Patent Publication Number: US-11662150-B2

Title: Heat exchanger having curved fluid passages for a gas turbine engine

Description:
FIELD 
     The present subject matter relates to gas turbine engines and, more particularly, to heat exchanger having curved fluid passages for a gas turbine engine. 
     BACKGROUND 
     A turbofan engine generally includes a fan, a compressor section, a combustion section, and a turbine section. More specifically, the fan generates a flow of pressurized air. A portion of this air flow is used as propulsive thrust for propelling an aircraft, while the remaining air is supplied to the compressor section. The compressor section, in turn, progressively increases the pressure of received air and supplies this compressed air to the combustion section. The compressed air and a fuel mix within the combustion section and burn within a combustion chamber to generate high-pressure and high-temperature combustion gases. The combustion gases flow through the turbine section before exiting the engine. In this respect, the turbine section converts energy from the combustion gases into rotational energy. This rotational energy, in turn, is used to drive the compressor section and/or the fan via various shaft and/or gearboxes. 
     Typically, a turbofan engine includes various heat exchangers to heat or cool the fluids that support the operation of the engine. For example, the engine may include one or more heat exchangers that cool the oil circulated through the gearbox(es) of the engine. While conventional heat exchangers generally provide sufficient heating/cooling to the fluids of the engine, such heat exchangers increase the overall weight of the engine. 
     Accordingly, an improved heat exchanger for a gas turbine engine would be welcomed in the technology. In particular, a heat exchanger for a gas turbine engine having a reduced weight would be welcomed in the technology. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present subject matter is directed to a heat exchanger for a gas turbine engine. The heat exchanger includes a heat exchanger body having a first surface and a second surface oriented at least partially at an oblique angle relative to the first surface. The heat exchanger body defines a plenum extending between the first and second surfaces. Furthermore, the heat exchanger body defines a fluid passage extending through the second surface such that the fluid passage is in fluid communication with the plenum. The fluid passage, in turn, includes first and second portions. The first portion intersects the plenum at an intersection and defines a line of projection extending normal to the second surface. The second portion defines a line of projection extending normal to the first surface. The fluid passage further includes a curved portion extending from the first portion to the second portion. 
     In another aspect, the present subject matter is directed to a gas turbine engine. The gas turbine engine includes a compressor, a combustor, a turbine, and a heat exchanger in operative association with at least one of the compressor, the combustor, or the turbine. The heat exchanger, in turn, includes a heat exchanger body having a first surface and a second surface oriented at least partially at an oblique angle relative to the first surface. The heat exchanger body defines a plenum extending between the first and second surfaces. Furthermore, the heat exchanger body defines a fluid passage extending through the second surface such that the fluid passage is in fluid communication with the plenum. The fluid passage, in turn, includes first and second portions. The first portion intersects the plenum at an intersection and defines a line of projection extending normal to the second surface. The second portion defines a line of projection extending normal to the first surface. The fluid passage further includes a curved portion extending from the first portion to the second portion. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG.  1    is a schematic cross-sectional view of one embodiment of a gas turbine engine; 
         FIG.  2    is a schematic view of one embodiment of a heat exchanger suitable for use with a gas turbine engine; 
         FIG.  3    is a partial cross-sectional view of one embodiment of a heat exchanger suitable for use with a gas turbine engine, particularly illustrating various portions of a plurality of fluid passages defined by a body of the heat exchanger; 
         FIG.  4    is a partial cross-sectional view of one embodiment of a heat exchanger suitable for use with a gas turbine engine, particularly illustrating an intersection between a fluid passage defined by a heat exchanger body and a plenum defined by the body; 
         FIG.  5    is another partial cross-sectional view of one embodiment of a heat exchanger suitable for use with a gas turbine engine, particularly illustrating a plenum defined by a heat exchanger body; and 
         FIG.  6    is a further partial cross-sectional view of one embodiment of a heat exchanger suitable for use with a gas turbine engine, particularly illustrating the relative positioning of first and second pluralities of the fluid passages defined by a heat exchanger body. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. 
     Furthermore, the terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. 
