Patent Publication Number: US-11384936-B2

Title: Pre-diffuser for a gas turbine engine

Description:
BACKGROUND 
     The present disclosure relates to a gas turbine engine and, more particularly, to a pre-diffuser therefor. 
     Gas turbine engines include a compressor section to pressurize a supply of air, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. The compressor section discharges air into a pre-diffuser upstream of the combustion section. The pre-diffuser converts a portion of dynamic pressure to static pressure. A diffuser receives the air from the pre-diffuser and supplies the compressed core flow around an aerodynamically-shaped cowl of the combustion chamber. The core flow is typically separating into three branches. One branch is the cowl passage to supply air to fuel nozzles and for dome cooling. The other branches are annular outer plenum and inner plenums where air is introduced into the combustor for cooling and to complete the combustion process. A further portion of the air may be utilized for turbine cooling. 
     The pre-diffuser is exposed to large thermal gradients and requires various features for anti-rotation, axial retention, and centrality with respect to the central engine axis. These features may result in local discontinuities which may generate stress risers and consequently reduced operational life. 
     SUMMARY 
     A hot fairing structure for a pre-diffuser according to one disclosed non-limiting embodiment of the present disclosure includes a ring-strut-ring structure that comprises a multiple of hollow struts; and a multiple of diffusion passage ducts attached to the ring-strut-ring structure. 
     A further aspect of the present disclosure includes that the hot fairing structure is a cast full ring structure. 
     A further aspect of the present disclosure includes that the multiple of diffusion passage ducts are manufactured of sheet metal. 
     A further aspect of the present disclosure includes that the multiple of diffusion passage ducts are welded to the ring-strut-ring structure. 
     A further aspect of the present disclosure includes that each of the multiple of hollow struts include a cavity. 
     A further aspect of the present disclosure includes a passage in communication with each cavity. 
     A further aspect of the present disclosure includes that an inlet to each of the multiple of diffusion passages are smaller than an exit from the diffusion passage through the ring-strut-ring structure. 
     A further aspect of the present disclosure includes that each of the multiple of hollow struts align with one of a respective multiple of exit guide vanes of an exit guide vane ring. 
     A further aspect of the present disclosure includes a full ring hot fairing radial flange that extends transverse to the multiple of diffusion passages. 
     A further aspect of the present disclosure includes a first anti-rotation feature on one side of the full ring hot fairing radial flange and a second anti-rotation feature on an opposite side of the full ring hot fairing radial flange. 
     A further aspect of the present disclosure includes that the first anti-rotation feature engages an exit guide vane ring. 
     A further aspect of the present disclosure includes that the second anti-rotation feature engages a static structure. 
     A pre-diffuser for a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes an exit guide vane ring having a multiple of exit guide vanes defined around an engine longitudinal axis; a ring-strut-ring structure adjacent to the exit guide vane ring to form a multiple of diffusion passages defined around the engine longitudinal axis, an inlet to each of the multiple of diffusion passages smaller than an exit from each of the multiple diffusion passage through the ring-strut-ring structure; a diffusion passage duct attached to the ring-strut-ring structure at the exit from each of the multiple diffusion passage. 
     A further aspect of the present disclosure includes that the hot fairing structure is a cast full ring structure. 
     A further aspect of the present disclosure includes that the multiple of diffusion passage ducts are manufactured of sheet metal. 
     A further aspect of the present disclosure includes that the multiple of diffusion passage ducts are welded to the ring-strut-ring structure. 
     A further aspect of the present disclosure includes an outer radial interface between a radial outer surface of the hot fairing structure and the exit guide vane ring, the outer radial interface being a full hoop structure; and an anti-rotation feature between the hot fairing structure and the exit guide vane ring, the anti-rotation features inboard of the multiple of diffusion passages. 
     A further aspect of the present disclosure includes comprising a hot fairing radial flange that extends radially inward from the hot fairing structure and an exit guide vane radial flange that extends radially inward from the exit guide vane ring, the seal located between the exit guide vane radial flange and the hot fairing radial flange. 
