Abstract:
A turbine engine cooling arrangement includes a core passage for receiving a core flow for combustion, a first airflow source including a first passage adjacent the core passage for conveying a first airflow, and a second airflow source including a second passage adjacent the first passage for conveying a second airflow. A heat exchanger is thermally connected with the first passage and the second passage for transferring heat between the first airflow and the second airflow.

Description:
BACKGROUND OF THE INVENTION 
     This disclosure relates to cooling arrangements and, more particularly, to an air-to-air cooling arrangement for a gas turbine engine. 
     Gas turbine engines are known and used for propulsion in vehicles, such as an aircraft. For example, a typical gas turbine engine includes a combustion section for combusting fuel and air to generate hot combustion gases. The combustion gases expand in a turbine section to provide rotational power that is used to propel the vehicle. The combustion gases are then discharged from of the engine through an exhaust nozzle. 
     Typically, the combustion is designed to occur in a particular temperature range to maximize the efficiency of the engine. However, the temperature at surfaces of engine components may be limited by the materials that are used to construct the engine. For example, the surface temperature in the combustor, turbine section, and exhaust nozzle cannot exceed the operating temperatures of the materials used to construct these components, although the temperature in the gas path of the combination gases may exceed this. 
     Accordingly, there is a need for a cooling method and arrangement that maintains the exhaust nozzle at a desirable temperature. 
     SUMMARY OF THE INVENTION 
     An example turbine engine cooling arrangement includes a core passage for receiving a core flow for combustion, a first airflow source including a first passage adjacent the core passage for conveying a first airflow, and a second airflow source including a second passage adjacent the first passage for conveying a second airflow. A heat exchanger is thermally connected with the first passage and the second passage for transferring heat between the first airflow and the second airflow. 
     In one example, a turbine engine includes a core passage having a combustion section and a turbine section for receiving a core flow for combustion. An engine inlet section divides inlet air into a first bypass flow and a second bypass flow. A first bypass passage is located radially outwards of the core passage for receiving the first bypass flow. A second bypass passage is located radially outwards of the first bypass passage for receiving the second bypass flow, and the heat exchanger is thermally connected with the first bypass passage and the second bypass passage for transferring heat therebetween. 
     An example method of providing cooling for use in a turbine engine includes the steps of establishing a core flow for combustion, a first airflow, and a second airflow. The first airflow includes a first temperature and a first pressure and the second airflow includes a second temperature that is lower than the first temperature and a second pressure that is lower than the first pressure. Heat is transferred from the first airflow to the second airflow to cool the first airflow. In one example, the cooled first airflow is used to maintain a desired temperature of an exhaust section of the turbine engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  illustrates selected portions of an example gas turbine engine. 
         FIG. 2  illustrates an example heat pipe for use in the gas turbine engine. 
         FIG. 3  illustrates another example heat pipe for use in the gas turbine engine. 
         FIG. 4  illustrates an example of one of the heat pipes. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates selected portions of an example gas turbine engine  10 , such as a gas turbine engine  10  used for propulsion. The gas turbine engine  10  is circumferentially disposed about an engine centerline  12 . In this example, the engine  10  includes an inlet section  13  having a first fan  14   a  and a second fan  14   b . A compressor section  16 , a combustion section  18 , and a turbine section  20  are located downstream from the inlet section  13 . 
     The fan  14   b  is decoupled from the fan  14   a , as disclosed for example in copending application Ser. No. 11/977,874 filed Oct. 26, 2007, now U.S. Pat. No. 8,028,513 issued on Oct. 4, 2011. For example, the fan  14   b  is mounted to an outer shroud (not shown) outboard of the fan  14   a  to enable the fans  14   a  and  14   b  to rotate at different speeds. In this example, the fan  14   a  is coupled in a known manner with the turbine section  20 , such as through a low spool shaft of the engine  10 . An electric drive may be used to drive the fan  14   b  at a different speed than the fan  14   a . In other examples, the engine  10  may be modified from the illustrated example, depending on the type of engine and its intended use. 
     As is known, air compressed in the compressor section  16  is mixed with fuel that is burned in the combustion section  18  to produce hot combustion stream that is expanded in the turbine section  20  to drive the fans  14   a  and  14   b .  FIG. 1  is a somewhat schematic presentation for illustrative purposes only and is not a limitation on the disclosed examples. 
