BACKGROUND 1. Field

[0001] The present invention relates to gas turbine engines, and more specifically to a damping for fabricated hollow turbine blades.

2. Description of the Related Art

[0002] In an axial flow industrial gas turbine engine, hot compressed gas is produced. The hot gas flow is passed through a turbine and expands to produce mechanical work used to drive an electric generator for power production. The turbine generally includes multiple stages of stator vanes and rotor blades to convert the energy from the hot gas flow into mechanical energy that drives the rotor shaft of the engine.

[0003] A combustion system receives air from a compressor and raises it to a high energy level by mixing in fuel and burning the mixture, after which products of the combustor are expanded through the turbine. [0004] Gas turbines are becoming larger, more efficient, and more robust. Large blades and vanes are being utilized, especially in the hot section of the engine system. Turbine blades with hollow cavities operate in an environment with many sources of vibratory excitation. These vibratory sources include combustion cans, up-stream and down-stream vanes as well as low order excitations to name a few. [0005] Hot gas path turbine blades may employ some form of damping to manage vibratory excitations during operation. Damping is primarily managed by under-platform dampers. These dampers provide damping by relative movements of the adjacent blade platforms. If a vibratory mode has low relative movement at the platform, then the damper will not be effective. In addition, these under platform dampers also act as flow discouragers. SUMMARY

[0006] In one aspect of the present invention, a damping system for a fabricated hollow turbine blade comprises: a hollow turbine blade comprising: an internal frame, wherein the internal frame comprises at least a leading edge a trailing edge, at least one rib, a tip, a root, and an interior surface forming at least one cavity, wherein the internal frame is exposed in an open configuration; a wall and an opposite side wall attached to opposite sides of the internal frame; and at least one internal damper attached to the wall or the opposite side wall facing the at least one cavity within the internal frame, wherein the at least one internal damper makes contact with the wall, the opposite side wall and/or the interior surface of the internal frame.

[0007] In another aspect of the present invention, a method for attaching an internal damping system to a fabricated hollow blade comprises: fabricating a turbine blade comprising an internal frame comprising at least a leading edge a trailing edge, at least one rib, a tip, a root, and an interior surface forming at least one cavity, wherein the internal frame is exposed in an open configuration; attaching at least one internal damper to a wall or an opposite side wall; and integrally attaching the wall to the internal frame or the wall and the opposite side wall to the internal frame, wherein the at least one internal damper is positioned to make contact with the wall, the opposite side wall and/or the interior surface of the internal frame within the at least one cavity of the internal frame, wherein the attachment of the wall or the wall and the opposite side wall to the internal frame closes the open configuration.

[0008] These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention. [0010] FIG 1 is a cross- sectional view of a hollow fabricated blade in an exemplary embodiment of the present invention;

[0011] FIG 2 is a cross-sectional radial view of a hollow fabricated blade in an exemplary embodiment of the present invention taken along the section line A-A in Fig 1;

[0012] FIG 3 is a cross- sectional view of a hollow fabricated blade in an exemplary embodiment of the present invention;

[0013] FIG 4 is a radial view of a hollow fabricated blade in an exemplary embodiment of the present invention; [0014] FIG 5 is a radial view of a hollow fabricated blade in an exemplary embodiment of the present invention;

[0015] FIG 6 is a cross- sectional view of a hollow fabricated blade in an exemplary embodiment of the present invention;

[0016] FIG 7 is a cross-sectional radial view of a hollow fabricated blade in an exemplary embodiment of the present invention taken along the section line A-A in Fig

6;

[0017] FIG 8 is a cross-sectional span-wise view of a hollow fabricated blade in an exemplary embodiment of the present invention taken along the section line B-B in Fig 6;

[0018] FIG 9 is a is a cross-sectional view of a hollow fabricated blade in an exemplary embodiment of the present invention;

[0019] FIG 10 is a cross-sectional span-wise view of a hollow fabricated blade in an exemplary embodiment of the present invention taken along the section line C-C in Fig 9; [0020] FIG 11 is a is a cross-sectional view of a hollow fabricated blade in an exemplary embodiment of the present invention; and

[0021] FIG 12 is a cross-sectional span-wise view of a hollow fabricated blade in an exemplary embodiment of the present invention taken along the section line D-D in Fig 11.

DETAILED DESCRIPTION

[0022] In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

[0023] Broadly, an embodiment of the present invention provides a damping system and method for attaching the damping system for a fabricated hollow turbine blade includes an internal frame that includes at least a leading edge, a trailing edge, at least one rib, a tip, a root, and an interior surface forming at least one cavity. The internal frame is exposed in an open configuration. A wall and an opposite side wall are attached to opposite sides of the internal frame. At least one internal damper is attached to a wall or the opposite side wall facing the at least one cavity within the internal frame. The at least one internal damper makes contact with the wall, the opposite side wall and/or the interior surface of the internal frame.

