Internal cooling circuits in turbine blades

Abstract

Turbine blade with a blade (25) defined by outer walls (26, 27), wherein a concave pressure-side outer wall (26) and a convex suction-side outer wall (27) are connected to each other along the leading and trailing edges (28, 29) and form a radially extending chamber between them for receiving a coolant flow, wherein the turbine blade further comprises: a rib arrangement that subdivides the chamber into radially extending flow passages (40), wherein the rib arrangement includes the following: a skeletal line rib (62) running alongside one of the outer walls (26, 27) to define a near-wall flow chamber in between, and Transverse ribs (66) running between the skeletal line rib (62) and one of the outer walls (26, 27) to divide the near-wall flow chamber into successively stacked flow passages (40), each of the flow passages (40) being defined inwards by a skeletal line rib segment (73) of the skeletal line rib (62), wherein the skeletal line rib segment (73) of the skeletal line rib (62) has a tapered profile (72) from one of the flow passages (40), wherein the tapered profile (72) comprises a profile that tapers from opposite ends (75) to an intermediate neck (74), and wherein the skeletal line rib (62) having the tapered profile (72) has a wavy or sinusoidal shape and the skeletal line rib segment (73) of the skeletal line rib (62) is substantially convex or concave with respect to an adjacent flow path (40), wherein the tapered profile (72) provides the substantially convex or concave curved skeletal line rib segment (73) of the wavy or sinusoidal skeletal line rib (62) with a compliance to straighten itself in response to a tensile stress and to bend further in response to a compressive stress.

Description

GENERAL STATE OF THE ART

[0001] The present invention relates to turbine airfoils and, more particularly, to hollow turbine airfoils such as rotor blades or vanes having internal channels for passing fluids such as air to cool the airfoils.

[0002] Internal combustion or gas turbine engines (hereinafter "gas turbines") comprise a compressor, a combustion chamber, and a turbine. As is well known, compressed air is mixed with fuel in the compressor, ignited in the combustion chamber, and then expanded by the turbine to generate power. The components within the turbine, specifically the circumferentially arranged rotor blades and vanes, are exposed to a hostile environment characterized by the extremely high temperatures and pressures of the combustion products that are expanded by them. To withstand the repetitive thermal cycles, as well as the extreme temperatures and mechanical stresses of this environment, the blades must have a robust structure and be actively cooled.

[0003] As can be seen, turbine blades and vanes often contain internal passages or circuits that form a cooling system through which a coolant, usually air bled from the compressor, is circulated. Such cooling circuits are usually formed by internal fins that provide the necessary structural support for the airfoil and include multiple flow paths designed to maintain the airfoil within an acceptable temperature profile. The air flowing through these cooling circuits is often exhausted through film cooling ports formed at the leading edge, trailing edge, suction side, and pressure side of the airfoil.

[0004] Gas turbine efficiency clearly increases with increasing firing temperatures. As a result, there is a constant need for technological advances that enable turbine blades to withstand ever higher temperatures. These advances sometimes involve new materials that can withstand higher temperatures, but just as often, they involve improving the internal layout of the airfoil to improve the design and cooling performance of the blade. However, since the use of coolant reduces engine efficiency, new designs that rely too heavily on higher coolant consumption levels are simply trading one performance disadvantage for another. As a result, there continues to be a need for new airfoil designs that offer internal airfoil designs and coolant recirculation that improve coolant efficiency.

[0005] One factor that further complicates the design of internally cooled airfoils is the temperature differential that develops during operation between the inner and outer structures of the airfoil. That is, because they are in contact with the hot gas path, the outer walls of the airfoil are usually at much higher temperatures during operation than many of the inner ribs, where, for example, coolant flows through passages defined on either side of them. In fact, a common airfoil design involves a "four-wall" arrangement in which longer inner ribs run parallel to the pressure and suction side outer walls. It is known that high cooling efficiency can be achieved by the near-wall flow passages formed in the four-wall arrangement, but the outer walls experience a significantly higher degree of thermal expansion than the inner walls.This unbalanced expansion causes the development of stresses at the connection points of the inner ribs and outer walls, which can cause short-cycle fatigue, which can shorten the life of the blade.

[0006] US 2011 / 0 236 221 A1 discloses a turbine blade with an airfoil having a concave pressure-side outer wall and a convex suction-side outer wall, which form a radially extending chamber between them for receiving a coolant flow. The turbine blade further includes a rib arrangement that subdivides the chamber into radially extending flow passages. The rib arrangement comprises a wave-shaped pressure-side skeleton line rib that runs adjacent to and along the pressure-side outer wall to define therebetween a flow chamber near the pressure sidewall, a curved suction-side skeleton line rib that runs adjacent to and along the suction-side outer wall to define therebetween a flow chamber near the suction sidewall, and transverse ribs that run in such a way that they each subdivide the pressure-side and suction-side flow chambers into successively stacked flow passages.

[0007] JP 2011-247 261 A and US 5 562 409 A each disclose a turbine blade having a skeleton line rib extending adjacent to and along an outer wall of the turbine blade and having at least one skeleton line rib segment defining an inner flow passage and having a profile narrowing toward the center of the skeleton line rib segment.

[0008] In light of the above, the development of airfoil designs that utilize coolant more efficiently while reducing stresses caused by unbalanced thermal expansion between the inner and outer regions remains a significant technological challenge for the industry. SUMMARY OF THE INVENTION

[0009] To achieve the above-mentioned object, the invention provides a turbine blade comprising an airfoil defined by outer walls, wherein a concavely shaped pressure-side outer wall and a convexly shaped suction-side outer wall are connected to each other along the leading and trailing edges and form a radially extending chamber for receiving a coolant flow therebetween. The turbine blade further includes a rib arrangement that subdivides the chamber into radially extending flow passages.The rib arrangement comprises: a skeletal rib extending adjacent one of the outer walls to define a near-wall flow chamber therebetween; and transverse ribs extending between the skeletal rib and the one of the outer walls to divide the near-wall flow chamber into successively stacked flow passages, each of the flow passages being defined inwardly by a segment of the skeletal rib. The segment of the skeletal rib of one of the flow passages has a tapered profile, including a profile that tapers from opposite ends to a throat disposed therebetween.The skeleton line rib having the narrowing profile has a wavy or sinusoidal shape, and the skeleton line rib segment of the skeleton line rib is substantially convexly or concavely curved with respect to an adjacent flow path, wherein the narrowing profile provides the substantially convexly or concavely curved skeleton line rib segment of the wavy or sinusoidal skeleton line rib with compliance to straighten in response to a tensile load and to further deflect in response to a compressive load.

