Patent Application
20090232644
This invention relates generally to the use of ceramic matrix composite (CMC) vanes, and more particularly, to CMC vane insulators and methods of use.
Gaps or seams may enable hot gases from the gas flow path of a gas or steam turbine to leak into un-cooled or unprotected vane components. To facilitate reducing gas flow through such gaps, at least some known turbines pressurize these gaps with compressor air, also called purge air, to cause a positive outflow from the vane into the hot gas flow path. However, directing purge air at the interface between the vane and metallic support structure may cause undesirably high stresses to develop on the vane which over time, may reduce the life expectancy of the CMC vane.
At least some gas or steam turbines use ceramic materials having a higher temperature capability than the metallic type materials. One specific class of such non-metallic low thermal expansion materials is ceramic matrix composite (CMC) materials which can endure significantly higher temperatures than metals and also require reduced cooling requirements that can be translated into increased engine efficiency and output. However, because of the substantial difference in coefficients of thermal expansion between CMC materials and supporting metallic structures, substantial thermal stresses may develop in the CMC material which may adversely affect the life and functionality of vanes fabricated from CMC materials.
In one aspect, a method for assembling a gas or steam turbine is provided. The method includes providing an insulator and positioning the insulator between a vane support and a vane such that the insulator facilitates preventing hot gas migration into the vane, and such that during operation, hot gas is channeled from a high pressure side of the vane to a low pressure side of the vane.
In another aspect, a vane assembly for a turbine rotor assembly is provided. The vane assembly includes a vane support and an insulator including a base portion and a projecting portion, the base portion includes a top surface and a bottom surface, the projecting portion extends from the base portion and includes at least one channel defined therein and positioned to substantially circumscribe an outer surface of the projecting portion. The assembly also includes a vane, and the insulator is coupled to the vane support such that the projecting portion is between the vane and a nozzle support strut to facilitate hot gas flow from a pressure side of the projecting portion to a suction side of the projecting portion.
In yet another aspect, an insulator for use with a vane assembly is provided. The insulator includes a base portion including a top surface and a bottom surface, a projecting portion extending from the top surface, the projecting portion includes an outer surface that substantially circumscribes the projecting portion and at least one channel defined in the outer surface. The insulator also includes at least one rib defined in the outer surface. The at least one rib is positioned between a pair of the at least one channel such that hot gas is facilitated to be channeled from a high pressure side of the vane assembly to a low pressure side of the vane assembly.
In operation, depending on the type of turbine, high pressure hot gas or steam enters an inlet end (not shown) of turbine 10 and moves through turbine 10 parallel to the axis of rotor 12. The hot gas or steam strikes a row of nozzles 18 and is directed against buckets 16. The hot gas or steam then passes through the remaining stages, thus forcing buckets 16 and rotor 12 to rotate.
Suction and pressure sidewalls 58 and 59, respectively, extend longitudinally, in span between radially inner band 56 and radially outer band 54. A vane root 64 is defined as being adjacent inner band 56, and a vane tip 66 is defined as being adjacent outer band 54. Additionally, suction and pressure sidewalls 58 and 59, respectively, define a cooling cavity 67 within vane 52.
Outer band 54 and inner band 56 each include an opening 72 and 76, respectively, extending therethrough. Moreover, outer band 54 includes an outer countersink portion 74 and an inner band 56 includes an inner countersink portion 78. Outer countersink portion 74 is sized and shaped to correspond to the outer periphery of vane tip 66 such that vane tip 66 fits within portion 74. Likewise, inner countersink portion 78 is sized and shaped to correspond to the outer periphery of vane root 64 such that vane root 64 fits within inner countersink portion 78. Turbine nozzle 50 includes a nozzle support strut 68 that extends through CMC vane 52. A radially inner end 80 of nozzle support strut 68 extends outward from vane root 64 and a radially outer end 82 of nozzle support strut 68 extends outward from vane tip 66.
