Wall cooling arrangement for a gas turbine engine

A wall arrangement for the main gas path of a gas turbine engine, including: a wall segment which defines the main gas path, the wall segment having a gas path side, an outboard side and a support wall extending from the outboard side towards a supporting structure, and a channel member abutting the support wall and having one or more channels defined by the abutment of the support wall and channel member, the one or more channel having radially separated inlet and outlet.

TECHNICAL FIELD OF INVENTION

This invention relates to a wall arrangement for a gas turbine engine. The wall arrangement is particularly advantageous when used with a Ceramic Matrix Composite, CMC, wall segment. However, it may be used where a surface cooling of a metallic component is required.

BACKGROUND OF INVENTION

With reference toFIG. 1, a ducted fan gas turbine engine generally indicated at10has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake11, a propulsive fan12, an intermediate pressure compressor13, a high-pressure compressor14, combustion equipment15, a high-pressure turbine16, and intermediate pressure turbine17, a low-pressure turbine18and a core engine exhaust nozzle19. A nacelle21generally surrounds the engine10and defines the intake11, a bypass duct22and a bypass exhaust nozzle23.

The gas turbine engine10works in a conventional manner so that air entering the intake11is accelerated by the fan12to produce two air flows: a first air flow A into the intermediate pressure compressor13and a second air flow B which passes through the bypass duct22to provide propulsive thrust. The intermediate pressure compressor13compresses the air flow A directed into it before delivering that air to the high pressure compressor14where further compression takes place.

The performance of gas turbine engines, whether measured in terms of efficiency or specific output, is improved by increasing the turbine gas temperature. For any engine cycle compression ratio or bypass ratio, increasing the turbine entry gas temperature produces more specific thrust (e.g. engine thrust per unit of air mass flow). It is therefore desirable to operate the turbines at the highest possible temperatures. However, as turbine entry temperatures increase, the life of a turbine generally shortens, necessitating the development of better materials and/or the introduction of improved cooling systems.

One group of improved materials includes so-called ceramic matrix composite, CMC, materials, CMCs offer superior temperature and creep resistant properties for gas turbine engines and have a considerably lower density than their superalloy counterparts making them ideal for aeroengines. Further, because they have a higher temperature tolerance, CMC materials require less cooling which acts to increase specific fuel consumption further.

CMC materials generally consist of ceramic fibres embedded with a ceramic body. There are different materials available for fibres and the body. Two of the more promising materials for gas turbine engines are silicon carbide fibres within a body of silicon carbide, so-called SiC/SiC, and aluminium oxide fibres within an aluminium oxide body, which is referred to simply as an oxide CMC. The processes for manufacturing CMC materials are reasonably well known and understood in the art.

FIG. 2shows a high pressure turbine section of the engine shown inFIG. 1. Thus, there is shown an nozzle guide vane212and turbine blade214in flow series having aerofoil sections within the main gas path216. The turbine blade includes a tip218which is radially shrouded by a seal segment220. The seal segment220bounds and defines the main gas path216on the outboard side of the turbine core. The seal segment220in the example shown is manufactured from a CMC material so as to provide some of the advantages outlined above.

The seal segment220includes a radially inboard gas washed surface222with radially extending supporting walls224which project towards and append from the engine casing via an intermediate support structure in the form of a so-called carrier226. The walls224include forward facing hooks which mate with corresponding formations on the carrier226. The carrier226is attached to the engine casing230.FIG. 2shows a single seal segment220in streamwise section but it will be appreciated that this is one of many circumferentially arranged seal segments220configured to provide an annular wall around the turbine wheel.

Although CMC components are much improved with regard to thermal performance, there is still a requirement to cool them. However, the cooling must be done in such a way that the thermal differential across any part of the component is kept to a minimum to prevent the associated thermal strain which may lead to cracking and failure of parts.

The wall arrangement shown inFIG. 2uses two sources of cooling air having different temperatures and pressures to provide cooling to the outboard side of the seal segment. A dual source cooling of this type promotes more efficient use of cooling air which ultimately improves the efficiency of the engine. However, internal cooling passages are difficult to manufacture and can lead to deleterious thermal stress.

