Abstract:
A heat exchanger apparatus includes: (a) an airfoil having opposed pressure and suction sides, a root, a tip, and spaced-apart leading and trailing edges; and (b) a plenum integrally formed within the airfoil which is configured to receive a flow of circulating working fluid; and (c) inlet and outlet ports communicating with the plenum and an exterior of the airfoil.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to gas turbine engines and methods for oil cooling in such engines. 
         [0002]    Gas turbine engines are commonly provided with a circulating oil system for lubricating and cooling various engine components such as bearings, gearboxes, electrical generators, and the like. In operation the oil absorbs a substantial amount of heat that must be rejected to the external environment in order to maintain the oil at acceptable temperatures. Electric generator oil cooling typically uses one or more air-to-oil heat exchangers (referred to as “air cooled oil coolers” or “ACOCs”), sometimes in series with fuel-to-oil heat exchangers and fuel return-to-tank systems (“FRTT”) in a complex cooling network. 
         [0003]    Aircraft gas turbine engines have been evolving to “hotter” generator and lubrication systems with more rigorous duty cycles. Physically packaging large ACOCs is more challenging because of smaller engines, increased need for acoustic treatment, and more controls and accessories hardware. Furthermore, transient operational modes can create “pinch points” because of lack of sufficient cooling air flow. for the new generation of electrical starter-generators creates a unique challenge to cooling oil during transient start-modes, when there is insufficient air to cool the system. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    These and other shortcomings of the prior art are addressed by the present invention, which provides a gas turbine engine airfoil structure which includes an integral heat exchanger apparatus. 
         [0005]    According to one aspect of the invention, a heat exchanger apparatus includes: (a) an airfoil having opposed pressure and suction sides, a root, a tip, and spaced-apart leading and trailing edges; and (b) a plenum integrally formed within the airfoil which is configured to receive a flow of circulating working fluid; and (c) inlet and outlet ports communicating with the plenum and an exterior of the airfoil. 
         [0006]    According to another aspect of the invention, a guide vane apparatus for a gas turbine engine includes: (a) a stationary airfoil having opposed pressure and suction sides, a root, a tip, and spaced-apart leading and trailing edges, wherein the tip is coupled to a stationary annular casing; and (b) a plenum integrally formed within the airfoil which is configured to receive a flow of circulating working fluid; and (c) inlet and outlet ports communicating with the plenum and an exterior of the airfoil. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0008]      FIG. 1  is a schematic cross-sectional view of a gas turbine engine incorporating a heat exchanger system constructed according to an aspect of the present invention; 
           [0009]      FIG. 2  is an enlarged view of a portion of the gas turbine engine of  FIG. 1 ; 
           [0010]      FIG. 3  is a side view of an outlet guide vane constructed in accordance with an aspect of the present invention; 
           [0011]      FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 3 ; 
           [0012]      FIG. 5  is a perspective view of the outlet guide vane of  FIG. 3 , with a cover removed to show the internal construction thereof; 
           [0013]      FIG. 6  is a perspective view of an alternative outlet guide vane, with a cover removed to show the internal construction thereof; 
           [0014]      FIG. 7  is a perspective view of an alternative outlet guide vane, with a cover removed to show the internal construction thereof; and 
           [0015]      FIG. 8  is a partially-sectioned perspective view of an outlet guide vane and a fluid coupling apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 1 and 2  depict a gas turbine engine  10  incorporating an OGV heat exchanger apparatus constructed according to an aspect of the present invention. while the illustrated example is a high-bypass turbofan engine, the principles of the present invention are also applicable to other types of engines, such as low-bypass, turbojet, etc. The engine  10  has a longitudinal center line or axis A and an outer stationary annular casing  12  disposed concentrically about and coaxially along the axis A. The engine  10  has a fan  14 , booster  16 , compressor  18 , combustor  20 , high pressure turbine  22 , and low pressure turbine  24  arranged in serial flow relationship. In operation, pressurized air from the compressor  18  is mixed with fuel in the combustor  20  and ignited, thereby generating combustion gases. Some work is extracted from these gases by the high pressure turbine  22  which drives the compressor  18  via an outer shaft  26 . The combustion gases then flow into a low pressure turbine  24 , which drives the fan  14  and booster  16  via an inner shaft  28 . The inner and outer shafts  28  and  26  are rotatably mounted in bearings  30  which are themselves mounted in a fan frame  32  and a turbine rear frame  34 . 
