Patent Publication Number: US-10309227-B2

Title: Multi-turn cooling circuits for turbine blades

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to co-pending U.S. application Ser. Nos. 15/334,474, 15/334,454, 15/334,585, 15/334,448, 15/334,501, 15/334,517, 15/334,450, 15/334,471, and 15/334,483, all filed on Oct. 26, 2016. 
     TECHNICAL FIELD 
     The disclosure relates generally to turbine systems, and more particularly, to multi-turn cooling circuits for turbine blades of a turbine system. 
     BACKGROUND 
     Gas turbine systems are one example of turbomachines widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor section, a combustor section, and a turbine section. During operation of a gas turbine system, various components in the system, such as turbine blades and nozzle airfoils, are subjected to high temperature flows, which can cause the components to fail. Since higher temperature flows generally result in increased performance, efficiency, and power output of a gas turbine system, it is advantageous to cool the components that are subjected to high temperature flows to allow the gas turbine system to operate at increased temperatures. 
     A multi-wall airfoil for a turbine blade typically contains an intricate maze of internal cooling passages. Cooling air (or other suitable coolant) provided by, for example, a compressor of a gas turbine system, may be passed through and out of the cooling passages to cool various portions of the multi-wall airfoil and/or turbine blade. Cooling circuits formed by one or more cooling passages in a multi-wall airfoil may include, for example, internal near wall cooling circuits, internal central cooling circuits, tip cooling circuits, and cooling circuits adjacent the leading and trailing edges of the multi-wall airfoil. 
     SUMMARY 
     A first embodiment may include a trailing edge cooling system for a turbine blade. The trailing edge cooling system includes: a cooling circuit including: an outward leg extending axially toward a trailing edge of the turbine blade; a return leg positioned adjacent the outward leg and extending axially from the trailing edge of the turbine blade; and a plurality of turn legs fluidly coupling the outward leg and the return leg, the plurality of turn legs including: a turn leg positioned directly adjacent the trailing edge of the turbine blade; and a distinct turn leg positioned axially adjacent the turn leg, opposite the trailing edge of the turbine blade, the distinct turn leg oriented non-parallel to at least one of the outward leg and the return leg. 
     Another embodiment may include a turbine blade including: a trailing edge cooling system disposed within the turbine blade, the trailing edge cooling system including: a plurality of cooling circuits extending at least partially along a radial length of a trailing edge of the turbine blade, at least one of the cooling circuits including: an outward leg extending axially toward the trailing edge of the turbine blade; a return leg positioned adjacent the outward leg and extending axially from the trailing edge of the turbine blade; and a plurality of turn legs fluidly coupling the outward leg and the return leg, the plurality of turn legs including: a turn leg positioned directly adjacent the trailing edge of the turbine blade; and a distinct turn leg positioned axially adjacent the turn leg, opposite the trailing edge of the turbine blade, the distinct turn leg oriented non-parallel to at least one of the outward leg and the return leg. 
     A further embodiment may include a turbomachine, including: a turbine component including a plurality of turbine blades; and a trailing edge cooling system disposed within at least one of the plurality of turbine blades, the trailing edge cooling system including: a plurality of cooling circuits extending at least partially along a radial length of a trailing edge of the turbine blade, at least one of the plurality of cooling circuit including: an outward leg extending axially toward the trailing edge of the turbine blade; a return leg positioned adjacent the outward leg and extending axially from the trailing edge of the turbine blade; and a plurality of turn legs fluidly coupling the outward leg and the return leg, the plurality of turn legs including: a turn leg positioned directly adjacent the trailing edge of the turbine blade; and a distinct turn leg positioned axially adjacent the turn leg, opposite the trailing edge of the turbine blade, the distinct turn leg oriented non-parallel to at least one of the outward leg and the return leg. 
     The illustrative aspects of the present disclosure solve the problems herein described and/or other problems not discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure. 
         FIG. 1  is a perspective view of a turbine blade having a multi-wall airfoil according to various embodiments. 
         FIG. 2  is a cross-sectional view of the turbine blade of  FIG. 1 , taken along line X-X in  FIG. 1  according to various embodiments. 
         FIG. 3  is a side view of cooling circuits including a plurality of turn legs of a trailing edge cooling system according to various embodiments. 
         FIG. 4  is a top cross-sectional view of the cooling circuit of  FIG. 3  according to various embodiments. 
         FIG. 5  depicts the section shown in  FIGS. 3 and 4  of the turbine blade of  FIG. 1  according to various embodiments. 
         FIG. 6  is a side view of cooling circuits including a plurality of turn legs of a trailing edge cooling system according to additional embodiments. 
         FIG. 7  is a side view of cooling circuits including a plurality of turn legs of a trailing edge cooling system according to another embodiment. 
         FIG. 8  is a side view of cooling circuits including a plurality of turn legs of a trailing edge cooling system according to further embodiments. 
         FIG. 9  is a side view of cooling circuits including a plurality of turn legs of a trailing edge cooling system according to additional embodiments. 