The invention seeks to provide an improved cooling arrangement for a gas turbine engine.

STATEMENTS OF INVENTION

The present invention provides a wall arrangement according to the appended claims.

Described below are wall arrangements for the main gas path of a gas turbine engine, comprising: a wall segment which defines the main gas path, the wall segment having a gas path side, an outboard side and a support wall extending from the outboard side towards a supporting structure, and a channel member abutting the support wall and having one or more channels defined by the abutment of the support wall and channel member, the one or more channel having radially separated inlet and outlet.

Either or both the channel member or support wall may include at least one recess in an abutting surface thereof, the abutting surface being in contact with a corresponding surface of the support wall such that corresponding surface of the supporting wall and recess define the channel.

The recesses may be provided by a plurality of protrusions located on the abutting surface. The protrusions may be arranged to provide a separation of the upstream surface of the channel member and supporting wall when the two are in an abutting relation. The protrusions may be pedestals or ribs. The ribs may be elongate and arranged longitudinally. The recesses support wall may include one or more recesses. The support wall recesses may be in addition to or as an alternative to the channel member recesses.

The channel member is provided on a downstream side of the support wall. The inlet and outlet may be at radial extremes of the channel member.

The inlet may be located within an inlet portion which extends axially fore of the downstream supporting wall so as to radially shroud the distal end of the supporting wall. The distal end is with respect to the main gas path and principal axis of the engine.

The inlet portion may be separated from the supporting wall. The inlet portion may be inclined relative to the radially outer surface of the supporting wall so as to provide a convergent channel therebetween.

The outlet may include an outlet portion which extends axially downstream from the supporting wall. The outlet portion may abut the outboard side of the wall segment. The one or more channels may extend at least to the outlet portion. The outlet portion may terminate local to the junction between the supporting wall and outboard side of the wall segment. Alternatively, the outlet portion may extend fully to a trailing edge portion of the wall segment. The outlet portion may include a one more outlets apertures corresponding to the one or more channels. The one or more outlet apertures may be located in a flow alignment with a downstream component so as to provide a cooling flow thereto.

The support wall may fluidically partition a space outboard of the wall segment to provide an upstream and a downstream chamber. The channel member inlet may be provided in fluid communication with the upstream chamber. The outlet is in fluid communication with the downstream chamber. The upstream and downstream chamber may provide a holding space for cooling air. The cooling air may have different operating temperatures and pressures in the upstream and downstream chambers. The upstream chamber may include air of a higher pressure than the downstream chamber.

The wall segment may comprise a CMC material.

The wall arrangement may further comprise a carrier which provides radial support for the wall segment. The engine casing may include at least one appendage in an abutting relation with the wall segment. The at least one appendage may be provided on a downstream side so as to provide axial retention of the wall segment.

The at least one appendage may be a protrusion or projection extending from the engine casing. The protrusion or projection may be a flange or lug. The appendage may engage with the carrier to provide additional axial retention thereof.

The channel member may be sandwiched between the appendage of the engine casing and the supporting wall.

The wall segment may be attached to a carrier structure. The carrier may be attached to an engine casing via an intermediate attachment.

The carrier may include a metering through-hole local to the inlet of the channel member.

Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination. For example features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

DETAILED DESCRIPTION OF INVENTION

Thus,FIG. 3provides a wall arrangement310for a gas turbine engine. The wall arrangement310includes a wall segment312in the form of a seal segment, a carrier314and an engine casing316. The wall segment312defines and bounds the main gas path on the outboard side of a turbine blade318and as such has a gas path side320, and an outboard side322. It will be appreciated that the wall arrangement310is one of a plurality of circumferentially adjacent segments which form an annulus around the turbine blades as is well known in the art.

The wall segment312includes a supporting wall324which extends from the outboard side in a generally radial direction towards the engine casing316. The supporting wall324includes a birdsmouth or hook326at a distal end thereof which receives a corresponding feature of the carrier. The supporting wall324fluidically partitions the space outboard of the wall segment312to provide upstream and downstream chambers328,330. In use, the upstream and downstream chambers are provided with cooling air of different relative pressures.

