Patent Publication Number: US-9840930-B2

Title: Internal cooling system with insert forming nearwall cooling channels in midchord cooling cavities of a gas turbine airfoil

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 airfoil. 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 the 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. 
     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 therein that forms 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. The cooling fluid flow controllers may be collected into spanwise extending rows, and the internal cooling system may include one or more bypass flow reducers extending from the insert toward the outer wall to direct the cooling fluids through the channels created by the cooling fluid flow controllers, thereby increasing the effectiveness of the internal cooling system. 
     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 and a cooling system positioned within interior aspects of the generally elongated hollow airfoil. The cooling system may include one or more midchord 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 the outer wall forming the generally elongated hollow airfoil toward the insert, where the cooling fluid flow controllers form a plurality of alternating zigzag channels extending downstream toward the trailing edge. One or more bypass flow reducers may extend from the insert toward the outer wall to reduce flow of cooling fluids. 
     One or more of the cooling fluid flow controllers may have a cross-sectional area formed by a pressure side that is on an opposite side from a suction side. The pressure and suction sides may be coupled together via a leading edge and trailing edge on an opposite end of the cooling fluid flow controller from the leading edge. A first spanwise extending row of cooling fluid flow controllers may include a plurality of cooling fluid flow controllers having a cross-sectional areas formed by a pressure side that is on an opposite side from a suction side, whereby the pressure and suction sides are coupled together via a leading edge and trailing edge on an opposite end of the at least one cooling fluid flow controller from the leading edge. A pressure side of one cooling fluid flow controller may be adjacent to a suction side of an adjacent cooling fluid flow controller. In another embodiment, each of the cooling fluid flow controllers within the first spanwise extending row of cooling fluid flow controllers may be positioned similarly, such that a pressure side of one cooling fluid flow controller is adjacent to a suction side of an adjacent cooling fluid flow controller, except for a cooling fluid flow controller at an end of the first spanwise extending row. The internal cooling system may include a second spanwise extending row of cooling fluid flow controllers positioned downstream from the first spanwise extending row of cooling fluid flow controllers. The second spanwise extending row of cooling fluid flow controllers may have one or more cooling fluid flow controllers with a pressure side on an opposite side of the cooling fluid flow controller than in the first spanwise extending row of cooling fluid flow controllers, thereby causing cooling fluid flowing through the second spanwise extending row of cooling fluid flow controllers to be directed downstream with a spanwise vector that is opposite to a spanwise vector imparted on the cooling fluid by the first spanwise extending row of cooling fluid flow controllers. As such, a zigzag flow channel is created. 
     In at least one embodiment, the midchord cooling cavity may include one or more ribs separating the midchord cooling cavity into a leading edge cooling cavity and a trailing edge cooling cavity. One or more impingement standoffs may extend from the outer wall forming the suction side radially inward toward the insert. The plurality of cooling fluid flow controllers may extend from the outer wall forming the pressure side of the generally elongated hollow airfoil. The insert may include a plurality of impingement holes directed toward the suction side of the generally elongated hollow airfoil. In at least one embodiment, the bypass flow reducer may be formed from a plurality of bypass flow reducers. One or more of the plurality of bypass flow reducers may be positioned between adjacent spanwise extending rows of cooling fluid flow controllers. 
     One or more forward support ribs may extend from an upstream end of the insert into contact with an upstream insert support, and an aft support rib extending from a downstream end of the insert into contact with a downstream insert support. The forward support rib extending from the upstream end of the insert may make contact with a pressure side of the upstream insert support, and the aft support rib extending from the downstream end of the insert may make contact with a pressure side of the downstream insert support. 
     During use, cooling fluids may be supplied from a compressor or other such source to the inner chamber of the insert of the internal cooling system. Cooling fluids may fill the insert and generally flow spanwise throughout the insert. Cooling fluids are passed through the cooling fluid exhaust outlet into the nearwall cooling channel on the pressure side and through the impingement holes into the nearwall cooling channel near the suction side. The cooling fluids in the nearwall cooling channel on the pressure side are prevented from flowing into the nearwall cooling channel on the suction side via the inset and the forward support rib and the aft support rib. The cooling fluids flowing from the impingement holes into the nearwall cooling channel near the suction side impinge upon the inner surface of the outer wall forming the suction side. 
     The cooling fluids in the nearwall cooling channel on the pressure side are directed toward an inner surface of the outer wall forming the pressure side by a first bypass flow reducer where the cooling fluids flow through a first row of cooling fluid flow controllers rather than flowing in between the small gap between a proximal end of the cooling fluid flow controllers and the insert. The bypass flow reducers direct the cooling fluids towards the outer wall forming the pressure side, thereby substantially reducing the flow of cooling fluids between the gap created between the proximal end of the cooling fluid flow controllers and the insert. In addition, the bypass flow reducers direct the cooling fluids towards the outer wall forming the pressure side, which directs the cooling fluids towards the outer wall, 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 zigzagging back and forth and increasing in temperature moving toward the trailing edge as the cooling fluids pick up heat from the outer wall and the cooling fluid flow controllers. The cooling fluids may also flow past one or more rows of pin fins and may be exhausted from the film cooling holes. The cooling fluids may also form film cooling on an outer surface of the outer wall via the film cooling holes at the leading edge that are configured to form a showerhead and the other film cooling holes in the outer walls forming the pressure and suction sides. 