     Additionally, the terms “low,” “high,” or their respective comparative degrees (e.g., lower, higher, where applicable) each refer to relative speeds within an engine, unless otherwise specified. For example, a “low-pressure turbine” operates at a pressure generally lower than a “high-pressure turbine.” Alternatively, unless otherwise specified, the aforementioned terms may be understood in their superlative degree. For example, a “low-pressure turbine” may refer to the lowest maximum pressure turbine within a turbine section, and a “high-pressure turbine” may refer to the highest maximum pressure turbine within the turbine section. 
     In general, the present subject matter is directed to a heat exchanger suitable for use with a gas turbine engine. In several embodiments, the heat exchanger includes a heat exchanger body defining a plenum therein. The plenum, in turn, extends between first and second surfaces of the heat exchanger body, with the second surface oriented at least partially at an oblique angle relative to the first surface. Furthermore, the heat exchanger body further defines a plurality of fluid passages extending through the second surface such that the fluid passages are fluid communication with the plenum. Each fluid passage, in turn, includes first and second portions. Specifically, the first portion of each fluid passage intersects the plenum at an intersection and defines a line of projection (e.g., a centerline) extending normal to the second surface of the heat exchanger body. Moreover, the second portion of each fluid passage define a line of projection (e.g., a centerline) extending normal to the first surface. Additionally, each fluid passage further includes a curved portion extending from the corresponding first portion to the corresponding second portion. 
     Positioning the first portion of each fluid passage such that its line of projection extends normal to the second surface (i.e., the surface through which the passages extend to intersect the plenum) of the heat exchanger reduces the weight of the heater exchanger. More specifically, such a configuration reduces the stress concentrations present at the intersections of the fluid passages and the plenum during operation of the heat exchanger. This, in turn, allows the heat exchanger to be formed from lighter materials than conventional heat exchangers (e.g., aluminum instead of steel), while still maintaining the same size envelope and operating under the same fluid pressures. 
     Referring now to the drawings,  FIG.  1    is a schematic cross-sectional view of one embodiment of a gas turbine engine  10 . In the illustrated embodiment, the engine  10  is configured as a high-bypass turbofan engine. However, in alternative embodiments, the engine  10  may be configured as a propfan engine, a turbojet engine, a turboprop engine, a turboshaft gas turbine engine, or any other suitable type of gas turbine engine. Furthermore, as shown in  FIG.  1   , the engine  10  defines a longitudinal direction L, a radial direction R, and a circumferential direction C. In general, the longitudinal direction L extends parallel to an axial centerline  12  of the engine  10 , the radial direction R extends orthogonally outward from the axial centerline  12 , and the circumferential direction C extends generally concentrically around the axial centerline  12 . 
     In general, the engine  10  includes a fan  14 , a low-pressure (LP) spool  16 , and a high pressure (HP) spool  18  at least partially encased by an annular nacelle  20 . More specifically, the fan  14  may include a fan rotor  22  and a plurality of fan blades  24  (one is shown) coupled to the fan rotor  22 . In this respect, the fan blades  24  are spaced apart from each other along the circumferential direction C and extend outward from the fan rotor  22  along the radial direction R. Moreover, the LP and HP spools  16 ,  18  are positioned downstream from the fan  14  along the axial centerline  12  (i.e., in the longitudinal direction L). As shown, the LP spool  16  is rotatably coupled to the fan rotor  22 , thereby permitting the LP spool  16  to rotate the fan  14 . Additionally, a plurality of outlet guide vanes or struts  26  spaced apart from each other in the circumferential direction C extend between an outer casing  28  surrounding the LP and HP spools  16 ,  18  and the nacelle  20  along the radial direction R. As such, the struts  26  support the nacelle  20  relative to the outer casing  28  such that the outer casing  28  and the nacelle  20  define a bypass airflow passage  30  positioned therebetween. 
