Turbine ring assembly with inter-sector connections

A turbine ring assembly includes a ring support structure and a plurality of CMC ring sectors forming a turbine ring. Each ring sector is K-shaped in radial section, with tabs extending from the outside face of the annular base over end portions of the annular base, the tabs and the end portions of each ring sector being held respectively facing tabs and end portions of ring sectors that are adjacent in the ring. The turbine ring assembly has a plurality of rigid gaskets, each extending axially between adjacent ring sectors, and resilient holder devices exerting a force suitable for holding the gaskets in contact with the end portions or the tabs of two adjacent ring sectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to French Patent Application No. 1552816, filed Apr. 1, 2015, the entire contents of this application is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to a turbine ring assembly for a turbine engine, which assembly comprises a ring support structure and a plurality of single-piece ring sectors made of ceramic matrix composite material.

The field of application of the invention is in particular that of gas turbine aeroengines. Nevertheless, the invention is applicable to other turbine engines, e.g. industrial gas turbines.

Ceramic matrix composite materials (CMCs) are known for conserving their mechanical properties at high temperatures, thereby making them suitable for constituting hot structural elements.

In gas turbine aeroengines, improving efficiency and reducing certain polluting emissions has led to seeking operation at ever-higher temperatures. When a turbine ring assembly is made entirely out of metal, it is necessary to cool all of the elements of the assembly, and in particular the turbine ring, which is subjected to the hottest streams. Such cooling has a significant impact on the performance of the engine since the cooling stream that is used is taken from the main stream through the engine. In addition, the use of metal for the turbine ring puts a limit on potential increases of temperature in the turbine, even though such increases would nevertheless make it possible to improve the performance of aeroengines.

That is why it has already been envisaged to use CMCs for various hot portions of engines, particularly since CMCs present the additional advantage of density that is lower than that of the refractory metals that have traditionally been used.

Thus, making turbine ring sectors as single pieces of CMC is described in particular in Document US 2012/0027572. Each ring sector comprises an annular base having an inside face that defines the inside face of the turbine ring and an outside face from which there extend two tab-forming portions with ends that are engaged in housings of a metal ring support structure.

The use of CMC ring sectors makes it possible to reduce significantly the ventilation needed for cooling the turbine ring. Nevertheless, although each ring sector is fastened individually to the ring support structure, holding the sectors in position relative to one another can sometimes be problematic since it can be difficult to control the shape of the turbine ring made up of the sectors. Furthermore, another problem resides in the stresses generated by the imposed movements. In addition, sealing between the gas flow passage on the inside of the ring sectors and the outside of the ring sectors remains a problem at the edges of adjacent ring sectors.

OBJECT AND SUMMARY OF THE INVENTION

The invention seeks to avoid such drawbacks, and for this purpose it proposes a turbine ring assembly comprising a ring support structure and a plurality of ring sectors made of ceramic matrix composite material making up a turbine ring, each ring sector comprising an annular base with, in a radial direction of the turbine ring, an inside face defining the inside face of the turbine ring and an outside face facing the inside face of the ring support structure, each said annular base including at each circumferential end a circumferential edge that is held facing a circumferential edge of the circumferential end of the annular base of a ring sector that is adjacent in the turbine ring, the assembly being characterized in that each ring sector presents a K-shape in a plane defined by the radial direction and the circumferential direction of the turbine ring, with tabs extending from the outside face of the annular base over the end portions of said annular base, circumferential edges of the tabs and the circumferential edges of the circumferential ends of each ring sector being held respectively facing the circumferential edges of tabs and the circumferential edges of ring sectors that are adjacent in the ring, and in that the turbine ring assembly includes a plurality of rigid gaskets, each rigid gasket extending axially between two adjacent ring sectors, together with resilient holder devices exerting force holding the gaskets in contact with the circumferential ends or the tabs of two adjacent ring sectors.

The rigid gaskets arranged and held in this way between the ring sectors serve to create a mechanical connection between adjacent ring sectors that improves holding the ring sectors in position, and consequently that improves controlling the shape of the turbine ring. By placing and holding a gasket over the zone where the axial edges of the sectors face one another in the ring, leaks of the gas stream flowing inside the passage formed by the inside face of the ring sectors are limited. In addition, since the gaskets are held by resilient holder devices, the gaskets are held in position and consequently the passage is sealed, even in the event of movements imposed by differential thermal expansion.

