Patent Publication Number: US-2023141484-A1

Title: Co and counter flow heat exchanger

Description:
TECHNICAL FIELD 
     This disclosure relates to airfoils and, in particular, airfoil cooling schemes. 
     BACKGROUND 
     Present airfoil cooling systems suffer from a variety of drawbacks, limitations, and disadvantages. Accordingly, there is a need for inventive systems, methods, components, and apparatuses described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views. 
         FIG.  1    illustrates a cross-sectional view of an airfoil; 
         FIG.  2    illustrates a cross-sectional view of an example of a dual feed circuit of an airfoil; and 
         FIG.  3    illustrates an example of a spar and coversheet of a dual feed circuit; 
         FIG.  4    illustrates another example of a spar and coversheet of a dual feed circuit; and 
         FIG.  5    illustrates an example of a method to cool an airfoil. 
     
    
    
     DETAILED DESCRIPTION 
     In a first example, a dual-wall airfoil may comprise a spar. The spar has a chord axis and a span axis. The dual-wall airfoil comprises a coversheet on the spar and a dual feed circuit between the spar and the coversheet. The dual feed circuit includes a first dam, a second dam spaced apart from the first dam along the chord axis of the spar, a first inlet disposed adjacent to the first dam, a second inlet disposed adjacent to the second dam, a circuit outlet disposed between the first inlet and the second inlet, and diamond and/or hexangular pedestals disposed on an outer surface of the spar. The outer surface of the spar faces the coversheet. The diamond and/or hexangular pedestals are located between the first inlet and the second inlet. The diamond and/or hexangular pedestals form multiple cooling channels between the first inlet and the circuit outlet and between the second inlet and the circuit outlet. No other circuit inlets are located between the first inlet and the second inlet. 
     In a second example, a dual-wall airfoil comprises the spar. The spar includes a plurality of internal cavities. The internal cavities include a first cavity disposed at a leading edge of the airfoil, a second cavity disposed at a trailing edge of the airfoil, a third cavity disposed between the first cavity and the second cavity. The spar further comprises the coversheet on the spar and the dual feed circuit disposed between the spar and the coversheet. The dual feed circuit includes the first dam, the second dam, the first inlet disposed adjacent to the first dam, the second inlet disposed adjacent to the second dam, and the circuit outlet disposed between the first inlet and the second inlet. The first inlet connects the first cavity to the dual feed circuit and the second inlet may connect the third cavity to the dual feed circuit. Alternatively or additionally, the first inlet connects the third cavity to the dual feed circuit and the second inlet connects the second cavity to the dual feed circuit. 
     In a third example, a method of cooling the airfoil comprises: supplying a cooling fluid to the first internal cavity of an airfoil spar and the second internal cavity of the airfoil spar. The method comprises directing the cooling fluid from the first internal cavity through the first inlet to a dual feed circuit. The first inlet is immediately adjacent to the first dam of the dual feed circuit. The method comprises directing the cooling fluid from the second internal cavity though the second inlet to the dual feed circuit. The second inlet may be adjacent to the second dam of the dual feed circuit. The method comprises directing the cooling fluid from the first inlet downstream through a plurality of diamond and/or hexangular pedestals and through the circuit outlet. The method comprises directing the cooling fluid from the second inlet upstream through the plurality of diamond and/or hexangular pedestals and through the circuit outlet. The method comprises directing the cooling fluid from the circuit outlet along an outer surface of the airfoil downstream of the circuit outlet. 
     One interesting feature of the systems and methods described below may be that dual feed circuits provide an effective airfoil cooling scheme while using less flow and/or delta pressure as compared to exclusively co-fed or counter-fed circuits. For example, by providing a dual feed circuit, which uses both co and counter flow feeds, the upstream side of the circuit is cooled using a co-fed heat exchanger while the downstream side of the circuit is fed using a counter-fed heat exchanger. The two inlets for the dual feed circuit (one upstream and one downstream of the outlet) and lower sink pressure (of the downstream inlet versus the upstream inlet) raises the pressure difference in the dual feed circuit to drive more coolant than an exclusively counter-fed circuit. 
