Turbine engine turbine including a nozzle stage made of ceramic matrix composite material

Abstract

A turbine engine turbine including a nozzle stage made of ceramic matrix composite material and including a plurality of annular sectors forming an annulus presenting an inner shroud and an outer shroud, each sector having an inner platform forming a portion of the inner shroud, an outer platform forming a portion of the outer shroud, and at least one airfoil extending between the outer and inner platforms and secured thereto. A metal ring includes at least one annular sector, and presents an outer surface in contact with the surface of the inner shroud opposite from the surface from which the airfoils extend, the metal ring presenting an outside diameter at its outer surface that is greater than the diameter of the inner shroud such that the nozzle stage is held in compression between a casing and the metal ring.

Claims

1. A turbine engine turbine comprising: a casing; a turbine nozzle stage; and a metal ring for supporting abradable material, the turbine nozzle stage being made of ceramic matrix composite material and comprising a plurality of annular sectors forming an annulus presenting an inner shroud and an outer shroud, each annular sector having an inner platform forming a portion of the inner shroud, an outer platform forming a portion of the outer shroud, and an airfoil extending between the outer platform and the inner platform and secured thereto, the metal ring comprising a sector that is at least partially annular, wherein the metal ring presents an outer surface in contact with an inner surface of the inner shroud of the turbine nozzle stage opposite from an outer surface of the inner shroud from which each airfoil of the plurality of annular sector extends, and wherein, in a pre-assembly state at an ambient temperature, an outside diameter of the outer surface of the metal ring is greater than a diameter of the inner surface of the inner shroud of the turbine nozzle stage at each axial position from upstream to downstream of the metal ring and of the turbine nozzle stage such that the turbine nozzle stage is held in compression between the casing and the metal ring in an assembled state.

2. The turbine according to claim 1, wherein the outer shroud includes an annular rib having at least one crenellation and extending from a surface of the outer shroud that faces the casing, and the casing includes at least one tooth projecting from an inner circumferential surface of the casing towards the turbine nozzle stage and arranged facing said at least one crenellation of the annular rib of the turbine nozzle stage in such a manner that said at least one tooth of the casing cooperates with said at least one crenellation in the annular rib of the turbine nozzle stage in order to prevent the turbine nozzle stage from moving in rotation.

3. The turbine according to claim 2, wherein the casing further includes a shoulder projecting towards the turbine nozzle stage, the shoulder of the casing and the annular rib of the outer shroud of the turbine nozzle stage being dimensioned so that the shoulder of the casing forms an abutment against which the annular rib bears.

4. The turbine according to claim 1, including a flow passage formed by a passage between the outer shroud and the inner shroud of the turbine nozzle stage and within which there flows a gas stream in a flow direction, an inner surface of said inner shroud and said outer surface of the metal ring both presenting negative slopes in the flow direction of the gas stream.

5. The turbine according to claim 1, wherein the inner shroud of the turbine nozzle stage presents an orifice or a notch, and the metal ring includes a lug projecting from the outer surface of the metal ring and suitable for co-operating with the notch or orifice in the inner shroud so as to prevent the metal ring from moving axially or in rotation, the lug being formed by a pin or a peg or a screw forming a peg projecting from the outer surface of the metal ring.

6. The turbine according to claim 1, wherein the metal ring presents an I-shaped section.

7. The turbine according to claim 1, further including at least one gasket arranged between the inner shroud of the turbine nozzle stage and the outer surface of the metal ring.

8. The turbine according to claim 1, further including at least one gasket arranged between the outer shroud of the turbine nozzle stage and an inner surface of the casing.

9. The turbine according to claim 1, wherein the metal ring is made as a single piece.

10. A turbojet including the turbine engine turbine according to claim 1, wherein the turbine engine turbine is a high-pressure turbine or a low-pressure turbine.

11. An aircraft including at least one turbojet according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be better understood on reading the following description given by way of non-limiting indication and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic section view of a portion of a turbine engine turbine in a first embodiment of the invention;

(3) FIG. 2 is a diagrammatic perspective view of the turbine portion of FIG. 1;

(4) FIG. 3 is a fragmentary perspective view of the turbine nozzle of FIG. 1; and

(5) FIG. 4 is a diagrammatic section view of a portion of a turbine engine turbine in a second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) FIG. 1 is a diagrammatic section view of a turbine engine turbine in a first embodiment of the invention.

(7) A high-pressure turbine 1 of a turbine engine, e.g. an aviation turbine engine, as shown in part in FIG. 1, comprises a plurality of stationary nozzle stages 2 that alternate with rotor wheels 3 in the flow direction, as indicated by an arrow in FIG. 1, of the gas stream F through the turbine 1, which nozzles and rotor wheels are mounted in a turbine casing 4.

