Patent Publication Number: US-9890660-B2

Title: Diaphragm assembly bolted joint stress reduction

Description:
TECHNICAL FIELD 
     The present disclosure generally pertains to gas turbine engines, and is directed toward a diaphragm assembly including a spacer for a bolted joint bearing stress reduction. 
     BACKGROUND 
     Gas turbine engines include compressor, combustor, and turbine sections. Components of a gas turbine engine are subjected to high temperatures during operation, in particular, the components of the first stage of the turbine section. Some of these components are cooled by air directed through internal cooling passages from the compressor section. In one such passage, air may be directed through a diaphragm and into a preswirler fastened to the diaphragm. A loss in tension of the preswirler-diaphragm fastener may lead to uncontrolled loss or leakage of compressed air. 
     U.S. Pat. No. 7,494,362 to Dieterle et al. discloses a connector plug assembly. The connector plug assembly includes a body member, a first threaded shaft portion, a second threaded shaft portion, an electrically-conductive inner sleeve and an electrically-insulative outer sleeve. The body member extends along and about a longitudinal axis and has a first body member end surface, an opposite second body member end surface and an outer surface disposed between the first and second body member end surfaces. The first threaded shaft portion projects from the first body member end surface and the second threaded shaft portion projects from the second body member end surface. The first and second threaded shafts extend along and about the longitudinal axis. The inner sleeve extends along and about the longitudinal axis and the inner sleeve is connected to and surrounds the body member. The outer sleeve extends along and about the longitudinal axis and the outer sleeve is connected to and surrounds the inner sleeve. 
     The present disclosure is directed toward overcoming one or more of the problems discovered by the inventors or that is known in the art. 
     SUMMARY OF THE DISCLOSURE 
     In one embodiment, a spacer for a coupling between a diaphragm and a preswirler of a diaphragm assembly of a gas turbine engine is disclosed. The spacer includes a base, a spacing portion, and a spacing body edge. The base includes a base body, a contact surface, and a base edge. The base body includes a first hollow cylinder shape with a first outer diameter relative to a spacer axis. The contact surface is at an end of the base body and includes an annular shape. The base edge is a radially outer edge of the contact surface. The spacing portion includes a spacing body and a spacing flange. The spacing body extends axially about the spacer axis from the base from an end opposite the contact surface and in an axial direction away from the contact surface. The spacing body includes a second hollow cylinder shape with a second outer diameter that is smaller than the first outer diameter. The spacing flange extends radially outward from the spacing body and is spaced apart from the base forming an annular gap there between. The spacing body edge is located at an intersection of the spacing body and the base body. A reference line extending from the spacing body edge to the base edge within a cross-sectional plane that includes the spacer axis forms a base edge angle from 10 to 30 degrees with the spacer axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary gas turbine engine. 
         FIG. 2  is a cross-sectional view of a portion of the first stage  401  of the turbine  400  of  FIG. 1 . 
         FIG. 3  is a detailed cross-sectional view of the coupling between the diaphragm and the preswirler of  FIG. 2 . 
         FIG. 4  is a perspective view of the spacer of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the spacer of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The systems and methods disclosed herein include a diaphragm assembly including a diaphragm and a preswirler coupled together using outer diameter couplers and inner diameter couplers. Spacers are located within counterbores of the diaphragm to increase the contact load caused by the outer diameter couplers on the diaphragm. The spacers are configured to distribute the contract stress over a larger area. The spacers may also be configured with a groove proximal the contact surface of the spacers to reduce the rigidity of the spacer and reduce the formation of Hertzian stress. 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine  100 . Some of the surfaces have been left out or exaggerated (here and in other figures) for clarity and ease of explanation. Also, the disclosure may reference a forward and an aft direction. Generally, all references to “forward” and “aft” are associated with the flow direction of primary air (i.e., air used in the combustion process), unless specified otherwise. For example, forward is “upstream” relative to primary air flow, and aft is “downstream” relative to primary air flow. 
     In addition, the disclosure may generally reference a center axis  95  of rotation of the gas turbine engine, which may be generally defined by the longitudinal axis of its shaft  120  (supported by a plurality of bearing assemblies  150 ). The center axis  95  may be common to or shared with various other engine concentric components. All references to radial, axial, and circumferential directions and measures refer to center axis  95 , unless specified otherwise, and terms such as “inner” and “outer” generally indicate a lesser or greater radial distance from center axis  95 , wherein a radial  96  may be in any direction perpendicular and radiating outward from center axis  95 . 
