CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of U.S.

Provisional Application No. 62/523,335, filed June 22, 2017, the entirety of which is incorporated by reference herein.

FIELD

[0002] Aspects of the invention relate in general to turbine engines and, more particularly, to ring seals in the turbine section of a turbine engine.

BACKGROUND

[0003] A gas turbine engine typically has a compressor section, a combustion section having a number of combustors, and a turbine section. Ambient air is compressed in the compressor section and conveyed to the combustors in the combustion section. The combustors combine the compressed air with a fuel and ignite the mixture creating combustion products. The combustion products flow in a turbulent manner and at a high velocity. The combustion products are routed to the turbine section via transition ducts. Within the turbine section are rows of vane assemblies. Rotating blade assemblies are coupled to a turbine rotor. As the combustion product expands through the turbine section, the combustion product causes the blade assemblies and turbine rotor to rotate. The turbine rotor may be linked to an electric generator and used to generate electricity.

[0004] Within the gas turbine engine, located between the rows of vanes are ring segments. These ring segments are exposed to severe pressure boundaries and extreme temperatures. The severe pressure boundaries create large loads that the part must handle. Therefore, the ring segments used in gas turbine engines should be designed to handle these environmental conditions.

SUMMARY

[000S] Briefly described, aspects of the present disclosure relate to providing a method and apparatus for forming ring seals.

[0006] An aspect of the present invention may be a gas turbine engine comprising; a ring seal comprising a plurality of ring segments. Each ring segment comprises a forward rail, a middle rail and an aft rail, wherein the forward rail, the middle rail and the aft rail extend circumferentially; wherein the middle rail has a first side and a second side, wherein the first side is angled away from the second side towards the forward rail; wherein the second side is angled away from the first side towards the aft rail, and wherein the first side is flush against the forward rail and the second side is flush against the aft rail thereby accommodating loads generated by the gas turbine engine.

[0007] Another aspect of the present invention may be a ring segment for a gas turbine engine comprising: a forward rail, a middle rail and an aft rail, wherein the forward rail, the middle rail and the aft rail extend circumferentially; wherein the middle rail has a first side and a second side, wherein the first side is angled away from the second side towards the forward rail; wherein the second side is angled away from the first side towards the aft rail, and wherein the first side is flush against the forward rail and the second side is flush against the aft rail.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 is a sectional view of the gas turbine engine.

[0009] Fig. 2 is a view of the ring segment.

[0010] Fig. 3 is an isometric partial view of the ring segment.

[0011] Fig. 4 is a cross-sectional view of the ring segment.

[0012] Fig. 5 is a sectional view of the fully assembled ring segment.

DETAILED DESCRIPTION

[0013] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to

implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods.

[0014] The components described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components that would perform the same or a similar function as the components described herein are intended to be embraced within die scope of embodiments of the present disclosure.

[0015] FIG. 1 shows a gas turbine engine 10. The gas turbine engine 10 has a compressor section 12, a combustor section 14 and a turbine section 16. Working gases flow downstream from the combustor section 14. In the turbine section 16 there are alternating rows of stationary vanes 18 and rotating blades 20. Each row of rotating blades 20 is formed by a plurality of rotating blades 20 attached to a disc 22 secured on a rotor 24. The illustrated rotating blades 20 extend radially outward from the discs 22 and terminate in a region known as the blade tip 26. Each row of stationary vanes 18 is formed by attaching a plurality of stationary vanes 18 to a vane carrier 28. The illustrated stationary vanes 18 extend radially inward from the inner peripheral surface 30 of the vane carrier 28. The vane carrier 28 is attached to an outer casing 32, which encloses the turbine section 16 of the engine 10.

[0016] Between the rows of stationary vanes 18, a ring seal 34 is advantageously attached to the inner peripheral surface 30 of the vane carrier 28. The ring seal 34 is a stationary component that functions as a hot gas path guide between the rows of vanes 18 at the locations of the rotating blades 20. The ring seal 34 is formed by a plurality of ring segments 35, discussed in more detail below. The ring segments 35 extend circumferentially in order to form the circular ring seal 34.

[0017] During engine operation, high temperature, high velocity gases flow through the rows of vanes 18 and blades 20 in the turbine section 16. The ring seals 34 are exposed to these gases as well.

