Patent Publication Number: US-2018045059-A1

Title: Internal cooling system with insert forming nearwall cooling channels in an aft cooling cavity of a gas turbine airfoil including heat dissipating ribs

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to gas turbine engines, and more particularly to internal cooling systems for airfoils in gas turbine engines. 
     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 vane and blade assemblies to high temperatures. As a result, turbine vanes and blades must be made of materials capable of withstanding such high temperatures, or must include cooling features to enable the component to survive in an environment which exceeds the capability of the material. Turbine engines typically include a plurality of rows of stationary turbine vanes extending radially inward from a shell and include a plurality of rows of rotatable turbine blades attached to a rotor assembly for turning the rotor. 
     Typically, the turbine vanes are exposed to high temperature combustor gases that heat the airfoils. The airfoils include internal cooling systems for reducing the temperature of the airfoils. Airfoils have had internal inserts forming nearwall cooling channels. However, most inserts are formed from plain sheet metal with a plurality of impingement holes therein to provide impingement cooling on the pressure and suction sides of the airfoil. The upstream post impingement air pass downstream impingement jets and forms cross flow before exiting through film holes. The cross flow can bend the impinging jets away from the impingement target surface and reduce the cooling effectiveness. To reduce the amount of cross flow, the post impingement air has been vented out through exterior film holes. However, the greater the number of film cooling holes, the less efficient usage of cooling air is. The impingement holes consume cooling air pressure and often pose a problem at the leading edge, where showerhead holes experience high stagnation gas pressure on the external surface. Thus, a need for a more efficient internal cooling system for gas turbine airfoils exists. 
     SUMMARY OF THE INVENTION 
     An airfoil for a gas turbine engine in which the airfoil includes an internal cooling system with one or more internal cavities having an insert contained within an aft cooling cavity to form nearwall cooling channels having enhanced flow patterns is disclosed. The flow of cooling fluids in the nearwall cooling channels may be controlled via a plurality of cooling fluid flow controllers extending from the outer wall forming the generally hollow elongated airfoil. In addition, heat may be extracted in the midchord region via one or more heat dissipating ribs extending partially between an inner surface of the suction side and the insert. In at least one embodiment, the heat dissipating ribs may extend in a generally chordwise direction and be positioned from an inner diameter of the airfoil to an outer diameter of the airfoil between the cooling fluid flow controllers and a rib separating a forward cooling cavity from the aft cooling cavity. The heat dissipating ribs have been shown to increase the surface area by at least 60 percent, reduce localized hot spot outer wall temperature by up to 60 degrees Celsius while having a negligible impact on mass flow rate. 
     In at least one embodiment, the turbine airfoil for a gas turbine engine may be formed from a generally elongated hollow airfoil formed from an outer wall, and having a leading edge, a trailing edge, a pressure side, a suction side, and inner endwall at a first end and an outer endwall at a second end that is generally on an opposite side of the generally elongated hollow airfoil from the first end. The turbine airfoil may also include a cooling system positioned within interior aspects of the generally elongated hollow airfoil. The cooling system may include one or more aft cooling cavities in which an insert is positioned that forms a pressure side nearwall cooling channel and a suction side nearwall cooling channel. A plurality of cooling fluid flow controllers may extend from an inner surface of the outer wall forming the suction side of the generally elongated hollow airfoil toward the insert. The cooling fluid flow controllers may form a plurality of alternating zigzag channels extending downstream toward the trailing edge. One or more heat dissipating ribs may extend partially between the inner surface of the suction side and the insert. 
     The heat dissipating rib may extend generally in a chordwise direction such as a direction from the leading edge to the trailing edge. The heat dissipating rib may be attached to an inner surface of the outer wall forming the suction side and may extend inwardly from the inner surface of the suction side. The heat dissipating rib may extend at least partially onto a rib dividing the aft cooling cavity from a forward cooling cavity. The rib may extend generally orthogonally from the inner surface of the outer wall forming the suction side. The heat dissipating rib may have a curved outer head cross-sectional profile taken orthogonal to a longitudinal axis of the heat dissipating rib. The heat dissipating rib may have a curved upstream end and a tapered downstream end. In at least one embodiment, the heat dissipating rib may have a pitch of between about 0.3 mm and 1.6 mm. The heat dissipating rib  152  may have an amplitude of between about 0.4 mm and about 3.2 mm. 