[0010] The narrowing profile may comprise a cross-sectional profile.

[0011] The skeleton line rib segment of a turbine blade mentioned above may comprise a cross-rib-cross-rib segment in which each of the opposite ends is defined at an intersection with one of the cross ribs.

[0012] The transverse ribs of an above-mentioned turbine blade can form at least two axially stacked flow passages, wherein the segment of the skeleton line rib for each of the two axially stacked flow passages has the narrowing profile.

[0013] The transverse ribs of a turbine blade mentioned above can form three successively stacked flow passages, wherein the segment of the skeleton line rib for each of the three successively stacked flow passages has the narrowing profile.

[0014] The segments of the skeleton line rib for the three successively stacked flow passages of a turbine blade mentioned above may have a wavy axis.

[0015] The wavy axis of a turbine blade mentioned above may have at least a reciprocating “S” shape.

[0016] The skeleton line rib of a turbine blade mentioned above may comprise a pressure-side skeleton line rib extending alongside and close to the pressure-side outer wall, the transverse ribs extending between the pressure-side skeleton line rib and the pressure-side outer wall to form the three sequentially stacked flow passages, the flow passages being respectively defined by the pressure-side outer wall, two opposing transverse ribs and, opposite the pressure-side outer wall, the segment of the pressure-side skeleton line rib.

[0017] The pressure-side skeleton line rib of a turbine blade mentioned above may comprise a wavy profile including at least two consecutive reciprocating “S” shapes.

[0018] The skeleton line rib of an above-mentioned turbine blade may comprise a suction-side skeleton line rib extending alongside and close to the suction-side outer wall, wherein the transverse ribs extend between the suction-side skeleton line rib and the suction-side outer wall to form the three sequentially stacked flow passages, the flow passages being respectively defined by the suction-side outer wall, two opposing transverse ribs and, opposite the suction-side outer wall, the segment of the suction-side skeleton line rib.

[0019] The suction side skeleton line rib of a turbine blade mentioned above may comprise a wavy profile including at least two consecutive reciprocating “S” shapes.

[0020] The rib arrangement of a turbine blade mentioned above can include two skeleton line ribs: a pressure-side skeleton line rib running alongside the pressure-side outer wall and forming a near-wall flow chamber therebetween, and a suction-side skeleton line rib running alongside the suction-side outer wall and forming a near-wall flow chamber therebetween, wherein the transverse ribs run between the pressure-side skeleton line rib and the pressure-side outer wall to form at least two successively stacked flow passages, wherein the segment of the pressure-side skeleton line rib for each of the two successively stacked flow passages each has the narrowing profile, and wherein the transverse ribs run between the suction-side skeleton line rib and the suction-side outer wall to form at least two successively stacked flow passages,wherein the segment of the suction-side skeleton line rib for each of the two successively stacked flow passages has the narrowing profile.

[0021] The pressure-side skeleton line rib and / or the suction-side skeleton line rib of a turbine blade mentioned above may have a wavy profile including at least two consecutive reciprocating “S” shapes.

[0022] The throat of the tapered profile of a turbine blade mentioned above may be located near a midpoint between the opposite ends of the segments of the skeleton line rib.

[0023] Each of the opposite ends of a turbine blade mentioned above may have an end thickness and the throat may have a throat thickness, wherein the end thickness is at least 1.5 times the throat thickness.

[0024] Each of the opposite ends has an end thickness and the neck has a neck thickness, wherein the end thickness may be at least twice the neck thickness.

[0025] The narrowing between each of the opposite ends and the throat of a turbine blade mentioned above may be smooth.

[0026] The turbine blade of a turbine blade mentioned above may comprise a turbine blade.

[0027] These and other features of the present application will become apparent upon examination of the following detailed description of the preferred embodiments when considered in conjunction with the drawings and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and other features of this invention will be more fully understood and appreciated upon careful study of the following more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic representation of an exemplary turbine engine in which certain embodiments of the present application may be used, Fig. 2 a sectional view of the compressor section of the combustion turbine engine of Fig. 1 is, Fig. 3 a sectional view of the turbine section of the combustion turbine engine of Fig. 1 is, Fig. 4 is a perspective view of a turbine blade of the type in which embodiments of the present invention may be employed, Fig. 5 is a cross-sectional view of a turbine blade having an inner wall or rib arrangement according to a conventional design, Fig. 6 is a cross-sectional view of a turbine blade having an inner wall arrangement according to an embodiment not belonging to the claimed invention, Fig. 7 is a cross-sectional view of a turbine blade having an inner wall or rib arrangement according to an alternative embodiment not per se belonging to the claimed invention, and Fig. 8 is a cross-sectional view of a turbine blade having an inner wall or rib arrangement according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] In more detail, in order to clearly describe the current invention, it is necessary to use certain terminology when referring to and describing relevant machine component(s) within a gas turbine. Wherever possible, common industry terminology is used and employed in a manner consistent with its accepted meaning. Unless otherwise indicated, such terminology is to be broadly interpreted in accordance with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will recognize that a particular component may often be referred to using several different or overlapping terms. What may be described herein as a single component may, in another context, include multiple components and be referred to as consisting of multiple components.Alternatively, what is described herein as including multiple components may be referred to elsewhere as a single component. Accordingly, in understanding the scope of the present invention, attention should be paid not only to the terminology and description provided herein, but also to the structure, arrangement, function, and / or use of the component.

