Turbine blade having friction and impact vibration damping elements

Abstract

To provide a vibration damping system which reduces blade vibration with a simple arrangement and does not add extra mass to a blade so that it does not add additional centrifugal force to a blade root or require a change in a blade configuration.SOLUTION: A turbine blade 114 includes an airfoil body 138 having an outer tip 148 and a platform; and a part-span shroud 150 positioned between the outer tip and the platform of the airfoil body. The part-span shroud has a first opening 160 having a first inner surface 162 therein. The airfoil body includes a second opening 164 extending radially from the first opening and having a second inner surface 166. A first elongated vibration-damping element 176 is disposed in the first opening, and a second elongated vibration-damping element 178 is disposed radially in the second opening.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure generally relates to vibration attenuation in an article. Further, the present disclosure relates to attenuation of blades used in a turbine.

Background Art

[0002] The turbine and compressor sections in an axial flow turbine system generally include a rotor assembly having a rotating disk and a plurality of rotor blades disposed around the disk. Each blade includes a base, an airfoil, and a platform located in a transition area between the base and the airfoil. The base of the blade is received in a complementary shaped recess in the disk. The platforms of the blades extend laterally outward and collectively form a flow path for fluid passing through the rotor stage. The leading edge of each blade is generally referred to as the leading edge, and the trailing edge is referred to as the trailing edge. "Forward" is defined as upstream of "rearward" in the gas flow through the system.

[0003] One concern in the operation of a turbine is that turbine blades tend to be exposed to vibratory stresses during operation. For example, fluctuations in gas temperature, pressure, and / or density can excite vibrations in the rotor assembly as a whole, particularly in the airfoils of the blades. In many installations, frequent acceleration and deceleration of the turbine subjects the blades to vibratory stresses at at least a particular primary frequency, and often to vibratory stresses at secondary or tertiary frequencies. Even under steady state operating conditions of maximum speed and maximum load, turbine blades are often excited by periodic or "pulsing" forces from the upstream flow and are thus also subject to vibratory stresses. When a blade is exposed to vibratory stresses, the amplitude of the vibration can easily increase to an extent that can change the operation.

[0004] The blade can be damped to avoid or reduce large vibration stresses. As one approach to dealing with vibrations during turbine operation, for example, the natural frequency of the blade can be changed to avoid resonance by changing the physical structure of the blade. For example, a mid-span shroud that couples adjacent blades can be used. In another example, a tip shroud can cause friction between adjacent blades to dissipate kinetic energy during operation. Structural changes or additions can change the aerodynamic performance of the blade and further cause additional problems by increasing weight and / or length.

[0005] In another example, it is known to attach a damper to the outer surface of the airfoil. Adding a damper to the outer surface is known to be disadvantageous as the damper is exposed to the harsh corrosive environment within the engine. As soon as the damper begins to corrode, its effectiveness can be impaired. In addition, corrosion can cause the damper to detach from the airfoil.

[0006] In other approaches, a mechanism that passively absorbs the kinetic energy that causes vibrations during use is used. A cavity in one example, or a baffle in another example, can be provided adjacent to the outer end of the blade to absorb pressure fluctuations during operation. In another case, a high-pressure air flow can be directed from an upstream location to the leading edge of the blade stage. SUMMARY OF THE INVENTION

[0007] A first aspect of the present disclosure provides a turbine blade comprising an airfoil body having an outer end and a platform, a first opening located between the outer end of the airfoil body and the platform and having a first inner surface, the first opening being a mid-span shroud extending through the airfoil body, a second opening within the airfoil body extending radially outward from the first opening and having a second inner surface, a first elongated vibration damping element disposed within the first opening, and a second elongated vibration damping element radially disposed within the second opening and having a free radially outer end and a radially inner end coupled to the first elongated vibration damping element.

