TECHNICAL FIELD
The application relates generally to gas turbine engines and, more particularly, to combustor heat shield sealing.
BACKGROUND OF THE ART
Heat shields such as those used to protect the combustor liners, are exposed to hot gases in the primary combustion zone. The amount of coolant available for cooling the heat shields must be minimized to improve the combustion efficiency and to reduce smoke, unburned hydrocarbon and CO/NOx emission.
It is thus suitable to reduce coolant leakage between the combustor heat shields and the combustor shell.
SUMMARY
In one aspect, there is provided a method of providing a seal between a combustor liner and a rail of a heat shield mounted to an inner surface of the combustor liner, the method comprising: locally deforming the combustor liner in sealing engagement with the rail by applying a pressure on the outer surface of the combustor liner over the rail of the heat shield.
In another aspect, there is provided a sealing clip for a combustor of a gas turbine engine, the combustor having a combustor liner and a heat shield mounted to an inner surface of the combustor liner with a back surface of the heat shield in spaced-apart facing relationship with the inner surface of the combustor liner, the heat shield having a sealing rail extending from the back side thereof; the sealing clip comprising: an elongated body configured to embrace an outer surface of the combustor liner in an overlying relationship to the sealing rail of the heat shield, the elongated body extending between opposed anchoring points configured for engagement with bolts on the outer surface of the combustor liner.
In a further aspect, there is provided a combustor of a gas turbine engine, the combustor comprising: a combustor liner defining a combustion chamber, a heat shield mounted to an inner surface of the combustor liner in the combustion chamber, the heat shield having a rail projecting from a back face thereof, a sealing clip mounted in pressing engagement to an outer surface of the combustor liner over the rail of the heat shield, the sealing clip locally deforming the combustor liner in sealing engagement against the rail of the heat shield.
DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures in which:
FIG. 1 is a schematic cross-section view of a gas turbine engine;
FIG. 2 is an enlarged isometric view of a portion of a combustor of the gas turbine engine and illustrating a sealing clip bolted down on the combustor liner to locally deform the liner in sealing engagement with an underlying sealing rail projecting from the back surface of a heat shield mounted to the inner surface of the combustor liner;
FIG. 3 is a fragmentary isometric view of a section of the combustor illustrating local forces transferred from the clip to the liner in order to reduce any existing leakage gap between the rail of the heat shield and the combustor liner; and
FIG. 4 is a cross-section view of the combustor liner with the sealing clip locally pressing the combustor liner in sealing engagement with the sealing rail of the combustor heat shield.
DETAILED DESCRIPTION
FIG. 1 illustrates a 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 compressor section 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. 1, the combustor 16 may comprise a reverse flow annular combustor shell including a radially inner liner 20a and a radially outer liner 20b, defining a combustion chamber 22. The combustor 16 has a bulkhead or inlet dome portion 24. The combustor 16 further has an exit portion 26 for communicating combustion gases with the turbine section 18. Fuel nozzles 28 extend through the dome portion 24 of the combustor 16 to deliver a fuel-air mixture to the combustion chamber 22.
As shown in FIG. 2, a plurality of impingement holes 30 may be defined in the combustor liners for cooling purposes. Dilution holes may also be provided for combustion purposes. The liners 20a, 20b may have any suitable configuration. The liners are typically made out of sheet metal, though any suitable material(s) and manufacturing method(s) may be used.
As can be appreciated from FIG. 3, the inner surface 21 of the combustor liners 20a, 20b is lined with heat shields 32 of ceramic for example that protect the combustor liners from direct exposure to hot combustion gases. The heat shields 32 may be bolted to the liners 20a, 20b. Each heat shield 32 may be provided on the back surface thereof with a number of studs 38 extending through corresponding mounting holes defined in the combustor liners 20a, 20b. Nuts 40 are threadably engaged on a threaded end portion of each stud 38 outwardly of the combustor 16 to securely hold the heat shields 32 in position on the inner surface 21 of the liners 20a, 20b.
Compressed air passes through the impingement holes 30 in the combustor liners 20a, 20b into an intermediate cooling cavity 34 between the liners 20a, 20b and the combustor heat shields 32. The air passes through the cooling cavity 34 and is admitted into the combustion chamber 22 through perforations in the heat shields 32, thereby creating a cooling air curtain along the hot inner surfaces of the heat shields 32.