     The outer casing  28  generally surrounds or encases, in serial flow order, a compressor section  32 , a combustion section  34 , a turbine section  36 , and an exhaust section  38 . For example, in some embodiments, the compressor section  32  may include a low-pressure (LP) compressor  40  of the LP spool  16  and a high-pressure (HP) compressor  42  of the HP spool  18  positioned downstream from the LP compressor  40  along the axial centerline  12 . Each compressor  40 ,  42  may, in turn, include one or more rows of stator vanes  44  interdigitated with one or more rows of compressor rotor blades  46 . Moreover, in some embodiments, the turbine section  36  includes a high-pressure (HP) turbine  48  of the HP spool  18  and a low-pressure (LP) turbine  50  of the LP spool  16  positioned downstream from the HP turbine  48  along the axial centerline  12 . Each turbine  48 ,  50  may, in turn, include one or more rows of stator vanes  52  interdigitated with one or more rows of turbine rotor blades  54 . 
     Additionally, the LP spool  16  includes the low-pressure (LP) shaft  56  and the HP spool  18  includes a high pressure (HP) shaft  58  positioned concentrically around the LP shaft  56 . In such embodiments, the HP shaft  56  rotatably couples the rotor blades  54  of the HP turbine  48  and the rotor blades  46  of the HP compressor  42  such that rotation of the HP turbine rotor blades  54  rotatably drives HP compressor rotor blades  46 . As shown, the LP shaft  56  is directly coupled to the rotor blades  54  of the LP turbine  50  and the rotor blades  46  of the LP compressor  40 . Furthermore, the LP shaft  56  is coupled to the fan  14  via a gearbox  60 . In this respect, the rotation of the LP turbine rotor blades  54  rotatably drives the LP compressor rotor blades  46  and the fan blades  24 . 
     In several embodiments, the engine  10  may generate thrust to propel an aircraft. More specifically, during operation, air (indicated by arrow  62 ) enters an inlet portion  64  of the engine  10 . The fan  14  supplies a first portion (indicated by arrow  66 ) of the air  62  to the bypass airflow passage  30  and a second portion (indicated by arrow  68 ) of the air  62  to the compressor section  32 . The second portion  68  of the air  62  first flows through the LP compressor  40  in which the rotor blades  46  therein progressively compress the second portion  68  of the air  62 . Next, the second portion  68  of the air  62  flows through the HP compressor  42  in which the rotor blades  46  therein continue progressively compressing the second portion  68  of the air  62 . The compressed second portion  68  of the air  62  is subsequently delivered to the combustion section  34 . In the combustion section  34 , the second portion  68  of the air  62  mixes with fuel and burns to generate high-temperature and high-pressure combustion gases  70 . Thereafter, the combustion gases  70  flow through the HP turbine  48  which the HP turbine rotor blades  54  extract a first portion of kinetic and/or thermal energy therefrom. This energy extraction rotates the HP shaft  58 , thereby driving the HP compressor  42 . The combustion gases  70  then flow through the LP turbine  50  in which the LP turbine rotor blades  54  extract a second portion of kinetic and/or thermal energy therefrom. This energy extraction rotates the LP shaft  56 , thereby driving the LP compressor  40  and the fan  14  via the gearbox  60 . The combustion gases  70  then exit the engine  10  through the exhaust section  38 . 
     Additionally, the engine  10  may include one or more heat exchangers  100 . In general, the heat exchanger(s)  100  heat and/or cool one or more fluids (e.g., oil, fuel, and/or the like) that support the operation of the engine  10 . Specifically, in several embodiments, the heat exchanger(s)  100  may be operative association with one or more components of the engine  10 , such as the fan  14 , the compressor section  32 , the combustion section  34 , and/or the turbine section  36 . For example, in the illustrated embodiment, the engine  10  includes a heat exchanger  100  in operative association with the gearbox  60 . In such an embodiment, the heat exchanger  100  may be configured as a fuel-oil heat exchanger that transfers heat from the oil circulating the gearbox  60  to the fuel supplied to the combustion section  34 . However, in alternative embodiments, the heat exchanger(s)  100  may be in operative association with any other suitable component(s) of the engine  10 . Moreover, in further embodiments, the engine  10  may include any other suitable number or type of heat exchanger  100 . 
     The configuration of the gas turbine engine  10  described above and shown in  FIG.  1    is provided only to place the present subject matter in an exemplary field of use. Thus, the present subject matter may be readily adaptable to any manner of gas turbine engine configuration, including other types of aviation-based gas turbine engines, marine-based gas turbine engines, and/or land-based/industrial gas turbine engines. 
