Industrial gas turbine multi-axial thermal isolator

Abstract

A multi-axial thermal isolator device for isolating structures formed of differing materials. The device is rigidly attached to both structures and is capable of movement as the result of relative thermal expansion of the structures. The device has a substantially C or Z-shaped configuration with a curved portion forming an angle &thgr; in the range of about 0-10 degrees. The device provides a means for thermal decay between adjacent structures when the parts are subjected to large changes in temperature.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention generally relates to industrial gas turbine engines capable of emitting very low exhaust emissions. In particular, the present invention is directed to a thermal isolator device for connecting a large cast iron combustor casing to a relatively thin compressor and turbine casing without allowing thermal interference, especially during system startup and shut down transient conditions.

[0002] With recent power shortages in many cities, the need for generating power in heavily populated areas is increasingly important. If industrial gas turbine engine assemblies are to be located in generating plants located within such heavily populated areas, it would be considered advantageous to utilize low emission engine assemblies whenever possible. To lower the development costs of the gas turbine engine assembly, it has been suggested that engine compressor and turbine sections of aerospace engines be employed with a clean burning combustion system.

[0003] The combustion system must be designed to accommodate any special burner and control valves to modulate the airflow. As a result, typical combustion system consist of very large diameter structures or casings, usually several times the size of the gas generator core diameter. To reduce the cost of the combustion system, the casing is usually made of low cost cast iron weighing in excess of several thousand pounds. In comparison, the aerospace engines are typically made of lightweight sheet metal materials weighing only a few hundred pounds. When the assemblies are joined to form the engine system, the differences in the coefficient of thermal expansion of the various casing materials may create destructive thermal interference unless effectively thermally isolated from one another.

[0004] A number of devices have been employed in an attempt to overcome the problem of thermal interference. In one assembly, flat members or struts are positioned to maintain structural alignment by relying on the flexibility of the flat members to take up thermal deflection. A problem with such a device is not axis symmetric and relies on a single isolating location rather than a pair of assemblies located at the engine compressor and at the turbine power section. Finally, the flat members do not account for relatively slow thermal decay as needed to afford sufficient time for the casings to heat up during startup.

[0005] In another conventional assembly, a double walled sheet metal split ring having first and second axially opposed loops is employed. The loops are disposed in grooves of the adjoining members and serve as a seal while apparently accommodating radial and axial movements. Because the seal can slide, it can become misaligned. Furthermore the shape of the metal part does not allow for thermal decay as needed when the casings begin to heat up.

[0006] In a further known device, sheet metal seal spring clips serve as seal elements to take up thermal growth. The clips are fixedly attached to the engine sections and can become misaligned. There is no ability to function in an axis symmetric way to thermally isolate the sections and there is no ability to allow the desirable thermal decay.

[0007] By employing floating seals, the rigidity of the engine system is potentially compromised as well as creating the potential for misalignment. None of the conventional systems appears to consider the desirability of allowing a relatively slow thermal decay in order to provide time for the structures to heat up during startup. There is clearly a need for a device capable of joining the heavy, cast iron combustor assembly with the lightweight compressor and turbine housing while, at the same time, creating a relatively slow thermal decay time between the various housing sections.

SUMMARY OF THE INVENTION

[0008] In one aspect of the present invention, a thermal isolator device is positioned to compensate for thermal expansion from one engine structure to another in all directions. The multi-axial isolator has a curved shape that may take the general form of the letter “Z” or the letter “C”. Alternatively, the isolator device may take the form of a hairpin loop at the mid-section with flanged connections at either end. Preferably the isolator is formed as a single piece but may be formed of curved sections joined to one another. The isolator is made of either cast or forged nickel based alloys necessary to withstand the high temperature environment present in gas turbine engine assemblies.

[0009] The outer diameter “O/D” of one isolator may be mechanically fastened to either the heavy cast iron casing of the combustor or the thin metal sheet metal casing of the compressor. The inner diameter “I/D” of the isolator will be mechanically fastened to the adjacent casing. A similar isolator may be mechanically fastened between the combustor and the turbine casings. In another aspect of the invention, the O/D of each isolator may be mechanically fastened to the compressor or turbine and the I/D fastened to the combustor. The thickness and specific angle formed by the isolator as well as its length is specifically designed to withstand the heavy weight of the structures while providing adequate length for thermal decay. The axial stiffness of the thermal isolator is specifically designed to carry any potential increase of the loads, i.e., blow-off loads generated by the engine assembly.

