Patent Publication Number: US-2023141827-A1

Title: Arrangement of pedestals of varying aspect ratio for dual-wall cooling of an airfoil

Description:
TECHNICAL FIELD 
     This disclosure relates generally to airfoils with dual-wall cooling and more particularly to a pedestal arrangement for dual-wall cooling of an airfoil. 
     BACKGROUND 
     Gas turbine engines include a compressor, combustor and turbine in flow series along a common shaft. Compressed air from the compressor is mixed with fuel in the combustor to generate hot combustion gases that rotate the turbine blades and drive the compressor. Improvements in the thrust and efficiency of gas turbine engines are linked to increasing turbine entry temperatures, which places a heavy burden on turbine blades. Consequently, there is significant interest in developing improved cooling techniques for airfoils in gas turbine engines. Dual-wall or double-wall cooling configurations are promising advancements for the cooling of turbine blades. 
    
    
     
       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    is an exploded assembly view of an exemplary airfoil with dual-wall cooling that includes an exemplary arrangement of pedestals of varying aspect ratios. 
         FIG.  2    is a close-up view of part of the arrangement of pedestals shown in  FIG.  1   . 
         FIG.  3    is a cross-sectional view of an exemplary gas turbine engine that may include the airfoil described in this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A dual-wall or double-wall airfoil for a gas turbine engine may include a hollow spar that is partially or completely surrounded by suction side and pressure side coversheets (or “skins”) and spaced apart from the coversheets by raised features on the outer surface of the spar. These raised features may include pedestals and/or rails arranged to define flow pathways for coolant (e.g., air) between the outer surface of the spar and the respective coversheet. The coolant may provide heat transfer and cooling as it traverses the flow pathways before exiting, typically through exit holes in the respective coversheet or through exit slots. After exit, the coolant may flow in a layer over a hot external surface of the airfoil, providing film cooling. The coolant is delivered into the flow pathways from one or more coolant cavities in the spar. Traditional square pedestal arrays can provide high heat transfer, but may also generate a large pressure drop that is generally not desirable for long flow pathways. Smooth, straight rails tend to be associated with a lower pressure drop, but they may be unable to provide sufficient heat transfer and may be susceptible to being blocked with particulate debris. It is also important to manage the temperature of the coolant, since, as the coolant absorbs heat and increases in temperature, it may become less effective at cooling the airfoil. 
       FIG.  1    illustrates an airfoil with dual-wall cooling for a gas turbine engine that may provide advantages over previous designs by utilizing raised features having different aspect ratios. The airfoil  100  comprises a spar  102  having a pressure side wall  104  and a suction side wall  106  meeting at a leading edge  108  and a trailing edge  110  of the airfoil  100 . Each of the pressure side wall  104  and the suction side wall  106  includes raised features  118  on an outer surface  104   a , 106   a  thereof. It is noted that the suction side of the airfoil  100  is shown in  FIG.  1    and thus the raised features  118  on the pressure side wall  104   a  are not visible. A pressure side coversheet  114  overlies the pressure side wall  104 , and an inner surface  114   a  of the pressure side coversheet  114  is in contact with (e.g., bonded to or integrally formed with) the raised features  118  on the outer surface  104   a  of the pressure side wall  104 , thereby defining pressure side flow pathways between the pressure side wall  104  and the pressure side coversheet  114 . A suction side coversheet  116  overlies the suction side wall  106 , and an inner surface  116   a  of the suction side coversheet  116  is in contact with (e.g., bonded to or integrally formed with) the raised features  118  on the outer surface  106   a  of the suction side wall  106 , thereby defining suction side flow pathways between the suction side wall  106  and the suction side coversheet  116 . An interior of the spar  102  includes one or more coolant cavities  112  for providing coolant to the pressure side and suction side flow pathways through inlet holes  122  in the pressure and suction side walls  104 , 106 . 
     The raised features  118  on the outer surface  104   a  of the pressure side wall  104  and/or the suction side wall  106  may include an arrangement  130  of pedestals  120  having different aspect ratios, where each pedestal  120  has an aspect ratio in the range from about 1:1 to about 5:1. The aspect ratio is equivalent to the length L (long axis) divided by the width W (short axis) of the pedestal, as illustrated in  FIG.  2   . Advantageously, in order to control heat transfer, coolant temperature, and pressure drop, the aspect ratio of the pedestals  120  is varied within the arrangement. For example, the aspect ratio may increase and/or decrease across the arrangement  130 , as shown in  FIG.  2   , where the pedestals  120  transition from an aspect ratio of about 3.5:1 to an aspect ratio of about 1:1 moving from left to right across the schematic, which corresponds to a chordal direction  132 , as shown in  FIG.  1   . The increase and/or decrease in aspect ratio within the arrangement  130  may be described by a linear, quadratic, exponential, step or other function. 
