Wall elements for gas turbine engine components

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 in FIG. 1;

FIG. 3 is a diagrammatic vertical cross-section through part of the wall structure of the combustor shown in FIG. 1.

Referring to FIG. 1, a gas turbine engine generally indicated at 10 has a principal axis X-X. The engine 10 comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high pressure compressor 14, a combustor 15, a high pressure turbine 16, an intermediate pressure turbine 17, a low pressure turbine 18 and an exhaust nozzle 19.

The gas turbine engine 10 works in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 which produces two air flows: a first air flow into the intermediate pressure compressor 13 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 the high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high pressure compressor 14 is directed into the combustor 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low pressure turbine 16, 17, 18 respectively drive the high and intermediate pressure compressors 14 and 13, and the fan 12 by suitable interconnecting shafts.

Referring to FIG. 2, the combustor 15 is constituted by an annular combustion chamber 20 having radially inner and outer wall structures 21 and 22 respectively. The combustion chamber 20 is secured to an engine casing 23 by a plurality of pins 24 (only one of which is shown). Fuel is directed into the chamber 20 through a number of injector nozzles 25 (only one of which is shown) located at the upstream end of the combustion chamber 20. Fuel injector nozzles 25 are circumferentially spaced around the engine 10 and serve to spray fuel into air delivered from the high pressure compressor 14. The resulting fuel/air mixture is then combusted within the chamber 20.

The combustion process which takes place generates a large amount of heat. It is therefore necessary to arrange that the inner and outer wall structures 21 and 22 are capable of withstanding this heat.

The inner and outer wall structures 21 and 22 are generally of the same construction and comprise an outer wall 27 and an inner wall 28. The inner wall 28 is made up of a plurality of discrete wall elements in the form of tiles 29, which are all of the same general rectangular configuration and are positioned adjacent each other. The circumferentially extending edges 30,31 of adjacent tiles overlap each other. Each tile 29 is provided with threaded studs 32 which project through apertures in the outer wall 27. Nuts 34 are screwed onto threaded studs 32 and tightened against the outer wall 27, thereby securing the tiles 29 in place.

Both the radially outer and inner outer walls 27 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 a tile 29 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 to FIG. 3, there is shown part of the inner wall structure 21 showing two overlapping tiles. 29A, 29B. Each of the tiles 29A, 29B comprises a main body portion 36 which, in combination with the main body portions of each of the other tiles 22, defines the inner wall 28. A plurality of heat removal members in the form of upstanding substantially cylindrical pedestals 38 extend from each body member 36 towards the inner wall of the combustor 27 which forms the outer wall of the combustor wall structure. The downstream edge region 31 of tile 29A overlaps the upstream edge region 30 of tile 29B.

The body member 36 and outer wall of the wall structure 27 define a duct 37 that extends therebetween. Cooling air is supplied to the duct 37 through an aperture 40 extending through the outer wall 27. The flow bifurcates to provide an upstream flow 42 that flows substantially in the opposite direction to the general flow of combustion gasses through the combustor and a downstream flow 44 that flows generally in the same direction as combustion gasses through the combustor.

The body member has a thermal barrier coating 64 on the surface facing the combustion chamber 20 to provide further heat resistance.

At the downstream end of tile 29A the downstream flow mixes with the upstream flow from tile 29B and is then exhausted as a film of cooling air over the combustor facing surface of the body member 36 of tile 29B. The confluence of the flows occurs where the outer wall 27 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 the body member 36 has a circumferentially arranged local thickening 50 which follows the radial step of the outer cold-skin wall 27. 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 the duct 37 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.

Pedestals 38 are provided on the region of local thickening 50. 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

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 to claim 1, wherein the outer wall has a plurality of apertures for feeding cooling air into the duct.

3. A wall structure according to claim 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 to claim 3, wherein the body portion provides the local thickening.

5. A wall structure according to claim 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 to claim 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.