Abstract:
A turbine blade for a turbine engine having an internal cooling system formed from at least one cavity for receiving cooling air from a turbine blade assembly, passing the cooling air through the internal cooling system, and expelling the cooling air through orifices in a leading edge forming a showerhead, orifices in a trailing edge and in other locations. The showerhead includes exhaust orifices extending at various angles relative to each other through an outer wall forming the turbine blade. The exhaust orifices may form rows of orifices that are offset generally orthogonally and generally parallel to a longitudinal axis of the blade. The exhaust orifices are configured to effectively cool the leading edge portion of the blade and to reduce the likelihood of cracking of the outer wall forming the leading edge.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention is directed generally to turbine blades, and more particularly to the cooling systems of turbine blades having internal cooling systems.  
       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 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 as shown in  FIGS. 2 and 3  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]     Typically, conventional turbine blades have a collection of exhaust orifices in the leading edge forming a showerhead for exhausting cooling gases onto the leading edge of the turbine blade. Many conventional configurations of the showerhead orifices have the orifices aligned in the same orientation. Aligning the orifices in the same orientation of the showerhead often leads to cracking of the leading edge, as shown in  FIG. 4 , which is often referred to as zipper effect cracking as the cracks extend between adjacent orifices radially along the leading edge. Thus, a configuration of orifices for a leading edge is needed that produces an effective film cooling gas distribution and reduces the likelihood of zipper cracks forming in the leading edge of the blade.  
       SUMMARY OF THE INVENTION  
       [0005]     This invention relates to a cooling system in a turbine blade capable of being used in turbine engines. The cooling system includes a plurality of exhaust orifices in a leading edge of the turbine blade forming a showerhead for providing film cooling gases to outer surfaces of the turbine blade. The exhaust orifices forming the showerhead may be positioned to reduce the likelihood of zipper effect cracking in the leading edge and to effectively cool the leading edge of the turbine blade.  
         [0006]     The turbine blade may be formed from a generally elongated blade having a leading edge, a trailing edge, and a tip at a first end. The blade may also include 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 of a turbine blade assembly. The blade may also include one or more cooling cavities extending from the root through a substantial portion of the blade generally along a longitudinal axis of the blade for supplying cooling gases from the root to various portions of the turbine blade. A plurality of exhaust orifices at various locations across the turbine blade enable cooling gases flowing through the cooling cavities to be exhausted from the blade and used in film cooling applications on the turbine blade.  
         [0007]     At least a portion of the exhaust orifices are positioned in the leading edge of the turbine blade forming a showerhead in which cooling gases from the cooling cavity is exhausted to be used in film cooling applications. The exhaust orifices extend from an outer surface of the turbine blade to the cooling cavity. The exhaust orifices form at least first and second rows of orifices positioned along the longitudinal axis of the blade. The first row of orifices may be offset from the second row of orifices orthogonal to the longitudinal axis of the blade. Some of the orifices forming the first row may extend through an outer wall of the turbine blade at a first angle relative to a longitudinal axis in a plane generally orthogonal to a chordwise direction, and other orifices forming the first row may extend through the outer wall at a second angle that differs from the first angle. In at least one embodiment, the first angle is measured moving from the longitudinal axis in a first direction in a plane generally orthogonal to a chordwise direction and the second angle is measured moving from the longitudinal axis in a second direction generally opposite to the first direction in a plane generally orthogonal to a chordwise direction. The first and second angles may or may not be equal, and may be between about five degrees and about 45 degrees. The second row may also be formed from orifices positioned at first and second angles relative to the longitudinal axis.  
         [0008]     The first and second rows may be formed from an alternating pattern of orifices positioned in the first and second angles relative to the longitudinal axis. Additional rows may also be placed in the alternating pattern. Positioning the first and second rows in the alternating pattern reduces the likelihood that the leading edge will suffer a crack, often referred to as a zipper crack, in the outer wall of the turbine blade, even if the orifices are placed in a high density configuration. The orifices forming the first and second rows may also be formed in the following repeating pattern: an orifice at the first angle relative to the longitudinal axis, an orifice positioned along the longitudinal axis, an orifice at the second angle relative to the longitudinal axis, an orifice positioned along the longitudinal axis, and an orifice at the first angle relative to the longitudinal axis.  