     An 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. 
     Another advantage of the invention is that the unique pressure distribution expands the insert outwardly and pushes the whole insert against the forward support rib and the aft support rib. 
     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 vane including the internal cooling system. 
         FIG. 2  is a cross-section view of the turbine vane taken at section line  2 - 2  in  FIG. 1  of the internal cooling system, including the leading edge and trailing edge cooling cavities. 
         FIG. 3  is a cross-section view of the turbine vane taken at section line  3 - 3  in  FIG. 2 . 
         FIG. 4  is a detail view of the cooling fluids controllers and pin fins of the internal cooling system taken a detail line  4 - 4  in  FIG. 3 . 
         FIG. 5  is a detail view of the insert of the internal cooling system taken at detail line  5 - 5  in  FIG. 3 . 
         FIG. 6  is a perspective view of a cross-sectional view of the inner surface of the outer wall forming the pressure and suction sides together with the cooling fluids controllers, pin fins and impingement standoffs extending radially inward taken at section line  6 - 6  in  FIG. 3 . 
         FIG. 7  is a cross-section view of the casting core forming the nearwall cooling channel at the suction side of the internal cooling system taken at section line  7 - 7  in  FIG. 3 . 
         FIG. 8  is a detail view of the cooling fluids controllers and pin fins of the internal cooling system in the trailing edge cooling cavity taken a detail line  8 - 8  in  FIG. 7 . 
         FIG. 9  is a cross-section view of the casting core forming the nearwall cooling channel at the pressure side of the internal cooling system taken at section line  9 - 9  in  FIG. 3 . 
         FIG. 10  is a detail view of the cooling fluids controllers and pin fins of the internal cooling system in the leading edge cooling cavity taken a detail line  10 - 10  in  FIG. 9 . 
         FIG. 11  is a suction side side view of the insert. 
         FIG. 12  is a pressure side view of the insert. 
         FIG. 13  is a cross-sectional view of an inner surface of the suction side taken at section line  13 - 13  in  FIG. 1 . 
         FIG. 14  is a detail view of the inner surface of the suction side taken at detail  14 - 14  in  FIG. 13 . 
         FIG. 15  is a perspective view of the insert. 
         FIG. 16  is an end view of the insert. 
         FIG. 17  is a detail, end view of the insert of the internal cooling system, with the insert showing the exhaust film cooling holes, taken at detail line  5 - 5  in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-17 , 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 therein that forms 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 . The cooling fluid flow controllers  22  may be collected into spanwise extending rows  28 , and the internal cooling system  14  may include one or more bypass flow reducers  30  extending from the insert  18  toward the outer wall  24  to direct the cooling fluids through the 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, 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. 1, 3, 5, and 17 , the cooling system  14  may include one or more midchord cooling cavities  45  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 , as shown in  FIGS. 2, 4 and 8-10 , may extend from the outer wall  24  forming 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 also include one or more bypass flow reducers  30  extending from the insert  18  toward the outer wall  24  to reduce flow of cooling fluids. 
     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 . A first spanwise extending row  64  of cooling fluid flow controllers  22  may include a plurality of cooling fluid flow controllers  22  having 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, as shown in  FIGS. 3, 5 and 17 , the midchord cooling cavity  45  may include one or more ribs  72  separating the midchord cooling cavity  45  into a leading edge cooling cavity  74  and a trailing edge cooling cavity  76 . One or more impingement standoffs  77  may extend from the outer wall  24  forming the suction side  38  radially inward toward the insert  18 . A plurality of cooling fluid flow controllers  22  may extend from the outer wall  22  forming the pressure side  36  of the generally elongated hollow airfoil  26 . The insert  18  may include one or more impingement holes  78  directed toward the suction side  38  of the generally elongated hollow airfoil  26 . In another embodiment, the insert  18  may include a plurality of impingement holes  78  directed toward the suction side  38  of the generally elongated hollow airfoil  26 . The impingement holes  78  may form a plurality of spanwise extending rows  80 , as shown in  FIG. 11 . 
     In at least one embodiment, as shown in  FIGS. 3, 5, 12, 15 and 16 , 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 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 insert  18  to the inner surface  82  of the outer wall  24  forming the pressure side  36 . An insert  18  may have bypass flow reducers  30  with all the same height and lengths or varying heights and lengths. 
     The internal cooling system  14  may include a forward support rib  84 , as shown in  FIGS. 3, 5, 15 and 17 , extending from an upstream end  86  of the insert  18  into contact with an upstream insert support  88  and an aft support rib  90  extending from a downstream end  92  of the insert  18  into contact with a downstream insert support  94 . The forward support rib  84  extending from the upstream end  86  of the insert  18  may contact with a pressure side  96  of the upstream insert support  88 , and the aft support rib  90  extending from the downstream end  92  of the insert  18  may contact a pressure side  98  of the downstream insert support  94 . During operation, high pressure in the nearwall cooling channel  20  near the pressure side  36  forces the insert  18  toward the suction side  38 , thereby seating the forward support rib  84  against the upstream insert support  88 , and the aft support rib  90  against the downstream insert support  94 . 