     Alternatively, or in addition, by having the dual feed supply an outlet positioned between the two inlets, the downstream portion of the circuit also benefits from film cooling as cooling fluid exits the outlet. Alternatively, or in addition, an interesting feature of the systems and methods described below may be that by having two inlets, or two rows of inlets each disposed on an opposite end of the circuit, the inlet holes can be larger to mitigate blockage risk and to ensure adequate film coverage downstream of the outlet. 
     Alternatively, or in addition, dual feed circuits may be used in areas where there is a relatively high exit pressure, for example, on the pressure side and/or near the leading edge, in order to provide adequate cooling efficiently. Alternatively, or in addition, dual feed circuits allow for more flexibility in packaging the circuit on the airfoil, as the circuit inlets can be positioned independent from the circuit outlet to avoid internal ribs of the spar. 
       FIG.  1    illustrates an example of an airfoil  100 . The airfoil  100  may include a spar  102 , a coversheet  104 , an internal cavity  106 , a pressure side  108 , a suction side  110 , a leading edge  112 , a trailing edge  114 , a chord axis  116 , a heat exchanging circuit  118 , a circuit inlet  120 , and/or a circuit outlet  122 . 
     The leading edge  112  may be any point at the front of the airfoil  100 . The airfoil  100  is designed to have a fluid flow  126 , such as a flow of hot gases exiting a combustor of a gas turbine engine, flow around the airfoil  100 . The front of the airfoil  100  may be considered the side of the airfoil  100  facing into the fluid flow  126 . Alternatively, or additionally, the leading edge  112  may be the most upstream edge of the airfoil  100 . Upstream refers to a direction opposite of the direction of the fluid flow  126 . Alternatively or in addition, the leading edge  112  may be at a stagnation point, which is where a flow velocity of the fluid flow  126  is reduced to zero. The trailing edge  114  may be at the back of the airfoil  100 . The back of the airfoil  100  may be the side of the airfoil opposite of the front and/or opposite of the leading edge of the airfoil  100 . The trailing edge  114  may be the most downstream edge of the airfoil  100 . Downstream refers to the direction of the fluid flow  126 . The leading edge  112  may be opposite the trailing edge  114 . The pressure side  108  of the airfoil  100  is a side designed to have a comparatively higher static pressure than the suction side  110  in the presence of the fluid flow  126  so as to contribute to a lift force generated by the airfoil  100 . The pressure side  108  may extend from the leading edge  112  to the trailing edge  114  of the airfoil  100 . The suction side  110  may extend from the leading edge  112  to the trailing edge  114  of the airfoil  100  on a side that is opposite of the pressure side  108 . The chord axis  116  may extend along the chord-wise length of the airfoil  100 , in some examples connecting the leading edge  112  and the trailing edge  114 . 
     The spar  102  may form an inner structure of the airfoil  100 . For example, the spar  102  may form an inner wall of the airfoil  100  and one or more internal cavities  106  of the airfoil  100 . One or more internal ribs  124  may separate multiple internal cavities  106 . The coversheet  104  may form an outer wall of the airfoil  100 . The coversheet  104  may surround and/or encompass the spar  102 . The heat exchanging circuit  118  may be disposed in between the spar  102  and the coversheet  104 . Multiple heat exchanging circuits  118  may be disposed between the spar  102   and coversheet  104 . The heat exchanging circuits  118  may be located around the circumference of the spar  102 . Each heat exchanging circuit  118  may include a circuit inlet  120  and a circuit outlet  122 . The circuit inlet  120  may connect the heat exchanging circuit  118  to an internal cavity  106  so that the internal cavity  106  is in fluid communication with the heat exchanging circuit. The circuit outlet  122  may connect the heat exchanging circuit  118  to a flow of fluid external to the airfoil  100  so that the heat exchanging circuit  118  is in fluid communication with a fluid flowing  126  over and/or around the airfoil  100  and/or the outer surface of the coversheet  104 . 