     In at least one embodiment, the cooling system may include one or more heat dissipating ribs formed from a plurality of heat dissipating ribs extending partially between the inner surface of the suction side and the insert. The plurality of heat dissipating ribs may be aligned with each other. The plurality of heat dissipating ribs may each be separated an equal distance from each other. The plurality of heat dissipating ribs may extend in a chordwise direction and may be positioned adjacent each other from an inner diameter of the airfoil to an outer diameter of the airfoil. A chordwise length of the heat dissipating ribs may reduce moving from the outer diameter of the airfoil to the inner diameter of the airfoil. 
     An advantage of the heat dissipating ribs in the midchord region of the aft cavity upstream from the cooling fluid flow controllers is that the heat dissipating ribs reduce localized hot spot outer wall temperature by up to 60 degrees Celsius. 
     Another advantage of the heat dissipating ribs in the midchord region of the aft cavity upstream from the cooling fluid flow controllers is that the heat dissipating ribs have a negligible impact on mass flow rate. 
     Yet another advantage of the heat dissipating ribs in the midchord region of the aft cavity upstream from the cooling fluid flow controllers is that the heat dissipating ribs may also have up to a 40 percent increase in heat flux for the mid chord region  150  containing the heat dissipating ribs  152 . 
     Another advantage of the heat dissipating ribs in the midchord region of the aft cavity upstream from the cooling fluid flow controllers is that the heat dissipating ribs may increase the surface area by at least 60 percent. 
     Still another advantage of the internal cooling system is that the cooling fluid flow controllers significantly increase the exposed surface area within the cooling system for better cooling system performance. 
     Another advantage of the internal cooling system is that the insert having the bypass flow reducers directs cooling fluids towards the outer wall to increase cooling rather than using a higher number of impingement holes in the insert, which would only increase the problems associated with cross flow. 
     Yet another advantage of the internal cooling system is that the bypass flow reducers effectively force more high speed cooling air into the zigzag flow channels formed by the multiple rows of cooling fluids flow controllers adjacent to the hot exterior walls of the airfoil. 
     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 including the internal cooling system. 
         FIG. 2  is a partial perspective view of the turbine airfoil of  FIG. 1 , taken along section line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a cross-sectional, perspective view of the turbine airfoil taken along section line  3 - 3  in  FIG. 1 . 
         FIG. 4  is a cross-sectional view of the turbine airfoil taken along section line  3 - 3  in  FIG. 2 . 
         FIG. 5  is a detail view of components of the internal cooling system shown within the trailing edge channel taken at detail view  5  in  FIG. 2 . 
         FIG. 6  is a perspective, detail view of the components of the internal cooling system shown within the trailing edge channel in  FIG. 5 . 
         FIG. 7  is a pressure side view of the turbine airfoil including the internal cooling system, taken along section line  2 - 2  in  FIG. 1 . 
         FIG. 8  is a suction side view of the turbine airfoil including the internal cooling system, taken along section line  7 - 7  in  FIG. 1 . 
         FIG. 9  is a cross-sectional view of the turbine airfoil taken along section line  9 - 9  in  FIG. 7  and showing components of the internal cooling system protruding from an outer wall forming the suction side. 
         FIG. 10  is a cross-sectional view of the turbine airfoil taken along section line  10 - 10  in  FIG. 8  and showing components of the internal cooling system protruding from an outer wall forming the pressure side. 
         FIG. 11  is a perspective view of the inner surfaces of the outer wall forming the turbine airfoil and including components of the internal cooling system extending inwardly from the outer wall. 
         FIG. 12  is a detail perspective view of the inner surfaces of the outer wall forming the turbine airfoil and including components of the internal cooling system extending inwardly from the outer wall taken as detail  12 - 12 , as shown in  FIG. 11 . 
         FIG. 13  is a perspective view of the cross-sectional view of the airfoil shown in  FIG. 10 . 