[0008] A further aspect of the present disclosure provides an article comprising an airfoil body having an outer end and a platform, a first opening located between the outer end of the airfoil body and the platform and having a first inner surface, the first opening being a mid-span shroud extending through the airfoil body, a first elongated vibration damping element disposed within the first opening and engaging the first inner surface with friction to damp vibration, a second elongated vibration damping element radially disposed within a second opening of the airfoil body and having a radially inner end coupled to the first elongated vibration damping element and a free radially outer end for damping vibration by impacting a second inner surface of the second opening.

[0009] Another aspect of the present disclosure provides a method for damping vibration in a turbine blade, the method comprising damping vibration by friction in a mid-span shroud having a first opening located between an outer end of an airfoil body of the turbine blade and a platform and having a first inner surface and a first elongated vibration damping element disposed within the first opening and engaging the first inner surface with friction, and damping vibration by impact of a second elongated vibration damping element radially disposed within a second opening of the airfoil body and having a radially inner end coupled to the first elongated vibration damping element and a radially outer end capable of damping vibration by impacting an inner surface of the second opening.

[0010] Exemplary aspects of the present disclosure are designed to solve the problems described herein and / or other problems not discussed.

[0011] These and other features of the present disclosure will be more readily understood by considering the following detailed description of various aspects of the present disclosure in conjunction with the accompanying drawings that illustrate various embodiments of the present disclosure.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0013] Note that the drawings of the present disclosure are not necessarily to scale. The drawings are intended to illustrate only typical aspects of the present disclosure and should not, therefore, be considered as limiting the scope of the present disclosure. In the drawings, like reference numerals represent like elements among the drawings.

[0014] As a first issue, in order to clearly explain the current technology, it is considered necessary to select specific specialized terms when referring to and describing the relevant mechanical components within the turbine system. When doing so, to the extent possible, general industrial specialized terms are used and utilized in a manner that does not conflict with their generally recognized meanings. Unless otherwise stated, such specialized terms should be given a broad interpretation that does not conflict with the context of this application and the technical scope of the appended claims. A person skilled in the art will, in many cases, be able to understand that a particular component can be referred to using several different terms or partially overlapping terms. What is described herein as a single component may, in another context, include multiple components and may be referred to as consisting of multiple components. Alternatively, what is described herein as including multiple components may, elsewhere, be referred to as a single component.

[0015] In addition, several descriptive terms may be regularly used in this specification, and it is clear that it would be useful to define these terms at the beginning of this section. These terms and their definitions are as follows, unless otherwise stated. As used herein, "downstream" and "upstream" are terms indicating the direction with respect to the flow of a working fluid through a turbine system, or a coolant through, for example, an air flow through a combustor or one of the component systems of a turbine. The term "downstream" corresponds to the direction of the fluid flow, and the term "upstream" refers to the direction opposite to the flow. In a counterflow configuration, it is understood that the upstream and downstream directions may change depending on the location within the turbine system. The terms "front" and "rear" refer to directions, unless otherwise specified, with "front" referring to the front end of the turbine system and "rear" referring to the rear portion of the turbine system.

[0016] In many cases, it is necessary to describe components at various radial positions with respect to a central axis. The term "radial" refers to movement or position perpendicular to the axis. In such cases, if a first component is located closer to the axis compared to a second component, this can be described herein as the first component being "radially inward" or "closer in" to the second component. On the other hand, if a first component is located farther from the axis compared to a second component, this can be described herein as the first component being "radially outward" or "farther out" from the second component. The term "axial" refers to movement or position parallel to the axis. Finally, the term "circumferential" refers to movement or position around the axis. It will be understood that such terms can be applied in relation to the central axis of a turbine system, such as the axis of a rotor of a turbine system.

[0017] In addition, several descriptive terms may be used regularly herein as described below. The terms "first," "second," and "third" can be used interchangeably to distinguish one component from another and are not intended to indicate the location or importance of individual components.