     The airfoil  100  is a dual wall airfoil, wherein the coversheet  104  is the outer wall and the spar  102  is the inner wall. The airfoil  100  may be part of a gas turbine engine, for example, the airfoil  100  may be a blade and/or vane of the gas turbine engine. The gas turbine engine may be configured to supply power to and/or provide propulsion for an aircraft. Examples of the aircraft may include a helicopter, an airplane, an unmanned space vehicle, a fixed wing vehicle, a variable wing vehicle, a rotary wing vehicle, an unmanned combat aerial vehicle, a tailless aircraft, a hover craft, and any other airborne and/or extraterrestrial (spacecraft) vehicle. Alternatively, or in addition, the gas turbine engine may be utilized in a configuration unrelated to an aircraft such as, for example, an industrial application, an energy application, a power plant, a pumping set, a marine application (for example, for naval propulsion), a weapon system, a security system, a perimeter defense or security system. 
     The spar  102  may be any structure that extends along a span axis (shown in  FIG.  3   ) of the airfoil  100  and through the center of the airfoil  100 . The spar  102  may comprise any rigid structural material, for example, a metal and/or a composite material. The internal cavities  106  may extend inside the spar  102  along the span axis. The spar  102  may include a single internal cavity  106  or multiple internal cavities  106 . In some examples, the internal cavities  106  may be divided by internal ribs  124  into an upstream internal cavity  106  at the front of the airfoil  100 , a downstream internal cavity  106  at the back of the airfoil  100 , and/or one or more central internal cavities  106  disposed between the upstream and downstream internal cavities  106 . The number of internal cavities  106  may vary. For example, the spar  102  may have as few as one single internal cavity  106  or as many as six internal cavities  106 . A dual-feed circuit may be fed by one or two internal cavities  106 . The internal cavities  106  feeding the dual-feed circuit may not be adjacent to each other. For example, two internal cavities  106  that feed the same dual-feed circuit may have a third internal cavity  106  disposed between the two internal cavities  106 , third internal cavity  106  may not feed the same dual-feed circuit that the other two internal cavities  106  feed. 
     The coversheet  104  may be any structure positioned on the spar  102  that forms an outer layer of the airfoil  100 . The coversheet  104  may be made of any material capable of forming an outer surface of the airfoil  100 , for example, a metal alloy. 
     The heat exchanging circuit  118  may be formed by the gap and/or space between the outer surface of the spar  102  and the inner surface of the coversheet  104 . The heat exchanging circuit  118  may be a cooling circuit, by which the airfoil  100  is cooled. The heat exchanging circuit  118  may include a channel formed between the spar  102  and the coversheet  104 . The heat exchanging circuit  118  may be a dual feed circuit, a counter feed circuit, and/or a co feed circuit. A dual feed circuit may include at least two circuit inlets  120  and at least one circuit outlet  122 . The two circuit inlets  120  may be spaced apart from each other along the chord axis  116  of the airfoil  100 , wherein the circuit inlets  120  are disposed at an opposite ends of the dual feed circuit. For example, a circuit inlet  120  may be disposed adjacent to an upstream end of the dual feed circuit, or the end of the dual feed circuit closest to the leading edge  112  of the airfoil  100 . Another circuit inlet  120  may be disposed at the downstream end of the dual feed circuit, or the end of the dual feed circuit closest to the trailing edge  114  of the airfoil  100 . The circuit outlet  122  may be disposed between the two circuit inlets  120  along the chord axis  116 , for example, at an approximate midpoint of the dual feed circuit along the chord axis  116 . The airfoil  100  may comprise one or more dual feed circuits. The dual feed circuit may, for example, be disposed along the pressure side  108  of the airfoil  100  and/or near the leading edge  112  of the airfoil  100 . 
