Abstract:
A cooling system for a turbine airfoil of a turbine engine having suction side platform cooling channels and pressure side platform cooling channels for cooling hot spots in a platform attached to a turbine blade. The cooling system may include one or more pressure side platform cooling chambers having a diffusion slot for cooling downstream platforms on the suction side of the turbine blade. The diffusion slots reduce the velocity of the cooling fluids released from the platform to increase the capacity of the film cooling of downstream platforms.

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to turbine airfoils, and more particularly to cooling systems in hollow turbine airfoils. 
     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 having a platform at one end and an elongated portion forming a blade that extends outwardly from the platform coupled to the root portion. 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 a blade 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. Thus, a need exists for a cooling system capable of providing sufficient cooling to turbine airfoils. 
     Conventional cooling systems positioned in platforms of turbine airfoils typically include internal cooling channels. While these cooling channels reduce the temperature of portions of the platform, there are several drawbacks. For instance, the use of film cooling for the entire blade platform requires that the supply pressure of the cooling air at the blade dead rim cavity be higher than the peak blade platform external gas side pressure, which induces a high leakage flow around the blade attachment region and impacts performance. In addition, conventional designs often include cooling channels extending from the platform edge into the cooling cavities of the airfoil, which causes unacceptable stress levels at the internal airfoil and platform cooling cavities, thereby yielding a low blade life. Furthermore, conventional platform cooling systems often create localized hot spots proximate to the pressure side of the airfoil and proximate to the suction side, further reducing the blade life. Thus, there exists a need for a turbine blade with a platform cooling system that overcomes these shortcomings. 
     SUMMARY OF THE INVENTION 
     This invention is directed to a turbine airfoil cooling system for a turbine airfoil used in turbine engines. In particular, the turbine airfoil cooling system includes a plurality of internal cavities positioned between outer walls of the turbine airfoil. The cooling system may include a plurality of platform cooling channels positioned in a platform of the turbine airfoil. In particular, the platform may include one or more suction side platform cooling channels positioned proximate to a suction side of the turbine airfoil and one or more pressure side platform cooling channels positioned proximate to a pressure side of the turbine airfoil. The pressure side platform cooling channels may include one or more diffusion slots extending through a side edge of the platform to cool an adjacent turbine airfoil via film cooling. Such a configuration of cooling fluids creates a double use of cooling fluids that improves the overall platform cooling efficiency, reduces the platform metal temperature and reduces cooling fluid consumption. 
     The turbine airfoil may be formed, in general, from a generally elongated, hollow airfoil having a leading edge, a trailing edge, a tip section at a first end, a root coupled to the airfoil at an end generally opposite the first end for supporting the airfoil and for coupling the airfoil to a disc and a platform at the intersection between the root and the generally elongated, hollow airfoil and extending generally orthogonal to a longitudinal axis of the generally elongated, hollow airfoil. The airfoil may include a cooling system formed from at least one cavity in the elongated, hollow airfoil. 
     The cooling system may include one or more suction side platform edge cooling channels in the platform and extending generally along a first outer edge of the platform on a suction side of the generally elongated, hollow airfoil. One or more suction side platform cooling channels may be positioned in the platform and may extend from the at least one suction side platform edge cooling channel to a downstream edge of the platform generally along the suction side of the generally elongated, hollow airfoil. The cooling system may, in one embodiment, include a plurality of suction side platform edge cooling channels positioned generally parallel to each other and tangential to at least a portion of the suction side of the elongated airfoil. 
     The cooling system may also include one or more pressure side platform cooling channels in the platform and extending generally along an outer edge of the platform on a pressure side of the generally elongated, hollow airfoil. In at least one embodiment, the cooling system may include a plurality of pressure side platform cooling channels extending from the upstream edge toward the downstream edge but terminating before passing under the airfoil. The pressure side platform cooling channels may be positioned generally parallel to each other or in other configurations. One or more, or all of the pressure side platform cooling channels may include a diffusion slot extending at an acute angle from the at least one pressure side platform cooling channel to a second side edge of the platform on the pressure side of the generally elongated, hollow airfoil that is generally opposite to the first side edge. The diffusion slots may be positioned adjacent to each other along the second side edge between an upstream edge to the downstream edge. The diffusion slots may have a ratio of the cross-sectional area of the exhaust opening relative to the cross-sectional area of the inlet opening that is generally between about 2 to 1 and about 7 to 1, and may be about 5 to 1. The pressure side platform cooling channels may include a length to diameter ratio of between about 25 to 1 and about 70 to 1. The diffusion slot may be positioned to direct cooling fluids in close proximity and generally tangential to the suction side of an adjacent turbine blade to create film cooling on the outer surface of the platform of the adjacent turbine blade. 