[0030] Several descriptive terms may also be used regularly herein, and it should be useful to define these terms at the beginning of this section. These terms and their definitions, unless otherwise noted, are as follows. "Downstream" and "upstream," as used herein, are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the air flow through the combustor or the coolant flow through one of the turbine component systems. The term "downstream" corresponds to the fluid flow direction, and the term "upstream" refers to the direction opposite the flow. The terms "front" and "rear," without further specificity, refer to directions, where "front" refers to the front or compressor end of the engine and "rear" refers to the rear or turbine end of the engine.Often, parts must be described that are located at different radial positions with respect to a central axis. The term "radial" refers to movement or position perpendicular to an axis. In cases such as this, if a first component is closer to the axis than a second component, the first component is stated herein to be "radially inward" or "inboard" of the second component. Conversely, if the first component is farther from the axis than the second component, the first component may be stated herein to be "radially outward" or "outboard" of the second component. The term "axial" refers to movement or position parallel to an axis. Finally, the term "circumferential" refers to movement or position about an axis. It will be appreciated that such terms can be applied with respect to the central axis of the turbine.

[0031] As a background, now referring to the figures, the Fig. 1 to 4 illustrate an exemplary combustion turbine engine in which embodiments of the present invention may be used. Those skilled in the art will understand that the present invention is not limited to this particular type of use. The present invention may be used in combustion turbine engines such as those used in power generation, aircraft, and other types of machines. Unless otherwise stated, the examples provided are not intended to be limiting.

[0032] Fig. Figure 1 is a schematic diagram of a combustion turbine engine 10. In general, combustion turbine engines operate by extracting energy from a pressurized hot gas stream produced by the combustion of a fuel in a stream of compressed air. As shown in Fig. 1, the combustion turbine engine 10 may be configured with a compressor 11 (axial compressor) mechanically coupled to a downstream turbine section or turbine 13 by a common shaft or rotor, and a combustion chamber 12 positioned between the compressor 11 and the turbine 13.

[0033] Fig. Figure 2 illustrates a view of an exemplary multi-stage axial compressor (compressor 11) used in the combustion turbine engine of Fig. 1 can be used. As shown, the compressor 11 may include multiple stages. Each stage may include a row of compressor blades 14 followed by a row of compressor guide vanes 15. Therefore, a first stage may include a row of compressor blades 14 rotating around a central shaft, followed by a row of compressor guide vanes 15 that remain stationary during operation.

[0034] Fig. 3 illustrates a partial view of an exemplary turbine section or turbine 13 used in the combustion turbine engine of Fig. 1 can be used. The turbine 13 may include multiple stages. Three example stages are shown, but there may be more or fewer stages in the turbine 13. A first stage includes a plurality of turbine blades 16 that rotate about the shaft during operation and a plurality of guide vanes 17 that remain stationary during operation. The turbine guide vanes 17 are generally circumferentially spaced apart and fixed about the axis of rotation. The turbine blades 16 may be mounted on a turbine wheel (not shown) for rotation about the shaft (not shown). A second stage of the turbine 13 is also shown. The second stage similarly includes a plurality of circumferentially spaced apart turbine guide vanes 17 followed by a plurality of circumferentially spaced apart turbine blades 16, also mounted on a turbine wheel for rotation.A third stage is also shown and similarly includes a plurality of turbine guide vanes 17 and turbine blades 16. Note that the turbine guide vanes 17 and the turbine blades 16 are located in the hot gas path of the turbine 13. The direction of flow of the hot gases through the hot gas path is indicated by the arrow. One of ordinary skill in the art will recognize that the turbine 13 may have more, or in some cases fewer, stages than that shown in FIG. Fig. 3. Each additional stage may include a row of turbine guide vanes 17 followed by a row of turbine blades 16.

[0035] In one operating example, the rotation of the compressor blades 14 within the compressor 11 can compress a flow of air. Energy can be released in the combustion chamber 12 when the compressed air is mixed with a fuel and ignited. The resulting flow of hot gases from the combustion chamber 12, which may be referred to as the working fluid, is then directed over the turbine blades 16, with the working fluid flow causing the turbine blades 16 to rotate about the shaft. As a result, the flow energy of the working fluid is converted into the mechanical energy of the rotating blades and, due to the connection between the blades and the shaft, the rotating shaft. The mechanical energy of the shaft can then be used to drive the rotation of the compressor blades 14, thus producing the necessary supply of compressed air, and can also be used, for example, to drive a generator to generate electricity.

[0036] Fig. 4 is a perspective view of a turbine blade 16 of the type in which embodiments of the present invention may be employed. The turbine blade 16 includes a root 21 by which the blade 16 is attached to an impeller. The root 21 may include a dovetail configured for installation in a corresponding dovetail groove in the outer rim of the impeller. The root 21 may further include a shank extending between the dovetail and a platform 24 disposed at the junction of the airfoil 25 and the root 21 and defining a portion of the inboard boundary of the flow path through the turbine 13. It should be noted that the airfoil 25 is the active component of the blade 16, intercepting the working fluid flow and causing the impeller to rotate.While the blade in this example is a turbine blade 16, it should be appreciated that the present invention may be applied to other types of blades within the combustion turbine engine 10, including turbine guide vanes 17. It can be seen that the airfoil 25 of the blade 16 includes a concave pressure-side outer wall 26 and a circumferentially or transversely opposed convex suction-side outer wall 27 extending axially between opposite leading and trailing edges 28 and 29, respectively. The sidewalls 26 and 27 also extend from the platform 24 in the radial direction to an outboard tip 31. (It should be appreciated that the application of the present invention may not be limited to turbine blades, but may also be applicable to guide vanes.)The use of blades in the several embodiments described herein is exemplary unless otherwise noted.).