       FIG.  2    is a schematic view of one embodiment of a heat exchanger  100  suitable for use with a gas turbine engine. In general, the heat exchanger  100  is configured to transfer heat between a first fluid (indicated by arrows  102 ) and second fluid (indicated by arrows  104 ). For example, as mentioned above, in one embodiment, the heat exchanger  100  may be configured to transfer heat between oil and fuel. However, in alternative embodiments, the heat exchanger  100  may be configured to transfer heat between any other suitable fluids. 
     The heat exchanger  100  includes a heat exchanger body  106  defining various fluid passages, plena, and openings therein through which the first and second fluid  102 ,  104  flow. In several embodiments, the body  106  defines a first inlet plenum  108 A, a first outlet plenum  108 B, and a first plurality of fluid passages (indicated by solid lines  110 ) extending from the first inlet plenum  108 A to the first outlet plenum  108 B. In this respect, the first fluid  102  enters the heat exchanger  100  (e.g., via an associated port) and flows into the first inlet plenum  108 A. Thereafter, the first fluid  102  flows through the first plurality of fluid passages  110  before flowing into the first outlet plenum  108 B and exiting the heat exchanger  100  (e.g., via an associated port). Furthermore, the body  106  defines a second inlet plenum  108 C, a second outlet plenum  108 D, and a second plurality of fluid passages (indicated by dashed lines  112 ) extending from the second inlet plenum  108 C to the second outlet plenum  108 D. As such, the second fluid  104  enters the heat exchanger  100  (e.g., via an associated access port) and flows into the second inlet plenum  108 C. Thereafter, the second fluid  104  flows through the second plurality of fluid passages  112  before flowing into the second outlet plenum  108 D and exiting the heat exchanger  100  (e.g., via an associated access port). As shown, portions of the first plurality of fluid passages  110  are routed through the body  106  in close proximity to portions of the second plurality of fluid passages  112 , thereby permitting heat transfer between the first and second fluids. 
     As shown in  FIG.  2   , the first and second pluralities of fluid passages  110 ,  112  each include two fluid passages. However, the first and second pluralities of fluid passages  110 ,  112  may each include any other suitable number of fluid passages, such a twenty, fifty, or one hundred fluid passages. 
       FIG.  3    is partial, cross-sectional view of the heat exchanger  100 . In several embodiments, the heat exchanger body  106  defines a plenum  108  and an access port  116  in fluid communication with the plenum  108 . Specifically, in the embodiment shown in  FIG.  3   , the access port  116  extends from an exterior surface  114  of the body  106  to a first interior surface  115  of the body  106 . For example, as shown in  FIG.  5   , in some embodiments, the access port  116  has a non-polygonal shape, such a circle, ellipse, oval, filleted/rounded-off rectangle, and or the like. However, in alternative embodiments, the access port  116  may have any other suitable shape. Moreover, the the plenum  108  may correspond to any of the plena  108 A,  108 B,  108 C,  108 D shown in  FIG.  2   . The plenum  108  extends inward (i.e., relative to the exterior surface  114  of the body  106 ) from the first interior surface  115  to a second interior surface  118  of the heat exchanger body  106 . As shown, the second interior surface  118  is oriented at least partially at an oblique angle (indicated by arrow  120 ) relative to the first interior surface  115 . In this respect, the plenum  108  corresponds three-dimensional cavity or space positioned inward of the exterior surface  114  of the body  106 . For example, in one embodiment, the plenum  108  may have a conical shape. Moreover, in the illustrated embodiment, the plenum  108  has a closed configuration (i.e., the plenum  108  is defined between two interior surface of the heat exchanger body  106 ). However, in alternative embodiments, the plenum  108  may have any other suitable shape, such as a spherical shape. Furthermore, the plenum  108  may have an open configuration. In such a configuration, the plenum  108  extends from an opening defined by the exterior surface  114  to the interior surface  118 , with the interior surface  118  intersecting and being oblique to the exterior surface  114 . 