         FIG. 10  is a side view of cooling circuits including a plurality of turn legs of a trailing edge cooling system according to further embodiments. 
         FIG. 11  is a schematic diagram of a gas turbine system according to various embodiments. 
     
    
    
     It is noted that the drawings of the disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     As indicated above, the disclosure relates generally to turbine systems, and more particularly, to multi-turn cooling circuits for turbine blades of a turbine system. As used herein, an airfoil of a turbine blade may include, for example, a multi-wall airfoil for a rotating turbine blade or a nozzle or airfoil for a stationary vane utilized by turbine systems. 
     According to embodiments, a trailing edge cooling circuit with flow reuse is provided for cooling a turbine blade, and specifically a multi-wall airfoil, of a turbine system (e.g., a gas turbine system). A flow of coolant is reused after flowing through the trailing edge cooling circuit. After passing through the trailing edge cooling circuit, the flow of coolant may be collected and used to cool other sections of the airfoil and/or turbine blade. For example, the flow of coolant may be directed to at least one of the pressure or suction sides of the multi-wall airfoil of the turbine blade for convection and/or film cooling. Further, the flow of coolant may be provided to other cooling circuits within the turbine blade, including tip, and platform cooling circuits. 
     Traditional trailing edge cooling circuits typically eject the flow of coolant out of a turbine blade after it flows through a trailing edge cooling circuit. This is not an efficient use of the coolant, since the coolant may not have been used to its maximum heat capacity before being exhausted from the turbine blade. Contrastingly, according to embodiments, a flow of coolant, after passing through a trailing edge cooling circuit, is used for further cooling of the multi-wall airfoil and/or turbine blade. 
     In the Figures (see, e.g.,  FIG. 11 ), the “A” axis represents an axial orientation. As used herein, the terms “axial” and/or “axially” refer to the relative position/direction of objects along axis A, which is substantially parallel with the axis of rotation of the turbine system (in particular, the rotor section). As further used herein, the terms “radial” and/or “radially” refer to the relative position/direction of objects along an axis “R” (see, e.g.,  FIG. 1 ), which is substantially perpendicular with axis A and intersects axis A at only one location. Finally, the term “circumferential” refers to movement or position around axis A (e.g., axis “C”). 
     Turning to  FIG. 1 , a perspective view of a turbine blade  2  is shown. Turbine blade  2  includes a shank  4  and a multi-wall airfoil  6  coupled to and extending radially outward from shank  4 . Multi-wall airfoil  6  includes a pressure side  8 , an opposed suction side  10 , and a tip area  52 . Multi-wall airfoil  6  further includes a leading edge  14  between pressure side  8  and suction side  10 , as well as a trailing edge  16  between pressure side  8  and suction side  10  on a side opposing leading edge  14 . Multi-wall airfoil  6  extends radially away from a pressure side platform  5  and a suction side platform  7 . 
     shank  4  and multi-wall airfoil  6  of turbine blade  2  may each be formed of one or more metals (e.g., nickel, alloys of nickel, etc.) and may be formed (e.g., cast, forged or otherwise machined) according to conventional approaches. Shank  4  and multi-wall airfoil  6  may be integrally formed (e.g., cast, forged, three-dimensionally printed, etc.), or may be formed as separate components which are subsequently joined (e.g., via welding, brazing, bonding or other coupling mechanism). 
       FIG. 2  depicts a cross-sectional view of multi-wall airfoil  6  taken along line X-X of  FIG. 1 . As shown, multi-wall airfoil  6  may include a plurality of internal passages. In embodiments, multi-wall airfoil  6  includes at least one leading edge passage  18 , at least one pressure side (near wall) passage  20 , at least one suction side (near wall) passage  22 , at least one trailing edge passage  24 , and at least one central passage  26 . The number of passages  18 ,  20 ,  22 ,  24 ,  26  within multi-wall airfoil  6  may vary, of course, depending upon for example, the specific configuration, size, intended use, etc., of multi-wall airfoil  6 . To this extent, the number of passages  18 ,  20 ,  22 ,  24 ,  26  shown in the embodiments disclosed herein is not meant to be limiting. According to embodiments, various cooling circuits can be provided using different combinations of passages  18 ,  20 ,  22 ,  24 ,  26 . 
     An embodiment including a trailing edge cooling system  30  is depicted in  FIGS. 3-5 . As the name indicates, trailing edge cooling system  30  is located adjacent trailing edge  16  of multi-wall airfoil  6 , between pressure side  8  and suction side  10  of multi-wall airfoil  6 . 
