Patent Publication Number: US-8118553-B2

Title: Turbine airfoil cooling system with dual serpentine cooling chambers

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. 
     SUMMARY OF THE INVENTION 
     This invention relates 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 an inward serpentine cooling channel and an outward serpentine cooling channel within interior aspects of the airfoil. The inward and outward serpentine cooling channels form dual cooling channels. The dual cooling channels are configured to first pass cooling fluids through the inward serpentine cooling channel proximate a root of the airfoil and then to the outward serpentine cooling channel. This configuration partitions the airfoil in half and preheats the cooling fluid for the outward serpentine cooling channel and yields a better creep capability for the airfoil. 
     The turbine airfoil may be formed from a generally elongated, hollow airfoil having a leading edge, a trailing edge, a tip at a first end, a root coupled to the airfoil at an end generally opposite to the first end for supporting the airfoil and for coupling the airfoil to a disc, and a cooling system formed from at least one cavity in the elongated, hollow airfoil. An outer wall may form an outer surface of the generally elongated airfoil. The cooling system may be formed from dual serpentine cooling channels comprising a radially inward serpentine cooling channel of the cooling system that is formed from a winding channel with portions extending in a spanwise direction between the root and a point between the root and the tip. A radially outward serpentine cooling channel of the cooling system may be formed from a winding channel with portions extending in a spanwise direction between the tip and the point between the root and the tip. 
     In one embodiment, the radially inward serpentine cooling channel may be a triple pass channel. The radially inward serpentine cooling channel may be formed from an outward bound first pass, an inward bound second pass, and an outward bound third pass. The first and second passes may be separated by a rib extending from the root toward the tip and terminating before reaching the center rib and the second and third passes may be separated by a leading edge rib extending spanwise from proximate an intersection between the generally elongated airfoil and the root toward the tip and terminating before reaching the tip. The radially inward serpentine cooling channel may include an inlet at the intersection of the root and the trailing edge, may be directed radially inwardly to receive cooling fluids from aspects of the cooling system positioned within the root and may include an outlet at the leading edge. A first pass of the radially inward serpentine cooling channel may include a plurality of metering slots positioned in the trailing edge. A plurality of pin fins may extend between the outer wall forming the pressure side and the outer wall forming the suction side in the radially inward serpentine cooling channel. The radially inward serpentine cooling channel and the radially outward serpentine cooling channel may be separated from each other by a center rib extending generally chordwise. 
     The radially outward serpentine cooling channel may be formed from an outward bound first pass, an inward bound second pass, and an outward bound third pass, wherein the first and second passes are separated by the leading edge rib and wherein the second and third passes are separated by a rib extending spanwise from the tip inward toward the center rib and terminating before contacting the center rib. The radially outward serpentine cooling channel may include an inlet in communication with the outlet of the radially inward serpentine cooling channel at the leading edge and may include at least one outlet at the trailing edge to exhaust the cooling fluids. The outlet at the trailing edge may be formed from a plurality of metering slots positioned in the trailing edge. A plurality of protrusions forming trip strips may extend from the outer wall forming the pressure side and from the outer wall forming the suction side in the radially outward serpentine cooling channel. 
     An advantage of this invention is that the airfoil is partitioned with dual serpentine cooling channels that allows for re-circulated heated cooling air from the inward serpentine cooling channel to be routed to the outward serpentine cooling channel. 
     Another advantage of this invention is that the serpentine cooling channels yield higher cooling effectiveness levels than conventionally drilled radial hole cooling designs. 
     Yet another advantage of this invention is that the triple pass serpentine cooling channels yields a lower and more uniform blade sectional mass average temperature for the blade lower span, which improves blade creep life capability. 
     Another advantage of this invention is that the inward, forward flowing, serpentine cooling channel includes a trailing edge feed and provides cooling fluids for the airfoil root section, which improves airfoil high cycle fatigue (HCF). 
     Still another advantage of this invention is that the turbine vane cooling channel provides cooling for the airfoil thin section, thereby improving the airfoil oxidation capability which allows for a higher operating temperature for future engine upgrades and increased cooling loads. 
     Another advantage of this invention is that the use of cooling fluid for cooling the inward span first and then cooling the outward span allows for the temperature of the outer wall forming the airfoil to be maintained within the allowable 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 perspective view of a turbine airfoil having features according to the instant invention. 
         FIG. 2  is a cross-sectional view of the turbine airfoil, also referred to as a filleted view, shown in  FIG. 1  taken along line  2 - 2 . 
         FIG. 3  is a schematic diagram of the cooling fluid flow through the turbine airfoil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-3 , 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 an inward serpentine cooling channel  18  and an outward serpentine cooling channel  20  within interior aspects of the airfoil  12 . The inward and outward serpentine cooling channels  18 ,  20  form dual cooling channels. The dual cooling channels are configured to first pass cooling fluids through the inward serpentine cooling channel proximate a root  22  of the airfoil  12  and then to the outward serpentine cooling channel  20 . This configuration partitions the airfoil  12  in half and preheats the cooling fluid for the outward serpentine cooling channel  20  and yields a better creep capability for the airfoil  12 . 