         FIG. 14  is a detail view of the heat dissipating ribs shown in  FIG. 13  at detail  14 - 14 . 
         FIG. 15  is a cross-sectional view of the heat dissipating ribs taken as section line  15 - 15  in  FIG. 14 . 
         FIG. 16  is a graph of the bond coat temperature at the midspan region of the airfoil showing the temperature at the midchord region having a smooth surface ( FIG. 18 ) and one with heat dissipating ribs ( FIG. 19 ). 
         FIG. 17  is a graph showing the Mid-Span band average change in suction side exterior metal temperature. 
         FIG. 18  is a detail view at detail  18 - 18  in  FIG. 13  without heat dissipating ribs in the midchord region. 
         FIG. 19  is a detail view at detail  18 - 18  in  FIG. 13  with heat dissipating ribs in the midchord region. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-19 , an airfoil  10  for a gas turbine engine in which the airfoil  10  includes an internal cooling system  14  with one or more internal cavities  16  having an insert  18  contained within an aft cooling cavity  76  to form nearwall cooling channels  20  having enhanced flow patterns is disclosed. The flow of cooling fluids in the nearwall cooling channels  20  may be controlled via a plurality of cooling fluid flow controllers  22  extending from the outer wall  24  forming the generally hollow elongated airfoil  26 . In addition, heat may be extracted in the midchord region  150  via one or more heat dissipating ribs  152  extending partially between an inner surface  144  of the suction side  38  and the insert  18 . In at least one embodiment, the heat dissipating ribs  152  may extend in a generally chordwise direction and be positioned from an inner diameter  92  of the airfoil  26  to an outer diameter  98  of the insert  18  between the cooling fluid flow controllers  22  and a rib  72  separating a forward cooling cavity  74  from the aft cooling cavity  74 . The heat dissipating ribs  152  have been shown to increase the surface area by at least 60 percent, reduce localized hot spot outer wall temperature by up to 60 degrees Celsius while having a negligible impact on mass flow rate. 
     In at least one embodiment, as shown in  FIG. 1 , the airfoil  10  may be a turbine airfoil  10  for a gas turbine engine and may include a generally elongated hollow airfoil  26  formed from an outer wall  24 , and having a leading edge  32 , a trailing edge  34 , a pressure side  36 , a suction side  38 , and inner endwall  40  at a first end  42  and an outer endwall  44  at a second end  46  that is generally on an opposite side of the generally elongated hollow airfoil  26  from the first end  42  and a cooling system  14  positioned within interior aspects of the generally elongated hollow airfoil  26 . As shown in  FIGS. 3 and 4 , the cooling system  14  may include one or more midchord cooling cavities  45 . In at least one embodiment, the midchord cooling cavity  45  may include one or more ribs  72  separating the midchord cooling cavity  45  into a forward cooling cavity  74  and an aft cooling cavity  76  and forming an upstream end of the aft cooling cavity  76 . The cooling system  14  may include one or more aft cooling cavities  76  in which an aft insert  18  may be positioned that forms a pressure side nearwall cooling channel  48  and a suction side nearwall cooling channel  50 . A plurality of cooling fluid flow controllers  22 , as shown in  FIGS. 7, 8, 13 and 14 , may extend from the outer wall  24  forming the generally elongated hollow airfoil  26  toward the aft insert  18 . The cooling fluid flow controllers  22  may form a plurality of alternating zigzag channels  52  extending downstream toward the trailing edge  34 , as shown in  FIG. 7 . The aft insert  18  may be positioned within the aft cooling cavity  76  such that a gap  110 , as shown in  FIGS. 3 and 4 , exists between an end  111  of the cooling fluid flow controllers  22  and the aft insert  18 . In at least one embodiment, the gap  110  may be less than about 0.8 millimeters. In another embodiment, the gap  110  may be about 0.3 millimeters. 