The supporting wall324is located in the axial downstream half of the wall segment312. A fore hook332is provided towards an upstream edge of the wall segment312. The fore hook332receives a corresponding feature of the carrier. Both the fore hook332and the supporting wall hook326are forward facing so as to receive the carrier from an upstream direction.

The carrier314provides an intermediate support between the engine casing316and wall segment312. The carrier314includes an upstream wall334and a downstream wall336which engage with the fore hook332and supporting wall hook326of the wall segment312. The outboard end of the upstream334and downstream336walls include further hook features which attach to corresponding engagements on the engine casing316. The downstream carrier hook attachment provides a circumferential slot which receives the hook326of the wall segment312and that of the engine casing316in a radially adjacent and separated relation.

A bracing wall338extends between the upstream334and downstream336walls of the carrier314in an axial and radial direction so as to react the axial loading of the wall segment312to the downstream engine casing attachment. The bracing wall includes one or more metering holes340which governs the pressure in the upstream chamber328.

The downstream wall336of the carrier includes one or more through-holes342to fluidically connect the upstream328and downstream330chambers. In use, the through-hole342provides a metered amount of cooling air from chamber328down the back of the support wall324and wall segment312and exhausts it in a downstream direction and towards the trailing edge of the wall segment. The arrangement is configured to maintain a pressure bulkhead seal between the upstream and downstream chambers328and330.

The through-hole342includes an inlet and outlet. The outlet is positioned radially outboard of the wall segment supporting arm so as to pass air over the supporting wall324without the need of a further through-hole in the supporting wall324.

The engine casing316is a substantially tubular member and provides support and containment for the turbine. The engine casing includes fore344and aft346hooks which engage with and support the carrier314. The aft hook346includes an axial restriant in the form of a lug or flange348which extends axially downstream and radially inwards. The flange348resides on the downstream side of the wall segment312supporting wall324. A first end of the flange348is attached to the engine casing at a common location to the aft hook346, however, the flange may attach to the engine casing separately to the carrier support features.

Thus, the engine casing provides direct axial restraint of the wall segment316and carrier314. The direct axial restraint is provided by an abutting contact with an integral appendage of the engine casing. The appendage may be provided by the hook or flange described above and shown inFIG. 3, or may be an alternative protrusion.

A channel member350(additionally shown inFIG. 5) is located on the downstream side of the wall segment supporting wall324. The channel member350is adjacent to and abuts the downstream side of the supporting wall324and extends in radial and circumferential directions to cover the extent of the supporting wall324, the interface between the two being provided by corresponding respective abutting surfaces.

The channel member350includes axially extending inlet352and outlet354portions. The inlet portion352is outboard of the supporting wall326and extends in a generally upstream axial direction so as to pass over the wall segment hook, thereby shrouding it. The inlet portion352extends forward from the downstream side of the supporting wall326towards the carrier314. Thus, a first end of the channel member350is proximate to a wall of the carrier314; potentially abutting the carrier wall314under some load conditions. The outlet portion354is located proximate to the outboard side322of the wall segment312and extends in a generally downstream direction.

The channel member350includes a plurality of recesses356in a surface thereof. The recesses356are elongate and extend radially inwards from the inlet portion352to the outlet portion354thereof. The recesses356are thus provided by radially extending walls which partition the abutting surface into a plurality of circumferentially separated discrete flow channels which are substantially rectangular in lateral section. It will be appreciated, that channel shapes other than rectangular, may be beneficial for managing the flow of cooling air therein. Further, the surfaces of the channel member350and/or wall segment312may include surface features to promote cooling. Such features may include strips or pedestals as well known in the art of turbine cooling.

The channels and recesses may be provided by a plurality of protrusions located on the abutting surface. The protrusions would act to provide a separation and spacing of the upstream surface of the channel member350and supporting wall326when the two are in an abutting relation. Hence, the recesses may be provided by a general separation of the flow passage walls and may include a plurality of interconnected generally parallel flow paths. The protrusions may be pedestals or ribs. The ribs may be elongate and arranged longitudinally parallel relation. It will be appreciated that such features may also be preferentially arranged to enhance heat transfer between the cooling air flow and components.