         [0009]     By positioning the exhaust orifices in the leading edge in these manners, the exhaust orifices provide more efficient convection on the leading edge and thereby reduce operating temperatures of the leading edge. In addition, these patterns of exhaust orifices increase the distances between adjacent exhaust orifices in the radial direction, which is along the longitudinal axis of the blade, and reduce the conduction distance between hot gas side surface in the chordwise direction, thereby increasing convection efficiency without compromising the strength of the leading edge. Instead, these patterns reduce the likelihood of zipper effect cracking along the leading edge.  
         [0010]     These and other embodiments are described in more detail below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     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.  
         [0012]      FIG. 1  is a perspective view of a conventional turbine blade.  
         [0013]      FIG. 2  is cross-sectional view of the turbine blade shown in  FIG. 1  taken along section line  2 - 2 .  
         [0014]      FIG. 3  is a partial cross-sectional detail view of the turbine blade taken at detail  3  in  FIG. 2 .  
         [0015]      FIG. 4  is a detail view of a leading edge shown in  FIG. 3  viewed in the direction of arrow  4 .  
         [0016]      FIG. 5  is a perspective view of a turbine blade of this invention.  
         [0017]      FIG. 6  is a cross-sectional view of the turbine blade shown in  FIG. 5  taken along section line  6 - 6 .  
         [0018]      FIG. 7  is a partial cross-sectional detail view of the turbine blade taken at detail  7  in  FIG. 6 .  
         [0019]      FIG. 8  is a partial cross-sectional view of the outer wall forming the leading edge shown in  FIG. 7  taken at section line  8 - 8 .  
         [0020]      FIG. 9  is a detail view of the leading edge of the turbine blade shown in  FIG. 7  as viewed in the direction of arrows  9 .  
         [0021]      FIG. 10  is a detail view of the leading edge of the turbine blade having an alternative configuration of exhaust orifices as shown in  FIG. 7  and viewed in the direction of arrows  9 .  
         [0022]      FIG. 11  is a detail view of the leading edge of the turbine blade having an alternative configuration of exhaust orifices as shown in  FIG. 7  and viewed in the direction of arrows  9 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     As shown in  FIGS. 5-11 , 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 formed from a cavity  14 , as shown in  FIG. 6 , positioned between two or more walls  24  of the turbine blade  12 . As shown in  FIG. 5 , 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 surface  22  adapted for use, for example, in a first stage of an axial flow turbine engine. Outer surface  22  may be formed from walls  24  having a generally concave shaped portion forming pressure side  26  and may have a generally convex shaped portion forming suction side  28 .  
         [0024]     The blade  20  may include one or more cooling channels  32 , as shown in  FIG. 6 , 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 exhausted out of the blade  20 . The cooling channels  32  are not limited to a particular configuration but may be any configuration necessary to adequately cool the blade  20 . In at least one embodiment, as shown in  FIG. 6 , the cooling channels  32  may include a plurality of channels  32  extending generally along a longitudinal axis  42  of the blade  20 . The blade  20  may be formed from a leading edge  34 , a trailing edge  36 , and a tip  38  at an end generally opposite to the root  16 .  
         [0025]     The leading edge  34  may include a plurality of exhaust orifices  44  forming a showerhead  46  for exhausting cooling air from the cooling channels  32  to flow along the outer surface  22  of the blade. The plurality of exhaust orifices  44  may form one or more rows of orifices  44 . In at least one embodiment, a first row of exhaust orifices  44  and a second row of exhaust orifices  50  may be formed. The exhaust orifices  44  may be positioned in a nonorthogonal position relative to an outer surface  22  of the blade  20 . For instance, as shown in  FIG. 8 , the exhaust orifices  44  may be positioned at an angle β of between about 20 degrees and about 35 degrees relative to the outer surface  22  of the blade  20 . The distance  3 D between adjacent exhaust orifices  44  along the longitudinal axis  42  may be about three times the diameter of the exhaust orifices  44 . The exhaust orifices  44  may be positioned such that air flowing from the root  16  through the cooling channels  32  radially outward toward the tip  38  may flow easily through the exhaust orifices  44 .  
         [0026]     The first row  48  and the second row  50  of orifices  44  may be offset relative to each other generally orthogonal to the longitudinal axis  42  of the blade  20  such that the first and second rows  48 ,  50  generally follow the longitudinal axis  42 . In at least one embodiment, as shown in  FIGS. 9-10 , a third row  52  may also be offset relative to each other generally orthogonal to the longitudinal axis  42  of the blade  20  such that the first and second rows  48 ,  50  generally follow the longitudinal axis  42 . In addition to the rows  48 ,  50 ,  52  being offset orthogonally relative to the longitudinal axis  42 , the first, second, and third rows  48 ,  50 ,  52  may be offset relative to each other along the longitudinal axis  42 . In other words, the first, second, and third rows  48 ,  50 ,  52  may be offset radially along the blade  20 .  
