Patent Publication Number: US-2017370232-A1

Title: Turbine airfoil cooling system with chordwise extending squealer tip cooling channel

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Development of this invention was supported in part by the United States Department of Energy, Advanced Turbine Development Program, Contract No. DE-FC26-05NT42644. Accordingly, the United States Government may have certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     This invention is directed generally to turbine blades, and more particularly to cooling systems at airfoil tips for 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. 
     Typically, turbine blade is 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 tip of a turbine blade often has a tip feature to reduce the size of the gap between ring segments and blades in the gas path of the turbine to prevent tip flow leakage, which reduces the amount of torque generated by the turbine blades. The tip features are often referred to as squealer tips and are frequently incorporated onto the tips of blades to help reduce aerodynamic losses in turbine stages. These features are designed to minimize the leakage between the blade tip and the ring segment. 
     SUMMARY OF THE INVENTION 
     An internal cooling system for an airfoil in a turbine engine whereby the cooling system includes a chordwise extending tip cooling channel radially inward of a squealer tip and formed at least in part by an inner wall with a nonlinear outer surface is disclosed. The nonlinear outer surface of the inner wall of the chordwise extending tip cooling channel may be formed from pressure and suction side sections that intersect at a point that is closer to the inner surface of an outer wall forming at least a portion of the squealer tip than other aspects of the pressure side section and the suction side sections. The configurations of the pressure and suction side sections reduces the flow cross-sectional area, which accelerates the cooling fluid flow in a chordwise direction within the chordwise extending tip cooling channel and directs cooling fluid toward the pressure and suction side outer walls for improved cooling efficiency. 
     In at least one embodiment, the turbine airfoil may include a generally elongated blade having a leading edge, a trailing edge, a squealer tip at a first end, a root coupled to the blade at a second end generally opposite the first end for supporting the blade and for coupling the blade to a disc, and an internal cooling system formed from at least one cavity positioned within the generally elongated blade. The internal cooling system may include one or more chordwise extending tip cooling channels formed at least in part by an inner surface of an outer wall forming at least a portion of the squealer tip. The chordwise extending tip cooling channel may include an inner wall formed from a pressure side section that has an outer surface that is nonparallel and nonorthogonal to an inner surface of a pressure side outer wall, and a suction side section that has an outer surface that is nonparallel and nonorthogonal to an inner surface of a suction side outer wall. The outer surfaces of the pressure side section and the suction side sections forming the inner wall of the chordwise extending tip cooling channel may be nonparallel and nonorthogonal relative to each other. An intersection between the outer surfaces of the pressure side section and the suction side section forming the inner wall of the at least one chordwise extending tip cooling channel may be closer to the inner surface of an outer wall forming at least a portion of the squealer tip than other aspects of the pressure side section and the suction side sections forming the outer wall of the at least one chordwise extending tip cooling channel. 
     In at least one embodiment, an intersection between the outer surfaces of the pressure side section and the suction side sections forming the inner wall of the chordwise extending tip cooling channel may be curved to form a fillet. An intersection between the outer surface of the pressure side section forming the inner wall of the chordwise extending tip cooling channel and the inner surface of the pressure side outer wall may be curved to form a fillet. Similarly, an intersection between the outer surface of the suction side section forming the inner wall of the chordwise extending tip cooling channel and the inner surface of the suction side outer wall may be curved to form a fillet. The internal cooling system may include a plurality of turbulators on the inner surface of the pressure side outer wall. The internal cooling system may also include a plurality of turbulators on the inner surface of the suction side outer wall. The internal cooling system may also include a plurality of turbulators on the inner surface of the outer wall forming at least a portion of the squealer tip. 
