TECHNICAL FIELD
The application relates generally to gas turbine engine and, more particularly, to combustor heat shield panels.
BACKGROUND OF THE ART
Gas turbine combustors are the subject of continual improvement, to provide better cooling, better mixing, better fuel efficiency, better performance, etc. at a lower cost. For example, heat shields are known to provide better protection to the combustor, but heat shields also require cooling. A plurality of bolt connections is typically used to secure the heat shield panels in place on the inside of the combustor shell. A bolt connection is provided in each corner of the panel to ensure proper sealing between the panel and the inside of the combustor shell. The number and positioning of bolts constitutes an obstacle to the admission of cooling air through the combustor shell to cool down the heat shield. Usually, the interface between the panels is hard to cool since the heat shield sealing rails make cooling difficult, and hot spots may occur.
SUMMARY
In one aspect there is provided a combustor heat shield assembly comprising a circumferential array of heat shield panels individually mounted to an inner surface of a combustor shell, each heat shield panel having opposed front and back faces, the back face facing the inner surface of the combustor shell and being spaced therefrom to define an air gap, the front and back faces having a perimeter including opposed lateral edges extending between opposed circumferentially extending edges, wherein the lateral edges of adjacent heat shield panels have complementary non-linear profiles defining an asymmetric heat shield panel interface relative to a mean line between said circumferentially extending edges.
In a second aspect, there is provided a gas turbine engine combustor comprising a combustor shell circumscribing a combustion chamber, at least one circumferential array of heat shield panels mounted to an interior side of the combustor shell, each heat shield panel having opposed front and back faces, the back face facing the inner surface of the combustor shell and being spaced therefrom to define an air gap, the front and back faces having a perimeter including opposed lateral edges extending between opposed circumferentially extending edges, wherein the lateral edges of adjacent heat shield panels have mutually corresponding surface contours defining a non-linear heat shield panel interface between the opposed circumferentially extending edges.
DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures, in which:
FIG. 1 is a schematic cross-sectional view of a turbofan gas turbine engine;
FIG. 2 is a schematic cross-section view of an annular combustor including a combustor shell and heat shield panels bolted to the combustor shell;
FIG. 3a a front isometric view of two adjacent heat shield panels of a circumferential array of panels and illustrating the interlocking engagement between the adjacent panels;
FIG. 3b is a front enlarged view of a lateral end portion of one of the two heat shield panels shown in FIG. 3a and illustrating details of the interlocking features of the panel;
FIG. 4a is a back isometric view of a portion of the circumferential array of heat shield panels and illustrating the distribution of studs on the panels; and
FIG. 4b is a back enlarged view of the lateral end portion of one of the panel and illustrating the interlocking features thereof in relation to the positioning of the studs.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a turbofan gas turbine engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a multistage compressor 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases.
The combustor 16 is housed in a plenum 17 supplied with compressed air from compressor 14. As shown in FIG. 2, the combustor 16 typically comprises a sheet metal shell 20 including radially inner and radially outer liners 24, 26 extending from a bulkhead 28 so as to define an annular combustion chamber 21. A plurality of circumferentially spaced-apart nozzles (only one being shown at 30 in FIG. 2) are provided at the bulkhead 28 to inject a fuel/air mixture into the combustion chamber 21. Sparkplugs (not shown) are provided along the upstream end portion of the combustion chamber 21 downstream of the tip of the nozzles in order to initiate combustion of the fuel/air mixture delivered into the combustion chamber 21.
The radially inner and outer liners 24, 26 and the bulkhead 28 are provided on their hot interior side with heat shields. The heat shields can be segmented to provide a thermally decoupled combustor arrangement. For instance, circumferential arrays of heat shield panels 32a, 32b can be respectively mounted to the hot interior side of the radially inner and radially outer liners 24, 26, and another circumferential array of heat shield panels 32c can be mounted to the hot interior side of the bulkhead 28. It is understood that more than one circumferential array of heat shield panels can be mounted axially along the inner and outer liners 24, 26. Reference numeral 32 will be used herein after to generally refer to the heat shield panels irrespectively of their positions on the combustor shell 20.