     The example engine  10  includes a cooling arrangement  28  having a core passage  30 , a first airflow source  32 , and a second airflow source  34  that receive inlet air  37  that enters the engine  10 . In this example, the first airflow source includes a first bypass passage  39   a , and the second airflow source  34  includes a second bypass passage  39   b . The inlet section  13  divides the inlet air  37  between the core passage  30 , the first bypass passage  39   a , and the second bypass passage  39   b . The compressor section  16 , the combustion section  18 , and the turbine section  20  are included at least partially within the core passage  30 . In the disclosed example, the first bypass passage  39   a  is located radially outwards of the core passage  30  relative to the engine centerline  12 , and the second bypass passage  39   b  is located radially outwards of the first bypass passage  39   a  relative to the engine centerline  12 . 
     The core passage  30 , the first bypass passage  39   a , and the second bypass passage  39   b  each terminate at an engine exhaust section  36 , such as an exhaust nozzle. In this example, the engine exhaust section  36  includes a convergent section  38  and a divergent section  40  for discharging an exhaust flow from the core passage  30 . 
     The first bypass passage  39   a  includes a first outlet  42  located at the divergent section  40  and another outlet  44  located axially forward of the divergent section  40  at the convergent section  38 . Each of the outlets  42  and  44  of the first bypass passage  39   a  may include a plurality of film cooling slots  46  that provide a fluid connection between the first bypass passage  39   a  and the core passage  30 . 
     The second bypass passage  39   b  also includes an outlet  48  that is located at the divergent section  40  of the engine exhaust section  36  and that is axially aft of the outlets  42  and  44  of the first bypass passage  39   a . It is to be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
     The cooling arrangement  28  also includes a heat exchanger  54  that is thermally connected with the first bypass passage  39   a  and the second bypass passage  39   b . In this example, the heat exchanger  54  includes a plurality of heat pipes  56  each having one end that is at least partially within the first bypass passage  39   a  and another end that is at least partially within the second bypass passage  39   b . Alternatively, other types of heat exchangers may be used. Given this description, one of ordinary skill in the art will recognize suitable types of heat exchangers to meet their particular needs. 
     In operation, the engine  10  receives inlet air  37  into the inlet section  13 . The inlet section  13  divides the inlet air into a core flow  60 , a first airflow  62 , and a second airflow  64 . The core flow  60  flows through the core passage  30 , the first airflow  62  flows through the first bypass passage  39   a , and the second airflow  64  flows through the second bypass passage  39   b . The core flow  60  is utilized for combustion within the combustion section  18 . 
     The engine  10  utilizes the first airflow  62  and the second airflow  64  for cooling the engine exhaust section  36 . In the disclosed example, the first airflow  62  and the second airflow  64  have different associated air pressures and temperatures. For example, the first airflow  62  has a first temperature and a first pressure, and the second airflow  64  has a second temperature that is less than the first temperature and a second pressure that is less than the first pressure. The difference in temperature and pressure may be controlled using the fans  14   a  and  14   b , such as by controlling fan speed of each fan  14   a  and  14   b.    
     The first airflow  62  and the second airflow  64  stream over the heat pipes  56  of the heat exchanger  54 . The heat pipes  56  transfer heat from the first airflow  62  to the second airflow  64  to thereby cool the first airflow  62 . The cooled first airflow  62  is then discharged through the outlet  42  to cool the divergent section  40  of the engine exhaust section  36 . 
     In the illustrated example, the obstruction caused by the heat pipes  56  within the first bypass passage  39   a  causes a natural pressure loss of the first airflow  62 . The pressure loss provides the benefit of reducing liner blow-off loads to the divergent section  40 . In some instances, it may be possible to directly use the second airflow  64  for cooling; however, if the second pressure of the second airflow  64  is relatively low, it may not be suitable for direct cooling of the engine exhaust section  36 , for example. 
     In the illustrated example, a portion of the first airflow  62  is also discharged through the outlet  44  to cool the convergent section  38 . The second airflow  64  is discharged through the outlet  48  at the divergent section  40  to provide additional cooling of the divergent section  40 . 
     The disclosed cooling arrangement  28  thereby utilizes the different temperature of the first and second airflows in the heat exchanger  54  to provide cooled air to the divergent section  40  of the engine exhaust section  36 . Using air-to-air heat exchange in combination with the first and second bypass flows may provide the benefit of avoiding or eliminating heat exchangers that utilize somewhat more complex circulatory coolant systems. Additionally, the added cooling provided by the “cooled” first airflow  62  may permit the use of other materials within the engine exhaust section  36 . For example, the additional cooling may allow the use of lighter weight or less expensive alloy or organic composite materials. 