[0018] Utilizing ring seals made from metallic superalloys sometimes requires active cooling systems and thermal barrier coatings so that the ring seal can withstand the extreme temperatures to which it is exposed. As an alternative, the ring seals 34 may be made from ceramic matrix composite (CMC) materials, which have higher temperature capabilities than metal alloys. By utilizing such CMC materials, cooling air can be reduced, which has a direct impact on engine performance, emissions control and operating economics.

[0019] However, CMC materials have other disadvantages. For example, CMC materials (oxide and non-oxide based) have anisotropic strength properties such that the inteiiaminar tensile strength (the "through thickness" tensile strength) of CMC can be substantially less than the in-plane strength. Anisotropic shrinkage of the matrix and the fibers can result disadvantageous.}' in delamination defects, particularly in small radius corners and tightly-curved sections, which can further reduce the interlaminar tensile strength of the material.

[0020] Oxide/oxide CMCs have a low thermal conductivity of only about 1/10* that of a metal (2 W/mK compared to about 20 W/mK for a metal ). The CMC surface temperature can be kept below limits by use of a thermal barrier coating, however thermal barrier coatings are only effective if a sufficiently high heat flux can be pulled through the CMC wall.

[0021] Since CMCs are thermal insulators, it is difficult to pull sufficiently high flux through thick walls. One solution to this problem is to use internal cooling holes in the CMC to direct the cooling air closer to the hot wall and increase heat flux. These cooling holes can be drilled or produced in situ, or otherwise manufactured into the CMC. Internal cooling is effective thermally. A disadvantage is that internal cooling significantly increases thermal stress in the part which may lead to cracking, delamination and reduced component life.

[0022] Use of internal cooling holes may be avoided if the CMC component were thinner; however, in ring seals 34, thickness is desired so as to accommodate the backside pressure load. Bending loads can also be reduced by reducing the axial span of the part, and also by reducing the backside pressure on the part. Ring segment 35 discussed below reduces bending loads so mat internal cooling channels are not necessary in order to maintain the ring seals 34 in a thermally acceptable zone.

[0023] Now turning to Figs. 2-5, the ring segment 35 will be discussed in detail . The ring segment 35 uses multiple sub-segments in order to reduce the span of the pressure load. The sub-segments are assembled together in order to form the ring segment 35, which in turn is used to form the ring seal 34. Sub-segments forming the ring segment 35 include a forward rail 41, a middle rail 42 and an aft rail 43. The aft rail 43 is located further downstream than the forward rail 41. The directions downstream (and upstream) are defined by the direction in which the hot working gases flow through the gas turbine engine 10 from the combustor section 14, i.e. gases flowing from the combustor section 14 are moving downstream.

[0024] The forward rail 41, the middle rail 42, and the aft rail 43 are made of a CMC material. The shape of the rails and interaction between the rails when assembled enables the usage of these materials. A metal top plate 37 is used to secure and provide strength to the fully assembled ring segment 35. The CMC material out of which the rails can be made are an oxide/oxide CMC, for example a CMC made from Nextel 720 Fabric. Each of the forward rail 41, the middle rail 42 and the aft rail 43 may have a circumferential length that is the same as one vane segment and/or up to half of the engine segment.

[0025] The forward rail 41 is shaped similarly to the aft rail 43. The forward rail 41 has a forward rail base 46, a forward rail first side 47 and a forward rail second side 48. The forward rail 41 has a radius of curvature that is greater than or that may match the engine flowpath. The flowpath expands as the flow progresses downstream in the turbine. The surface radius of the CMC ring segments 35 matches the expansion. However, it should be understood that in some instances the flow path may be conical in which case the surface radius of the CMC ring segments 35 would remain correspond to this. The radius of curvature is such that when the ring segments 35 are fully assembled they form the full circle of the ring seal 34. Thus the radius of curvature of the forward rail 41 is the same as the other forward rails that form the ring seal 34.

