Abstract:
A turbine blade for a turbine engine having a cooling system with at least one serpentine cooling channel in internal aspects of the turbine blade. The serpentine cooling channel includes at least one root turn proximate to a root of the turbine blade. The root turn may have a generally rectangular shape and may account for reduced pressure losses relative to conventional curved root turns. One or more refresh holes may be positioned in a rib proximate to the root turn to provide the root turn with cooling fluids that have bypassed the first and second legs of the serpentine cooling channel.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention is directed generally to turbine blades, and more particularly to hollow turbine blades having internal cooling channels for passing cooling fluids, such as air, to cool the blades.  
       BACKGROUND  
       [0002]     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.  
         [0003]     Typically, turbine blades, as shown in  FIG. 1 , are formed from a root portion and a platform at one end and an elongated portion forming a blade that extends outwardly from the platform. 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.  
         [0004]     Conventional turbine blades may have one or more root turns, as shown in  FIG. 2 , which are located proximate to the root. Conventional root turns are typically curved elements of the flow path that change the direction of cooling fluid flow about 180 degrees in a serpentine formation in the root. While a conventional root turn successfully redirects cooling fluid flow from flowing spanwise towards a root to flowing spanwise towards the blade tip, a conventional root turn causes the cooling fluids flowing through the conventional root turn to undergo a significant pressure loss. Such a pressure loss often causes undesirable hot spots to develop in portions of the turbine blades. Thus, an internal cooling system having reduced pressure loss cooling fluid turns is needed.  
       SUMMARY OF THE INVENTION  
       [0005]     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 the turbine blade. The turbine blade may be a generally elongated blade having a leading edge, a trailing edge, a tip at a first end, a root coupled to the blade at an end generally opposite the first end for supporting the blade and for coupling the blade to a disc, at least one cavity forming a cooling system in the blade, and at least one outer wall defining the cavity forming at least a portion of the cooling system. The cooling system includes at least one serpentine cooling channel for directing cooling fluids through internal aspects of the turbine blade.  
         [0006]     The serpentine cooling channel may be formed from a first leg extending generally from the root towards the blade tip, a second leg in communication with the first leg and extending towards the root, and a third leg in communication with the second leg through a root turn and extending generally towards the tip. The root turn is configured to reduce the pressure loss associated with conventional root turns. For instance, the root turn may be formed from a first rib extending from the root spanwise towards the tip and separating the first and second legs, a second rib extending from the root towards the tip and forming a portion of the third leg, and a third rib extending between the first and second ribs. In at least one embodiment, the third leg may be substantially straight. The third rib may be positioned generally orthogonal to the first and third ribs. In other embodiments, the third rib may be positioned nonorthogonally to the first or second rib, or both. In at least one embodiment, the first, second, and third ribs form a generally rectangular root turn. The root turn may have different sizes, but in at least one embodiment, the root turn has a spanwise length that is at least as long as about half of a length of the second leg of the serpentine channel.  
         [0007]     The turbine blade cooling system may also include one or more refresh holes extending between the first leg and the second leg and positioned proximate to the root turn to direct cooling fluid into the upstream portion of the root turn. The refresh hole may have a bell shaped inlet and a straight outlet. The refresh hole may also be positioned relative to a direction in which the cooling fluid is flowing through the second leg of the serpentine cooling channel such that the cooling fluid expelled from the refresh hole is directed into the root turn in the same general direction as the cooling fluid flowing through the root turn. For example, the refresh hole may be positioned between about 15 degrees and about 75 degrees relative to the direction of flow of the cooling fluid through the second leg, and, in at least one embodiment, may be positioned about 45 degrees relative to the direction of fluid flow.  
         [0008]     The root turn advantageously reduces the pressure loss coefficient associated with conventional root turns. In fact, the root turn of the instant invention reduces a pressure loss coefficient to about 0.6 in at least one embodiment, from about 2.0 experienced in conventional designs.  
         [0009]     Another advantage of the invention is the refresh holes reduce the total flow needed to cool a portion of a turbine blade because at least a portion of the cooling fluids do not pass through the first and second legs of the serpentine cooling channel; rather, some of the cooling fluids pass through the refresh hole and directly into the root turn. Thus, the fluid that passes through the refresh hole does not pick up heat from the first and second legs of the serpentine cooling channel. Therefore, cooling fluids are capable of being passed through the root turn and the third leg in reduced amounts, yet still accomplish the same amount of cooling.  
         [0010]     Yet another advantage of the invention is that the root turn is easier to manufacture than many conventional root turns.  
         [0011]     Still another advantage of the invention is that the angle at which cooling fluids are added to the root turn enables a greater amount of cooling fluid to be added to the root turn than in conventional root turns.  
         [0012]     These and other embodiments are described in more detail below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     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.  
         [0014]      FIG. 1  is a perspective view of a conventional turbine blade.  
         [0015]      FIG. 2  is a cross-sectional view of the conventional turbine blade shown in  FIG. 1  taken along section line  2 - 2 .  
         [0016]      FIG. 3  is a perspective view of a turbine blade having features according to the instant invention.  
         [0017]      FIG. 4  is cross-sectional view of the turbine blade shown in  FIG. 3  taken along section line  4 - 4 .  