     A further aspect of the present disclosure includes a static structure flange that abuts the hot fairing radial flange; a clamp ring that abuts the exit guide vane radial flange; and a multiple of fasteners that fasten the clamp ring to the static structure flange. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation of the invention will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a schematic cross-section of a gas turbine engine. 
         FIG. 2  is a partial longitudinal cross-sectional view of a pre-diffuser according to one non-limiting embodiment that may be used with the gas turbine engine shown in  FIG. 1 . 
         FIG. 3  is an expanded cross-sectional view of the pre-diffuser. 
         FIG. 4  is a perspective view of the pre-diffuser. 
         FIG. 5  is a view from front of the pre-diffuser. 
         FIG. 6  is a view from rear of the pre-diffuser. 
         FIG. 7  is a perspective view of the hot fairing structure of the pre-diffuser. 
         FIG. 8  is a perspective view of the exit guide vane ring of the pre-diffuser. 
         FIG. 9  is a perspective view of the hot fairing structure from an opposite direction as that of  FIG. 7 . 
         FIG. 10  is a perspective view of the static structure. 
         FIG. 11  is an expanded longitudinal cross-sectional view of an outer radial interface between the hot fairing structure  102  and the exit guide vane ring of the pre-diffuser. 
         FIG. 12  is an exploded perspective view of the hot fairing structure of the pre-diffuser. 
         FIG. 13  is an exploded cross-sectional view taken along line  13 - 13  in  FIG. 5 . 
         FIG. 14  is an exploded cross-sectional view taken along line  14 - 14  in  FIG. 13 . 
         FIG. 15  is an exploded cross-sectional view taken along line  14 - 14  in  FIG. 13  of another embodiment. 
     
    
    
     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 engines might include other systems or features. The fan section  22  drives air along a bypass flowpath while the compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26 , then expansion through the turbine section  28 . Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines. 
     The engine  20  generally includes a low spool  30  and a high spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine case structure  36  via several bearing structures  38 . The low spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor (LPC)  44  and a low pressure turbine (LPT)  46 . The inner shaft  40  drives the fan  42  directly or through a geared architecture  48  to drive the fan  42  at a lower speed than the low spool  30 . An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system. 
     The high spool  32  includes an outer shaft  50  that interconnects a high pressure compressor (HPC)  52  and high pressure turbine (HPT)  54 . A combustor  56  is arranged between the HPC  52  and the HPT  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes. Core airflow is compressed by the low pressure compressor  44 , then the high pressure compressor  52 , mixed with the fuel and burned in the combustor  56 , then expanded over the HPT  54  and LPT  46 . The HPT  54  and LPT  46  rotationally drive the respective high spool  32  and low spool  30  in response to the expansion. 
     With reference to  FIG. 2 , the combustor  56  generally includes an outer liner  60 , an inner liner  62  and a diffuser case module  64 . The outer liner  60  and the inner liner  62  are spaced apart such that a combustion chamber  66  is defined therebetween. The combustion chamber  66  is generally annular in shape. The outer liner  60  and the inner liner  62  are spaced radially inward of the outer diffuser case  64  to define an annular outer plenum  76  and an annular inner plenum  78 . It should be understood that although a particular combustor is illustrated, other combustor types with various combustor liner arrangements will also benefit herefrom. It should be further understood that the disclosed cooling flow paths are but an illustrated embodiment and should not be limited only thereto. 
     The liners  60 ,  62  contain the combustion products for direction toward the turbine section  28 . Each liner  60 ,  62  generally includes a respective support shell  68 ,  70  which supports one or more heat shields  72 ,  74  that are attached thereto with fasteners  75 . 
     The combustor  56  also includes a forward assembly  80  downstream of the compressor section  24  to receive compressed airflow through a pre-diffuser  100  into the combustor section  26 . The pre-diffuser  100  includes a hot fairing structure  102  and an exit guide vane ring  104 . The exit guide vane ring  104  includes a row of Exit Guide Vanes (EGVs)  108  downstream of the HPC  52 . The EGVs  108  are static engine components which direct core airflow from the HPC  52  between outboard and inboard walls  110  and  112 . 
