Abstract:
A method and apparatus for cooling a fluid in a bypass gas turbine engine involves directing the fluid to the bypass duct of the engine to allow for heat exchange from the fluid to bypass air passing through the bypass air duct.

Description:
FIELD OF THE INVENTION 
   The present invention relates to gas turbine engines, and more particularly to a cooling apparatus for cooling of fluid used in a bypass gas turbine engine. 
   BACKGROUND OF THE INVENTION 
   Lubricating oil used in aircraft gas turbine engines must be cooled. Without proper cooling, poor cooling and/or lubrication of gear and bearings results which may cause problems for engine operation. In addition to employing conventional radiator-type oil coolers, the prior art also describes directing oil through inlet guide vanes or support struts to achieve a cooling benefit from air ingested by the engine. 
   Nevertheless, there is still a need for improvement of the lubricating oil cooling apparatus for gas turbine engines. 
   SUMMARY OF THE INVENTION 
   One object of the present invention is to provide a cooling apparatus for cooling of fluid used in a bypass gas turbine engine. 
   In accordance with one aspect of the present invention, there is a cooling apparatus provided for cooling of a fluid in a bypass gas turbine engine, which comprises a heat exchanger having a fluid passageway mounted to at least one wall of a bypass duct of the engine. The fluid passageway is in fluid communication with a source of the fluid to be cooled and the heat exchanger is in thermal contact with air passing through the bypass duct. 
   In accordance with another aspect of the present invention, there is a gas turbine engine provided, which comprises a bypass duct adapted to direct bypass air through the engine. The engine further comprises a fluid passageway provided on the bypass duct. The fluid passageway is in fluid communication with an oil system of the gas turbine engine and has thermal contact with the air passing through the bypass duct. 
   In accordance with a further aspect of the present invention, there is a method provided for cooling a fluid in a bypass gas turbine engine, which comprises a step of directing the fluid to flow directly along a surface defining a periphery of a bypass duct of the engine to thereby permit heat exchange between the fluid and bypass air passing through the bypass duct. 
   The present invention advantageously provides a cooling apparatus and method for cooling, for example, the lubricating oil used in a bypass gas turbine engine in an effective manner, and the cooling apparatus is light weight and relatively simple. 
   Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will now be made to the accompanying drawings, showing by way of illustration preferred embodiments, in which: 
       FIG. 1  is a schematic cross-sectional view of a bypass gas turbine engine, showing an exemplary application of the present invention; 
       FIG. 2  is an isometric view of the outer bypass duct of  FIG. 1  incorporating one embodiment of the present invention; 
       FIG. 3  is an enlarged partial isometric view of  FIG. 2 ; and 
       FIG. 4  is a partial schematic cross-sectional view of the bypass as turbine engine of  FIG. 1 , showing an alternative location of the heat exchanger according to another embodiment of the present invention. 
   

   It should be noted that throughout the appended drawings, like features are identified by like reference numerals. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A bypass gas turbine engine seen generally in  FIG. 1  includes a housing nacelle  10 , a low-pressure spool assembly seen generally at  12  which includes a fan  11 , a low-pressure compressor  13  and a low-pressure turbine  15 , a high-pressure spool assembly seen generally at  14  which includes a high-pressure compressor  17 , a high-pressure turbine  19  and a gear  21 , a combustor  23  and an accessory-drive assembly  25 . An annular bypass duct  43  is defined between an inner bypass duct wall  44  and an outer bypass duct wall  39 . A stream of bypass air which is compressed by the fan  11 , is directed through the annular bypass duct  43  and discharged therefrom to produce thrust. 
   The engine has a lubricating system (not indicated) including a pump  29  and a heat-exchanger  45  mounted in this embodiment, to the outer bypass duct wall  39 . The heat exchanger  45  is connected in fluid communication with the lubricating system of the engine to allow relatively hot oil to flow therethrough and be thereby cooled by the fast moving stream of bypass air passing through the annular bypass duct  43 . 