     Additionally or alternatively the heat exchanging circuits  118  may be a co-feed and/or a counter-feed circuit. A co-feed circuit may have a circuit inlet  120  at an upstream end of the co-feed circuit, or the end of the co-feed circuit closest to the leading edge  112  of the airfoil  100 . A co-feed circuit may have a circuit outlet  122  at a downstream end of the co-feed circuit, or the end of the co feed circuit closest to the trailing edge  114  of the airfoil. A counter-feed circuit may have a circuit inlet  120  at downstream end of the counter-feed circuit, or the end of the counter-feed circuit closest to the trailing edge  114  of the airfoil  100 . A counter-feed circuit may have a circuit outlet  122  at an upstream end of the counter-feed circuit, or the end of the counter-feed circuit closest to the leading edge  112  of the airfoil. The airfoil  100  may include one or more dual feed circuits, co-feed circuits, and/or co-flow circuits around the airfoil  100  between the spar  102  and the coversheet  104 . 
     A dual-feed circuit may, for example, be disposed at a midpoint along the chord axis  116  of the pressure side  108 . A co-feed circuit may extend downstream from a downstream end of the dual-feed circuit, towards the trailing edge  114 , and along the pressure side  108  of the airfoil  100 , extending between the dual-feed circuit and the trailing edge  114  of the airfoil  100 . For example, the co-feed circuit may extend from the dual-feed circuit to another heat exchanging circuit  118  that extends to, or covers, the trailing edge  114  of the airfoil  100 . Additionally or alternatively, a counter-feed circuit may extend upstream from an upstream end of the dual-feed circuit, towards the leading edge  112 , and along the pressure side of the airfoil  100 , extending between the dual-feed circuit and the leading edge  112  of the airfoil  100 . For example, the counter-feed circuit may extend from the dual-feed circuit to another heat exchanging circuit  118  that extends to, or covers, the leading edge  112  of the airfoil  100 . 
     The circuit inlets  120  may be any sort of aperture in the spar  102 , extending through the spar  102  wall from an internal cavity  106  to a heat exchanging circuit  118 . The circuit inlets  120  may be, for example, a through-hole formed via machining or casting. The circuit inlets  120  may be perpendicular to the spar  102  wall, or may be formed at an acute or obtuse angle with the spar  102  wall. The circuit outlets  122  may be any sort of aperture in the coversheet  104 , extending through the coversheet  104  from the heat exchanging circuit  118  and past the outer surface of the coversheet  104  and/or airfoil  100 . The circuit outlets  122  may, for example, be film holes formed at an angle with the coversheet  104  to direct cooling fluid in a film over the outer surface of the coversheet  104  and/or airfoil  100  downstream from the circuit outlet  122 . 
     During operation, a cooling fluid may flow from a cooling fluid source (not shown) into the internal cavities  106 . For example, the cooling fluid may flow through a shank of the airfoil  100  into the internal cavities  106 . The cooling fluid may come from an upstream component of the turbine engine, for example, bypass air from an upstream compressor. The cooling fluid and the fluid flow  126  may be the same fluid that originates from upstream and then is split between a cooling fluid flow and the hot fluid flow  126 . The cooling fluid may flow from the internal cavities  106 , through the circuit inlets  120  and into the heat exchanging circuits  118 . The cooling fluid may flow from the circuit inlets  120 , through the heat exchanging circuits  118 , and towards the circuit outlets  122 . In a dual feed circuit, for example, the cooling fluid may flow through a first internal cavity  106 , through the circuit inlet  120  disposed near the end of the dual feed circuit closest to the leading edge  112  of the airfoil  100 , flow downstream or towards the trailing edge  114  of the airfoil  100  to the circuit outlet  122 , out the circuit outlet  122 , and over the surface of the coversheet  104  downstream from the circuit outlet  122 . In a dual feed circuit the cooling fluid may also flow through a second internal cavity  106 , through the circuit inlet  120  disposed near the end of the dual feed circuit closest to the trailing edge  114  of the airfoil  100 , flow upstream or towards the leading edge  112  of the airfoil  100  to the circuit outlet  122 , combine with the cooling fluid flowing from the circuit inlet  120  closest to the leading edge  112  of the airfoil  100 , out the circuit outlet  122 , and over the surface of the coversheet  104  downstream from the circuit outlet  122 . 