     Additionally, as mentioned above, the heat exchanger body  106  defines the first and second pluralities of fluid passages  110 ,  112 . As shown, several fluid passages  110 ,  112  extend through the interior surface  118  and intersect the plenum  108  at a corresponding intersection  122 . In this respect, the fluid passages  110 ,  112  are in fluid communication with the plenum  108  via the corresponding intersections  122 . As such, fluid is able to flow from the plenum  108  into the fluid passages  110 ,  112  or from the fluid passages  110 ,  112  into the plenum  108 . Although  FIG.  3    shows four fluid passages  110 ,  112  intersecting the plenum  108 , any suitable number (e.g., twenty, fifty, or more) of fluid passages  110 ,  112  may intersect the plenum  108 . 
     As shown, each fluid passage  110 ,  112  includes a first portion (indicated by arrows  124 ), a second portion (indicated by arrows  126 ), and a curved portion (indicated by arrows  128 ). In several embodiments, the first portion  124  of each fluid passage  110 ,  112  is positioned proximal to the plenum  108  such that the first portion  124  extends through the interior surface  118  and intersects the plenum  108  at the corresponding intersection  122 . Furthermore, the first portion  124  of each fluid passage  110 ,  112  defines a line of projection  130  that extends normal or perpendicular to the interior surface  118  of the heat exchanger body  106 . Specifically, the line of projection  130  of the first portion  124  of each fluid passage  110 ,  112  is normal to the section of the interior surface  118  through which the corresponding first portion  124  extends. As will be described below, such an orientation of the first portion  124  of each fluid passage  110 ,  112  reduces the stress concentrations present at the intersections  122 . The second portion  126  of each fluid passage  110 ,  112  is distal to the plenum  108  and defines a line of projection  132  extending normal or perpendicular to the interior surface  115  or the exterior surface  114  of the body  106 . Moreover, the curved portion  128  of each fluid passage  110 ,  112  extends from and fluidly couples the corresponding first portion  124  to the corresponding portion  126 . Thus, each curved portion  128  provides a transition between the corresponding first and second portions  124 , which have differing orientations. Additionally, in some embodiments, the first, second, and curved portions of the fluid passages  110 ,  112  have the same diameter and cross-sectional shape. 
     In the illustrated embodiment, the lines of projections  130 ,  132  correspond to the centerlines of the first and second portions  124 ,  126  of the fluid passages  110 ,  112 . However, in alternative embodiments, the lines of projections  130 ,  132  may correspond to any other suitable lines defined by the first and second portions  124 ,  126  of the fluid passages  110 ,  112 . 
     Referring now to  FIG.  4   , the heat exchanger body  106  may define one or more stress-reducing features  134 . More specifically, as described above, the first portion  124  of one of the fluid passages  110 ,  112  extends through the interior surface  118  and intersects the plenum  108  at each intersection  122 . In this respect, the heat exchanger body  106  may define a stress-reducing feature  134  at each intersection  122 . The stress-reducing features  134 , in turn, distribute stress over a larger area, thereby reducing the stress concentrations present at the intersections  122  during operation of the heat exchanger  100 . As will be described below, positioning the first portions  124  of the fluid passages  110 ,  112  such that their lines of projection  130  are normal to the interior surface  118  permits the formation of the stress-reducing features  134  at the intersections  122 . 
     The stress-reducing feature(s)  134  may correspond to any suitable feature(s) defined by the heat exchanger body  106  located at the intersections  122  that distributes stress over a larger area. For example, in the illustrated embodiment, the stress-reducing features  134  are configured as fillets. However, in other embodiments, the stress-reducing feature(s)  134  may be configured as other rounded edges, chamfers or other beveled edges, and/or the like. 
       FIG.  5    is a partial cross-sectional of view of the heat exchanger  100 . As mentioned above, the fluid passages  110 ,  112  intersect the plenum  108  at the intersections  122 . In several embodiments, the intersections  122  are arranged non-uniformly or staggered along the interior surface  118  defining the plenum  108 . Specifically, in some embodiments, the intersections  122  may be arranged in concentric rings along the interior surface  118 . For example, in the illustrated embodiment, the intersections  122  corresponding to a first set of the fluid passages  110 ,  112  are arranged in a first ring (indicated by dashed line  136 ) along the interior surface  118 . Moreover, in the illustrated embodiment, the intersections  122  corresponding to a second set of the fluid passages  110 ,  112  are arranged in a second ring (indicated by dashed line  138 ) along the interior surface  118 . The second ring  138  may, in turn, enclose and/or be concentric with the first ring  136 . However, in alternative embodiments, the intersections  122  may be arranged in any other suitable manner along the interior surface  118  defining the plenum  108 . 
