Patent Publication Number: US-2018045218-A1

Title: Shim for gas turbine engine

Description:
BACKGROUND 
     A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines. 
     The high pressure turbine drives the high pressure compressor through an outer shaft to form a high spool, and the low pressure turbine drives the low pressure compressor through an inner shaft to form a low spool. The fan section may also be driven by the low inner shaft. A direct drive gas turbine engine includes a fan section driven by the low spool such that the low pressure compressor, low pressure turbine and fan section rotate at a common speed in a common direction. 
     A speed reduction device, such as an epicyclical gear assembly, may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section. In such engine architectures, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at a reduced speed. 
     SUMMARY 
     A joint for a gas turbine engine according to an example of the present disclosure includes a first component that has a first ring portion and a first annular radial flange extending from the first ring portion, and a second component that has a second ring portion and a second annular radial flange extending from the second ring portion. The first annular radial flange and the second annular radial flange are spaced apart by a gap that has a variable gap size that is subject to a stacking tolerance. An annular shim disk is disposed in the gap, and a plurality of fasteners are secured through the first annular radial flange, the annular shim disk, and the second annular radial flange. 
     In a further embodiment of any of the foregoing embodiments, the annular shim disk is monolithic. 
     In a further embodiment of any of the foregoing embodiments, the annular shim disk includes a plurality of circular orifices through which the plurality of fasteners are secured. 
     In a further embodiment of any of the foregoing embodiments, the circular orifices are circumferentially-arranged in a series that is uninterrupted by any non-circular orifices. 
     In a further embodiment of any of the foregoing embodiments, the circular orifices are non-uniformly circumferentially-arranged. 
     In a further embodiment of any of the foregoing embodiments, the second annular radial flange is scalloped. 
     In a further embodiment of any of the foregoing embodiments, the first component includes an air seal extending from the first ring portion. The first annular radial flange extends radially outwards from the first ring portion and the air seal extends radially inwards from the first ring portion. 
     In a further embodiment of any of the foregoing embodiments, the annular shim disk has radially inner and outer edges, and uniform axial thickness from the radially outer edge to the radially inner edge. 
     A gas turbine engine according to an example of the present disclosure includes a compressor section that has a plurality of compressor case segments that are in a stacked arrangement along an axis. The compressor case segments have respective axial dimensions which are variable within respective dimensional tolerances. The stacked arrangement has a stacked dimension which is variable within a stacking tolerance corresponding to the dimensional tolerances. A joint has a first component that has a first ring portion and a first annular radial flange extending from the first ring portion. The first component is stacked adjacent the second compressor case. A second component has a second ring portion and a second annular radial flange extending from the second ring portion. The second component is affixed such that the first annular radial flange and the second annular radial flange are spaced apart by a gap that has a variable gap size that is subject to the stacking tolerance. An annular shim disk is disposed in the gap, and a plurality of fasteners are secured through the first annular radial flange, the annular shim disk, and the second annular radial flange. 
     In a further embodiment of any of the foregoing embodiments, the compressor section includes a low pressure compressor and a high pressure compressor, and the joint is located in the high pressure compressor. 
     In a further embodiment of any of the foregoing embodiments, the joint is at an aft end of the high pressure compressor. 
     In a further embodiment of any of the foregoing embodiments, the annular shim disk is monolithic. 
     In a further embodiment of any of the foregoing embodiments, the annular shim disk includes a plurality of circular orifices through which the plurality of fasteners are secured. 
     In a further embodiment of any of the foregoing embodiments, the circular orifices are circumferentially-arranged in a series that is uninterrupted by any non-circular orifices. 
     In a further embodiment of any of the foregoing embodiments, the circular orifices are non-uniformly circumferentially-arranged. 
     In a further embodiment of any of the foregoing embodiments, the second annular radial flange is scalloped. 
     In a further embodiment of any of the foregoing embodiments, the first component includes an air seal extending from the first ring portion, the first annular radial flange extending radially outwards from the first ring portion and the air seal extending radially inwards from the first ring portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  illustrates an example gas turbine engine. 