     Trailing edge cooling system  30  includes a plurality of radially spaced (i.e., along the “R” axis (see, e.g.,  FIG. 1 )) cooling circuits  32  (only two are shown), each including an outward leg  34 , a plurality of turn legs  36 , and a return leg  38 . Outward leg  34  extends axially toward and/or substantially perpendicular to trailing edge  16  of multi-wall airfoil  6 . Return leg  38  extends axially toward leading edge  14  of multi-wall airfoil  6 . Additionally as shown in  FIG. 3 , return leg  38  extends axially away from and/or substantially perpendicular to trailing edge  16  of multi-wall airfoil  6 . As such, outward leg  34  and return leg  38  may be, for example, positioned and/or oriented substantially in parallel with respect to one another. Return leg  38  for each cooling circuit  32  forming trailing edge cooling system  30  may be positioned below and/or closer to shank  4  of turbine blade  2  than the corresponding outward leg  34  in fluid communication with return leg  38 . In embodiments, trailing edge cooling system  30 , and/or the plurality of cooling circuits  32  forming trailing edge cooling system  30 , may extend along the entire radial length (L) ( FIG. 5 ) of trailing edge  16  of multi-wall airfoil  6 . In other embodiments, trailing edge cooling system  30  may partially extend along one or more portions of trailing edge  16  of multi-wall airfoil  6 . 
     In each cooling circuit  32 , outward leg  34  is radially offset along the “R” axis relative to return leg  38  by the plurality of turn legs  36 . To this extent, the plurality of turn legs  36  fluidly couples outward leg  34  of cooling circuit  32  to return leg  38  of cooling circuit  32 , as discussed herein. In the non-limiting embodiment shown in  FIG. 3 , for example, outward leg  34  is positioned radially outward relative to return leg  36  in each of cooling circuits  32 . In other embodiments, in one or more of cooling circuits  32 , the radial positioning of outward leg  34  relative to return leg  38  may be reversed such that outward leg  34  is positioned radially inward relative to return leg  38 . A non-limiting position  28  of the portion of trailing edge cooling system  30  depicted in  FIG. 3  within multi-wall airfoil  6  is illustrated in  FIG. 5 . 
     As shown in  FIG. 4 , in addition to a radial offset, outward leg  34  may be circumferentially offset by the plurality of turn legs  36  at an angle α relative to return leg  38 . In this configuration, outward leg  34  extends along suction side  10  of multi-wall airfoil  6 , while return leg  38  extends along pressure side  8  of multi-wall airfoil  6 . The radial and circumferential offsets may vary, for example, based on geometric and heat capacity constraints on trailing edge cooling system  30  and/or other factors. In other embodiments, outward leg  34  may extend along pressure side  8  of multi-wall airfoil  6 , while return leg  38  may extend along suction side  10  of multi-wall airfoil  6 . 
     As shown in  FIG. 3 , the plurality of turn legs  36  may include various turn legs for (fluidly) coupling, joining and/or providing outward leg  34  to be in fluid communication with return leg  38 . Specifically, outward leg  34  may be in fluid communication with return leg  38  via the plurality of turn legs  36  of cooling circuit  32 , such that a coolant  40  may pass from and/or flow through outward leg  34 , through the plurality of turn legs  36 , and to return leg  38 , as discussed herein. As shown in  FIG. 3 , the plurality of turn legs  36  of cooling circuit  32  may be positioned adjacent to trailing edge  16  of multi-wall airfoil  6 . Specifically, one turn leg of the plurality of turn legs  36  may be positioned directly adjacent, extend radially adjacent to and/or may be substantially parallel to trailing edge  16  of multi-wall airfoil  6 . As discussed in detail below, the plurality of turn legs  36  of cooling circuit  32 , and specifically the turn leg of the plurality of turn legs  36  that may be positioned directly adjacent to and/or radially extend substantially parallel to trailing edge  16 , may provide the greatest amount of heat transfer to cool trailing edge  16  of multi-wall airfoil  6 . 
     In a non-limiting example shown in  FIG. 3 , the plurality of turn legs  36  may include a first turn leg  42 , a second turn leg  44  and a third turn leg  46 . First turn leg  42  of the plurality of turn legs  36  may be positioned between outward leg  34  and return leg  38 , and more specifically, may be in direct fluid communication with and/or fluidly coupled with outward leg  34  and return leg  38 . First turn leg  42  may form a first turn, curve, bend and/or change in flow direction for coolant  40  within cooling circuit  32 . First turn leg  42  may be oriented and/or formed to be non-parallel with outward leg  34  and/or return leg  38 . In a non-limiting example shown in  FIG. 3 , first turn leg  42  may extend substantially perpendicular from outward leg  34 . Specifically, first turn leg  42  of the plurality of turn legs  36  may extend radially upward, away from and/or above outward leg  34 , such that first turn leg  42  is positioned and/or oriented substantially perpendicular to outward leg  34 . First turn leg  42  may radially extend above and/or away from outward leg  34  toward tip area  52  of multi-wall airfoil  6  (see, e.g.,  FIG. 1 ). As shown in the non-limiting example of  FIG. 3 , first turn leg  42  may also radially extend substantially parallel to trailing edge  16  of multi-wall airfoil  6 . As a result of return leg  38  being positioned below and substantially parallel to outward leg  34 , it is understood that first turn leg  42  may also be positioned substantially perpendicular to and/or may radially extend away from and/or above return leg  38 . 
