Patent Publication Number: US-10329956-B2

Title: Multi-function boss for a turbine exhaust case

Description:
BACKGROUND 
     The present disclosure relates generally to gas turbine engines, and more particularly to bosses and service line apertures in a turbine exhaust case of an industrial gas turbine engine. 
     A turbine exhaust case is a structural frame that supports engine bearing loads while providing a gas path at or near the aft end of a gas turbine engine. Some aeroengines utilize a turbine exhaust case to help mount the gas turbine engine to an aircraft airframe. In industrial applications, a turbine exhaust case is more commonly used to couple gas turbine engines to a power turbine that powers an electrical generator. Industrial turbine exhaust cases can, for instance, be situated between a low pressure engine turbine and a generator power turbine. A turbine exhaust case must bear shaft loads from interior bearings, and must be capable of sustained operation at high temperatures. 
     Turbine exhaust cases serve two primary purposes: airflow channeling and structural support. Turbine exhaust cases typically comprise structures with inner and outer rings connected by radial struts. The struts and rings often define a core flow path from fore to aft, while simultaneously mechanically supporting shaft bearings situated axially inward of the inner ring. The components of a turbine exhaust case are exposed to very high temperatures along the core flow path. Various approaches and architectures have been employed to handle these high temperatures. Some turbine exhaust case frames utilize high-temperature, high-stress capable materials to both define the core flow path and bear mechanical loads. Other frame architectures separate these two functions, pairing a structural frame for mechanical loads with a high-temperature capable fairing to define the core flow path. In industrial applications, turbine exhaust cases are sometimes anchored to installation structures to support the gas turbine engine, and can carry service lines for cooling or lubrication. 
     SUMMARY 
     The present disclosure is directed toward a turbine exhaust case frame comprising an inner ring, an outer ring, and a plurality of load-bearing struts. The inner ring is configured to carry load from inner bearings. The outer ring features a multi-function boss with a service line aperture and a mounting point for the turbine exhaust case. The load-bearing struts connect the inner ring to the outer ring, and have a service line passage extending from the service line aperture to the inner ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified partial cross-sectional view of an embodiment of a gas turbine engine. 
         FIG. 2  is a perspective view of a turbine exhaust case of the gas turbine engine of  FIG. 1   
         FIG. 3  is a close-up exploded perspective view of a multi-function boss assembly of the turbine exhaust case of  FIG. 2   
         FIG. 4  is a cross-sectional view of the turbine exhaust case of  FIG. 2  illustrating the multi-function boss of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a simplified partial cross-sectional view of gas turbine engine  10 , comprising inlet  12 , compressor  14  (with low pressure compressor  16  and high pressure compressor  18 ), combustor  20 , engine turbine  22  (with high pressure turbine  24  and low pressure turbine  26 ), turbine exhaust case  28 , power turbine  30 , low pressure shaft  32 , high pressure shaft  34 , and power shaft  36 . Gas turbine engine  10  can, for instance, be an industrial power turbine. 
     Low pressure shaft  32 , high pressure shaft  34 , and power shaft  36  are situated along rotational axis A. In the depicted embodiment, low pressure shaft  32  and high pressure shaft  34  are arranged concentrically, while power shaft  36  is disposed axially aft of low pressure shaft  32  and high pressure shaft  34 . Low pressure shaft  32  defines a low pressure spool including low pressure compressor  16  and low pressure turbine  26 . High pressure shaft  34  analogously defines a high pressure spool including high pressure compressor  18  and high pressure compressor  24 . As is well known in the art of gas turbines, airflow F is received at inlet  12 , then pressurized by low pressure compressor  16  and high pressure compressor  18 . Fuel is injected at combustor  20 , where the resulting fuel-air mixture is ignited. Expanding combustion gasses rotate high pressure turbine  24  and low pressure turbine  26 , thereby driving high and low pressure compressors  18  and  16  through high pressure shaft  34  and low pressure shaft  32 , respectively. Although compressor  14  and engine turbine  22  are depicted as two-spool components with high and low sections on separate shafts, single spool or 3+ spool embodiments of compressor  14  and engine turbine  22  are also possible. Turbine exhaust case  28  carries airflow from low pressure turbine  26  to power turbine  30 , where this airflow drives power shaft  36 . Power shaft  36  can, for instance, drive an electrical generator, pump, mechanical gearbox, or other accessory (not shown). 
