Patent Application
20060120860
This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus to control gas turbine engine rotor assembly tip clearances during rotor assembly operation.
Gas turbine engines typically include an engine casing that extends circumferentially around a compressor, and a turbine including a rotor assembly and a stator assembly. The rotor assembly includes at least one row of rotating blades that extend radially outward from a blade root to a blade tip. A radial tip clearance is defined between the rotating blade tips and a shroud attached to the engine casing.
During engine operation, the thermal environment in the engine varies and may cause thermal expansion or contraction of the rotor and stator assemblies. Such thermal growth or contraction may not occur uniformly in magnitude or rate. As a result, inadvertent rubbing between the rotor blade tips and the casing may occur or the radial clearances may be more open than the design intent. Continued rubbing between the rotor blade tips and engine casing may lead to premature failure of the rotor blade or larger clearances at other operating conditions which can result in loss of engine performance.
To facilitate optimizing engine performance and to minimize inadvertent rubbing between the rotor blade tips and an inner surface of the shroud, at least some known engines include a clearance control system. The clearance control system channels cooling air to the engine casing to facilitate controlling thermal growth of the engine casing and to thus, facilitate minimizing inadvertent blade tip rubbing. Such cooling air may be channeled from a fan assembly, a booster, or from compressor bleed air sources to impinge on the casing. The effectiveness of the clearance control system may be dependent upon the heat transfer coefficient of clearance control system components.
In one aspect, a method of assembling a gas turbine engine is provided. The method comprises coupling a rotor assembly including a plurality of circumferentially-spaced rotor blades downstream from, and in flow communication with, a compressor, coupling a casing assembly circumferentially around the rotor assembly such that a clearance is defined between an inner shroud surface of the casing assembly and the rotor blade tips, and coupling a clearance control system to the casing assembly to facilitate maintaining the clearance between the casing assembly and the rotor blade tips, wherein at least a portion of an external surface of the clearance control system is formed with a textured pattern that facilitates maintaining the clearance.
In another aspect, a clearance control system for a gas turbine engine including a compressor, a fan assembly, and at least one turbine including at least one row of rotor blades is provided. The clearance control system includes an engine casing assembly that extends circumferentially around the turbine such that a clearance is defined between a tip of the turbine blades and the casing assembly, and a manifold for distributing cooling air. At least a portion of an external surface of the clearance control system includes a textured pattern that facilitates maintaining the clearance.
In a further aspect, a gas turbine engine is provided. The engine includes a compressor, a turbine downstream from and in flow communication with the compressor, an engine casing extending circumferentially around the compressor and the turbine, and a clearance control system. The turbine includes at least one row of circumferentially-spaced rotor blades. The clearance control system includes an engine casing assembly that extends circumferentially around the turbine such that a clearance is defined between a tip of the rotor blades and the casing assembly. At least a portion of an external surface of the clearance control system includes a textured pattern that extends across the external surface. The textured pattern facilitates the clearance control system maintaining the clearance.
A clearance control system for a gas turbine engine that facilitates maintaining a clearance gap defined between static casing assemblies and adjacent rotating components is described below in detail. Cooling air supplied towards the static casing assemblies from the clearance control system can come from any source inside the engine according to design. For example, the cooling air may be channeled from, but is not limited to being bled from, a fan assembly, intermediate stages of a compressor, or the compressor discharge. In addition, the cooling air may also facilitate reducing disk thermal growth, which typically accounts for the majority of the total closure of blade tip clearances. Moreover, the clearance control system described in detail below facilitates tighter clearances during engine operation.
Referring to the drawings,
During operation, air flows axially through fan assembly 12, in a direction that is substantially parallel to a central axis 34 extending through engine 10, and compressed air is supplied to high pressure compressor 14. The highly compressed air is delivered to combustor 16. Combustion gas flow (not shown in
High pressure turbine 18 is coupled substantially coaxially with, and downstream from, compressor 14 (shown in
Circumscribing the row of high pressure blades 70, and in close clearance relationship therewith, is an annular shroud or static casing assembly 71. Shroud assembly 71 is radially inward from a surrounding turbine casing 75. In the exemplary embodiment, shroud assembly 71 includes a plurality of shroud members or arcuate sectors 72 coupled to shroud hangers 74 and C-clip 76. Adjacent shroud members 72 are coupled together to circumscribe blades 70.