[0026] Both forward rail first side 47 and the forward rail second side 46 are angled with respect to the forward rail base 46. Both the forward rail first side 47 and the forward rail second side 46 are angled such that the angle by which they extend directs them towards the center of the forward rail base 46. In other words they are angled inwards. The angle a at which they are slanted may be between 25°-75° and preferably is between 35°-55°. The angle at which the forward rail second side 48 is angled should be such that it complements the angle of the middle rail first side 57. In cross-section the forward rail 41 has a trapezoidal shape without a top portion, thus having a "U" shaped cross-section.

[0027] The middle rail 42 has a middle rail base 56, a middle rail first side 57 and a middle rail second side 58. The middle rail 42 has a radius of curvature that is greater than or that may match the engine flowpath, the radius of curvature is the arc of the ring segment 35. The radius of curvature is such that when the ring segments 35 are fully assembled they form the full circle of the ring seal 34. Thus the radius of curvature of the middle rail 42 is the same as the other middle rails 42 forming the ring seal 34 and matches at the forward rails 41.

[0028] The middle rail first side 57 and the middle rail second side 58 are angled with respect to the middle rail base 56. Both the middle rail first side 57 and the middle rail second side 58 are angled away from the center of the middle rail base 56. In other words they are angled outwards. The angle β at which the middle rail first side 57 and the middle rail second side 58 are angled is such that it complements the forward rail second side 48 and aft rail first side 67, respectively. The middle rail first side 57 and the middle rail second side 58 complement the forward rail second side 48 and the aft rail first side 67 such that when the rail segment 35 is fully assembled the middle rail first side 57 is flush against the forward rail second side 48 and the middle rail second side 58 is flush against the aft rail first side 67. The angle β may be between 155°- 105° and is preferably between 145° to 125°

[0029] The aft rail 43 is shaped similarly to the forward rail 41. The aft rail 43 has an aft rail base 66, an aft rail first side 67 and an aft rail second side 68. The aft rail 43 has a radius of curvature greater than or matching the engine flowpath. The CMC rails, aft rail 41, middle rail 42 and forward rail 43 form the flow path (the gas path surface). This radius of curvature is slightly larger than the swept radius of the largest blade. The difference in curvature is the blade tip clearance, which is typically on the order of 1.0 to 1.5-mm. The radius of curvature is such that when the ring segments 35 are fully assembled they form the full circle of the ring seal34. Thus the radius of curvature of the aft rail 43 is the same as the other aft rails 43 forming the ring seal 34.

[0030] Both aft rail first side 67 and the aft rail second side 68 are angled with respect to the aft rail base 66. Both the aft rail first side 67 and the aft rail second side 68 are angled such that the angle by which they extend directs them towards the center of the aft rail base 66. In other words they are angled inwards. The angle a at which they are slanted may be between 25°-75° and preferably is between 35°-55°. The angle at which the aft rail first side 67 is angled should be such that it

complements the angle of the middle rail second side 58. In cross-section the aft rail 43 has a trapezoidal shape without a top portion, thus having a "ΙΓ shaped cross- section. [0031] It should be understood that while the forward rail first side 47 is angled inward at the same angle as the forward rail second side 48, forward rail first side 47 may have an angle that is different than that of the forward rail second side 48.

Likewise, aft rail second side 68 may have an angle that is different than that of aft rail first side 67. The sides that are adjacent to the middle rail 42 are those sides that impact the formation of the ring segment 35. As discussed above, the middle rail 42 has the middle rail first side 57 angled away from the middle rail second side 58 so that the middle rail first side 57 and the middle rail second side 58 are flush against the forward rail 41 and aft rail 42 so as secure them in a stable fashion.

[0032] Located within the forward rail 41 and within the aft rail 43 are plunger rails 40. The plunger rails 40 are sized and shaped to fit within the space created by the angled rails of the forward rail 41 and the aft rail 43. The plunger rails 40 extend in a circumferential direction in a similar manner as the forward rail 41 and the aft rail 43. The plunger rails 40 may have a cross-sectional shape that is similar to a half- moon. The half-moon cross sectional shape can permit the plunger rail 40 to fit securely within the forward rail 41 and the aft rail 43, which have U-shaped cross sections. In an alternative embodiment it is possible to have plunger rails 40 placed within the spaces created by middle rails 42 that are angled in the same manner as forward rail 41 and aft rail 43.