     During use, cooling fluids may flow into the cooling system from a cooling fluid supply source. More particularly, cooling fluids may pass into the suction side platform edge cooling channel through an inlet and into the pressure side platform cooling channel through an inlet. The cooling fluids may pass through the suction side platform edge cooling channel and into the suction side platform cooling channels, where the cooling fluids reduce the temperature of the platform and local hot spot. The cooling fluids may be exhausted through the downstream edge of the platform. 
     The cooling fluids may also flow through the pressure side platform cooling channel where the temperature of the local hot spot is reduced. The cooling fluids may flow into the diffusion slots where the velocity of the cooling fluids is reduced. The cooling fluids may then be released from the diffusion slots of the pressure side platform cooling channel through the exhaust openings. The cooling fluids may form a layer of film cooling air immediately proximate to the outer surface of the platform. This configuration of the cooling system cools the platform with both external film cooling and internal convection. This double use of cooling fluids improves the overall platform cooling efficiency, reduces the platform metal temperature and reduces cooling fluid consumption. 
     An advantage of this invention is that the diffusion slots of the pressure side platform cooling channels, together with the suction side platform cooling channels, create a double use of cooling fluids that cooling internal aspects of the platform with convective cooling and an external surface of the platform with convective film cooling. Such use of the cooling fluids increases the efficiency of the cooling fluids and reduces the temperature gradient of the platform across its width. 
     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 airfoil having features according to the instant invention. 
         FIG. 2  is a cross-sectional view of the turbine airfoil shown in  FIG. 1  taken along line  2 - 2 . 
         FIG. 3  is a perspective view of a diffusion slot of a pressure side platform cooling channel. 
         FIG. 4  is a cross-sectional view of the turbine airfoil shown in  FIG. 1  taken along line  2 - 2  in which the turbine airfoil is positioned adjacent to another turbine airfoil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-4 , this invention is directed to a turbine airfoil cooling system  10  for a turbine airfoil  12  used in turbine engines. In particular, the turbine airfoil cooling system  10  includes a plurality of internal cavities  14 , as shown in  FIG. 2 , positioned between outer walls  16  of the turbine airfoil  12 . The cooling system  10  may include a plurality of platform cooling channels  18  positioned in a platform  20  of the turbine airfoil  12 . In particular, the platform  20  may include one or more suction side platform cooling channels  22  positioned proximate to a suction side  24  of the turbine airfoil  12  and one or more pressure side platform cooling channels  26  positioned proximate to a pressure side  28  of the turbine airfoil  12 . The pressure side platform cooling channels  26  may include one or more diffusion slots  30  extending through a side edge  32  of the platform  20  to cool an adjacent turbine airfoil via film cooling. 
     As shown in  FIG. 1 , the turbine airfoil  12  may be formed from a generally elongated, hollow airfoil  34  coupled to a root  36  at the platform  20 . The turbine airfoil  12  may be formed from conventional metals or other acceptable materials. The generally elongated airfoil  34  may extend from the root  36  to a tip section  38  and include a leading edge  40  and trailing edge  42 . The generally elongated airfoil  34  may have an outer wall  16  adapted for use, for example, in a first stage of an axial flow turbine engine. Outer wall  16  may form a generally concave shaped portion forming pressure side  28  and may form a generally convex shaped portion forming suction side  24 . The platform  20  may extend from the airfoil  34 , as shown in  FIG. 2 , in particular, the platform  20  may extend upstream from the airfoil  34  to form an upstream edge  44 , downstream to form a downstream edge  46 , and outwardly to form a first side edge  48  and a second side edge  50 . 