[0010] In another aspect of the invention, the thermal isolator device of the present invention may be in any structural interface that requires thermal isolation between adjacent assemblies due to the difference in the coefficient of thermal expansion of the materials.

[0011] In another aspect of the invention, a method is shown for creating a gas turbine engine assembly from the heavy casing of an industrial combustor and thin sheet metal casings of an aircraft compressor and gas turbine.

[0012] These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic view of a gas turbine engine assembly including the thermal isolator device of the present invention;

[0014] FIG. 2 is a perspective view of a thermal isolator device utilized in the engine assembly of FIG. 1;

[0015] FIG. 3 a cross-section view taken in a plane along the X axis of the engine centerline in FIG. 2;

[0016] FIG. 4 is a perspective view of another thermal isolator device utilized in the engine assembly of FIG. 1;

[0017] FIG. 5 is cross-sectional view taken in a plane along the X axis of the engine centerline in FIG. 4; and

[0018] FIGS. 6a and 6b are cross-sectional views of thermal isolator devices utilized in the engine assembly of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The following detailed description is of the best currently contemplated modes of carrying out the present invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

[0020] Referring to FIG. 1, an industrial gas turbine engine assembly 10 includes a combustor system 12 encased in a conventional cast iron casing which may easily weigh thousands of pounds. A compressor 14 positioned upstream from combustor system 12 may be fabricated as thin-wall structures (casting, machining or sheet metal), as typically used in aerospace engines. A turbine 16 is positioned downstream of combustor system 12 as indicated by arrow R. In a manner similar to compressor 14, turbine 16 may be housed in a lightweight sheet metal casing of the type utilized with aerospace engine assemblies.

[0021] A first thermal isolating device 18 may be fastened at one side combustor assembly 12 and at the other side to compressor 14. A second, similar thermal isolating device 18 may be fastened at one side to combustor assembly 12 and at the other side to turbine 16. During operation of gas turbine engine assembly 10, air, as indicated by arrow A, can flow through compressor 14, combustor 12 and turbine 16 before being exhausted as indicated by arrow E. During operation of gas turbine engine assembly 10, the airflow stream in the various engine components may have temperatures that exceed 600 degrees F. in the compressor section, whereas in the combustor and turbine sections, temperatures in excess of 2000 degrees F. are not uncommon

[0022] As the engine components heat the air stream, the outer casings can rapidly begin to heat. Because of the significant difference in the mass of the casings, they can tend to thermally expand at significantly different rates. As will be explained, each of the thermal isolator devices 18 may be capable of changing shape as needed to compensate for the differing rate of thermal expansion of the adjacent engine components. By compensating for the differences in thermal expansion, isolator devices may function as thermal spring like connecting members. At the same time, isolator devices 18 may effectively prevent any component from thermally affecting its adjacent engine component.

[0023] Referring now to FIGS. 2 and 3, wherein a typical thermal isolator device 18 is shown. Isolator device 18 is formed as a continuous cylindrical member. The cross-sectional shape of isolator device 18 in FIG. 3 may have an I/D portion 22 of reduced diameter as compared to an O/D portion 24. The middle connecting portion 25 of isolator device 18 has a gradually increasing radius such that isolator device 18 may have a generally cone-shaped appearance as shown in FIG. 2. O/D portion 24 may include a flange 26 having a number of through openings 27 circumferentially spaced to allow fastening bolts to extend through openings 27 and through openings formed in one of the engine component casings, not shown. Likewise, I/D 22 also may include a flange 28 with a number of circumferentially spaced through openings 29 to allow for fastening of flange 27 with one of the engine components, (not shown).

[0024] In the isolator device 18 shown in FIG. 3, the length L of device 18 may have a ratio to the radius R, the distance to the engine center line, ECL, of device 18, L/R, that is substantially about 0.5 to 0.6. The angle &thgr; of inclination of middle portion may be substantially about 0 to 10 degrees compared to a line parallel to the ECL.