       FIG.  2    illustrates a cross section view of a dual feed circuit  200  of airfoil  100 . The dual feed circuit  200  of  FIG.  2    may be a heat exchanging circuit  118  of  FIG.  1   . The dual feed circuit  200  may be disposed between the spar  102  and the coversheet  104  of the airfoil  100 . The dual feed circuit  200  may comprise an upstream circuit inlet  202 , a downstream circuit inlet  204 , an upstream dam  208 , a downstream dam  206 , and a circuit outlet  122 . As mentioned above, the terms “upstream” and “downstream” are in reference to the direction that hot gas flows over the outer surface of the coversheet  104 . 
     The upstream circuit inlet  202  may include one of the circuit inlets  120  from  FIG.  1    and may be disposed adjacent to the upstream dam  208 , which may be at the end of the dual feed circuit  200  that is closest to the leading edge  112  of the airfoil  100 . The downstream circuit inlet  204  may be one of the circuit inlets  120  shown in  FIG.  1    and may be disposed adjacent to the downstream dam  206 . The downstream dam  206  may be at the end of the dual feed circuit  200  closest to the trailing edge  114  of the airfoil  100 . 
     The upstream dam  208  and the downstream dam  206  may extend between the spar  102  and the coversheet  104  along each respective end of the dual feed circuit  200  so that cooling fluid may only enter or exit the dual feed circuit  200  from the circuit inlets  120 ,  202 ,  204  and/or the circuit outlet  122 . The dams  206 ,  208  may be made of the same material as the spar  102  and/or the coversheet  104 . For example, the dams  206 ,  208  may be part of a unitary structure with the spar  102  and/or the coversheet  104 . Additionally, or alternatively, the dams  206 ,  208  may be a different material from the spar  102  and/or the coversheet  104 . For example, the dams  206 ,  208  may be a baffle or seal inserted between the spar  102  and coversheet  104 . 
     During operation, cooling fluid  210  may flow from two of the internal cavities  106  through the upstream circuit inlet  202  and through the downstream circuit inlet  204 . Cooling fluid  210  may flow downstream from the upstream circuit inlet  202 , through the upstream portion of the dual feed circuit, and out the circuit outlet  122 . Alternatively or in addition, cooling fluid  210  may flow upstream from the downstream circuit inlet  204 , through the downstream portion of the dual feed circuit  200 , and out the circuit outlet  122 . Cooling fluid  210  may flow out the circuit outlet  122  and form a film of cooling fluid over the outer surface of the coversheet  104  downstream of the circuit outlet  122  to cool the outer surface from the flow of hot gas external to the airfoil  100 . 
       FIG.  3    illustrates an exploded view of an example of the spar  102  and of the coversheet  104  of the dual feed circuit  200  of the airfoil  100 . The spar  102  may comprise a plurality of pedestals  300  and cooling channels  302 . The spar  102  may also comprise a plurality of upstream circuit inlets  202  and downstream circuit inlets  204 . The coversheet  104  may comprise a plurality of circuit outlets  122 . 
     The pedestals  300  may be part of a unitary structure with the spar  102 . For example, the pedestals  300  may extend out away from the spar  102  towards the coversheet  104 . The pedestals  300  may contact the coversheet  104 . For example, the coversheet  104  may be joined to the spar  102  at the pedestals  300 . The pedestal  300  may, for example, be square, diamond, and/or hexangular in shape and disposed in a repeating pattern. Cooling channels  302  may be formed in between the pedestals  300 , spar  102 , and coversheet  104 . 
