Turbomachine turbine having a CMC nozzle with load absorption and positional adjustment

Abstract

A turbine including a casing and a nozzle including an outer metallic shroud secured to the casing, an inner metallic shroud, and a plurality of nozzle segments made of CMC forming a crown extending between the outer shroud and the inner shroud, each segment including a strut, an inner platform, an outer platform and at least one airfoil having a hollow profile traversed by the strut, wherein for each airfoil, the outer platform includes an axial stop extending in outward radial protrusion from the outer platform, and the outer metallic shroud comprises a complementary axial stop extending in inward radial protrusion from the outer metallic shroud, the axial stop being upstream and axially bearing against the complementary axial stop, and machined with an angle of machining chosen to adjust the orientation of said at least one blade of the segment with respect to the axial direction.

Claims

1. A method for manufacturing a turbomachine turbine, wherein the turbomachine turbine comprises a casing, an outer support shroud made of metal secured to the casing and defining an axial direction and a radial direction, an inner support shroud made of metal, an annular turbine nozzle including a plurality of nozzle segments made of ceramic matrix composite material forming a crown extending between the outer support shroud and the inner support shroud, each segment including an inner platform, an outer platform and at least one airfoil extending radially between the inner and outer platforms and having a hollow profile defining an inner housing extending radially, and the turbine further comprising, for each segment, at least one strut secured to the outer metallic support shroud and radially traversing the segment via the housing of an airfoil, for each segment, the outer platform comprising a radially outer surface facing the outer metallic shroud and an axial stop extending in radial protrusion from the radially outer surface of the outer platform, and the outer metallic shroud comprises a radially inner surface facing the outer platform and a complementary axial stop extending in radial protrusion from the radially inner surface of the outer metallic shroud, the axial stop bearing along the axial direction against the complementary axial stop and located upstream of the complementary axial stop with respect to the direction of a stream of air intended to flow through the turbine, and a surface of the axial stop in contact with the complementary axial stop having an angle of machining with respect to a plane orthogonal to the axial direction, the angle of machining being chosen to adjust an orientation of said at least one airfoil of the segment with respect to the axial direction, and wherein the annular turbine nozzle is formed of the ceramic matrix composite material in a first step, then the orientation of the at least one airfoil is controlled in a second step, then the angle of machining of the surface of the axial stop in contact with the complementary axial stop is determined to adjust the orientation of said at least one airfoil with respect to the outer metallic shroud in a third step, the surface of the axial stop in contact with the complementary axial stop is machined in a fourth step, and the annular turbine nozzle is assembled on the outer and inner support shrouds and on the casing of the turbine in a fifth step.

2. The method as claimed in claim 1, wherein the struts and the outer metallic shroud are made as a single part.

3. The method as claimed in claim 1, wherein the outer metallic shroud comprises, along the axial direction, an upstream end and a downstream end, the complementary axial stop being located on the downstream end.

4. The method as claimed in claim 1, wherein the strut is hollow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic section view of a segment of a turbine according to an embodiment of the invention.

(2) FIG. 2 is a schematic perspective top view of a ring segment of the turbine of FIG. 1.

(3) FIG. 3 shows a schematic perspective bottom view of an outer support shroud of the turbine of FIG. 1.

(4) FIG. 4 schematically represents the angle formed by the airfoil before the machining of the bearing surface of the axial stop for three different examples.

(5) FIG. 5 shows, for the three configurations of FIG. 4, the angle of machining of the axial stops of the airfoils.

(6) FIG. 6 schematically represents the differences in through section between two airfoils for the three configurations of FIG. 4.

DESCRIPTION OF THE EMBODIMENTS

(7) FIG. 1 illustrates a schematic section view of a segment of a turbine according to an embodiment of the invention. A high-pressure turbine 1 of a turbomachine, for example an aeronautical turbojet engine, as partially shown in FIG. 1, comprises a plurality of fixed nozzles 2 which alternate with impellers in the direction of flow of the of the gas stream F, indicated by an arrow in FIG. 1, in the turbine 1 and which are installed in a turbine casing.

(8) Each impeller comprises a plurality of blades having an inner shroud, and at least one airfoil extending from the inner shroud and linked to it. On the inner side of the inner shroud, the blade extends in a root engaged in a housing of a disc. On the outer side, the tip of each blade faces an abradable material borne by a ring to provide the seal at the blade tips.