[0037] Fig. Figure 5 shows the structure of an inner wall such as may be found in the airfoil 25 of a rotor blade of conventional design. As indicated, the outer surface of the airfoil 25 may be defined by a relatively thin pressure-side outer wall 26 and suction-side outer wall 27, which may be connected by a plurality of radially extending and intersecting ribs 60. The ribs 60 are designed to provide structural support to the airfoil 25 and also to define a plurality of radially extending and substantially separate flow passages 40. The ribs 60 typically extend radially to separate the flow passages over a majority of the radial height of the airfoil 25, but, as discussed further below, the flow passage may be connected along the outer edge of the airfoil to define a cooling circuit.That is, the flow passages 40 may be in fluid communication at the outboard or inboard edge of the airfoil 25, as well as via a number of smaller connecting passages or impingement ports (not shown) that may be positioned therebetween. In this way, certain of the flow passages 40 may together form a tortuous or serpentine cooling circuit. Film cooling holes (not shown) may also be provided to provide outlets through which coolant is discharged from the flow passages 40 onto the outer surface of the airfoil 25.

[0038] The ribs 60 may be of two different types, which may then be further subdivided as provided herein. A first type, a skeleton line rib 62, is usually a longer rib that runs parallel or approximately parallel to the skeleton line of the airfoil, which is a reference line extending from the leading edge 28 to the trailing edge 29 and connecting the midpoints between the pressure-side outer wall 28 and the suction-side outer wall 27. As is often the case, the conventional arrangement of Fig. 5 two skeleton line ribs 62, a pressure-side skeleton line rib 63, which may also be referred to as the pressure-side inner wall given how offset from and close to the pressure-side outer wall 26, and a suction-side skeleton line rib 64, which may also be referred to as the suction-side inner wall given how offset from and close to the suction-side outer wall 27. As mentioned, this type of construction is often referred to as a "four-wall" arrangement due to the predominance of four main walls, which include the two side walls 26, 27 and the two skeleton line ribs 63, 64.

[0039] The second rib type is referred to herein as a cross rib 66. Cross ribs 66 are the shorter ribs shown connecting the walls and inner ribs of the four-wall assembly. As indicated, the four walls may be connected by a number of cross ribs 66, which may be further classified depending on which of the walls they are connected to. As used herein, the cross ribs 66 connecting the pressure-side outer wall 26 to the pressure-side skeleton line rib 63 are referred to as the pressure-side cross ribs 67. The cross ribs 66 connecting the suction-side outer wall 27 to the suction-side skeleton line rib 64 are referred to as the suction-side cross ribs 68. Finally, the cross ribs 66 connecting the pressure-side skeleton line rib 63 to the suction-side skeleton line rib 64 are referred to as the middle cross ribs 69.

[0040] In general, the purpose of the four-wall internal arrangement in an airfoil 25 is to provide efficient near-wall cooling, with the cooling air flowing in channels adjacent to the outer walls 26, 27 of the airfoil 25. It should be noted that near-wall cooling is advantageous because the cooling air is in close proximity to the hot outer surfaces of the airfoil, and the resulting heat transfer coefficients are high due to the high flow velocity achieved by throttling the flow through narrow channels. However, such designs are prone to short-cycle fatigue due to different degrees of thermal expansion experienced within the airfoil 25, which can ultimately shorten the life of the blade. For example, the thermal expansion of the suction-side outer walls 27 is greater during operation than that of the suction-side skeleton line rib 64.This differential expansion typically results in an increase in the length of the blade's skeletal line 25, thereby causing stresses between each of these structures and the structures connecting them. Furthermore, the thermal expansion of the pressure-side outer wall 26 is also greater than that of the cooler pressure-side skeletal line rib 63. In this case, the difference results in a shortening of the length of the blade's skeletal line 25, thereby causing stresses between each of these structures and the structures connecting them. The opposing forces within the blade, which tend to shorten the blade's skeletal line in one case and lengthen it in the other, can lead to further stress concentrations.The various ways in which these forces manifest themselves become a significant determining factor in the partial life of the blade 16, given the particular structural arrangement of an airfoil and the manner in which the forces are then balanced and compensated.

[0041] More specifically, in a more common situation, the suction-side outer wall 27 tends to bend outward at the apex of its curvature when contact with the high temperatures of the hot gas path causes it to thermally expand. It can be seen that the suction-side skeleton line rib 64, which is an inner wall, does not experience the same degree of thermal expansion and therefore does not have the same tendency to bend outward. The skeleton line rib 64 then resists the thermally induced enlargement of the outer wall 27. Because conventional designs have skeleton line ribs 62 formed with stiff geometries that offer little or no compliance, the resulting resistance and stress concentrations can be substantial.The problem is further complicated by the fact that the transverse ribs 66 used to connect the skeleton line rib 62 to the outer wall 27 are formed with linear profiles and are generally oriented at right angles to the walls to which they are connected. Given this fact, as heated structures expand at significantly different expansion rates, the transverse ribs 66 effectively maintain the "cold" spatial relationship between the outer wall 27 and the skeleton line rib 64. Accordingly, conventional arrangements with little or no "giveness" built into the structure are ill-suited to mitigating stresses concentrated in certain regions of the structure. The differential thermal expansion leads to low-cycle fatigue problems, which shorten component life.

[0042] In the past, many different internal cooling systems and structural arrangements for airfoils have been evaluated and attempts have been made to rectify this problem. One such approach proposes supercooling the outer walls 26, 27 so that the temperature difference and thereby the thermal expansion difference are reduced. It should be noted, however, that the way this is usually achieved is by increasing the amount of coolant circulated through the airfoil. Because coolant is usually air bled from the compressor, its increased consumption impairs the efficiency of the machine and is thus a solution that is preferably avoided. Other solutions have proposed the use of improved manufacturing processes and / or more complicated internal cooling structures that use the same amount of coolant but use it more efficiently.While these solutions have proven effective in some respects, each adds additional cost to either operating the machine or manufacturing the part and does nothing to directly address the underlying problem, namely the geometric deficiencies of conventional design given how airfoils expand due to heat during operation.

