EP1890010B1 - Ceramic turbine shroud assembly - Google Patents
Ceramic turbine shroud assembly Download PDFInfo
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- EP1890010B1 EP1890010B1 EP07253097.5A EP07253097A EP1890010B1 EP 1890010 B1 EP1890010 B1 EP 1890010B1 EP 07253097 A EP07253097 A EP 07253097A EP 1890010 B1 EP1890010 B1 EP 1890010B1
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- European Patent Office
- Prior art keywords
- ring
- ceramic shroud
- shroud
- ceramic
- clamp ring
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
- F01D11/08—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2300/00—Materials; Properties thereof
- F05D2300/20—Oxide or non-oxide ceramics
- F05D2300/21—Oxide ceramics
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Turbine Rotor Nozzle Sealing (AREA)
Description
- The present invention relates to an outer shroud assembly for use in a gas turbine engine. More particularly, the present invention relates to a ceramic shroud assembly including a metal clamp ring shrink fitted around a ceramic shroud ring, where the metal clamp ring is configured to attach to a turbine engine casing.
- As gas turbine engine operating temperatures have been elevated in order to increase engine efficiency, many metal alloy ("metal") gas turbine engine components, such as a shroud or rotor blade, have been targeted to be replaced by ceramic equivalents. Ceramic materials are able to withstand higher operating temperatures and require less cooling than metals. Ceramic components are also generally less sensitive to thermal expansion than metal components because ceramic materials generally exhibit a lower coefficient of thermal expansion (CTE) than a metal.
- In one type of gas turbine engine, a static shroud ring is disposed radially outwardly from a turbine rotor, which includes a plurality of blades radially extending from a disc. The shroud ring at least partially defines a flow path for combustion gases as the gases pass from a combustor through turbine stages. There is typically a gap between the shroud ring and rotor blade tips in order to accommodate thermal expansion of both components during operation of the engine. The gap decreases during engine operation as the rotor blades thermally expand in a radial direction in reaction to high operating temperatures. It has been found that ceramic rotor blade tips experience a reduced radial displacement as compared to metal rotor blades because ceramic materials possess a lower CTE than metals. As a result, in a gas turbine engine incorporating ceramic rotor blades, there is a relatively large gap (or clearance) between the blade tips and the shroud ring. It is generally desirable to minimize the gap between a blade tip and shroud ring in order to minimize the percentage of hot combustion gases that leak through the tip region of the blade. The leakage reduces the amount of energy that is transferred from the gas flow to the turbine blades, which penalizes engine performance.
- In order to minimize losses induced by relatively large clearances between rotor blade tips and static shroud rings, some gas turbine engines are able to reduce the clearance by utilizing a ceramic shroud ring rather than a metal shroud ring. A ceramic shroud ring undergoes less thermal distortion during engine operation than many metal shroud rings due to the higher stiffness, lower CTE, and higher thermal conductivity of ceramic materials as compared to metals. Furthermore, a ceramic shroud requires less cooling than a metal shroud because ceramic material is capable of withstanding higher operating temperatures.
- In contrast to many metal shroud rings, it is difficult to attach a ceramic shroud ring to a metal gas turbine engine casing because the ceramic material exhibits a low ductility and a lower CTE than the metal casing. In general, stresses may generate at an interface between a ceramic component and a metal component because the ceramic and metal components react differently to the same temperature.
US 4087199 discloses a ceramic turbine shroud assembly. - The present invention in one aspect provides a ceramic shroud assembly as claimed in claim 1. The shroud assembly allows a ceramic shroud to be attached to a metal gas turbine engine casing in a manner that compensates for a difference in CTEs between the ceramic and metal materials. The metal ring may be a metal clamp ring attaching the ceramic shroud to the gas turbine engine casing.
- In a further aspect of the invention, there is provided a method of assembling a ceramic shroud assembly, as claimed in claim 15.