     A gas turbine engine  100  includes an inlet  110 , a shaft  120 , a compressor  200 , a combustor  300 , a turbine  400 , an exhaust  500 , and a power output coupling  600 . The gas turbine engine  100  may have a single shaft or a dual shaft configuration. 
     The compressor  200  includes a compressor rotor assembly  210 , compressor stationary vanes (stators)  250 , and inlet guide vanes  255 . The compressor rotor assembly  210  mechanically couples to shaft  120 . As illustrated, the compressor rotor assembly  210  is an axial flow rotor assembly. The compressor rotor assembly  210  includes one or more compressor disk assemblies  220 . Each compressor disk assembly  220  includes a compressor rotor disk that is circumferentially populated with compressor rotor blades. Stators  250  axially follow each of the compressor disk assemblies  220 . Each compressor disk assembly  220  paired with the adjacent stators  250  that follow the compressor disk assembly  220  is considered a compressor stage. Compressor  200  includes multiple compressor stages. Inlet guide vanes  255  axially precede the compressor stages. 
     The combustor  300  includes one or more combustion chambers  305 , one or more fuel injectors  310 . 
     The turbine  400  includes a turbine rotor assembly  410  and turbine nozzle assemblies  450 . The turbine rotor assembly  410  mechanically couples to the shaft  120 . As illustrated, the turbine rotor assembly  410  is an axial flow rotor assembly. The turbine rotor assembly  410  includes one or more turbine disk assemblies  420 . Each turbine disk assembly  420  includes a turbine disk  421  (shown in  FIG. 2 ) that is circumferentially populated with turbine blades  425  (shown in  FIG. 2 ). Turbine nozzle assemblies  450  may include turbine nozzles  455  and a turbine diaphragm assembly  460  supporting the turbine nozzles  455 . A turbine nozzle assembly  450  may axially precede each of the turbine disk assemblies  420 . Each turbine disk assembly  420  paired with the adjacent turbine nozzle assembly  450  that precedes the turbine disk assembly  420  is considered a turbine stage. The turbine first stage  401  may be the axially forward stage of turbine  400  adjacent combustor  300 . Turbine  400  includes multiple turbine stages. 
     A turbine diaphragm assembly  460  may include a diaphragm  461  and a preswirler  470  coupled to the diaphragm  461 . The coupling between the preswirler  470  and the diaphragm  461  may include spacers  430 . 
     The exhaust  500  includes an exhaust diffuser  510  and an exhaust collector  520 . The power output coupling  600  may be located at an end of shaft  120 . 
       FIG. 2  is a cross-sectional view of a portion of the first stage  401  of the turbine  400  of  FIG. 1 . The diaphragm  461  may generally be a solid of revolution configured to support turbine nozzles  455 . The diaphragm  461  may include a mounting portion  468  with cooling holes or slots that extend axially through the mounting portion  468  that provide a pathway for compressed air to the preswirler  470 . The mounting portion  468  includes a plurality of outer diameter holes  465 . The outer diameter holes  465  extend axially through the mounting portion  468  and may be evenly spaced circumferentially about the axis of the diaphragm  461 . The mounting portion  468  also includes a plurality of inner diameter holes  466 . The inner diameter holes  466  are located radially inward from the outer diameter holes  465 . The inner diameter holes  466  extend axially through the mounting portion  468  and may be evenly spaced circumferentially about the axis of the diaphragm  461 . The mounting portion  468  may also include a cavity  469 . Cavity  469  may be an annular cavity located in the aft side of mounting portion  468 . The preswirler  470  may sit within the cavity  469  of the diaphragm  461  when mounted to the diaphragm  461 . 
     The preswirler  470  may generally include an annular shape and may be press fit to the diaphragm and may be adjoining the mounting portion  468 . The preswirler  470  may include an outer ring  471 , an inner ring  474  defining a passage  53  for cooling air there between, and vanes  477 . The outer ring  471  may include an outer body portion  472 , an outer swirling portion  473 , and first holes  482  (only one visible in  FIG. 2 ). Outer swirling portion  473  may include a hollow cylinder shape. Outer swirling portion  473  may extend from outer body portion  472  in the axial direction and may be located aft of outer body portion  472 . First holes  482  may be located in outer body portion  472  and may be threaded. First holes  482  are configured to receive the outer diameter couplers  447  for mounting the preswirler  470  to the diaphragm  461  and are configured to align with outer diameter holes  465 . The outer ring  471  may include at least ten first holes  482 . 
