Gas turbine inlet vane structure utilizing a stable ceramic spherical interface arrangement

Abstract

An improved ceramic inlet vane structure for axial flow gas turbines, comprising an array of three ceramic blades arranged in a vane segment. Each blade has a spherical interface between its radially inner and outer ends and their respective supportive end caps. The three points of contact between the inner ends of the three blades and their respective inner end caps in the vane segment generally define a triangle. The points of contact between the outer ends of each the three blades and their respective outer end caps in the vane segment also generally define a triangle. Each group of inner and outer end caps themselves are restrained by a shoe having a single spherical interface with inner and outer shroud members respectively. The four spherical interface points on the inner portions and on the outer portions of each vane segment define a tetrahedron. This configuration provides high stability with a slight freedom of movement within each vane segment and a slight freedom of movement within each blade. An annular arrray of vane segments comprises the inlet nozzle of a gas turbine.

Government Interests

The invention herein described was made in the course of or under a contract or subcontract thereunder, with the Department of Defense.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to turbines, and more particularly to ceramic inlet nozzle structures for gas turbines.

2. Description of the Prior Art

Gas turbines presently employ integral first stage metal inlet vane segments. As inlet temperatures are increased to increase turbine efficiency, cooling of the metal inlet vanes is necessary. Providing cooling fluid for the metal vanes utilizes some of the power produced by the turbines, hence it decreases the overall efficiency of that unit. Ceramics have been introduced as a high temperature material from which to construct the inlet vane segments. Ceramics, however, are structurally most stable when used in a compressed state. Gas turbine inlet nozzles during operation have an array of forces generated therein that are not strictly compressive. The forces generated therein may be in shear or tension, and are produced because of thermal expansion, movement of adjacent members, and the like.

An object of this invention is to overcome the problems associated with the prior art.

Another object of this invention is to design a structural arrangement within the inlet nozzle so that those forces generated within the ceramic blades and supportive end caps will be of minimal deleteriousness.

Yet another object of this invention is to provide a stable vane segment arrangement that will permit a slight freedom of elongation and rotation for the individual blades within that vane segment.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an improved inlet nozzle structure for a gas turbine. Vane segments, an annular array of which comprise the inlet nozzle, themselves are comprised of three radially directed ceramic blades. Each blade has its own supportive radially inner and radially outer ceramic end cap. Each radial end of each of the ceramic blades has a generally hemispherical cavity disposed within it. Each adjacent ceramic end cap has a generally hemispherical cavity aligned with its respective cavity in its radially adjacent blade. A ceramic sphere is disposed in each cavity between each of the ceramic blades and each ceramic end cap. This provides a spherical interface therebetween. The ceramic sphere permits slight freedom of pivotal motion of the blades with respect to one another and with respect to the vane structure itself. Each array of radially inner spheres and each array of radially outer spheres define corners of a triangle. Each array of end caps is restrained by a shoe having a spherical interface with its respective inner and outer shroud. The four inner and four outer points of spherical interface each define a tetrahedron. The radially outer vertex of the outer tetrahedron being compressed radially inwardly, all of the spherical interface points providing a support arrangement that is very stable, and which also permits slight elongation and rotation of its components.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a portion of an inlet nozzle of a gas turbine, showing a vane segment constructed in accordance with the principles of this invention;

FIG. 2 is a schematic diagram of a three blade stable vane assembly utilizing a spherical interface arrangement;

FIG. 3 is a longitudinal sectional view of the middle blade and spherical interface support arrangements of the stable vane assembly;

FIG. 4 is a longitudinal sectional view of an end blade in a vane segment and a spherical interface arrangement for the blades in a vane segment;

FIG. 5 is another embodiment of a spherical interface arrangement for the blades in a vane segment;

FIG. 6 is yet another embodiment of a spherical interface arrangement for the blades on a vane segment;

FIG. 6a is still another embodiment of a spherical interface arrangement for the blades on a vane segment; and,

FIG. 7 is a stop arrangement for preventing excessive twist in each blade.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, and particularly to FIG. 1, there is shown a portion of an inlet arrangement of an axial flow gas turbine 10 having a stable inlet nozzle arrangement 12.

The gas turbine 10 includes a turbine axis 14, an outer cylinder 16, an annular array of vane segments 18 which comprise the inlet nozzle arrangement 12, and at least one rotor disc 20 with an array of rotating blades 22. A fixed plunger biasing arrangement 23 is disposed radially outwardly of each array of vane segments 18 to maintain each array of vane segments 18 in a generally compressed state.