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FIG. 1 is a partial cross-sectional view of a gas turbine engine including a combustion chamber and a first compressor turbine stage incorporating a ceramic shroud assembly in accordance with the present invention, which includes an insulating and compliant layer of material disposed between a metal clamp ring and a ceramic shroud, and an axial restraint ring for axially restraining the ceramic shroud. -
FIG. 2 is a perspective assembly view of a shroud assembly, which illustrates a process of shrink fitting a metal clamp ring around a ceramic shroud and an interlayer. -
FIG. 3 is a perspective view of an alternate embodiment of a clamp ring of a ceramic shroud assembly of the present invention, where the clamp ring includes a plurality of axially extending slots. -
FIG. 4 is a plan view of axial restraint ring, which includes a plurality of radially extending cuts along its inner radius. -
FIG. 5 is a partial perspective cross-sectional view of a turbine vane, first stage turbine rotor, and a second embodiment of a ceramic shroud assembly, which includes a shroud that is tapered at an angle S with respect an axial centerline of a turbine engine. -
FIG. 6 is a perspective view of a third embodiment of a shroud assembly, which includes a shroud with anti-rotation tabs that are configured to engage with openings in a clamp ring. -
FIG. 7 is a partial perspective cross-sectional view of a fourth embodiment of a shroud assembly, which includes a shroud with an anti-rotation tab that is configured to engage with an opening in a clamp ring, the opening including a leaf spring that positions the tab within the opening. -
FIG. 1 is a partial cross-sectional view ofgas turbine engine 10, which includescombustion chamber 12,turbine engine casing 13, and firstcompressor turbine stage 14. Firstcompressor turbine stage 14 includes a plurality ofnozzle vanes 16 circumferentially arranged aboutcasing 13,rotor blades 18 radially extending from a rotor disc (not shown), andceramic shroud assembly 20 in accordance with the present invention. Shroudassembly 20 is attached toturbine engine casing 13. - During operation of
gas turbine engine 10, hot gases fromcombustion chamber 12 enter first highpressure turbine stage 14 throughturbine inlet region 22. More specifically, the hot gases move downstream (indicated by arrow 24) in an aft direction past a plurality ofnozzle vanes 16. Nozzle vanes 16 direct the flow of hot gases pastrotor blades 18, which radially extend from a rotor disc (not shown), as known in the art.Rotor blades 18 may be attached to the rotor disk using a mechanical attachment, such as a dovetail attachment, or may be integral with the rotor (i.e., an integrally bladed rotor). As known in the art,shroud assembly 20 defines an outer surface for guiding the flow of hot gases through firstcompressor turbine stage 14, while platform 21 positioned on an opposite end ofrotor blade 18 fromshroud assembly 20 defines an inner flow path surface. -
Ceramic shroud assembly 20 in accordance with the present invention includesclamp ring 26,ceramic shroud 28,interlayer 30, which is positioned betweenclamp ring 26 andceramic shroud 28, andaxial restraint ring 32. Shroudassembly 20 allows for relative movement between ceramic and metal parts (i.e., betweenmetal casing 13 and ceramic shroud 28), which helps compensate for a difference in thermal growth betweenmetal casing 13 andceramic shroud 28. As discussed in the Background section, whenmetal casing 13 andceramic shroud 28 are directly interfaced, stresses may generate at the interface because of the difference in CTE values between the ceramic and metal materials. The stresses may causeshroud 28 to fail. Furthermore, it is relatively difficult to attachceramic shroud 28 to metal gasturbine engine casing 13 because the ceramic material exhibits a low ductility. -
Shroud assembly 20 of the present invention allowsceramic shroud 28 to be attached tometal casing 13 usingmetal clamp ring 26, which is configured to attach tometal turbine casing 13, such as by a mechanical attachment means (e.g., bolts). As discussed in further detail below,metal clamp ring 26 is shrink fit aroundceramic shroud 28 andinterlayer 30, which allowsmetal clamp ring 26 andshroud 28 to be attached, yet allows for relative thermal growth therebetween without generating undue stress onshroud 28. Shrink fitting is a process in which heat is used to produce a very strong joint between two components, one of which is at least partially inserted into the other. In the present invention,clamp ring 26 is heated to a "preheat temperature," which causesclamp ring 26 to expand. Upon expansion,ceramic shroud 28 andinterlayer 30 are inserted intoclamp ring 26. Afterclamp ring 26 cools,clamp ring 26 contracts, thereby compressing (or "clamping")ceramic shroud 28 and interlayer 30. In this way,clamp ring 26 holdsshroud assembly 20 together by interference fit. -