     The internal cooling system  14  may include one or more film cooling holes  100 , as shown in  FIGS. 4 and 17 , extending through the outer wall  24  to exhaust cooling fluids from the nearwall cooling channel  20 . The film cooling holes  100  may be positioned at the leading edge  32  to form a showerhead and may extend through the pressure and suction sides  36 ,  38 . The film cooling holes  100  may have any appropriate length and cross-sectional shape. The film cooling holes in the pressure side  36 , nearest to the rib  72  separating the leading edge cooling cavity  74  from the trailing edge cavity  76 , may be formed from multiple spanwise extending rows, such as, but not limited to, two rows, and may be positioned at an acute angel relative to the pressure side  36 , such as, but not limited to, about 30 degrees offset from orthogonal. The film cooling holes  100  may also be positioned at areas of highest pressure at the leading edge  32 . 
     The internal cooling system  14  may include one or more rows of pin fins  102  extending from the outer wall  24  at the insert  18  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  extending from the outer wall  24  at the insert  18  downstream from the cooling fluid flow controllers  22  may be positioned in one or more spanwise extending rows  28  of pin fins  108 . 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 wall  24  of about 1.5 millimeters. The insert  18  may include one or more cooling fluid exhaust outlets  104  at the leading edge  32  for supplying cooling fluids to a nearwall cooling chamber  20  formed between the outer wall  24  forming the pressure side  36  and the insert  18 . One or more bypass flow reducers  30  may extend from the insert  18  immediately downstream from the cooling fluid exhaust outlet  104  at the leading edge  32  for supplying cooling fluids to a nearwall cooling chamber  20  formed between the outer wall  24  forming the pressure side  36  and the insert  18 . 
     The trailing edge cooling cavity  76  may include a plurality of cooling fluid flow controllers  22 . In at least one embodiment, the plurality of cooling fluid flow controllers  22  may be positioned in one or more generally spanwise extending rows. The spanwise extending rows may be generally parallel to each other and may be parallel to the rib  72  separating the midchord cooling cavity  45  into the leading edge cooling cavity  74  and the trailing edge cooling cavity  76 . The cooling fluid flow controllers  22  in the trailing edge cooling cavity  76  may extend from the outer wall  24  forming the pressure side  36  to the outer wall  24  forming the suction side  38 . One or more rows of pin fins  102  may be positioned between the spanwise extending rows of cooling fluid flow controllers  22  and the trailing edge  34 . Pin fins  102  within adjacent rows of pin fins  102  may be offset from each other in the spanwise direction. 
     During use, cooling fluids may be supplied from a compressor or other such source to the inner chamber  106  of the insert  18  of the internal cooling system  14 . Cooling fluids may fill the insert  18  and generally flow spanwise throughout the insert  18 . Cooling fluids are passed through the cooling fluid exhaust outlet  104  into the nearwall cooling channel  20  on the pressure side  36  and through the impingement holes  78  into the nearwall cooling channel  20  near the suction side  38 . The cooling fluids in the nearwall cooling channel  20  on the pressure side  36  are prevented from flowing into the nearwall cooling channel  20  on the suction side  38  via the inset  18  and the forward support rib  84  and the aft support rib  90 . The cooling fluids flowing from the impingement holes  78  into the nearwall cooling channel  20  near the suction side  38  impinge upon the inner surface of the outer wall  24  forming the suction side  38 . 
     The cooling fluids in the nearwall cooling channel  20  on the pressure side  36  are directed toward an inner surface of the outer wall  24  forming the pressure side  36  by a first bypass flow reducer  30  where the cooling fluids flow through a first row of cooling fluid flow controllers  22  rather than flowing in between the small gap between a proximal end  108  of the cooling fluid flow controllers  22  and the insert  18 . The bypass flow reducers  30  direct the cooling fluids towards the outer wall  24  forming the pressure side  36 , thereby substantially reducing the flow of cooling fluids between the gap  110  created between the proximal end  108  of the cooling fluid flow controllers  22  and the insert  18 . The gap may be about 0.2 millimeters in size due to assembly. Tighter tolerances on either side would aide flow and HIT characteristics, while increased clearances would negatively affect flow and H/T. In addition, the bypass flow reducers  30  direct the cooling fluids towards the outer wall  24  forming the pressure side  36 , which directs the cooling fluids towards the outer wall  24 , 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  24  and the cooling fluid flow controllers  22 . The cooling fluids may also flow past one or more rows of pin fins  102  and may be exhausted from the film cooling holes  100 . The cooling fluids may also form film cooling on an outer surface of the outer wall  24  via the film cooling holes  100  at the leading edge  32  that are configured to form a showerhead and the other film cooling holes in the outer walls  24  forming the pressure and suction sides  36 ,  38 . 
     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.