Combustor cooling system

A gas turbine engine has a combustor supported in a gas generator case. A baffle apparatus is attached to the gas generator case, surrounding an upstream section of the combustor to create at least one passage for directing an air flow discharged from a compressor diffuser to pass therethrough for cooling the combustor. The at least one passage extends from an upstream end of the combustor and has a passage exit immediately upstream of a dilution hole in the combustor. The baffle apparatus is configured to increase a velocity of the air flow entering the at least one passage and passing over the combustor.

TECHNICAL FIELD

The application relates generally to gas turbine engines and more particularly, to a combustor cooling system for such engines.

BACKGROUND OF THE ART

Gas turbine engines have a combustor wherein a combustion reaction takes place to generate high temperature combustion gases to power turbines positioned downstream of the combustor. Various techniques have been devised to maintain the temperature of the combustor walls below critical levels. For example, coolant air from the compressor of the engine is often directed to the combustor walls such as along a cord side or back side thereof which is not directly exposed to the not gases of the combustion. The compressor supplies air under pressure to the combustor for both combustion and cooling purposes. Various ways of disbursing the air for the two purposes have been proposed. In the conventional arrangement, a majority of compressor air is mixed with fuel for the combustion reaction taking place within the combustor while the remaining air supplied by the compressor is utilized to cool the combustor and other engine components. It is a challenge to meet the anticipated future NOx/CO Smoke emission regulations, particularly for small aero gas turbine engines, because high pressure combustion systems must minimize compressed air utilization for combustor wall cooling and at the same time meet the greater cooling air demands of smaller combustors.

Accordingly, there is a need for an improved combustor cooling system.

SUMMARY

In one aspect, there is provided a gas turbine engine having a gas generator section comprising: a combustor supported within a gas generator case and positioned downstream of a compressor diffuser, the combustor defining combustion chamber therein and including an upstream end of the combustor to which a fuel/air mixer is attached and a downstream end of the combustor which defines a combustion chamber exit, a baffle apparatus attached to the gas generator case and surrounding the combustor, at least one passage being thereby formed between the baffle apparatus and the combustor for directing an air flow discharged from the compressor diffuser to pass over and to cool the combustor, the at least one passage extending from upstream end of the combustor and extending over only a portion of a primary zone of the combustor, the baffle apparatus being configured to increase a velocity of the air flow flowing through the at least one passage and passing over the combustor.

In another aspect, there is provided a gas turbine engine having a gas generator section comprising an annular outer case and an annular inner case defining an annulus therebetween, an annular combustor positioned in the annulus and including first and second annular combustor wall defining an annular combustion chamber therebetween, the annular combustor including an upstream end to which a fuel/air mixer is attached and a downstream end which defines a combustion chamber exit, a baffle apparatus attached to the annular outer and inner cases, the baffle apparatus being in an annular configuration and surrounding a section of the annular combustor to thereby provide a first annular passage between the first annular combustor wall and the baffle apparatus and a second annular passage between the second annular combustor wall and the bathe apparatus for directing an air flow discharged from the compressor diffuser to pass therethrough for cooling the first and second annular combustor walls, the respective first and second annular passages extending from the upstream end of the annular combustor and having a respective passage exit immediately upstream of a dilution hole in the respective first and second annular combustor wall, the baffle apparatus being configured to increase a velocity of the air flow flowing through the respective first and second passages and passing over the section of the annular combustor.

In a further aspect there is provided a method of cooling a combustor of a gas turbine engine, the combustor being positioned downstream of a compressor diffuser and supported within a gas generator case, the method comprising a step of attaching a baffle apparatus to the gas generator case to create a passage for directing a portion of the air flow discharged from the compressor diffuser to flow over a portion of a combustor wall and discharging the portion of air flow from the passage in a location immediately upstream of a dilution hole in the combustor wall, thereby coding the portion of the combustor wall by the portion of air flow in an increased velocity.

DETAILED DESCRIPTION

Referring toFIG. 1, a turbofan a gas turbine engine includes a fan case10a core casing13, a low pressure which includes fan assembly14, a low pressure compressor assembly18and a low pressure turbine assembly18connected by a shaft12and a high pressure spool assembly which includes a high pressure compressor assembly22and a high pressure turbine assembly24, connected by a turbine shaft20. The core casing13surrounds the low and high pressure spool assemblies to define a main fluid path therethrough. The engine includes a gas generator section25including a combustor26provided in the main fluid path to generate combustion gases to power the high pressure turbine assembly24and the low pressure turbine assembly18.

The terms “axial”, “radial” and “circumferential” used for various components below, are defined with respect to a main engine axis28. The terms “upstream” and “downstream” used for various components below are defined with respect to the flow direction of air or gases flowing in and/or through the main fluid path of the engine.