     The pedestals  120  in the arrangement  130  and the raised features  118  in general may have a height that corresponds to the spacing between the outer surface  104   a , 106   a  of the side wall  104 , 106  and the respective coversheet  114 , 116 . The pedestals  120  may have a cross-sectional shape that is described as hexangular, or as a stretched hexagon, when the aspect ratio is greater than 1:1. An aspect ratio of greater than 1:1 may alternatively be achieved with a cross-sectional shape described as an elongated diamond, where the elongated diamond comprises two (opposing) included angles of greater than 90 degrees and two (opposing) included angles of less than 90 degrees. If the aspect ratio is 1:1 or about 1:1, the cross-sectional shape may be a hexagonal or diamond shape. 
     The aspect ratio may be varied along a predetermined direction, such as along the chordal direction  132  or along the radial direction  134 , or along a direction having both chordal and radial components. In one example, it may be beneficial for the aspect ratio of the pedestals  120  to increase toward the trailing edge  110  and/or the leading edge  108  of the airfoil  100 . Also or alternatively, the aspect ratio may decrease toward a midspan  136  of the airfoil  100 , where heat may be concentrated. Some adjacent pedestals  120  may have the same aspect ratio along the direction of variation; i.e., there may be some local regions where the aspect ratio remains unchanged as part of an overall increasing or decreasing trend. Preferably, the long axes of the pedestals  120  are aligned with the direction of coolant flow, which may be the chordal direction  132 , as illustrated, the radial direction  134 , or a direction having both chordal and radial components. 
     As shown in  FIGS.  1  and  2   , the aspect ratio may vary (increase and/or decrease) along the direction of coolant flow. The pedestals  120  may be arranged and sized such that adjacent flow paths merge and/or split at the same transverse location, that is, along the same line perpendicular to the flow paths, as shown for example in  FIGS.  1  and  2   , where the flow paths in this example are along the chordal direction  134 . By choosing a suitable arrangement and aspect ratio for the pedestals  120 , uniform flow can be achieved and distortions in flow intersections may be avoided. It is contemplated that such distortions may be minimized for situations in which the adjacent flow paths do not merge and/or split at the same transverse location by incorporating a slow (linear) transition or by incorporating a fast (step change) transition in aspect ratio. For example, a higher aspect ratio pedestal may have a length which is a multiple of the length of an adjacent (e.g., a radially adjacent) lower aspect ratio pedestal. 
     The arrangement  130  of pedestals  120  may be on the outer surface  104   a  of the pressure side wall  104  and/or on the outer surface  106   a  of the suction side wall  106 . In one example, as shown in  FIG.  1   , a midspan cooling circuit  138  on the suction side of the airfoil  100  may include the arrangement  130  of pedestals  120 . The midspan cooling circuit  138  may be configured to deliver coolant to the leading edge  108  of the airfoil  100 , and may be adjacent to a trailing edge cooling circuit  140  configured to deliver coolant to the trailing edge  110  of the airfoil  100 . The midspan and trailing edge cooling circuits  138 , 140  may be separated by a radial dam between the inlet holes  122  that deliver coolant to each circuit  138 , 140 . The raised features  118  of the trailing edge cooling circuit  140  typically comprise rails  142 , which may be understood to have an aspect ratio (length:width) greater than 5:1, such as up to 10:1, or higher. The arrangement  130  of pedestals  120  may extend in the direction of the leading edge  108  over just part of the midspan cooling circuit  138  and may be separated from a section  144  of raised features  118  positioned nearer to the leading edge  108  by a radial spacing  146  on the outer wall  106   a , as shown in  FIG.  1   . The section  144  of raised features  118  may or may not include pedestals  120  of varying aspect ratio. The radial spacing  146  may be a consequence of the casting process to fabricate the airfoil  100 , where multiple dies may be employed, although the airfoil  100  is not limited to this fabrication method. The arrangement  130  of pedestals  120  having the variable aspect ratio may extend over (only) a portion of the midspan cooling circuit  138  in a chordal direction, as shown, and/or in a radial direction. In such examples, the arrangement  130  may be adjacent to one or more other arrangements of raised features (e.g., pedestals or rails)  118  which may not exhibit a spatial variation in aspect ratio. 
     In other examples, the arrangement  130  of pedestals  120  of varying aspect ratio may extend over an entirety of the midspan cooling circuit  138  in one or both of the chordal and radial directions  132 , 134 . It is also contemplated that the arrangement  130  of pedestals  120  may extend over an entirety of the suction side wall  106  and/or the pressure side wall  104  of the airfoil  100 . In one such example, a first cooling circuit configured to deliver coolant to the leading edge  108  may include a first part of the arrangement  130  and a second cooling circuit configured to deliver coolant to the trailing edge  110  of the airfoil  100  may include a second part of the arrangement  130 , where the aspect ratio of the pedestals  120  in each of the first and second parts of the arrangement  130  may be varied to control heat transfer and pressure drop as needed. 