[0043] The present invention generally teaches certain curved, bubble-like, sinusoidal, or undulating inner fins (hereinafter "undulating fins") that eliminate unbalanced thermal loads often found in the airfoil of turbine blades. Within this general concept, the present invention describes several methods for achieving this, including undulating skeleton line fins 62 and / or cross fins 66, as well as certain types of angled connections between them and skeleton line fins 62 that have a tapered profile between connecting cross fins 66.It should be noted that these new arrangements—which, as outlined in the appended claims, may be used separately or in combination—reduce the stiffness of the internal structure of the airfoil 25 to provide targeted flexibility that disperses stress concentrations and transfers stresses to other structural regions that can better withstand them. This may involve, for example, dissipating stress to a region that distributes the stress over a larger area or perhaps a structure that relinquishes tensile stresses in favor of a compressive load, which is usually preferred. In this way, life-shortening stress concentrations and stresses can be avoided.

[0044] Fig. 6 to 8 provide cross-sectional views of a turbine blade 16 having an inner wall arrangement according to embodiments, wherein the embodiments of the Fig. 6 and Fig. 7 as such do not include all essential features of the claimed invention and as such do not belong to it, while the embodiment according to Fig. 8 of the present invention. The present invention includes the arrangement of ribs 60 used as both structural support and partitions that divide hollow airfoils 25 into interconnected radially extending flow passages 40. These flow passages 40 direct coolant flow through the airfoil 25 in a unique manner so that its use is more targeted and efficient. While the examples given herein are shown as they might be used in turbine blades 16, it will be appreciated that the same concepts can be employed in turbine vanes 17. Fig. Figure 6 illustrates a rib assembly having a skeleton line rib 62 with a wavy profile (it is intended that the term “profile” as used herein refers to the shape that the ribs have in the cross-sectional views of the Fig. 6 through 8). A skeleton line rib 62, as described above, is one of the longer ribs that extends from a position near the leading edge 28 of the airfoil 25 toward the trailing edge 29. These ribs are referred to as "skeleton line ribs" because the path they describe is approximately parallel to the skeleton line of the airfoil 25, which is a reference line passing between the leading edge 28 and the trailing edge 29 of the airfoil 25 through a collection of points that are equidistant between the concave pressure-side outer wall 26 and the convex suction-side outer wall 27. According to the present invention, a "wavy profile" includes one that has a noticeably curved and sinusoidal shape, as indicated. That is, the "wavy profile" is one that presents a reciprocating "S" profile.

[0045] The wavy segment or length of the skeleton line rib 62 may vary depending on design criteria. In the examples provided, the wavy skeleton line rib 62 typically extends from a position near the leading edge 28 of the airfoil 25 to a position beyond the center of the skeleton line of the airfoil 25. It should be noted that the wavy portion of the skeleton line rib 62 may be shorter in length while still providing the same types of performance benefits discussed herein. The number of bends, as well as the length of the wavy segment of the skeleton line rib 62, may be varied to achieve the best results. In certain embodiments, the wavy skeleton line rib 62 of the present invention is defined by the number of complete reciprocating "S" shapes it contains.In a preferred embodiment of this type, the undulating skeleton line rib 62 includes at least one continuous reciprocating "S" shape. In another embodiment, the undulating skeleton line rib 62 includes at least two consecutive and continuous reciprocating "S" shapes. It will be appreciated that the shapes shown in FIGS. Fig. 6 and Fig. 7 each describe paths that have more than two complete "S" shapes. Regarding the overall length, the wavy segment of the skeletal line rib 62 may extend over a significant portion of the length of the skeletal line of the airfoil 25. For example, as shown in Fig. 6 and Fig. 7, in a preferred embodiment, the wavy portion of the skeleton line rib 62 constitutes over 69% of the length of the skeleton line of the airfoil 25. That is, the wavy portion of the skeleton line rib 62 originates near the leading edge 28 of the airfoil 25 and extends rearward and well beyond the apex of the curvature of the airfoil 25.

[0046] It should be noted that a wavy skeleton line rib 62, given its serpentine profile, describes a path that varies in direction. The wavy skeleton line rib 62 of the present invention can still be described as having a generally arching path over which it serpentines, and that this path usually runs from a starting point near the leading edge 28 to an aft point near the trailing edge 29 of the airfoil. It should be noted that in the case of a wavy skeleton line rib 62, it is this generally arching path that is roughly parallel to the skeleton line of the airfoil 25.

[0047] Many known arrangements of the blade 25, such as the four-walled example of Fig. 5, include two skeleton line ribs 62. This type of arrangement can be described as having a pressure-side skeleton line rib 63 located near the pressure-side outer wall 26 and a suction-side skeleton line rib 64 located near the suction-side outer wall 27. The present invention, as shown in the Fig. 6 and Fig. 7, may include arrangements in which both the suction-side skeleton line rib 64 and the pressure-side skeleton line rib 63 are formed as wavy ribs. In alternative embodiments, only one of these skeleton line ribs 62 may have a wavy profile. It should be noted that the present invention may also be used in arrangements with only a single skeleton line rib 62.

[0048] For airfoils 25 that include two skeleton line ribs 62, it should be noted that the pressure-side skeleton line rib 63 and the suction-side skeleton line rib 64 define a central flow passage 40. The undulating profile for the pressure-side skeleton line rib 63 and the suction-side skeleton line rib 64 can each be defined relative to the shape assumed by successive segments of the skeleton line rib 62 facing the central flow path 40. That is, the undulating profile of the skeleton line rib 62 can be described, for example, relative to the central flow path 40 as including two successive segments in which a first concave segment transitions into a second convex segment.In an alternative embodiment, the wavy profile may have four consecutive segments in which: a first concave segment transitions into a second convex segment, the second convex segment transitions into a third concave segment, and the third concave segment transitions into a fourth convex segment.