     In addition to defining an airflow path from low pressure turbine  26  to power turbine  30 , turbine exhaust case  28  can support one or more shaft loads. Turbine exhaust case  28  can, for instance, support low pressure shaft  32  via bearing compartments (not shown) disposed to communicate load from low pressure shaft  32  to a structural frame of turbine exhaust case  28 . 
       FIG. 2  provides a perspective view of one embodiment of frame  100  of turbine exhaust case  28 . Frame  100  comprises outer ring  102 , inner ring  104 , struts  106 , installation mounts  108  (with installation mounting holes  110 ), power turbine connection flange  112  (with power turbine connection holes  114 ), and multi-function bosses  116  (with outer step surface  118 , inner step surface  120 , mounting hole  122 , service line aperture  124 , and seal plate mounting holes  126 ). 
     Frame  100  is a rigid support structure that can, for instance, be formed in a unitary steel casting. Frame  100  supports a vane fairing (not shown) that defines at least a portion of a core flow path for airflow F from low pressure turbine  26  to power turbine  30 . Frame  100  further acts as a structural support for shaft loads, communicating loads from bearing supports affixed to inner ring  104  through struts  106  to outer ring  102 , where turbine exhaust case  28  is anchored to installation structures. Inner ring  104  is a cylindrical support structure that interfaces with bearing supports to receive shaft loads. Struts  106  are circumferentially distributed supports extending radially from inner ring  104  to outer ring  102 . One or more of struts  106  include at least one service line channel extending from service line aperture  124 , as explained in greater detail below with respect to  FIG. 4 . 
     Outer ring  102  serves as the outermost case and mounting surface of turbine exhaust case  28 , and includes a plurality of attachment features, including installation mounts  108 , power turbine connection flange  110 , and multi-function bosses  116 . These features can be formed integrally in (i.e., unitarily and monolithically within) outer ring  102 . Installation mounts  108  are mounting flanges with power turbine connection holes  114 , and are substantially triangularly shaped for downward-facing horizontal load surfaces. Installation mounts  108  are secured via fasteners such as bolts, screws, pins, or rivets through installation mounting holes  110  to mounting brackets (not shown) so as to support turbine exhaust frame  28  in gas turbine engine  10 . Power turbine connection flange  112  is an annular flange abutting power turbine  30 . Turbine exhaust case  28  is secured to power turbine  30  by bolts, screws, pins, rives, or similar fasteners through power turbine connection holes  114  to power turbine  30 . In some instances, installation mounts  108  can carry installation loads from power shaft  36  of power turbine  30  as well as low pressure shaft  32 . 
     Each multi-function boss  116  is a hollow boss extending substantially radially outward from outer ring  102 . In the depicted embodiment, each multi-function boss  116  has a stair-stepped profile with two adjacent parallel flat surfaces. Outer step surface  118  is located axially aft and radially outward of inner step surface  120 . In this embodiment, inner step surface  120  is recessed relative to outer step surface  118  to provide clearance for a heavy mounting fastener such as a bolt, screw, lug, pin, or rivet secured in mounting hole  122 . In other embodiments, multi-function boss  116  can be a single flat plateau surface. 
     Mounting holes  122  are located in a heavy body of multi-function boss  116  on inner step surface  120  to receive mounting bolts or similar hardware to anchor turbine exhaust case  28 . Mounting holes  122  can, for instance, be threaded attachment points for securing turbine exhaust case  28  in an installation position with bolts or screws, supplemental or alternative to installation mounts  108 . Mounting holes  122  can additionally or alternatively be used to secure frame  100  for transportation prior to installation. 
