WO2016178689A1

WO2016178689A1 - Turbine airfoil with internal cooling channels

Info

Publication number: WO2016178689A1
Application number: PCT/US2015/029673
Authority: WO
Inventors: Jr. Nicholas F. MARTIN; Gary B. Merrill; JR. Samuel R. MILLER; Alexander Ralph Beeck
Original assignee: Siemens Aktiengesellschaft; Siemens Energy, Inc.
Priority date: 2015-05-07
Filing date: 2015-05-07
Publication date: 2016-11-10
Also published as: CN107636254A; JP2018519453A; EP3292277A1; US20180135432A1

Abstract

A turbine airfoil (10) with an internal cooling system (12) having one or more bladders (14) forming near-wall cooling channels (16) is disclosed. The bladder (14) may be conformed to a shape of an inner surface (44) forming a cavity (18) within the internal cooling system (12). One or more standoff ribs (56) may extend radially inward from the inner surface (44) forming the cavity (18) to maintain the bladder (14) in position off of the inner surface (44) so that the near-wall cooling channel (16) is formed between the bladder (14) and the inner surface (44). The near-wall cooling channel (16) may be formed by inserting a bladder (14) into the cavity (18) in a first insertable position (22) and expanding the bladder (14) into a second expanded position (24). In at least one embodiment, the chamber (26) formed by the bladder (14) may be dead space that does not contain cooling fluids as a part of the cooling system (12).

Description

TURBINE AIRFOIL WITH INTERNAL COOLING CHANNELS

FIELD OF THE INVENTION

This invention is directed generally to gas turbine engines, and more particularly to internal cooling systems for airfoils in gas turbine engines.

BACKGROUND

Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Typical turbine combustor

configurations expose turbine vane and blade assemblies to high temperatures. As a result, turbine vanes and blades must be made of materials capable of

withstanding such high temperatures, or must include cooling features to enable the component to survive in an environment which exceeds the capability of the material. Turbine engines typically include a plurality of rows of stationary turbine vanes extending radially inward from a shell and include a plurality of rows of rotatable turbine blades attached to a rotor assembly for turning the rotor.

Typically, the turbine blades and vanes are exposed to high temperature combustor gases that heat the airfoil. These airfoils include internal cooling systems for reducing the temperature of the airfoils. One of the internal cooling systems is described as near-wall cooling. In near-wall cooling, the internal cooling flow is directed to the vicinity near the wall to be cooled. Some airfoils include a four wall design forming near-wall cooling channels. Cooling air is passed through the near- wall cooling channels to cool the outer wall. However, the four wall design has an inherent structural problem due to the significant differences in operating

temperatures between the outer and inner walls. The outer walls will operate at significantly higher temperatures than the inner walls because the outer walls are subjected to the hot gas path air whereas the inner walls are not contacted by the hot gas path air and operate near the temperature of the cooling air. This difference in operating temperature between the inner and outer walls creates high thermally induced stress in the walls and can greatly limit the life of the airfoils. In addition, forming complex cores required for multiwall definition in turbine airfoils formed by investment casting is challenging. Thus, a need exists for reducing thermal stress between the outer and inner walls of near-walled cooled gas turbine airfoils and overcoming the challenges in creating complex cooling systems.

SUMMARY OF THE INVENTION

A turbine airfoil with an internal cooling system having one or more bladders forming near-wall cooling channels is disclosed. The bladder may be conformed to a shape of an inner surface forming a cavity within the internal cooling system. One or more standoff ribs may extend radially inward from the inner surface forming the cavity to maintain the bladder in position off of the inner surface so that the near-wall cooling channel is formed between the bladder and the inner surface. The near-wall cooling channel may be formed by inserting a bladder into the cavity in a first insertable position and expanding the bladder into a second expanded position. In at least one embodiment, the chamber formed by the bladder may be dead space that does not contain cooling fluids as a part of the cooling system.