         FIG. 2  illustrates an example of a stacked arrangement of a compressor case. 
         FIG. 3  illustrates an example joint in the engine of  FIG. 1 . 
         FIG. 4A  illustrates an axial view of an annular shim disk. 
         FIG. 4B  illustrates a partial view of the annular shim disk of  FIG. 4A . 
         FIG. 5  illustrates a sectioned view of the annular shim disk of  FIG. 4B . 
         FIG. 6  illustrates a partial view of a component of a joint. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engine designs can include an augmentor section (not shown) among other systems or features. 
     The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, the examples herein are not limited to use with two-spool turbofans and may be applied to other types of turbomachinery, including direct drive engine architectures, three-spool engine architectures, and ground-based turbines. 
     The engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as a geared architecture  48 , to drive the fan  42  at a lower speed than the low speed spool  30 . 
     The high speed spool  32  includes an outer shaft  50  that interconnects a second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports the bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of gear system  48 . 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines, including direct drive turbofans. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
     The compressor section  24  of the engine  20  includes a compressor case  62 . The compressor case  62  may be a sectioned case that has a plurality of annular compressor case segments  64 , which are shown in  FIG. 2 . Although shown schematically, each case segment  64  may have a different geometry in accordance with the axial position of the given case segment  64  in the compressor section  24 . The case segments  64  are stacked together during assembly of the compressor section  24 , as represented at  66 , to form a stacked arrangement  68 . The case segments  64  may be stacked directly in contact with each other or there may be seals or other intermediary components between the case segments  64 . Although three case segments  64  are shown, it is to be understood that the stacked arrangement  68  may have two case segments  64  or additional case segments. For instance, the stacked arrangement  68  has seven or eight case segments  64 . 
     The case segments  64  have respective axial dimensions, represented at D 1 , D 2 , and D 3 , which are variable within respective dimensional tolerances, represented at T 1 , T 2 , and T 3 . The stacked arrangement  68  has a stacked dimension, represented at D 4 , which is variable within a stacking tolerance, represented at T 4 . The stacking tolerance T 4  corresponds to the dimensional tolerances D 1 , D 2 , and D 3 . For example, if the dimensional tolerances D 1 , D 2 , and D 3  were each+/−2 units, the stacking tolerance T 4  may be+/−6 units. If the dimensional tolerances D 1 , D 2 , and D 3  were, respectively, +/−1 unit, +/−2 units, and +/−2 units, the stacking tolerance T 4  may be+/−5 units. In practice, actual stacking tolerance may be reduced through selection of the case segments  64 . 
       FIG. 3  depicts a location at an aft end  70  of the high pressure compressor  52 . The aft end  70  includes a joint  72  between the rear of the stacked arrangement  68  and an inner diffuser  74 , which is just prior to the combustor  56 . The joint  72  includes a first component  76 , a second component  78 , an annular shim disk  80 , and a plurality of fasteners  82  (one shown), such as bolts, that secure the annular shim disk  80  between the first component  76  and the second component  78 . 
     The first component  76  in this example includes a first ring portion  76   a  and a first annular radial flange  76   b  that extends radially outwards from the first ring portion  76   a . In this example, the first component  76  also includes an air seal  76   c  that extends radially inwards from the first ring portion  76   a . In other types of joints the first component may not have an air seal. The second component  78  in this example includes a second ring portion  78   a  and a second annular radial flange  78   b  that extends radially outwards from the second ring portion  78   a . The first annular radial flange  76   b  and the second annular radial flange  78   b  are spaced apart by a gap, represented at G. 
     The second component  78 , which in this example is a seal ring, is affixed with respect to the diffuser  74  or other component in the engine  20 . The first component  76  is adjacent the stacked arrangement  68 . The axial position of the first component  76  is thus dependent on the position of the stacked arrangement  68 , which can vary in accordance with the stacking tolerance T 4 . Therefore, the gap G has a variable gap size that is subject to the stacking tolerance T 4 . The annular shim disk  80  may be selected from among a group of similar annular shim disks that have different sizes to fill gaps G of different gap sizes. The flanges  76   b / 78   b  have orifices for receiving the fasteners  82 . 