     In at least one embodiment, the inner surfaces of the pressure side section and the suction side sections forming the inner wall of the chordwise extending tip cooling channel are nonparallel and nonorthogonal relative to each other and may be aligned with the outer surfaces of the pressure side section and the suction side sections forming the inner wall of the chordwise extending tip cooling channel. The chordwise extending tip cooling channel may have one or more inlets in fluid communication with a leading edge cooling channel extending spanwise with at least a portion of the leading edge cooling channel being defined by an inner surface of an outer wall forming the leading edge of the generally elongated blade. The pressure and suction side sections forming the inner wall of the chordwise extending tip cooling channel may form at least a portion of a midchord serpentine cooling channel. 
     In at least one embodiment, the squealer tip may include an upstream, radially extending rib and a downstream, radially extending rib. The upstream, radially extending rib may include an upstream contact surface that is nonorthogonal and nonparallel with a longitudinal axis of the generally elongated blade such that an innermost corner of the upstream contact surface extends further upstream than an outermost corner of the upstream contact surface and includes a downstream contact surface that is nonorthogonal and nonparallel with the longitudinal axis of the generally elongated blade such that an innermost corner of the downstream contact surface extends further downstream than an outermost corner of the downstream contact surface. The downstream, radially extending rib may include a downstream contact surface that is nonorthogonal and nonparallel with a longitudinal axis of the generally elongated blade such that an innermost corner of the downstream contact surface extends further downstream than an outermost corner of the downstream contact surface and includes an upstream contact surface that is nonorthogonal and nonparallel with the longitudinal axis of the generally elongated blade such that an innermost corner of the upstream contact surface extends further upstream than an outermost corner of the upstream contact surface. 
     The internal cooling system may also include one or more pressure side film cooling holes positioned in the upstream, radially extending rib with an outlet in the upstream contact surface in the upstream, radially extending rib and an inlet that couples the pressure side film cooling hole with the chordwise extending tip cooling channel of the internal cooling system. The internal cooling system may also include one or more suction side film cooling holes positioned upstream of the downstream, radially extending rib with an outlet in the squealer tip between the upstream and downstream, radially extending ribs. 
     During use, cooling fluids may flow into the leading edge cooling channel via the inlet. The cooling fluids may flow from a cooling fluid source into the inlet of the leading edge cooling channel at an inner end of the airfoil. The cooling fluids flow through the leading edge cooling channel and are passed into the inlet of the chordwise extending tip cooling channel. The pressure and suction side sections direct the cooling fluid into contact with the inner surfaces of the pressure and suction side outer walls. By directing the cooling fluid into contact with the inner surfaces of the pressure and suction side outer walls, the cooling efficiency of the internal cooling system is enhanced. In addition, the turbulators on the inner surfaces of the pressure and suction side outer walls may further increase the efficiency of the internal cooling system. The turbulators on the inner surface of the outer wall forming at least a portion of the squealer tip may further increase the cooling of the squealer tip. The cooling fluid may be exhausted from the chordwise extending tip cooling channel via pressure and suction side film cooling holes and via the outlet proximate to the trailing edge of the airfoil. The cooling fluid exhausted via the pressure and suction side film cooling holes may be used for cooling the squealer tip. 
     An advantage of the internal cooling system is that the chordwise extending tip cooling channel directs cooling fluid toward the pressure and suction side outer walls for improved convection on the inner surfaces of the pressure and suction side outer walls and thereby improved cooling efficiency of the internal cooling system. 
     Another advantage of the internal cooling system is that the pressure and suction side sections forming the inner wall of the chordwise internal cooling system reduces the flow cross-sectional area, which accelerates the cooling fluid flow in a chordwise direction within the chordwise extending tip cooling channel and increases the cooling efficiency of the internal cooling system. 
     Yet another advantage of the internal cooling system is that the squealer tip has more reliable convective cooling in the squealer tip for better blade tip life and therefore lower tip leakage flow. 
     Another advantage of the internal cooling system is that the pressure side cooling hole is positioned in a chamfered surface enabling the cooling holes to be positioned on the surface at hot spots and for the cooling holes to have longer lengths for better cooling. 