         [0017]    The fan frame  32  has a central hub  36  connected to an annular fan casing  38  by an annular array of radially extending fan outlet guide vanes (“OGVs”)  40  which extend across the fan flowpath. In this example, each of the OGVs  40  is both an aero-turning element and a structural support for the fan casing  38 . In other configurations, separate members are provided for the aerodynamic and structural functions. While the concepts of the present invention will be described using the OGVs  40  as an example, it will be understood that those concepts are applicable to any stationary airfoil-type structure within the engine  10 . 
         [0018]    Some or all of the fan OGVs  40  in the engine  10  include heat exchangers integrated into their structure.  FIGS. 3-5  illustrate one of the fan OGVs  40  in more detail. The OGV comprises an airfoil  42  having a leading edge  44 , a trailing edge  46 , a tip  48 , a root  50 , a convex suction side  52 , and a concave pressure side  54 . An arcuate inner platform  56  is disposed at the root  50  of the airfoil  42 . 
         [0019]    The airfoil  42  is assembled from a body  58  and a cover  60 . The body  58  and the cover  60  are both made from a material with suitable strength and weight characteristics for the intended application. One example of a suitable alloy is a 7000 series aluminum alloy, in particular a 7075 aluminum alloy. The body  58  is a unitary component which may be produced by forging, for example. It incorporates a plenum  62  (see  FIG. 4 ) configured as a pocket formed in its pressure side  54 . Alternatively or in addition, the plenum  62  could also comprise a pocket formed in the suction side  52 . There is a continuous ledge  64  disposed around the periphery of the plenum  62  that receives the periphery of the cover  60 . The cover  60  may be secured to the ledge  64  by any means which provides a secure, leak-free joint, such as adhesive bonding, fusion welding, or a solid-state bond such as that produced by friction stir welding. The cover  60  may further be secured to structures of the airfoil  42  within the perimeter of the plenum  62  (e.g. walls, ribs, etc., described in more detail below) in order to prevent fluid leakage between various channels and flow paths defined within the airfoil  42 . This ledge  64  has an average width “W” which is selected to be as narrow as possible to save weight and material, while still leaving enough material for a full penetration weld through the cover  60 . In the illustrated example, the width W is less than about 1.27 cm (0.5 in.) and is preferably about 0.89 cm (0.35 in.) 
         [0020]    The cover  60  is a unitary component including inner and outer surfaces which fits down into the plenum  62  so that the outer surface  65  is substantially flush with the pressure side  22  of the airfoil  42 . The outer surface  65  of the cover  60  forms a portion of the pressure side  22  of the airfoil  42 . In plan view, the cover  60  is generally rectangular with radiused corners. It serves only as an aerodynamic element and may have a relatively small thickness, for example approximately 2 mm (0.08 in.). To provide an acceptable weld joint, the periphery of the cover  60  is fitted to the periphery of the plenum  62  with a small lateral tolerance “L”, for example about 0.127 mm (0.005 in.) 
         [0021]    The plenum  62  provides a space within the OGV  40  for a flow of working fluid, for example lubrication oil. The plenum  62  is integral to the OGV  40 , or in other words, the plenum  62  is defined by the structure of the OGV  40  itself, rather than any intermediate structure, such as filler materials used in the prior art. In operation, this results in working fluid being in intimate contact with the inner surface of the skin of the 
         [0022]    OGV  40  so as to maximize heat transfer rate. The interior of the plenum  62 , i.e. its size, shape, surface texture, and arrangement of internal walls or other features, may be configured to maximize heat transfer between the working fluid and the OGV  40 , minimize pressure loses, and so forth. As used herein the term “plenum” refers to the entire volume available for flow of working fluid within the OGV  40 , regardless of whether it is configured as a unitary space or several smaller spaces. 
         [0023]    For example, as shown in  FIGS. 4 and 5  the interior of the plenum  62  is configured as a plurality of parallel channels  66  running in a generally radial (i.e. spanwise) direction and separated by walls or ribs. Groups of the channels  66  (for example five) may be arranged into serpentine “passes” which are shown schematically by the arrows labeled  68 . A four-passage arrangement is shown. The passes may be defined by channels integrally formed within the OGV  40  or by a tube or header structure external to the OGV  40 . The channels  66  may be formed, for example, by a machining process before the cover  60  is installed as described above. In the illustrated example, the width of each of the channels  66  is approximately 6.4 mm (0.25 in.). For ease of design, the number of channels  66  and their cross-sectional design may be selected so that the flow area of each pass  68  is substantially equal to a commonly available tubing size. 