     The cooling fluid flow controllers  22  may be collected into spanwise extending rows  28 . In at least one embodiment, the cooling fluid flow controllers  22  may be positioned within a pressure side nearwall cooling channel  48  and a suction side nearwall cooling channel  50  that are both in fluid communication with a trailing edge channel  30 . The trailing edge channel  30  may also include cooling fluid flow controllers  22  extending between the outer walls  13 ,  12  forming the pressure and suction sides  36 ,  38 , thereby increasing the effectiveness of the internal cooling system  14 . The internal cooling system  14  may include one or more bypass flow reducers  31  extending from the insert  18  toward the outer wall  24  to direct the cooling fluids through the nearwall cooling channels  20  created by the cooling fluid flow controllers  22 , thereby increasing the effectiveness of the internal cooling system  14 . 
     In at least one embodiment, the internal cooling system  1 , as shown in  FIG. 4 , the cooling fluid flow controllers  22  may form a plurality of alternating zigzag channels  52  extending in a generally chordwise direction downstream toward the trailing edge  34 . The zigzag channels  52  may be formed from one or more cooling fluid flow controllers  22  having a cross-sectional area formed by a pressure side  54  that is on an opposite side from a suction side  56 , whereby the pressure and suction sides  54 ,  56  may be coupled together via a leading edge  58  and trailing edge  60  on an opposite end of the cooling fluid flow controller  22  from the leading edge  58 . The pressure side  54  may have a generally concave curved surface and the suction side  56  may have a generally convex curved surface. In at least one embodiment, the plurality of cooling fluid flow controllers  22  may extend from the outer wall  13  forming the pressure side  36  of the generally elongated hollow airfoil  26 . Similarly, the plurality of cooling fluid flow controllers  22  may extend from the outer wall  12  forming the suction side  38  of the generally elongated hollow airfoil  26 . 
     A plurality of cooling fluid flow controllers  22  may be collected into a first spanwise extending row  64  of cooling fluid flow controllers  22 . One or more of the cooling fluid flow controllers  22  forming the first spanwise extending row  64  may have cross-sectional areas formed by a pressure side  54  that is on an opposite side from a suction side  56 , whereby the pressure and suction sides  54 ,  56  are coupled together via a leading edge  58  and trailing edge  60  on an opposite end of the cooling fluid flow controller  22  from the leading edge  58 . A pressure side  54  of one cooling fluid flow controller  22  may be adjacent to a suction side  56  of an adjacent cooling fluid flow controller  22 . In at least one embodiment, each of the cooling fluid flow controllers  22  within the first spanwise extending row  64  of cooling fluid flow controllers  22  may be positioned similarly, such that a pressure side  54  of one cooling fluid flow controller  22  is adjacent to a suction side  56  of an adjacent cooling fluid flow controller  22 , except for a cooling fluid flow controller  22  at an end of the first spanwise extending row  64  where there is no adjacent cooling fluid flow controller  22 . 
     The internal cooling system  14  may also include a second spanwise extending row  66  of cooling fluid flow controllers  22  positioned downstream from the first spanwise extending row  64  of cooling fluid flow controllers  22 . The second spanwise extending row  66  of cooling fluid flow controllers  22  may have one or more cooling fluid flow controllers  22  with a pressure side  54  on an opposite side of the cooling fluid flow controller  22  than in the first spanwise extending row of cooling fluid flow controllers  22 , thereby causing cooling fluid flowing through the second spanwise extending row  66  of cooling fluid flow controllers  22  to be directed downstream with a spanwise vector  68  that is opposite to a spanwise vector  70  imparted on the cooling fluid by the first spanwise extending row  64  of cooling fluid flow controllers  22 . In at least one embodiment, each of the cooling fluid flow controllers  22  forming the second spanwise extending row  66  of cooling fluid flow controllers  22  has a pressure side  54  on an opposite side of the cooling fluid flow controller  22  than in the first spanwise extending row  64  of cooling fluid flow controllers  22 . The pressure side nearwall cooling channel  48  or the suction side nearwall cooling channel  50 , or both, may include a repetitive pattern of first and second spanwise extending rows  94 ,  96  of cooling fluid flow controllers  22  to form alternating zigzag channels  52  extending generally chordwise towards the trailing edge  34 . 
