Abstract:
An adaptive cooling structure comprises a mounting support, a liner, and a spacer. The mounting support has a coolant aperture for directing cooling air through the support. The liner has a first surface facing away from the mounting support and a second surface facing towards the support. The liner is coupled to the mounting support, and the spacer is positioned between the support and the liner. The positioning of the spacer creates a chamber between the mounting support and the liner, thus allowing the cooling air to impinge on the second surface of the liner. The liner wall is configured to deflect away from the mounting support to expand the chamber, thus allowing the cooling air to further impinge on the second surface of the liner.

Description:
BACKGROUND 
       [0001]    The present invention relates to cooling systems, and in particular, to a system and method for adaptive impingement cooling for use in hot environments such as those found in gas turbine engines. 
         [0002]    Gas turbine engines operate according to a continuous Brayton cycle where a pressurized air and fuel mixture is ignited in a combustor to produce a flowing stream of hot gas. The air is compressed, used for combustion, expands through a turbine, and finally exits the engine. Some gas turbine engines also include an augmentation system downstream of the turbine, where fuel is also introduced and ignited to increase thrust. Most often, the temperature of the primary air is higher than the melting temperatures of the materials that form the combustor, turbine, and augmentation system components. As a result, adequate cooling is integral to the function of gas turbine engines. 
         [0003]    It is common to combine the benefits of both impingement cooling and film cooling in gas turbine engines. This combination of impingement and film cooling is particularly useful in parts such as combustors and augmentation systems where local hot spots develop. Current practice is to design impingement cooling structures neglecting the deformation that occurs in local hot spots as the temperature in the hot spots increases. As a result, impingement cooling effectiveness decreases as the deformation develops, causing hot spots to become even hotter. Cooling effectiveness should be the highest at local hot spots. 
       SUMMARY 
       [0004]    An adaptive cooling structure comprises a mounting support, a liner, and a spacer. The mounting support has a coolant aperture for directing cooling air through the support. The liner has a first surface facing away from the mounting support and a second surface facing towards the support. The liner is coupled to the mounting support, and the spacer is positioned between the support and the liner. The positioning of the spacer creates a chamber between the mounting support and the liner, thus allowing the cooling air to impinge on the second surface of the liner. The liner wall is configured to deflect away from the mounting support to expand the chamber, thus allowing the cooling air to further impinge on the second surface of the liner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a simplified cross-sectional view of an embodiment of a gas turbine engine which employs the adaptive impingement cooling system and method of the present invention. 
           [0006]      FIG. 2  is a partial isometric view of an embodiment of the adaptive cooling structure of the present invention. 
           [0007]      FIG. 3  is a cross-sectional view of the embodiment of the adaptive cooling structure in  FIG. 2  at a non-hot spot location. 
           [0008]      FIG. 4  is a cross-sectional view of the embodiment of the adaptive cooling structure in  FIG. 2  at a hot spot location. 
           [0009]      FIG. 5  is a graph showing preferred ranges of impingement effectiveness for designing the adaptive cooling structure of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is a simplified cross-sectional view of mixed flow turbofan engine  10  which can employ the adaptive impingement cooling system and method of the present invention. Turbofan engine  10  includes augmentation system  12 , fan duct  14 , drive fan  16 , low pressure compressor  18 , high pressure compressor  20 , combustor  22 , high pressure turbine  24 , low pressure turbine  26 , and exhaust nozzle  28 . Drive fan  16  and low pressure compressor  18  are driven by low pressure turbine  26  with shaft  30 . High pressure compressor  20  is driven by high pressure turbine  24  with shaft  32 . High pressure compressor  20 , combustor  22 , high pressure turbine  24  and shaft  32  comprise the core of turbofan engine  10 . Augmentation system  12  includes augmenter duct  34  and augmenter liner  36 . 