         [0018]      FIG. 5  is a detail of the root turn shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     As shown in  FIGS. 3-5 , 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. 4 , positioned between outer walls  22 . Outer walls  22  form a housing  24  of the turbine blade  12 , as shown in  FIG. 3 . 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 . The turbine blade may also include a tip  36  generally opposite the root  16  and 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 have a generally concave shaped portion forming pressure side  26  and may have a generally convex shaped portion forming suction side  28 .  
         [0020]     The cavity  14 , as shown in  FIG. 4 , 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. 3 , the orifices  34  may be positioned in a leading edge  38 , a trailing edge  40 , the pressure side  26 , and the suction side  28  to provide film cooling. The orifices  34  provide a pathway from the cavity  14  through the outer wall  22 .  
         [0021]     As shown in  FIG. 4 , the cavity  14  forming the cooling system  10  may have at least one serpentine cooling channel  42 . The exemplary turbine blade shown in  FIG. 4  includes two serpentine cooling channels  42 ; however, for ease in discussion, only one of the serpentine cooling channels is described below. The serpentine cooling channel  42  shown in  FIG. 4  is a triple pass cooling channel  42 ; however, the invention is not limited to this configuration. Instead, the serpentine cooling channel  42  may be formed from cooling channels having other number of passes. The serpentine cooling channel  42  may be formed from a first leg  44  extending spanwise generally from the root  16  towards the tip  36 , a second leg  46  in communication with the first leg  44  and extending towards the root  16  from an end of the first leg  44  closest the tip  36 , and a third leg  48  in communication with the second leg  46  via a root turn  50  and extending generally towards the tip  36 . The first and second legs  44  and  46  may be separated by one or more ribs  52 . Likewise, second and third legs  46  and  48  may be separated by one or more ribs  54 .  
         [0022]     The root turn  50  may be formed from the rib  52  extending spanwise from the root  16  towards the tip  36  and separating the first and second legs  44  and  46 , a rib  56  extending spanwise from the root  16  towards the tip  36  and forming a portion of the third leg  48 , and a rib  58  extending between the rib  52  and the rib  56 . In at least one embodiment, the rib  56  may be substantially straight, as shown in  FIG. 4 . The rib  58  may, in at least one embodiment, be positioned generally orthogonal to ribs  52  and  56 . In another embodiment, the rib  58  may be positioned nonorthogonally relative to the ribs  52  and  56 . The root turn  50 , as extending spanwise from the rib  58  to the rib  54 , may have a spanwise length that is at least as long as about half of a spanwise length of the second leg  46  of the serpentine cooling channel  42 . In at least one embodiment, a mouth  59  of the second leg  46  has a cross-sectional area that is greater than or equal to the cross-sectional area of the third leg  48  proximate to the root turn  50 . This relationship establishes proper flow through the root turn  50 . If the cross-sectional area at mouth  59  is less than the cross-sectional area of the third leg  48 , then the cooling fluid flowing through the mouth  59  undergoes a sudden expansion that causes flow separation, recirculation, and pressure loss. Further, the flow of cooling fluids may not be able to fill the third leg  48  downstream of the root turn  50  when the cross-sectional area at mouth  59  is less than the cross-sectional area of the third leg  48 .  
         [0023]     The turbine blade cooling system  10  may also include one or more refresh holes  60 , as shown in  FIGS. 4 and 5 . The refresh hole  60  may be positioned in the rib  52  proximate to an end of the rib  54  for injecting cooling fluid into the root turn  50  on an upstream side  62  of the root turn  50 . The refresh hole  60  may be aligned such that a centerline  64  of the refresh hole is at an angle α with a value between about 15 degrees and about 75 degrees relative to the flow of cooling fluids through the second leg  46 . In at least one embodiment, the angle α may be about 45 degrees. The refresh hole  60  may have a bell mouth inlet section  68  and a straight exit region  70  or a convergent section for pushing the flow. The mouth section  68  may be positioned to draw cooling fluids from the cavity  14  before the cooling fluid enters the serpentine cooling channel  42 , which provides cooling fluids to the root turn  50  that have yet to pick up heat from the outer walls  22  of the turbine blade  20 .  
         [0024]     By including the refresh hole  60  proximate to the mouth  59  on the upstream portion of the root turn  50 , the cooling fluids passing through the refresh hole  60  influence the cooling fluids flowing through the second leg  46  and into the root turn  50 . In fact, the refresh hole  60  in the root turn  50  reduces the pressure loss compared to conventional designs. The refresh hole  60  enables cooling fluids to bypass the first and second legs  44  and  46  and therefore enter the root turn  16  at a lower temperature than had the cooling fluids flowed through the first and second legs  44  and  46 .  
         [0025]     In operation, cooling fluids flow into the cooling cavity  14  through the root  16 . A portion of the cooling fluids enter the first leg  44 , pass into the second leg  46 , and pass into the root turn  50 . Simultaneously, cooling fluids pass through the refresh hole  60  and mix with the cooling fluids flowing from the second leg  46 . The elimination of the conventional root turn geometry shown in  FIG. 2  eliminates the constraint on the cooling fluid flow through a serpentine cooling channel, which allows the cooling fluid to form a free stream tube in the root turn  50 . The embodiment shown in  FIG. 4  has been shown to reduce pressure loss coefficient from 2.0 to about 0.6 as compared with a conventional root turn shown in  FIG. 2 .  
         [0026]     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.