     Still another advantage of this invention is that the cooling holes also provide exit film cooling at the chamfered surface, thereby reducing the temperature of the airfoil at a location that is typically a hot spot, which is an area of material having an increased temperature. 
     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 partial cross-sectional, perspective view of a turbine engine with airfoils including internal cooling systems with chordwise extending tip cooling channels. 
         FIG. 2  is a perspective view of an airfoil with an internal cooling system having a chordwise extending tip cooling channel usable in the turbine engine shown in  FIG. 1 . 
         FIG. 3  is cross-section fillet view of the airfoil with an internal cooling system having a chordwise extending tip cooling channel taken along section line  3 - 3  in  FIG. 2 . 
         FIG. 4  is a partial cross-sectional view of internal cooling system having a chordwise extending tip cooling channel taken along section line  4 - 4  in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-4 , an internal cooling system  10  for an airfoil  12  in a turbine engine  14  whereby the cooling system  10  includes a chordwise extending tip cooling channel  16  radially inward of a squealer tip  18  and formed at least in part by an inner wall  20  with a nonlinear outer surface  22  is disclosed. The nonlinear outer surface  22  of the inner wall  20  of the chordwise extending tip cooling channel  16  may be formed from pressure and suction side sections  24 ,  26  that intersect at a point  28  that is closer to an inner surface  30  of an outer wall  32  forming at least a portion of the squealer tip  18  than other aspects of the pressure side section  24  and the suction side sections  26 . The configurations of the pressure and suction side sections  24 ,  26  reduces the flow cross-sectional area, which accelerates the cooling fluid flow in a chordwise direction within the chordwise extending tip cooling channel  16  and directs cooling fluid toward the pressure and suction side outer walls  34 ,  36  for improved cooling efficiency. 
     In at least one embodiment, the turbine airfoil  12  may be formed from a generally elongated blade  40  having a leading edge  42 , a trailing edge  44 , a squealer tip  18  at a first end  46 , a root  48  coupled to the blade  40  at a second end  50  generally opposite the first end  46  for supporting the blade  40  and for coupling the blade  40  to a disc, and an internal cooling system  10  formed from at least one cavity  52  positioned within the generally elongated blade  40 . The internal cooling system  10  may include one or more chordwise extending tip cooling channels  16  formed at least in part by an inner surface  30  of an outer wall  32  forming at least a portion of the squealer tip  18 . The chordwise extending tip cooling channel  16  may include an inner wall  20  formed from a pressure side section  24  that has an outer surface  54  that is nonparallel and nonorthogonal to the inner surface  58  of the pressure side outer wall  34 . The outer surface  54  of the pressure side section  24  may be positioned between 30 degrees and 75 degrees relative to the inner surface  58  of the pressure side outer wall  34 . The chordwise extending tip cooling channel  16  may also include a suction side section  26  that has an outer surface  56  that is nonparallel and nonorthogonal to an inner surface  60  of a suction side outer wall  36 . The outer surface  56  of the suction side section  26  may be positioned between 30 degrees and 75 degrees relative to the inner surface  60  of the suction side outer wall  36 . The outer surfaces  54 ,  56  of the pressure side section  24  and the suction side section  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16  may be nonparallel and nonorthogonal relative to each other. In at least one embodiment, the outer surfaces  54 ,  56  of the pressure side section  24  and the suction side section  26  extend for at least a portion of the inner wall  20  of the chordwise extending tip cooling channel  16 . In at least one embodiment, the pressure and suction side sections  24 ,  26  may extend for an entirety of the inner wall  20  of the chordwise extending tip cooling channel  16 . 