     As shown in  FIGS. 5 and 6 , the inner surface  144  of the outer wall  12  and outer wall  13  may include one or more mini-ribs  146  protruding inwardly within the zigzag channels  52  and extending toward the trailing edge  60 . The mini-ribs  146  may extend generally orthogonal to a direction of the cooling fluid flow through the zigzag channels  52 . The mini-ribs  146  may have a width less than a distance between adjacent cooling fluid flow controllers  22  or may extend into contact with adjacent cooling fluid flow controllers  22 . The mini-ribs  146  may also have a height less than ½ of a height of the zigzag channels  52 . In another embodiment, the mini-ribs  146  may have a height less than ¼ of a height of the zigzag channels  52 . In yet another embodiment, the mini-ribs  146  may have a height less than ⅛ of a height of the zigzag channels  52 . The mini-ribs  146  may have a thickness in the direction of flow of the cooling fluids less than ½ of a distance between adjacent mini-ribs  146 . 
     In at least one embodiment, as shown in  FIGS. 3 and 4 , one of the pressure side nearwall cooling channel  48  and the suction side nearwall cooling channel  50 , or both, may be in fluid communication with the trailing edge channel  30 . The insert  18  may include one or more refresher holes  84  to supply the trailing edge channel  30  in addition to the pressure side nearwall cooling channel  48  and the suction side nearwall cooling channel  50  supplies to the trailing edge channel  30 . The refresher holes  84  may be aligned into one or more spanwise extending rows in close proximity to an aft end  86  of the insert  18 . The refresher holes  84  may have any appropriate size, length and shape to effectively exhaust cooling fluids from the insert  18  to the trailing edge channel  30 . The insert  18  in the aft cooling cavity  76  may include one or more inlets  88 , as shown in  FIG. 2 , in fluid communication with a cooling fluid supply  90  positioned in an inner diameter  92  of the generally elongated hollow airfoil  26 . As such, cooling fluids are received into the insert  18  in the aft cooling cavity  76  via the inlet  88  at the inner diameter  92  and flow radially outward toward the outer endwall  44 . At least a portion of the cooling fluids flow through the refresher holes  84  into the trailing edge channel  30 . 
     The trailing edge channel  30  may include a plurality of cooling fluid flow controllers  22  extending from the outer wall  13  forming the pressure side  36  to the outer wall  12  forming the suction side  38 , whereby the cooling fluid flow controllers  22  may form a plurality of alternating zigzag channels  52 . The plurality of cooling fluid flow controllers  22  in the trailing edge channel  30  may be collected into a first spanwise extending row  94  of cooling fluid flow controllers  22 . One or more of the cooling fluid flow controllers  22  forming the first spanwise extending row  94  within the trailing edge channel  30  may have cross-sectional areas formed by a pressure side  54  that is on an opposite side from a suction side  56 , whereby the pressure and suction sides  54 ,  56  are coupled together via a leading edge  58  and a trailing edge  60  on an opposite end of the cooling fluid flow controller  22  from the leading edge  58 . One or more of the cooling fluid flow controllers  22  within the first spanwise extending row  94  of cooling fluid flow controllers  22  may include a pressure side  54  of one cooling fluid flow controller  22  is adjacent to a suction side  56  of an adjacent cooling fluid flow controller  22 . In at least one embodiment, each of the cooling fluid flow controllers  22  within the first spanwise extending row  94  of cooling fluid flow controllers  22  is positioned similarly, such that a pressure side  54  of one cooling fluid flow controller  22  is adjacent to a suction side  56  of an adjacent cooling fluid flow controller  22 , except for a cooling fluid flow controller  22  at an end of the first spanwise extending row  94 . 
     The trailing edge channel  30  may also include one or more second spanwise extending rows  96  of cooling fluid flow controllers  22  positioned downstream from the first spanwise extending row  94  of cooling fluid flow controllers  22 . The second spanwise extending row  96  of cooling fluid flow controllers  22  may have one or more cooling fluid flow controllers  22  with a pressure side  54  on an opposite side of the cooling fluid flow controller  22  than in the first spanwise extending row  94  of cooling fluid flow controllers  22 , thereby causing cooling fluid flowing through the second spanwise extending row  96  of cooling fluid flow controllers  22  to be directed downstream with a spanwise vector  68  that is opposite to a spanwise vector  70  imparted on the cooling fluid by the first spanwise extending row  94  of cooling fluid flow controllers  22 . The trailing edge channel  30  may include a repetitive pattern of first and second spanwise extending rows  94 ,  96  of cooling fluid flow controllers  22  to form alternating zigzag channels  52  extending generally chordwise towards the trailing edge  34 . 