In the exemplary embodiment, outer surface 94 includes a plurality of substantially parallel self-contained channels 102 and a plurality of substantially parallel ribs 104, such that each channel 102 is positioned between a pair of adjacent corresponding ribs 104 such that a square wave profile is defined. It should be appreciated that although the exemplary embodiment uses substantially parallel channels 102, other embodiments may use any orientation for channels 102, such as, but not limited to, channels 102 that are not parallel, that enables insulator 84 to function as described herein. In the exemplary embodiment, channels 102 and ribs 104 have substantially rectangular cross-sectional areas. Depending on the operating conditions, a single channel 102 may be adequate. However, during operating conditions with increased hot gas flow 110 that facilitates migration into CMC vane 52, additional channels 102 are used to accommodate the increased hot gas 110 flow. Channels 102 are designed to provide effective resistance to radial flow of hot gas 110, by providing a flow path of least resistance about the vane 52.
It should be appreciated that although base 86 has an elliptical shape in the exemplary embodiment, in other embodiments, base 86 may be non-elliptically shaped. It should be further appreciated that member 92 may extend at any angle away from base 86, and that channels 102 and ribs 104 may have any cross-sectional area that enables channels 102 and venting channels 106 to function as described herein. Moreover, it should be appreciated that ribs 104 define a reduced contact area with CMC vane 52 and thereby facilitate reducing heat transfer between CMC vane 52 and inner band 56.
By channeling hot gas 110 from the high pressure side 98 to the suction side 96 of CMC vane 52, and using PM2000 material for insulator 84, the exemplary embodiment facilitates controlling hot gas 110 leakage into vane 52 using minimal to no purge air. Moreover, the exemplary embodiment facilitates reducing thermal gradients in the CMC vane 52 and facilitates protecting inner band 56 from the direct impingement of hot gas 110.
Insulator countersink 192 also defines a sidewall 198 including a plurality of substantially parallel self-contained channels 200 and a plurality of substantially parallel ribs 202. It should be appreciated that although the exemplary embodiment uses substantially parallel channels 200, other embodiments may use any orientation for channels 200, such as, but not limited to, channels that are not parallel, that enable insulator 184 to function as described herein. Each channel 200 is positioned between a pair of adjacent corresponding ribs 202, such that a square wave profile is defined. Channels 200 and ribs 202 have substantially rectangular cross-sections. Sidewall 198 includes a pressure side 204 opposing pressure sidewall 59 and a suction side 206 opposing suction sidewall 58. Suction side 206 includes a plurality of substantially rectangularly shaped venting channels 208 extending from top surface 188 towards countersink bottom surface 196. Venting channels 208 are in flow communication with channels 200. In the exemplary embodiment, venting channels 208 have a substantially rectangular cross-sectional area and intersect with channels 200 at generally right angles. However, it should be appreciated that venting channels 208 may have any cross-sectional area and/or may intersect with channels 200 at any angle that enables venting channels 200 to function as described herein.
It should be further appreciated that channels 200 and ribs 202 may have any cross-sectional area that enable channels 200 and venting channels 208 to function as described herein. Moreover, it should be appreciated that ribs 202 define a reduced contact area with CMC vane 52 and thereby facilitate reducing heat transfer between CMC vane 52 and inner band 56.
By channeling hot gas 110 from the high pressure side 204 to the suction side 206 of CMC vane 52, and using PM2000 material for insulator 184, the exemplary embodiment facilitates controlling hot gas 110 leakage into vane 52 using minimal to no purge air. Moreover, the exemplary embodiment facilitates reducing thermal gradients in the CMC vane 52 and facilitates protecting inner band 56 from the direct impingement of hot gas 110.
In each embodiment the above-described insulators facilitate thermal balance across CMC vane 52, facilitate minimizing thermal gradients and facilitate improving CMC vane 52 durability. More specifically, in each embodiment, the insulator facilitates controlling hot gas migration by channeling high pressure hot gas 110 from the high pressure side of CMC vane 52 towards the low pressure side of CMC vane 52. As a result, turbine operation facilitates using less purge air and reduces CMC vane stresses. Accordingly, gas or steam turbine performance and component useful life are each facilitated to be enhanced in a cost effective and reliable means. It should be appreciated that the embodiments described herein may also be used with stationary vanes.
Exemplary embodiments of insulators are described above in detail. The insulators are not limited to use with the specific gas or steam turbine embodiments described herein, but rather, the insulators can be utilized independently and separately from other insulator components described herein. Moreover, the invention is not limited to the embodiments of the insulators described above in detail. Rather, other variations of insulator embodiments may be utilized within the spirit and scope of the claims.
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.