     Second turn leg  44  of the plurality of turn legs  36  may be in direct fluid communication with and/or fluidly coupled with first turn leg  42 . Additionally, and as discussed herein, second turn leg  44  may be in direct fluid communication with and/or fluidly coupled with third turn leg  46 , and may be positioned between first turn leg  42  and third turn leg  46  of the plurality of turn legs  36 . Second turn leg  44  may form a second turn, curve, bend and/or change in flow direction for coolant  40  within cooling circuit  32  from first turn leg  42 . Second turn leg  44  of the plurality of turn legs  36  may extend substantially perpendicular from first turn leg  42 . Specifically in the non-limiting example shown in  FIG. 3 , second turn leg  44  may extend axially away from and/or may extend axially toward trailing edge  16  of multi-wall airfoil  6 , such that second turn leg  44  is substantially perpendicular to first turn leg  42 . As a result, second turn leg  44  may also extend substantially perpendicular to trailing edge  16  of multi-wall airfoil  6 , and may be substantially parallel to outward leg  34  and/or return leg  38 . As shown in  FIG. 3 , second turn leg  44  of cooling circuit  32  may be positioned radially above and/or closer to tip area  52  than the corresponding outward leg  34  and/or return leg  38  of cooling circuit  32 . 
     As shown in  FIG. 3 , third turn leg  46  of the plurality of turn legs  36  may be in direct fluid communication with and may be positioned between second turn leg  44  and return leg  38 . That is, third turn leg  46  may be positioned between second turn leg  44  and return leg  38  to fluidly couple the plurality of turn legs  36 , and specifically second turn leg  44 , to return leg  38  of cooling circuit  32 . Similar to first turn leg  42  and second turn leg  44 , third turn leg  46  may form a third turn, curve, bend and/or change in flow direction for coolant  40  within cooling circuit  32 . Also similar to first turn leg  42 , third turn leg  46  may be oriented and/or formed to be non-parallel with outward leg  34  and/or return leg  38 . In a non-limiting example shown in  FIG. 3 , third turn leg  46  of the plurality of turn legs  36  may extend substantially perpendicular to return leg  38 . Specifically, third turn leg  46  may extend radially downward, away from and/or substantially below second turn leg  44  toward return leg  38  and/or shank  4  of turbine blade  2  (see, e.g.,  FIG. 1 ). Third turn leg  46  may also radially extend substantially parallel to first turn leg  42  and, may extend radially adjacent to and/or substantially parallel to trailing edge  16  of multi-wall airfoil  6 . Additionally, third turn leg  46  of the plurality of turn legs  36  may be positioned directly adjacent trailing edge  16  of multi-wall airfoil  6 , such that no other component, cooling circuit  32  or the like is positioned between third turn leg  46  and trailing edge  16 . In the non-limiting example shown in  FIG. 3 , at least a portion of third turn leg  46  may be positioned and/or radially extend above outward leg  34  and/or return leg  38 . The portion of third turn leg  46  that may be positioned and/or radially extend above outward leg  34  and/or return leg  38  may be a portion of third turn leg  46  positioned directly adjacent second turn leg  44  and/or axially aligned with first turn leg  42 . Because outward leg  34  is substantially parallel to return leg  38 , it is understood that third turn leg  46  may also be positioned substantially perpendicular to outward leg  34 . 
     Third turn leg  46  may include a length (L 3 ) substantially longer than the remaining turn legs (e.g., first turn leg  42 , second turn leg  44 ) of the plurality of turn legs  36  of cooling circuit  32 . Specifically, third turn leg  46  may include an outer wall  48  which includes a length (L 3 ) that may be greater than the length (L 1 ) of first turn leg  42  and/or the length (L 2 ) of second turn leg  44 . As shown in  FIG. 3 , outer wall  48  of third turn leg  46  may be substantially parallel to and may be positioned directly adjacent to trailing edge  16  of multi-wall airfoil  6 . As such, outer wall  48  of third turn leg  46  may be the closest portion and/or component of cooling circuit  32  to trailing edge  16  of multi-wall airfoil  6 . As discussed herein, the orientation and/or positioning of each of the turn legs of the plurality of turn legs  36 , as well as the length of outer wall  48  of third turn leg  46 , may improve the heat transfer within cooling circuit  32 . 
     A flow of coolant  40 , for example, air generated by a compressor  104  of a gas turbine system  102  ( FIG. 11 ), flows into trailing edge cooling system  30  via at least one coolant feed  70 . Each coolant feed  70  may be formed, for example, using one of trailing edge passages  24  depicted in  FIG. 2  or may be provided using any other suitable source or supply plenum of coolant in multi-wall airfoil  6 . At each cooling circuit  32 , a portion  72  of the flow of coolant  40  passes into outward leg  34  of cooling circuit  32  and flows towards the plurality of turn legs  36 . Portion  72  of coolant  40  is redirected and/or moved in various directions as the coolant flows through the plurality of turn legs  36  of cooling circuit  32 , as discussed herein. Portion  72  of coolant  40  subsequently flows into return leg  38  of cooling circuit  32  from the plurality of turn legs  36 . Portion  72  of the flow of coolant  40  passing into each outward leg  34  may be the same for each cooling circuit  32 . Alternatively, portion  72  of the flow of coolant  40  passing into each outward leg  34  may be different for different sets (i.e., one or more) of cooling circuits  32 . 