The recesses356are provided in the upstream surface of the channel member350which is proximate to and abuts the corresponding opposing surface of the support wall324. Thus, the recesses356and supporting wall define a channel in unison.

The channel extends from the inlet portion352to the outlet portion354to provide a fluid communication between the two. Hence, the fluid communication provides a metered flow of cooling air from an upstream high pressure chamber to a downstream lower pressure chamber.

It will be appreciated that in some examples, the support wall324may provide the recesses for a cooling flow. In this instance, the channel member350may include a planar surface to enclose the channel, or include a further recess to supplement the over flow area.

The inlet portion includes an axially extending wall which extends radially upstream over the distal end of the supporting wall so as to shroud it. The inlet portion wall is inclined relative to the radially outer surface of the supporting wall such that the separating gap is in the form of a convergent channel upstream of the inlet, the inlet being provided at the junction of the supporting wall surface and abutting surface of the channel member.

The radially inner end of the channel member350terminates in an axially extending wall portion which abuts the outboard side of the wall segment, thereby providing an outlet portion. The outlet portion includes recesses in the abutting surface thereof which combine with the outboard side to provide the flow channels in a similar fashion to the supporting wall described above.

The exhausting flow may be used to cool an upstream edge or portion of a downstream component such as the adjacent nozzle guide vane platform which may be made from a metallic material and require a greater degree of cooling. Thus, the outlet portion which is located proximate to or abutting the radial outboard side of the wall segment312may extend to a greater or lesser extent than that shown inFIG. 3. The outlet portion may extend fully to a trailing edge portion of the wall segment.

The channel member350is sandwiched between the axially restraining flange of the engine casing.

The carrier314and wall segment312hook include a seal therebetween in the form of a rope seal358. The rope seal358provides a more predictable seal under operating conditions which results in a more accurate metering of cooling air from through-hole342The wall segment312of the described example is made from a CMC material as known in the art. However, it will be appreciated that the wall surface cooling arrangement provided by the invention may find utilisation for walls constructed from alternative materials, such as metal as is well known in the art for gas turbines.

The channel member350may be constructed from any suitable material known in the art. Thus, the channel member may, for example, be made from the same material as the carrier or the wall segment.

It will be appreciated that the channel member will generally form a full annulus around principal axis of the engine when assembly, but will typically be made up from numerous segments. The circumferential extent of the segments may match that of the wall segment314, or by a multiple thereof. For example, the channel member350may be twice the arcuate length of the wall segment and carrier which are formed as a cassette prior to attachment to the engine casing.

In use, cooling air of a first pressure is provided in the upstream chamber and cooling air of a second pressure on the downstream side. The two sources of cooling air will typically be provided by separate stages of a compressor. The cooling air provided to the upstream chamber328enters through one or more inlets360located in the upstream wall. The metered air flow is then provided to the radially inner sub-chamber before passing through the downstream wall of the carrier314via the inlet through-hole which is local to the inlet of the channel member350.

FIG. 4shows an alternative wall arrangement410. The wall arrangement410is similar in many respects to that ofFIG. 3with some specific differences highlighted below. Thus, the description of features inFIG. 3, may be attributed toFIG. 4where appropriate.

FIG. 4shows a wall arrangement410which includes a wall segment412, a carrier414and an engine casing416. The wall segment412defines and bounds the main gas path on the outboard side of a turbine blade418and as such has a gas path side420, and an outboard side422. It will be appreciated that the wall arrangement410is one of a plurality of circumferentially adjacent segments which form an annulus around the turbine blades as is well known in the art.

The wall segment412includes a supporting wall424which extends from the outboard side in a generally radial direction towards the engine casing416. The supporting wall424includes a birdsmouth or hook426at a distal end thereof which receives a corresponding feature of the carrier. The supporting wall424fluidically partitions the space outboard of the wall segment412to provide upstream and downstream chambers428,430. In use, the upstream and downstream chambers are provided with cooling air of different relative pressures to provide cooling to the wall segment412.