In at least one embodiment, the turbine airfoil may be formed from a generally elongated hollow airfoil formed from an outer wall, and having a leading edge, a trailing edge, a pressure side, a suction side, and a cooling system positioned within interior aspects of the generally elongated hollow airfoil and formed by at least one cavity. The turbine airfoil may include one or more bladders positioned within one or more cavities of the cooling system. The bladder may form one or more near-wall cooling channels between an outer surface of the bladder and an inner surface forming the cavity of the cooling system. The bladder may be formed from a continuous, nonlinear wall. In at least one embodiment, the bladder may define an internal chamber that is a dead space. The bladder may define a sealed internal chamber not in fluid communication with the cooling system such that cooling fluids cannot be exchanged with between the sealed internal chamber and the cooling system. In other embodiments, the cooling system may be configured to control or limit the flow of cooling fluids into an internal chamber of the bladder.

The turbine airfoil may further include one or more standoff ribs extending from the inner surface forming the cavity of the cooling system and into contact with the bladder. In particular, a first section of the at least one bladder laterally adjacent to a portion of the bladder in contact with a tip of the standoff rib may be positioned closer to the inner surface forming the cavity of the cooling system than the tip of the standoff rib. A second section of the bladder may be positioned on an opposite side of the standoff rib from the first section, wherein the second section of the bladder laterally adjacent to a portion of the bladder in contact with a tip of the standoff rib may be positioned closer to the inner surface forming the cavity of the cooling system than the tip of the standoff rib. In at least one embodiment, the standoff rib may include a plurality of standoff ribs extending from the inner surface forming the cavity of the cooling system and into contact with the bladder. The bladder between two adjacent standoff ribs may be curved from a tip of a first standoff rib toward the inner surface forming the cavity of the cooling system to an outermost point and may be curved away from the inner surface forming the cavity of the cooling system and from the outermost point to a tip of a second standoff rib. In an embodiment of the turbine airfoil with a plurality of standoff ribs, the bladder extending between each of the plurality of standoff ribs may be curved from a tip of a first standoff rib toward the inner surface forming the cavity of the cooling system to an outermost point and may be curved away from the inner surface forming the cavity of the cooling system and from the outermost point to a tip of a second standoff rib.

In at least one embodiment, the standoff ribs may be positioned to direct cooling fluids within the near-wall cooling channels. The plurality of standoff ribs may be formed from a plurality of serpentine shaped ribs extending spanwise and may be offset chordwise from each other. The plurality of standoff ribs may be positioned nonparallel and nonorthogonal with a spanwise extending direction and may be formed into chordwise extending rows.

The bladder may be formed from a material that is different from a material forming the outer wall of the generally elongated hollow airfoil. In at least one embodiment, the bladder may be formed from a material having greater plasticity than the material forming the outer wall of the generally elongated hollow airfoil. In at least one embodiment, the bladder may be formed from a first section having a first thickness and a second section having a second thickness that is greater the first section. The first section may be formed from a material having a tapered thickness.

The airfoil may be formed from a method including positioning a generally elongated hollow airfoil formed from an outer wall, and having a leading edge, a trailing edge, a pressure side, a suction side, and a cooling system positioned within interior aspects of the generally elongated hollow airfoil and formed by at least one cavity. The method may include inserting one or more bladders within the cavity of the cooling system, wherein the bladder forms at least one near-wall cooling channel between an outer surface of the bladder and an inner surface forming the cavity of the cooling system. The method may also include expanding the bladder from a first insertable position to a second expanded position within the cavity in the cooling system, wherein the second expanded position of the bladder has a larger volume than a volume of the bladder in the first insertable position.

In at least one embodiment, expanding the bladder from a first insertable position to a second expanded position within the cavity in the cooling system may cause the bladder to become locked in place within the cavity in the cooling system. Expanding the bladder from a first insertable position to a second expanded position within the cavity in the cooling system may include applying pressure within the bladder to expand the bladder from the first insertable position to the second expanded position. In another embodiment, expanding the bladder from a first insertable position to a second expanded position within the cavity in the cooling system may include evacuating the near-wall cooling channel between the outer surface of the bladder and the inner surface forming the cavity of the cooling system to expand the bladder from the first insertable position to the second expanded position. Expanding the bladder from a first insertable position to a second expanded position within the cavity in the cooling system may further include heating the bladder to expand the bladder and to deform the bladder partially about at least one standoff rib extending from the inner surface forming the cavity to lock the bladder within the cavity forming the cooling system.