(9) Throughout this text, the terms inner or internal and outer or external are used with reference to the position or the orientation with respect to the axis of rotation of the turbine 1 which defines the axial direction D.sub.A of the turbine 1.

(10) The blades of the impeller can be conventional metallic blades or blades made of CMC material obtained for example as described in the documents WO 2010/061140, WO 2010/116066, and WO 2011/080443.

(11) At least one of the nozzles 2 of the turbine 1 is formed by joining several annular nozzle segments 20 made of CMC material to form an entire ring. The arrow D.sub.A indicates the axial direction of the nozzle 2 while the arrow D.sub.R indicates the radial direction of the nozzle 2 and the reference D.sub.C indicates the circumferential direction.

(12) Each nozzle segment 20 of the nozzle 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 attached to them. In a variant, several airfoils could extend between the inner and outer platforms of one and the same nozzle segment. Once assembled with the casing of the turbine 1, the segments 20 form a single crown of nozzles 2 having an inner shroud formed by the juxtaposition of the inner platforms 24 of the segments 20 and an outer shroud formed by the juxtaposition of the outer platforms 26 of the segments 20.

(13) The inner shroud and the outer shroud together form a fluid flow path 45 inside which the gas stream F flows during the operation of the turbine 1.

(14) Throughout the text, the terms upstream and downstream are used with reference to the direction of flow of the gas stream F in the path 45 indicated by an arrow.

(15) The inner platforms 24 each have an outer surface 24e intended to be in contact with the gas stream F, and therefore radially disposed facing the outer platforms 26 forming the outer shroud. The inner platforms 24 moreover have an inner surface 24i disposed facing the axis of rotation of the turbine 1.

(16) The outer platforms 26 each have an outer surface 26e disposed facing the radially outer casing. The outer platforms 26 moreover have an inner surface 26i intended to be in contact with the gas stream F, and therefore radially disposed facing the inner platforms 24 forming the inner shroud and facing the axis of rotation of the turbine 1.

(17) The nozzle 2 is retained between an inner metallic shroud 5 and an outer metallic shroud 9 between which extends the crown formed by the assembly of the ring segments 20 of the nozzle 2. The outer metallic shroud 9 is secured to the casing and has an inner surface 91 and an outer surface 92 along the radial direction D.sub.R.

(18) As illustrated in FIG. 1, and also in FIG. 2 which shows a schematic top perspective view of a nozzle segment 20, each airfoil 28 has a hollow profile having an inner housing 280 extending over the entire height of the airfoil 28, i.e. between the inner platform 24 and the outer platform 26 of the ring segment 20. The inner platform 24 of each nozzle segment 20 comprises an orifice 245 the shape of which corresponds to the section of the inner housing 280 in the plane wherein the inner platform 24 extends. Similarly, the outer platform 26 of each nozzle segment 20 comprises an orifice 265 the shape of which corresponds to the section of the inner housing 280 in the plane wherein the inner platform 26 extends. The orifices 245 and 265 of the inner 24 and outer 26 platforms are made in the extension of the inner housing 280 of the airfoil 28.

(19) The inner housing 280 of the airfoil 28 and the orifices 245 and 265 of the inner 24 and outer 26 platforms may be connected to a cooling system delivering a stream of cooling air from the casing into the airfoil 28 and the inner 24 and outer 26 platforms.

(20) As illustrated in FIG. 1 and in FIG. 3 which shows a schematic bottom perspective view of an outer support shroud 9, the outer support shroud 9 comprises, for each nozzle segment 20, a strut 6 extending in the radial direction D.sub.R from the inner surface 91 of the outer metallic shroud 9.

(21) As illustrated, the strut 6 comprises a rod 62 extending in protrusion from the head 61 in the radial direction D.sub.R inward and configured to traverse the outer metallic shroud 9, the inner housing 280 of the airfoil 28 and the orifices 245 and 265 of the inner 24 and outer 26 platforms being aligned with the inner housing 280 of the airfoil 28.

(22) In other words, the strut 6 comprises a first radially inward end 6i and a second radially outer end 6e, a body 62 extending substantially along the radial direction D.sub.R between the first and second ends 6i and 6e of the strut 6.