As shown in FIGS. 3 and 4, rails 36 extend from the back face of the heat shields 32 to compartmentalize the cooling cavity 34 and direct the flow of cooling air. The rails 36 conform closely to the inner surface 21 of the combustor liners 20a, 20b. However, due to manufacturing tolerances a leakage gap remains between the rails 36 and the liners 20a, 20b. In other words, the rails 36 sealed against the combustor liners with a gap (e.g. 0.002″-0.004″) between. Air leakage occurs through this gap since compressed cooling air is contained within the cooling cavity 34 under a higher pressure than the combustion gases within the combustion chamber 22. Compressed air is intended to pass from the plenum 17 through the perforated liners 20a, 20b into the cooling cavity 34, then into the combustion chamber 22 through the perforated heat shields 32. However leakage through the gap between the rails 36 and the inner surface 21 of the liners 20a, 20b is uncontrolled and undesirable which can decrease engine efficiency through increased use of compressed cooling air and unintended dilution of combustion gases. Leakage is especially undesirable in smaller engines since manufacturing tolerances are similar to those of larger engines; however the proportion of leakage relative to controlled air flow is greater in smaller engines. The same size of gap will lead to a generally greater proportion of leaked air relative to controlled air in a smaller engine compared to a larger engine. For some small engine combustors, much of cooling flow may be wasted and leaked through those gaps. The cooling flow could be better utilized with reduction in leakage flow.
Airflow leakage between the combustor liners 20a, 20b and the rails 36 of the combustor heat shields 32 may be reduced by applying force locally on the liners at the appropriate location. As will be seen hereinafter, this may even be done without blocking any impingement holes 30 using existing fastening structures. As shown in FIGS. 2 and 3, airflow leakage may be reduced by bolting down a sealing clip 42 on the outer surface 23 of the liners 20a, 20b directly over an associated one of the rails 36. The sealing clip 42 has an elongated body 44 extending between two opposed anchoring points 46. The elongated body 44 is configured to follow the profile of the combustor liners. The length of the elongated body 44 is selected so as to generally correspond to that of the underlying rail 36. Each anchoring point 46 comprises a washer like portion defining a central hole for receiving a corresponding one of the studs 38 extending from the back face of the heat shields 32. This allows controlling the liner deformation using existing studs. It can be appreciated from, FIG. 2, that the anchoring points 46 are axially offset with respect to the elongated body 44. The relative position of the elongated body 44 and the anchoring points 46 is set by the location of the studs 38 and the rails 36 on the heat shields 32. However, it is understood that non-existing threaded connections could be used as well to bolt the sealing clip 42 onto the liner. According to this embodiment, the relative disposition of the anchoring points and the elongated body would no longer be function of the relative location of the heat shield studs and rails.
As schematically depicted in FIG. 3, the local force can be applied on the liner over the rail 36 by tightening the nuts 40 on the threaded studs 38. The torque on the nuts 40 is transferred to the elongated body 44 of the sealing clip 42 which in turn uniformly distribute the pressure on the liner along the underlying rail 36 of the heat shield 32. The geometry of the sealing clip 42 controls the liner deformation locally and reduces the leakage gap between the rail of the combustor heat shield and the liner.
According to the illustrated embodiment the elongated body 44 is provided in the form of a low profile metal bar having a trapezoidal tapering section. However, it is understood that the elongated body 44 could adopt various configurations.
It is also understood that other apparatus could be used to locally deform the combustor liner in sealing engagement with a heat shield rail by applying a pressure locally on the outer surface of the combustor liner. The present method of reducing airflow leakage is thus not limited to the use of the sealing clip shown in FIGS. 2-4. Indeed other tools may be used for applying local forces on the outer surface of the combustor liner along the length of the rail of the heat shield. According to some application, the tool used for applying local forces on the outer surface of the liner may be removed once the liner has been locally deformed in sealing engagement with the underlying rail of the heat shield. According to other applications, the tool, such as sealing clip 42, may be left on the combustor liner during engine operation.
From the foregoing, it can be appreciated that the above described embodiments may be used to reduce the flow leakage between the combustor heat shields and liner without tightening existing sheet metal/casting profile tolerances, which increases cost.
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. For example, it is understood that the principles of the present invention could be applied to various types of combustor and heat shields. Still other 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
10184661
