Blade to stator heat shield interface in a gas turbine

Abstract

Gas turbine unit having an axis parallel to the main gas flow, the gas turbine unit comprising: a blade having a tip; a stator heat shield having an inner surface facing the blade tip; wherein the inner surface of the stator heat shield and the blade tip define a variable clearance depending on the applied thermal condition; wherein the blade tip is configured to have a cylindrical shape along the axial direction in a hot running condition starting from a conical shape along the axial direction in a cold starting condition.

Claims

1. Gas turbine unit having a central axis (A) parallel to a main gas flow, the gas turbine unit comprising: a blade having a tip, a leading edge and a trailing edge; and a stator heat shield having an inner surface facing the blade tip; wherein the inner surface of the stator heat shield and the blade tip define a variable clearance depending on a thermal condition; and wherein: wherein the blade tip includes the leading edge and the trailing edge, configured such that: when in the cold starting condition, along the axial direction, the leading edge of the blade tip is arranged at a radial distance from the axis (A) that is greater than the radial distance from trailing edge of the blade tip to the axis (A); when in the hot running condition, along the axial direction, the trailing edge of the blade tip and the leading edge of the blade tip are arranged at a same radial distance from the axis (A); and when in the cold starting condition, along the axial direction, a straight line (T) connecting the leading edge of the blade tip to the trailing edge of the blade tip defines with the axis (A) an angle (α) between 1° and 2°; and an annulus having a curved inner surface along a circumferential direction, and wherein the inner surface of the stator heat shield, directly facing the blade tip, is configured to have a curved shape along the circumferential direction equal to the annulus when in the hot running condition, starting from a curved shape along the circumferential direction non-equal to the annulus when in the cold starting condition.

2. Gas turbine unit as claimed in claim 1, wherein the tip is a surface generated by a plurality of straight lines parallel to axis (A).

3. Gas turbine unit as claimed in claim 1, wherein the gas turbine unit comprises: a vane carrier having a curved inner surface along a circumferential direction; wherein an outer surface of the stator heat shield includes a plurality of hooks; and wherein a hook inner surface is configured to have a curved shape along the circumferential direction equal to a curved inner surface of the vane carrier when in a hot running condition, starting from a curved shape along the circumferential direction non-equal to the vane carrier curved inner edge when in a cold starting condition.

4. Gas turbine unit as claimed in claim 3, wherein the stator heat shield comprises: a leading edge hook, arranged upstream with respect to a main hot gas flow; a trailing edge hook, arranged downstream with respect to the main hot gas flow; and a middle hook located between the leading and the trailing edge hooks.

5. Gas turbine unit as claimed in claim 4, configured such that when in the cold starting condition, a middle portion of the middle hook inner surface is arranged at a radial distance from an axis (A) that is greater than a radial distance from the curved inner edge of the vane carrier to the axis (A), side portions of the middle hook inner surface along the circumferential direction being in abutment with the vane carrier.

6. Gas turbine unit as claimed in claim 5, configured such that when in the hot running condition, a middle clearance between the middle portion of the middle hook inner surface and the vane carrier is equal or greater than side clearances between the side portions of the middle hook inner surface and the vane carrier.

7. Gas turbine unit as claimed in claim 6, configured such that when in the hot running condition, the middle portion of the middle hook inner surface is in abutment with the vane carrier, the side portions of the middle hook inner surface along the circumferential direction being in abutment with the vane carrier.

8. Gas turbine unit as claimed in claim 1, wherein the inner surface of the stator heat shield is configured to have a cylindrical shape along the axial direction in a hot running condition starting from a non-cylindrical shape along the axial direction in a cold starting condition.

9. Gas turbine unit as claimed in claim 8, wherein the inner surface of the stator heat shield comprises: a upstream edge and a downstream edge, configured such that: when in the cold starting condition, along an axial direction, the downstream edge and the upstream edge are radially closer to an axis (A) than a middle portion of the inner surface of the stator heat shield; and when in the hot running condition, along the axial direction the downstream edge, the upstream edge and the middle portion of the inner surface of the stator heat shield are arranged at a same radial distance from the axis (A), and the inner surface of the stator heat shield is a surface generated by a plurality of straight lines parallel to axis (A).