(23) The strut 6 is hollow to convey air into the cavity radially inward of the inner shroud in order to pressurize it and thus avoid the air circulating in the flow path extending between the inner and outer platforms of the nozzle segments from being reintroduced outside this flow path and thus reducing the performance and increasing the risk of the parts overheating. The strut 6 thus comprises an inner housing 60 extending in the radial direction D.sub.R between the first and second ends 6i and 6e of the strut 6.

(24) The outer metallic shroud 9 comprises an upstream end 94 and a downstream end 95 along the axial direction D.sub.A. On its downstream end 95, the outer metallic shroud 9 comprises a shoulder 96 extending radially inward from the inner surface 91 of the outer metallic shroud 9 over the entire circumference of the outer metallic shroud 9, and forming a bearing surface 960 along the axial direction D.sub.A, the bearing surface 960 of the outer metallic shroud being oriented along the axial direction D.sub.A face-to-face with the flow of the stream F, in other words facing upstream.

(25) The outer platform 26 comprises an axial stop 260 extending radially outward from the outer surface 26e of the outer platform 26, the axial stop 260 having an axial bearing surface 262 oriented along the axial direction D.sub.A along the direction of flow of the stream F, i.e. facing downstream. The axial bearing surface 262 of the axial stop 260 is thus facing, and even in contact with, the bearing surface 960 of the shoulder 96 of the outer metallic shroud 9.

(26) To ensure that each segment 20 of the annular nozzle 2 has the same through section between these airfoils 28, the orientation of the airfoils with respect to the axial direction D.sub.A is adjusted by machining, during the assembly of the turbine 1, the axial bearing surface 262 of the axial stop 260, before finalizing the assembly of the nozzle 2 with the outer metallic shroud 9.

(27) As illustrated in FIG. 4, during the formation of the CMC material ring segments 20, the segments 20 may slightly vary from one another and have slight differences in the angle formed, in a plane orthogonal to the radial direction D.sub.R, between the axial bearing surface 262 of the axial stop 260 and the direction of the airfoil 28, particularly the direction of a trailing edge 282 of the airfoil 28. In FIG. 4, three different angles .sub.1, and .sub.2 are thus observed, with in particular the size relationship .sub.1<<.sub.2. In FIG. 4, the direction of the reference airfoil 28 forming the angle is shown in dashes each time, while the directions of the actual airfoils 28 are shown in dot-and-dash lines for the two airfoils having an angle .sub.1 and an angle .sub.2. The difference between the actual angle (.sub.1 and .sub.2) and the reference angle forms an angle of variation respectively denoted .sub.1 and .sub.2.

(28) As illustrated in FIG. 5, the variation in the direction of the airfoils 28 gives rise to a variation in the distance L between the airfoils 28, and therefore of the through section. FIG. 5 shows three pairs of segments in which the top airfoil always has the same direction of the trailing edge, in this case a direction forming the reference angle with the axial bearing surface 262 of the axial stop 260 of the outer platform 26, and the bottom airfoil having a direction forming first the angle .sub.1, then the same reference angle then the angle .sub.2. This has the consequence of obtaining three different lengths L, L.sub.1 and L.sub.2 between the airfoils of the three pairs, and thus three different through sections.

(29) To offset any such variations and adjust the orientation of the segments 20 and therefore of the airfoils 28, the axial bearing surface 262 of the axial stops 260 of the outer platforms 26 is machined with an angle corresponding to said angle of variation .sub.1 or .sub.2 for example, as illustrated in FIG. 6 which shows three different axial stops 260 in top view.

(30) Furthermore, the internal support shroud 5 comprises orifices configured to receive the struts 6. The strut 6 provides a means for attaching the CMC nozzle segment 20 from the top, while minimizing the bending moment, insofar as the bending length is reduced by approximately half due to the strut 6 traversing the nozzle segment. Each nozzle segment 20 is thus retained deterministically, i.e. in such a way as to avoid the nozzle segment 20 from starting to vibrate and by controlling its position, while also allowing the nozzle segment 20 to deform under the effects of temperature and pressure inter alia, independently of the metallic interface parts.

(31) If each nozzle segment were to comprise several airfoils, the turbine would comprise, at the most, a corresponding number of struts for each nozzle segment.

(32) The turbomachine turbine according to the invention comprises a turbine nozzle at least partly made of CMC, the installation of which is simplified and adapted to retain its nozzle segments deterministically while allowing the segments to deform independently of the metallic interface parts, and while improving the seal between the strut and the outer metallic shroud.