Patent Publication Number: US-6902372-B2

Title: Cooling system for a turbine blade

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to turbine blades, and more particularly to hollow turbine blades having an intricate maze of cooling channels for passing gases, such as air, to cool the blades. 
     BACKGROUND 
     Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures. In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures. 
     Typically, turbine blades are formed from a root portion at one end and an elongated portion forming a blade that extends outwardly from a platform coupled to the root portion at an opposite end of the turbine blade. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge. The inner aspects of most turbine blades typically contain an intricate maze of cooling channels forming a cooling system. The cooling channels in the blades receive air from the compressor of the turbine engine and pass the air through the blade. The cooling channels often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature. However, centrifugal forces and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots. Localized hot spots, depending on their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade. 
     Operation of a turbine engine results is high stresses being generated in numerous areas of a turbine blade. Some turbine blades have outer walls, referred to herein as housings, formed from double walls, such as an inner wall and an outer wall. Typically, cooling air flows through a cavity defined by the inner and outer walls to cool the outer wall. However, uneven heating in the inner and outer walls of a turbine blade still often exists. 
     Thus, a need exists for a turbine blade that effectively dissipates heat in a turbine blade. 
     SUMMARY OF THE INVENTION 
     This invention relates to a turbine blade capable of being used in turbine engines and having a turbine blade cooling system for dissipating heat from inner aspects of the blade. The turbine blade may be a generally elongated blade having a leading edge, a trailing edge, and a tip at a first end opposite a root for supporting the blade and for coupling the blade to a disc. The turbine blade may also include at least one cavity forming a cooling system. The cooling system may be defined in part by an outer wall defining the cavity and may include an impingement cooling system in the trailing edge of the blade. The impingement cooling system may be particularly suited for use in blades having conical tips, which often generate a greater amount of trailing edge tip vibration than blades having tips with other configurations. Even so, the cooling system may be used in turbine blades having tips with other configurations. 
     The impingement cooling system may include one or more first impingement ribs positioned generally parallel to the trailing edge of the elongated blade and in contact with the outer wall. The cooling system may also include one or more second impingement ribs oblique to the first impingement rib and extending from the first impingement rib toward the trailing edge. In addition, the cooling system may include one or more third impingement ribs oblique to the first impingement rib and intersecting the second impingement rib. The third impingement rib may extend from the first impingement rib toward the trailing edge of the elongated blade. Intersection of the third impingement rib with the second impingement rib creates at least one triangular cavity. In at least one embodiment, the turbine blade may include a plurality of triangular cavities in the trailing edge of the blade. 
     Orifices may be placed in the ribs to provide gas flow paths through the impingement cooling system, and in particular, through the plurality of triangular cavities. In at least one embodiment, the first impingement rib may include one or more orifices providing an opening into a triangular cavity through which cooling gases may pass and provide axial impingement cooling. The cooling system may also include one or more orifices in the second impingement rib for providing a gas flow path into a triangular cavity and provide oblique impingement cooling. In some embodiments, the cooling system may include one or more orifices in the third impingement rib and provide oblique impingement cooling. 
     In at least one embodiment, the cooling system may include three first impingement ribs identified as an outer impingement rib, a middle impingement rib, and an inner impingement rib. A plurality of second and third impingement ribs may extend from the inner impingement rib and may intersect each other, thereby forming a plurality of triangular cavities. Orifices in the first impingement ribs provide axial impingement cooling to the first impingement ribs, and the orifices in the second and third impingement orifices may provide oblique impingement cooling to these ribs. 
     The first, second, and third impingement ribs increase the cooling capacity of the cooling system in the trailing edge of the turbine blade because, in part, the ribs increase the convective surface upon which the turbine blade may release heat to the cooling gases flowing through the cooling system in the turbine blade. Not only do the ribs increase the cooling capacity of the turbine blade, but the impingement ribs also increase the stiffness of the turbine blade, thereby reducing trailing edge vibration of the turbine blade tip. 
     During operation, cooling gases flow from the root of the blade through inner aspects of the blade in a cooling system. At least a portion of the cooling gases entering the cooling system of the turbine blade through the base passes through the impingement orifices in the trailing edge of the blade. Cooling gases first pass through orifices in the first impingement rib and into a triangular cavity. The cooling gases are then passed through one or more orifices in the second and third impingement ribs. The cooling gases pass through the triangular cavities formed in the trailing edge and are exhausted through a plurality of orifices in the trailing edge of the turbine blade. 
     These and other embodiments are described in more detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention. 
         FIG. 1  is a perspective view of a turbine blade having features according to the instant invention. 
         FIG. 2  is cross-sectional view of the turbine blade shown in  FIGS. 1 and 4  taken along line  2 — 2 . 
         FIG. 3  is a cross-sectional view, referred to as a filleted view, of the turbine blade shown in  FIG. 1  taken along line  3 — 3 . 
         FIG. 4  is a cross-sectional view of the turbine blade shown in  FIG. 3  taken along line  4 — 4 . 
         FIG. 5  is a cross-sectional view of the turbine blade shown in  FIG. 4  taken along line  5 — 5 . 