The supporting wall424is axially located in the downstream half of the wall segment412. A fore hook432is provided towards an upstream edge of the wall segment412and a corresponding feature of the carrier414. Both the fore hook434and the supporting wall hook426are forward facing so as to receive the carrier hooks from an upstream direction.

The carrier414provides an intermediate support between the engine casing416and wall segment412. The carrier414includes an upstream wall434and a downstream wall436which engage with the fore hook432and supporting wall hook436of the wall segment412. The outboard end of the upstream434and downstream436walls include further hook features which attach to corresponding engagements on the engine casing416. A bracing wall438extends between the upstream434and downstream436walls of the carrier414with an axial and radial inclination so as to react the axial loading of the wall segment to the downstream engine casing attachment. Thus, the bracing wall extends from a radially inner upstream location to a radially outer downstream location adjacent the downstream hook436.

The downstream wall436of the carrier414includes one or more through-holes442to fluidically connect the upstream428and downstream430chambers. The through-hole442includes an inlet and outlet. The outlet is positioned radially outboard of the wall segment supporting wall424so as to pass air over the radially distal end of the supporting wall424.

The engine casing416is a substantially tubular housing which provides support and containment for the turbine. The engine casing416includes fore444and aft446hooks which engage with and support the carrier414. The aft hook446includes an axial restriant in the form of a lug or flange448which extends axially downstream and radially inwards. The flange448resides on the downstream side of the wall segment412supporting wall424. A first end of the flange448is attached to the engine casing at a common location to the aft hook446, however, the flange448may attach to the engine casing416separate to the carrier support features in some examples.

A channel member450(additionally shown inFIGS. 6aand 6b) is located on the downstream side of the wall segment supporting wall424. The channel member450is adjacent to and abuts the downstream side of the supporting wall424and extends in a radial and circumferential direction to cover the extent of the supporting wall424. The channel member450includes an inlet452towards at the radially outboard end, and an axially extending outlet454portion. The inlet452is located adjacent the distal end of the supporting wall424by the supporting wall424. The outlet portion454is located proximate to the outboard side422of the wall segment412and extends in a generally downstream direction. Thus, in the streamwise section ofFIG. 4, the channel member includes is generally L-shaped.

The channel member450includes a plurality of recesses456in a surface thereof. The recesses456are elongate and extend radially from the inlet portion452to the outlet portion454. The recesses456are substantially rectangular in lateral section. As with the previously described example, it will be appreciated that other channel shapes may be beneficial for managing the flow of cooling air therein, and the surfaces of the channel member450, or wall segment412may include surface features to promote cooling.

The recesses456are provided in the upstream surface of the channel member450which is proximate to and abuts the corresponding opposing surface of the support wall424. Thus, the recesses456and supporting wall define a channel in unison. The channel extends from the inlet portion452to the outlet portion454to provide a fluid communication between the two.

It will be appreciated that in some examples, the support wall424may provide the recesses for a cooling flow. In this instance, the channel member450may include a planar surface to enclose the channel, or include a further recess to supplement the over flow area.

The channel member is sandwiched between the axially restraining flange of the engine casing.

The wall arrangement410shown inFIG. 4includes an additional or intermediate support structure460which resides between engine casing416and carrier414. The intermediate support460includes fore and aft facing hooks which engage with corresponding carrier414and engine casing416hooks, respectively.

The intermediate member460provides an axial retention feature in the form of an axially extending wall portion466and radial flange468which provides an axial restraint face. The axially extending wall portion466which partially defines the hook feature which engages with the engine casing hook. An end of the axially extending wall portion terminates in a radial flange which falls downstream of and provides axial retention face for the wall segment, via the channel member.

It will be appreciated that although the examples above show forward facing hooks, the channel members may be placed on an upstream side of the supporting wall where rearward facing hooks are used.

It will be understood that the invention is not limited to the described examples and embodiments and various modifications and improvements can be made without departing from the concepts described herein and the scope of the claims. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more described features.