Patent Application
20080025842
Aspects of the present invention relate to a turbine vane assembly that includes removable platform inserts. Various embodiments of a turbine vane assembly according to aspects of the invention will be explained, but the detailed description is intended only as exemplary. Embodiments of the invention are shown in
Each end region 17,19 of the airfoil 12 can transition into a respective one of the platforms 22, 24. The airfoil 12 can be substantially centered on each of the platforms 22, 24, such as shown in
The airfoil 12 and the platform frames 26, 28 can be formed in any of a number of ways. In one embodiment, the airfoil 12 and the platform frames 26, 28 can be a unitary structure formed by, for example, casting or forging. That is, the airfoil 12 and at least a portion of each platform frame 26, 28 can be formed as a single piece. Alternatively, at least one of the inner platform frame 26, the outer platform frame 28 and the airfoil 12 can be formed separately and subsequently joined in any suitable manner. For example, the airfoil 12 can be unitary with one of the platform frames 26 or 28, and the other platform frame can be separately formed. The outer platform frame 28 can be operatively connected to the airfoil 12 at the outer end region 19; the inner platform frame 26 can be operatively connected to the airfoil 12 at the inner end region 17.
According to aspects of the invention, at least one of the platform frames 26, 28 can include a receptacle to receive an insert 34. Aspects of the invention will be explained in the context of both the inner and outer platform frames 26, 28 being so adapted, but it will be understood that aspects of the invention are not limited to such an embodiment. In one embodiment, the receptacle can be a recess 36. The inner platform frame 26 can include a recess 36 that opens to the hot gas path face 30 of the inner platform 22. From the gas path face 30, the recess 36 can extend at a depth into the thickness of the inner platform frame 26. Similarly, the outer platform frame 28 can include a recess 36 that can open to the hot gas path face 32 of the outer platform 24 and can extend therefrom at a depth into the thickness of the outer platform frame 28. In some instances, the receptacle can be a passage 39 that extends through the thickness of the platforms 26, 28 (see
The inner and outer platforms 22, 24 can be completed by placing an insert 34 into each recess 36 of the respective platform frame 26, 28. The inserts 34 and the recesses 36 can be configured so that the inserts 34 are substantially matingly received within the recess 36. When installed, a portion of each insert 34 can form a portion of the gas path face 30 or 32 of the respective platform 22 or 24. Ideally, the inserts 34 are substantially flush with those portions of the inner and platform frames 26, 28 that form the gas path faces 30, 32.
The inserts 34 can be made of any of a number of materials. For example, the inserts 34 can be made of ceramic matrix composite (CMC), such as a silicone-carbide CMC. In one embodiment, the inserts 34 can be made of an oxide-based hybrid CMC system, such as disclosed in U.S. Pat. Nos. 6,676,783; 6,641,907; 6,287,511; and 6,013,592, which are incorporated herein by reference. The inserts 34 can be made of metal, such as a single crystal advanced alloy. In one embodiment, the inserts 34 can be made of the same material as the respective platform frame 26, 28 in which they are received, such as IN939 alloy and ECY768 alloy. The inserts 34 can be made of a material that may or may not have a greater resistance to heat compared to the material of the platform frames 26, 28. For example, the inserts 34 can be made of a material with a lower heat resistance than the material of the receiving platform frames 26, 28. The inserts 34 can be made from an inexpensive material so that the cost of a replacement insert would not significantly add to the overall costs over the life of the engine.
It should be noted that the material of the inserts 34 of the outer platform 24 can be identical to the material of the inserts 34 of the inner platform 22, but they can also be different. Likewise, in embodiments where one or both platforms 22, 24 have a plurality of inserts 34, the inserts 34 associated with one of the platforms can all be made of the same material or at least one of the inserts 34 be made of a different material.