     The dual-wall airfoil  100  described herein may be fabricated using investment casting and diffusion bonding methods known in the art, such as described in U.S. Pat. No. 6,003,754, entitled “Airfoil for a Gas Turbine Engine and Method of Manufacture,” which is hereby incorporated by reference in its entirety. The airfoil  100 , including the spar  102  and the pressure and suction side coversheets  114 , 116 , may be formed from one or more materials that have high melting points, good oxidation/corrosion resistance and high-temperature strength. For example, a nickel-base alloy, a titanium-base alloy, and/or an iron-base alloy may be suitable. The alloy may have an equiaxed, directionally solidified, or single-crystal microstructure. The raised features  118  may be integrally formed with the spar  102 , or, more specifically, may be integrally formed on the respective suction or pressure side wall  106 , 104 . The raised features  118  may be bonded to or integrally formed with the respective suction or pressure side coversheet  114 , 116 . The airfoil  100  may have a single-piece or a multi-piece construction. 
     A gas turbine engine  300 , such as that shown in  FIG.  3   , may include the airfoil  100  described above, e.g., as a nozzle guide vane or a turbine blade  312  in the turbine section  310 . In some examples, the gas turbine engine  300  may supply power to and/or provide propulsion of an aircraft, e.g., 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/or an extraterrestrial (spacecraft) vehicle. Also or alternatively, the gas turbine engine  300  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. 
     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;, . . . or &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 an airfoil including an arrangement of pedestals of varying aspect ratio for dual-wall cooling, the airfoil comprising: a spar having a pressure side wall and a suction side wall meeting at a leading edge and a trailing edge of the airfoil, each of the pressure side wall and the suction side wall including raised features on an outer surface thereof, an interior of the spar including one or more coolant cavities; and a pressure side coversheet overlying the pressure side wall, an inner surface of the pressure side coversheet being in contact with the raised features on the outer surface of the pressure side wall, thereby defining pressure side flow pathways between the pressure side wall and the pressure side coversheet, the pressure side flow pathways being in fluid communication with the one or more coolant cavities; a suction side coversheet overlying the suction side wall, an inner surface of the suction side coversheet being in contact with the raised features on the outer surface of the suction side wall, thereby defining suction side flow pathways between the suction side wall and the suction side coversheet, the suction side flow pathways being in fluid communication with the one or more coolant cavities, wherein the raised features on the outer surface of the pressure side wall and/or the suction side wall include an arrangement of pedestals, each pedestal comprising an aspect ratio in a range from about 1:1 to about 5:1, and wherein the aspect ratio of the pedestals is varied within the arrangement. 
     A second aspect relates to the airfoil of the first aspect, wherein the pedestals in the arrangement have a cross-sectional shape selected from the group consisting of diamond, elongated diamond, hexagonal, and hexangular. 
     A third aspect relates to the airfoil of the first or second aspect, wherein the arrangement of pedestals is on the outer surface of the pressure side wall. 
     A fourth aspect relates to the airfoil of any preceding aspect, wherein the arrangement of pedestals is on the outer surface of the suction side wall. 
     A fifth aspect relates to the airfoil of any preceding aspect, wherein the aspect ratio increases and/or decreases across the arrangement. 
     A sixth aspect relates to the airfoil of any preceding aspect, wherein the aspect ratio is varied along a chordal direction. 
     A seventh aspect relates to the airfoil of any preceding aspect, wherein the aspect ratio is varied along a radial direction. 
     An eighth aspect relates to the airfoil of any preceding aspect, wherein the aspect ratio is varied along a direction having a chordal component and a radial component. 
     A ninth aspect relates to the airfoil of any preceding aspect, wherein the aspect ratio decreases toward a midspan of the airfoil. 
     A tenth aspect relates to the airfoil of any preceding aspect, wherein the aspect ratio increases toward a trailing edge and/or a leading edge of the airfoil. 
     An eleventh aspect relates to the airfoil of any preceding aspect, wherein long axes of the pedestals are aligned with a direction of coolant flow over the respective outer surface. 
     A twelfth aspect relates to the airfoil of any preceding aspect, wherein long axes of the pedestals are aligned with a chordal direction. 
     A thirteenth aspect relates to the airfoil of any preceding aspect, wherein long axes of the pedestals are aligned with a radial direction. 
     A fourteenth aspect relates to the airfoil of any preceding aspect, wherein long axes of the pedestals are aligned with a direction having a chordal component and a radial component. 
     A fifteenth aspect relates to the airfoil of any preceding aspect, wherein a midspan cooling circuit configured to deliver coolant to the leading edge of the airfoil includes the arrangement of pedestals. 
     A sixteenth aspect relates to the airfoil of the fifteenth aspect, wherein the arrangement of pedestals extends over an entirety of the midspan cooling circuit. 
     A seventeenth aspect relates to the airfoil of the fifteenth aspect, wherein the arrangement of pedestals extends over just part of the midspan cooling circuit and is separated from a section of raised features positioned nearer to the leading edge by a radial spacing on the respective outer wall. 
     An eighteenth aspect relates to the airfoil of the fifteenth aspect, wherein the arrangement of pedestals is adjacent to a trailing edge cooling circuit configured to deliver coolant to the trailing edge of the airfoil, wherein the raised features of the trailing edge cooling circuit comprise rails. 
     A nineteenth aspect relates a gas turbine engine including the airfoil of any preceding aspect. 
     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.