Patent Application
20180347399
The application relates generally to gas turbine engines and, more particularly, to turbine shrouds.
Turbine blade tip shrouds are typically radially located on a turbine support case about the tip of the turbine blades to control blade tip clearance. In order to preserve its mechanical properties, the turbine support case needs to be protected from the hot gas flowing across the turbine blades.
Therefore, in one aspect of the present disclosure, there is provided a turbine shroud segment forming part of a circumferentially segmented shroud assembly surrounding a circumferential array of turbine blades of a gas turbine engine; the turbine shroud segment comprising: a platform extending axially from an upstream end portion to a downstream end portion relative to a flow of gas through the gas turbine engine, and a heat shield extension projecting radially inwardly and in an upstream direction from the upstream end portion of the platform
In another aspect, there is provided a turbine section of a gas turbine engine, the turbine section comprising: a turbine support case extending about an axis; a circumferential array of turbine blades disposed within the turbine support case for rotation about the axis; and a circumferentially segmented turbine shroud mounted to the turbine support case about the circumferential array of turbine blades, the circumferentially segmented turbine shroud comprising a plurality of shroud segments disposed circumferentially one adjacent to another, each shroud segment having a platform extending axially from an upstream end portion to a downstream end portion relative to a flow of gas through the turbine section, each shroud segment further having a heat shield extension projecting radially inwardly and in an upstream direction from the upstream end portion of the platform to a location upstream of the circumferential array of turbine blades.
In a further aspect, there is provided a method of thermally protecting a turbine support case surrounding a hot gas path: comprising defining a cooling cavity on a gas path facing side of the turbine support case, and controlling a bleeding of cooling air from the cooling cavity into the hot gas path with a gap defined between a heat shield extension of a circumferentially segmented turbine shroud and an adjacent turbine shroud structure.
Reference is now made to the accompanying figures in which:
As shown in
The turbine section 18 further comprises a vane ring 28 including an array of circumferentially spaced-apart vanes 28a. In one embodiment, the vane ring 28 is provided in the form of a full ring. However, it is understood that the vane ring 28 could be circumferentially segmented to reduce thermal stress. A turbine rotor including an array of circumferentially spaced-apart turbine blades 30 is disposed immediately downstream of the vane ring 28 for extracting power from the flow of hot gases received from vanes 28a. The turbine rotor is housed within the inner case 26. A turbine blade tip shroud 32 (also herein referred to as a turbine shroud) is radially located on the inner case 26 around the tip of the turbine blades 30. According to the illustrated embodiment, the turbine shroud 32 is circumferentially segmented into a plurality of segments assembled on the inner case 26 to form a complete ring about the turbine blades 30. Each shroud segment has a platform 34 having a hot gas path side surface 34a and an opposed back surface 34b extending axially from an upstream end 34c to a downstream end 34d and circumferentially between opposed axially extending edges. The platform 34 defines a curvature in the circumferential direction to allow the shroud segments to collectively define a ring about the turbine blades 30. A layer of abradable material 35 may be provided on the hot gas path side surface 34a of the platform 34 in closed facing relationship with sealing fins 33 extending radially outwardly from the tip of the turbine blades 30. The fins 33 and the layer of abradable material 35 cooperate to improve control tip clearance and, thus, minimize hot combustion gas leakage over the tip of the turbine blades 30.
As can be appreciated from
One or more biasing members 44, such as springs or the like, may be provided between the inner case 26 and the platform 34 of the shroud segments to spring load or urge the shroud segments radially inwardly in contact with the inner lip of groove 36 and the back surface of the shroud platform 40 of the downstream stage of vanes 42.
Still referring to
According to one embodiment, the inner case 26 is also configured to act as a blade containment device. In order to preserve the mechanical properties of the inner case for blade containment, the inner case 26 needs to be protected from the hot gas flowing through the gas path 23. To that end, it is herein proposed to provide the shroud segments with heat shield extensions 52. Each shroud segment and associated heat shield extension 52 are of unitary construction and can be machined from a solid block of material. The heat shield extensions 52 project radially inwardly and in an upstream direction from an upstream end portion of the platforms 34 of the associated shroud segments to jointly form a complete heat shield ring structure (i.e. a full 360 degrees segmented heat shield ring). Since this part is segmented, the hoop is removed and the thermal stress in the part is reduced substantially. This results in improved durability as compared to a full heat shield ring.
In the exemplary embodiment shown in
The cooling air in the cooling cavity 54 is provided at a pressure greater than the pressure prevailing in the hot gas path 23, thereby preventing hot gas ingestion through the radial gap 56 at the interface between the heat shield extensions 52 and the radially outer surface of the radially outer shroud platform 28b of the vane ring 28. The amount of cooling air allowed to seep through the sealing interface into the gas path 23 is controlled by the radial gap 56, which acts as a metering orifice. As shown in
Now referring to
Referring to
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 heat shield segments could cooperate with adjacent engine structures other than the exemplified upstream vane ring and inner case. It is also under stood that the cooling air cavity on the gas path side of the inner case could be connected to any suitable source of coolant and is thus not limited to being fluidly coupled to the outer plenum. 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.