[0024] A gas turbine engine may comprise a compressor section, a combustor and a turbine section. The compressor section compresses ambient air. The combustor combines the compressed air with a fuel and ignites the mixture creating combustion products comprising hot gases that form a working fluid. The working fluid travels to the turbine section. Within the turbine section are circumferential rows of vanes and blades, the blades being coupled to a rotor. Each pair of rows of vanes and blades forms a stage in the turbine section. The turbine section comprises a fixed turbine casing, which houses the vanes, blades and rotor. A blade of a gas turbine receives high temperature gases from a combustion system in order to produce mechanical work of a shaft rotation.

[0025] The turbine blades can be produced with a casting process. As a result of the traditional casting process, the internal cavities normally used for cooling the part, have limited access for inserts. Additionally, there is no access in these cavities to attach dampers to the cavity walls.

[0026] A fabricated blade process to manufacture a cooled turbine blade that includes an internal damping system is desirable. Embodiments of the present invention provide an internal damping system for fabricated hollow turbine blades. The internal damping system, as will be discussed in detail below, will provide improved contact within the blades with increased contact along the length of the damper providing increased dampening and cooling features.

[0027] As is shown in Figures 1 through 12, a turbine blade 10 may have an airfoil. The turbine blade 10 may be referred to as the airfoil, or turbine blade airfoil. The turbine blade airfoil 10 may include a trailing edge 14 and a leading edge 12 joined by a pressure side 16 and a suction side 18 to provide the outer surface 20 extending from a platform (not shown) and a root 26 of the blade 10 in a radial direction to a tip 30. The turbine blade 10 may be fabricated in a piecemeal fashion. Each embodiment may have at least one coversheet or wall 32. In certain embodiments, a fabricated turbine blade 10 may be produced by casting an internal frame 24 with the leading edge 12, trailing edge 14, ribs 22, and a root 26. The cover sheets, or walls 32, may then be attached to the internal frame 24 that includes an internal frame surface 52. A wall 32 and an opposite side wall 54 may be produced. In other embodiments, the fabricated turbine blade 10 may be produced by casting a solid blade 10. The solid blade 10 may then be machined from one side to create the internal frame 24 as well as the opposite side wall 54 creating an open side. The open side of the machined section may be closed off by an integrally attached wall 32 to create a finished blade 10. With each embodiment there is at least one cavity 34 created within the walls 32 of the blade 10. The following Figures represent multiple embodiments, however, other embodiments are envisioned as long as there is access to the internal cavity 34 at some point prior to the completion of the manufacturing of the turbine blade 10. The internal frame 24 provides an exposed open configuration prior to the addition of walls and the completion of the turbine blade 10. The at least one wall 32 may be a convex coversheet, a concave coversheet, or a convex coversheet and a concave coversheet in embodiments requiring two coversheets 32, 54. In certain embodiments, a recess cutout 38 along the internal frame 24 may allow for at least one wall 32 to be positioned and attached securely. The recess cutout 38 may provide for a smooth outer surface 20 and interior surface 52. [0028] In certain embodiments, the at least one wall 32 may be attached to a coversheet attachment location 42 located along an internal frame boundary as well as being attached to at least one internal rib 22. With any of these fabricated turbine blade 10 configurations, cavities 34 are formed creating a hollow blade geometry. The open blade frame internal frame 24 and separate wall or walls 32 allow for internal damping features that would not be possible in a conventionally cast blade.

[0029] In one embodiment as shown in Figures 1, 2, and 3, a damper system 50 may include at least one internal damper 36 that may be attached to a wall 32 and configured to contact the opposite wall 52 along a damping contact location 44. The at least one internal damper 36 may be attached at a damper attachment location 40. The cross section shape, orientation in a cavity 34, straight or curved, and length of the at least one internal damper 36 may be determined by a mode to be damped and the relative motion between the cavity walls 32 and 52. Additionally, the location of the attachment of the at least one internal damper 36 may depend on the mode to be damped and the relative motion between the cavity walls 32 and 52. An example of a location of attachment may be along the root of the blade 10. The mode shape dependent on the overall properties of the blade 10 and the movement of the blade 10. The at least one damper 36 may be attached to the wall 32 prior to attaching the wall to the internal frame 24.

[0030] The size and shape of each internal damper 36 may be determined by mechanical and aerodynamic requirements such as the size of the cavity 34, the contact surface for damping, and the airfoil radial growth and untwist at operating conditions. The cross-section of the internal damper 36 is C-shaped in Figures 4 and 5, however, the internal damper 36 can be any shape that may be required for the cavity 34 geometry and damping characteristics. [0031] The cross sectional width or diameter of the internal damper 36 may be sized to provide more (or less) contact surface or more (or less) weight which provides more (or less) centrifugal force/damping friction. In certain embodiments, the at least one internal damper 36 may be in segments as is shown in Figure 3. The at least one internal damper 36 may be positioned rotated away from a radial direction of the blade 10. In certain embodiments, the at least one internal damper 36 may have a non-linear mostly radially oriented configuration as is shown in Figure 1.