Clamp ring 26 is formed of a metal, such as a nickel-base alloy.Front face 26A ofclamp ring 26 abutsaxial restraint ring 32, whileaft face 26B abuts an aft surface ofceramic shroud assembly 20.Flange 26C ofclamp ring 26 is configured to mate withcasing 13. In alternate embodiments,flange 26C may extend fromclamp ring 26 in a different direction or may be removed fromclamp ring 26, depending on a structure ofcasing 13. In one embodiment,clamp ring 26 andturbine casing 13 exhibit similar CTE values. In another embodiment,clamp ring 26 andturbine casing 13 exhibit different CTE values andclamp ring 26 is attached toturbine casing 13 using an attachment means allowing for relative growth therebetween (e.g., a U-slot). However, in either embodiment,metal clamp ring 26 andmetal casing 13 interface, rather thanmetal casing 13 interfacing directly withceramic shroud 28, which helps prevent the formation of stresses at an interface betweenceramic shroud 28 andmetal casing 13. -
Clamp ring 26 includes a plurality ofcooling holes 27, which are circumferentially positioned nearfront face 26A. Similarly,casing 13 includes a plurality ofcooling holes 36. In order to coolshroud 28, which is exposed to hot combustion gases, cooling air is bled from a compressor region ofturbine engine 10 to plenum 34 and throughcooling holes 36 incasing 13 andcooling holes 27 inclamp ring 26.Air seal 38 may optionally be placed nearaft face 26B ofclamp ring 26 in order to help direct cooling air fromcooling holes 36 throughcooling holes 27, and minimize cooling air leakage. -
Ceramic shroud 28 is a continuous uninterrupted annular ring having a substantially constant thickness (measured in a radial direction). Of course, in alternate embodiments,shroud 28 may also be formed of a plurality of split shroud segments in an annular arrangement. However, a continuous ring improves sealing about the outer flow path throughfirst compressor stage 14, which helps increase the efficiency ofturbine engine 10 by minimizing leakages of hot gases.Ceramic shroud 28 maybe formed of any suitable material known in the art, such as silicon nitride. -
Interlayer 30 is formed of a thermally insulating and compliant material exhibiting a relatively high compressive yield stress (e.g., greater than about 6 x 106 kilopascals (kPa)). In one embodiment,interlayer 30 is formed of mica, which exhibits a through thickness CTE of about 15 x 10-6/°C to about 20 x 10-6/°C. - During operation of
gas turbine engine 10, high operating temperatures causeclamp ring 26 andshroud 28 to expand (i.e., thermal growth).Clamp ring 26 is formed of a metal, whileshroud 28 is formed of a ceramic material, and due to the difference in CTE values between metals and ceramics,clamp ring 26 is likely to encounter more thermal growth thanshroud 28 during operation ofgas turbine engine 10. In order to help absorb the thermal growth mismatch and help prevent stresses from forming betweenclamp ring 26 andshroud 28 due to the difference in CTE values,interlayer 30 is positioned betweenclamp ring 26 andshroud 28.Interlayer 30 is formed of a compliant and thermally insulative material. The compliancy ofinterlayer 30 helps absorb the thermal growth mismatch betweenclamp ring interlayer 30 is also thermally insulative,interlayer 30 also helps isolateclamp ring 26 from combustion gases and heat flow from shroud 28 (which is at a high temperature due to the flow of hot gases between platform 21 and shroud 28) to clampring 26. Finally,interlayer 30 also helps prevent any chemical reaction betweenclamp ring 26 andshroud 28, which are formed of different materials. -
Interlayer 30 includesfirst portion 30A andsecond portion 30B. A thickness offirst portion 30A is greater than a thickness ofsecond portion 30B. In the embodiment illustrated inFIG. 1 ,first portion 30A ofinterlayer 30 is about 2.54 millimeters (100 mils) thick, whilesecond portion 30B is about 1.27 millimeters (50 mils) thick. In the embodiment shown inFIG. 1 , onlyfirst portion 30A ofinterlayer 30 contacts bothclamp ring 26 andshroud 28.First portion 30A is preferably substantially centered in the middle (i.e., midway between frontaxial face 28A and aftaxial face 28B) ofshroud 28 so thatshroud 28 does not cone under the compressive stress ofclamp ring 26.Second portion 30B covers approximately one-third of an aft portion (i.e:, the portion closest to aftaxial face 28B) ofshroud 28, as well as aftaxial face 28B.Second portion 30B ofinterlayer 30 thermally insulates the aft portion ofshroud 28, as well as aftaxial face 28, which helps to even out a temperature distribution acrossshroud 28. In alternate embodiments, the percentage ofshroud 28 covered byinterlayer 30 may be adjusted, depending upon the desired temperature distribution acrossshroud 28. -