The method may also include pretreating an outer surface of the bladder with a metal braze so that the bladder is joined to metal contacting the bladder after the bladder has been expanded. The step of pretreating an outer surface of the bladder may also include pretreating the outer surface of the bladder with a foil that may chemically bond the bladder wall to rib surfaces to ensure a seamless and continuous joint, which may be required for heat transfer.

An advantage of the internal cooling system is that the internal bladder may be created in a very simple process that is better suited for complex cooling configurations than conventional investment casting.

These and other embodiments are described in more detail below. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention.

Figure 1 is a perspective view of a turbine airfoil.

Figure 2 is a cross-sectional view of turbine airfoil taken at section line 2-2 in

Figure 1 with a bladder in a first insertable position within a cavity of the cooling system.

Figure 3 is a partial cross-sectional view of one side of the turbine airfoil taken in a view taken at section line 2-2 in Figure 1 .

Figure 4 is a partial cross-sectional view of the bladder in a first insertable position within a cavity of the cooling system as shown in Figure 2.

Figure 5 is a cross-sectional view of turbine airfoil taken at section line 2-2 in Figure 1 with a bladder in a second expanded position within a cavity of the cooling system.

Figure 6 is a cross-sectional view of turbine airfoil taken at section line 6-6 in

Figure 1 with a bladder in a first insertable position within a cavity of the cooling system in a platform of the airfoil and a bladder in a second expanded position within a cavity of the cooling system in a platform of the airfoil.

Figure 7 is a cross-sectional view of turbine airfoil taken at section line 7-7 in Figure 1 with a bladders in second expanded positions within cavities of the cooling system. Figure 8 is a cross-sectional view of turbine airfoil, such as a turbine vane with an outer and inner endwalls, taken at section line 8-8 in Figure 1 with a bladder in a first insertable position within a cavity of the cooling system.

Figure 9 is a cross-sectional view of turbine airfoil, such as a turbine vane with an outer and inner endwalls, taken at section line 9-9 in Figure 1 with a bladder in a second expanded position within a cavity of the cooling system.

Figure 10 is a cross-sectional filleted view of an inner surface of an outer wall of the turbine airfoil, taken at section line 10-10 in Figure 1 with spanwise extending serpentine shaped standoff ribs.

Figure 1 1 is a cross-sectional filleted view of an inner surface of an outer wall of the turbine airfoil, taken at section line 1 1 -1 1 in Figure 1 with chordwise extending rows of angled standoff ribs.

Figure 12 is a cross-sectional filleted view of an inner surface of an outer wall of the turbine airfoil, taken at section line 12-12 in Figure 1 with spanwise extending serpentine shaped standoff ribs that are smaller, tighter serpentine channels than shown in Figure 1 0.

Figure 13 is a detail view of the tip of the turbine airfoil of Figure 1 with the cooling system with standoff ribs and bladder shown in dashed phantom lines.

Figure 14 is a cross-sectional view of the airfoil tip taken at section line 14-14 in Figure 13.

Figure 15 is a cross-sectional view of the airfoil tip taken at section line 15-15 in Figure 13.

Figure 16 is a partial cross-sectional view of an alternative bladder in a first insertable position with a tapered section.

Figure 17 is a partial cavity cross-sectional, detail view of a bladder having a spanwise section with a linear taper.

Figure 18 is a partial cross-sectional, detail view of a bladder having a spanwise section with a nonlinear taper.