     The trailing edge channel  30  may include one or more rows of pin fins  102  extending from the outer wall  13  forming the pressure side  36  to the outer wall  12  forming the suction side  38  and downstream from the cooling fluid flow controllers  22 . The pin fins  102  may have a generally circular cross-sectional area or other appropriate shape. The pin fins  102  may be positioned in one or more spanwise extending rows  104  of pin fins  102 . In at least one embodiment, the pin fins  102  may have a minimum distance between each other or between an adjacent structure other than the outer walls  12 ,  13  of about 1.5 millimeters. 
     The aft insert  18  may include one or more pressure side exhaust outlets  112  on a side of the aft insert  18  positioned closest to the outer wall  13  forming the pressure side  36  of the airfoil  26 . The pressure side exhaust outlet  112  may be positioned near a forward wall  116  of the aft insert  18 . The pressure side exhaust outlets  112  may be aligned into spanwise extending rows  118 . In at least one embodiment, the aft insert  18  may include a plurality of pressure side exhaust outlets  112  formed into two spanwise extending rows  118  on the side of the aft insert  18  positioned closest to the outer wall  13  forming the pressure side  36  of the airfoil  26 . The pressure side exhaust outlets  112  supply cooling fluids to the pressure side nearwall cooling channel  48 . 
     The aft insert  18  may include one or more suction side exhaust outlets  120  on a side of the aft insert  18  positioned closest to the outer wall  12  forming the suction side  38  of the airfoil  26 . The suction side exhaust outlet  120  may be positioned near a forward wall  116  of the aft insert  18 . The suction side exhaust outlets  120  may be aligned into spanwise extending rows  118 . In at least one embodiment, the aft insert  18  may include a plurality of suction side exhaust outlets  120  formed into two spanwise extending rows  118  on the side of the aft insert  18  positioned closest to the outer wall  12  forming the suction side  36  of the airfoil  26 . The suction side exhaust outlets  120  supply cooling fluids to the suction side nearwall cooling channel  50 . 
     The cooling system  14  may also include one or more bypass flow reducers  31  extending from the aft insert  18  toward the outer wall  13  forming the pressure side  36  or the outer wall  12  forming the suction side  38 , or both, to reduce flow of cooling fluids through the gap  110 . In at least one embodiment, as shown in  FIGS. 3 and 4 , the internal cooling system  14  may include a plurality of bypass flow reducers  30 . One or more of the plurality of bypass flow reducers  30  may be positioned between adjacent spanwise extending rows  28  of cooling fluid flow controllers  22 . The bypass flow reducer  30  may extend less than half a distance from the aft insert  18  to an inner surface  82  of the outer wall  24  forming the pressure side  36 . In other embodiments, the bypass flow reducer  30  may extend more than half a distance from the aft insert  18  to the inner surface  82  of the outer wall  24  forming the pressure side  36 . An aft insert  18  may have bypass flow reducers  30  with all the same height and lengths or varying heights and lengths. 
     The cooling system  14  may include one or more film cooling holes  136  in the outer wall  13  forming the pressure side  36 . The film cooling hole  136  may exhaust cooling fluids from the pressure side nearwall cooling channel  48  near the rib  72  positioned between the forward and aft cooling cavities  74 ,  76 . The film cooling holes  136  may be positioned in a spanwise extending row. 
