The invention relates generally to a rim seal for a gas turbine engine, and in particular to a rim seal for use within an annular space between rotating blades and a non-rotating adjacent structure in a gas turbine engine.
In a gas turbine engine, rotating elements, such as compressors and turbine rotors, operate at a very high rotation speed. Their blades are also subjected to intense pressure and heat.
Compressors and turbine rotors are mounted between non-rotating structures within the engine. These structures are designed to be as close as possible to the rotating blade platforms. This mitigates pressurized air ingestion inside the gas turbine engine.
Although various rim seal arrangements have been suggested in the past, there is always a need to provide an improved rim seal yielding better results than previous seals.
In one aspect, the present concept provides a rim seal for an annular space between blade platforms and a non-rotating adjacent structure in a gas turbine engine, the rim seal being connectable to the non-rotating structure and made of an abradable material.
In a second aspect, the present concept provides an annular abradable rim seal for mitigating combustion gas ingestion on a side of blades in a gas turbine engine, the seal having an outer peripheral portion configured and disposed to be at least partially in friction engagement with blade platforms during operation of the engine.
In a third aspect, the present concept provides a method of sealing an annular space between blade platforms and a non-rotating structure immediately adjacent to the blade platforms in a gas turbine engine, the method comprising securing to the non-rotating structure an abradable annular seal provided in the annular space; and operating the gas turbine engine to carve a notch in the seal with the side of the blades.
DESCRIPTION OF THE DRAWINGS
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
FIG. 1 is a schematic cross-sectional view of an example of a gas turbine engine; and
FIG. 2 is a schematic longitudinal cross-sectional view of an example of an improved rim seal.
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 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. In this example, the turbine section 18 includes a high pressure turbine stage 20 and a low pressure turbine stage 22.
FIG. 2 schematically shows the downstream side of a turbine wheel disc 24 which can be the rotor of either one of the high pressure turbine stage 20 or the low pressure turbine stage 22. The wheel disc 24 has a plurality of radially interspaced blades 26. In the figure, a blade 26 can be seen having an airfoil section 28 extending radially outwardly from a blade platform 30. A non-rotating structure 32 is present adjacent to the blades 26. The non-rotating structure 32 can be the inner wall of an interturbine duct in the case of the high pressure turbine stage 20 or the inner wall of an exhaust duct in the case of the low pressure turbine stage 22, for example.
It should be noted that the improved rim seal is not limited for use with turbine blades or at the outlet of a turbine stage. The rim seal can also be used on either sides of a compressor rotor or on the inlet of the turbine rotor.
An annular space 34 is defined immediately adjacent to the blades of the wheel disc 24, between the side of the blade platforms 30 and an end 36 of the non-rotating structure 32. A rim seal 38, connected to the end 36 of the non-rotating structure 32, substantially fills the inner side of the annular space 34. The rim seal 38 is made of an abradable material such as honeycomb-shaped light material, for example.
In the illustrated example, each blade platform 26 has a protruding portion 40 on the side thereof. Together, the protruding portion 40 defines an annular recess 42. The rim seal 38 is set within the annular recess 42 along an overlap distance with respect to the edge of the protruding portions 40. A gap 44 referred to as a cold gap 44 is provided between the protruding portions 40 and the rim seal 38 along the overlap distance at ambient conditions. During operation of the gas turbine engine, the temperature rises and causes thermal expansion to close the cold gap 44. A light rub then occurs between the protruding portions 40 and the rim seal 38. This increases the sealing effect. Interference between the rim seal and the protruding portions results in abrasion of the rim seal abradable material and the creation of a notch 46.
The relative radial position of the flat portion 48 adjacent the notch 46 can be selected to arrive as flush as possible with the outer surface 50 of the blade platforms 26 and the outer surface 52 of the adjacent non-rotating structure 32 during operation of the engine, to minimize aerodynamic disruptions in the gas flow. A carefully selected flat portion 48 configuration can thus contribute to more closely obtain a smooth surface transition between the outer surface 50 of the blade platform 26 and the outer surface 52 of the non-rotating structure 32. The notch 46 can be machined prior to installation of the rim seal 38. Alternately, it can be carved in the rim seal 38 by abrasion with the protruding portions 40 during engine operation, or can be made by a combination of pre-machining and abrasion during operation.
In the illustrated example, a flanged support bracket 54, also made of sheet material, is connected to the end 36 and provides a support flange 56 on which the rim seal 38 can be brazed. The abradable rim seal 38 can be secured both to the flange 56 and to the end 36 of the non-rotating structure 32.
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, the annular rim seal can be used with other types of non-rotating structures than the one described and illustrated herein. Many different types of abradable materials exist and the exact choice thereof is left to those skilled in the art. The seal-holding bracket is optional, many different configurations can be used to connect the abradable rim seal to the edge of the non-rotating structure. 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.