Axial restraint ring 32 abutsfront face 26A ofclamp ring 26A andfront face 28A ofshroud 28, and helps restrainshroud 28 in an axial direction. Details of one embodiment ofaxial restraint ring 32 are described in reference toFIG. 4 . -
FIG. 2 is a perspective assembly view ofshroud assembly 20, which illustrates a process of shrink fittingmetal clamp ring 26 aroundshroud 28 andinterlayer 30.Metal clamp ring 26 has radius R1 and includes a plurality of cooling holes 27 nearfront face 26A. In order to shrinkfit clamp ring 26 aroundshroud 28 andinterlayer 30,clamp ring 26 is heated to a preheat temperature in order to expandclamp ring 26 to a size sufficient enough to receiveshroud 28 andinterlayer 30. Upon heating to a preheat temperature,metal clamp ring 26 expands to metal clamp ring 26 (shown in phantom) having radius R2. The difference between R1 and R2 depends upon the material whichmetal clamp ring 26 is constructed of, as well as the preheat temperature. As those skilled in the art recognize, in general, the higher the preheat temperature, the greater the difference between R1 and R2. - After heating
clamp ring 26,shroud 28 andinterlayer 30, which are typically at room temperature (approximately 21-23 °C) (i.e., unexpanded), are introduced into expandedclamp ring 26. In one embodiment,interlayer 30 is attached toshroud 28 before being introduced intoclamp ring 26. Becauseclamp ring 26 is expanded to radius R2,shroud 28 andinterlayer 30, which are approximately at room temperature, are able to fit withinclamp ring 26.First portion 30A ofinterlayer 30 has outer radius R3, whilesecond portion 30B ofinterlayer 30 has outer radius R4, which is less than radius R3. In one embodiment, outer radius R3 offirst portion 30A is approximately equal to radius R2 of heated and expandedclamp ring 26. - The preheat temperature of
clamp ring 26 affects a clamp load which is applied toceramic shroud 28 andinterlayer 30. Generally, the higher the preheat temperature, the higher the clamp load and the higher the stress inclamp ring 26 for a given radius at the preheat temperature (aftermetal clamp ring 26 is brought back down to room temperature). This relationship is attributable to the fact that in a typical shrink fit process, theamount clamp ring 26 expands (i.e., the difference between R1 and R2) is generally proportional to theamount clamp ring 26 shrinks upon being returned to room temperature. Themore clamp ring 26 shrinks, the greater the stresses generated inclamp ring 26 and the greater theload clamp ring 26 exerts onshroud 28. As a result of the relationship betweenclamp ring 26 expansion, stresses inclamp ring 26, and clamp loads, the preheat temperature is chosen based on the desirable stresses and clamp loads. The preheat temperature is preferably low enough to preventmetal clamp ring 26 from exceeding its yield limit or creep strength. On the other hand, the preheat temperature is preferably high enough to achieve a clamp load that is sufficient enough to holdshroud assembly 20 together during all engine 10 (FIG. 1 ) operation levels (e.g., from start-up to shutdown). - A finite element analysis was conducted with respect to one embodiment of gas turbine engine 10 (
FIG. 1 ). The following preheat temperatures and associated stresses and clamp loads resulted:Table 1: Stresses and Clamp Loads Resulting From Various Preheat Temperatures 1 2 3 4 5 6 7 Preheat Temperature (°C) Maximum Von Mises Stress in Metal Clamp at Room Temperature (kPa) Maximum Von Mises Stress in Metal Clamp at Engine Steady State Conditions (kPa) First Principal Stress in Ceramic Shroud at Room Temperature (kPa) First Principal Stress in Ceramic Shroud at Engine Steady State Conditions (kPa) Clamp Load at Room Temperature (kiloNewton (kN)) Clamp Load at Engine Steady State Conditions (kN) 204 (400 °F) 3.86 X 105 (56 ksi) 1.65 X 105 (24 ksi) 2.76 x 104 (4 ksi) 6.21 x 104 (9 ksi) 42.26 (9500 lbf) 7.18 (1600 lbf) 260 (500 °F) 4.96 X 105 (72 ksi) 4.96 X 105 (40 ksi) 3.45 x 104 (5 ksi) 6.21 x 104 (9 ksi) 53.38 (12000 lbf) 22.24 (5000 lbf) 316 (600 °F) 6.07 x 105 (88 ksi) 6.07 x 105 (60 ksi) 4.14 x 104 (6 ksi) 6.21 x 104 (9 ksi) 66.72 (15000 lbf) 40.03 (9000 lbf) - The finite element analysis was conducted with respect to three preheat temperatures, which are listed in Column 1 of Table 1. Column 2 lists the maximum Von Mises stress values for