Referring toFIGS. 1 and 2, the gas generator section25of the engine according to one embodiment may be configured with a gas generator case (which is also part of the core casing13of the engine) including annular outer and inner cases30,32to define an annulus34therebetween for accommodating compressor air (indicated by arrows36) discharged from a compressor diffuser38. The combustor26may be disposed within the annulus34downstream of the compressor diffuser38and may be supported by the annular outer and inner cases30,32, and is thus surrounded by the compressor air36within the annulus34.

The combustor26may include first and second annular combustor walls40,42to define an annular combustion chamber44therebetween. The combustor26in this embodiment may be of an axial type in which the first and second annular combustor wall40,42extend substantially axially from an upstream end46to a downstream end48of the combustor26, or at least an upstream portion47of the respective first and second annular combustor was40,42is axially oriented.

An annular dome wall50may be provided, joining the first and second annular combustor walls40,42to form the upstream end46of the combustor26. One or more fuel/air mixers52and one or more fuel nozzles54may be attached to the annular dome wall50.

The fuel/air mixer52may have air passages for receiving compressor air36to be mixed with fuel injected from the fuel nozzle54, thereby generating a swirling mixture of fuel and air to be burned in a combustion reaction taking place substantially in a primary zone of the annular combustion chamber44. The primary zone may be defined by the upstream portions47of the respective first and second annular combustor walls40,42. A plurality of dilution holes56may be defined in the respective first and second combustor walls40,42immediately downstream of the upstream portions47of the respective first and second annular combustor walls40,42. Compressor air36in the annulus34may enter into the combustion chamber44via the dilution holes56to precipitate completion of the combustion reaction in which some fuel which was unburned in the primary zone, will be fully burned. The completion of the combustion reaction may substantially take place in a dilution zone defined by downstream portions49of the first and second annular combustion walls40,42which join the upstream portions47at, and extend from the location of the dilution holes56(including the location area of the dilution holes56and immediately downstream of the upstream portions47) to the downstream and48of the annular combustor26. The downstream end48of the annular combustor26may define a combustion chamber exit51to discharge combustion gases generated in the combustion chamber44, through a high pressure turbine vane58into the high pressure turbine assembly24.

A baffle apparatus according to one embodiment may be in an annular configuration, surrounding an upstream section of the annular combustor26which defines the primary zone of the annular combustion chamber44therein. The baffle apparatus may include first and second annular baffles60,62, each having an annular upstream baffle end60a,62aand an annular downstream baffle id60b,62b. The upstream baffle end60aof the first annular baffle60may be attached to the annular outer case30, for example in a proximity of the compressor diffuser38, and the downstream baffle end60bof the first annular baffle60may be located immediately upstream of the dilution holes56in the first annular combustor wall40. The upstream baffle end62aof the second annular baffle62may be attached to the annular inner case32, for example in a proximity of the compressor diffuser38, and the downstream baffle end62bof the second annular baffle62may be located immediately upstream of the dilution holes56in the second annular combustor wall42.

The first and second annular baffles60,62may have respective upstream portions thereof defining an annular cavity63therebetween located upstream of the annular combustor26and being in fluid communication with the compressor diffuser38and with the fuel/air mixer52. The first and second annular baffles60,62may have respective downstream portions thereof spaced apart from the respective first and second annular combustor walls40,42.

Therefore, a first annular passage64may be defined between the first annular combustor wall40and the first annular baffle60, and a second annular passage66may be defined between the second annular combustor wall42and the second annular baffle62. The respective first and second annular passages64,66may extend from the upstream end46of the annular combustor26and may have a respective passage exit immediately upstream of the dilution holes56in the respective first and second annular combustion walls40,42.

The annular upstream baffle ends60a,62aof the first and second annular baffles60,62may be sealingly attached to the respective annular outer and inner cases30,32, such that the compressor air36discharged from the compressor diffuser38is forced to enter directly into the annular combustion chamber44via the fuel/air mixer52and to enter into the annulus34via the respective first and second annular passages64,66. Optionally, no compressor air36may enter a space within the annulus34and surrounding the annular combustor26without pa through the respective passages64,66.

The first and second annular passages64,66may provide an air passage cross-section smaller than the air passage cross-section of the annular cavity63defined within the upstream portions of the first and second annular baffles60,62, thereby increasing a velocity of the compressor air36when the compressor air36enters the respective first and second annular passages64,66and passes over the upstream section of the annular combustor26which defines the primary zone of the annular combustion chamber44therein, resulting in enhanced cooling performance at the upstream section of the annular combustor26.