     portion  72  of the flow of coolant  40  flowing through cooling circuit  32  may flow through outward leg  34  to the plurality of turn legs  36  and may subsequently be redirected and/or moved in various directions through the plurality of turn legs  36 . In a non-limiting example shown in  FIG. 3 , portion  72  of coolant  40  flows through outward leg  34  to first turn leg  42  of the plurality of turn legs  36  and may be redirected radially upward and/or perpendicularly away from outward leg  34  as the coolant flows through first turn leg  42 . Portion  72  of coolant  40  may then flow from first turn leg  42  to second turn leg  44  of the plurality of turn legs  36  of cooling circuit  32 . More specifically, portion  72  of coolant  40  may be axially redirected toward trailing edge  16  of multi-wall airfoil  6  and/or may flow perpendicularly from first turn leg  42  as the coolant flows through second turn leg  44 . Portion  72  of coolant  40  may subsequently flow from second turn leg  44  to third turn leg  46 , and ultimately to return leg  38 . In the non-limiting example shown in  FIG. 3 , portion  72  of coolant  40  may be radially redirected toward return leg  38  and/or may flow perpendicularly from second turn leg  44  as the coolant flows through third turn leg  46 . Additionally, portion  72  of coolant  40  flowing through third turn leg  46  may flow substantially parallel to trailing edge  16  of multi-wall airfoil  6  and may flow over outer wall  48  of third turn leg  46 . Once portion  72  of coolant  40  flows through third turn leg  46 , it is redirected and/or moved into return leg  38 . That is, portion  72  of coolant  40  is axially redirected into return leg  38  from third turn leg  46  and/or redirected to flow substantially perpendicular to and/or axially away from trailing edge  16  of multi-wall airfoil  6 . 
     The orientation and/or positioning of each of the turn legs of the plurality of turn legs  36  may improve the heat transfer within cooling circuit  32 . That is, the orientation of each of the plurality of turn legs  36 , the position or orientation (e.g., adjacent, parallel) of one turn leg (e.g., third turn leg  46 ) of the plurality of turn legs  36  with respect to trailing edge  16  and/or the flow path in which coolant  40  flows through the plurality of turn legs  36  may improve heat transfer and/or the cooling of trailing edge  16  of multi-wall airfoil  6  of turbine blade  2 . In the non-limiting example shown in  FIG. 3 , a portion of the plurality of turn legs  36  (e.g., first turn leg  42 , second turn leg  44 ) are positioned and/or oriented within cooling circuit  32  to allow for third turn leg  46  to be positioned directly adjacent to and extend radially adjacent or substantially parallel to trailing edge  16 . As a result of the position and/or orientation of third turn leg  46  with respect to trailing edge  16 , the greatest amount of heat transfer may occur between third turn leg  46  and trailing edge  16  to adequately cool trailing edge  16  of multi-wall airfoil  6 . 
     According to embodiments, portion  72  of coolant  40  in the plurality of cooling circuits  32  of trailing edge cooling system  30  flow out of return legs  38  of cooling circuits  32  into a plenum or collection passage  74 . A single plenum or collection passage  74  may be provided, however multiple plenums or collection passages  74  may also be utilized. Collection passage  74  may be formed, for example, using one of trailing edge passages  24  depicted in  FIG. 2  or may be provided using one or more other passages and/or passages within multi-wall airfoil  6 . Although shown as flowing radially outward through collection passage  74  in  FIG. 3 , the “used” coolant may instead flow radially inward through collection passage  74 . 
     Collection coolant  76 , or a portion thereof, flowing into and through collection passage  74  may be directed (e.g. using one or more passages (e.g., passages  18 - 24 ) and/or passages within multi-wall airfoil  6 ) to one or more additional cooling circuits of multi-wall airfoil  6 . To this extent, at least some of the remaining heat capacity of collection coolant  76  is exploited for cooling purposes instead of being inefficiently expelled from trailing edge  16  of multi-wall airfoil  6 . 
     Collection coolant  76 , or a portion thereof, may be used to provide film cooling to various areas of multi-wall airfoil  6 . For example, as depicted in  FIGS. 1 and 2 , collection coolant  76  may be used to provide cooling film  50  to one or more of pressure side  8 , suction side  10 , pressure side platform  5 , suction side platform  7 , and tip area  52  of multi-wall airfoil  6 . 
     Collection coolant  76 , or a portion thereof, may also be used in a multi-passage (e.g., serpentine) cooling circuit in multi-wall airfoil  6 . For example, collection coolant  76  may be fed into a serpentine cooling circuit formed by a plurality of pressure side passages  20 , a plurality of suction side passages  22 , a plurality of trailing edge passages  24 , or combinations thereof. An illustrative serpentine cooling circuit  54  formed using a plurality of trailing edge passages  24  is depicted in  FIG. 2 . In serpentine cooling circuit  54 , at least a portion of collection coolant  76  flows in a first radial direction (e.g., out of the page) through a trailing edge passage  24 , in an opposite radial direction (e.g., into the page) through another trailing edge passage  24 , and in the first radial direction through yet another trailing edge passage  24 . Similar serpentine cooling circuits  54  may be formed using pressure side passages  20 , suction side passages  22 , central passages  26 , or combinations thereof. 