clamp ring 26 afterclamp ring 26 is heated to the respective preheat temperature listed in Column 1 to reach a radius R3 from radius R2 and subsequently cooled to room temperature. Column 3 lists, for each of the preheat temperatures, the maximum Von Mises stress value formetal clamp ring 26 during gas turbine engine 10 (FIG. 1 ) steady state conditions, at which conditionmetal clamp ring 26 is exposed to operating temperatures of up to 426 °C (about 800 F°). Column 4 lists, for each of the preheat temperatures, the first principal stress inshroud 28 at room temperature, aftermetal clamp ring 26 is shrink fit aroundshroud 28 andinterlayer 30. Column 5 lists, for each of the preheat temperatures, the first principal stress inshroud 28 duringgas turbine engine 10 steady-state conditions. Column 6 lists, for each of the preheat temperatures, the clamp loadmetal clamp ring 26 exerts onshroud 28 at room temperature. And finally, Column 7 lists, for each of the preheat temperatures, the clamp loadmetal clamp ring 26 exerts onshroud 28 duringgas turbine engine 10 steady-state conditions. - As seen from the data listed in Table 1, as the preheat temperature increases, the Von Mises stress in
clamp ring 26 and clamp load applied byclamp ring 26 increase at both room temperature andengine 10 steady-state conditions. Both the Von Mises stress and clamp load drop from room temperature conditions to steady-state conditions becauseclamp ring 26 expands in response to the increased operating temperatures, andclamp ring 26 expands more thanshroud 28 due to the difference to CTE ofceramic shroud 28 andmetal clamp ring 26. Whenclamp ring 26 expands more thanshroud 28, the amount of interference fit betweenclamp ring 26 andshroud 28 is decreased. In one embodiment,clamp ring 26 is formed of Inconel 783, which is an oxidation-resistant nickel-based superalloy. Inconel 783 exhibits a yield stress of about 7.58 x 106 kPa (about 110 ksi). At each of the preheat temperatures in Table 1, the maximum Von Mises stress forclamp ring 26 is below the yield stress of Inconel 783. Therefore, forclamp ring 26 formed of Inconel 783, preheat temperatures ranging from about 204 °C to about 316 °C are suitable. - Maintaining a suitable clamp load during engine transient conditions (i.e., when a transition is made from one engine power output level to another) is also in important factor in determining the preheat temperature. Due to different CTE and heat transfer characteristics of
metal clamp ring 26 andceramic shroud 28, a thermal response ofmetal clamp ring 26 andceramic shroud 28 to the same power output level can differ, which may impact the clamp load. For example, during engine start-up,ceramic shroud 28 typically heats up faster thanmetal clamp ring 26 because of a more rapid change in heat transfer boundary conditions ofshroud 28. That is, becauseshroud 28 is directly exposed to hot combustion gases,shroud 28 tends to heat up and expand faster thanclamp ring 26. Whenshroud 28 expands faster thanclamp ring 26, clamp load and stress inclamp ring 26 increases becauseshroud 28 pushes againstclamp ring 26. Therefore it is important to know what is the minimum clamp load during engine transient. - Engine start-up and shut-down were simulated using finite element analysis in order to determine the load exerted by
clamp ring 26 onshroud 28, and the Von Mises stress ofclamp ring 26. Table 2 illustrates the results of the finite element analysis for stresses and clamp loads duringengine 10 start-up conditions:Table 2: Stresses and Clamp Loads during Engine Start-up Conditions \Preheat Temperature (°C) Maximum Von Mises Stress in Metal Clamp (kPa) First Principal Stress in Ceramic Shroud at Engine Steady State Conditions (kPa) Minimum Clamp Load (kN) 260 (500 °F) 6.21 x 105 (90 ksi) 4.83 x 104 (7 ksi) 22.24 (5000 lbf) 316 (600 °F) 6.89 x 105 (100 ksi) 6.21 x 104 (9 ksi) 40.03 (9000 lbf) - Table 3 illustrates the results of the finite element analysis for stresses and clamp loads during
engine 10 shutdown conditions:Table 3: Stresses and Clamp Loads During Engine Shutdown Conditions Preheat Temperature (°C) Maximum Von Mises Stress in Metal Clamp (kPa) First Principal Stress in Ceramic Shroud at Engine Steady State Conditions (kPa) Minimum Clamp Load (kN) 260 (500 °F) 4.14 x 105 (60 ksi) 3.45 x 104 (5 ksi) 7.18 (1600 lbf) 316 (600 °F) 6.21 x 105 (90 ksi) 1.45 x 105 (21 ksi) 9.34 (2100 lbf) - In the embodiment in which
clamp ring 26 is formed of Inconel 783, the stresses inclamp ring 26 remain below the yield stress of Inconel 783 (about 7.58 x 105 kPa) duringengine 10 start-up and shutdown conditions when the preheat temperature ofclamp ring 26 is up to about 316 °C. Thus, for an Inconel 783 clamp ring 26 (or a material exhibiting similar properties), a preheat temperature of about 316 °C is suitable. - During
engine 10 shutdown,shroud 28 contracts faster thanclamp ring 26 and it is critical to maintain a minimum clamp load. As shown in Table 3, atengine 10 shutdown, minimum clamp loads drop compared to clamp loads at steady-state engine 10 operating conditions (detailed in Table 1). A concern atengine 10 shutdown is whetherclamp ring 26 will apply sufficient clamp load onshroud 28. As previously discussed, the preheat temperature is dependent upon the desirable clamp loads. For example, if a clamp load of approximately 7.18 kN needs to be maintained at all times to maintain the integrity ofshroud assembly 20, the lower limit of a preheat temperature is about 260 °C. - It is also desirable for