     The upstream circuit inlet  202  may comprise a plurality of upstream circuit inlets  202  disposed in a row extending along the span axis  304  of the airfoil  100  adjacent to the upstream dam  208 . Additionally or alternatively, the downstream circuit inlet  204  may comprise a plurality of downstream circuit inlets  204  disposed in a row extending along the span axis  304  of the airfoil  100  adjacent to the downstream dam  206 . The outer surface of the spar  102  may be unbroken and/or a continuous surface between the upstream circuit inlets  202  and the downstream circuit inlets  204 , meaning, for example, there may be no other circuit inlets, holes, and/or openings on the outer surface of the spar  102  between the upstream circuit inlets  202  and the downstream circuit inlets  204  along the chord axis  116  (shown in  FIG.  1   ). For example, there may not be any circuit inlets, holes, and/or openings between the pedestals of the dual feed circuit  200 . The only openings, holes, and/or apertures on the outer surface of the spar and/or pedestals may be the circuit inlets  202 ,  204 . 
     The circuit outlet  122  may comprise a plurality of circuit outlets  122 . The plurality of circuit outlets  122  may be disposed in a single row extending along the span axis  304 . Additionally, or alternatively, the circuit outlets  122  may be disposed in parallel rows. The circuit outlets  122  may be positioned at a midway point between the upstream circuit inlets  202  and the downstream circuit inlets  204 . Additionally, or alternatively, the circuit outlets  122  may be disposed closer towards the upstream circuit inlets  202  than the downstream circuit inlets  204 . Alternatively, the circuit outlets  122  may be disposed closer towards the downstream circuit inlets  204  than the upstream circuit inlets  202 . 
     During operation, cooling fluid  210  may flow through the downstream circuit inlets  204 , upstream through the cooling channels  302  between the pedestals  300 , and to the circuit outlets  122 . Additionally, or alternatively, cooling fluid may flow through the upstream circuit inlets  202 , downstream through the cooling channels  302  between the pedestals  300  to the circuit outlets  122 . 
       FIG.  4    illustrates an exploded view of an example of the dual feed circuit  200  of the airfoil  100 . The spar  102  may comprise a slot  400  extending along the span axis  304  through a row of the pedestals  300 . The slot  400  in the pedestals may correspond to a slot circuit outlet  402 . The slot circuit outlet  402  may be a circuit outlet  122  of  FIGS.  1 - 3   . The slot  400  through the pedestals and the slot circuit outlet  402  may extend along the spar  102  and the coversheet  104 , respectively, along the span axis. 
     During operation, the cooling fluid  210  may flow form the circuit inlets  202 ,  204 , through the cooling channels  302  between the pedestals  300 , through the slot  400  extending through the pedestals  300 , and out the slot circuit outlet  402 . 
       FIG.  5    illustrates a flow diagram of a method  500  to cool the airfoil  100 . The steps may include additional, different, or fewer operations than illustrated in  FIG.  5   . The steps may be executed in a different order than illustrated in  FIG.  5   . 
     During operation cooling fluid  210  may be supplied to a first internal cavity  106  of the airfoil  100  spar  102  ( 502 ). The first internal cavity  106  may be an upstream and/or leading edge internal cavity  106 . Additionally or alternatively, may be a central internal cavity  106 . During operation cooling fluid  210  may be supplied to a second internal cavity. The second internal cavity  106  may be a downstream and/or trailing edge internal cavity  106 . Additionally or alternatively, the second internal cavity  106  may be a central internal cavity  106 . 
     The cooling fluid  210  may be directed from the first internal cavity  106  through a first inlet  120 ,  202  to a dual feed circuit  118 ,  200  ( 504 ). The first inlet  202  may be an upstream circuit inlet  202 . The first inlet  202  may be adjacent to a first dam  208  of the dual feed circuit  118 ,  200 . The first dam  208  may be the upstream dam  208 . The cooling fluid  210  may be directed from the second internal cavity  106  though a second inlet  120 ,  204  to the dual feed circuit  118 ,  200  ( 506 ). The second inlet  204  may be a downstream circuit inlet  204 . The second inlet  204  may be adjacent to a second dam  206  of the dual feed circuit. The second dam  206  may be a downstream dam  206 . 