         FIG. 6  is a partial cross-sectional view of the turbine blade shown in  FIG. 4  taken along line  6 — 6 . 
         FIG. 7  is a partial cross-sectional-view of the turbine blade shown in  FIG. 4  taken along line  7 — 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1–7 , this invention is directed to a turbine blade cooling system  10  for turbine blades  12  used in turbine engines. In particular, turbine blade cooling system  10  is directed to a cooling system  10  located in a cavity  14 , as shown in  FIG. 2 , positioned between two or more walls forming a housing  24  of the turbine blade  12 . As shown in  FIG. 1 , the turbine blade  12  may be formed from a root  16  having a platform  18  and a generally elongated blade  20  coupled to the root  16  at the platform  18 . Blade  20  may have an outer wall  22  adapted for use, for example, in a first stage of an axial flow turbine engine. Outer wall  22  may be formed from a housing  24  having a generally concave shaped portion forming pressure side  26  and may have a generally convex shaped portion forming suction side  28 . 
     The cavity  14 , as shown in  FIG. 2 , may be positioned in inner aspects of the blade  20  for directing one or more gases, which may include air received from a compressor (not shown), through the blade  20  and out one or more orifices  34  in the blade  20 . As shown in  FIG. 1 , the orifices  34  may be positioned in a tip  36 , a leading edge  38 , or a trailing edge  40 , or any combination thereof, and have various configurations. The cavity  14  may be arranged in various configurations. For instance, as shown in  FIG. 2 , the cavity  14  may form cooling chambers that extend through the root  16  and the blade  20 . In particular, the cavity  14  may extend from the tip  36  to one or more orifices (not shown) in the root  16 . Alternatively, the cavity  14  may be formed only in portions of the root  16  and the blade  20 . The cavity  14  may have various configurations capable of passing a sufficient amount of cooling gases through the elongated blade  20  to cool the blade  20 . As shown in  FIG. 2 , the cavity  14  may have be a triple pass serpentine cooling system. In other embodiments, the cavity  14  may be a five pass serpentine cooling system or any other configuration that adequately cools the elongated blade  20 . In addition, the cavity  14  is not limited to the configuration shown in  FIG. 2 , but may have other configurations. 
     The turbine blade cooling system  10  may include an impingement cooling system  42  in the trailing edge  40  of the elongated blade  20 . The impingement cooling system  42  may be formed from a plurality of ribs for directing cooling gases through the trailing edge  40  of the elongated blade  20  and removing heat from the elongated blade  20 . In particular, the impingement cooling system  42  may be formed from one or more first impingement ribs  44 . In at least one embodiment first impingement rib  44  may be positioned generally parallel to the trailing edge of the elongated blade  20  and may extend between an inner wall  46  and an outer wall  48 . As shown in  FIG. 4 , the impingement cooling system  42  may include three first impingement ribs  44 , which are identified as outer impingement rib  50 , inner impingement rib  52 , and middle impingement rib  54 . Each of the outer, inner, and middle impingement ribs  50 ,  52  and  54 , may be positioned generally parallel to each other. The impingement cooling system  42  is not limited to three first impingement ribs  44 , but may include other numbers of ribs  44 . 
     The impingement cooling system  42  may also include one or more second impingement ribs  56  oblique to the first impingement rib  44  and extending from the first impingement rib  44  toward the trailing edge  40 . The second impingement rib  56  may extend between the inner and outer walls  46  and  48  and may be positioned between about 45 degrees and about 75 degrees relative to the first impingement rib  44 . In at least one embodiment, the second impingement rib  56  may be about 60 degrees relative to the first impingement rib  44 . 
     The impingement cooling system  42  may also include one or more third impingement ribs  58  oblique to the first impingement rib  44 . The third impingement rib  58  may extend from the at least one first impingement rib  44  toward the trailing edge  40  and intersect the second impingement rib  56 , thereby forming a triangular cavity  60 . The third impingement rib  58  may be positioned between about 45 degrees and about 75 degrees relative to the first impingement rib  44 . In at least one embodiment, the third impingement rib  58  may be about 60 degrees relative to the first impingement rib  44 . The third impingement rib  58  may extend from the inner wall  46  to the outer wall  48  of the blade  20 . The third impingement rib  58  may extend from the first impingement rib  44  at an angle measured oppositely to the angle from which the second impingement rib  56  extend from the first impingement rib  44 , as shown in  FIG. 4 , so that the second and third impingement ribs  56  and  58  intersect. 
     An orifice  62  may be positioned in the first impingement rib  44  so as to provide a gas pathway through the first impingement rib  44  into the triangular cavity  60 . Orifice  62  enables axial impingement cooling to occur along the first impingement rib  44 . As shown in  FIG. 4 , the triangular cavity  60  may include a single orifice  62 ; however, in other embodiments, two or more orifices  62  may be located in the first impingement rib  44  proximate to a single triangular cavity  60  providing a plurality of gas pathways through the first impingement rib  44  into the triangular cavity  60 . 