[0018] Embodiments of the present disclosure provide an article or a turbine blade comprising a vibration damping system including friction and impact vibration damping elements. The article or turbine blade can include an airfoil body having an outer end and a platform, and a mid-span shroud disposed between the outer end of the airfoil body and the platform. The mid-span shroud has a first opening having a first inner surface therein. The airfoil body includes a second opening that extends radially from the first opening and has a second inner surface. A first elongated vibration damping element is disposed within the first opening, and a second elongated vibration damping element is disposed radially within the second opening. The second elongated vibration damping element includes a free radially outer end and a radially inner end coupled to the first elongated vibration damping element. The first elongated vibration damping element damps vibrations by friction, and the second elongated vibration damping element damps vibrations by utilizing collisions within the second opening. The vibration damping system including these vibration damping elements reduces blade vibrations with a simple configuration and does not add extra mass to the blade, thus not applying additional centrifugal force to the blade root or requiring a change in the blade configuration.

[0019] Referring to the drawings, FIG. 1 is a schematic view of an exemplary machine including a turbine to which the teachings of the present disclosure can be applied. FIG. 1 shows a turbomachine 90 in the form of a combustion turbine or gas turbine (GT) system 100 (hereinafter referred to as "GT system 100"). GT system 100 includes a compressor 102 and a combustor 104. Combustor 104 includes a combustion region 105 and a fuel nozzle section 106. Further, GT system 100 includes a turbine 108 and a common compressor / turbine shaft 110 (hereinafter referred to as "rotor 110").

[0020] In one embodiment, the GT system 100 is a 7HA.03 engine commercially available from General Electric Company of Greenville, South Carolina. The present disclosure is not limited to any particular GT system and can be implemented in connection with, for example, other HA, F, B, LM, GT, TM, and E class engine models of General Electric Company, as well as other engines including engine models of other companies. More importantly, the teachings of the present disclosure are not necessarily applicable only to the turbines of GT systems, but are applicable to substantially any type of turbine, such as steam turbines, jet engines, compressors (such as the compressor in FIG. 1), turbofans, turbochargers, and the like. Thus, the reference to the turbine 108 of the GT system 100 is for illustrative purposes only and not limiting.

[0021] FIG. 2 shows a cross-sectional view of an exemplary portion of the turbine 108. In the illustrated example, the turbine 108 includes four stages L0 - L3 that can be used in the GT system 100 of FIG. 1. The four stages are referred to as L0, L1, L2, and L3. Stage L0 is the first stage and is the (radially) smallest of the four stages. Stage L1 is the second stage and is arranged axially adjacent to the first stage L0. Stage L2 is the third stage and is arranged axially adjacent to the second stage L1. Stage L3 is the fourth and last stage and is the (radially) largest stage. It should be understood that the four stages are shown only as an example and that each turbine may have more or fewer stages than four.

[0022] A plurality of stationary vanes or nozzles 112 cooperate with a plurality of rotating turbine blades 114 (hereinafter, "blades 114") to form each stage L0 - L3 of the turbine 108 and define a portion of the working fluid path through the turbine 108. The blades 114 of each stage are coupled to the rotor 110 (FIG. 1) by respective rotor wheels 116 that couple them around the rotor 110 (FIG. 1). That is, the blades 114 are mechanically coupled to the rotor 110 in a circumferentially spaced-apart manner, for example, by the rotor wheels 116. The stationary nozzle section 115 includes a plurality of stationary blades 112 arranged circumferentially spaced around the rotor 110 (FIG. 1). Each nozzle 112 can include at least one end wall (or platform) 120, 122 connected to the airfoil 124. In the illustrated example, the nozzle 112 includes an outer radial end wall 120 and an inner radial end wall 122. The outer radial end wall 120 couples the nozzle 112 to the stationary casing 124 of the turbine 108.

[0023] Referring to FIGS. 1 and 2, during operation, air flows through compressor 102 and the pressurized air is supplied to combustor 104. Specifically, the pressurized air is supplied to fuel nozzle section 106 integrated with combustor 104. Fuel nozzle section 106 communicates with combustion region 105. Further, fuel nozzle section 106 also communicates with a fuel source (not shown in FIG. 1) and guides fuel and air to combustion region 105. Combustor 104 ignites the fuel and burns the fuel. Combustor 104 communicates with turbine 108, and in turbine 108, the thermal energy of the gas flow is converted into mechanical rotational energy by guiding the burned fuel, such as a working fluid, into the path of the working fluid to rotate blade 114. Turbine 108 is rotatably coupled to rotor 110 and drives rotor 110. Compressor 102 is rotatably coupled to rotor 110. At least one end of rotor 110 may extend axially away from compressor 102 or turbine 108 and may be attached to a load or machine (not shown), such as a generator, a load compressor, and / or another turbine, although not limited thereto.