The heat shield panels 32 are mounted to the combustor shell 20 with the back face of the heat shield panels 32 in closed facing, space-apart, relationship with the interior surface of the combustor shell 20. The back face of the heat shield panels 32 and the interior surface of the combustor shell 20 define an air gap 34 for receiving cooling air to cool down the heat shield panels 32. Cooling holes, such as impingement holes (not shown), are defined in the combustor shell 20 for directing air from the plenum 17 into the air gap 34. Sealing rails 36 projecting from the back side of the heat shield panels 32 into sealing engagement with the interior surface of the combustor shell 20 provide for the compartmentalization of the air gap 34 formed by each array of heat shield panels 32 and the interior side of the combustor shell 20. The sealing rails 36 may take various forms. For instance, they can take the form of a ring 36a (FIGS. 4a and 4b) surrounding a fuel nozzle opening 38 defined in a bulkhead heat shield 32c, a peripheral rim or even just a ridge extending integrally from the back side of a heat shield panel. The term “sealing rail” is herein intended to encompass all types of sealing surfaces projecting from the back side of the heat shields for engagement with the interior side of the combustor shell.
As shown in FIG. 2, bolted connections 40 may be provided for individually securing the heat shield panels 32 in position relative to the combustor shell 20 with the sealing rails 36 of the panels in sealing contact with the interior side of the combustor shell 20. As shown in FIG. 2, the bolted connections 40 may, for instance, include self-locking nuts 42 threadably engaged on the threaded distal end of studs 44 projecting from the back side of the heat shield panels 32. The studs 44 may be integrally cast with the panels 32. Alternatively, the studs may be joined to the panels by any suitable joining techniques.
More particularly, as shown in FIG. 4a with reference to the bulkhead heat shield panels 32c, each individual heat shield panel has a plurality of studs 44 projecting from the back side thereof for engagement in corresponding mounting holes defined in the combustor shell 20. The threaded distal end of the studs 44 extends beyond the shell exterior surface for engagement with the nuts 42. After engagement of the nuts 42 with the exterior surface of the combustor shell 20, the continued tightening of the nuts 42 causes the sealing rails 36 of the heat shield panels to be drawn against the interior surface of the combustor shell 20. To ensure proper sealing contact between the rails 36 and the interior surface of the combustor shell 20 a plurality of bolted connections is provided for each panel. Typically, a stud is provided at each corner of the panels and other studs are provided along the opposed circumferential edges of the panel. The provision of so many threaded connections on a combustor shell may be problematic, especially for small gas turbine engines. The number of threaded connections and, thus, the number of required studs and corresponding mounting holes in the combustor shell, may be reduced by providing interlocking features between adjacent heat shield panels to provide a load transfer path to transfer the holding force of a bolted connection of one panel to an adjacent one of the panels, thereby allowing to eliminate a bolted connection on said adjacent one of the panels.
FIGS. 3a, 3b, 4a and 4b illustrate one example of an interlocking scheme in which adjacent heat shield panels are used to provide the force to ensure sealing of the heat shield panels to the combustor shell with a reduced number of bolted connections. The exemplary embodiment is disclosed in relation to the bulkhead heat shield panels 32c but it is understood that similar arrangements could be provided for the heat shield panels 32a, 32b mounted to the radially inner and outer liners 24, 26.
As can be appreciated from FIG. 4a, a single stud 44 may be provided at each opposed lateral ends of the heat shield panels with the studs adjacent to the interface between two adjacent panels being diametrically opposed to each other. For instance, for each pair of adjacent panels, a first panel 32c′ may have a stud 44′ provided in a first corner thereof and a second adjacent panel 32c″ may have a stud 44″ provided in a second corner thereof, the first and second corners being diametrically opposed to each other. The stud 44′ of the first panel 32c′ faces a studless corner area 45″ of the second panel 32c″. Likewise, the stud 44″ of the second panel 32c″ faces a studless corner area 45′ of the first panel 32c′. The need for a stud in each of the studless corners may be avoided by the provision of overlapping portions between the first and second adjacent panels 32c′ and 32c″. The overlapping portions are configured to transfer a force from the stud 44″ of the second panel 32c″ to the studless corner area 45′ of the first panel 32c′ and from the stud 44′ of the first panel 32c′ to the studless corner area 45″ of the second panel 32c″.