     Service line apertures  124  are apertures leading to service line passages through a corresponding strut  106  (see  FIG. 4  and accompanying description). Service line apertures  124  provide inlet points for service lines for cooling and lubrication of turbine exhaust case  28 . Service line apertures  124  can, for instance, receive oil supply and/or scavenging lines for bearings situated radially inward of inner ring  104 , and air supply lines carrying cooling air to maintain operating temperatures of frame  100  and adjacent components of turbine exhaust case  28 . A seal plate can be secured to outer step surface  118  (see  FIG. 3 , described below) to retain cooling air and maintain air pressure within turbine exhaust case  28  via seal plate mounting holes  126 . 
       FIG. 3  is a close-up exploded perspective view of an assembly that includes multi-function boss  116 , seal plate  200  (with service line hole  202 , seal plate mounting holes  204 , and service line mounting holes  206 ), service line fasteners  208 , service line  210  (with service line connection  212 ), and seal plate fasteners  214 . 
     Each multi-function boss  116  includes outer step surface  118 , inner step surface  120 , mounting hole  122 , service line aperture  124 , and seal plate mounting holes  126  as described above with respect to  FIG. 2 . Seal plate  200  is a flat plate secured to outer step surface  118  by seal plate fasteners  214 , which pass through seal plate mounting holes  204  and  126  in seal plate  200  and outer step surface  118 , respectively. Seal plate  200  accepts a number of service lines  210 , which are attached to seal plate  200  by means of service line fasteners  208 , which are secured in seal plate  200  at service line mounting holes  206 . 
     In the depicted embodiment, service line aperture  124  is a single aperture configured to carry multiple service lines. In alternative embodiments, multi-function boss  116  can carry a plurality of service line apertures providing ingress to separate service line passages through strut  106 . The depicted embodiment of service line aperture  124  has the advantage of allowing all multi-function bosses  116  to be formed identically, regardless of the number or type of service lines that will eventually pass through each multi-function boss  116 , which can vary depending on angular position. Seal plate  200  covers service line aperture  124  to retain cooling air and maintain air pressure within turbine exhaust case  28 . In the depicted embodiment, seal plate  200  has two service line holes  202 , one of which is occupied by service line  210 . Service line  210  comprises one or more tubes, pipes, or other suitable conduits connected in fluid communication carrying, e.g., oil or air for lubrication or cooling, and connects to an oil or air supply via service line connection  212 . Depending on the number service lines  210  required at the angular location of each multi-function boss  116 , seal plates  200  with different numbers of service line holes  202  can be used. Although one service line hole  202  is depicted as unoccupied in  FIG. 3 , this is only for illustrative purposes. Angular locations with only one service line, for instance, can be equipped with corresponding seal plates  200  with only one service line hole  202 , so that no service line holes  202  are left open once turbine exhaust case  28  is fully assembled. In some embodiments, some seal plates  200  may have no service line holes  202  at all. 
       FIG. 4  is a cross-sectional view of turbine exhaust case  28  with seal plate  200  secured atop outer step surface  118  of multi-function boss  116 .  FIG. 3  depicts frame  100  with outer ring  102 , inner ring  104 , strut  106 , multi-function boss  116 , and service line passage  128 . As described above with respect to  FIG. 1 , frame  100  has outer step surface  118 , inner step surface  120 , mounting hole  122 , and service line aperture  124 , and seal plate mounting holes  126 . Seal plate  200  is secured atop service line aperture  124  by seal plate fasteners  214 , and carries service line  210  with service line connection  212 .  FIG. 4  further depicts fairing  300  with outer platform  302 , inner platform  304 , and fairing vane  306 . Fairing vane  306  surrounds strut  106 , while inner platform  204  and outer platform bracket inner ring  104  and outer ring  102 , respectively. Fairing  300  defines at least a portion of an aerodynamic airflow section path through turbine exhaust case  28 , and can for instance be formed of a high-temperature capable superalloy such as Inconel or another nickel-based superalloy. As shown in  FIG. 4 , service line  212  passes through service line passage  128   
     As shown in  FIG. 4 , service line  212  passes through service line passage  128 , which extends through strut  106 . In the depicted embodiment, service line passage  128  is a contoured passage with a shape selected to retain and space apart up to three service lines at distinct chordwise locations. This contour includes partial circular cross-sectional regions, as shown in  FIG. 3 , corresponding to each service line. In alternative embodiments, service line passage  128  can include more or fewer such service line retention locations, or can be an uncontoured passage without defined spacers for each service line. 