     The inner ring  474  may be located radially inward from outer ring  471 . Inner ring  474  may include an inner body portion  475 , an inner swirling portion  476 , and second holes  483  (only one visible in  FIG. 2 ). Inner body portion  475  may generally be axially aligned with and located radially inward from outer body portion  472 . Inner swirling portion  476  may generally be axially aligned with and located radially inward from outer swirling portion  473 . Inner swirling portion  476  may include a hollow cylinder shape. Inner swirling portion  476  may extend from inner body portion  475  in the axial direction and may be located aft of inner body portion  475 . Second holes  483  may be located in inner body portion  475  and may be threaded. Second holes  483  are configured to receive the inner diameter couplers  448  for mounting the preswirler  470  to the diaphragm  461  and are configured to align with inner diameter holes  466 . The inner ring  474  may include at least ten second holes  483 . 
     Vanes  477  extend between outer ring  471  and inner ring  474 . In the embodiment illustrated, vanes  477  extend between outer swirling portion  473  and inner swirling portion  476 . Vanes  477  are generally angled to partially redirect air in a circumferential direction. 
     A spacer  430  may be located between the head of the each outer diameter coupler  447  and the diaphragm  461 . The outer diameter couplers  447  and the spacers  430  may secure the inner turbine seal  402  to the diaphragm  461 . In one embodiment the outer diameter couplers  447  and the inner diameter couplers  448  may be bolts. Alternative couplers such as rivets may also be used. 
       FIG. 3  is a detailed cross-sectional view of the coupling between the diaphragm  461  and the preswirler  470  of  FIG. 2 . Diaphragm  461  may include a counterbore  463  at each outer diameter hole  465 . The counterbore  463  may be located opposite the cavity  469 . Each counterbore  463  may include a counterbore surface  462  and a counterbore edge  464 . Counterbore surface  462  may be an annular surface configured to contact the spacer  430 . Counterbore edge  464  may be the radially outer edge of counterbore surface  462 . Counterbore edge  464  may include an edge break, such as a fillet or chamfer. 
     A lock plate  459  may be located between an outer diameter coupler  447  and a spacer  430 . 
       FIG. 4  is a perspective view of the spacer  430  of  FIG. 3 .  FIG. 5  is a cross-sectional view of the spacer  430  of  FIG. 4 . Referring to  FIGS. 3-5 , spacer  430  is a solid of revolution revolved about spacer axis  429  forming a spacer bore  440 . In some embodiments, spacer  430  is forged of a single piece of material. In some embodiments, spacer  430  is machined from a single piece of material. All references to radial, axial, and circumferential directions and measures with regard to spacer  430  refer to spacer axis  429 , and terms such as “inner” and “outer” generally indicate a lesser or greater radial distance from spacer axis  429 , wherein a radial may be in any direction perpendicular and radiating outward from spacer axis  429 . Spacer  430  includes a spacing portion  431  and a base  435 . Spacing portion  431  and base  435  may share spacer axis  429  as a common axis. Spacer bore  440  extends through spacing portion  431  and base  435 , and is coaxial to spacing portion  431  and base  435 . Spacing portion  431  may generally be located outside of counterbore  463 , while base  435  may generally be located within counterbore  463 . 
     Spacing portion  431  may include a spacing body  432  and a spacing flange  434 . Spacing body  432  may include a hollow cylinder shape. The diameter of spacing body  432  may be smaller than the diameter of base  435 . Spacing body  432  may extend axially from base  435 . Spacing body  432  may extend from an end opposite the contact surface  439  (described below) and in an axial direction away from the contact surface  439 . Spacing body  432  may include a spacing body surface  428 . Spacing body surface  428  may be a cylindrical surface and may be the radially outer surface of spacing body  432 . Spacing flange  434  may extend radially outward from spacing body  432  and may be adjacent spacing body surface  428 . Spacing flange  434  may be spaced apart from base  435  forming a gap  433  there between. Gap  433  may include an annular shape defined by the outer surface of spacing body  432  and annular surfaces of spacing flange  434  and base  435  that face each other. 
     Base  435  may include a base body  437 , a base flange  438 , and a groove  436 . Base body  437  may include a hollow cylinder shape and may include a base body surface  427 . Base body surface  427  may be the radially outer surface of base body  437  and may include a cylindrical shape. Base body  437  is contiguous to spacing body  432 . Base body  437  may form a spacing body edge  442  with spacing body  432 . Spacing body edge  442  may be located at an intersection of spacing body surface  428  and base body  437  and may be distal to spacing flange  434 . Spacing body edge  442  may include an edge break, such as a fillet or chamfer. Base body  437  may include contact surface  439  and base edge  443 . Contact surface  439  may be an annular surface of base body  437  located at an end of base body opposite spacing body  432 . Contact surface  439  is configured to contact counterbore surface  462  when spacer  430  is within the diaphragm assembly  460 . Base edge  443  may be the radially outer edge of contact surface  439 . Base edge  443  may include an edge break, such as a fillet or chamfer. 