[0024] Figures 3 and 4 respectively show a perspective view and a side view of a type of blade 114 in which an embodiment of the vibration damping system 128 of the present disclosure can be employed. Each of the plurality of blades 114 includes a root or base 130 that attaches the blade 114 to the rotor 110 (FIG. 1). The base 130 can include a dovetail 132 configured to be attached to a corresponding dovetail slot around the rotor wheel 116 (FIG. 2) of the rotor 110 (FIG. 1). The base 130 can further include a shank 134 extending between the dovetail 132 and the platform 136, and the platform 136 is disposed at the junction of the airfoil body 138 and the base 130 and defines a part of the inner boundary of the path of the working fluid through the turbine 108 (FIG. 2). It will be appreciated that the airfoil body 138 of the blade 114 is the active component of the blade 114 that captures the flow of the working fluid and causes the rotation of the rotor 110 (FIG. 1). The airfoil body 138 of the blade 114 includes a concave positive pressure side (PS) outer wall 140 and a convex negative pressure side (SS) outer wall 142 on the opposite side in the circumferential or transverse direction, and it will be understood that these outer walls extend axially between the opposite leading edge 144 and trailing edge 146 respectively. Further, the side walls 140 and 142 extend radially from the platform 136 to the outer end 148. Thus, the airfoil body 138 extends from the platform 136 to the outer end 148.

[0025] Furthermore, the blade 114 can include a mid-span shroud 150 extending from each of the outer walls 140, 142. The mid-span shroud 150 is disposed radially between the outer end 148 of the airfoil body 138 and the platform 130, that is, radially outside the platform 136. As will be appreciated, the mid-span shroud 150 can be positioned along the radial span of the blade 114 and can interact or mate with the mid-span shrouds 150 of adjacent blades, particularly to reduce the vibration of each blade 114. In one example, the mid-span shroud 150 is disposed radially outside the midpoint of the airfoil body 138 from the platform 136 such that it is located closer to the outer end 148 than to the platform 136, which is particularly advantageous for improving the damping of vibrations near the outer end 148 in longer blades. However, the mid-span shroud 150 can be disposed at any radial position between the outer end 148 and the platform 136. Although an exemplary blade 114 has been described, it will be understood that the blades can be of various structures in various types of turbines.

[0026] As described above, during operation of the turbine, the blade 114 can be excited to vibrate by several different forcing functions. For example, fluctuations in the temperature, pressure, and / or density of the working fluid can excite vibrations throughout the rotor assembly, particularly at the blade airfoil and / or outer end. Gases exiting upstream of the turbine and / or compressor section in a periodic or "pulsing" mode can also excite unwanted vibrations. Embodiments of the present disclosure are directed to reducing the vibration of large rotating turbine blades 114 without significantly changing the blade design.

[0027] FIG. 5 shows an enlarged perspective view of blade 114 including outer end 148 in the vicinity of mid-span shroud 150, and FIG. 6 shows a top cross-sectional view of blade 114 taken along line 6-6 of FIG. 5. As described above, mid-span shroud 150 is disposed between outer end 148 of airfoil body 138 and platform 136 (FIG. 3). Typically, mid-span shroud 150 is a solid material or includes small cooling passages therein. According to an embodiment of the present disclosure, mid-span shroud 150 includes a first opening 160 having a first inner surface 162. First opening 160 extends in a substantially straight manner over the entire or at least a majority of the longitudinal length of mid-span shroud 150 and extends through airfoil body 138. Further, blade 114 includes a second opening 164 within airfoil body 138 that extends radially outward from first opening 160 and has a second inner surface 166. Second opening 164 opens into first opening 160 and is aligned with first opening 160. That is, first and second openings 160, 164 intersect each other, for example, in a radially outer region 168 (FIG. 5) of first opening 160. The user can determine at which position along the length of first opening 160 the two openings meet, for example, based on a desired vibration attenuation and / or the internal structure of airfoil body 138. First and second openings 160, 164 can be formed using any currently known or later developed techniques, such as machining (drilling, etc.) or additive manufacturing.