     The turbine airfoil  12  may be formed from a generally elongated, hollow airfoil  24  coupled to a root  22  at a platform  28 . The turbine airfoil  12  may be formed from conventional metals or other acceptable materials. The generally elongated airfoil  24  may extend from the root  22  to a tip  30  and include a leading edge  32  and trailing edge  34 . Airfoil  24  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  36  and may form a generally convex shaped portion forming suction side  38 . 
     As shown in  FIG. 2 , the cooling system  10  may be formed from dual serpentine cooling channels  18 ,  20  comprising a radially inward serpentine cooling channel  18  of the cooling system  10  that is formed from a winding channel with portions extending in a spanwise direction between the root  22  and a point  40  between the root  22  and the tip  30  and a radially outward serpentine cooling channel  20  of the cooling system  10  that is formed from a winding channel with portions extending in a spanwise direction between the tip  30  and the point  40  between the root  22  and the tip  30 . The inward serpentine cooling channel  18  may be separated from the outward serpentine cooling channel  20  by a center rib  42  extending generally chordwise. The inward serpentine cooling channel  18  may be a forward flowing cooling channel, and the outward serpentine cooling channel  20  may be an aft flowing cooling channel. 
     In at least one embodiment, the radially inward serpentine cooling channel  18  may be formed from a triple pass channel. In particular, the radially inward serpentine cooling channel  18  may be formed from an outward bound first pass  44 , an inward bound second pass  46 , and an outward bound third pass  48 . The first and second passes  44 ,  46  may be separated by a rib  50  extending from the root  22  toward the tip  30  and terminating before reaching the center rib  42 . The second and third passes  46 ,  48  may be separated by a leading edge rib  52  extending spanwise from proximate an intersection between the generally elongated airfoil  24  and the root  22  toward the tip  30  and terminating before reaching the tip  30 . 
     The radially outward serpentine cooling channel  20  may also be formed from a triple pass channel. In particular, the radially outward serpentine cooling channel  20  may be formed from an outward bound first pass  54 , an inward bound second pass  56 , and an outward bound third pass  58 . The first and second passes  54 ,  56  may be separated by the leading edge rib  52 . The second and third passes  56 ,  58  may be separated by a rib  60  extending spanwise from the tip  30  inward toward the center rib  42  and terminating before contacting the center rib  42 . 
     The radially inward serpentine cooling channel  18  may include an inlet  62  at the intersection  64  of the root  22  and the trailing edge  34  and is directed radially inwardly to receive cooling fluids from a channel  66  of the cooling system  10  positioned within the root  22  and includes an outlet  68  at the leading edge  32 . Similarly, the radially outward serpentine cooling channel  20  may include an inlet  70  in communication with the outlet  68  of the radially inward serpentine cooling channel  18  at the leading edge  32  and includes one or more outlets  72  at the trailing edge  34  to exhaust the cooling fluids. 
     The first pass  44  of the radially inward serpentine cooling channel  18  may include a plurality of metering slots  74  positioned in the trailing edge  34 . Likewise, the outlet  72  at the trailing edge  34  may be formed from a plurality of metering slots  74  positioned in the trailing edge  34 . The metering slots  74  may be sized accordingly. 
     A plurality of pin fins  76  may extend between the outer wall  16  forming the pressure side  36  and the outer wall  16  forming the suction side  38  in the radially inward serpentine cooling channel  18 . The pin fins  76  may included in the inward serpentine cooling channel  18  to reduce the amount of cross-sectional area to increase the velocity of the cooling fluid. Increasing the velocity of the cooling fluids increases the internal heat transfer coefficient. 
     The outward serpentine cooling channel  20  may include a plurality of protrusions  78  forming trip strips  80  extending from the outer wall  16  forming the pressure side  36  and from the outer wall  16  forming the suction side  38  in the radially outward serpentine cooling channel  20 . The trip strips  80  are used rather than the pin fins because the outer span of the airfoil  24  is relatively thin, which may reduce casting yields. Thus, the trip strips  80  are used to increase the internal heat transfer efficiency of the outward serpentine cooling channel  20 . 
     During use, cooling fluids may flow into the cooling system  10  from a cooling fluid supply source through the inlet  62  of the channel  66 . The cooling fluids may flow into the inward serpentine channel  18  and impinge on pin fins  76  positioned within the first, second and third passes  44 ,  46  and  48 . A portion of the cooling fluids may be exhausted through the metering slots  74  in the first pass  44 . The cooling fluids may be exhausted from the outlet  68  of the inward serpentine cooling channel  18  into the inlet  70  of the outward serpentine cooling channel  20 . The cooling fluids may then pass through the first, second and third passes  54 ,  56  and  58 . The cooling fluids may be exhausted through the exhaust orifices in the third pass  58 . 
     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.