     Base flange  438  extends radially outward from base body  437 . Base flange  438  may be axially adjacent spacing body  432  and may form a base body edge  441  with base body  437 . The diameter of base flange  438  may be the same or similar to the diameter of counterbore  463 . Base flange  438  may be configured to locate spacer  430  within counterbore  463 . Groove  436  may be formed in base body  437  and may extend annularly about base body  437 . Groove  436  is an annular shape and may include a circular or rectangular cross-section. Groove  436  may also include one or more edge breaks. In the embodiment illustrated, groove  436  includes a circular cross-section where the depth of groove  436  is less than the radius of groove  436 . Groove  436  may be proximal contact surface  439  and may be axially spaced apart from contact surface  439 . Groove  436  may located at base body surface  427  and may extend into base body  437  from base body surface  427 . 
     Referring to  FIG. 5 , base edge  443  is axially spaced apart from spacing body edge  442  at a base axial length  449 , the axial length of base  435 . Base edge  443  is also located outward from spacing body edge  442  at an edge differential  446 , the radial distance between base edge  443  and spacing body edge  442 . In some embodiments, the ratio of the base axial length  449  over the edge differential  446  is from 1.7 to 5.7. In other embodiments, the ratio of the base axial length  449  over the edge differential  446  is from 3 to 5. In yet other embodiments, the ratio of the base axial length  449  over the edge differential  446  is from 3.3 to 4.0. In still other embodiments, the ratio of the base axial length  449  over the edge differential  446  is within a predetermined tolerance of 3.66, such as plus or minus 0.25, 0.28, or 0.30. 
     In some embodiments, a reference line  444  extending from spacing body edge  442  to base edge  443  within a cross-sectional plane that includes spacer axis  429  forms a base edge angle  445  with spacer axis  429  from 10-30 degrees. In other embodiments, base edge angle  445  is from 12-19 degrees. In yet other embodiments, base edge angle is from 10-20 degrees. In yet other embodiments, base edge angle  445  is from 12-19 degrees. In still other embodiments, base edge angle is from 14-17 degrees. In still further embodiments, base edge angle  445  is within a predetermined tolerance of 15.3 degrees, such as 1 degree, 1.1 degrees, or 1.5 degrees. 
     Referring again to  FIG. 3 , inner turbine seal  402  may include a slip fit portion  403 . The gap  433  may be configured to receive the inner turbine seal  402  via a slip fit at the slip fit portion  403 . 
     One or more of the above components (or their subcomponents) may be made from cast iron, stainless steel and/or durable, high temperature materials known as “superalloys”. A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys may include materials such as HASTELLOY, alloy x, INCONEL, WASPALOY, RENE alloys, HAYNES alloys, alloy 188, alloy 230, INCOLOY, MP98T, TMS alloys, and CMSX single crystal alloys. In some embodiments, diaphragms  461  are cast iron and spacers  430  are Inconel 718. 
     INDUSTRIAL APPLICABILITY 
     Gas turbine engines may be suited for any number of industrial applications such as various aspects of the oil and gas industry (including transmission, gathering, storage, withdrawal, and lifting of oil and natural gas), the power generation industry, cogeneration, aerospace, and other transportation industries. 
     Referring to  FIG. 1 , a gas (typically air  10 ) enters the inlet  110  as a “working fluid”, and is compressed by the compressor  200 . In the compressor  200 , the working fluid is compressed in an annular flow path  115  by the series of compressor disk assemblies  220 . In particular, the air  10  is compressed in numbered “stages”, the stages being associated with each compressor disk assembly  220 . For example, “4th stage air” may be associated with the 4th compressor disk assembly  220  in the downstream or “aft” direction, going from the inlet  110  towards the exhaust  500 ). Likewise, each turbine disk assembly  420  may be associated with a numbered stage. 
     Once compressed air  10  leaves the compressor  200 , it enters the combustor  300 , where it is diffused and fuel is added. Air  10  and fuel are injected into the combustion chamber  305  via fuel injector  310  and combusted. Energy is extracted from the combustion reaction via the turbine  400  by each stage of the series of turbine disk assemblies  420 . Exhaust gas  90  may then be diffused in exhaust diffuser  510 , collected and redirected. Exhaust gas  90  exits the system via an exhaust collector  520  and may be further processed (e.g., to reduce harmful emissions, and/or to recover heat from the exhaust gas  90 ). 