[0025] Another aspect of the invention is shown in FIGS. 4 and 5, wherein an isolator device 18 is shown to have a substantially C-shaped configuration. Isolator device 18 may include an outer flange 32 formed at the O/D end portion and an inner flange 34 formed at an I/D end portion. The end portions can be radially spaced from one another and separated by a substantially C-shaped middle portion 36. The upper and lower leg portions 33 and 35 of middle portion 36 may each have a thickness of substantially about 0.15 to 0.25 inches. The ratio of the length L of isolator device 18 to the radius R, the distance from ECL, L/R can be substantially about 0.2 to 0.3. Because of its curved shape, isolator device 18 may naturally function as a spring while thermally isolating adjacent engine components from one another. Circumferentially spaced through openings 37 can extend through outer flange 32, while circumferentially spaced through openings 38 can extend through inner flange 34.

[0026] The specific shape of thermal isolator device 18 may vary as the particular need of the engine assembly 10 is considered. A pair of isolator devices 18 are shown in FIGS. 6a and 6b, wherein the particular shape of each device provides effective thermal isolation between adjacent casings. Referring now to FIG. 6a, thermal isolator device 18 has a substantially C-shaped cross-section including an I/D end with an inner flange 40 and an O/D end with an outer flange 42. A radially inner leg portion 44 of substantially constant diameter may connect inner flange 40 with a radially outer leg portion 46 of increasing radius that may be connected to outer flange 42. In the isolator device 18 shown in FIG. 6a, the length of the device, L and the radius R, the distance to the EGC may have a ratio L/R of substantially about 0.2 to 0.3. The outer leg 46 may have a thickness of substantially about 0.15 to 0.25 inches and the inner leg thickness of substantially about 0.05 to 0.10 inches. The angle between the inner and outer leg portions 42 and 46 is substantially about 0 to 5 degrees.

[0027] The isolator device 18 shown in FIG. 6b has in reverse C shape formed by curved middle portion 50. An outer end flange portion 52 may be integrally attached to middle portion 50, as is an inner end flange portion 54. The length L of the device 18 can have a ratio to the radius R of the distance to the ECL, L/R of substantially about 0.1 to 0.2. Middle portion 50 may have an inner leg portion 56 that is slightly longer than an outer leg portion 58. By varying the relative length of the leg portions forming middle portion 50, it is possible to control the thermal decay of isolator device 18.

[0028] In another aspect of the present invention, it is possible to vary the angle of inclination of the middle portion of the isolator device 18 to the horizon at an angle &thgr; of substantially about 0 to 10 degrees. Isolator device 18 may be permanently fastened at the I/D and O/D to the adjacent engine components. There is no need for cooling air holes in the thermal isolator 18.

[0029] In another aspect of the invention, a method is shown for creating a gas turbine engine assembly. Referring again to FIG. 1, the thin-walled casing of the compressor 14 is positioned upstream from the heavy casing of combustor 12. In a similar manner, the thin-walled casing of the gas turbine 16 may be positioned downstream from combustor 12. A first isolator device 18 may be positioned between the casings of compressor 14 and combustor 12 with a second isolator device 18 positioned between the casings of combustor 12 and gas turbine 16. A plurality of bolts, (not shown), are then positioned to extend through openings in each casing and aligned openings in an adjacent isolator device. The bolts are tightened to rigidly fasten the isolators to the components, creating a unitary gas turbine engine assembly wherein the casings are thermally isolated from each other and are capable of expanding at differing rates without adversely affecting an adjacent casing. The isolator devices are formed with leg portions of differing length making it possible to tune the time that each isolator device takes to decay when subjected to temperature spikes that may arise during startup or termination of the engine assembly.

[0030] Because of its unique ability to tune the thermal isolator device 18 by adjusting the length of the leg portions relative to one another, the present invention is not limited to using legs of equal length. Likewise, there is no need for gaskets to seal the outer and inner flanges to the engine components. There is no need to employ bellows to compensate for thermal expansion of the components.

[0031] It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. A thermal isolator device for joining two structures having differing rates of thermal expansion, comprising:

an isolator structure having a middle portion and pair of opposite disposed end portions forming a curved configuration;

each end portion having a fastening assembly adaptable for rigidly joining one of the two structures; and

the middle portion capable of relative to the end portions while thermally isolating the attached structures from one another.

2. The thermal isolator device according to claim 1, wherein each fastening assembly comprises a flange portion mounted on one end of the structure with a plurality of through openings extending through each flange portion to allow connecting members to extend through and rigidly connect each flange portion with one of the structures.