     The pressure side section  24  and the suction side section  26  may intersect at the point  28 . The intersection  28  between the outer surfaces  54 ,  56  of the pressure side section  24  and the suction side section  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16  is closer to the inner surface  30  of the outer wall  32  forming at least a portion of the squealer tip  18  than other aspects of the pressure side section  24  and the suction side section  26  forming the outer wall  32  of the chordwise extending tip cooling channel  16 . The intersection  28  between the outer surfaces  54  of the pressure side section  24  and the suction side section  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16  may be curved to form a fillet. An intersection  62  between the outer surface  54  of the pressure side section  24  forming the inner wall  20  of the chordwise extending tip cooling channel  16  and the inner surface  58  of the pressure side outer wall  34  may be curved to form a fillet or have another appropriate configuration. An intersection  64  between the outer surface  56  of the suction side section  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16  and the inner surface  60  of the suction side outer wall  36  may be curved to form a fillet or have another appropriate configuration. 
     The internal cooling system  10  may include other elements to enhance the cooling capacity and efficiency. In at least one embodiment, the internal cooling system  10  may include a plurality of turbulators  66  on the inner surface  58  of the pressure side outer wall  34 . The turbulators  66  may extend from the inner surface  58  of the pressure side outer wall  34  toward the suction side  65 . The internal cooling system  10  may include a plurality of turbulators  66  on the inner surface  60  of the suction side outer wall  36 . The turbulators  66  may extend from the inner surface  60  of the suction side outer wall  36  toward the pressure side  68 . One or more turbulators  66  may extend on the inner surface  30  of the outer wall  32  forming at least a portion of the squealer tip  18 . 
     The inner surfaces  70 ,  72  of the pressure side section  24  and the suction side section  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16  may be nonparallel and nonorthogonal relative to each other and may be aligned with the outer surface  54 ,  56  of the pressure side and the suction side sections  24 ,  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16 . An intersection  74  between the inner surfaces  70 ,  72  of the pressure and suction side sections  24 ,  26  is curved to form a fillet. Wherein an intersection  76  between the inner surface  70  of the pressure side section  24  and the inner surface  58  of the pressure side outer wall  34  is curved to form a fillet. Wherein an intersection  78  between the inner surface  72  of the suction side section  26  and the inner surface  60  of the suction side outer wall  36  is curved to form a fillet. 
     In at least one embodiment, as shown in  FIG. 3 , the chordwise extending tip cooling channel  16  may have one or more inlets  80  in fluid communication with a leading edge cooling channel  82  extending spanwise with at least a portion of the leading edge cooling channel  82  being defined by an inner surface  84  of an outer wall  32  forming the leading edge  42  of the generally elongated blade  40 . In at least one embodiment, the chordwise extending tip cooling channel  16  may include an inlet  80  proximate to the leading edge  42  of the airfoil  12  and may include an outlet  86  proximate to the trailing edge  44  of the airfoil  12 . The leading edge cooling channel  82  may include an inlet  160  at an inner end  50  of the airfoil  12  that is in communication with a cooling fluid source. 
     The pressure and suction side sections  24 ,  26  forming the inner wall  20  of the chordwise extending tip cooling channel  16  may form at least a portion of a midchord serpentine cooling channel  88 . The midchord serpentine cooling channel  88  may be a triple pass serpentine cooling channel. The midchord serpentine cooling channel  88  may have a first inlet  90  at an inner end  92  of the a first leg  94  of the midchord serpentine cooling channel  88 . In at least one embodiment, the midchord serpentine cooling channel  88  may include a second inlet  96  at a second turn  98 , which is an inner turn between the second and third legs  100 ,  102  of the midchord serpentine cooling channel  88 . Cooling fluid may enter the first leg  94  via first inlet  90 , flow through first turn  91  and into the second leg  100 . The cooling fluid may flow from the second leg  100 , through second turn  98  and into the third leg  102 . As the cooling fluid is flowing into the third leg  102 , additional cooling fluid from the second inlet  96  is added to the cooling fluid flow into the third leg  102 . Cooling fluid in the third leg  102  may flow into a trailing edge cooling channel  156  and may be exhausted through one or more trailing edge exhaust orifices  158  in the trailing edge  44 . 