       FIG.  6    is another partial cross-sectional view of the heat exchanger  100 . As mentioned above, each fluid passage  110 ,  112  includes a second portion  126 . As show, the second portions  126  of the fluid passages  110 ,  112  are arranged into a plurality of rows  140  and a plurality of columns  142 . The second portions  126  may be evenly spaced apart from each other within each row  140  and within each column  142 . Arranging the second portions  126  of the fluid passages  110 ,  112  into rows  140  and columns  142  may allow the fluid passages  110  to be routed in close proximity to the fluid passages  112 , thereby permitting heat transfer between the first and second fluids. However, in alternative embodiments, the second portions  126  of the fluid passages  110 ,  112  may be arranged in any other suitable manner. 
     In several embodiments, the heat exchanger  100  may be monolithic or formed as single integral component. As such, the heat exchanger  100  may be formed using a suitable additive manufacturing method. The term “additive manufacturing” refers to any process resulting in a useful, three-dimensional object and includes a step of sequentially forming the shape of the object one layer at a time. Additive manufacturing processes include three-dimensional printing (3DP) processes, laser-net-shape manufacturing, direct metal laser sintering (DMLS), direct metal laser melting (DMLM), plasma transferred arc, freeform fabrication, and the like. A particular type of additive manufacturing process uses an energy beam (e.g., an electron beam or electromagnetic radiation, such as a laser beam) to sinter or melt a powder material. Additive manufacturing processes typically employ metal powder materials or wire as a raw material. 
     Positioning of the first portions  124  of the fluid passages  110 ,  112  such that the lines of projection  130  (e.g., the centerlines) of the first portions  124  are normal to the interior surface  118  defining the plenum  108  through which the passages  110 ,  112  extend reduces the weight of the heat exchanger  100 . Specifically, such positioning of the first portions  124  allows the intersections  122  between the fluid passages  110 ,  112  and the plenum  108  to be non-uniformly arranged or staggered along the interior surface  118 . The positioning of the first portions  124  and the non-uniform positioning of the intersections  122 , in turn, reduce the stress concentrations present at the intersections  122  during operation of the heat exchanger  100 . Furthermore, the non-uniform positioning allows for the formation of stress-reducing features (e.g., fillets) at the intersections  122 , which further reduce the stress concentrations present during operation. As such, the heat exchanger  100  may be formed from lighter materials than conventional heat exchangers (e.g., aluminum instead of steel), while still maintaining the same size envelope and operating under the same fluid pressures. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     A heat exchanger for a gas turbine engine, the heat exchanger comprising: a heat exchanger body including a first surface and a second surface oriented at least partially at an oblique angle relative to the first surface, the heat exchanger body defining a plenum extending between the first and second surfaces, the heat exchanger body further defining a fluid passage extending through the second surface such that the fluid passage is in fluid communication with the plenum, wherein the fluid passage includes first and second portions, the first portion intersecting the plenum at an intersection and defining a line of projection extending normal to the second surface, the second portion defining a line of projection extending normal to the first surface, the fluid passage further including a curved portion extending from the first portion to the second portion. 
     The heat exchanger of one or more of these clauses, wherein the heat exchanger body defines a stress-reducing feature at the intersection of the first portion of the fluid passage and the plenum. 
     The heat exchanger of one or more of these clauses, wherein the heat exchanger body further defines a plurality of the fluid passages extending through the second surface such that the plurality of fluid passages is in fluid communication with the plenum, each fluid passage includes the first and second portions, each first portion intersecting the plenum at a corresponding intersection and defining a line of projection extending normal to the second surface, each second portion defining a line of projection extending normal to the first surface, each fluid passage further including a curved portion extending from the corresponding first portion to the corresponding second portion. 