ceramic shroud 28 to remain under compression for substantially all engine conditions because ceramic material is stronger in a compressive stress state than in a tensile stress state. For an Inconel 783clamp ring 26, it has been found that if the preheat temperature is selected in the range of about 260 °C to about 316 °C,ceramic shroud 28 remains under compression for all engine conditions, while at the same time,clamp ring 26 operates below its yield limit. -
FIG. 3' is a perspective view of an alternate embodiment ofclamp ring 40, which includes a plurality of axially-extendingslots 42 extending fromfront face 40A toaft face 40B, and a plurality of cooling holes 44.Slots 42 increase the radial compliance ofclamp ring 40 and allow a shroud (e.g.,shroud 28 ofFIG. 1 ) disposedinside clamp ring 40 to expand without generating undue stress on the shroud orclamp ring 40. -
FIG. 4 is a plan view ofaxial restraint ring 32, which includesslot 45 and a plurality of radially extendingcuts 46 alonginner radius 32A. In the embodiment illustrated inFIG. 1 ,axial restraint ring 32 is a snap ring, which, as known in the art, is a discontinuous annular ring that can be distorted to decrease its diameter. In order to fitaxial restraint ring 32 into assembly 20 (shown inFIG. 1 ) and retainaxial restraint 32 in place, a force is applied toaxial restraint ring 32 in order to decrease its diameter, as shown in phantom.Axial restraint ring 32 is then fit into turbine casing 13 (shown inFIG. 1 ), after which, the force applied toaxial restraint ring 32 is released, thereby increasing the diameter ofaxial restraint ring 32, allowingaxial restraint ring 32 to "snap" into place. Becauseaxial restraint ring 32 is a greater diameter than casing 13,axial restraint ring 32 exerts a radial force on casing 13, which helpsaxial restraint ring 32 retain its position.Axial restraint ring 32 is formed of any suitable material, such as a nickel-based alloy (e.g., Inconel 625). - Radial cuts 46 in
axial restraint ring 32 define a plurality ofradial tabs 48 that are configured to push againstfront face 28A of shroud 28 (shown inFIG. 1 ) in order to axiallyrestraint shroud 28 and prevent movement ofshroud 28 in an upstream direction 25 (shown inFIG. 1 ). In one embodiment,tabs 48 are coated with a coating that reduces heat transfer fromshroud 28 totabs 48 and prevents reaction betweenaxial restraint ring 32 andshroud 28. The coating may be, for example, a ceramic thermal barrier coating known in the art, such as yttria stabilized zirconia. Radial cuts 46 also allow for cooling air from chamber 34 (which has flowed through cooling holes 36 incasing 13 and cooling holes 27 in metal clamp ring 26) to coolaxial restraint ring 32. -
FIG. 5 is a partial perspective cross-sectional view ofturbine engine casing 50,turbine vane 52,turbine rotor 53, and a second embodiment ofceramic shroud assembly 54, which is similar toceramic shroud assembly 20 ofFIG. 1 , except thatshroud 58 is tapered at angle S with respect toline 66, which is parallel to an axial centerline ofturbine engine 10, fromfront face 58A toaft face 58B. In the embodiment illustrated inFIG. 5 , angle S is about 10 degrees.Shroud assembly 54 further includesclamp ring 56, which is attached toturbine casing 50,interlayer 60, firstaxial restraint ring 62, and secondaxial restraint ring 64.Clamp ring 56 is also tapered to matchshroud 58, such thatclamp ring 56 andshroud 58 have similar contours.Interlayer 60 is similar tointerlayer 30 ofFIG. 1 . Firstaxial restraint ring 62 helps locateclamp ring 56 such thatclamp ring 56 does not move in an upstream direction (indicated by arrow 25). - Taper angle S of
shroud 58 is governed by a frictional coefficient that is necessary to keepshroud 58 located axially (i.e., preventshroud 58 from moving in aft (or downstream) direction 24 or upstream direction 25). For a high coefficient of friction (e.g., 0.6), taper angle S may be up to 31° with respect toline 66 without compromising the axial location ofshroud 58. Although there is a radial component to the force with whichclamp ring 56compresses shroud 58, the embodiment ofshroud assembly 54 inFIG. 5 also provides an axial force that pushesshroud 58 in the aft direction (indicated by arrow 24), against aft surface 56B ofclamp ring 56, thereby helping to preventshroud 58 from moving in the aft direction 24. As an additional measure for maintaining the axial location ofshroud 58,front face 58A ofshroud 58 is axially restrained by secondaxial restraint ring 64. -