   Referring to  FIGS. 2 and 3 , the outer bypass duct wall  39  is defined by an annular body  47  preferably made of sheet metal or other suitable metal configuration. Metal is preferred to provide good heat transfer properties. The front end of the annular body  47  has an opening with a radially extending flange  49  to be connected to an intermediate case  46  which is further connected to a fan case  50  (see  FIG. 1 ). The rear end of the annular body  47  has a radially extending flange  51  to be connected with an engine exhaust duct  48  (see  FIG. 1 ). A cooler  53 , in this example comprised of a piece of sheet metal with a depressed portion  55  fabricated preferably in a sheet metal stamping or other metal forming process, is provided. The depressed portion  55  is preferably formed as a labyrinth-like fluid passageway  54  or serpentine or tortuous passageway  54  which is defined between the cooler  53  and the annular body  47  of the outer bypass duct wall  39 , to thereby configure heat exchanger  45 . The cooler  53  is preferably attached at the rear end of the annular body  47 . 
   The cooler  53  is preferably sealingly mounted to the outer bypass duct wall  39 , for example by welding, such that a fluid in fluid passageway  54  is directed over the surface of the outer bypass duct wall  39 . Direct contact between the flowing fluid and outer bypass duct wall  39  permits heat exchange. 
   Preferably, a pair of tube fittings used as connectors are welded in fluid communication the fluid passageway  54 , thereby forming an inlet  57  and an outlet  59  of the fluid passageway  55 . The inlet  57  is preferably in fluid communication with a source of the lubricating oil to be cooled, for example, from a bearing cavity  61  of a main shaft of the engine, or a gear arrangement (not shown), etc., preferably including an oil pump (not shown). The outlet  59  is preferably in fluid communication with a fluid return device, such as an oil tank  63  or oil scavenging system. 
   Referring to  FIGS. 1-3 , the heat exchanger  45  is preferably integrally attached to the outer surface of the outer bypass duct wall  39 , thereby being positioned adjacent but outside the annular bypass duct  43  and thereby thermally contacting the fast-moving stream of bypass air flowing through the annular bypass duct  43 . Heat is exchanged from the heat exchanger  45  to the fast-moving stream of bypass air in duct  43 . 
   The cooling of the heat exchanger  45  can be altered by altering the size and/or configuration and/or placement of the heat exchanger  45 . Advantageously, there is a relatively large surface of the annular body of the outer bypass duct wall  39  which is available for use in conjunction with the heat exchanger  45 . 
   Heat exchanger  45  can be mounted to inner bypass duct wall  44 . Heat exchanger  45  can be placed outside of the flow in bypass duct  43  (i.e as depicted in  FIG. 1 ) or can be provided directly in the flow passing through bypass duct  43  (i.e as depicted in  FIG. 4 ). The configuration of  FIG. 1  is preferred to minimize air flow losses and flow noise by minimizing air flow path disturbances in bypass duct  43  caused by heat exchanger  45 . The configuration of  FIG. 1  also reduces the possibility that oil (or whatever fluid is to be cooled) can leak into the bypass flow. 
   The heat exchanger  45  can be formed in any appropriate shape and can be mounted in any suitable fashion. For example, the heat exchanger  45  need not be serpentine, and/or may be attached by a metal band around the annular body  47  of the outer bypass duct wall  39 , and/or may form a discontinuous ring around the engine and define a discontinuous annular fluid passageway between the metal band and the outer bypass duct wall  39 . Another embodiment (not shown) comprises a metal tube(s) mounted to the outer bypass duct wall  39 . The heat exchanger  45  may be completely contained, and need not necessarily require co-operation from the bypass duct to contain the fluid to be cooled, as cooler  53  does above. 
   The engine case and bypass arrangement can be of any suitable type, as well. 
   Still other modifications to the above-described embodiments of the present invention will be apparent to those skilled in the art upon reading the present disclosure, and such modifications are intended to be within the scope of the appended claims. The foregoing description is therefore intended to be exemplary rather than limiting, and the scope of the invention is intended to be limited solely by the appended claims.