     As shown in  FIGS. 4A and 4B , the annular shim disk  80  has circular orifices  84 , which axially align with the orifices in the flanges  76   b / 78   b  to receive the fasteners  82  there through. The circular orifices  84  are circumferentially-arranged. For instance, the circular orifices  84  may be non-uniformly arranged to provide mistake-proof assembly of the annular shim disk  80  in only one orientation. Additionally, the circular orifices  84  may be circumferentially-arranged in a series that is uninterrupted by any non-circular orifices. As an example, the annular shim disk  80  does not have any elongated slots or other openings in between the circular orifices. 
     The annular shim disk  80  is a single-piece ring. For example, the single-piece ring can be a monolithic body that does not have seams or the ring can be formed from arc segments that are metallurgically affixed together to form a single piece. In one example, the ring is machined as a single-piece from a starting workpiece. 
     As shown in  FIG. 5 , the annular shim disk  80  has an outer edge  80   a , an inner edge  80   b , and a uniform axial thickness, represented at t, from the outer edge  80   a  to the inner edge  80   b . For instance, the annular shim disk  80  has the same or substantially same axial thickness at all circumferential locations. 
     The annular shim disk  80  serves to fill the gap G and reduce stresses on the first component  76  and the second component  78  in comparison to a segmented shim (described further below). The fasteners  82  clamp the annular shim disk  80  between the flanges  76   b / 78   b . The uniform thickness of the annular shim disk  80  facilitates the reduction of stress concentrations on the flanges  76   b / 78   b  under the clamping force. Additionally, one or both of the flanges  76   b / 78   b  may mechanically and/or thermally deflect during operation of the engine  20 . In particular, as shown in  FIG. 6 , the second annular radial flange  78   b  of the second component  78  (e.g., a seal ring) may be scalloped, which may permit a greater degree of deflection and thus a greater potential to produce elevated local stresses. Such scalloping may be used to permit rapid thermal change during engine acceleration to accommodate dimensional changes in other components, such as an integrally bladed rotor in the compressor section  24 . 
     Such deflection potentially applies a local load on the annular shim disk  80 . However, because the annular shim disk  80  has the circular orifices  84  (rather than elongated slot orifices, for example) and does not have extraneous openings, the annular shim disk  80  bears, and more evenly distributes, the load of deflection. Additionally, the annular shim disk  80  may enhance sealing at the joint  72  because it is a single piece with no radial seam through which air can escape. Although the examples herein are described with respect to the joint  72  being located in the high pressure compressor  52 , it is to be understood that similar joints that are subject to stacking tolerances may also benefit from this disclosure. 
     In comparison to the annular shim disk  80 , a segmented shim includes eight arc segments. The arc segments are not bonded to each other but are individually secured in the joint (e.g., in place of the annular shim disk  80 ). Such a segmented shim may lead to higher stresses in comparison to the annular shim disk  80 . The segments typically vary in thickness and thus add dimensional variation, may shift relative to one another in the joint, may clamp with different loads, and may include circumferentially elongated slots (to receive the fasteners and accommodate misalignment due to positioning of the arc segments). Deflection of one or both of the flanges  76   b / 78   b  may cause higher local stresses because of the non-uniform thickness, shifting, clamping loads, and elongated slots of the segmented shim. The higher local stress has the potential to reduce durability of one or more components in such a joint, such as low cycle fatigue durability and/or thermo-mechanical fatigue durability. The annular shim disk  80 , however, facilitates a reduction in local stresses and potentially enhances durability of the first component  76 , the second component  78 , or both. For instance, in a computer analysis stress simulation of a range of maximum and minimum stresses, the annular shim disk  80  experienced a stress range 50% lower than the segmented shim and the annular shim disk  80  reduced the stress range in the second component  78  by over 30% in comparison to the segmented shim. Enhancement in durability may also provide greater flexibility to redesign other, surrounding components, which might otherwise reduce durability below acceptable levels. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the figures or all of the portions schematically shown in the figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.