10. Gas turbine unit as claimed in claim 9, configured such that when in a cold starting condition, along the axial direction the downstream edge and the upstream edge are arranged at a same radial distance from the axis (A).

11. Gas turbine unit as claimed in claim 10, wherein the middle portion of the inner surface of the stator heat shield is rounded connected to the upstream edge and the downstream edge.

12. Gas turbine unit as claimed in claim 1, configured such that when in the cold starting condition, the middle portion of the inner surface of the stator heat shield along the circumferential direction is arranged at a radial distance from the axis (A) that is greater than the radial distance from the annulus to the axis (A).

Description

BRIEF DESCRIPTION OF DRAWING

(1) Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

(2) The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

(3) FIG. 1 is a schematic view along the axial direction of the blade tip to stator heat shield interface according to the prior art in the cold starting condition;

(4) FIG. 2 is a schematic view along the axial direction of the blade tip to stator heat shield interface according to the prior art in the hot running condition;

(5) FIG. 3 is a schematic view along the circumferential direction of the blade tip to stator heat shield interface according to the prior art in the cold starting condition;

(6) FIG. 4 is a schematic view along the circumferential direction of the blade tip to stator heat shield interface according to the prior art in the hot running condition;

(7) FIG. 5 is a schematic view along the axial direction of the blade tip to stator heat shield interface according to an embodiment of the invention in the cold starting condition;

(8) FIG. 6 is a schematic view along the axial direction of the blade tip to stator heat shield interface according to an embodiment of the invention in the hot running condition;

(9) FIG. 7 is an enlarged view of a portion of FIG. 5;

(10) FIG. 8 is a schematic view along the circumferential direction of the blade tip to stator heat shield interface according to an embodiment of the invention in the cold starting condition;

(11) FIG. 9 is a schematic view along the circumferential direction of the blade tip to stator heat shield interface according to an embodiment of the invention in the hot running condition;

DETAILED DESCRIPTION OF THE INVENTION

(12) In cooperation with the attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to preferable embodiments, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention.

(13) Reference is now made to the drawing FIGS. 5-9 to describe the present invention in detail. In particular, the FIGS. 5-9 disclose a blade 1 with a blade tip 2 and a stator heat shield 3 with an inner surface 4. The blade tip 2 and the inner surface 4 of the stator heat shield 3 are configured to thermally deform under the hot running condition to have a controlled cylindrical shape along the axial direction. This particular shape allows to control and to reduce the tip clearance, to reduce the overtip flow, to increase the efficiency and performance and to increase the lifetime.

(14) From the following description it will be clear that the blade tip 2 and the inner surface 4 of the stator heat shield 3 become cylindrical along the axial direction due to a particular “pre-shaping” provided in the cold condition.

(15) Reference is made to FIG. 5, which is a schematic view along the axial direction A, parallel to the main gas flow M, of the blade 1 to stator heat shield 3 interface according to an embodiment of the invention in the cold starting condition, Reference is also made to FIG. 7, which is an enlarged view of a portion of FIG. 5.

(16) In particular, FIGS. 5 and 7 disclose a blade 1 having a tip 2, a stator heat shield 3 having a inner surface 4 facing the blade tip 2. Referring to the main gas flow direction M, the blade tip 2 comprises a leading edge 5 a trailing edge 6, wherein along the axial direction the leading edge 5 is arranged at a higher distance from the axis A than the tip trailing edge 6. In other words, as disclosed in FIG. 7, the tip 2 in the cold start condition is “conical”, i.e. the straight line T connecting the leading edge 5 to the trailing edge 6 defines with the axis A and angle α between 1° and 2°, preferably 1.5°.

(17) The inner surface 4 of the stator heat shield 3 comprises an upstream edge 7 and a downstream edge 8. In the cold starting condition disclosed in FIGS. 5 and 7, along the axial direction the downstream edge 8 and the upstream edge 7 are closer to the axis A than the middle portion 9 of the inner surface 4 of the stator heat shield 3. Moreover, in the cold starting condition the downstream edge 8 and the upstream edge 7 are arranged at the same distance from the axis A and the middle portion 9 of the inner surface 4 of the stator heat shield 3 is rounded connected to the upstream edge 7 and to the downstream edge 8.