Each shroud member 72 includes a radially outer surface 84 and an opposite radially inner surface 86. A clearance gap 88 is defined between shroud inner surface 86 and tips 89 of rotor blades 70. More specifically, clearance gap 88 is defined as the distance between turbine blade tips 89 and an inner surface of turbine shroud 72.
Stationary turbine nozzles 52 are positioned between combustor 16 and turbine blades 70, and between the rows of turbine blades 70, if more than one turbine stage is involved. Nozzles 52 direct the combustion gases toward turbine blades 70 such that the impingement of combustion gases on blades 70 imparts a rotation of turbine disk 60. A turbine center frame 77 and a plurality of stationary stator vanes (not shown in
A clearance control system 100 facilitates controlling clearance gap 88 during engine operation. More specifically, in the exemplary embodiment, clearance control system 100 facilitates controlling gap 88 between rotor blade tips 89 and shroud member inner surfaces 86. Clearance control system 100 is coupled in flow communication to a cooling air supply source via a manifold 114. The cooling air exits manifold 114 and impinges on surfaces 120 and 122 extending from casing 75. The cooing air supply source may be any cooling air supply source that enables clearance control system 100 to function as described herein, such as, but not limited to, fan air, an intermediate stage of compressor 14, and/or a discharge of compressor 14. In the exemplary embodiment, cooling air 116 is bled from an intermediate stage of compressor 14 for stage 2 nozzles and shrouds cooling.
In the exemplary embodiment, manifold 114 extends circumferentially around turbine casing 75 and enables cooling air 112 to substantially uniformly impinge against surfaces 120 and 122. The thermal radial displacement of surfaces 120 and 122 facilitates limiting casing displacement, thus facilitating control of clearance gap 88. Casing 75 extends substantially circumferentially and includes at least some portions of external surface 118, i.e., see for example, surfaces 120, 122, and/or 124, that are positioned in flow communication with cooling air discharged from manifold 114. In one embodiment, surfaces 120 and 122 extend over portions of clearance control system 100 components such as, but not limited to, turbine casing, rings, and/or flanges.
At least a portion of an external surface 118 of turbine casing 75 is formed with a textured pattern (not shown in
During engine operation, compressor discharge pressure air 130 is channeled from compressor 14 towards shroud assembly 71 and clearance gap 88. In addition, cooling air 116 is directed through turbine casing 75 to facilitate cooling a stage 2 nozzle of turbine 18, and/or stage 2 shroud assembly 71, and/or to facilitate purging turbine middle seal cavities (not shown). The combination of cooling air 116 as well as external cooling of casing 75 facilitates enhanced control of clearance gap 88 and facilitates increasing the heat transfer effectiveness of casing surfaces 118, 120, and/or 122. The textured pattern extending at least partially across external surface 118 facilitates increasing the effective heat transfer, i.e., cooling, of surface 118 of clearance control system 100. As a result of the increased effective heat transfer of clearance control system 100, clearance gap 88 is facilitated to be more effectively maintained than is controllable through known clearance control systems. Moreover, the improved clearance gap control is achievable without increasing the amount of cooling air 112 and 116 supplied to clearance control system 100. As a result, turbine efficiency is facilitated to be increased while fuel burn is facilitated to be reduced.
In the exemplary embodiment, peaks 204 extend a height h away from surface 200, and extend across substantially all of impingement surface 200. In alternative embodiments, pattern 202 extends only partially across impingement surface 200. Accordingly, as should be appreciated by one of ordinary skill in the art, the overall size, shape, spacing of peaks 204 and valleys 206, as well as the orientation, pattern, and placement of peaks and valleys 206 may be variably selected depending on the application, within the spirit and scope of the claims.
The above-described clearance control system provides a cost-effective and reliable means for increasing the heat transfer effectiveness of the static casing assembly. More specifically, the textured surface of the impingement surface facilitates increasing the overall heat transfer area and heat transfer coefficients of the impingement surface and thus, facilitates increasing the heat transfer effectiveness of impingement surface. Therefore, the increased effective heat transfer of the impingement surface enables the associated static casing assembly to facilitate more effectively controlling the clearance gap without increasing the amount of cooling air supplied to the turbine casing. Thus, the clearance control system facilitates extending a useful life of the rotor assembly in a cost-effective and reliable manner.
An exemplary embodiment of a combustor casing is described above in detail. The casing illustrated is not limited to the specific embodiments described herein, but rather, components of each may be utilized independently and separately from other components described herein.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