According to an aspect of the turbine ring assembly of the invention, the ring support structure has an upstream annular radial flange and a downstream annular radial flange with the ring sectors being held between them without being attached to said flanges, each gasket having an upstream end passing through a slot formed in the upstream radial flange and a downstream end passing through a slot formed in the downstream radial flange. Since the ring sectors are not fastened directly to the support structure, the imposed movements are significantly reduced, and consequently the stresses on the ring sectors are significantly reduced. The ring sectors can thus be positioned more easily relative to one another in order to define a more coherent shape for the turbine ring.

Advantageously, each resilient holder device comprises at least one spring element present beside the outside face of the ring support structure. Thus, the spring elements are spaced away from the hot stream flowing in the passage and they are exposed only to temperatures that are compatible with the material from which the spring element(s) is/are made. There is therefore no need to cool these elements, and it is possible to use more ordinary materials for fabricating them, such as metal materials.

In another aspect of the turbine ring assembly of the invention, the gaskets are constituted by strips of ceramic matrix composite material.

In another embodiment of a turbine ring assembly of the invention, each resilient holder device comprises a bolt and a spring, the bolt having a head present between the outside face of a gasket and tabs of two adjacent sectors, the spring being mounted in a prestressed state between a shroud of the ring support structure and a nut fastened to the end of the bolt remote from its end having the head.

In another embodiment of a turbine ring assembly of the invention, each resilient holder device comprises a finger having a free end pressing against a ring sector, there being a spring element mounted in a prestressed state against each finger. In an aspect of this embodiment, an annular gasket extends over the ring sectors, said annular gasket being interposed between the free ends of the fingers of the resilient holder devices and the ring sectors.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2show a high-pressure turbine ring assembly10in an embodiment of the invention. The assembly10comprises a CMC turbine ring11and a metal ring support structure12. The turbine ring11surrounds a set of rotary blades5. The turbine ring11is made up of a plurality of ring sectors110, withFIGS. 1 and 2being perspective views showing a portion of the high-pressure turbine ring assembly10with an axial section showing the edges of a ring sector110. Arrow DApoints in the axial direction of the turbine ring11and arrow DRpoints in the radial direction of the turbine ring11.

As shown inFIG. 3, each ring sector110is K-shaped in a plane defined by the radial direction DRand by the circumferential direction of the turbine ring11, the sector having an annular base111with its inside face in the radial direction DRcoated in a layer112of abradable material, this inside face defining the flow passage for the gas stream through the turbine. Substantially S-shaped tabs113,114extend from the outside face of the annular base111in the radial direction DR, over its entire width, and above circumferential ends1110and1111of the annular base111. Each annular sector110thus has two circumferential edges1110a&113aand1111b&114bat each of its ends. The edges1110aand113asituated on a first end of a sector110are for being held facing respective edges1111band114bof the ring sector that is adjacent in the turbine ring.

The ring support structure12is secured to a turbine casing13. The structure12has an upstream annular radial flange121and a downstream annular radial flange122that extend from a shroud123of the turbine casing. The terms “upstream” and “downstream” are used herein with reference to the flow direction of the gas stream through the turbine (arrow F inFIGS. 1 and 2). The flanges121and122present respective bottom edges121aand122a.

The ring sectors110are arranged in annular manner between the flanges121and122of the metal ring support structure12, the inside face of the ring having the layer112of abradable material extending beyond the bottom edges121aand122aof the flanges121and122.

In order to provide good sealing between the flow passage for the gas stream through the turbine and the outside of the turbine ring, gaskets130are placed between adjacent ring sectors at their facing edges. More precisely, the gaskets130are dimensioned and placed in such a manner as to cover the end portions1111and1110of the annular bases111of two adjacent ring sectors110in the axial direction of the ring21(i.e. parallel to the flow direction F). The gaskets130are placed in respective housings115, each having its bottom formed by the circumferential ends1111and1110of two adjacent sectors in combination, the top portion of each housing115being formed by the tabs114and113of two adjacent sectors in combination. In this example, the gaskets130are made of CMC. The upstream ends131and the downstream ends132of the gaskets130pass through respective slots1210and1220formed respectively in the upstream and downstream flanges121and122(FIGS. 1 and 2).