The downstream portion of the first annular baffle60may be parallel to the upstream portion47of the first annular combustor wall40. The downstream portion of the second annular baffle62may be parallel to the upstream portion47of the second annular combustor wall42. Therefore, the first and second annular passages64,66may each have a substantially consistent width which may be selectively adjusted to achieve a required velocity of the air flow of the combustor air36passing over the cold side (back side) of the upstream portions47of the respective first and second annular combustor walls40,42.

A plurality of dome heat shields68may be provided to and spaced apart from an inner side of the annular dome wall50in order to prevent the annular dome wall50from being exposed directly to the combustion gases in the annular combustion chamber44. The annular dome wall50may define a plurality of cooling holes70for introduction of the compressor air36boated within the annular cavity63, into the primary zone of the annular combustion chamber44. The compressor air36after entering the cooling holes70, passes through the space between the annular dome wall50and the plurality of dome heat shields68and is then directed by the dome heat shields68to form a cooling air film36awhich flows along and cools a hot side (exposed directly to the combustion gases in the annular combustion chamber44) of the upstream portions47of the respective annular combustor walls40,42.

Optionally, the upstream portions47of the respective annular combustor walls40,42which extend from the annular dome wall50to a location immediately upstream of the dilution holes56, may be free of holes extending therethrough, such as diffusion holes.

Optionally, a plurality of heat transfer augmentation elements72may be provided, such as fins, ridges, etc., projecting from a cold side (back side, not exposed to the combustion gases) of the respective first and second annular combustor walls40,42. The heat transfer augmentation elements72may be positioned on the cold side of the upstream portions47of the respective annular combustor walls40,42.

The portion of the compressor air36passing through and then being discharged from the first and second annular passages64,66, enters the annulus34with reduced velocity and recovered pressure. Some of the compressor air36in the annulus34enters the dilution zone defined within a downstream section of the annular combustor26, through the dilution holes56, to participate in completion of the combustion reaction taking place in the dilution zone. Optionally, a plurality of effusion holes74may be provided, extending through the downstream portions49of the respective first and second annular combustor walls40,42and being inclined at an angle with respect to the respective first and second annular combustor walls40,42, to allow compressor air36to pass therethrough from within the annulus34and surrounding the downstream section of the annular combustor26, to enter into the dilution zone of the annular combustion chamber44, resulting in film cooling of a hot side of the downstream portions49of the respective first and second annular combustor walls40,42.

FIG. 3illustrates another embodiment in which the annular combustor26′ is also of an annular axial type, similar to the annular combustor26ofFIG. 2, such that at least the upstream portion of the first and second annular combustor walls40,42may be radially spaced apart one from the other and may extend substantially axially. Structures and features ofFIG. 3which are similar to those shown inFIG. 2will not be redundantly described herein. In contrast to the annular passages64,66each having a substantially consistent flow passing area, as shown inFIG. 2, the first and second annular passages64,66ofFIG. 3, may each have a varying flow passing area to form one or more throat areas76which may have a minimum cross-section of the respective annular passages64,66, or may have a relatively reduced cross-section. The throat areas76may be selectively located in one or more hot spots of the respective first and second annular combustor walls40,42, as indicated by numeral78. The local temperatures of the combustor walls in these hot spots are much higher than the remaining areas and more effective cooling is desirable. With such selectively positioned throat areas76, the compressor air36flowing through the respective annular passages64′,66′, increases in velocity to a predetermined level when passing through the throat areas76of the passages, resulting in enhanced cooling performance at those particular not spots of the respective first and second annular combustor walls40,42. The throat areas may be provided by, for example local dimples and/or circumferential/axial wave form dimples in the respective first and second annular baffles60,62.

FIG. 4illustrates a further embodiment in which the baffle apparatus having the first and second annular baffles60,62is also applicable to an annular combustor26″ which is of an annular radial type. The upstream portion47″ of the respective first and second annular combustor walls40,42of the annular radial combustor26″ may be axially spaced apart one from the other and may extend substantially radially. The other structures and features of the embodiment ofFIG. 4which are similar to those shown inFIG. 2will not be redundantly described herein.

Some embodiments may advantageously provide a combustor cooling system which reduces the need for compressor air for cooling purposes and thereby provides more compressor air for the combustion reaction in the primary zone of the combustion chamber, to facilitate improvement in NOx/CO/smoke emissions.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the described subject matter. For example, a turbofan gas turbine engine has been taken as an example to illustrate application of the described subject matter. Nevertheless, gas turbine engines of other types may also be applicable to the described subject matter. The above-described embodiments relate to a baffle apparatus used for annular combustors, however the general principle of the described baffle apparatus may also be applicable to combustors of other types such as a can combustor which has one annular combustor wall defining a combustion chamber therein. In such a case, the baffle apparatus may have an annular baffle surrounding an upstream portion of the can combustor. Still other modifications which fall within the scope of the described subject matter will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.