Gas turbine clearance control devices

1. A clearance control device for controlling clearance between rotary blade tips and a stationary bushing of a gas turbine, said stationary bushing including an annular casing that has a longitudinal axis and that is provided with at least two annular ridges axially spaced apart from each other and extending radially outwards of said casing, said clearance control device including a circular tuning unit that surrounds the casing of the stationary bushing, said tuning unit including:

an air circulation device configured to circulate air, said air circulation device including at least three annular air flow ducts axially spaced apart one from another and disposed on either side of side faces of each of the ridges;

an air supply device configured to supply air to the air flow ducts; and

an air discharge mechanism configured to discharge air on the ridges in order to modify the temperature of the stationary bushing;

wherein, for each air flow duct, the air discharge mechanism includes at least one top row having a number N of perforations disposed facing one of the side faces of the ridges and at least one bottom row having a number 2N of perforations aligned with each other on said bottom row along a perimeter of said air flow duct and disposed facing a connection radius that connects the ridges to the casing of the stationary bushing.

2. A device according to claim 1 , in which the ridges include an upstream ridge and a downstream ridge and the ducts include an upstream duct disposed upstream from the upstream ridge, a downstream duct disposed downstream from the downstream ridge, and a central duct disposed between the upstream ridge and the downstream ridge, wherein the central duct has at least two top rows each having N perforations disposed facing the side faces of the upstream ridge and of the downstream ridge, and at least two bottom rows each having 2N perforations disposed facing connection radii that connect the upstream wing and the downstream wing to the casing of the stationary bushing.

3. A device according to claim 2 , wherein the upstream duct and the downstream duct each has substantially identical air outflow section, and the central duct has an air outflow section that is substantially twice as large as the air outflow section of said upstream duct and of said downstream duct together.

4. A device according to claim 2 , wherein said upstream and downstream ducts each have only one bottom row with said 2N perforations aligned with each other around the longitudinal axis of the casing, and

wherein said central duct has only two top rows, each top row having no more than said N perforations, and

wherein said central duct has only one bottom row with said 2N perforations aligned with each other around the longitudinal axis of the casing and facing an upstream connection radius that connects the upstream ridge to the casing of the stationary bushing, and only one bottom row with said 2N perforations aligned with each other around the longitudinal axis of the casing and facing a downstream connection radius that connects the downstream ridge to the casing of the stationary bushing.

5. A device according to claim 1 , wherein the N perforations in each top row and the 2N perforations in each bottom row have substantially identical air outflow sections.

6. A device according to claim 1 , wherein the N perforations in each top row and the 2N perforations in each bottom row are regularly spaced apart around the longitudinal axis of the casing of the stationary bushing.

7. A device according to claim 1 , in which each of the perforations in the top row and each of the perforations in the bottom row presents a substantially circular right section, wherein the angular space between two adjacent perforations of a same top row corresponds to at least three times the diameter of said perforations.

8. A device according to claim 1 , wherein the air flow ducts fit the shape of the ridges approximately.

9. A device according to claim 1 , wherein for at least one of said air flow ducts, said top row includes no more than said N perforations and said air discharge mechanism includes only one bottom row with said 2N perforations aligned with each other around the longitudinal axis of the casing.

10. A device according to claim 9 , wherein said 2N perforations of said at least one bottom row do not face said side faces of the ridges that said N perforations of said at least one top row face.

11. A device according to claim 1 , wherein said 2N perforations of said at least one bottom row do not face said side faces of the ridges that said N perforations of said at least one top row face.

12. A turbomachine having a clearance control device according to claim 1 .

13. A device according to claim 1 , wherein the air flow ducts fit the shape of the ridges approximately.

14. A clearance control device for controlling clearance between rotary blade tips and a stationary bushing of a gas turbine, said stationary bushing including an annular casing that has a longitudinal axis and that is provided with at least two annular ridges axially spaced apart from each other and extending radially outwards of said casing, said clearance control device including a circular tuning unit that surrounds the casing of the stationary bushing, said tuning unit including:

an air circulation device configured to circulate air, said air circulation device including at least three annular air flow ducts axially spaced apart one from another and disposed on either side of side faces of each of the ridges;

an air supply device configured to supply air to the air flow ducts; and

an air discharge mechanism configured to discharge air on the ridges in order to modify the temperature of the stationary bushing;

wherein, for each air flow duct, the air discharge mechanism includes at least one top row having a number N of perforations disposed facing one of the side faces of the ridges and at least one bottom row having a number 2N of perforations disposed facing a connection radius that connects the ridges to the casing of the stationary bushing, and

wherein the N perforations in each top row are staggered with respect to the 2N perforations in each bottom row.

15. A clearance control device for controlling clearance between rotary blade tips and a stationary bushing of a gas turbine, said stationary bushing including an annular casing that has a longitudinal axis and that is provided with at least one upstream ridge and one downstream ridge extending radially outwards of said casing, said clearance control device including a circular tuning unit that surrounds the casing of the stationary bushing, said tuning unit including:

an upstream air flow duct positioned upstream from said upstream ridge, a central air flow duct positioned between said upstream ridge and said downstream ridge, and a downstream air flow duct position downstream of said downstream ridge,

wherein said upstream air duct has 3N perforations distributed over only two rows, with a top row being defined by N perforations and a bottom row being defined by 2N perforations, said N perforations of said top row facing said upstream ridge and said 2N perforations of said bottom row facing a connection radius that connects the upstream ridge to the casing,

wherein said central air duct has 6N perforations distributed over only four rows, with an upstream top row defined by N perforations, a downstream top row defined by N perforations, an upstream bottom row defined by 2N perforations, and a downstream bottom row defined by 2N perforations, said N perforations of said upstream top row facing said upstream ridge, said N perforations of said downstream top row facing said downstream ridge, said 2N perforations of said upstream bottom row facing said connection radius that connects the upstream ridge to the casing, and said 2N perforations of said downstream bottom row facing a connection radius that connects the downstream ridge to the casing,

wherein said downstream air duct has 3N perforations distributed over only two rows, with a top row being defined by N perforations and a bottom row being defined by 2N perforations, said N perforations of said top row facing said downstream ridge and said 2N perforations of said bottom row facing said connection radius that connects the downstream ridge to the casing.

16. A device according to claim 15 , wherein the upstream air duct and the downstream air duct each has substantially identical air outflow section, and the central air duct has an air outflow section that is substantially twice as large as the air outflow section of said upstream duct and of said downstream duct together.

17. A device according to claim 15 , wherein the N perforations in each top row and the 2N perforations in each bottom row have substantially identical air outflow sections.

18. A device according to claim 15 , wherein the N perforations in each top row and the 2N perforations in each bottom row are regularly spaced apart around the longitudinal axis of the casing of the stationary bushing.

19. A device according to claim 15 , wherein each of the perforations in the top rows and each of the perforations in the bottom rows presents a substantially circular right section, wherein the angular space between two adjacent perforations of a same top row corresponds to at least three times the diameter of said perforations.