Referring concurrently to FIGS. 3a, 3b, 4a and 4b, it can be appreciated that the overlapping portions can take the form of tabs extending from the lateral adjoining edges of the first and second adjacent panels 32c′, 32c″ for engagement with corresponding seats (e.g. recesses or slots) defined in the other one of the first and second adjacent panels. For instance, a first tab 48′ (FIG. 3b) may extend from the lateral edge of the first panel 32c′ generally in alignment with the stud 44′ for mating engagement in a recess 50″ (FIG. 4b) defined in the front face of the second panel 32c″ at a location generally corresponding or adjacent to the studless corner area 45″. The tension in stud 44′ of the first panel 32c′ is transferred to the studless area 45″ of the second panel 32c″ via the tab 48′, thereby ensuring proper sealing contact between the second panel 32c″ and the combustor shell 20 in the vicinity of the boltless corner area. Likewise, a second tab 48″ (FIG. 4b) may extend from the lateral edge of the second panel 32c″ generally in alignment with the stud 44″ for mating engagement in a recess 50′ (FIG. 3b) defined in the front face of the first panel 32c′ at a location generally corresponding or adjacent to the studless corner area 45′. The tension in stud 44″ of the second panel 32c″ is transferred to the studless area 45′ of the first panel 32c′ via tab 48″.
As can be appreciated from the foregoing, the load transmission paths provided by the tabs 48′, 48″ bearing against the adjacent studless regions 45′, 45″ of the adjacent panels allow the use of a single bolt connection for two adjacent corners of two different panels. It is understood that the above arrangement is not limited to corner studs and that similar load transmission paths could be used in combination with studs disposed at different locations on the back side of the panels. In this way, the number of required bolted connections can be significantly reduced.
It is also contemplated to use two tabs on a first adjacent heat shield panel and two mating recesses on the second adjacent panel. The tabs would be aligned with adjacent studs provided at the top and bottom corners of the first heat shield panels. In this way the studs in the opposed facing corners of the second panel could be eliminated.
Furthermore, as depicted by dotted line 52 in FIG. 3a, the adjoining lateral edges of adjacent panels 32c′, 32c″ may have complementary non-linear profiles. More particularly, the adjoining lateral edges of first and second adjacent heat shield panels 32c′, 32c″ may have mutually corresponding surface contours defining a non-linear heat shield panel interface. In the illustrated embodiment, the heat shield panel interface is curved. However, it is understood that the adjoining lateral edges of the panels could have other non-linear profiles. As can be appreciated from FIG. 3a, the non-linear lateral edges 52 are asymmetric relative to a mean line extending centrally across the panel faces between the top and bottom circumferentially extending edges of the panels. It can also be readily appreciated from FIG. 3a that panel 32c″ with its opposed “S”-shaped lateral edges 52 is asymmetric about a central radial plane A of the panel. The use of asymmetric panels provides for increased space for the disposition of the studs and nuts as well as providing more room for the tabs and complementary seats. This arrangement may be use to replace one stud by the use of tabs and slots in combination with the non-straight edge profile. The sealing of the area of two adjacent corners may now be done by the use of only one stud. This at the same time, allows more surface area of the heat shields to be exposed for the use of impingement cooling. It facilitates cooling by providing more room to get air flow in through the combustor shell 20 into the gap 34 between the heat shield panels 32 and the interior surface of the combustor shell 20. It thus allows for more efficient cooling and therefore contributes to ensure that durability requirements are met. It is noted that the asymmetric aspect could be used with or without the overlapping lateral features described herein above. Usually, the plane of symmetry is hard to cool since the sealing rails of two adjacent heat shield panels occupy the area taking away coolable surface area where hot spots may occur. Therefore, moving the sealing rails away from the plane of symmetry opens up the area to allow for cooling.
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 invention disclosed. Any modifications which fall within the scope of the present invention 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.
Patent Grant
9534784