     The heat exchanger of one or more of these clauses, wherein the intersections of the first portions of the plurality of the fluid passages and the plenum are non-uniformly arranged along the interior surface. 
     The heat exchanger of one or more of these clauses, wherein the intersections corresponding to a first set of the plurality of fluid passages are arranged in a first ring along the interior surface and the intersections corresponding to a second set of the plurality of fluid passages are arranged in a second ring along the interior surface, the second ring enclosing the first ring. 
     The heat exchanger of one or more of these clauses, wherein the second portions of the plurality of fluid passages are uniformly spaced apart within the heat exchanger body. 
     The heat exchanger of one or more of these clauses, wherein the plurality of fluid passages corresponds to a first plurality of passages through which a first fluid is configured to flow, the heat exchanger body further defining a second plurality of fluid passages through which a second fluid is configured to flow, the second plurality of fluid passages positioned relative to the first plurality of fluid passages such that the second fluid is in thermal communication with the first fluid. 
     The heat exchanger of one or more of these clauses, wherein the second portions of the first plurality of fluid passages are arranged in a plurality of rows and a plurality of columns. 
     The heat exchanger of one or more of these clauses, wherein the first portion, the second portion, and the curved portion of the fluid passage have a same diameter and a same cross-sectional shape. 
     The heat exchanger of one or more of these clauses, wherein the heat exchanger body is monolithic. 
     The heat exchanger of one or more of these clauses, wherein the plenum is spherical or conical. 
     A gas turbine engine, comprising: a compressor, a combustor, a turbine, and a heat exchanger in operative association with at least one of the compressor, the combustor, or the turbine, the heat exchanger comprising: a heat exchanger body including a first surface and a second surface oriented at least partially at an oblique angle relative to the first surface, the heat exchanger body defining a plenum extending between the first and second surfaces, the heat exchanger body further defining a fluid passage extending through the second surface such that the fluid passage is in fluid communication with the plenum, wherein the fluid passage includes first and second portions, the first portion intersecting the plenum at an intersection and defining a line of projection extending normal to the second surface, the second portion defining a line of projection extending normal to the first surface, each fluid passage further including a curved portion extending from the first portion to the second portion. 
     The gas turbine engine of one or more of these clauses, wherein the heat exchanger body defines a stress-reducing feature at the intersection of the first portion of the fluid passage and the plenum. 
     The gas turbine engine of one or more of these clauses, wherein the heat exchanger body further defines a plurality of the fluid passages extending through the second surface such that the plurality of fluid passages is in fluid communication with the plenum, each fluid passage includes the first and second portions, each first portion intersecting the plenum at a corresponding intersection and defining a line of projection extending normal to the second surface, each second portion defining a line of projection extending normal to the first surface, the fluid passage further including a curved portion extending from the corresponding first portion to the corresponding second portion. 
     The gas turbine engine of one or more of these clauses, wherein the intersections of the first portions of the plurality of fluid passages and the plenum are non-uniformly arranged along the interior surface. 
     The gas turbine engine of one or more of these clauses, wherein the intersections corresponding to a first set of the plurality of fluid passages are arranged in a first ring along the interior surface and the intersections corresponding to a second set of the plurality of fluid passages are arranged in a second ring along the interior surface, the second ring enclosing the first ring. 
     The gas turbine engine of one or more of these clauses, wherein the second portions of the plurality of fluid passages are uniformly spaced apart within the heat exchanger body. 
     The gas turbine engine of one or more of these clauses, wherein the plurality of fluid passages corresponds to a first plurality of passages through which a first fluid is configured to flow, the heat exchanger body further defining a second plurality of fluid passages through which a second fluid is configured to flow, the second plurality of fluid passages positioned relative to the first plurality of fluid passages such that the second fluid is in thermal communication with the first fluid. 
     The gas turbine engine of one or more of these clauses, wherein the second portions of the first plurality of fluid passages are arranged in a plurality of rows and a plurality of columns. 
     The gas turbine engine of one or more of these clauses, wherein the first portion, the second portion, and the curved portion of the fluid passage have a same diameter and a same cross-sectional shape.