In some instances, it may be desirable to coat, cover or otherwise treat at least a portion of the inserts 34 so as to provide one or more types of protection from the turbine environment, among other things. For example, in the case of inserts 34 made of CMC, at least those portions of the inserts 34 that form the gas path faces 30, 32 of the vane assembly 10 can be coated with a thermal insulating material, which can be, for example, a friable graded insulation (FGI) 37 (see
To prevent the insert liberating during engine operation and entering the gas flow path, which can result in significant damage, each insert 34 can be retainably received in a respective one of the recesses 36. The inserts 34 can be retained in the recesses 36 in any of a number of ways. For example, the recesses 36 can be configured as a keyway or a dovetail, as shown in
The inserts 34 can have any suitable shape. For example, the inserts 34 can be generally rectangular, triangular, polygonal, oval, circular, and irregular, just to name a few possibilities. However, aspects of the invention are not limited to any particular shape. The heats shields 34 can be sized and shaped as needed to provide the desired area of coverage. Likewise, the location of the inserts 34 on the platforms 22, 24 can be optimized as needed. For instance, the inserts 34 can be positioned in critical areas, such as areas that are known hot spots during engine operation. The inserts 34 can even be used to form a majority of one or both of the platform gas path faces 30, 32 of the vane assembly 10. There can be any number of inserts 34 associated with each platform 22, 24, though the quantity of inserts 34 associated with the inner platform 22 may or may not be the same as the quantity of inserts 34 associated with the outer platform 24. In the embodiment, there can be two inserts 34 associated with at least one of the platforms 22, 24. For example, one insert 34 can be located between the pressure side 14 of the airfoil 12 and a first circumferential side 38 of the platforms 22, 24. The other insert 34 can be located between the suction side 16 of the airfoil 12 and a second circumferential side 40 of the platforms 22, 24. Of course, the inserts 34 can be located in various other places as well. For instance, as shown in
The size, location, quantity, arrangement, areas of coverage, etc. of the inserts 34 on the inner platform 22 may or may not be substantially identical in one or more these respects with the inserts 34 on the outer platform 24. For instance, there can be two inserts 34 on the outer platform 24, while the inner platform 22 can have one. Further, an image of an insert 34 on one of the platforms 22, 24 can be projected onto the gas path face 30, 32 of the opposite platform. In one embodiment, the projected image can at least partially overlap at least one of the inserts 34 on the opposite platform. Alternatively, the projected image may not overlap any of the inserts 34 on the opposite platform.
In a given row of turbine vanes, at least one of the vanes in the row can be a vane assembly 10 in accordance with aspects of the invention. Similarly, the quantity and arrangement of the vane assemblies 10 in a given row of vanes may or may not be identical to another row in the turbine section.
During engine operation, a coolant, such as air, can be supplied to the platforms to cool the platform frames 26, 28 as well as the inserts 34. The inserts 34 can act as heat shields. However, if an insert 34 degrades or becomes damaged, then an outtage can be scheduled for replacement of the inserts 34. The platform frames 26, 28 and the airfoil 12 can be reused, thereby minimizing scrap and potentially extending the overall vane life.
The turbine vane assembly 10 according to aspects of the invention can include fail safe features in the event of substantial or total failure of one or more inserts 34. To that end, one or more passages 48 can extend through the platforms 22, 24 and open to the recesses 36, as shown in
The turbine vane assembly 10 according to aspects of the invention can provide numerous advantages over known turbine vanes. As described above, the turbine vane assembly 10 can provide for improved maintainability (less and easier maintenance), reduced repair costs, and reduced scrap. Further, the vane assembly 10 according to aspects of the invention can reduce cooling air consumption compared to known turbine vanes. For instance, the gas path faces of the platforms of known turbine vanes are film cooled, and the backside of the platforms are cooled as well. With inserts made of certain material systems in accordance with aspects of the invention, it may be possible to eliminate platform film cooling and/or significantly reduce the amount of backside cooling. Such cooling savings allow the cooling air to be used for other purposes in the engine.
The foregoing description is provided in the context of various embodiments of a turbine vane assembly in accordance with aspects of the invention. Thus, it will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the following claims.