[0033] When assembled, the plunger rails 40 are secured to top plate 37 via bolts 36 through bolt holes 44. The top plate 37 and the plunger rails 40 are made of metal and provide a stable and strong surface for the forward rail 41, middle rail 42 and aft rail 43 to be secured to. Because CMC materials have low thermal expansion, a low thermal expansion alloy for the plunger rails 40, such as EN-909 or NILO-k may be used. In this way, the sliding contact wear between the CMC and the plunger rails 40 can be minimized.

[0034] The plunger rails 40 will function well if there is a known spring load pulling the plunger rails 40 to the metal top plate 37 and if the bolts 36 can slide to relieve thermal growth mismatch stress between the top plate 37 and the plunger rails 40. Spring load can be achieved by using a Belleville washer (not shown) with the bolt 36. For example, each bolt 36 can be designed to have 1000 lbs of spring load. In this way, a load is maintained even if there is some relaxation in the bolt assembly. Sliding can be achieved by using racetrack holes in the top plate 37, and designing for appropriate sliding stress.

[0035] Located on the top plate 37 are stops 39. When the ring segment 35 is assembled, the stops 39 are adjacent to the sides of the middle rail 42 and further help to secure the components of the ring segment 35 together. A bracket 38 is located at each end of the top plate 37. The bracket 38 is able to secure the top plate 37 to other top plates 37 via the ring segment connector 49. The bracket 38 is connected by nuts and bolts, or may be screwed together instead.

[0036] When the ring segment 35 is assembled, the air flow may pass through the forward rail 41, the middle rail 42 and the aft rail 43. In an embodiment, the air flow passes through an inner channel 71, a middle channel 72, and an outer channel 73 in a circumferential direction. The inner channel 71 is formed from the surface of the plunger rail 40 and the surface of the forward rail base 46. The outer channel 73 is formed from the surface of the plunger rail 40 and the surface of the aft rail base 66. The middle channel 72 is formed between the surface of the top plate 37 and the surface of the middle rail base 56. The inner channel 71, the middle channel 72 and the outer channel 73 direct the flow of air throughout ring seal 34 and help to cool and maintain the temperature of the ring segments 35. The cooling air is sufficient to keep the CMC material out of which the forward rail 41, the middle rail 42 and the aft rail 43 are made within an operational range.

[0037] The cooling air that flows through the ring segment 35 is such that it does not detract from the ability of the rails to handle the stress loads generated by the gas turbine engine 10.

[0038] Assembling the ring segment 35 may occur in the following manner. First the middle rail 42 is placed against the stops 39. The plunger rails 40 are then inserted into the forward rail 41 and the aft rail 43. The plunger rails 40 fit securely within the forward rail 41 and the aft rail 43 since as discussed above they may have a half-moon shaped cross section while the forward rail 41 and the aft rail 43 may have a U shaped cross section.

[0039] After the insertion of the plunger rails 40 into the forward rail 41 and the aft rail 43 the plunger rails 40 are secured to the top plate 37 using the bolts 36. The bolts 36 are then lightened to a torque level that will pull the plunger rails 40 towards the top plate 37. Pulling the plunger rails 40 toward the top plate 37 further pushes the forward rail 41, the aft rail 43 and the middle rail towards the stops 39. The forces generated by pulling the plunger rails 40 toward the top plate 37 should maintain the position of the middle rail 42. However, additional bolts may be applied if deemed necessary to stabilize the forward rail 41, the aft rail 43 and the middle rail 42.

[0040] The ring segment 35 discussed above reduces bending loads via the usage of die forward rail 41, middle rail 42, and aft rail 43, which are all made of a CMC material. The assembly of the rails in this manner permits the ring segment 35 to form the ring seal 34 without needing axially running cooling channels within the ring seal 34 so that internal cooling channels are not necessary in order to keep the ring seals 34 in a thermally acceptable zone.

[0041] Additional benefits of the ring segment 35 discussed above may be reduced CMC thickness for the rails due to reduced axial span. Furthermore, the ring segment 35 may reduce backside pressure. The top plate 37 may also be a unitary metal plate thus enhancing structural integrity. The geometry of the rails simplifies

manufacturing. Furthermore, the use of plunger rails 40 mechanically secures the ring segment 35 instead of the use of additional hardware.

[0042] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many

modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.