         [0011]    Ambient air A Ambient  enters turbofan engine  10  at inlet  38  through drive fan  16 . Drive fan  16  is rotated by low pressure turbine  26  to accelerate A Ambient  thereby producing a major portion of the thrust output of turbofan engine  10 . Accelerated A Ambient  is divided into two streams of air: primary air A P  and secondary air A S . Secondary air A S , also known as bypass air, passes into fan duct  14  where it passes on to augmentation system  12 . Primary air A P , also known as hot air, is a stream of air that is directed first into low pressure compressor  18  and then into high pressure compressor  20 . Pressurized primary air A P  is then passed into combustor  22  where it is mixed with a fuel supply and ignited to produce the high energy gases used to turn high pressure turbine  24  and low pressure turbine  26 . Combusted primary air A P  and secondary air A S  are passed through augmentor duct  34  and into augmentation system  12  where a secondary combustion process can be carried out. Augmentation liner  36  prevents heat damage to augmentation system  12  and turbofan engine  10 . Exhausted air A Ex  exits turbofan engine  10  through exhaust nozzle  28 . The adaptive cooling structure of the present invention can be used in combustor  22  or augmentation system  12 . 
         [0012]    Referring now to  FIG. 2 , adaptive cooling structure  40 , such as augmentation liner  36  in augmentation system  12  or a heat shield in combustor  22  ( FIG. 1 ), is exposed directly to hot air A p . Adaptive cooling structure  40  includes liner  42  and mounting support  44 . Liner  42  is affixed to mounting support  44  by fastening means  46  such as threaded studs, bolts, rivets, welds, or other suitable fastening means. Liner  42  includes liner wall  48  with one or more film apertures  50 . Liner wall  48  has first surface  52  facing away from the mounting support  44  and second surface  54  facing towards mounting support  44 . Liner wall  48  may be made from a high temperature, cast, forged or sheet material such as nickel or cobalt for example. First surface  52  may also include one or more layers of thermal barrier coating (TBC)  56 , such as a metallic or ceramic material, for improved insulation from hot air A p . Thermal gradient lines  58  depict the temperature differential across first surface  52  and indicate that hot spot location  60  is present in the area of liner  42 . Spallation of TBC layer  56  is also indicative of the presence of hot spot location  60 . Mounting support  44  includes one or more coolant apertures  62 . 
         [0013]    Coolant apertures  62  in mounting support  44  direct cooling air A C , such as pressurized air bled from compressor  18  or  20  ( FIG. 1 ), to second surface  54  of liner  42 . Coolant apertures  62  are perpendicular to the flow of hot air A p . In an alternative embodiment, coolant apertures  62  can be angled to the flow. Cooling air A C  provides cooling to reduce the operating temperature of mounting support  44  as it flows through coolant apertures  62 . Cooling air A C  exits coolant apertures  62 , flows between mounting support  44  and liner wall  48 , impinging on second surface  54 . Cooling air A C  exits liner  42  through film apertures  50  in liner wall  48 , and provides film cooling of first surface  52 . In an alternative embodiment, liner  42  is porous instead of having film apertures  50 , and cooling air A C  exits liner  42  through the pores. 
         [0014]    The present invention combines the benefits of both impingement cooling and film cooling and is particularly useful in parts such as combustor  22  and augmentation system  12  ( FIG. 1 ) where local hot spots develop. When liner wall  48  of adaptive cooling structure  40  is exposed to hot air A p , hot spot location  60  causes liner wall  48  to deflect away from mounting support  44  (as seen in  FIG. 4 ). Impingement cooling has parameters which when engineered can provide an increased impingement rate upon deflection of liner wall  48 . Thus, the present invention configures these parameters to accommodate such deflections as ignoring these parameters results in a less efficient cooling structure. 
         [0015]      FIG. 3  is a cross-sectional view of adaptive cooling structure  40  taken at a non-hot spot location along line  3 - 3  of  FIG. 2 . Liner  42  of adaptive cooling structure  40  includes mounting post  64 . Mounting post  64  with fastening means  46  is surrounded by spacer  66  and extends from second surface  54  of liner wall  48  through mounting support  44 . Nut  68  secures mounting post  64  to mounting support  44  via fastening means (threads)  46 . Spacer  66 , such as a washer or other suitable spacer, creates chamber  70  between mounting support  44  and liner  42  for impingement cooling. Chamber  70  has distance L between mounting support  44  and liner  42 . Coolant apertures  62  have a circular cross section with diameter D. In other embodiments, coolant apertures  62  can have a non-circular cross section with effective diameter D. 