Figure 19 is a flow diagram showing the method of creating the near-wall cooling channels with a bladder. DETAILED DESCRIPTION OF THE INVENTION

As shown in Figures 1-1 9, a turbine airfoil 10 with an internal cooling system 12 having one or more bladders 14 forming near-wall cooling channels 16 is disclosed. The bladder 14 may be conformed to a shape of an inner surface 16 forming a cavity 1 8 within the internal cooling system 12. One or more standoff ribs 20 may extend radially inward from the inner surface 16 forming the cavity 1 6 to maintain the bladder 14 in position off of the inner surface 16 so that the near-wall cooling channel 16 is formed between the bladder 14 and the inner surface 16. The near-wall cooling channel 16 may be formed by inserting a bladder 14 into the cavity 16 in a first insertable position 22 and expanding the bladder 14 into a second expanded position 24. In at least one embodiment, the chamber 26 formed by the bladder 14 may be dead space that does not contain cooling fluids as a part of the cooling system 12.

In at least one embodiment, the turbine airfoil 10 may be formed from a generally elongated hollow airfoil 30 formed from an outer wall 32, and having a leading edge 34, a trailing edge 36, a pressure side 38, a suction side 40, and the cooling system 12 positioned within interior aspects of the generally elongated hollow airfoil 30 and formed by one or more cavities 18. The airfoil 30 may have any conventional shape and configuration or heretofore yet to be conceived shapes and configurations. The airfoil 30 may or may not include a platform 48 with aspects of the cooling system 12. One or more bladders 14 may be positioned within the cavity 18 of the cooling system 12. The bladder 14 may form one or more near-wall cooling channels 16 between an outer surface 42 of the bladder 14 and an inner surface 44 forming the cavity 1 8 of the cooling system 12.

The bladder 14 may be formed from a continuous, nonlinear wall 46. The bladder 14 may be formed from a material that is different from a material forming the outer wall 32 of the generally elongated hollow airfoil 30. The bladder 14 may be formed from a material that is different from a material forming the inner surface 44 of the cavity 18 forming at least a portion of the cooling system 12. The bladder 14 may be formed from a material having greater plasticity than the material forming the outer wall 32 of the generally elongated hollow airfoil 30 or forming the inner surface 44 of the cavity 18 forming at least a portion of the cooling system 12. The material forming the bladder 14 may have a large plastic deformation range such that the material can be plastically deformed without fracture. In at least one embodiment, as shown in Figure 4, the bladder 14 may be formed from a first section 50 having a first thickness and a second section 52 having a second thickness that is greater the first section 50. In another embodiment, the bladder 14 may be formed from a first section 50 and a second section 52, as shown in Figure 16, whereby the first section 50 is formed from a material having a tapered thickness. The material may taper from a first thickness to a second thickness that is thinner than the first thickness. The second section 52 may also be tapered. The thickness of the first section 50 may be tapered linearly, as shown in Figure 17. Alternatively, the thickness of the first section may be tapered nonlinearly as shown in Figure 18.

The bladder 14 may define an internal chamber 26 that is a dead space. In particular, the bladder 14 may be sealed and not in fluid communication with the cooling system 12. As such, cooling fluids from the cooling system 12 do not flow into the bladder 14. The bladder 14 may define a sealed internal chamber 26 not in fluid communication with the cooling system 21 such that cooling fluids cannot be exchanged with between the sealed internal chamber 26 and the cooling system 12.

The cooling system 12 may include one or more standoff ribs 20 extending from the inner surface 44 forming the cavity 18 of the cooling system 12 and into contact with the bladder 14. The standoff ribs 20 may have consistent cross- sections. The standoff ribs 20 may also include tips 58 configured to contact the expanded bladder 14 and to prevent the bladder 14 from being punctured. In at least one embodiment, the standoff ribs 20 may include one or more protection members 96 attached to the tips 58 of the standoff ribs 20. In at least one

