Patent Publication Number: US-7217097-B2

Title: Cooling system with internal flow guide within a turbine blade of a turbine engine

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to turbine blades, and more particularly to the components of cooling systems located in hollow turbine 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, as shown in  FIG. 1 , 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, as shown in  FIG. 2 , 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. 
     Some conventional turbine blades incorporate serpentine cooling channels for directing cooling fluids through internal aspects of a turbine blade. Often times, the channels forming the cooling channels are nearly equal in cross-sectional area. The cooling channel proximate to the leading edge has a chordwise cross-section with a generally triangular shape. The apex of the triangular shaped cooling channel is the leading edge of the turbine blade. The configuration of the cross-sectional area negatively affects the distribution of cooling fluids to the leading edge and reduces the cooling fluid flow velocity as well as the internal heat transfer coefficient. 
     Other conventional cooling systems have attempted to overcome the negative impacts of the shape of the cross-section of the leading edge cooling channel by decreasing the size of the leading edge cooling channel relative to the downstream return cooling channel, as shown in  FIG. 2 . In short, the central rib has been shifted closer to the leading edge, thereby resulting in a leading edge cooling channel having a reduced cross-sectional area. The reduced cross-sectional area in the leading edge cooling channel increases the velocity of the cooling fluids, but causes the separation of cooling fluid flow in the tip region and a temperature increase at the blade tip. Therefore, while the reduced cross-sectional area of the leading edge cooling channel reduces the temperature at the leading edge, the temperature in the tip region has increased. Thus, a need exists for a cooling system for a turbine blade with a serpentine cooling channel that has increased heat transfer capabilities. 
     SUMMARY OF THE INVENTION 
     This invention relates to a turbine blade cooling system formed from at least one cooling channel having a flow guide positioned in the cooling channel extending from a first turn to a second turn in the cooling channel. In at least one embodiment, the cooling channel may be a configured as a serpentine cooling channel, such as, but not limited to, a triple pass serpentine cooling channel. The flow guide may include a first turn section positioned in a first turn of the cooling channel, a second turn section positioned in a second turn of the cooling channel, and a flow guide body extending from the first turn section to the second turn section. The flow guide eliminates blade tip section flow separation thereby greatly enhancing the blade tip region cooling and reducing blade tip turn pressure loss while providing support to the mid-chord region and improving cooling fluid flow characteristics through the blade root turn. The turbine blade may be formed from 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, and at least one serpentine cooling channel forming the cooling system in the blade. 
     The first turn section of the flow guide may be positioned in the first turn of the cooling channel such that a leading end of the flow guide may extend closer to the leading edge of the turbine blade. The first turn section, in at least one embodiment, may be formed from a section that is generally parallel to the tip of the blade and may include a radius portion that couples the first turn section to the flow guide body. In at least one embodiment, the second turn section, which is downstream from the first root turn section, may include a trailing end positioned closer to the trailing edge than the second rib forming a portion of the cooling channel. The second turn section may be formed in the shape of quarter circle or other configuration redirecting the flow of cooling fluids with minimal pressure loss. In at least one embodiment, the flow guide may be positioned in the cooling channel generally equidistant from the first and second ribs forming the cooling channel. 
     During operation, cooling fluids flow into the cooling system from the root. At least a portion of the cooling fluids enter the cooling channel and pass through an outflow section of the cooling channel at a high flow velocity, thereby generating a high internal heat transfer coefficient and impingement. The cooling flow is then divided into two flow streams as the cooling fluids encounter the leading end of the flow guide. A portion of the cooling fluids accelerates and enters the outer flow path and impinges on the inner surface of the blade tip. The cooling fluids also impinge onto the inner surface of the blade tip near the trailing edge of the blade before flowing in the direction of the blade root. The outer flow path may receive a disproportionately larger amount of the cooling fluids, which causes corners in the first turn to receive more cooling fluids. The cooling fluids flow on either side of the flow guide through the mid-chord region of the cooling channel. The flow guide provides support to the mid-chord region while directing the cooling fluids to the second turn. As the cooling fluids enter the second turn, the configuration of the flow guide in the root turn provides a smooth cooling flow for a large root turn, thereby reducing the root section turn loss. 
     An advantage of this invention is that the flow guide eliminates the cooling fluid separation problem that exists in conventional cooling channels and effectively cools the first turn of the cooling channel. 
     Another advantage of this invention is that flow guide reduces the blade tip turn pressure loss while providing mid-chord region support. 
     Yet another advantage of this invention is that the flow guide improves the cooling fluid flow characteristics through the turbine blade root turn. 
     Still another advantage of this invention is that the flow guide increases the amount of heat transfer in the cooling system by causing cooling fluids to impinge on the leading edge of the flow guide and to impinge on the aft corner of the turbine blade tip before exiting from the root turn. The combination of reduced cooling fluid flow separation and the impingement cooling greatly increase the cooling in the tip of the 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 conventional turbine blade having features according to the instant invention. 
         FIG. 2  is cross-sectional view, referred to as a filleted view, of the conventional turbine blade shown in  FIG. 1 . 
         FIG. 3  is a perspective view of a turbine blade having features according to the instant invention. 
         FIG. 4  is cross-sectional view, referred to as a filleted view, of the turbine blade shown in  FIG. 3  taken along line  4 — 4 . 
         FIG. 5  is a partial cross-sectional view of the turbine blade shown in  FIG. 4  taken along line  5 — 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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, the turbine blade cooling system  10  is directed to a cooling system  10  formed at least from a cooling channel  14 , as shown in  FIG. 2 , positioned between two or more walls forming a housing  16  of the turbine blade  12 . In at least one embodiment, the cooling channel  14  may be formed from a serpentine cooling chamber, and may be, as shown in  FIGS. 4 and 5 , a triple pass cooling chamber. The cooling system  10  may include a flow guide  11  positioned in the cooling channel  14  for enhancing tip region cooling, reducing turbine blade tip turn pressure loss, providing mid-chord region  13  support, and improving flow characteristics in the blade root turn  15 . 