[0049] In certain embodiments, the present invention teaches certain arrangements of transverse ribs 66 that may be employed to tune the compliance of the airfoil 25. Transverse ribs 66, as used herein, are the shorter ribs that run transversely through the airfoil 25. Transverse ribs 66 are used to connect skeleton line ribs 62 to other skeleton line ribs or to one of the outer walls 26, 27 of the airfoil 25. It should be noted that with such an arrangement, transverse ribs 66 also serve as partitions to the flow passages 40 formed between the outer walls 26, 27 and the skeleton line ribs 62. As illustrated, the pressure-side outer wall 26 and the pressure-side skeleton line rib 63 are arranged to define a pressure-side flow passage 40 therebetween.Likewise, the suction-side outer wall 27 and the suction-side skeleton line rib 64 are arranged to define a suction-side flow passage 40 therebetween. The central flow passage 40 is defined between the suction-side skeleton line rib 64 and the pressure-side skeleton line rib 63. As indicated, these flow passages 40 can then be further subdivided by the transverse ribs 66. In certain embodiments of the present invention, a plurality of pressure-side transverse ribs 67 connect the pressure-side outer wall 26 to the pressure-side skeleton line rib 63. The pressure-side transverse ribs 67 thus subdivide the pressure-side flow passage 40 into a number of separate, axially stacked flow passages 40.Likewise, a plurality of suction-side transverse ribs 68 connect the suction-side outer wall 27 to the suction-side skeleton line rib 64 and subdivide the suction-side flow passage 40 into a number of separate, axially stacked flow passages 40. Middle transverse ribs 69 connect the pressure-side skeleton line rib 63 to the suction-side skeleton line rib 64 and subdivide the middle flow passage in a similar manner.

[0050] The skeleton line ribs 62 and the transverse ribs 66 may be arranged as radially extending walls. That is, these ribs may have the configurations shown in the cross-sectional views of the Fig. 6 to 8 while extending radially between the two ends of the airfoil 25. In this manner, the pressure-side flow passages, the suction-side flow passages, and the intermediate flow passages 40 may extend radially between an inboard end near the interface between the airfoil 25 and the root 21 and an outboard end near the outboard tip of the airfoil 25. In use, a coolant supply may be delivered via a supply passage extending through a root 21 to one or more of the inboard ends of the flow passages 40. It should be noted that the flow passages 40 may be selectively interconnected at their inboard or outboard ends to establish a tortuous coolant path through the airfoil 25.

[0051] As in Fig. 6, rib assemblies of the present invention may include a plurality of transverse ribs 66 on each of the pressure and suction sides of the airfoil 25. In a preferred embodiment, at least five pressure-side transverse ribs 67 and five suction-side transverse ribs 68 may be included. A plurality of central transverse ribs 69 may also be provided, but in other embodiments, a single transverse rib 69 may be used. In the preferred embodiments, as shown, the present invention may include at least two central transverse ribs 69. The present invention further describes an interconnection structure by which the transverse ribs 66 are connected to the outer walls 26, 27 and / or the skeleton line ribs 62.It will be appreciated that the angle at which the transverse ribs 66 intersect such walls 26, 27, 62 may be described as a "joint angle" (it will be appreciated that said "joint angle" is the smaller of the two angles formed on either side of each end of a transverse rib between the transverse rib and the wall intersected thereby). In conventional airfoil assemblies, as noted above, the joint angle is a steep one, generally close to 90°. It will be appreciated that steep angles such as this result in a stiff structure. The present invention teaches angles significantly less than 90° as a method by which the structure of the airfoil 25, or target areas of the structure, can be made more compliant. According to one embodiment, as shown in FIGS. Fig. 6 and Fig. 7, at least two of the pressure-side transverse ribs 67 may be arranged to have a connection angle of less than 60 degrees with the pressure-side outer wall 26. According to other embodiments, as indicated, at least two of the suction-side transverse ribs 68 may be arranged to form a connection angle of less than 60 degrees with the suction-side outer wall 27. The central transverse ribs 69 may be similarly formed, and arrangements of the present invention include at least one connection angle of less than 60 degrees at each of the suction-side skeleton line rib 64 and the pressure-side skeleton line rib 63.Where greater compliance is required, embodiments may include three of the pressure-side transverse ribs 67 and three of the suction-side transverse ribs 68 being arranged to have a connection angle to the outer walls 26, 27 of less than 60 degrees, and at least two of the central transverse ribs 69 being arranged to form a connection angle of less than 60 degrees to each of the suction-side skeleton line rib 64 and the pressure-side skeleton line rib 63.

[0052] The present invention further describes another way in which the transverse ribs 66 can improve structural compliance. Transverse ribs 66 are typically formed with a linear profile, which, as will be appreciated, results in a stiff and rigid arrangement. According to certain embodiments of the present invention, transverse ribs 66 are arranged having a curved profile. Specifically, as in each of the examples in the Fig. 6 to 8, the transverse ribs 69 may include a curved, arched, or bulging profile. With this profile, the transverse ribs 66 become much more compliant and more able to accommodate relative movement between the structural walls they interconnect. The direction in which the curved, bulging profile of the transverse rib is oriented can be manipulated to accommodate the types of expected loads. According to a preferred embodiment, as shown in Fig. 6, the curvature of the central transverse rib 69 may be directed such that the concave end surface of the central transverse rib 69 is directed toward the leading edge 28 of the airfoil 25. This orientation may be applied to all or a fraction of the transverse ribs 69 included in a particular structure. In an alternative embodiment, the curvature of the central transverse ribs 69 may be directed such that the convex end surface of the transverse rib is directed away from the leading edge 28 of the airfoil 25. This profile type may be used on all or a fraction of the central transverse ribs 69.