         [0024]      FIG. 6  illustrates an OGV  140  incorporating an alternative plenum  162 . The plenum  162  includes a central septum  164  which runs in a generally spanwise direction in approximately a mid-chord location within the plenum  162 . A plurality of inner walls  166  extend forward and aft from the septum  164  at intervals along its length. A plurality of outer walls  168  extend inboard from the periphery of the plenum  162  at alternate spanwise locations relative to the inner walls  166 . Together, the septum  164  and inner and outer walls  166  and  168  define a serpentine flowpath which follows a generally “U”-shaped path through the plenum  162 . 
         [0025]      FIG. 7  illustrates yet another alternative OGV  240  incorporating an alternative plenum  262 . An array of first walls  264  lie in a first plane and extend across the plenum at a first acute angle. An array of second walls  266  lie underneath the first walls  264  in a second plane and extend across the plenum  262  perpendicular to the first walls  264 . Working fluid is introduced to the first plane and flows parallel to the first walls  264  until it reaches their ends, where it flows across to the second plane and parallel to the second walls  266 , thus generating a cross-flow action. 
         [0026]      FIG. 8  illustrates a structure for transferring working fluid to and from the OGV  40 . The structure will be explained with reference to the OGV  40  shown in  FIGS. 3-5 , with the understanding that the same structure is applicable to the alternative configurations described above. The tip  48  of the OGV  40  has inlet and outlet ports  72  and  74  formed therein, communicating with the plenum  62 . An inlet jumper tube assembly  76  is coupled to the inlet port  72 , and an outlet jumper tube assembly  78  is coupled to the outlet port  74 . The ports  72  and  74  are substantially identical in construction, accordingly only the inlet port  72  and its associated inlet jumper tube assembly  76  will be described in detail. The inlet port  72  has an opening  79  located at the outer face of the OGV  40 . The inner end of a generally cylindrical jumper tube  80  is received in the inlet port  72 . The jumper tube  80  spans the radial gap between the tip  48  of the OGV  40  and the fan casing  38  and passes through an opening in the fan casing  38 . The outer end of the jumper tube  80  is received in a hollow retainer  82 . Seals  84  and  86 , such as the illustrated “O”-rings, prevent leakage between the jumper tube-to-OGV and jumper tube-to-retainer interfaces, while permitting some relative motion between the OGV  40  and the fan casing  38 . The retainer  82  is secured to the outer surface of the fan casing  38 . in the illustrated example, the retainer  82  is clamped to the fan casing  38  using fasteners of a conventional type such as bolts (not shown) passing through holes  88  in the fan casing  38  and a mounting flange  90  of the retainer  82 . The outer end of the retainer  82  has a fluid fitting  92  installed therein, which in the illustrated example is an elbow. The fluid fitting  92  is connected in turn to a supply tube (not shown). 
         [0027]    In operation, hot working fluid from the engine (e.g. lubricating oil or accessory cooling oil) is ported to the inlet jumper tube assembly  76 . the working fluid flows through the plenum  62  where heat is removed from the fluid by transfer to the airflow surrounding the OGV (in this case fan bypass flow). The heated oil then passes out through the outlet jumper tube assembly  78  and back to the remainder of the oil system. The oil circulation flow through the OGVs  40  may be parallel or serial as dictated by the particular application. It will be understood that the oil system incorporates pumps, filters, lines, valves, tanks, and other equipment as needed to provide a flow of pressurized oil. Such components are well-known and therefore not illustrated here. 
         [0028]    Using the concepts described herein, turbine engine OGVs will incorporate an oil cooling function, in addition to aero-turning and structural functions. The oil cooling function is performed at the periphery of the vane to take advantage of the heat exchange along the pressure and suction sides of the airfoil and as such is This concept has several advantages. Among them are substantially lower oil pressure drop than prior art ACOCs, as well as lower noise levels, and a substantial weight savings from eliminating ACOCs and the associated engine “FRTT”. A significant improvement in specific fuel consumption (“SFC”) is expected as well. 
         [0029]    The foregoing has described an airfoil structure with integrated heat exchanger for a gas turbine engine and a method for its operation. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only.