     Collection coolant  76  may also be used for impingement cooling, or together with pin fins. For example, in the non-limiting example depicted in  FIG. 2 , at least a portion of collection coolant  76  may be directed to a central passage  26 , through an impingement hole  56 , and onto a forward surface  58  of a leading edge passage  18  to provide impingement cooling of leading edge  14  of multi-wall airfoil  6 . Other uses of coolant  40  for impingement are also envisioned. At least a portion of collection coolant  76  may also be directed through a set of cooling pin fins  60  (e.g., within a passage (e.g., a trailing edge passage  24 )). Many other cooling applications employing collection coolant  76  are also possible. 
       FIG. 6  depicts another non-limiting example of a trailing edge cooling system  30  including a cooling circuit  32  having a plurality of turn legs  36 . With comparison to  FIG. 3 , the non-limiting example of cooling circuit  32  shown in  FIG. 6  may include smooth, curved and/or less severe transitions (e.g., 90° turns) and/or corners between the plurality of turn legs  36  of cooling circuit  32 . That is, in the non-limiting example shown in  FIG. 3 , the transitions and/or corners formed between each of the plurality of turn legs  36  of cooling circuit  32  are substantially perpendicular, sharp and/or angular (e.g., 90 degrees). In the non-limiting example shown in  FIG. 6 , transitions and/or corners formed between each of the plurality of turn legs  36  of cooling circuit  32  are substantially curved, rounded and/or smooth. The rounded or curved transitions and/or corners formed between each of the plurality of turn legs  36  may allow for better flow through cooling circuit  32  at the plurality of turn legs  36  and/or may substantially prevent coolant  40  from becoming trapped within the plurality of turn legs  36 . This may in turn help to improve heat transfer and/or cooling within multi-wall airfoil  6  of turbine blade  2 , as discussed above. 
       FIG. 7  depicts an additional non-limiting example of a trailing edge cooling system  30  including a cooling circuit  32  having a plurality of turn legs  36 . With comparison to  FIG. 3 , the non-limiting example of cooling circuit  32  shown in  FIG. 7  may include a distinct orientation for the plurality of turn legs  36 . Specifically, the plurality of turn legs  36  of cooling circuits  32  shown in  FIG. 7  may be substantially flipped and/or mirrored from the plurality of turn legs  36  depicted in  FIG. 3 . As shown in  FIG. 7 , and similar to  FIG. 3 , first turn leg  42  may be in direct fluid communication with outward leg  34 , third turn leg  46  may be in direct fluid communication with return leg  38 , and second turn leg  44  may be in direct fluid communication with and positioned between first turn leg  42  and third turn leg  46 . 
     However, distinct from cooling circuits  32  depicted in  FIG. 3 , first turn leg  42  may be positioned directly adjacent trailing edge  16 . Specifically, and as shown in  FIG. 7 , first turn leg  42  may be positioned directly adjacent to, and may extend radially adjacent and/or substantially parallel to trailing edge  16  of multi-wall  6 . First turn leg  42  may extend radially downward from outward leg  34 , adjacent trailing edge  16 , and toward/beyond return leg  38 . Additionally as shown in  FIG. 7 , first turn leg  42  may also include outer wall  48  positioned directly adjacent to and/or substantially parallel to trailing edge  16 , as similarly described herein. Second turn leg  44  may extend substantially perpendicular to and/or axially away from first turn leg  42  and/or trailing edge  16  of multi-wall airfoil  6 . Additionally, third turn leg  46  may extend radially upward, and/or substantially perpendicular to second turn leg  44 , toward return leg  38 . Additionally, third turn leg  46  may extend radially and substantially parallel to first turn leg  42  and/or trailing edge  16  of multi-wall airfoil  6 . 
     In the non-limiting example shown in  FIG. 7 , portion  72  of the flow of coolant  40  may also follow a distinct flow path within cooling circuits  32  than that described herein with respect to  FIG. 3 . As shown in  FIG. 7 , portion  72  of the flow of coolant  40  may flow axially toward trailing edge  16  through outward leg  36 . Subsequently, portion  72  of the flow of coolant  40  may flow into first turn leg  42  of the plurality of turn legs  36  of cooling circuit  32 . Specifically, portion  72  of coolant  40  may flow into and may flow radially downward through first turn leg  42 , along outer wall  48 , and directly adjacent to and/or substantially parallel to trailing edge  16  of multi-wall airfoil  6 . After flowing through first turn leg  42 , portion  72  of coolant  40  may flow axially and/or perpendicularly away from trailing edge  16  through second turn leg  44 . Next, portion  72  of coolant  40  may flow radially upward and substantially parallel to first turn leg  42  and/or trailing edge  16 , as portion  72  of coolant  40  flows through third turn leg  46  of the plurality of turn legs  36  of cooling circuit  32 . Finally, portion  72  of coolant  40  may flow axially away from trailing edge  16  through return leg  38 , and may, for example, be provided to other portions of multi-airfoil  6  to provide film cooling, as discussed herein. 