[0053] According to the present invention, the internal structure of an airfoil can include undulating ribs along the airfoil's skeleton line direction. By making the skeleton line rib 62 a spring in this manner, the inner spine of the airfoil can be made more compliant, thus achieving performance benefits. In addition, the transverse ribs of the airfoil structure can be curved to further soften the load path and to create more compliant connections with the ribs 62 and the outer walls 26, 27 connected by them. While normal linear rib designs experience high stress and short-cycle fatigue due to the thermal conflict between the inner cooling space walls and the much hotter outer walls, the present invention provides a spring-like structure that can better disperse stress concentrations, which, as provided herein, can be used to improve the component's service life.

[0054] The Fig. 7 and Fig. 8 illustrate the aspect of the present invention in which one or more skeleton line rib segments 73 of a skeleton line rib 62 are formed with a tapered profile 72. According to the present invention, and as used herein, a "tapered profile" is one in which the rib thickness narrows from opposite ends 75 of the skeleton line rib segment 73 to form a neck or narrow region therebetween. Described otherwise, a tapered profile is one in which the skeleton line rib segment 73 has a thickness that gradually widens or thickens in both directions as it extends outward from the neck 74. It will be appreciated that the tapered profile 72 in this arrangement resembles an hourglass shape.

[0055] The tapered profile 72 of the present invention may be incorporated into flow passages 40 defined inwardly by a skeleton line rib 62. In preferred embodiments, as indicated, the tapered profile 72 is applied to a skeleton line rib segment 73, which is defined with respect to the array of near-wall flow passages 40 formed between the skeleton line rib 62 and one of the outer walls 26, 27 of the airfoil 25. In preferred embodiments, the skeleton line rib segment 73 with the tapered profile 72 is defined between successive transverse ribs 66. Specifically, it will be appreciated that the near-wall flow passages are defined between two successive transverse ribs 66 connecting the outer wall 26, 27 of the airfoil 25 to a skeleton line rib 62.In preferred embodiments, the skeleton line rib segment 73 to which the tapered profile 72 is applied is the length of the skeleton line rib 62 defined between the points at which each of these consecutive ribs 66 intersects the skeleton line rib 62. The skeleton line rib segment 73 thus defined may be referred to as a cross-rib-cross-rib segment.

[0056] As in Fig. As indicated in Figure 8, the tapered profile 72 can be used with skeleton line ribs 62 having a wavy or sinusoidal shape, in which case it can be used with any of the arrangements discussed above in relation to other aspects of the present invention. However, the tapered profile 72 is not limited to this type of use. As shown in Fig. 7, the tapered profile 72 may be used in conjunction with traditionally formed skeleton line ribs 62, i.e., those having an axis that is substantially linear. In preferred embodiments, the tapered profile 72 may be used on the skeleton line ribs 62 of two or more successively formed flow passages 40. However, it will be appreciated that the tapered profile 72 may still provide certain performance advantages when used on the skeleton line rib segment 73 of a single flow passage 40. It will also be appreciated that the tapered profile 72 may be used on skeleton line rib segments 73 of the pressure side skeleton line ribs 62, the suction side skeleton line ribs 62, or both.

[0057] As in the Fig. 7 and Fig. 8, the tapered profile 72 may include a curved or non-inventive linear shape according to the invention. In a preferred embodiment, the tapered profile 72 includes a contoured shape that progressively widens from the neck 74. As indicated, in a preferred embodiment, the neck 74 may be positioned at or near the midpoint of the skeleton line rib segment 73 of the skeleton line rib 62. It is understood that the neck 74 is described as having a "neck thickness," while each of the opposite ends 75 of the skeleton line rib segment 73 may be described as having a "final thickness," which in the Fig. 7 and 8, respectively, as distance or neck thickness 77 and distance or end thickness 78. In exemplary embodiments, the end thickness 78 of each of the ends 75 is at least 1.5 times the neck thickness 77. In an alternative embodiment, the end thickness 78 of each of the ends 75 is at least twice the neck thickness 77. The tapered profile between the opposite ends 75 and the neck 74 may taper in a smooth and / or constant manner, minimizing stress concentrations.

[0058] It will be appreciated that the tapered profile 72 of the present invention provides another way in which the compliance of the airfoil structure can be improved or further tuned to minimize or distribute stresses due to unbalanced thermal expansion. In a preferred embodiment, the tapered profile 72 can be used in conjunction with aspects of the undulating skeleton line ribs 62 to improve the compliance of the "spring" that these ribs generally form. In this case, it will be understood that the tapered profile 72 improves the spring action of the undulating walls and thereby reduces the stress experienced by the internal structure of the airfoil 25. In this sense, with further reference to Fig.8 that the tapered profile 72 provides the curved skeleton line rib segments 73 of the wavy ribs with the compliance to straighten in response to a tensile load and to flex further in response to a compressive load. As indicated, the tapered profile 72 can also be used with more conventional linear-type skeleton line ribs 62 (not according to the invention) as a means of providing the airfoil structure with at least some degree of improved compliance. The resulting lower stress level provided by this type of rib arrangement can be used to extend the life of the component.

[0059] The invention is defined by the claims set out below.

[0060] A turbine blade having an airfoil and a radially extending chamber therein for a coolant. The turbine blade may also include a rib arrangement dividing the chamber into radially extending flow passages. The rib arrangement may include a skeleton line rib defining a near-wall flow chamber, and transverse ribs extending between the skeleton line rib and one of the outer walls to divide the near-wall flow chamber into sequentially stacked flow passages, each including a segment of the skeleton line rib. The segment of the skeleton line rib of one of the flow passages may have a tapered profile including a profile that narrows from opposite ends to a throat disposed therebetween. LIST OF REFERENCE SYMBOLS: 10 Combustion turbine engine 11 compressors 12 Combustion chamber 13 turbines 14 Compressor blade 15 Compressor guide vane 16 turbine blades 17 Turbine guide vane 21 root 24 Platform 25 blade 26 Pressure-side outer wall 27 Suction-side outer wall 28 leading edge 29 trailing edge 31 Outer tip 40 flow passage 60 ribs 62 Skeletal line rib 63 Pressure-side skeletal line rib 64 Suction-side skeleton line rib 66 transverse rib 67 Pressure-side transverse rib 68 Suction-side cross rib 69 Middle transverse rib 72 Narrowing profile 73 Skeletal line rib segment 74 neck 75 End 77 neck thickness 78 final thickness