     As will now be described, at least the second airflow source  34  need not be a bypass passage as in the previous example.  FIG. 2  illustrates another example in which like components are represented with like reference numerals. In this example, a gas turbine engine  100  includes a second airflow source  134  having an external airflow scoop  102 . The external airflow scoop  102  extends radially outwards from an outer perimeter  104  of the engine  100 , such as on an outer cowl or nacelle. The external airflow scoop  102  is connected with a passage  106  that receives an inlet airflow  137  that flows around the outer perimeter  104 . 
     In operation, the inlet air  137  flows into the inlet section  13  and around the outer perimeter  104  of the engine  100 . The inlet section  13  divides the inlet air  137  into a core flow  60  and a first airflow  62 , and the external airflow scoop  102  directs at least a portion of the inlet airflow  137  into the passage  106  as a second airflow  164  that then flows over the heat pipes  56  of the heat exchanger  54 . 
     Similar to the example of  FIG. 1 , the first airflow  62  and the second airflow  164  have different associated air pressures and temperatures and stream over the heat pipes  56  of the heat exchanger  54  to subsequently cool the divergent section  40  of the engine exhaust section  36  as previously described. 
       FIG. 3  illustrates another example in which like components are represented with like reference numerals. In this example, a gas turbine engine  200  includes a second airflow source  234  having an auxiliary power unit  202 . For example, the auxiliary power unit  202  may be used to provide compressed air to start the engine  200 . In this regard, a passage  204   a  connects the auxiliary power unit  202  to the engine  200 . A valve  206  is disposed within the passage  204   a . The valve  206  is operative to direct flow through the passage  204   a  between the engine  200  and another passage  204   b  that is thermally connected with the heat exchanger  54 . 
     In operation, the inlet air  237  flows into the inlet section  13 , which divides the inlet air  237  into a core flow  60  and the first airflow  62 . The auxiliary power unit  202  produces a second airflow  262  that flows through the passage  204   a . When the valve  206  is in a first position, the second airflow  262  continues to flow through the passage  204   a  to the engine  200  for the starting function. However, when the valve  206  is moved to a second position, the second airflow  262  flows through the passage  204   b  and over the heat pipes  56  of the heat exchanger  54 . 
     Similar to the example of  FIG. 1 , the first airflow  62  and the second airflow  264  have different associated air pressures and temperatures and stream over the heat pipes  56  of the heat exchanger  54  to subsequently cool the divergent section  40  of the engine exhaust section  36  as previously described. 
     Thus, as disclosed by the examples herein, the heat exchanger  54  may be used in combination with the first airflow  62  from the first airflow source  32  and a second airflow (e.g.,  62 ,  162 , and  262 ) from a second airflow source (e.g.,  34 ,  134 , and  234 ) to cool the divergent section  40  of the engine exhaust section  36 , or even other sections of an engine. As can be appreciated, the source of the second airflow is not limited to any particular source and may be any airflow from any airflow source that is relatively cooler than the first airflow  60 . 
       FIG. 4  illustrates an example of one of the heat pipes  56 . In this example, the heat pipe  56  includes a sealed hollow tube  70  that contains a coolant  72 , such as water, ethylene glycol, methane, liquid sodium, or other suitable coolant. The heat pipe  56  includes a first end  74  that is thermally connected with the first bypass passage  32 , and a second end  76  that is thermally connected with the second bypass passage  34 . The interior of the heat pipe  56  defines a cooling circuit  78  for transporting the coolant  72  in an evaporated and liquid state. In the disclosed example, the heat pipe  56  includes a porous material  80  that facilitates transport of the coolant  72 , such as by using capillary forces. 
     Operationally, the coolant  72  transfers heat from the warmer first bypass flow  62  at the first end  74  to the relatively cooler second bypass flow  64  at the second end  76 . The coolant absorbs heat from the first bypass flow  62  and evaporates into vapor. The evaporated coolant  72  then moves through the open central portion of the heat pipe  56  toward the second end  76 . At the second end  76 , the second bypass flow  64  cools the evaporated coolant  72  and condenses it into a liquid, thereby rejecting the heat into the second bypass flow  64 . The porous material  80  then transports the condensed coolant  72  using capillary forces toward the first end  74  for another cooling cycle. In this manner, the coolant transfers the heat from the warmer first bypass flow  62  to the second bypass flow  64 . Additionally, the heat pipe  56  provides the benefit of passive heat transfer. That is, the heat exchanger  54  operates without mechanical assistance, such as without a mechanical pump or the like. 
     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 the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.