The vane segments 18 are preferably constructed from ceramic materials, to withstand the high temperatures, about 2500.degree.F, which exist within the inlet nozzle 12 due to the flow of hot gases therethrough from an array of combustion chambers, not shown. The vane segments 18 are maintained in the compressed state because ceramic materials are strongest in that mode.

The vane segments 18 are comprised of three individual ceramic airfoil blades 24, each blade 24 having its own supportive radially inner ceramic end caps 26, and their own radially outer ceramic end caps 28. An insulator and supportive member 30 is disposed radially outwardly of the outer ceramic end caps 28 and an insulator and supportive member 32 is disposed radially inwardly of the inner ceramic end caps 26.

Each end of each ceramic blade has a spherical interface arrangement 25 with its respective adjacent ceramic end cap 26 or 28. The preferred embodiment discloses a rolling spherical interface relationship with each blade 24 and respective end caps 26 and 28, that comprise, with a spherical pivot assembly 27 and 27', radially outwardly and inwardly respectively, of the outer and inner supportive members 30 and 32, a stable vane assembly 12.

The radially outer end of each ceramic blade 24 has a generally hemispherical cavity 34 disposed therein, as shown in FIGS. 1, 3 and 4. Each outer ceramic end cap 28 also has a generally hemispherical cavity 36 disposed therein, radially adjacent the cavity 34. A generally spherical ceramic member 38 is disposed between the two outer hemispherical cavities 34 and 36, and supportively maintained therebetween. The radially inner end of each ceramic blade 24 has a generally hemispherical cavity 40 disposed therein. Each inner ceramic end cap 26 also has a generally hemispherical cavity 42 disposed therein, radially adjacent the cavity 40 in the radially inner end of the blade 24. A generally spherical ceramic member 44 is disposed between the two inner hemispherical cavities 40 and 42, and supportively maintained therebetween.

The arrangement of the radially inner cavities 40 and 42 and their respective ceramic spheres 44 generally form the points of a triangle, the sides of which are indicated by dotted lines and the letters A, B and C on FIG. 2. A similar non-linear arrangement of the radially outer cavities 34 and 36 is also shown in FIG. 2, labeled A'.sub.1, B'.sub.1 and C'.sub.1. The radially inner and outer spherical interlock arrangements 25 each form a tetrahedron with spherical pivots 27' and 27, respectively. The radially inner and outer tetrahedrons, defined by A.sub.2 B.sub.2 C.sub.2 D and A'.sub.1 B'.sub.1 C'.sub.1 D' respectively, are each loaded in compression, due to the action of biasing member 23, and are able to pivot slightly about each radially extreme vertex, D and D'.

The use of three blades 24 in each vane segment 18 permits the use of spherical interfaces in a generally triangular arrangement as stated above. This triangular arrangement permits each vane segment 18 to bend unrestrained about any axis. Collapse of the three blades 24 in the vane segment 18 in the axial or circumferential direction cannot occur, since this would require a parallel displacement by the two planes defined by A.sub.2 B.sub.2 C.sub.2 and A'.sub.1 B'.sub.1 C'.sub.1, which however, is prevented by the fixed plunger biasing arrangement 23, mentioned earlier, to help keep each entire vane segment 18 in compression. Collapse by relative rotation of the two tetrahedrons defined by A.sub.2 B.sub.2 C.sub.2 D and A'.sub.1 B'.sub.1 C'.sub.1 D', cannot occur since it would be stopped by compression of any of the three blades 24. The relationship of the axial positioning of the spherical interfaces for the individual blades 24, is shown in FIGS. 3 and 4. FIG. 3 showing the middle blade 24 in each vane segment 18, and FIG. 4 showing an end blade 24 in each three blade vane segments. The non-linearity of the middle blade spherical interface 25 with respect to the end blade spherical interfaces 25 is shown in FIG. 1, and can be seen by comparing the axial displacement of the spherical interfaces 25 of FIGS. 3 and 4.

Each pivotable assembly 27 or 27', or radially extreme inner or outer vertex is a spherical interface, one part of each pivotable assembly being on the supportive member 30 and 32, or load plate, the other part being disposed on the outer or inner housing rings 39 and 37 respectively. The supportive members, 30 and 32 include hemispherical tenons 31 which pivotably mate with hemispherical cavities 33. The tenons 31 and cavities 33 comprise part of the spherical pivot assemblies 27 and 27'.