     Operating efficiency of a gas turbine engine generally increases with a higher combustion temperature. Thus, there is a trend in gas turbine engines to increase the temperatures. Gas reaching a turbine first stage  401  from a combustion chamber  305  may be 1000 degrees Fahrenheit or more. To operate at such high temperatures a portion of the compressed air of the compressor  200  of the gas turbine engine  100  may be diverted through internal passages or chambers to cool the turbine blades  425  in the turbine first stage  401 . 
     The gas reaching the turbine blades  425  in the turbine first stage  401  may also be under high pressure. The cooling air diverted from the compressor  200  may need to be at compressor discharge pressure to effectively cool turbine blades  425  in the turbine first stage  401 . Gas turbine engine  100  components containing the internal passages for the cooling air such as a diaphragm  461  and a preswirler  470  may be subject to elevated levels of stress. 
     Cooling air with a substantially axial flow is diverted from the compressor discharge to a path for cooling air  50 . The cooling air passes through the diaphragm  461  and into passage  53  of the preswirler  470 . The cooling air is redirected to include a tangential component by vanes  477  and into the turbine disk assembly  420 . The cooling air may be redirected such that the tangential component of the cooling air matches the angular velocity of the turbine disk assembly  420 . 
     Matching the angular velocity of the turbine disk assembly  420  may prevent an increase in the velocity of the cooling air. An increase in velocity of the cooling air would result in an increase in temperature and a pressure drop in the cooling air, which may reduce the effectiveness of the cooling air in cooling turbine blades  425 . An increase in velocity of the cooling air may also result in a loss in efficiency due to the work imparted by the turbine disk  421  on the cooling air. Once the cooling air passes into the turbine disk assembly, the cooling air cools the turbine disk assembly including the turbine blades  425 . The described arrangement may also be used in other stages. 
     The couplers, such as fasteners, that couple a preswirler to a diaphragm may lose tension due to high bearing loads and yielding of the various clamped components. This yielding may be caused by the temperature increase, pressure increase, and forces on the clamped components resulting from the cooling air entering the diaphragm and preswirler. The loss in tension may permit a leakage of cooling air causing a loss of efficiency in the gas turbine engine. 
     A diaphragm assembly  460  coupled together using outer diameter couplers  447  with spacers  430  and inner diameter couplers  448  to couple preswirler  470  to diaphragm  461  may form a more rigid connection and may reduce stress on the various components. The contact surfaces  439  of spacers  430  may contact counterbore surfaces  462  over a larger surface area, which may reduce the contact stress between spacers  430  and diaphragm  461  and may prevent diaphragm  461  from yielding at counterbore surface  462 . 
     Spacers  430  that are configured with gap  433  may better distribute the contact stresses between contact surface  439  and diaphragm  461  when the ratio of the base axial length  449  over the edge differential  446  is within the ratios provided herein and/or when the base edge angle  445  is within the ranges provided herein. Better distributing the contact stresses across contact surface  439  may further prevent diaphragm  461  from yielding and may reduce stresses within spacers  430 . 
     Providing spacers  430  with a groove  436  may reduce the rigidity of base body  437  at and around base edge  443  and may prevent or reduce the formation of Hertzian stresses at base edge  443 . 
     Base flange  438  may contact counterbore  463  to locate spacer  430  within counterbore  463 . Base flange  438  may create a radial offset between counterbore edge  464  and base edge  443 . Counterbore edge  464  may include a fillet. The radial offset may ensure that there is not interference between counterbore edge  464  including the fillet and base edge  443  and that base edge  443  contacts the counterbore surface  462  at a location that is offset from the counterbore edge  464 . 
     The connection including outer diameter couplers  447  and inner diameter couplers may also prevent deformation of the preswirler  470  and may increase the contact area between the preswirler  470  and the diaphragm  461 . An increase in contact area between the preswirler  470  and the diaphragm  461  may reduce stress and wear of various gas turbine engine components and increase efficiency. 
     The preceding detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. The described embodiments are not limited to use in conjunction with a particular type of gas turbine engine. Hence, although the present disclosure, for convenience of explanation, depicts and describes a particular diaphragm assembly, it will be appreciated that the diaphragm assembly in accordance with this disclosure can be implemented in various other configurations, can be used with various other types of gas turbine engines, and can be used in other types of machines. Furthermore, there is no intention to be bound by any theory presented in the preceding background or detailed description. It is also understood that the illustrations may include exaggerated dimensions to better illustrate the referenced items shown, and are not consider limiting unless expressly stated as such.