FIG. 6 is a perspective view of a third embodiment ofshroud assembly 70 including clamp ring 72 andshroud 74.Shroud assembly 70 also includes an interlayer (not shown) positioned between clamp ring 72 andshroud 74.Shroud assembly 70 is similar toshroud assembly 20 ofFIG. 1 , except thatshroud 74 includes a plurality ofanti-rotation tabs 76, which are configured to engage withcorresponding openings 78 in clamp ring 72.Anti-rotation tabs 76 circumferentially locateshroud 74 with respect to clamp ring 72, and help limit rotational movement ofshroud 74 aboutcenter axis 80. In addition, friction between clamp ring 72 andshroud 74 generated by the shrink-fit process helps circumferentially locateshroud 74. In the embodiment shown inFIG. 5 ,shroud 74 includes three equally spacedanti-rotation tabs 76. However, in alternate embodiments,shroud 74 may include any suitable number ofanti-rotation tabs 76, such as two, four, five, etc., as well as any suitable arrangement (e.g., equally or unequally spaced). In the alternate embodiments, clamp ring 72 includes a corresponding number ofopenings 78. -
FIG. 7 is a partial perspective cross-sectional view of gas turbine engine 82, which includes turbine casing 84 (similar toturbine casing 13 ofFIG. 1 ), stationary vane 86 (similar tostationary vane 16 ofFIG. 1 ), turbine rotor 88 (similar torotor blade 18 ofFIG. 1 ), and a fourth embodiment ofshroud assembly 90.Shroud assembly 90 includesclamp ring 92,shroud 94, and an interlayer (not shown inFIG. 7 ) positioned betweenclamp ring 92 andshroud 94. Similar toshroud 74 ofFIG. 6 ,shroud 94 includesanti-rotation tab 96, which is configured to engage with acorresponding opening 98 inclamp ring 92. However, unlike the third embodiment ofshroud assembly 70, in the fourth embodiment ofshroud assembly 90,openings 98 inclamp ring 92 each includeleaf spring 100.Leaf spring 100 allows opening 98 to be adaptable todifferent anti-rotation tab 96 locations by providing a range of locations for whichanti-rotation tab 96 may be introduced intoopening 98, while still allowingopening 98 to engage withanti-rotation tab 96.Leaf spring 100 preferably has a controlled stiffness that keepsshroud 94 in position without introducing high stress inshroud 94. In another embodiment, a second leaf spring is located on opening 98opposite leaf spring 100.Shroud assembly 90 may be modified to include any suitable number of leaf springs. - While a shroud assembly in accordance with the present invention has been described in reference to a first high pressure turbine stage, the inventive shroud assembly is suitable for incorporation into any turbine stage of a gas turbine engine, as well as any other application of a shroud ring.
Claims (17)
- A ceramic shroud assembly (20; 54; 70; 90) comprising:a ceramic shroud (28; 58; 74; 94) comprising:an inner surface;an outer surface opposite the inner surface;a first axial face (28B) extending between the inner surface and the outer surface; anda second axial face (28A) opposite the first axial face; characterised in that said ceramic shroud assembly further comprises:a first metal ring (26; 40; 56; 72; 92) shrink fitted around at least a part of the outer surface of the ceramic shroud and configured to attach to a turbine engine casing (13; 50; 84);a compliant and thermally-insulating layer (30; 60) positioned between the ceramic shroud and the first ring; anda second ring (32; 64) configured to axially restrain the ceramic shroud.
- The ceramic shroud assembly of claim 1, wherein the second ring (32) abuts the second axial face (28A) of the ceramic shroud (28).
- The ceramic shroud assembly of claim 2, wherein the second ring comprises:an inner surface adjacent to the ceramic shroud;an outer surface; anda plurality of radial slots (46) extending from the inner surface toward the outer surface and defining a plurality of radial tabs (48), the plurality of radial tabs (48) being configured to bias against the first axial face of the ceramic shroud (28).
- The ceramic shroud assembly of any preceding claim, wherein the first ring (26; 40; 56; 72; 92) is formed of a material comprising a nickel-based alloy.
- The ceramic shroud assembly of any preceding claim, wherein the first ring (40) includes a plurality of axial slots (42).
- The ceramic shroud assembly of any preceding claim, wherein the first ring (26; 40; 56; 72; 92) exhibits a Von Mises stress in a range of about 3.86 x 105 kilopascals to about 6.07 x 105 kilopascals at a temperature in a range of about 21 to about 23 degrees Celsius.
- The ceramic shroud assembly of any preceding claim, wherein the first ring (26; 40; 56; 72; 92), at engine steady state conditions, exhibits a Von Mises stress in a range of about 1.65 x 105 kilopascals to about 6.07 x 105 kilopascals at a shrink-fit temperature in a range of about 204.44 to about 315.56 degrees Celsius.