Claims

[1] Turbine blade with an airfoil (25) defined by outer walls (26, 27), wherein a concavely shaped pressure-side outer wall (26) and a convexly shaped suction-side outer wall (27) are connected to one another along the leading and trailing edges (28, 29) and form a radially extending chamber therebetween for receiving a coolant flow, the turbine blade further comprising: a rib arrangement dividing the chamber into radially extending flow passages (40), the rib arrangement including: a skeleton line rib (62) extending adjacent one of the outer walls (26, 27) to define a near-wall flow chamber therebetween, and Transverse ribs (66) extending between the skeleton line rib (62) and one of the outer walls (26, 27) to divide the near-wall flow chamber into successively stacked flow passages (40), each of the flow passages (40) being defined inwardly by a skeleton line rib segment (73) of the skeleton line rib (62), wherein the skeleton line rib segment (73) of the skeleton line rib (62) of one of the flow passages (40) has a narrowing profile (72), the narrowing profile (72) comprising a profile that narrows from opposite ends (75) to a throat (74) disposed therebetween, and wherein the skeleton line rib (62) having the narrowing profile (72) has a wavy or sinusoidal shape and the skeleton line rib segment (73) of the skeleton line rib (62) is substantially convexly or concavely curved with respect to an adjacent flow path (40), wherein the narrowing profile (72) provides the substantially convexly or concavely curved skeleton line rib segment (73) of the wavy or sinusoidal skeleton line rib (62) with compliance to straighten in response to a tensile load and to further deflect in response to a compressive load. [2] Turbine blade according to claim 1, wherein the tapered profile (72) comprises a cross-sectional profile and / or wherein the skeleton line rib segment (73) of the skeleton line rib (62) comprises a cross-rib-cross-rib segment in which each of the opposite ends (75) is defined at an intersection with one of the cross ribs (66), and / or wherein the cross ribs (66) form at least two axially stacked flow passages (40) and wherein the skeleton line rib segment (73) of the skeleton line rib (62) has the tapered profile (72) for each of the at least two axially stacked flow passages (40). [3] Turbine blade according to claim 2, wherein the transverse ribs (66) form three axially stacked flow passages (40), wherein the skeleton line rib segment (73) of the skeleton line rib (62) has the narrowing profile (72) for each of the three axially stacked flow passages (40). [4] Turbine blade according to claim 3, wherein the skeleton line rib segments (73) of the skeleton line rib (62) for the three successively stacked flow passages (40) have a wavy axis. [5] Turbine blade according to one of the preceding claims, wherein the skeleton line rib (62) comprises a pressure-side skeleton line rib (63) running alongside and close to the pressure-side outer wall (26), the transverse ribs (66) running between the pressure-side skeleton line rib (63) and the pressure-side outer wall (26) to form the three sequentially stacked flow passages (40), the flow passages (40) each being defined by the pressure-side outer wall (26), two opposing transverse ribs (66) and, opposite the pressure-side outer wall (26), the skeleton line rib segment (73) of the pressure-side skeleton line rib (63). [6] Turbine blade according to one of the preceding claims, wherein the skeleton line rib (62) comprises a suction-side skeleton line rib (64) which runs alongside and close to the suction-side outer wall (27), the transverse ribs (66) running between the suction-side skeleton line rib (64) and the suction-side outer wall (27) to form the three sequentially stacked flow passages (40), the flow passages (40) each being defined by the suction-side outer wall (27), two opposing transverse ribs (66) and, opposite the suction-side outer wall (27), the skeleton line rib segment (73) of the suction-side skeleton line rib (64). [7] Turbine blade according to one of the preceding claims, wherein the rib arrangement comprises two skeleton line ribs (62): a pressure-side skeleton line rib (63) running alongside the pressure-side outer wall (26) and forming a near-wall flow chamber therebetween, and a suction-side skeleton line rib (64) running alongside the suction-side outer wall (27) and forming a near-wall flow chamber therebetween, wherein the transverse ribs (66) run between the pressure-side skeleton line rib (63) and the pressure-side outer wall (26) to form at least two successively stacked flow passages (40), wherein the skeleton line rib segment (73) of the pressure-side skeleton line rib (63) has the tapered profile (72) for each of the two successively stacked flow passages (40),and wherein the transverse ribs (66) extend between the suction-side skeleton line rib (64) and the suction-side outer wall (27) to form at least two successively stacked flow passages (40), wherein the skeleton line rib segment (73) of the suction-side skeleton line rib (64) has the narrowing profile (72) for each of the two successively stacked flow passages (40). [8] Turbine blade according to one of claims 5 to 7, wherein the pressure-side skeleton line rib (63) and / or the suction-side skeleton line rib (64) has a wavy profile including at least two consecutive reciprocating "S" shapes. [9] Turbine blade according to one of the preceding claims, wherein the throat (74) of the narrowing profile (72) is arranged near a midpoint between the opposite ends (75) of the skeleton line rib segments (73) of the skeleton line rib (62) and / or wherein each of the opposite ends (75) has an end thickness (78) and the throat (74) has a throat thickness (77), and wherein the end thickness (78) is at least 1.5 times as great as the throat thickness (77), and / or wherein each of the opposite ends has an end thickness (78) and the throat (74) has a throat thickness (77), and wherein the end thickness (78) is at least twice as great as the throat thickness (77), and / or wherein the narrowing between each of the opposite ends (75) and the throat (74) is smooth. [10] Turbine blade according to one of the preceding claims, wherein the turbine blade comprises a turbine blade (16).

Images