     Each multi-function boss  116  provides a plurality of functions in a single, relatively easily- and inexpensively-cast feature. Multi-function bosses  116  provide mounting locations for turbine exhaust case  28  via mounting hole  122  in inner step surface  120 , and provide an interface for a plurality of service lines via service line apertures  124 . Service line aperture  124  can be generic to any number of service lines, and is sealed by sealing plate  200 , which is selected to accept a particular number of service lines for the angular location of each multi-function boss  116 . 
     DISCUSSION OF POSSIBLE EMBODIMENTS 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A turbine exhaust case frame comprising an inner ring, an outer ring, and a plurality of load-bearing struts. The inner ring is configured to carry load from inner bearings. The outer ring features a multi-function boss having a service line aperture and a mounting point for the turbine exhaust case. The load-bearing struts connect the inner ring to the outer ring, and have a service line passage extending from the service line aperture to the inner ring. 
     The turbine exhaust case frame of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     wherein the service line aperture is an aperture situated to receive a plurality of service lines. 
     wherein the service line aperture is contoured to retain a plurality of service lines at distinct axial locations. 
     wherein the service line aperture is configured to accept an air supply line. 
     wherein the service line aperture is configured to accept an oil supply line 
     wherein the service line aperture is configured to accept an oil scavenging line. 
     wherein the multi-function boss has a stair-step shape such that the service line interface is situated in an outer step surface of the boss, and the mounting point is situated in an inner step surface of the boss located axially forward and radially inward of the outer step surface. 
     wherein the outer ring comprises a plurality of bosses, each with the same configuration as the multi-function boss. 
     wherein the mounting point is a threaded mounting hole configured to receive mounting hardware. 
     A turbine exhaust case comprising a frame, a seal plate, and a service line. The frame has an inner ring configured to carry load from inner bearings, an outer ring with a multi-function boss having a service line aperture and a mounting point for the turbine exhaust case, and a plurality load-bearing struts connecting the inner ring to the outer ring, and having a service line passage extending from the service line aperture to the inner ring. The seal plate is disposed atop the service line aperture, and includes at least one service line hole. The service line extends through the service line hole, the service line aperture, and the service line passage. 
     The turbine exhaust case of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     wherein the frame is formed of cast steel. 
     wherein the seal plate is secured to the multi-function boss with seal plate fasteners. 
     and further comprising one or more service lines passing through the seal plate, the service line aperture, and the service line passage, and wherein the seal plate is selected to have a seal plate hole for each service line 
     further comprising a fairing disposed within the frame between the inner ring and the outer ring, the fairing defining an airflow path through the turbine exhaust case. 
     A method of installing a service line in a turbine exhaust case, the method comprising: attaching a first end of the service line to a seal plate through a service line hole; inserting a second end of the service line opposite the second end through a service line passage extending through a strut of a turbine exhaust case frame; and securing the seal plate to a multi-function boss on an outer ring of the frame, the multi-function seal plate having a service line aperture opening into the service line passage, and a mounting point for the turbine exhaust case. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     further comprising selecting the seal plate to have a number of service line holes corresponding to a number of service lines extending through the service line aperture. 
     wherein the service line passage is contoured to receive and position a plurality of service lines at distinct chordwise locations. 
     wherein the service line passage is contoured to receive and position three service lines at distinct chordwise locations. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.