- The ceramic shroud assembly of any preceding claim, wherein the compliant and insulating layer (30; 60) covers at least a part of the first axial face (28B) of the ceramic shroud (28; 58; 74; 94).
- The ceramic shroud assembly of any preceding claim, wherein the compliant and insulating layer (30) comprises:a first portion (30A) including a first thickness and configured to contact the ceramic shroud (28) and the first ring (26); anda second portion (30B) including a second thickness less than the first thickness, wherein the second portion is configured to contact the ceramic shroud (28).
- The ceramic shroud assembly of claim 9, wherein the first thickness is about 0.254 centimeters and the second thickness is about 0.127 centimeters.
- The ceramic shroud assembly of any preceding claim, wherein the outer surface of the ceramic shroud (74; 94) comprises an anti-rotation tab (76; 96), and the first ring (72; 92) comprises an opening (78; 98) configured to receive the anti-rotation tab of the ceramic shroud.
- The ceramic shroud assembly of claim 11, and further comprising:a leaf spring (100) positioned between the anti-rotation tab (96) and the opening (98) in the first ring (92).
- The ceramic shroud assembly of any preceding claim, wherein the ceramic shroud (58) is tapered from the first axial surface (58A) to the second axial surface (58B).
- The ceramic shroud assembly of claim 13, wherein the ceramic shroud (58) is tapered at an angle in a range of about 10 degrees to about 31 degrees with respect to a centerline (66) of the gas turbine engine (10).
- A method of assembling a ceramic shroud assembly (20; 54; 70; 90) suitable for use in a gas turbine engine, the method comprising:preheating a first ring (26; 40; 56; 72; 92) comprising an inner diameter to a preheat temperature, wherein after cooling down from the preheat temperature, a stress in the first ring is below a yield limit of the first ring;introducing a ceramic shroud (28; 58; 74; 94) into the first ring;introducing an insulating and compliant layer (30; 40) comprising an outer diameter into the first ring, wherein the insulating layer and complaint layer is positioned between the first ring and the ceramic shroud; andpositioning an axial restraint ring (32; 64) adjacent to the ceramic shroud.
- The method of claim 15, wherein the insulating and compliant layer (30; 60) is attached to the ceramic shroud (28; 58; 74; 94) prior to introducing the insulating and compliant layer and the ceramic shroud into the first ring (26; 40; 56; 72; 92).
- The method of claim 15 or 16, wherein the preheat temperature is in a range of about 204 to about 316 degrees Celsius.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/502,212 US7771160B2 (en) | 2006-08-10 | 2006-08-10 | Ceramic shroud assembly |
US11/502,079 US7665960B2 (en) | 2006-08-10 | 2006-08-10 | Turbine shroud thermal distortion control |
Publications (3)
Publication Number | Publication Date |
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EP1890010A2 EP1890010A2 (en) | 2008-02-20 |
EP1890010A3 EP1890010A3 (en) | 2011-08-10 |
EP1890010B1 true EP1890010B1 (en) | 2016-05-04 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP07253097.5A Active EP1890010B1 (en) | 2006-08-10 | 2007-08-07 | Ceramic turbine shroud assembly |
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EP (1) | EP1890010B1 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
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US7665960B2 (en) | 2006-08-10 | 2010-02-23 | United Technologies Corporation | Turbine shroud thermal distortion control |
CH699312A1 (en) | 2008-08-15 | 2010-02-15 | Alstom Technology Ltd | Blade arrangement for a gas turbine. |
US8167546B2 (en) | 2009-09-01 | 2012-05-01 | United Technologies Corporation | Ceramic turbine shroud support |
US8956700B2 (en) | 2011-10-19 | 2015-02-17 | General Electric Company | Method for adhering a coating to a substrate structure |
EP2807344B1 (en) * | 2012-01-26 | 2022-11-30 | Ansaldo Energia IP UK Limited | Stator component with segmented inner ring for a turbomachine |
CN108691577B (en) * | 2017-04-10 | 2019-09-20 | 清华大学 | The active clearance control structure of turbogenerator |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US4087199A (en) * | 1976-11-22 | 1978-05-02 | General Electric Company | Ceramic turbine shroud assembly |
DE3019920C2 (en) * | 1980-05-24 | 1982-12-30 | MTU Motoren- und Turbinen-Union München GmbH, 8000 München | Device for the outer casing of the rotor blades of axial turbines for gas turbine engines |
US4639388A (en) * | 1985-02-12 | 1987-01-27 | Chromalloy American Corporation | Ceramic-metal composites |
US6910853B2 (en) * | 2002-11-27 | 2005-06-28 | General Electric Company | Structures for attaching or sealing a space between components having different coefficients or rates of thermal expansion |
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EP1890010A3 (en) | 2011-08-10 |
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