     To provide additional cooling of the trailing edge of multi-wall airfoil/blade and/or to provide cooling film directly to the trailing edge, exhaust passages (not shown) may pass from any part of any of the cooling circuit(s) described herein through the trailing edge and out of the trailing edge and/or out of a side of the airfoil/blade adjacent to the trailing edge. Each exhaust passage(s) may be sized and/or positioned within the trailing edge to receive only a portion (e.g., less than half) of the coolant flowing in particular cooling circuit(s). Even with the inclusion of the exhaust passages(s), the majority (e.g., more than half) of the coolant may still flow through the cooling circuit(s), and specifically the return leg thereof, to subsequently be provided to distinct portions of multi-wall airfoil/blade for other purposes as described herein, e.g., film and/or impingement cooling. 
       FIGS. 8-10  depict additional, non-limiting examples of cooling circuits  32 A,  32 B of trailing edge cooling system  30 . As discussed below, portions of cooling circuits  32 A,  32 B shown in  FIGS. 8-10  may be substantially similar to cooling circuits previously discussed. Additionally, and as discussed in detail below, other portions of cooling circuit  32 A,  32 B may be formed and/or function in a distinct manner. As a result, at least a portion of coolant  40  may flow through trailing edge cooling system  30  shown in  FIGS. 8-10  in a unique or distinct path. 
     A shown in  FIG. 8 , first cooling circuit  32 A may be substantially similar to cooling circuit  32  of trailing edge cooling system  30  shown and discussed herein with respect to  FIG. 3 . Specifically, first cooling circuit  32 A and its various portions (e.g., outward leg  34 A, plurality of turn legs  36 A, return leg  38 A) may be configured, formed, oriented and/or function in a substantially similar fashion as outward leg  34 , the plurality of turn legs  36  and return leg  38  of cooling circuit  32  shown and discussed herein with respect to  FIG. 3 . Additionally, second cooling circuit  32 B may be substantially similar to cooling circuit  32  of trailing edge cooling system  30  shown and discussed herein with respect to  FIG. 7 . Specifically, second cooling circuit  32 B and its various portions (e.g., outward leg  34 B, plurality of turn legs  36 B, return leg  38 B) may be configured, formed, oriented and/or function in a substantially similar fashion as outward leg  34 , the plurality of turn legs  36  and return leg  38  of cooling circuit  32  shown and discussed herein with respect to  FIG. 7 . 
     A shown in  FIG. 9 , and similar to  FIG. 8  first cooling circuit  32 A and its various portions (e.g., outward leg  34 A, plurality of turn legs  36 A, return leg  38 A) may be configured, formed, oriented and/or function in a substantially similar fashion as outward leg  34 , the plurality of turn legs  36  and return leg  38  of cooling circuit  32  shown and discussed herein with respect to  FIG. 3 . However, distinct from  FIGS. 7  and  8 , second cooling circuit  32 B may be formed and/or function in a distinct manner than the non-limiting examples discussed herein. Specifically, and as shown in  FIG. 9 , outward leg  34 B of second cooling circuit  32 B may be positioned and/or formed radially below or under return leg  38 B. As a result, return leg  38 A of first cooling circuit  32 A may be positioned directly adjacent and/or radially above return leg  38 B of second cooling circuit  32 A. 
     As discussed herein, the plurality of turn legs  36 B of second cooling circuit  32 B may be coupled and/or in direct fluid communication with similar legs of second cooling circuit  32 B. For example, first turn leg  42 B may be in direct fluid communication with outward leg  44 B and second turn leg  44 B, respectively, and third turn leg  46 B may be in direct fluid communication with return leg  38 B and second turn leg  44 B, respectively. However, because of the distinct formation and/or configuration of second cooling circuit  32 B, the flow path of portion  72  of coolant  40  flowing through second cooling circuit  32 B may be unique. As shown in  FIG. 9 , and similarly discussed herein, portion  72  of coolant  40  may flow through outward leg  34 B in an axial direction toward trailing edge  16  of multi-wall airfoil  6 . Once portion  72  of coolant  40  reaches the plurality of turn legs  36 B of second cooling circuit  32 , the flow path of portion  72  may be unique before reaching return leg  38 B. Specifically, portion  72  of coolant  40  may flow radially downward through first turn leg  42 B, and then axially toward trailing edge  16  of multi-wall airfoil  6  through second turn leg  44 B. From second turn leg  44 B, portion  72  of coolant  40  may flow radially upward (e.g., toward tip area  52 ) through third turn leg  46 B, and into return leg  38 B. As shown in  FIG. 9 , and similarly discussed herein, portion  72  of coolant  40  flowing radially upward through third turn leg  46 B may also flow directly adjacent to and/or substantially parallel with trailing edge  16  of multi-wall airfoil  6 . Finally, portion  72  of coolant  40  may flow axially through return leg  38 B and/or axially away from trailing edge  16  of multi-wall airfoil  6 , and into collection passage  74 . 