[0028] The second opening 164 can be arranged in several ways in the airfoil body 138. In one example, as shown in FIG. 3, the airfoil body 138 can include a solid block of material, in which case the second opening 164 extends radially within the block of material. In another example shown in FIG. 6, the airfoil body 138 includes an internal rib or wall 169 that defines an elongated internal cavity 170 extending inwardly from the outer end 148 of the airfoil body 138. As is known in the art, the internal wall 169 and the elongated internal cavity 170 can take various forms to provide the desired structural integrity to the blade 114 and / or to provide the coolant as desired to keep the blade at a low temperature. In the example shown in FIG. 6, the second opening 164 extends radially within the internal wall 169. Since the internal structure of the blade 114 can be significantly different, it will be understood that the second opening 164 may extend within various alternative internal structures of the blade 114 other than the internal structure shown in the figures.

[0029] Furthermore, the vibration damping system 128 and the blade 114 can include a first elongated vibration damping element 176 disposed within the first opening 160 and a second elongated vibration damping element 178 disposed radially within the second opening 164. The first elongated vibration damping element 176 (hereinafter, the "first damping element 176") engages at least a portion of the first inner surface 162 of the first opening 160, enabling the first damping element 176 to damp vibrations by frictionally engaging the first inner surface 162 of the first opening 160. The user can define the degree of frictional engagement between the first damping element 176 and the first inner surface 162 to provide any desired amount of frictional damping.

[0030] The second elongated vibration damping element 178 (hereinafter, the "second damping element 178") is coupled to the first damping element 176, i.e., includes a radially inner end 180 (FIG. 5) located near the intersection of the openings 160, 164. Thus, the first damping element 176 and the second damping element 178 can collectively have an upside-down T-shape within the airfoil body 138. The T-shape may or may not be symmetric depending on the position of the second opening 164. The second damping element 178 can be coupled to the first damping element 176 in several ways. In one embodiment, the radially inner end 180 of the second damping element 178 is screwed into the opening 182 (FIG. 5) of the first damping element 176. In an alternative embodiment, they can be fixed to each other in any way having sufficient strength to prevent radial movement of the second damping element 178, such as press-fitting, for example.

[0031] However, the second damping element 178 is not frictionally engaged at the second opening 164. Rather, the second damping element 178 is free to move within the second opening 164 and includes a free radially outer end 184 that, in particular, impinges on the inner surface 166, i.e., vibrates within the second opening 164 without being obstructed by anything other than the second opening 164. In this regard, for example, as shown in the cross-sectional view of FIG. 7, the second opening 164 can have a dimension D1 that is larger than the corresponding outer dimension D2 of the second damping element 178. This structure allows for a limited range of movement within the second opening 164 for the second damping element 178 to damp vibrations by impinging on the second inner surface 166 of the second opening 164 and to enable fixing of the second damping element 178 to the first damping element 176. The magnitude of the allowed movement can be defined by the user to provide any desired amount of impact damping. In one example, but not limited thereto, the dimension D1 of the second opening 164 can be 1.8 centimeters (0.7 inches) and the maximum dimension D2 of the second damping element 178 can be 1.6 centimeters (0.6 inches). The spacing between the second opening 164 and the second damping element 178 need not be consistent around the element 178 and can vary depending on several factors such as the expected direction of vibration, the magnitude of the vibration, etc., although not limited thereto. In any case, the dimensions D1, D2 allow for sufficient space to enable fixing of the second damping element 178 to the first damping element 176, for example, space for rotation for screwing or space for press-fitting.