     The forward cooling cavity  74  may include one or more forward inserts  124 . The forward insert  124  may form a pressure side nearwall cooling channel  126  and a suction side nearwall cooling channel  128 . The forward insert  124  may include a plurality of impingement orifices  130  extending through a pressure side  132  of the forward insert  124  and a suction side  134  of the forward insert  124 . The impingement orifices  130  may have any appropriate configuration to enhance the cooling capacity of the forward insert  124  and internal cooling system  14 . The leading edge  32  of the airfoil  26  may include a plurality of film cooling holes  136  that form a showerhead array of film cooling holes  136 . The forward cooling cavity  74  may include an inlet  138  in connection with a fluid source that is outboard of the airfoil  26  and configured to feed cooling fluids to the inlet  138  and into the forward insert  124 . 
     In at least one embodiment, the cooling system  14  may include one or more aft cooling cavities  76  in which an insert  18  is positioned that forms a pressure side nearwall cooling channel  48  and a suction side nearwall cooling channel  50 . A plurality of cooling fluid flow controllers  22  may extend from an inner surface  144  of the outer wall  12  forming the suction side  38  of the generally elongated hollow airfoil  26  toward the insert  18 . The cooling fluid flow controllers  22  may form a plurality of alternating zigzag channels  52  extending downstream toward the trailing edge  34 . The cooling system  14  may include one or more heat dissipating ribs  152  extending partially between the inner surface  144  of the suction side  38  and the insert  18 , as shown in  FIGS. 13-19 . The heat dissipating ribs  152  have been shown to increase the surface area by at least 60 percent, reduce localized hot spot outer wall temperature by up to 60 degrees Celsius while having a negligible impact on mass flow rate. The heat dissipating ribs  152  may also have a 40 percent increase in heat flux for the mid chord region  150  containing the heat dissipating ribs  152 , as shown in  FIGS. 13-19 . 
     The heat dissipating rib  152  may extend generally in a chordwise direction such as a direction from the leading edge  32  to the trailing edge  34 . The heat dissipating rib  152  may be attached to an inner surface  144  of the outer wall  12  forming the suction side  38  and may extend inwardly from the inner surface  144  of the suction side  38 . The heat dissipating rib  152  may extend at least partially onto a rib  72  dividing the aft cooling cavity  76  from a forward cooling cavity  74 . The rib  72  may extend generally orthogonally from the inner surface  144  of the outer wall  12  forming the suction side  38 . In at least one embodiment, the heat dissipating rib  152  may have a curved outer head  156  cross-sectional profile taken orthogonal to a longitudinal axis  158  of the heat dissipating rib  152 , as shown in  FIG. 15 . The heat dissipating rib  152  may have a curved upstream end  160  and a tapered downstream end  162 . In at least one embodiment, the downstream end may be linearly tapered and have a linear surface. The heat dissipating rib  152  may have a pitch of between about 0.3 mm and 1.6 mm. The heat dissipating rib  152  may have an amplitude of between about 0.4 mm and about 3.2 mm. 
     In at least one embodiment, the cooling system  14  may include a plurality of heat dissipating ribs  152  extending partially between the inner surface  144  of the suction side  38  and the insert  18 . The plurality of heat dissipating ribs  152  are aligned with each other. The plurality of heat dissipating ribs  152  may each be separated an equal distance from each other. The plurality of heat dissipating ribs  152  may extend in a chordwise direction and may be positioned adjacent each other from an inner diameter  92  of the airfoil  26  to an outer diameter  98  of the airfoil  26 . A chordwise length of the heat dissipating ribs  152  may reduce in length moving from the outer diameter  98  of the airfoil  26  to the inner diameter  92  of the airfoil  26 . 
     During use, cooling fluids may be supplied from a compressor or other such cooling air source to the inner chamber  106  of the forward insert  124  of the internal cooling system  14 . Cooling fluids may fill the forward insert  124  and generally flow spanwise in a radially inward direction throughout the forward insert  124 . Cooling fluids are passed through the impingement orifices  130  into the pressure side nearwall cooling channel  126  and through the impingement orifices  130  into the suction side nearwall cooling channel  128 . The cooling fluids flowing from the impingement holes  130  impinge against the outer wall  13  forming the pressure side  36  and the outer wall  12  forming the suction side  38 , thereby cooling the outer walls  12 ,  13 . A portion of the cooling fluids from the pressure side and suction side nearwall cooling channels  126 ,  128  are exhausted from the internal cooling system  14  via the plurality of film cooling holes  136  forming the showerhead and the other film cooling holes. The cooling fluids may also form film cooling on an outer surface of the outer walls  12 ,  13  via the film cooling holes  136  at the leading edge  32  that are configured to form a showerhead and the other film cooling holes in the outer walls  12 ,  13  forming the pressure and suction sides  36 ,  38 . 