     One or more orifices  64  may be located in the second impingement rib  56  to provide oblique impingement cooling to the blade  20 . Second impingement rib  56  may include one or a plurality of orifices  64  along the length of the second impingement rib  56 . The orifices  64  are preferably positioned in the second impingement rib  56  proximate to a triangular cavity  60 . The orifices  64  may be oblique relative to the inner wall  46  or to the outer wall  48 , as shown in  FIG. 6 . The orifices  64  may be positioned so that the air passing through the orifices  64  is directed towards the inner wall  46  and towards the outer wall  48  in an alternating fashion moving towards the trailing edge  40 . 
     In at least one embodiment, as shown in  FIG. 2 , the impingement cooling system  42  includes three first impingement ribs  44 , and a plurality of second and third impingement ribs  56  and  58  forming a plurality of triangular cavities  60 . Each triangular cavity  60  may include an orifice  62  in the first impingement rib  44 , an orifice  64  in the second impingement rib  56 , and an orifice  66  in the third impingement rib  58 . The orifice  62  in the first impingement rib  44  provides axial impingement cooling to the first impingement rib  44 , and orifices  64  and  66  provide oblique impingement cooling to the second and third impingement ribs  56  and  58 , respectively. Orifices  64  and  66  may be oblique relative to the inner wall  46  and to the outer wall  48 , as shown in  FIG. 6 . 
     In each triangle  60 , orifices  64  and  66  may be positioned obliquely relative to the inner or outer walls  46  and  48  so that the orifice  64  directs gases to contact the inner wall  46  and the orifice  66  directs gases to contact the outer wall  48 , or vice versa. In addition, as shown in  FIG. 7 , the orifices  64  and  66  may be aligned relative to the inner and outer walls  46  and  48  so that the gases alternate between being directed towards the inner wall  46  and the outer wall  48  as the gas flows through the first impingement ribs  44  towards the trailing edge  40 . In particular, in at least one embodiment, the orifices  64  and  66  may be arranged so that a first orifice  66  in a third impingement rib  58  directs gases toward the inner wall  46 , an orifice  64  in a second impingement rib  56  directs gases toward an outer wall  48 , and an orifice  66  in another third impingement rib  58  directs gases toward the inner wall  46  from upstream toward the trailing edge  40  downstream. The orifices  64  and  66  may be positioned at angles between about 30 degrees and 60 degrees relative to the outer wall  46 , and may preferably be about 45 degrees. This configuration removes heat from the turbine blade  12  by impinging the gases on the first, second, and third impingement ribs  44 , as the gases flow through the impingement cooling system  42 . 
     While  FIG. 4  shows each triangular cavity  60  having at least one orifice  62 ,  64 , and  66 , in each of the first, second, and third impingement ribs  44 ,  56 , and  58 , the impingement cooling system  42  is not limited to such a configuration. Rather, one or more of the triangular cavities  60  may include only two orifices in any combination of two ribs selected from the first, second, and third impingement ribs  44 ,  56 , and  58 . For instance, a triangular cavity  60  may include an orifice  62  in the first impingement rib  44  and an orifice in the second impingement rib  56 , but not the third impingement rib  58 . 
     Orifices  62  in the first impingement ribs  44  may be positioned relative to each other so that the orifices  62  in the outer impingement rib  50  are offset radially relative to the orifices  62  in the middle impingement rib  54 . Likewise, the orifices  62  in the inner impingement rib  52  may be offset radially relative to the orifices  62  in the middle impingement rib  54 . In other embodiments, the orifices  62  in the inner impingement rib  52  may be offset radially relative to the orifices  62  in the middle impingement rib  54  and the orifices  62  in the outer impingement rib  50 . 
     The first, second, and third impingement ribs  44 ,  56 , and  58  increase the stiffness of the elongated blade  20 . These ribs  44 ,  56 , and  58  minimize vibrations in the tip  36  of the turbine blade  20 . In addition, the first, second, and third impingement ribs  44 ,  56 , and  58  of the first impingement rib  44  and the second and third impingement ribs  56  and  58  increase the surface area of the cavity  14 , which increases the surface area available for convection in the turbine blade  20 . 
     During operation, a cooling gas enters the cavity  14  through the root  16 . The cooling gases pass through one or more pathways formed in the cavity  14  and cool the turbine blade  12 . At least a portion of the gases flowing into the cavity  14  pass into the impingement cooling system  42  in the trailing edge  40 . The cooling gases enter the impingement cooling system  42  through the orifices  62  in the first impingement rib  44  and enter triangular cavities  60 . The cooling gases mix in the triangular cavities  60  and pass through the orifices  64  and  66  in the second and third impingement ribs  56  and  58 , respectively, and are directed towards either the inner wall  46  or the outer wall  48 . The cooling gases are then discharged from the impingement cooling system  42  through one or more exhaust orifices  68  in the trailing edge. In at least one embodiment, the exhaust orifices  68  are in the pressure side  26  of the housing  24  of the blade  20 . 
     The impingement cooling system  42  is particularly suited, in part, for use in a turbine blade  12  having a conical tip  38 , which often generate a greater amount of trailing edge tip vibration than blades having tips with other configurations. Even so, the impingement cooling system  42  may be used in blades with tips having other configurations. 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.