         [0027]     In one embodiment, as shown in  FIG. 9 , the first row  48  may be formed from exhaust orifices  44  positioned at different angles from each other relative to the longitudinal axis  42 . For instance, the first row  48  may be formed from exhaust orifices  44  at either a first angle α relative to the longitudinal axis  42  in a plane generally orthogonal to a chordwise direction or a second angle θ relative to the longitudinal axis  42  in a plane generally orthogonal to a chordwise direction. The first and second angles α, θ may have a value between about five degrees and about 45 degrees. As shown in  FIG. 9 , the first row  48  may include exhaust orifices  44  that alternate between being positioned at a first angle α and positioned at a second angle θ. The first angle α may be measured from the longitudinal axis  42  in a first direction, as indicated by an arrow on  FIG. 9  for the first angle α, in a plane generally orthogonal to a chordwise direction. The second angle θ may be measured from the longitudinal axis  42  in a second direction, as indicated by an arrow on  FIG. 9  for the second angle θ, in a plane generally orthogonal to a chordwise direction. In at least one embodiment, the first and second angles α, θ have equal or substantially equal values. In other embodiments, the first and second angles α, θ have different values.  
         [0028]     As shown in  FIG. 9 , the first and second rows  48 ,  50  of orifices  44  may be formed from orifices  44  alternating between first and second angles α, θ relative to the longitudinal axis  42 . In addition, the pattern of alternating orifices  44  in the first and second rows  48 ,  50  may be coordinated between the rows. For instance, the orifices  44  forming the second row  50  may be in the same position as the orifices  44  forming the first row  48 , except that rather than being positioned side by side, the orifices  44  in the second row  50  may be offset orthogonal to the longitudinal axis  42  and offset along the longitudinal axis  42 . This same pattern may be extended to the third row  52  of orifices  44  and other rows as well.  
         [0029]     The showerhead  46  may also be configured as shown in  FIG. 10 . For instance, the showerhead  46  may include orifices  44  forming the first, second, and third rows  48 ,  50 ,  52  of which one or more of the rows may have the following pattern. For instance, the first row  48  may have an orifice  44  positioned at the first angle α relative to the longitudinal axis  42 , an orifice  44  positioned generally parallel to the longitudinal axis  42 , an orifice  44  positioned at the second angle θ relative to the longitudinal axis  42 , an orifice  44  positioned generally parallel to the longitudinal axis  42 , and an orifice  44  positioned at the first angle α relative to the longitudinal axis  42 . The orifices  44 , may be spaced from each other within the row  48  a distance of about three times the diameter of the orifices  44 . In another embodiment, as shown in  FIG. 10 , the orifices  44  may be spaced closer in a configuration referred to as a high density showerhead  46 .  
         [0030]     As shown in  FIG. 11 , the showerhead  46  may be configured such that two rows may have an alternating pattern of orifices  44 . For instance, first and third rows  48 ,  52  may have the same pattern of angled orifices  44  that are offset from each other in a direction orthogonal to the longitudinal axis  42  and offset from each other in a direction along the longitudinal axis. However, second row  50  may have a pattern of orifices  44  aligned at the first and second angles α, θ that are opposite from the first and third rows  48 ,  52 . In this spirit, the showerhead  46  may have orifices  44  positioned in other patterns other than shown in  FIGS. 5-11 . The patterns illustrated in  FIGS. 5-11  are not mean to be limiting; rather, the patterns are mean to be illustrative of the patterns that may be created by placing the orifices  44  at the first and second angles α, θ. In at least one embodiment, adjacent rows  48 ,  50 ,  52  may each have different patterns of angluation of the orifices  42  forming the rows.  
         [0031]     During operation, cooling gases, which may be air, is passed through the root  16  of the blade  12 . The cooling gases flow throughout the internal cooling channels  32  of the blade  12  and are exhausted at various locations on the blade  12  for film cooling. At least a portion of the cooling fluids are exhausted through the orifices  44  forming the showerhead  46  in the leading edge  34 . The cooling gases impede combustion gases flowing past the blade  12  from contacting the leading edge  34 .  
         [0032]     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.