[0032] The at least one internal damper 36 may be added to the internal cavity 34 area of the blade 10 prior to the completion of the blade 10. As shown in Figures 2, 4, and 5, an embodiment may include the attachment of the at least one internal damper 36 to one of the walls 32 of the blade 10. The at least one internal damper 36 attached to one wall 32 may make contact with the opposite wall 52. In certain embodiments, such as in Figures 1, 2, and 3, the at least one internal damper 36 may be integrally attached. In order for the at least one internal damper 36 to be integrally attached, the at least one internal damper 36 in these embodiments are metallic in order to provide a way of integrally attaching such as with welding, transient liquid phase (TLP) bonding or the like.

[0033] In certain embodiments, a non-metallic internal damper 36, such as with a ceramic matrix composite (CMC) material, may be used in the damping system 50 within the cavity 34. Since the non-metallic internal damper 36 may not be attached in the same way as a metallic internal damper 36 may be, a different embodiment may be produced. In certain embodiments, the process can take advantage of blade twisting and a centrifugal load in order to maintain contact between the at least one non-metallic internal damper 36 and the cavity wall on either side of the internal frame as is shown in Figures 6-8. The twisting of the blade occurs from an axis moving from left to right in Figure 8. A radial load direction 46 is shown in Figure 8. The twisting of the blade 10 may allow for at least one internal damper 36 to maintain contact with the cavity wall 32. The non- metallic internal damper 36 may be attached to the at least one wall 32 by way of an attachment feature 48. In certain embodiments, the at least one internal damper 36 may include at least one metallic internal damper 36, at least one non-metallic internal damper 36, or at least one metallic internal damper 36 and at least one non-metallic internal damper 36.

[0034] In certain embodiments when the attachment feature 48 is used, there may include a weld or braze added after the at least one internal damper 36 may be inserted in place as is shown in Figures 9 through 12. The purpose of the attachment feature 48 in this situation is to keep the at least one internal damper 36 from sliding out of position. Figures 9 through 12 show several examples of what the attachment feature 48 may look like and function. In certain embodiments, the attachment feature 48 may include a shape that might engage with the wall 32, these shapes include a C-shape, a dovetail shape, or a similar shape that may engage with the wall 32 in order to trap and support the at least one damper 36.

[0035] Damping occurs when the at least one internal damper 36 is in contact with the opposite side wall 54 or the interior surface 52 of the internal frame 24. The shape of the at least one internal damper 36 may allow for constant contact within the internal frame 24. In embodiments where there are non-metallic internal dampers 36, contact may be maintained through the movement of the blade 10 itself with the radial load and the twisting of the blade while in motion. Damping contact locations may also include wall 32 to internal frame 24 locations such as the rib 22 as is shown in Figure 5. The damping may occur with the contact between the wall 32 and the rib 22 in this embodiment. The direct contact between the wall 32 and the rib 22 of the internal frame 24. In certain embodiments, this direct contact may be coupled with at least one internal damper 36 attached to the wall 32 providing contact against the internal frame 24 or the opposite side wall 54. In certain embodiments, an impingement internal damper 36 may also be used in the damping system 50. [0036] Another feature of the internally attached damping system 50 is the possibility of directing cooling flows 28 within the internal cavities 34 of the blade 10. As mentioned before, a blade of a gas turbine receives high temperature gases from a combustion system in order to produce mechanical work of a shaft rotation. Due to the high temperature gases, a cooling system may be provided internally to reduce the temperature levels throughout the blade. Higher temperatures may be found along the edges of the blade 10. As is demonstrated in Figure 4, the direction of the at least one internal damper 36 may allow for the directing of the air flow through the cavity 34. The direction of the air flow may be towards an edge of the blade 10 where there may be the highest temperatures. The at least one internal damper 36 may include a cooling hole pattern to help better distribute the cooling air flow 28. The at least one internal damper 36 with a cooling hole pattern may also act as an impingement guide as shown in Figure 4.

[0037] With a reduction in vibratory responses, a part may have an improved part life. The internal damping system 50 may allow for the damping of vibratory modes that under platform dampers are not able to affect such as when vibratory mode has a low relative movement at the platform. With at least one internal damper 36 attached to the internal walls of a cavity, the damping system 50 may allow for the application of damping where it may be the most effective. Integrally attached dampers 36 may also, as mentioned above, manage internal cooling flows and provide an enhanced mechanical damping.

[0038] While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.