     The squealer tip  18  may have any appropriate configuration. In at least one embodiment, as shown in  FIG. 4 , the squealer tip  18  may include an upstream, radially extending rib  104  and a downstream, radially extending rib  106 . The upstream, radially extending rib  104  may include an upstream contact surface  108  that is nonorthogonal and nonparallel with a longitudinal axis  110  of the generally elongated blade  40  such that an innermost corner  112  of the upstream contact surface  108  extends further upstream than an outermost corner  114  of the upstream contact surface  108 . The upstream, radially extending rib  104  may also include a downstream contact surface  116  that is nonorthogonal and nonparallel with the longitudinal axis  110  of the generally elongated blade  40  such that an innermost corner  118  of the downstream contact surface  116  extends further downstream than an outermost corner  120  of the downstream contact surface  116 . The downstream, radially extending rib  106  may include a downstream contact surface  122  that is nonorthogonal and nonparallel with a longitudinal axis  110  of the generally elongated blade  40  such that an innermost corner  124  of the downstream contact surface  122  extends further downstream than an outermost corner  126  of the downstream contact surface  122 . The downstream, radially extending rib  106  may also include an upstream contact surface  128  that is nonorthogonal and nonparallel with the longitudinal axis  110  of the generally elongated blade  40  such that an innermost corner  130  of the upstream contact surface  128  extends further upstream than an outermost corner  132  of the upstream contact surface  128 . 
     The internal cooling system  10  may also include one or more pressure side film cooling holes  134  positioned in the upstream, radially extending rib  104  with an outlet  136  in the upstream contact surface  108  in the upstream, radially extending rib  104  and an inlet  138  that couples the pressure side film cooling hole  134  with the chordwise extending tip cooling channel  16  of the internal cooling system  10 . The pressure side film cooling hole  134  may have a longitudinal axis  140  that is positioned nonparallel and nonlinear to the outer surface  142  forming the pressure side  68  of the airfoil  12 . The internal cooling system  10  may also include one or more suction side film cooling holes  150  positioned upstream of the downstream, radially extending rib  106  with an outlet  152  in the squealer tip  18  between the upstream and downstream, radially extending ribs  104 ,  106 . The suction side film cooling hole  150  may have a longitudinal axis  162  that is positioned nonparallel and nonlinear to the outer surface  154  of the squealer tip  18  between the upstream and downstream, radially extending ribs  104 ,  106  such that cooling fluid is exhausted from the suction side film cooling hole  150  with at least a partial downstream vector. 
     During use, cooling fluids may flow into the leading edge cooling channel  82  via the inlet  80 . The cooling fluids may flow from a cooling fluid source into the inlet  160  of the leading edge cooling channel  82  at an inner end  50  of the airfoil  12 . The cooling fluids flow through the leading edge cooling channel  82  and are passed into the inlet  80  of the chordwise extending tip cooling channel  16 . The pressure and suction side sections  24 ,  26  direct the cooling fluid into contact with the inner surfaces  58 ,  60  of the pressure and suction side outer walls  34 ,  36 . By directing the cooling fluid into contact with the inner surfaces  58 ,  60  of the pressure and suction side outer walls  34 ,  36 , the cooling efficiency of the internal cooling system  10  is enhanced. In addition, the turbulators  66  on the inner surfaces  58 ,  60  of the pressure and suction side outer walls  34 ,  36  may further increase the efficiency of the internal cooling system  10 . The cooling fluid may be exhausted from the chordwise extending tip cooling channel  16  via pressure and suction side film cooling holes  134 ,  150  and via the outlet  86  proximate to the trailing edge  44  of the airfoil  12 . The cooling fluid exhausted via the pressure and suction side film cooling holes  134 ,  150  may be used for cooling the squealer tip  18 . 
     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.