ring segment so as to increase the cooling air flow path length.