     Cooling fluids may be supplied to the aft insert  18  via the inlet  88 . The cooling fluids may be supplied from a channel in communication with the forward insert  124  or from another source. Cooling fluids may fill the aft insert  18  and may generally flow spanwise throughout the aft insert  18 . Cooling fluids are passed through the pressure side exhaust outlets  112  and into the pressure side nearwall cooling channel  48  and are passed through the suction side exhaust outlets  120  and into the suction side nearwall cooling channel  50 . The cooling fluids flowing through the pressure side exhaust outlets  112  and into the pressure side nearwall cooling channel  48  impinge upon the outer wall  13  forming the pressure side  36 . A portion of the cooling fluids may be exhausted through the film cooling orifices at an upstream end of the pressure side nearwall cooling channel  48  near the rib  72  form the upstream end of the pressure side nearwall cooling channel  48 . The cooling fluids flowing through the suction side exhaust outlets  120  and into the suction side nearwall cooling channel  50  impinge upon the outer wall  12  forming the suction side  38 . In particular, the cooling fluid strikes the heat dissipating ribs in the midchord region  150  upstream from the cooling fluid flow controllers  22 . The heat dissipating ribs  152  have been shown to reduce localized hot spot outer wall temperature by up to 60 degrees Celsius while having a negligible impact on mass flow rate. The heat dissipating ribs  152  may also have a 40 percent increase in heat flux for the mid chord region  150  containing the heat dissipating ribs  152 . 
     The cooling fluids in the pressure side nearwall cooling channel  48  on the pressure side  36  are directed toward an inner surface of the outer wall  13  forming the pressure side  36  by a first bypass flow reducer  31  where the cooling fluids flow through a first row of cooling fluid flow controllers  22  rather than flowing in between the small gap  110  between an end  111  of the cooling fluid flow controllers  22  and the aft insert  18 . The bypass flow reducers  31  direct the cooling fluids towards the outer wall  13  forming the pressure side  36 , thereby substantially reducing the flow of cooling fluids between the gap  110  created between the end  111  of the cooling fluid flow controllers  22  and the aft insert  18 . The gap  110  may be about 0.3 millimeters in size due to assembly. Tighter tolerances on either side would aide flow and H/T characteristics, while increased clearances would negatively affect flow and NTT. In addition, the bypass flow reducers  31  may direct the cooling fluids towards the outer wall  13  forming the pressure side  36 , which is most need of cooling due to its direct exposure to the combustor exhaust gases. The cooling fluids flow through successive rows of cooling fluid flow controllers  22  zigzagging back and forth and increasing in temperature moving toward the trailing edge  34  as the cooling fluids pick up heat from the outer wall  13  and the cooling fluid flow controllers  22 . The cooling fluids entering the suction side nearwall cooling channel  50  may flow substantially in the same manner as the fluids in the pressure side nearwall cooling channel  48  described above, and thus, for brevity, are not further reiterated here. 
     The cooling fluids from the pressure side nearwall cooling channel  48  and the suction side nearwall cooling channel  50  may be exhausted into the trailing edge channel  30 . In addition, cooling fluids from within the aft insert  18  may be exhausted directly into the trailing edge channel  30  via the refresher holes  84 . As the cooling fluids enter the trailing edge channel  30 , the cooling fluids pass through the first and second spanwise extending rows  94 ,  96 , whereby the cooling fluids strike the cooling fluid flow controllers  22  and increase in temperature. The first and second spanwise extending rows  94 ,  96  of fluid flow controllers  22  also impart a zigzag motion to the cooling fluids. The cooling fluids may also flow past one or more rows of pin fins  102  and may be exhausted from the trailing edge exhaust orifices  140 . 
     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.