US20080145211A1 - Wall elements for gas turbine engine components - Google Patents

Abstract

A wall structure for a gas turbine engine combustor has an inner wall and an outer wall defining a duct, the wall structure including an outer wall having a radial step and an inner wall overlapping the radial step, a duct being defined between the inner and outer walls for the passage of cooling air; the wall structure being characterised in that the inner wall has a local thickening opposing the radial step. The velocity of cooling air through the duct is maintained and heat transfer subsequently improved.

Description

• This invention relates to wall elements for gas turbine engine combustors.
• A typical gas turbine engine combustor includes a generally annular chamber having a plurality of fuel injectors at an upstream head end. Combustion air is provided through the head and through ports provided in the combustor walls downstream of the fuel injectors.
• In order to improve the thrust and fuel consumption of gas turbine engines, i.e. the thermal efficiency, it is necessary to use high compressor pressures and combustion temperatures. Higher compressor pressures give rise to higher compressor outlet temperatures and higher pressures in the combustion chamber.
• There is, therefore, a need to provide effective cooling of the combustion chamber walls. One cooling method which has been proposed is the provision of a double walled combustion chamber in which the inner wall is formed of a plurality of heat resistant tiles. Cooling air is directed into the duct between the outer walls and the tile from an aperture located midway along the tile. The flow of air bifurcates into upstream and downstream flows which are exhausted into the combustion chamber past the upstream and downstream edges of the tile. As the downstream flow approaches the end of the tile it is supplemented by air from the downstream tile before exiting to form a film over the downstream tile. The confluence of the flow with the flow from the downstream tile is typically at a region where the outer wall of the combustor steps radially. The radial step changes the velocity of the cooling air flow and affects the rate of heat removal at the rear edge of the tile which is also the location of the tile most susceptible to erosion.
• According to the present invention there is provided a wall structure for an annular gas turbine engine combustor arranged to have a general direction of fluid flow therethrough, the wall structure including an outer wall having a radial step and an inner wall overlapping the radial step, a duct being defined between the inner and outer walls for the passage of cooling air; the wall structure being characterised in that the inner wall has a local thickening opposing the radial step.
• The outer wall may have a plurality of apertures for feeding cooling air into the duct.
• Preferably the inner wall includes a plurality of wall elements, each wall element having a body portion aligned in use with the general direction of fluid flow through the combustor and a plurality of pedestals that extend within the duct from the body portion towards the outer wall.
• Preferably the body portion provides the local thickening.
• The downstream end of the body portion of an upstream wall element may overlap the upstream end of the body portion of a downstream wall element.
• Preferably the local thickening has a contour that follows the contour of the radial step.
• According to a second aspect of the invention there is provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls, the inner and outer walls defining a duct therebetween, the wall element having a body portion aligned in use with a general direction of fluid flow through the combustor, the wall element having a local thickening in its downstream end region the local thickening being adapted to oppose a radial step in the outer wall.
• Preferably the wall element has a plurality of pedestals arranged in use to extend within the duct from the body portion towards the outer wall.
• Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:—
• FIG. 1 is a sectional side view of the upper half of a gas turbine engine;
• FIG. 2 is a vertical cross-section through the combustor of the gas turbine engine shown inFIG. 1;
• FIG. 3 is a diagrammatic vertical cross-section through part of the wall structure of the combustor shown inFIG. 1.
• Referring toFIG. 1, a gas turbine engine generally indicated at10 has a principal axis X-X. Theengine10 comprises, in axial flow series, anair intake11, apropulsive fan12, anintermediate pressure compressor13, ahigh pressure compressor14, acombustor15, ahigh pressure turbine16, anintermediate pressure turbine17, alow pressure turbine18 and anexhaust nozzle19.
• Thegas turbine engine10 works in a conventional manner so that air entering theintake11 is accelerated by thefan12 which produces two air flows: a first air flow into theintermediate pressure compressor13 and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to thehigh pressure compressor14 where further compression takes place.
• The compressed air exhausted from thehigh pressure compressor14 is directed into thecombustor15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate andlow pressure turbines16,17,18 before being exhausted through thenozzle19 to provide additional propulsive thrust. The high, intermediate andlow pressure turbine16,17,18 respectively drive the high andintermediate pressure compressors14 and13, and thefan12 by suitable interconnecting shafts.
• Referring toFIG. 2, thecombustor15 is constituted by anannular combustion chamber20 having radially inner andouter wall structures21 and22 respectively. Thecombustion chamber20 is secured to anengine casing23 by a plurality of pins24 (only one of which is shown). Fuel is directed into thechamber20 through a number of injector nozzles25 (only one of which is shown) located at the upstream end of thecombustion chamber20.Fuel injector nozzles25 are circumferentially spaced around theengine10 and serve to spray fuel into air delivered from thehigh pressure compressor14. The resulting fuel/air mixture is then combusted within thechamber20.
• The combustion process which takes place generates a large amount of heat. It is therefore necessary to arrange that the inner andouter wall structures21 and22 are capable of withstanding this heat.
• The inner andouter wall structures21 and22 are generally of the same construction and comprise anouter wall27 and aninner wall28. Theinner wall28 is made up of a plurality of discrete wall elements in the form oftiles29, which are all of the same general rectangular configuration and are positioned adjacent each other. The circumferentially extendingedges30,31 of adjacent tiles overlap each other. Eachtile29 is provided with threadedstuds32 which project through apertures in theouter wall27.Nuts34 are screwed onto threadedstuds32 and tightened against theouter wall27, thereby securing thetiles29 in place.
• Both the radially outer and innerouter walls27 of the annular combustor have a series of radial steps that enable optimum use of the cooling air. Air which has passed through the pedestals of an upstream tile is relatively cool and can be used for film cooling the downstream combustor, which must be offset to present the file face at the exit point of the air flow emanating from the upstream tile. The step additionally strengthens the combustor against buckling under flame out or surge. The upstream end of atile29 lies adjacent the step whilst the downstream end of the upstream tile axially overlaps both the radial step and the upstream end of the downstream tile.
• Referring toFIG. 3, there is shown part of theinner wall structure21 showing two overlapping tiles.29A,29B. Each of thetiles29A,29B comprises amain body portion36 which, in combination with the main body portions of each of theother tiles22, defines theinner wall28. A plurality of heat removal members in the form of upstanding substantiallycylindrical pedestals38 extend from eachbody member36 towards the inner wall of thecombustor27 which forms the outer wall of the combustor wall structure. Thedownstream edge region31 oftile29A overlaps theupstream edge region30 of tile29B.
• Thebody member36 and outer wall of thewall structure27 define aduct37 that extends therebetween. Cooling air is supplied to theduct37 through anaperture40 extending through theouter wall27. The flow bifurcates to provide anupstream flow42 that flows substantially in the opposite direction to the general flow of combustion gasses through the combustor and adownstream flow44 that flows generally in the same direction as combustion gasses through the combustor.
• The body member has athermal barrier coating64 on the surface facing thecombustion chamber20 to provide further heat resistance.
• At the downstream end oftile29A the downstream flow mixes with the upstream flow from tile29B and is then exhausted as a film of cooling air over the combustor facing surface of thebody member36 of tile29B. The confluence of the flows occurs where theouter wall27 of the combustor wall structure steps radially.
• To avoid an excessive reduction in the velocity of the air flow through the duct at this point thebody member36 has a circumferentially arrangedlocal thickening50 which follows the radial step of the outer cold-skin wall27. The thickening is contoured to a maxima before reducing as it extends axially rearward. This enables a relatively constant velocity across the whole length of theduct37 thereby maintaining a relatively high heat removal rate, which drops if the velocity of cooling air flow drops significantly. The high heat removal is therefore maintained particularly at the downstream edge region of a tile where the tile temperature peaks and the tile integrity is at greatest risk.
• Pedestals38 are provided on the region oflocal thickening50. The length of the pedestals is maintained over the hump shaped local thickening maintaining the high heat removal afforded by these structures. The pedestals define a flow-path for the supplemental air from the downstream tile and which maximises the volume flow of cooling air within the pedestal array.
• Various modifications may be made without departing from the scope of the invention. For example, the degree of axial overlap of the upstream and downstream tiles may be varied to optimise the film of air over the downstream tile. Similarly, the pedestal length in the region of the hump could be adjusted to optimise heat removal and the shape of the hump/local thickening could be refined to maintain the optimum cooling air velocity.