[0032] The first and second damping elements 176, 178 can be made of the same material as the airfoil body 138, such as a superalloy, or can be made of other materials. In either case, the damping elements 176, 178 are typically configured such that the additional mass is minimized. The openings 160, 164 and the damping elements 176, 178 are shown in cross-section as either circular or elliptical / oval (FIG. 7), although it is emphasized that any of the elements can have a substantially any desired cross-section, including a polygonal cross-section (such as in FIG. 8) other than the illustrated cross-section. Thus, the damping element 176 or 178 can take the form of a rod or pin of any desired cross-sectional shape. In one embodiment, the second opening 164 has a circular cross-sectional shape and the second damping element 178 has a cross-sectional shape selected from the group consisting of a circle (FIG. 6), an ellipse (FIG. 7) with different major and minor axes of length, and a polygon (FIG. 8). As described above, the second opening 164 has a sufficient width to allow the second damping element 178 to be fixed to the first damping element 176, regardless of the cross-sectional shape, for example by rotating it for screwing.

[0033] The openings 160, 164 and the damping elements 176, 178 can be customized to provide the desired damping depending on a variety of factors including, but not limited to, the magnitude and / or direction of the expected vibrations, the size of the blade, the internal structure of the blade, the presence of a tip shroud, and / or the size and / or shape of the mid-span shroud 150. The damping elements 176, 178 can be inserted into the openings 160, 164 in any manner. For example, the first damping element 176 can be forced and frictionally pushed into the first opening 160, while the second damping element 178 can be inserted into the second opening 164 through the outer end 148 and coupled to the first damping element 176, for example by rotating the element 178 to thread the end 180 onto the first damping element 176. The second damping element 178 can be inserted into the second opening 164, for example, before closing the outer end 148 with a tip plate and / or tip rails (not shown).

[0034] Furthermore, embodiments of the present disclosure provide a method of damping the vibration of the turbine blade 114, i.e., a method of using the vibration damping system 128. During operation, the turbine blade 114 operates in a normal manner within the turbine 108 (FIG. 2). However, vibration damping due to friction occurs at the mid-span shroud 150 disposed between the outer end 148 of the airfoil body 138 of the turbine blade 114 and the platform 136 by frictional engagement of the first damping element 176 in the first opening 160. As described above, the first opening 160 has a first inner surface 162 on which the first damping element 176 is disposed such that the first damping element 176 frictionally engages the first inner surface 162 of the first opening 160. Simultaneously or contemporaneously, vibration damping occurs by the collision of the second damping element 178 radially disposed in the second opening 164 of the airfoil body 138. As described above, the second damping element 178 has a radially inner end 180 coupled to the first damping element 176 and a radially outer end 184 that can damp vibration by colliding with the inner surface 166 of the second opening 164.

[0035] Although embodiments of the present disclosure have been described herein as blades that are part of a turbine, it should be noted that the teachings of the present disclosure are applicable to a variety of other uses related to articles that include airfoils.

[0036] Embodiments of the present disclosure provide a combination of two different damping mechanisms in a T-shaped pin design. The first damping element 176, which is generally horizontal, dissipates energy by friction with the inner surface 162 of the first opening 160, and the second damping element 178 extending radially dissipates energy by collision with the inner surface 166 of the second opening 164. Thus, embodiments of the present disclosure effectively reduce the flexural vibration of the blade 114 with a simple design while leaving the tensile load of the blade and the original configuration of the blade and rotor intact.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, when the terms "comprise" and / or "comprising" are used herein, they specify the presence of the features, integers, steps, operations, elements, and / or components recited therein, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. "Optional" or "optionally" means that the event or circumstance so described may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0038] When an element or layer is described as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it can be directly on, engaged to, connected to, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is described as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, intervening elements or layers need not be present. Other terms used to describe the relationship between elements should be interpreted in a like manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] As used herein throughout the specification and claims, the language representing approximation can be applied to modify any quantitative expression that can vary within a reasonable amount without causing a change in the relevant basic function. Thus, values modified by terms such as “about,” “approximately,” and “substantially” are not limited to the exact values recited. In at least some instances, the language representing approximation can correspond to the precision of the instrument for measuring the value. Here, throughout the specification and claims, the limits of a range are combinable and / or interchangeable. Unless the context or language indicates otherwise, such ranges are identified and include all sub-ranges subsumed therein. “About” applied to a particular value of a range applies to both end values and can indicate + / - 10% of the recited value, unless particularly dependent on the precision of the instrument for measuring the value.

