Patent Application
20160290145
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 turbine ring assemblies are 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 very hot streams, typically above the temperature that can be withstood by the metal material. 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, holding the ring sectors in position remains a problem, in particular in the face of differential expansion that can occur between the metal support structure and the CMC ring sectors. In addition, another problem lies in the stresses generated by the imposed movements.
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 said assembly comprises resilient holder devices, each resilient holder device exerting a force on the circumferential ends of two adjacent ring sectors, holding said adjacent sectors in position, and in that each resilient holder device comprises a spring element present beside the outside face of the ring support structure.
By using resilient holder devices, it is ensured that the ring sectors are held in position in the event of differential expansion between the sectors and the support structure, with such movements being compensated by the resilient holding. In addition, by placing the ring element of each resilient holder device beside the outside face of the ring support structure, the spring element 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 spring elements, and it is then possible to use more ordinary materials for fabricating them, such as metal materials.
According to a characteristic of the turbine ring assembly of the invention, it includes a plurality of gaskets, each gasket extending axially over the circumferential ends of two adjacent sectors at the facing edges of said ends. The resilient holder devices exert force that holds the gaskets in contact with the circumferential ends of two adjacent ring sectors.
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.
According to an embodiment 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. 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 circumferential ends 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. Each resilient holder device exerts a force on the facing tabs of two adjacent ring sectors that is directed radially towards the outside of the turbine ring, holding the corresponding gasket in contact with the circumferential ends of two adjacent ring sectors. 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.
In an aspect of the embodiment of the turbine ring assembly of the invention, the gaskets are constituted by strips of ceramic matrix composite material.
In another aspect of the embodiment of the 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 the 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 the turbine ring assembly of the invention, the ring support structure includes tabs that extend from the inside face of a shroud, each tab including a folded-over portion. Each ring sector includes tabs extending from the outside face of its annular base, each tab having a folded-over portion engaged with the folded-over portion of a tab of the ring structure. Each resilient holder device exerts a pressing force on each gasket holding the gasket in contact with the circumferential ends of two adjacent ring sectors.
In another aspect of the embodiment of the turbine ring assembly of the invention, each resilient holder device comprises a shoe in contact with the top surface of the gasket, a rod extending vertically from the outside surface of the shoe, and a spring exerting a pressing force on the free end of the rod.
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:
As shown in
The ring support structure 12 is secured to a turbine casing 13. The structure 12 has an upstream annular radial flange 121 and a downstream annular radial flange 122 that extend from a shroud 123 of 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 in
The ring sectors 110 are arranged in annular manner between the flanges 121 and 122 of the metal ring support structure 12, the inside face of the ring having the layer 112 of abradable material extending beyond the bottom edges 121a and 122a of the flanges 121 and 122.
In order to provide good sealing between the flow passage for the gas stream through the turbine and the outside of the turbine ring, gaskets 130 are placed between adjacent ring sectors at their facing edges. More precisely, the gaskets 130 are dimensioned and placed in such a manner as to cover the end portions 1111 and 1110 of the annular bases 111 of two adjacent ring sectors 110. The gaskets 130 are placed in respective housings 115, each having its bottom formed by the circumferential ends 1111 and 1110 of two adjacent sectors in combination, the top portion of each housing 115 being formed by the tabs 114 and 113 of two adjacent sectors in combination. In this example, the gaskets 130 are made of CMC. The upstream ends 131 and the downstream ends 132 of the gaskets 130 pass through respective slots 1210 and 1220 formed respectively in the upstream and downstream flanges 121 and 122 (
The two adjacent ring sectors 110 and the gasket 130 present between the two adjacent sectors are held by a traction device 140 constituted by a bolt 141 and a spring 142. The bolt 141 has a head 1410 that is placed between the outer face 130a of the corresponding gasket 130 and the tabs 114 and 113 of two adjacent sectors. Notches 1140 and 1130 are formed respectively in the tabs 114 and 113 so as to pass the shank 1411 of the bolt 141. Likewise, orifices 1310 are formed in the shroud 131 of the turbine casing 13 so as to pass the shank 1411 of the bolt 141.
The spring 142 is a compression spring mounted in a prestressed state between the shroud 123 and a nut 1412 engaged on the end of the bolt 141 remote from its end having the head 1410. Thus, the spring 142 exerts a force on the nut 1412 that is directed radially towards the outside of the ring 11 in a direction D shown in
Since each spring 142 is placed beside the outside face of the ring support structure (outside face of the shroud 123), 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.
As shown in
The ring support structure 32 is secured to a turbine casing (not shown in
In order to provide good sealing between the flow passage for the gas stream through the turbine and the outside of the turbine ring, gaskets 330 are placed between adjacent ring sectors at their facing edges. More precisely, the gaskets 330 are dimensioned and placed in such a manner as to cover the circumferential ends 3111 and 3110 of two adjacent ring sectors 310. By way of example, the gaskets 330 are made of a thermally insulating material, such as a felt of oxide (alumina) fibers, or each of them made be made of an elastically deformable insulating material such as a fiber structure or an insulating foam, that is held inside a braid made with fibers that withstand high temperatures, such as ceramic fibers.
The ring sectors 310 and the gaskets 330 are held by a pressing device 340 constituted by a shoe 341 in contact with the top surface of the gasket 340, a rod 343 extending vertically from the outside surface of the shoe, and a spring 342 exerting a pressing force on the free end 3430 of the rod 343. Orifices 51 are formed through the shroud 50 to allow the rod 343 to pass.
The spring 342 is a compression spring mounted in the prestressed state between the free end 3430 of the rod 343 and an annular tab 52 extending from the outside surface 50a of the shroud 50. The tab 52 defines a housing between the inside surface 52b of said tab and the outside surface 50a, the height H2 of the housing being defined as a function of the height H1 of the rods 343 so that H1<H2, thereby enabling the springs 342 to be mounted in a prestressed state.
Thus, the spring 342 exerts a force on the rod 343 that is directed radially towards the inside of the ring 31 in a direction DI shown in
Since each spring 342 is placed beside the outside face of the ring support structure (outside face 50a of the shroud 50), it is spaced apart from the hot stream flowing in the passage and it is exposed only to temperatures that are compatible with the material of the spring. There is thus no need to cool the springs and materials such as metal materials can be used for fabricating them.
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 tabs 113 and 114 apart from the sectors 110 or corresponding to tabs 313 apart from the sectors 310.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1552815 | Apr 2015 | FR | national |