     The pre-diffuser  100  is secured to a static structure  106  to at least partially form the diffuser module between the compressor section  24  and the combustor section  26 . The hot fairing structure  102  is exposed to large thermal gradients and directs the core airflow while forming a shell within the relatively colder static structure  106 . The static structure  106  is thereby segregated from the core airflow and generally operates at a relatively lower temperature than the hot fairing structure  102 . The hot fairing structure  102  and the exit guide vane ring  104  are full ring structures that are assembled in a manner that allows common thermal growth yet still remain centered with respect to the static structure  106  along the engine central longitudinal axis A. 
     With reference to  FIG. 3 , the hot fairing structure  102  includes a ring-strut-ring structure  118  which forms a multiple of diffusion passages  120  that each communicate with one of a multiple of diffusion passage ducts  124  ( FIG. 4 ) that extend the diffusion passage of the ring-strut-ring structure  118  along each flow passage P. Each of the diffusion passages  120  in the ring-strut-ring structure  118  includes an inlet to the pre-diffuser  100  and a diffusion passage exit that mates with the diffusion passage duct  124 . Each of the diffusion passage ducts  124  include a diffusion duct inlet  126  ( FIG. 5 ) adjacent to the ring-strut-ring structure  118 . A diffusion duct exit  128  from each diffusion passage duct  124  provide the outlet from the pre-diffuser  100 . The diffusion duct exits  128  ( FIG. 6 ) are larger than the respective diffusion duct inlets  126  which are positioned between each of the EGVs  108 . In one example, the number of EGVs are 2-5 times more than the number of diffusion duct inlets  126 . In this embodiment, the diffusion passage ducts  124  expand primarily in the radial direction to the diffusion duct exits  128 . 
     The hot fairing structure  102  and the exit guide vane ring  104  include an anti-rotation interface  130  that positions the anti-rotation features  132 ,  134  in a region of low stress inboard of the diffusion passages  120 . In the disclosed embodiment, the hot fairing structure  102  may include a multiple of circumferentially located anti-rotation tabs  132  ( FIG. 7 ) that engage respective anti-rotation slots  134  ( FIG. 8 ) in the exit guide vane ring  104 . The inboard location of the anti-rotation features  132 ,  134  allow the multiple, static, hot components to grow and interact together, with low stress, and simultaneously remain aligned with the rotating components to facilitate a longer service life and engine efficiency. 
     An axial extension  140  of the hot fairing structure  102  extends along an inner diameter flow surface of the flow passage P. The axial extension  140  at least partially overlaps a recessed area  142  of the exit guide vane ring  104 . That is, the axial extension  140  extends in a direction opposite that of the core flow in the flow passage P and overlaps the recessed area  142  ( FIG. 8 ) in the exit guide vane ring  104 . 
     A hot fairing radial flange  150  extends from the hot fairing structure  102  parallel to an exit guide vane radial flange  152  of the exit guide vane ring  104 . A static structure flange  154  extends radially outwardly from the static structure  106  with respect to the engine axis A to abut the hot fairing radial flange  150 . That is, the static structure flange  154  operates as a mount location for the hot fairing structure  102  and the exit guide vane ring  104 . The hot fairing radial flange  150  also includes a multiple of circumferentially located anti-rotation tabs  156  ( FIG. 9 ) opposite the anti-rotation tabs  132  that engage respective anti-rotation slots  158  ( FIG. 10 ) in the static structure flange  154  of the static structure  106 . 
     A clamp ring  160  abuts the exit guide vane radial flange  152  to sandwich a seal member  170  between the exit guide vane radial flange  152  and the hot fairing radial flange  150 . A seal member  170 , e.g., a torsional spring seal, dogbone, or diamond seal, that accommodates compression of the hot fairing structure  102  and the exit guide vane ring  104  in response to axial assembly of the static structure modules. A multiple of circumferentially arranged fasteners  180  fastens the clamp ring  160  to the static structure  106 . 