         [0016]    Adaptive cooling structure  40  is directly exposed to hot air Ap. Cooling air A C  flows through coolant apertures  62  and enters chamber  70 , impinging on second surface  54 . Cooling air A C  exits first surface  52  through film apertures  50  in liner wall  48 , forming a film. Film apertures  50  have a circular cross section, but can have a non-circular cross section or can be flared. Film apertures  50  are angled with the flow of hot air A P . In alternative embodiments, film apertures  50  can be at another angle or can be perpendicular to the flow. The location of coolant apertures  62  is staggered in relation to film apertures  50 . In alternative embodiments, the location of coolant apertures  62  can be aligned with film apertures  50  or completely independent of the location of film apertures  50 . 
         [0017]    In impingement cooling a ratio L/D of distance L to diameter D of approximately three provides a preferred impingement heat transfer coefficient. When hot spot location  60  causes liner wall  48  to deflect away from mounting support  44  (as seen in  FIG. 4 ), distance L increases and ratio L/D increases as a result. Thus, the present invention is designed to accommodate the deformation by configuring adaptive cooling structure  40  with a ratio L/D lower than three. For adaptive cooling structure  40 , employing both impingement cooling and film cooling, the preferred as-fabricated ratio L/D is in the range between approximately two and three, and more specifically 2.5. The configuration of the present invention thus results in increased impingement cooling effectiveness upon deformation in the hot spot, where it is most needed. 
         [0018]      FIG. 4  is a cross-sectional view of adaptive cooling structure  40  taken at a hot spot location along line  4 - 4  of  FIG. 2 . Liner wall  48  is deflected away from mounting support  44  due to extreme heat caused by hot spot location  60 . Hot spot location  60  is exacerbated by an area of spalled TBC layer  56 . The deflection of liner wall  48  expanded chamber  70 , increasing distance L to L+ΔL at hot spot location  60  and in turn increasing ratio L/D of distance L to diameter D of coolant apertures  62 . 
         [0019]    Cooling air A C  flows through coolant apertures  62  and enters chamber  70 , impinging on second surface  54 . Cooling air A C  exits first surface  52  through film apertures  50  in liner wall  48 , forming a film. Impingement effectiveness is increased at hot spot location  60  as a result of the deflection of liner  48  away from mounting support  44 . As discussed in relation to  FIG. 3 , the fabrication of adaptive cooling structure  40  with a ratio L/D lower than the preferred ratio of three provides for increased impingement effectiveness when the deflection of liner wall  48  at hot spot location  60  increases distance L to L+ΔL. Thus, the preferred increased ratio L/D resulting from the deflection of liner wall  48  is between three and 3.5, which results in a preferred impingement heat transfer coefficient. In alternative embodiments, the increased ratio L/D ratio can be between approximately one and four or between two and four. 
         [0020]      FIG. 5  is a graph of ratio L/D versus impingement effectiveness H including preferred impingement effectiveness range  72 . If as-fabricated adaptive cooling structure  40  has ratio L/D in range  74 , less than approximately three, the deflection of liner wall  48  in hot spot location  60  will increase the impingement effectiveness to range  72 . If as-fabricated adaptive cooling structure  40  were to have ratio L/D equal to or greater than three, the deflection of liner wall  48  in hot spot location  60  would result in decreased impingement effectiveness range  76 . Thus, the present invention is specifically designed so the deflection of liner wall  48  results in ratio L/D in preferred impingement effectiveness range  72 . Impingement effectiveness range  72  can have L/D of between one and four, between two and four, or between 2.5 and 3.5. As discussed in relation to  FIG. 3 , the preferred as-fabricated range  74  has ratio L/D of between approximately two and three, but can be anything less than three. In one embodiment, decreased impingement effectiveness range  76  has ratio L/D of anything above four. 
         [0021]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.