3. The thermal isolator device according to claim 1, wherein the middle and end portions of the structure form a substantially C-shaped configuration

4. The thermal isolator device according to claim 1, wherein the middle and end portions of the structure form a substantially Z-shaped configuration.

5. The thermal isolator device according to claim 1, wherein the middle portion of the structure includes a pair leg portions forming an angle &thgr; in the range of about 0-10 degrees.

6. The thermal isolator device according to claim 5, wherein the pair of leg portions form an &thgr; of substantially 5 degrees.

7. The thermal isolator device according to claim 1, wherein the structure has a generally cylindrical configuration with a length L and radius from a center line R selected so that the ratio of the length to the radius, L/R is in the range of about 0.2 to 0.6.

8. A thermal isolator device for joining a thick, heavy combustor casing with thin sheet metal casings of the compressor and the gas turbine to form a gas turbine engine assembly, comprising:

an isolator structure having a middle portion and pair of opposite end portions;

the structure have a curved shape forming a C or Z-shaped configuration;

the opposite end portions each having a fastening assembly for rigidly joining the combustor casing as well as either the compressor or gas turbine casing to form the rigid gas turbine engine assembly; and

the middle portion capable of movement relative to the end portions while thermally isolating the casings of the combustor, compressor and gas turbine.

9. The thermal isolator device according to claim 8, wherein each fastening assembly comprises a flange member mounted on one end of the structure with a plurality of through openings extending through each flange portion to allow connecting members to extend through and join each flange portion with one of the adjacent casings.

10. The thermal isolator device according to claim 9, wherein the structure has a generally cylindrical configuration with a length L and radius from a center line of the structure R selected so that the ratio of the length to the radius L/R is in the range of about 0.2 to 0.6

11. The thermal isolator device according to claim &thgr;, wherein middle portion of the structure includes a pair of leg portions forming an angle &thgr; of between 0 to 10 degrees.

12. The thermal isolator device according to claim 8, wherein the middle portion forms an angle &thgr; with the horizon of between 0 and 5 degrees.

13. The thermal isolator device according to claim 8, wherein the structure is formed of a nickel based metallic alloy having a thickness in the range of about 0.10 to 0.25 inches.

14. A thermal isolator device for joining a thick combustor casing with both a gas turbine and a compressor each having casings of thin sheet metal to form a gas turbine engine, comprising:

an isolator structure rigidly attached to the combustor casing and either the compressor or turbine casing and having a curved C or Z-shaped confirmation, including a middle portion and a pair of oppositely disposed end portions;

wherein the middle portion is capable of movement relative to the end portions of the isolating structure to compensate for differences in thermal expansion of the combustor casing and either compressor or turbine casing.

15. The thermal isolator device according to claim 14, wherein through openings extend through each of the end portions, allowing fasteners to extend through the openings and into attachment with an adjacently disposed casing.

16. The thermal isolator device according to claim 14, wherein isolator structure is of a generally cylindrical shape with a length L and radius from a center line of the structure R selected to achieve a ratio in the range of about 0.2 to 0.6.

17. The thermal isolator device according to claim 14, wherein the middle portion includes a pair of leg portions of uneven length, with the leg portions forming an angle &thgr; of between about 0 and 10 degrees.

18. The thermal isolator device according to claim 14, wherein the middle portion forms an angle &thgr; with the horizon of between about 0 and 5 degrees.

19. The thermal isolator device according to claim 14, wherein isolator structure is formed of a nickel based metallic alloy having a thickness in the range of about 0.1 and 0.25 inches.

20. The thermal isolator device according to claim 15, wherein each of the end portions includes a flange having a plurality of the through openings circumferentially spaced from one another.

21. A method of forming a gas turbine engine assembly, comprising the steps of:

positioning a thin-walled compressor upstream from a thick-walled industrial combustor;

positioning a thin-walled gas turbine downstream from the thick-walled combustor;

rigidly fastening a first, cylindrically-shaped isolator device to both the combustor casing and the compressor casing; and

rigidly fastening a second, cylindrically-shaped isolator device to both the combustor casing and the gas turbine casing, whereby the first and second isolator devices thermally isolate the combustor from the compressor and the turbine during operation of the gas turbine engine assembly, while maintaining engine alignment for all rotating components.

22. The method of claim 21, including the step of rigidly attaching an outer diameter end portion of each isolator to the combustor casing and attaching an inner diameter end portion of each isolator to either the compressor or the gas turbine.