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 θ 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]    [0013]FIG. 1 is a schematic view of a gas turbine engine assembly including the thermal isolator device of the present invention;  
         [0014]    [0014]FIG. 2 is a perspective view of a thermal isolator device utilized in the engine assembly of FIG. 1;  
         [0015]    [0015]FIG. 3 a cross-section view taken in a plane along the X axis of the engine centerline in FIG. 2;  
         [0016]    [0016]FIG. 4 is a perspective view of another thermal isolator device utilized in the engine assembly of FIG. 1;  
         [0017]    [0017]FIG. 5 is cross-sectional view taken in a plane along the X axis of the engine centerline in FIG. 4; and  
         [0018]    [0018]FIGS. 6 a  and  6   b  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 θ 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. 6 a  and  6   b,  wherein the particular shape of each device provides effective thermal isolation between adjacent casings. Referring now to FIG. 6 a,  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. 6 a,  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. 6 b  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 θ 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.