     The cooling system  10 , as shown in  FIGS. 2-3 , may include one or more suction side platform cooling channels  22  positioned proximate to a suction side  24  of the turbine airfoil  12  and one or more pressure side platform cooling channels  26  positioned proximate to a pressure side  28  of the turbine airfoil  12 . The platform cooling channels  22 ,  26  may have a generally cylindrical cross-section or may have cross-sections with other appropriate configurations. The platform cooling channels  22 ,  26  may be positioned to reduce the temperature of local hot spot  52  in the platform  20  proximate to an intersection of the suction side  24  and the platform  20  by the trailing edge  42  and local hot spot  54  in the platform  20  proximate to an intersection of the pressure side  28  and the platform  20 . In particular, the cooling system  10  may include one or more suction side platform cooling channels  22 . One of the suction side platform cooling channels  22  may be a suction side platform edge cooling channel  56  that extends generally from a position proximate to the upstream edge  44  to the downstream edge  46  generally parallel to the first side edge  48 . One or more suction side platform cooling channels  22  may extend from the at least one suction side platform edge cooling channel  56  to the downstream edge  46  of the platform  20  generally along the suction side  24  of the generally elongated, hollow airfoil  34 . In at least one embodiment, the cooling system  10  may include a plurality of suction side platform cooling channels  22 , such as, but not limited to, three suction side platform cooling channels  22 , as shown in  FIG. 2 . The suction side platform cooling channels  22  may be positioned generally tangential to a portion of the suction side  24  of elongated airfoil  34  and may be aligned with each other. In at least one embodiment, the suction side platform cooling channels  22  may be parallel to each other. The suction side platform cooling channels  22  may exhaust cooling fluids through openings  58  in the downstream edge  46  of the platform  20 . 
     The cooling system  10  may also include one or more pressure side platform cooling channels  26  positioned proximate to a pressure side  28  of the turbine airfoil  12 . The pressure side platform cooling channels  26  may extend from proximate the upstream edge  44  of the platform  20  toward the downstream edge  46 . The pressure side platform cooling channels  26  may terminate before passing under the elongated airfoil  34 . One or more of the pressure side platform cooling channels  26  may include a diffusion slot  30  extending from the pressure side platform cooling channels  26  to the second side edge  50 . In at least one embodiment, the cooling system  10  may include a plurality of pressure side platform cooling channels  26 , such as, but not limited to three pressure side platform cooling channels  26 . The pressure side platform cooling channels  26  may have a generally circular cross-section or may have a cross-section with an alternative configuration. The pressure side platform cooling channels  26  may have a length to diameter ratio of between about 25 to 1 and about 70 to 1. The higher the length to diameter ratio, the more effective the cooling channel is. Higher length to diameter ratios provide more internal convective area for cooling as well as high internal heat transfer coefficients. 
     The diffusion slots  30  may be configured as shown in  FIG. 3 . In particular, the diffusion slots  30  may transition from a circular inlet opening  60  to a generally rectangular exhaust opening  62 . A ratio of the cross-sectional area of the exhaust opening  62  to the cross-sectional area of the inlet opening  60  may be generally between about 2 to 1 and about 7 to 1. In at least one embodiment, the ratio of a cross-sectional area taken at the exhaust opening  62  relative to the cross-sectional area of the inlet opening  60  is generally about 5 to 1. The diffusion slot may have a height to In addition, the thin cross-sectional area of the exhaust opening  62  exhausts the spent cooling fluid effectively to provide a uniform layer of cooling fluids to cool the second side edge  50  as well as outer surfaces of a platform of an adjacent turbine airfoil  64 , as shown in  FIG. 4 . 
     The suction side platform cooling channels  22  or the pressure side platform cooling channels  26 , or both, may include a plurality of trip strips  70 , as shown in  FIG. 2 , for enhancing the turbulence in the channels  22 ,  26 . The trip strips  70  may be positioned at various angles relative to the direction of flow. 
     During use, cooling fluids may flow into the cooling system  10  from a cooling fluid supply source (not shown). More particularly, cooling fluids may pass into the suction side platform edge cooling channel  56  through inlet  66  and into the pressure side platform cooling channel  26  through inlet  68 . The cooling fluids may pass through the suction side platform edge cooling channel  56  and into the suction side platform cooling channels  22 , where the cooling fluids reduce the temperature of the platform  20  and local hot spot  52 . The cooling fluids may be exhausted through the downstream edge  46  of the platform  20 . 
     The cooling fluids may also flow through the pressure side platform cooling channel  26  where the temperature of the local hot spot  54  is reduced. The cooling fluids may flow into the diffusion slots  30  where the velocity of the cooling fluids is reduced. The cooling fluids may then be released from the diffusion slots of the pressure side platform cooling channel  26  through the exhaust openings  62 . The cooling fluids may then impinge on a side surface of an adjacent turbine airfoil  64  and may form a layer of film cooling air immediately proximate to the outer surface of the platform. This configuration of the cooling system  10  cools the platform with both external film cooling and internal convection. This double use of cooling fluids improves the overall platform cooling efficiency, reduces the platform metal temperature and reduces cooling fluid consumption. 
     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.