Claims (7)

1. A wall structure for an annular gas turbine engine combustor arranged to have a general direction of fluid flow therethrough, the wall structure including an outer wall having a radial step and an inner wall overlapping the radial step, a duct being defined between the inner and outer walls for the passage of cooling air; the wall structure being characterised in that the inner wall has a local thickening opposing the radial step and a plurality of pedestals extending from the local thickening towards the outer wall.

2. A wall structure according toclaim 1, wherein the outer wall has a plurality of apertures for feeding cooling air into the duct.

3. A wall structure according toclaim 1, wherein the inner wall includes a plurality of wall elements, each wall element having a body portion aligned in use with the general direction of fluid flow through the combustor and a plurality of pedestals that extend within the duct from the body portion towards the outer wall.

4. A wall structure according toclaim 3, wherein the body portion provides the local thickening.

5. A wall structure according toclaim 3, wherein the downstream end of the body portion of an upstream wall element overlaps the upstream end of the body portion of a downstream wall element.

6. A wall structure according toclaim 1, wherein the local thickening has a contour that follows the contour of the radial step.

7. A wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls, the inner and outer walls defining a duct therebetween, the wall element having a body portion aligned in use with a general direction of fluid flow through the combustor, the wall element having a local thickening in its downstream end region the local thickening being adapted to oppose a radial step in the outer wall and having a plurality of pedestals arranged in use to extend within the duct from the body portion towards the outer wall.

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