     As shown in  FIG. 3 , the turbine blade  12  may be formed from a generally elongated blade  18  coupled to the root  20  at the platform  22 . Blade  18  may have an outer wall  24  adapted for use, for example, in a first stage of an axial flow turbine engine. Outer wall  24  may having a generally concave shaped portion forming pressure side  26  and a generally convex shaped portion forming suction side  28 . 
     The cooling channel  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  18  and out one or more orifices  30  in the blade  18  to reduce the temperature of the blade  18 . As shown in  FIG. 3 , the orifices  30  may be positioned in a tip  32 , a leading edge  34 , or a trailing edge  36 , or any combination thereof, and have various configurations. The channel  14  may be arranged in various configurations, and the cooling system  10  is not limited to a particular flow path. 
     The cooling system  10 , as shown in  FIG. 4 , may be formed from a cooling channel  14 , such as a serpentine cooling channel for directing cooling fluids through the turbine blade  12  to remove excess heat to prevent premature failure. A flow guide  11  may be positioned within the cooling channel  14  to enhance the flow of cooling fluids through the cooling channel  14 . In the embodiment shown in  FIG. 4 , the flow guide  11  may be used to enhance the flow of cooling fluids through a first turn  38 , a mid-chord region  13 , and a second turn  40 , which may be referred to as a root turn. 
     In the embodiment shown in  FIG. 4 , the first turn  38  of the cooling channel  14  is positioned proximate to the tip  32 , and the second turn  40  is a blade root turn  15  positioned proximate to the root  20  and platform  22 . The flow guide  11  may extend from the first turn  38  of the channel  14  to a second turn  40  of the channel  14 . A first turn section  42  of the flow guide  11  may be positioned in the first turn  38  of the channel  14 , and a second turn section  44  of the flow guide  11  may be positioned in the second turn  40 . A body  45  of the flow guide  11  may be positioned between the first and second turn sections  42 ,  44  and in the mid-chord region  13  of the turbine blade  12 . The body  45  may couple the first and second turn sections  42 ,  44  together. The flow guide  11  may also extend from a first inner surface  56  forming a portion of the cooling system  10  to a second inner surface  58  generally opposite the first inner surface  56 . 
     In at least one embodiment, as shown in  FIG. 4 , the first turn section  42  of the flow guide  11  may include a leading end  46  that may extend closer to the leading edge  34  of the turbine blade  12  than a first rib  48 . Similarly, the second turn section  44  of the flow guide  11  may include a trailing end  50  that may extend closer to the trailing edge  36  of the turbine blade  12  than a second rib  52 . The first turn section  42  may extend generally parallel to the tip  32  of the blade  12  and include a radius portion  54  that couples the first turn section  42  to the flow guide body  45 . The second turn section  44  may be formed in the shape of a quarter-circle in at least one embodiment. In at least one embodiment, the flow guide  11  may be positioned in the cooling channel  14  generally equidistant from the first and second ribs  48 ,  52  forming the cooling channel  14 . 
     The cooling channel  14  may or may not include protrusions  64 , which may also be referred to as trip strips or turbulators, extending from surfaces forming the chamber  14  for increasing the efficiency of the cooling system  10 . The protrusions  64  prevent or greatly limit the formation of a boundary layer of cooling fluids proximate to the surfaces forming the cooling channel  14 . The protrusions  64  may or may not be positioned generally parallel to each other and may or may not be positioned equidistant from each other throughout the cooling channel  14 . The protrusions  64  may be aligned at an angle greater than zero relative to a general direction of cooling fluid flow through the cooling system  10 . The protrusions  64  may also be aligned generally orthogonal to the flow of cooling fluids through the cooling channel. In at least one embodiment, there exist a plurality of protrusions  64  positioned throughout the cooling channel  14 . 
     The cooling channel  14  may also include a contaminant release orifice  66  at the tip  32  for releasing contaminants that may be in the cooling fluids flowing from the root  20 . The contaminant release orifice  66  may have any appropriate size. 
     During operation, cooling fluids flow into the cooling system  10  from the root  20 . At least a portion of the cooling fluids enter the cooling channel  14  and pass through an outflow section  60  of the cooling channel  14  at a high flow velocity, thereby generating a high internal heat transfer coefficient and impingement. The cooling flow is then divided into two flow streams as the cooling fluids encounter the leading end  46  of the flow guide  11 . A portion of the cooling fluids accelerates and enters the outer flow path  62  and impinges on the inner surface of the blade tip. The cooling fluids also impinge onto the inner surface of the blade tip near the trailing edge of the blade before flowing in the direction of the blade root. The outer flow path  62  may receive a disproportionately larger amount of the cooling fluids, which causes corners in the first turn  38  to receive more cooling fluids. The flow guide  11  eliminates the cooling fluid separation problem that exists in conventional cooling channels and effectively cools the first turn  38  of the cooling channel  14 . The combination of reduced fluid flow separation and the impingement cooling greatly increase the cooling in the tip  32  of the blade  12 . 
     The cooling fluids flow on either side of the flow guide  11  through the mid-chord region  13  of the cooling channel  14 . The flow guide  11  provides support to the mid-chord region  13  while directing the cooling fluids to the second turn  40 . As the cooling fluids enter the second turn  40 , the configuration of the flow guide in the root turn  15  provides a smooth cooling flow for a large root turn, thereby reducing the root section turn loss. 
     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.