(8) Each rotor wheel 3 comprises a plurality of blades 32 having an inner shroud 34, and at least one airfoil 38 extending from the inner shroud 34 and connected thereto. On the inside of the inner shroud 34, the blade is extended by a root engaged in a slot in a disk 33. On the outside, the tips of the blades 32 face an abradable material carried by an annulus 36 in order to provide sealing at the tips of the blades 32.

(9) Throughout the present specification, the terms “inner” and “outer” are used with reference to position or orientation relative to the axis of rotation X of the turbine 1.

(10) The blades 32 may be conventional metal blades or they may be CMC material blades, e.g. obtained as described in Documents WO 2010/061140, WO 2010/116066, WO 2011/080443.

(11) At least one of the nozzle stages, such as the nozzle stage 2 in FIG. 1, is formed by uniting a plurality of annular sectors 20 made of CMC material, as shown in FIG. 2, which is a perspective view of the turbine portion of FIG. 1.

(12) Each annular sector 20 of the nozzle stage 2 comprises an inner platform 24, an outer platform 26, and an airfoil 28 extending between the inner and outer platforms 24 and 26 and secured thereto. In a variant, a plurality of airfoils could extend between the inner and outer platforms of a single nozzle sector. Once they are assembled with the casing 4 of the turbine 1, the sectors 20 form a single nozzle annulus 2 presenting an inner shroud 240 made up by the juxtaposed inner platforms 24 of the sectors 20 and an outer shroud 260 made up of the juxtaposed outer platforms 26 of the sectors 20.

(13) The inner shroud 240 of the nozzle stage 2 presents an outer surface 24e and an inner surface 24i, and the outer shroud 260 of the nozzle stage 2 also presents an outer surface 26e and an inner surface 26i. Since the sectors 20 form the nozzle stage 2, the inner platform 24 of each section 20 thus presents an outer surface portion 24e and an inner surface portion 24i, and the outer platform 26 of each sector 20 likewise presents an outer surface portion 26e and an inner surface portion 26i. The airfoil 28 of each sector 20 extends between the outer surface 24e of the inner shroud 240 and the inner surface 26i of the outer shroud 260, and more particularly between the corresponding outer surface portion 24e and the corresponding inner surface portion 24i.

(14) The outer surfaces 24e and 34e of inner shrouds 240 and 34 of the nozzle stage 2 and of the rotor wheel 3, and the inner surfaces 26i and 36i of the outer shrouds 260 of the nozzle stage 2 and of the sealing annulus 36 for the rotor wheels 3 define a passage 45 for passing the gas stream F through the turbine 1.

(15) Throughout the specification, terms “upstream” and “downstream” are used with reference to the flow direction of the gas stream F in the passage 45 as indicated by an arrow.

(16) As can be seen in FIGS. 1 and 2, in this first embodiment, the turbine 1 has a metal ring 5 presenting a section of I-shape. The metal ring 5 thus has an inner shroud 54, an outer shroud 56, and a flat web 58 extending between the inner and outer shrouds 54 and 56 and secured thereto.

(17) In other embodiments, the metal ring 5 may present other shapes.

(18) The inner shroud 54 of the metal ring 5 presents an outer surface 54e and an inner surface 54i, and the outer shroud 56 also presents an outer surface 56e and an inner surface 56i. The flat web 58 extends between the outer surface 54e of the inner shroud 54 and the inner surface 56i of the outer shroud 56.

(19) The outer surface 56e of the metal ring 5 bears against the inner surface 24i of the inner shroud 240 of the nozzle 2 via a wire O-ring 59 and exerts a radial force towards the casing 4 on the nozzle 2. The wire O-ring 59 is thus clamped between the outer surface 56e of the metal ring 5 and the inner surface 24i of the inner shroud 240 of the nozzle stage 2, and provides sealing between these two elements.

(20) The metal ring 5 also supports on the inner surface 54i of the inner shroud 54 an abradable material 51 facing wipers 35 carried by the disk 33 in order to provide the passage 45 with sealing on the inside.

(21) The metal ring 5 may be made up of juxtaposed sectors each constituting an abradable cartridge, or it may be made as a single piece, as shown in FIG. 2.

(22) The diameter of the surface of the outer shroud 56 of the metal ring 5 that is in contact with the inner shroud 240 of the nozzle stage 2, i.e. the diameter of the outer surface 56e of the outer shroud 56 of the metal ring 5, is greater than the diameter of the surface of the inner shroud 240 of the nozzle stage 2 for each axial position from upstream to downstream of the metal ring 5 and of the nozzle stage 2, i.e. greater than the diameter of the inner surface 24i of the inner shroud 240 of the nozzle stage 2.