embodiment, the protection members 96 may be one or more side arms 98, as shown in Figures 2, 3, and 5, forming a T shape with the standoff ribs 20 to support the bladder inwardly of the inner surface 44 of the cavity 1 8. The protection members 96 may also be one or more bulbs 100, as shown in Figures 2, 3, and 5, attached to the tip 58 to support the bladder inwardly of the inner surface 44 of the cavity 18. The tips 58 may support the bladder 14 and prevent the bladder 14 from contacting the inner surface 44 of the cavity 18 in close proximity to the standoff rib 20. The tips 58 may cause the bladder 14 to droop around the standoff rib 20 in a nonlinear manner. In particular, as shown in Figure 2, a first section 60 of the bladder 14 laterally adjacent to a portion 64 of the bladder 14 in contact with a tip 58 of the standoff rib 20 may be positioned closer to the inner surface 44 forming the cavity 18 of the cooling system 12 than the tip 58 of the standoff rib 20. A second section 62 of the bladder 14 on an opposite side of the standoff rib 20 from the first section 60 and laterally adjacent to a portion 64 of the bladder 14 in contact with a tip 58 of the standoff rib 20 is positioned closer to the inner surface 44 forming the cavity 18 of the cooling system 12 than the tip 58 of the standoff rib 20.

In at least one embodiment, the cooling system 12 may include a plurality of standoff ribs 20 extending from the inner surface 44 forming the cavity 18 of the cooling system 12 and into contact with the bladder 14. The bladder 14 between two adjacent standoff ribs 20 may be curved from a tip 58 of a first standoff rib 66 toward the inner surface 44 forming the cavity 18 of the cooling system 12 to an outermost point 68 and is curved away from the inner surface 44 forming the cavity 18 of the cooling system 12 and from the outermost point 68 to a tip 58 of a second standoff rib 70. For the plurality of standoff ribs 20, the bladder 14 extending between each of the plurality of standoff ribs 20 may be curved from a tip 58 of a first standoff rib 66 toward the inner surface 44 forming the cavity 18 of the cooling system 12 to an outermost point 68 and may be curved away from the inner surface 44 forming the cavity 18 of the cooling system 12 and from the outermost point 68 to a tip 58 of a second standoff rib 70. The plurality of standoff ribs 20 may be formed from a plurality of serpentine shaped ribs 20 extending in a spanwise direction 72 and offset chordwise from each other, as shown in Figures 10 and 12. Alternatively, the plurality of standoff ribs 20 may be positioned nonparallel and nonorthogonal with a spanwise extending direction 72 and are formed into chordwise extending rows 74 extending in a chordwise direction 75, as shown in Figure 1 1 . The serpentine shaped ribs 20 and standoff ribs 20 forming the chordwise extending rows 74 may be positioned not too far apart such that the standoff ribs 20 support the bladder 14 and forming near-wall cooling channels 16 by preventing collapse of the bladder 14 against the inner surface 44 of the cavity 18 of the internal cooling system 12. The standoff ribs 20 including the serpentine shaped ribs 20 and standoff ribs 20 forming the chordwise extending rows 74 may be configured to divert cooling fluids with in the near-wall cooling channel 16 in either axial or radial directions, both directions or mixed directions. The standoff ribs 20 including the serpentine shaped ribs 20 and standoff ribs 20 forming the chordwise extending rows 74 may be configured to form the near-wall cooling channels 16 in any desired configuration for cooling fluid flow, such as, but not limited to, air, within the channels 16 for efficient cooling of the turbine airfoil 10. The standoff ribs 20, as shown in Figure 15 may include one or more orifices 76 to permit crossflow of cooling fluid within the near-wall cooling channel 16 to enhance heat transfer. Additional heat transfer features such as, but not limited to turbulators may be applied to the standoff ribs 20 to further optimize cooling fluid flow.