     The cooling fluid  210  may be directed from the first inlet  202  downstream through a plurality of diamond and/or hexangular pedestals  300  and through a circuit outlet  122  ( 508 ). The cooling fluid  201  may be directed from the second inlet  204   upstream through the plurality of diamond and/or hexangular pedestals  300  and through the circuit outlet  122  ( 510 ). The cooling fluid  210  may be directed from the circuit outlet  122  along an outer surface of the airfoil  100  downstream of the circuit outlet  122 . 
     Each component may include additional, different, or fewer components. Additionally, or alternatively, the airfoil  100  may be implemented with additional, different, or fewer components. For example, the airfoil  100  may include additional or fewer heat exchanging circuits  118 . The heat exchanging circuits  118  may include additional dams  206 ,  208 . The spar  102  may include additional or fewer internal cavities  106  and internal ribs  124 . The heat exchanging circuits  118  may include fewer or additional pedestals  300 . The pedestals  300  may be different or common shapes. The heat exchanging circuits  118  may include fewer or additional circuit inlets  120  and/or circuit outlets  122 . 
     The logic illustrated in the flow diagrams may include additional, different, or fewer operations than illustrated. The operations illustrated may be performed in an order different than illustrated. 
     To clarify the use of and to hereby provide notice to the public, the phrases “at least one of &lt;A&gt;, &lt;B&gt;, ... and &lt;N&gt;” or “at least one of &lt;A&gt;, &lt;B&gt;, ... &lt;N&gt;, or combinations thereof” or “&lt;A&gt;, &lt;B&gt;, ... and/or &lt;N&gt;” are defined by the Applicant in the broadest sense, superseding any other implied definitions hereinbefore or hereinafter unless expressly asserted by the Applicant to the contrary, to mean one or more elements selected from the group comprising A, B, ... and N. In other words, the phrases mean any combination of one or more of the elements A, B, ... or N including any one element alone or the one element in combination with one or more of the other elements which may also include, in combination, additional elements not listed. Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.” 
     While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible. Accordingly, the embodiments described herein are examples, not the only possible embodiments and implementations. 
     The subject-matter of the disclosure may also relate, among others, to the following aspects: 
     A first aspect relates to a dual-wall airfoil comprising: a spar having a chord axis and a span axis; a coversheet on the spar; and a dual feed circuit between the spar and the coversheet, the dual feed circuit including a first dam, a second dam spaced apart from the first dam along the chord axis of the spar, a first inlet disposed adjacent to the first dam, a second inlet disposed adjacent to the second dam, a circuit outlet disposed between the first inlet and the second inlet, and a plurality of diamond pedestals disposed on an outer surface of the spar, the outer surface of the spar facing the coversheet, the diamond pedestals located between the first inlet and the second inlet forming a plurality of cooling channels between the first inlet and the circuit outlet and between the second inlet and the circuit outlet, and wherein no other circuit inlets are located between the first inlet and the second inlet. 
     A second aspect relates to the dual-wall airfoil of aspect 1 wherein the first inlet includes a plurality of first inlets disposed in a row and extending parallel to the first dam, and wherein the second inlet includes a plurality of second inlets disposed in a row and extending parallel to the second dam. 
     A third aspect relates to the dual-wall airfoil of any preceding aspect, wherein the circuit outlet is disposed closer to the second dam than the first dam. 
     A fourth aspect relates to the dual-wall airfoil of any preceding aspect, wherein the circuit outlet is disposed closer to the first dam than the second dam. 
     A fifth aspect relates to the dual-wall airfoil of any preceding aspect, wherein the circuit outlet is a slot. 