An alternative embodiment of the spherical interface is shown in FIG. 5. A single ceramic airfoil blade 46 from a vane segment 18 is shown disposed between an inner ceramic end cap 48, and an outer ceramic end cap 50. The load plates or supportive members 30 and 32 are similar to the earlier shown embodiment. Each ceramic end cap 48 and 50 has a generally hemispherical cavity 52 disposed therein. The ceramic airfoil blade 46 has a generally hemispherical tenon 54 on both the radially inner and outer ends, disposed radially adjacent each cavity 52 in the end caps 48 and 50. The tenon 54 mates with each cavity 52 in their respective end caps 48 and 50. The non-linear or generally triangular arrangement of the spherical interfaces between the blades 46 and end caps 48 and 50 would be the same as that shown in FIGS. 1 and 2. A biasing means, 23, as shown in FIGS. 1 and 2, would provide a compressive force on each vane segment 18 having either the independent ceramic spheres 38 and 44, between the blade 24 and end caps 26 and 28, or the embodiment using a tenon 54 mating with cavities 52 in the end caps 48 and 50. One of the tensons 54 shown in FIG. 5, could be a ceramic sphere. The support arrangement would then be a combination of the embodiments of FIGS. 4 and 5, as shown in FIG. 6a.

Another possible embodiment, shown in FIG. 6 utilizes the disposition of a tenon 56 on each end cap 58 itself, mating with hemispherical cavities 60 on each end of an airfoil blade 62. Yet another embodiment shown in FIG. 6a, utilizes a tenon 72 and hemispherical cavity 74 arrangement between one end of a blade 75 and end cap 76, and a ceramic sphere 78 and two hemispherical cavities 79 and 81 in the blade 75 and other associated end cap 80.

With any of the above disclosed embodiments of interfacing, a ceramic stop 64 may be used. The ceramic stop 64 is a sphere having a quadrant removed. The stop 64 is restrained in a cavity 66 in an inner or outer end cap 68. The stop 64 being bonded to the end cap 68. A blade 69, before excessive twisting, will come into contact with wall portions 70 of the stop 64, and prevent failure of the blade 69 or collapse of the vane segment 18. The use of vane segments 18 described, in any case, require a different number of those vane segments 18 in a nozzle arrangement 12 than are usually present in the prior art. Additionally, the use of more support members 30 and 32, eliminate troublesome leakage paths, dangerous harmonics, and would reduce the number of seals required. It is understood that each alternative support embodiment utilizes the generally tetrahedronal pattern of support points in the assembled vane segment, and the triangular pattern of support points between the blades and their end caps.

The contact surfaces of the spherical interfaces have the advantage that they permit rotation in three directions, of each blade. The rotation may be caused by: compressive spring loading -- a normal load; gas loading -- tangential load; and gas twisting moment -- a twist load. The linkage stability realized through the arrangement of spherical interfaces disposed in tetrahedral arrays as disclosed above is insured with this configuration.

It will be apparent to those skilled in the art, after having had the benefit of this invention, that other embodiments are possible, and are so included within the scope of the claims.

Claims

We claim:

1. An inlet nozzle for a gas turbine having a radially inner shroud ring, a radially outer shroud ring coaxial with said inner shroud ring, and an annular array of vane segments compressively retained therebetween, each of said vane segments comprising:

a. three radially extending ceramic blades;

b. three separate outer supportive end caps forming an outer arcuate segment;

c. three separate inner supportive end caps forming an inner arcuate segment;

d. a first support means extending across said outer arcuate segment for retaining said outer end caps in proper orientation, with each end cap in opposed facing relationship to the radially outer end of a blade;

e. a second support means extending across said inner arcuate segment for retaining said inner end caps in proper orientation, with each end cap in opposed facing relationship to the radially inner end of a blade;

f. means providing a ball and socket engagement between said first support means and said outer shroud ring generally midway between the arcuate extent of said support means;

g. means providing a ball and socket engagement between said second support means and said inner shroud ring generally midway between the arcuate extent of said second support means;

h. means providing a ball and socket engagement between each end cap and the adjacent radial end of the blade associated therewith;

i. said ball and socket engagements between each of the three blades and their respective outer end caps being disposed such that each point of engagement determines a vertex of a first included triangle;

j. said ball and socket engagements between each of the three blades and their respective inner end caps being disposed such that each point of engagement determines the vertex of a second included triangle; and wherein,

k. said vertices of said first included triangle in conjunction with said ball and socket engagement of said outer shroud to said support means define a substantially stable tetrahedral relationship between the points of engagement for the radially outer support of each vane segment; and,

l. said vertices of said second included triangle in conjunction with said ball and socket engagement of said inner shroud to said inner support means define substantially stable tetrahedral relationship between the points of engagement for the radially inner support of each vane segment.