     Turning to the non-limiting example depicted in  FIG. 10 , portions of cooling circuits  32 A,  32 B may be may be substantially similar to cooling circuits  32 A,  32 B discussed herein with respect to  FIG. 9 . Specifically, outward legs  34 A,  34 B and the plurality of turn legs  36 A,  36 B of cooling circuits  32 A,  32 B shown in  FIG. 10  may be configured, formed and/or function in a substantially similar fashion as outward legs  34 A,  34 B and the plurality of turn legs  36 A,  36 B shown and discussed herein with respect to  FIG. 9 . Additionally, first outward leg  34 A may be substantially similar to second outward legs  34 B of cooling circuits  32 . Additionally, the first plurality of turn legs  36 A may be substantially similar to the second plurality of turn legs  36 B. However, second outward leg  34 B and the second plurality of turn legs  36 B may be oriented, formed and/or positioned as a “mirror image” of first outward leg  34 A and first plurality of turn legs  36 A, respectively. As a result, the flow of portion  72  of coolant  40  through the second plurality of turn legs  36 B may be distinct and/or opposite than the flow of coolant  40  through the first plurality of turn legs  36 A. As shown in  FIG. 10 , portion  72 B of coolant  40  may flow through second outward leg  34 B in a substantially similar manner (e.g., axially toward trailing edge  16 ) as portion  72 A of coolant  40  flowing through first outward leg  34 A. However, once portion  72 B of coolant  40  reaches the second plurality of turn legs  36 B, the flow path may vary and/or be the opposite of the flow of portion  72 A. Portion  72 B of coolant  40  may flow radially downward toward shank  4  of turbine blade  2  (see, e.g.,  FIG. 1 ) when flowing through first turn leg  42 B of the second plurality of turn legs  36 B. Portion  72 B of coolant  40  may flow axially toward trailing edge  16  of multi-wall airfoil  6  when flowing through second turn leg  44 B of the second plurality of turn legs  36 B, and subsequently may flow radially upward toward a single return leg  38  of cooling circuit  32 , as discussed herein. 
     As shown in  FIG. 10 , and distinct from the non-limiting examples previously discussed, two distinct sets of outward legs  34 A,  34 B and the plurality of turn legs  36 A,  36 B may share a single return leg  38 . Specifically, the first plurality of turn legs  36 A and the second plurality of turn legs  36 B may be in direct fluid communication and/or may be fluidly coupled to single return leg  38  of cooling circuit  32 . As previously discussed herein, single return leg  38  may extend substantially perpendicular to trailing edge  16  of multi-wall turbine airfoil  6 . Additionally, and as shown in  FIG. 10 , single return leg  38  may extend, be positioned between and/or may be substantially parallel to first outward leg  34 A and second outward leg  34 B of cooling circuit  32 . As discussed herein, the distinct portions  72 A,  72 B of coolant  40  that flows through the first plurality of turn legs  36 A and the second plurality of turn legs  36 B, respectively, may converge, combine and/or flow into and through single return leg  38  of cooling circuit  32 . 
       FIG. 11  shows a schematic view of gas turbomachine  102  as may be used herein. Gas turbomachine  102  may include a compressor  104 . Compressor  104  compresses an incoming flow of air  106 . Compressor  104  delivers a flow of compressed air  108  to a combustor  110 . Combustor  110  mixes the flow of compressed air  108  with a pressurized flow of fuel  112  and ignites the mixture to create a flow of combustion gases  114 . Although only a single combustor  110  is shown, gas turbine system  102  may include any number of combustors  110 . The flow of combustion gases  114  is in turn delivered to a turbine  116 , which typically includes a plurality of turbine blades  2  ( FIG. 1 ). The flow of combustion gases  114  drives turbine  116  to produce mechanical work. The mechanical work produced in turbine  116  drives compressor  104  via a shaft  118 , and may be used to drive an external load  120 , such as an electrical generator and/or the like. 
     In various embodiments, components described as being “fluidly coupled” to or “in fluid communication” with one another can be joined along one or more interfaces. In some embodiments, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are “coupled” to one another can be simultaneously formed to define a single continuous member. However, in other embodiments, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., fastening, ultrasonic welding, bonding). 
     When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element, it may be directly on, engaged, connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Additionally, in various embodiments, components described as being “substantially parallel” or “substantially perpendicular” with another component are understood to be exactly parallel/perpendicular to each other, or slightly angled from each other, within an acceptable range. In the latter instance, the acceptable range may be determined and/or defined as an angle that does not reduce or diminish the operation and/or function of the components described as being “substantially parallel” or “substantially perpendicular.” In non-limiting examples, components discussed herein as being “substantially parallel” or “substantially perpendicular,” may have no angular degree of variation (e.g., +/−0°), or alternatively, may have a small or minimal angular degree of variation (e.g., +/−15°). It is understood that the acceptable angular degree of variation discussed herein (e.g., +/−15°) is merely illustrative, and is not limiting. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.