The ring sectors110and the gaskets130are held by a traction device140constituted by a bolt141and a spring142. The bolt141has a head1410that is placed between the outer face130aof the corresponding gasket130and the tabs114and113of two adjacent sectors. Notches1140and1130are formed respectively in the tabs114and113so as to pass the shank1411of the bolt141. Likewise, orifices1310are formed in the shroud131of the turbine casing13so as to pass the shank1411of the bolt141.

The spring142is a compression spring mounted in a prestressed state between the shroud123and a nut1412engaged on the end of the bolt141remote from its end having the head1410. Thus, the spring142exerts a force on the nut1412that is directed radially towards the outside of the ring11in a direction D1shown inFIGS. 1 and 3and transmitted to the head1410of the bolt141via the shank1411of the bolt. The head1410then exerts a force that is directed in the direction D1on the tabs113and114of two adjacent sectors110. This force is also transmitted to the circumferential ends1110and1111of two adjacent sectors110that in turn exert a force FT that is directed radially towards the outside of the ring11against the gasket130interposed between the circumferential ends1110and1111of the tabs113and114of two adjacent sectors110. Under the effect of this force, the gaskets130are held in abutment against the top portions of the slots1210and1220formed respectively in the flanges121and122. Sealing between adjacent sectors, i.e. sealing between the gas flow passage on the inside of the ring sectors and on the outside of the ring sectors, is thus provided by the gaskets130. In addition, since both the ring sectors110and the gaskets130are held in position by resilient means (springs142), mechanical connection and sealing between the ring sectors is ensured even when movements are imposed by differential thermal expansion.

Since each spring142is placed beside the outside face of the ring support structure (outside face of the shroud123), it is spaced away from the hot stream flowing in the passage and is exposed only to temperatures that are compatible with the material of the spring. There is therefore no need to cool the springs, and it is possible to use materials such as metal materials for fabricating them.

FIG. 4shows a high-pressure turbine ring assembly20in accordance with another embodiment of the invention. The assembly20comprises a CMC turbine ring21and a metal ring support structure22. The turbine ring21surrounds a set of rotary blades6. The turbine ring21is made up of a plurality of ring sectors210, withFIG. 4being a perspective view showing a portion of the high-pressure turbine ring assembly20with an axial section showing the edges of a ring sector210.

As shown inFIG. 6, each ring sector210is of a shape similar to the shape of the above-described sectors110, i.e. it is K-shaped with an annular base211having its inside face coated in a layer212of abradable material defining the flow passage for the gas stream through the turbine. Substantially S-shaped tabs213,214extend from the outside face of the annular base211over its entire width and over the ends2110and2111of the annular base211. Each ring sector210thus has two circumferential edges2110a&213aand2111b&214bat each of its ends. The edges2110aand213asituated at a first end of a sector210are for being held respectively facing the edges2111band214bof the ring sector that is adjacent in the turbine ring.

The ring support structure22is secured to a turbine casing23. The structure22has an upstream annular radial flange221and a downstream annular radial flange222that extend from a shroud231of the turbine casing. The terms “upstream” and “downstream” are used with reference to the flow direction of the gas stream in the turbine (arrow F inFIG. 4). The flanges221and222present respective bottom edges221aand222a. The ring sectors210are arranged in annular manner between the flanges221and222of the metal ring support structure22, the inside face of the ring having a layer212of abradable material that projects beyond the bottom edges221aand222aof the flanges221and222.

In order to provide good sealing between the flow passage for the gas stream through the turbine and the outside of the turbine ring, gaskets230are placed between adjacent ring sectors at their facing ends. More precisely, the gaskets230are dimensioned and placed in such a manner as to cover simultaneously parts of both tabs214and213of two adjacent ring sectors110in the axial direction of the ring21(parallel to the flow direction F). Each gasket230is placed in a respective housing215having its bottom formed by the ends2111and2110of two adjacent sectors in combination, the top portion of the housing215being formed by the tabs214and213of two adjacent sectors in combination. In this example, the gaskets230are made of CMC. The upstream and downstream ends231and232of the gaskets230pass through respective slots2210and2220arranged respectively in the upstream and downstream flanges221and222(FIGS. 4 and 5).