(23) The nozzle stage 2 is thus held in compression against the casing 4 and the metal ring 5.

(24) The turbine 1 is assembled by initially positioning the sectors 20 of the nozzle stage 2 against an inner surface 4i of the casing 4 over its entire inside periphery, and then inserting the metal ring 5 that has been cooled to a temperature that enables its diameter to be reduced to a dimension that is smaller than the diameter of the inner surface 24i of the inner shroud 240 of the nozzle stage 2 for a given axial position. The metal ring 5 is then returned to ambient temperature while being held in position until it returns to its initial diameter and applies a radial force serving to hold the nozzle stage 2 pressed against the casing 4.

(25) During insertion of the metal ring 5 in the turbine 1, the sectors 20 of the nozzle stage 2 are held stationary in position by means of a specific tool. The specific tool may for example be in the form of a ring possessing teeth projecting in a direction parallel to the axis of rotation X of the turbine 1 so that the teeth can be inserted into the spaces between the airfoils 28 of the nozzle stage 2 and apply a radial force against the outer platform 26 of the sectors 20 making up the outer shroud 260 of the nozzle stage 2 in order to hold them pressed against the casing 4.

(26) FIG. 3 is a fragmentary exploded view in perspective of the metal ring 5 for a sector 20 of the nozzle stage 2, together with the casing 4.

(27) As can be seen in FIGS. 1 to 3, the outer shroud 260 of the nozzle stage 2 has an annular rib 6 presenting at least one crenellation 62 per sector 20. The annular rib 6 extends on the outer surface 26e of the outer shroud 260 of the nozzle stage 2.

(28) Facing each crenellation 62 in the annular rib 6, the casing 4 has a tooth 7 on its inner surface 4i, which tooth projects towards the axis of rotation X of the turbine 1, i.e. towards the nozzle stage 2. The teeth 7 are distributed over the entire circumference of the inner surface 4i of the casing 4 so as to have one tooth 7 facing each crenellation 62 in the annular rib 6 of the nozzle stage 2.

(29) In a variant, the casing could have only one tooth or indeed only a few teeth, or else pegs, suitable for co-operating with one or more crenellations 62 in the annular rib 6.

(30) The teeth 7 and the crenellations 62 are shaped to co-operate in such a manner as to prevent any movement in rotation of the nozzle stage 2 relative to the casing 4, which is itself stationary.

(31) As also shown in FIGS. 1 to 3, the casing 4 has a shoulder 8 projecting towards the nozzle stage 2. The shoulder 8 and the annular rib 6 of the outer shroud 260 of the nozzle stage 2 are dimensioned and shaped so as to co-operate in such a manner that the shoulder 8 forms a first axial abutment against which the rib 6 bears, thereby preventing any axial movement in the gas stream flow direction F indicated by the arrow in FIG. 1.

(32) In the presently-illustrated example, the outer surface 56e of the outer shroud 56 of the metal ring 5 also presents a negative slope in the flow direction F of the gas stream, as indicated by the arrow in FIG. 1, within the flow passage 45. This slope makes it possible to provide a second axial abutment for the metal ring 5, preventing any axial movement in a direction opposite to the flow direction F of the gas stream as indicated by the arrow in FIG. 1.

(33) The effectiveness of the second axial abutment is improved by the negative slope presented by the inner surface 4i of the casing 4 extending from the shoulder 8 to a downstream portion of the shoulder 8.

(34) In a second embodiment as shown in FIG. 4, the inner shroud 240 of the nozzle stage 2 presents an orifice 9, and the metal ring 5 has a tapped hole 11 and a screw 10 that is threaded over a portion only of its shank, the tapped hole 11 in the metal ring 5 being in alignment with the orifice 9 in the inner shroud 240 of the nozzle stage 2.

(35) The screw 10 is screwed into the tapped hole 11 until the non-threaded end of the screw 10 is inserted in the orifice 9 in the inner shroud 240 of the nozzle stage 2. An interference fit peg could equally well suffice. Under such circumstances, the hole 11 would not be tapped.

(36) The screw 10 forming a peg at its free end that is inserted in the nozzle stage 2 serves to provide both an axial abutment and means for preventing the metal ring 5 from moving in rotation.

(37) In the second embodiment, the presence of the orifice 9 and of the screw 10 makes it possible, optionally, to avoid having negative and positive slopes in the nozzle stage 2, given that the functions performed by those elements are performed by the assembly formed by the screw 10 and the orifice 9.

(38) The invention thus provides a turbine engine turbine having a turbine nozzle stage made of CMC that can be mounted in simplified manner and that is adapted to form a rigid assembly with improved sealing.