The generally elongated airfoil 30, as shown in Figures 13-15, may include a tip 104 formed from the outer wall 32. One or more standoff supports 20 may extend radially inward from the outer wall 32 and be separated from the pressure side 38, the suction side 40, or both, to form near-wall cooling channels 16. As shown in Figure 15, the bladder 14 may extend radially outward and partially into the near-wall cooling channels 16. Figures 13-15 shows a plurality of standoff supports 20 extending radially inward from the outer wall 32 forming the tip 104. Near-wall cooling channels 16 at the tip 104 of the airfoil 30 may extend between the pressure and suction sides 38, 40, and each of the near-wall cooling channels 16 may be coupled together with chordwise extending near-wall cooling channels 16, as shown in Figures 14 and 15. Using the configuration shown in Figure 13, the bladder 14 in the first insertable position 22, as shown in Figure 4, may be inserted into position through the root 28 of the airfoil 10 and later attached to the standoff supports 20 extending radially inward from the outer wall 32 forming the tip 104 once the bladder 14 has been expanded to the second expanded position 24. In at least some embodiments, insertion of the bladder 14 through the root section of the airfoil 10 may require opening up of the primary inlet channel in the root section. To do so would necessitate the brazing or diffusion bonding of a seal plate/insert to meter or reduce the primary inlets for functionality.

The turbine airfoil 10 may be configured to be super plastically deformed to form patterns of near-wall cooling channels 16 without damaging or distorting the airfoil 30. The standoff ribs 20 may be positioned to control bladder expansion. The bladder 14 in the first insertable position 22, as shown in Figure 2 and 4, may be inserted into position through the root 28 or tip 104 of the airfoil 10. An inner manifold 106 may be positioned at the point of insertion through the root 28 or tip 104 of the airfoil 10. The inner manifold 106 permits cooling fluid to flow to the near- wall cooling channels 16.

The turbine airfoil may be formed via a method 80, as shown in Figure 19, of positioning at 82 a generally elongated hollow airfoil 30 formed from an outer wall 32, and having a leading edge 34, a trailing edge 36, a pressure side 38, a suction side 40, and a cooling system 12 positioned within interior aspects of the generally elongated hollow airfoil 30 and formed by one or more cavities 18. The method 80 may also include inserting at 84 one or more bladders 14 within the cavity 18 of the cooling system 12, wherein the bladder 14 forms one or more near-wall cooling channels 16 between an outer surface 42 of the bladder 14 and an inner surface 44 forming the cavity 18 of the cooling system 12. The method 80 may also include expanding at 86 the bladder 14 from a first insertable position 22 to a second expanded position 24 within the cavity 18 in the cooling system 12. The second expanded position 24 of the bladder 14 may have a larger volume than a volume of the bladder 14 in the first insertable position 22. The bladder 14 may expand from the first insertable position 22 to the second expanded position 24 by undergoing significant deformation such that the material forming the bladder 14 may be plastically deformed without fracture.

In at least one embodiment, expanding at 86 the bladder 14 from a first insertable position 22 to a second expanded position 24 within the cavity 18 in the cooling system 12 may cause the bladder 14 to become locked in place within the cavity 18 in the cooling system 12. When the bladder 14 is locked in place, movement of the bladder 14 is substantially limited. The method 80 may also include pretreating at 88 an outer surface 42 of the bladder 14 with a metal braze so that the bladder 14 may be joined to metal contacting the bladder 14 after the bladder 14 has been expanded. The metal that the bladder 14 contacts may be the inner surface 44 forming the cavity 18. In at least one embodiment, the inner surface 44 may be an inner surface 44 of the outer wall 32 forming the generally elongated hollow airfoil 30. In other embodiments, the inner surface 44 of the cavity 18 may be an inner surface 44 of internal ribs or other components of the airfoil 30, such as, but not limited to, the platform 48, as shown in Figure 6. The method 80 may include in pretreating at 88 at an outer surface 42 of the bladder 14, pretreating the outer surface 42 of the bladder with a foil that may chemically bond the bladder wall 14 to rib surfaces to ensure a seamless and continuous joint, which may be used to facilitate effective heat transfer.