     An outer radial interface  190  between the hot fairing structure  102  and the exit guide vane ring  104  includes a radial interface  192  and an axial interface  194 . Since the outer radial interface  190  of the hot fairing structure  102  and the exit guide vane ring  104  are devoid of discontinuities and are uniform in cross-section around the circumference of the full hoop structures, service life is significantly increased. The anti-rotation interface  130  and the outer radial interface  190  are essentially hidden from the gas path and are located in low stress regions. 
     With reference to  FIG. 12 , the ring-strut-ring structure  118  may be cast from nickel alloys to provide for structural attachment and efficient sealing between turbine engine components combined with independently manufactured thin-wall diffusion passage ducts  124 . The diffusion passage ducts  124  can be manufactured by several methods including cast, sheet-metal formed, additively manufactured, or combinations thereof. The wall thickness and local stiffness of the diffusion passage ducts  124  can be tailored to a specific requirement thereof without excessive weight as is typical of cast components. The joining of the diffusion passage ducts  124  to the ring-strut-ring structure  118  to form each complete diffusion passage may be by brazing, bonding, welding, mechanical, or others. Light weight diffusion passage ducts  124  reduce the overall weight of the design, simplify the ring-strut-ring structure  118  casting process, and increase the natural frequencies of the hot fairing structure  102  by minimizing the cantilevered mass of the diffusion passage ducts  124 . 
     With reference to  FIG. 13 , the one-piece ring-strut-ring structure  118  of the hot fairing structure  102  includes a multiple of hollow struts  200  that align with the respective multiple of upstream EGVs  108  of the exit guide vane ring  104  and split the flow into two adjacent diffusion passage ducts  124  ( FIG. 14 ). Each of the multiple of hollow struts  200  are generally airfoil shaped. In this embodiment, the hollow struts  200  reduce thermal mass and thickness so that the transient thermal gradient within the strut is minimal. The hollow strut  200  includes a cavity  204  that may be manufactured with ceramic cores, and a core exit via a passage  202  may be located at a location that has the least impact on thermal stiffness. Alternatively, the struts  200  may be solid ( FIG. 15 ). 
     Each passage  202  is located along an axis D and is in communication with the cavity  204  in the hollow strut  200 . The passage  202  may be reinforced and permits diffusion air from the diffuser side of the pre-diffuser  100 , i.e., the air around the combustor  56 , to be received into the respective cavity  204 . The diffuser air facilitates thermal control of the ring-strut-ring structure  118  of the hot fairing structure  102  to reduce the mass of the ring-strut-ring structure  118 . The reduced mass of the ring-strut-ring structure  118  of the hot fairing structure  102  results in a more responsive thermal characteristic. The strut geometry maximizes the perimeter of the ring-strut-ring structure  118  that is engaged in torsional stiffness. That is, the mass close to the centroid  206  has little to no effect on stiffness. To resist multi-node sinusoidal waves travelling around the circumference of the hot fairing structure  102 , local torsional sectional properties of the ring-strut-ring structure  118  facilitate control of the natural frequencies of the hot fairing structure  102 . 
     The ring-strut-ring structure  118  with the hollow regions with the core breakout located close to the centroid  206  of the torsional section forms a pre-diffuser  100  that can have both high natural frequencies and more uniform transient thermal gradients which enables a lightweight, high performance low thermal stress design. The hot fairing structure  102  with a hollow leading edge region and the core opening on the aft side of the hollow strut  200 , is located about the mid-axis of the airfoil shape to connect outer diameter static structure, with minimal thermal mass, and an inner diameter static structure with distributed mass such that the transient thermal response is optimized to reduce thermal stress. 
     The ring-strut-ring structure  118  also allows coupled Exit Guide Vanes with the floating hot fairing to provide improved cyclic life. Light weight tubular flowpath extensions reduce the overall weight of the design, simplify the ring-strut-ring structure  118  casting process, and increase the natural frequencies of the hot fairing by minimizing the cantilevered mass of the tubes. Additionally, the torsionally stiff ring-strut-ring structure  118  ensures that the design can be incorporated with features on the inner diameter structure which facilitates attachment to other structures with the least amount of contact, yet have sufficient frequency margin with respect to engine operating vibration sources. 
     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. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.