     A sixth aspect relates to the dual-wall airfoil of any preceding aspect, wherein the spar further comprises a first internal cavity and a second internal cavity, wherein the first inlet extends through the spar from the first internal cavity to the dual feed circuit and the second inlet extends through the spar from the second internal cavity to the dual feed circuit. 
     A seventh aspect relates to the dual-wall airfoil of any preceding aspect, wherein the first internal cavity is disposed at a leading edge of the spar and the second internal cavity is disposed at a midpoint of the spar, wherein the dual feed circuit is in fluid communication with the first internal cavity at the leading edge of the spar. 
     An eight aspect relates to the dual-wall airfoil of any preceding aspect, wherein the second internal cavity is disposed at a trailing edge of the spar and the first internal cavity is disposed at a midpoint of the spar, wherein the dual feed circuit is in fluid communication with the second internal cavity at the trailing edge of the spar. 
     A ninth aspect relates to the dual-wall airfoil of any preceding aspect, wherein the circuit outlet comprises a plurality of film holes disposed in a row, the row of film holes extending along the span axis of the spar. 
     A tenth aspect relates to the dual-wall airfoil of any preceding aspect, wherein the circuit outlet comprises parallel rows of film holes. 
     An eleventh aspect relates to a dual-wall airfoil comprising: a spar, wherein the spar includes a plurality of internal cavities, the internal cavities including a first cavity disposed at a leading edge of the airfoil, a second cavity disposed at a trailing edge of the airfoil, a third cavity disposed between the first cavity and the second cavity; a coversheet on the spar; and a dual feed circuit disposed between the spar and the coversheet, the dual feed circuit including a first dam, a second dam, a first inlet disposed adjacent to the first dam, a second inlet disposed adjacent to the second dam, and a circuit outlet disposed between the first inlet and the second inlet, wherein the first inlet connects the first cavity to the dual feed circuit and the second inlet connects the third cavity to the dual feed circuit or wherein the first inlet connects the third cavity to the dual feed circuit and the second inlet connects the second cavity to the dual feed circuit. 
     A twelfth aspect relates to the dual-wall airfoil of any preceding aspect, wherein the dual feed circuit is a single dual feed circuit disposed on a pressure side of the airfoil. 
     A thirteenth aspect relates to the dual-wall airfoil of any preceding aspect, wherein an outer surface of the spar is a continuous, unbroken surface between the first inlet and the second inlet. 
     A fourteenth aspect relates to a method of cooling an airfoil, the method comprising: supplying a cooling fluid to a first internal cavity of an airfoil spar and a second internal cavity of the airfoil spar; directing the cooling fluid from the first internal cavity through a first inlet to a dual feed circuit, the first inlet adjacent to a first dam of the dual feed circuit; directing the cooling fluid from the second internal cavity though a second inlet to the dual feed circuit, the second inlet adjacent to a second dam of the dual feed circuit; directing the cooling fluid from the first inlet downstream through a plurality of diamond pedestals and through a circuit outlet; directing the cooling fluid from the second inlet upstream through the plurality of diamond pedestals and through the circuit outlet; and directing the cooling fluid from the circuit outlet along an outer surface of the airfoil downstream of the circuit outlet. 
     A fifteenth aspect relates to method of aspect 14, wherein the first internal cavity is disposed at a leading edge of the airfoil. 
     A sixteenth aspect relates to the method of any preceding aspect, wherein the second internal cavity is disposed at a trailing edge of the airfoil. 
     A seventeenth aspect relates to the method of any preceding aspect, wherein the first inlet comprises a single row of holes connecting the first internal cavity to the dual feed circuit. 
     An eighteenth aspect relates to the method of any preceding aspect, wherein the second inlet comprises a single row of holes connecting the second internal cavity to the dual feed circuit. 
     In addition to the features mentioned in each of the independent aspects enumerated above, some examples may show, alone or in combination, the optional features mentioned in the dependent aspects and/or as disclosed in the description above and shown in the figures.