Expanding at 86 the bladder 14 from a first insertable position 22 to a second expanded position 24 within the cavity 18 in the cooling system 12 comprises applying pressure within the bladder 14 to expand the bladder 14 from the first insertable position 22 to the second expanded position 24. The process of applying pressure within the bladder 14 to expand the bladder 14 may occur from an explosion, blow forming or any other appropriate method. Use of an explosive to create an explosion within the bladder 14 will instantaneously form the bladder to the standoff ribs 20. The process of applying pressure within the bladder 14 to expand the bladder 14 may include super plastically forming the bladder 14 to contact the support ribs 20. Such a process may require coupling of the bladder 12 to a pressure system (not shown) for pressurization, which may require custom

expendable interconnects for coupling the bladder to the pressure system. The expendable interconnects may be truncated, and the bladder 14 sealed after the bladder 14 has been expanded to prevent cooling fluids within the cooling system 12 from flowing into the internal chamber 26 formed within the bladder 14. Expanding at 86 the bladder 14 from a first insertable position 22 to a second expanded position 24 within the cavity 18 in the cooling system 12 may include evacuating the near-wall cooling channel 16 between the outer surface 42 of the bladder 14 and the inner surface 44 forming the cavity 1 8 of the cooling system 10 to expand the bladder 14 from the first insertable position 22 to the second expanded position 24. Expanding at 86 the bladder 14 from a first insertable position 22 to a second expanded position 24 within the cavity 18 in the cooling system 10 may include heating 90 the bladder 14 to expand the bladder 14 and to deform the bladder 14 partially about one or more standoff ribs 20 extending from the inner surface 44 forming the cavity 18 to lock, mechanically lock or chemically lock, or both, the bladder 14 within the cavity 18 forming the cooling system 12. The method 80 may also include forming at 92 the bladder 14 via edge bonded sheets, such as via diffusion bonding, are preformed into open bladders capable of further expansion through super plastic forming (SPF). The bladder 14 may be formed from any material having a large deformation range such that the material can be plastically deformed without fracture. The engineered features of the airfoil 30, such as, but not limited to, the outer wall 32 forming the airfoil 30, may be configured to support the airfoil 30, thereby enabling the bladder 14 to be formed from weaker materials and in thinner wall configurations. The bladder 14 typically will not experience high surface temperatures due to the bladder 14 being relatively isolated from the outer wall 32 forming the airfoil 30. As such, lower temperature capable materials may be used. In at least one embodiment, the bladder 14 may be formed from materials such as, but not limited to, materials used in high temperature sheet forming industries, including, but not limited to, nickel chromium based superalloys, such as, but not limited to, INCONEL 718 and titanium based alloys, such as, but not limited to, Ti 6A14V.

The generally elongated hollow airfoil 30 may be formed from an appropriate method of construction or from any appropriate material. In at least one

embodiment, the generally elongated hollow airfoil 30 may be formed via casting process with enhanced surface features, such as, but not limited to, standoff ribs 20 including geometric pedestals and the like, on the inner surface of the outer wall 32 forming the generally elongated hollow airfoil 30. The generally elongated hollow airfoil 30 may be formed with open near-wall cooling channels 16. The height , width, geometry and location of the standoff ribs 20 may be customized for desired applications. The protection members 96 may add more control of the super plastically forming bladder during the manufacturing process. The standoff ribs 20 may be positioned anywhere on the inner surface 44. The serpentine shaped ribs 20 shown in Figures 10 and 12 and the standoff ribs 20 forming the chordwise extending rows 74 shown in Figure 1 1 may be manufactured using flexible mold tooling. The serpentine shaped ribs 20 shown in Figures 10 and 12 and the standoff ribs 20 forming the chordwise extending rows 74 shown in Figure 1 1 allow for the development of a complex series of nonsliding, nonconformal interlocks configured to effectively secure the bladder 14 in place within the cavity 18 of the cooling system 12.

The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.