Each pair of adjacent ring sectors210and the gaskets230that is present between the adjacent ring sectors are held by a corresponding presser device240having a finger241. Each finger241is pivotally mounted on the casing23by a pin243housed both in a bore2411formed in a proximal portion2412of the finger241and in a fork235secured to the casing23. Each finger241has a free end2414in its distal portion2413, which end is for exerting a pressing or thrust force against the underlying ring sector so as to hold one or more gaskets230in contact with the tabs of the adjacent ring sectors. To this end, a spring element242is used that is constituted in this example by a rigid cable2420having at least one spring2421interposed between two ends of the cable2420. The cable2420with at least one spring2421is mounted in a prestressed state around the casing23and passes through a retaining portion2415present on each finger241. In a variant embodiment, the cable may be made directly out of an elastic material, the cable then being mounted on its own in a prestressed state around the casing and passing through each of the guide portions of the fingers.

Thus, the cable2420exerts a force on the fingers241that is directed in a direction D2as shown inFIGS. 4 and 6, and that is transmitted to the free ends2414of the fingers241. Each free end2414then exerts a thrust force on the underlying ring sector that is directed in the direction D2. This thrust force is also transmitted to the tabs213and214of the underlying ring sector210, which in turn exerts a thrust force FP directed radially towards the inside of the ring21against the gaskets230that are interposed between the circumferential ends2110and2111of the tabs213and214of adjacent neighboring sectors210. Under the effect of this thrust force, the gaskets230are held in abutment against the bottom portions of the slots2210and2220formed respectively in the flanges221and222. Sealing between adjacent sectors, i.e. sealing between the gas flow passage on the inside of the ring sectors and the outside of the ring sectors, is thus provided by the gaskets230. In addition, since both the gaskets230and the ring sectors210are held in position by resilient means (cable2420with springs2421), mechanical connection and sealing between the ring sectors is ensured even in the event of movements imposed by differential thermal expansion.

Since the cable2420with its spring2421and the fingers241are placed beside the outside face of the ring support structure (outside face of the shroud23), they are spaced apart from the hot stream flowing in the passage and they are exposed only to temperatures that are compatible with the materials suitable for being used for fabricating them, such as metal materials.

In the presently-described embodiment, the fingers241do not press directly against the ring sectors210. An annular gasket250extends over the ring sectors210and the gasket250is held in position by the fingers241that exert a force on a spacer260placed between the free ends2414of the fingers241and the annular gasket250. Under such circumstances, the thrust force exerted by the fingers241is transmitted to the ring sectors210via the spacer260and the annular gasket250. The gasket250is made of a thermally insulating material such as a felt of oxide (alumina) fibers, or it may be constituted by an elastically deformable insulating material such as a fiber structure or an insulating foam that is held inside a braid made using fibers that withstand high temperatures, such as ceramic fibers.

The turbine ring assembly20can also be made without any annular gasket or spacer. Under such circumstances, the free ends2414of the fingers241press directly against the top portions of the ring sectors210. Likewise, the fingers can exert a thrust force without using a spring cable as described above. By way of example, the fingers may be of a resilient nature and they may be mounted with prestress against the ring sectors, possibly with an annular gasket and a spacer being interposed. A spring element may also be provided between the fork and the proximal portion of each finger so as to transmit a pressing force to the fingers.

Each above-described ring sector is made of CMC by forming a fiber preform of shape close to the shape of the ring sector and by densifying the ring sector with a ceramic matrix.

In order to make the fiber preform, it is possible to use yarns made of ceramic fibers, e.g. SiC fiber yarns such as those sold by the Japanese supplier Nippon Carbon under the name “Nicalon”, or carbon fiber yarns.

The fiber preform is advantageously made by three-dimensional weaving, or by multilayer weaving with zones of non-interlinking being provided to make it possible to space preform portions corresponding to the tabs113and114apart from the sectors110or corresponding to the tabs213and214apart from the sectors210.

The weaving may be of the interlock type, as shown. Other three-dimensional or multilayer weaves can be used, such as for example multi-plain or multi-satin weaves. Reference may be made to Document WO 2006/136755.

After weaving, the blank may be shaped in order to obtain a ring sector preform that is consolidated and densified with a ceramic matrix, it being possible for densification to be performed in particular by chemical vapor infiltration (CVI) as is well known.

A detailed example of fabricating CMC ring sectors is described in particular in Document US 2012/0027572.