(18) Reference is made to FIG. 6, which is a schematic view along the axial direction of the blade tip 2 to stator heat shield 3 interface according to an embodiment of the invention in the hot running condition.

(19) Starting from the shape disclosed in FIG. 5, under the hot running condition the blade tip 2 and the inner surface 4 deform up to generate a shape as disclosed in FIG. 6. In particular, in FIG. 6 the tip leading edge 5 and the tip trailing edge 6 are aligned at the same distance from the axis A and the tip surface 2 is cylindrical along the axial direction, i.e. defined by a plurality of straight lines parallel to axis A.

(20) FIG. 6 discloses also the shape of the inner surface 4 of the stator heat shield 3 in the hot running condition. In particular, in this thermal condition, along the axial direction the downstream edge 8, the upstream leading edge and the middle portion 9 of the inner surface 4 are aligned at the same distance from the axis A. The inner surface 4 is therefore cylindrical along the axial direction, i.e. defined by a plurality of straight lines parallel to axis A.

(21) Reference is made to FIGS. 8 and 9, which are schematic views along the circumferential direction of the blade tip 2 to stator heat shield 3 interface according to an embodiment of the invention in the cold starting condition and in the hot running condition. In FIGS. 8 and 9 the numbers 12 and 13 refer respectively to the anulus and to the vane carrier of the gas turbine unit. These components have been represented only with dashed lines.

(22) In detail, reference is made to FIG. 8, which is a schematic view along the circumferential direction of the blade tip 2 to stator heat shield 3 interface according to an embodiment of the invention in the cold starting condition. The anulus 12 comprises an inner curved surface along the circumferential direction. In the cold starting condition, the inner surface 4 of the stator heat shield 3 is configured to have a curved shape along circumferential direction non-equal to the anulus 12. In particular, the middle portion 11 of the inner surface 4 along the circumferential direction is arranged at a higher distance from the axis A than the anulus surface.

(23) Similarly, the vane carrier 13 comprises a curved inner surface 14 along the circumferential direction whereas the outer surface of the stator heat shield 3 comprises a plurality of hooks oriented upstream to the main flow M and configured to couple to the vane carrier 13. According to the embodiment disclosed in the figures, the stator heat shield comprises three hooks, namely a leading edge hook 10′, upstream arranged with respect to the main hot gas flow, a trailing edge hook 10″, downstream arranged with respect to the main hot and a middle hook 10 located between the leading and the trailing hook.

(24) In particular, FIGS. 8 and 9 disclose the deformation of the middle hook 10 starting from a cold condition, FIG. 8, to a hot running condition, FIG. 9.

(25) In the cold starting condition of FIG. 8, the hook inner surface 15 is configured to have a curved shape along the circumferential direction non-equal to the vane carrier curved inner surface 14. In particular, the middle portion 16 of the hook inner surface 15 is arranged at a higher distance from the axis A than the curved inner surface 14 of the vane carrier. In this condition, the side portions of the middle hook inner surface 16 along circumferential direction are in abutment with the vane carrier 13.

(26) Reference is made to FIG. 9, which is a schematic view along the circumferential direction of the blade tip to stator heat shield interface according to an embodiment of the invention in the hot running condition.

(27) Starting from the shape disclosed in FIG. 8, under the hot running condition, the middle hook 10 and the inner surface 4 of the stator heat shield 3 deform up to generate a shape as disclosed in FIG. 9. In particular, in figure the inner surface 4 of the stator heat shield 3 is aligned to the anulus curved surface 12 and the hook inner surface 15 is aligned to carrier curved inner surface 14.

(28) As disclosed in FIG. 9, in the hot running condition both the middle portion 16 and the side portions 17 of the middle hook inner surface 15 along circumferential direction are in abutment with the vane carrier 13. In this way, the middle clearance is not less (equal or greater) than the side clearances between the middle hook 10 and the vane carrier 13. On the contrary, FIG. 4 of the prior art disclose side clearances larger than the middle clearance between the hook and the vane carrier.

(29) Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. Therefore, It is contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.