Claims

CLAIMS We claim:

1 . A turbine airfoil (10), characterized in that:

a generally elongated hollow airfoil (30) formed from an outer wall (32), and having a leading edge (34), a trailing edge (36), a pressure side (38), a suction side (40), and a cooling system (12) positioned within interior aspects of the generally elongated hollow airfoil (30) and formed by at least one cavity (18);

at least one bladder (14) positioned within the at least one cavity (18) of the cooling system (12), wherein the at least one bladder (14) forms at least one near- wall cooling channel (16) between an outer surface (42) of the at least one bladder (14) and an inner surface (44) forming the at least one cavity (18) of the cooling system (12);

wherein the at least one bladder (14) is formed from a continuous, nonlinear wall.

2. The turbine airfoil (10) of claim 1 , characterized in that the at least one bladder (14) defines an internal chamber that is a dead space.

3. The turbine airfoil (10) of claim 1 , further characterized in that at least one standoff rib (56) extending from the inner surface (44) forming the at least one cavity (18) of the cooling system (12) and into contact with the at least one bladder (14).

4. The turbine airfoil (10) of claim 3, characterized in that a first section (60) of the at least one bladder (14) laterally adjacent to a portion of the at least one bladder (14) in contact with a tip (58) of the at least one standoff rib (56) is positioned closer to the inner surface (44) forming the at least one cavity (18) of the cooling system (12) than the tip (58) of the at least one standoff rib (56).

5. The turbine airfoil (10) of claim 3, further characterized in that a second section of the at least one bladder (14) on an opposite side of the at least one standoff rib (56) from the first section (60), wherein the second section (62) of the at least one bladder (14) laterally adjacent to a portion of the at least one bladder (14) in contact with a tip (58) of the at least one standoff rib (56) is positioned closer to the inner surface (44) forming the at least one cavity (18) of the cooling system (12) than the tip (58) of the at least one standoff rib (56).

6. The turbine airfoil (10) of claim 3, characterized in that the at least one standoff rib (56) comprises a plurality of standoff ribs (56) extending from the inner surface (44) forming the at least one cavity (18) of the cooling system (12) and into contact with the at least one bladder (14).

7. The turbine airfoil (10) of claim 6, characterized in that the at least one bladder (14) between two adjacent standoff ribs (56) is curved from a tip (58) of a first standoff rib (66) toward the inner surface (44) forming the at least one cavity (18) of the cooling system (12) to an outermost point and is curved away from the inner surface (44) forming the at least one cavity (18) of the cooling system (12) and from the outermost point to a tip (58) of a second standoff rib (70).

8. The turbine airfoil (10) of claim 7, characterized in that the at least one bladder (14) extending between each of the plurality of standoff ribs (56) is curved from a tip (58) of a first standoff rib (66) toward the inner surface (44) forming the at least one cavity (18) of the cooling system (12) to an outermost point and is curved away from the inner surface (44) forming the at least one cavity (18) of the cooling system (12) and from the outermost point to a tip (58) of a second standoff rib (70).

9. The turbine airfoil (1 0) of claim 6, characterized in that the plurality of standoff ribs (56) are a plurality of serpentine shaped ribs (56) extending spanwise and offset chordwise from each other.

10. The turbine airfoil (10) of claim 6, characterized in that the plurality of standoff ribs (56) are positioned nonparallel and nonorthogonal with a spanwise extending direction (72) and are formed into chordwise extending rows (74).

1 1 . The turbine airfoil (10) of claim 1 , characterized in that the at least one bladder (14) is formed from a material that is different from a material forming the outer wall (32) of the generally elongated hollow airfoil (30).

12. The turbine airfoil (10) of claim 1 1 , characterized in that the at least one bladder (14) is formed from a material having greater plasticity than the material forming the outer wall (32) of the generally elongated hollow airfoil (30).

13. The turbine airfoil (10) of claim 1 , characterized in that the at least one bladder (14) may be formed from a first section (60) having a first thickness and a second section (62) having a second thickness that is greater the first section (60).

14. The turbine airfoil (10) of claim 1 , characterized in that the at least one bladder (14) may be formed from a first section (60) and a second section (62), whereby the first section (60) is formed from a material having a tapered thickness.