[0040] All corresponding structures, materials, acts, and equivalents of all means-plus-function or step-plus-function components in the following claims are intended to include any structure, material, or act for performing the function in combination with other claimed components specifically recited in other claims. The description of the present disclosure has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the forms disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present disclosure. Embodiments have been chosen and described in order to best explain the principles of the disclosure and its practical application, to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

Description of Reference Numerals

[0041] 90 Turbo machine 100 Gas turbine system 102 Compressor 104 Combustor 105 Combustion region 106 Fuel nozzle section 108 Turbine 110 Rotor, Compressor / Turbine Shaft 112 Nozzle, Fixed Blade 114 Blade 115 Fixed Nozzle Section 116 Rotor Wheel 120 Radially Outer End Wall 122 Radially Inner End Wall 124 Airfoil, Fixed Casing 128 Vibration Damping System 130 Base, Platform 132 Doubletail 134 Shank 136 Platform 138 Airfoil Body 140 Outer Wall, Side Wall 142 Outer Wall - 144 Leading Edge 146 Trailing Edge 148 Outer End 150 Mid-span Shroud 160 First Opening 162 First Inner Surface 164 Second Opening 166 Second Inner Surface 168 Radially Outer Range 169 Internal Wall 170 Internal Cavity 176 First Elongated Vibration Damping Element 178 Second Elongated Vibration Damping Element 180 Radially Inner End 182 Opening 184 Radially Outer End

Claims

**Claim 1** An airfoil body (138) having an outer end (148) and a platform (136), A mid-span shroud (150) located between the outer end (148) of the airfoil body (138) and the platform (136) and having a first opening (160) with a first inner surface (162), A second opening (164) within the airfoil body (138) extending radially from the first opening (160) and having a second inner surface (166), A first elongate vibration damping element (176) disposed within the first opening (160), A second elongate vibration damping element (178) disposed radially within the second opening (164) and including a free radially outer end (184) and a radially inner end (180) coupled to the first elongate vibration damping element (176) A turbine blade (114) comprising. **Claim 2** The second opening (164) has a dimension larger than the corresponding outer dimension of the second elongate vibration damping element (178), allowing a limited range of motion within the second opening (164) for damping vibrations by collision of the second elongate vibration damping element (178) with the second inner surface (166) of the second opening (164). The turbine blade (114) according to claim 1. **Claim 3** The first elongate vibration damping element (176) engages at least a portion of the first inner surface (162) of the first opening (160), enabling the first elongate vibration damping element (176) to damp vibrations through frictional engagement with the first inner surface (162) of the first opening (160). The turbine blade (114) according to claim 2. **Claim 4** The first elongate vibration damping element (176) engages at least a portion of the first inner surface (162) of the first opening (160), enabling the first elongate vibration damping element (176) to damp vibrations through frictional engagement with the first inner surface (162) of the first opening (160). The turbine blade (114) according to claim 1. **Claim 5** The airfoil body (138) includes an inner wall (169) defining an elongated internal cavity (170) extending from the outer end (148) of the airfoil body (138), and the second opening (164) extends radially within the inner wall (169). The turbine blade (114) according to claim 1.

6. The first elongated vibration damping element (176) and the second elongated vibration damping element (178) collectively have an upside-down T-shape in the airfoil body (138). The turbine blade (114) according to claim 1.

7. The radially inner end (180) of the second elongated vibration damping element (178) is coupled by screwing to the opening (182) of the first elongated vibration damping element (176). The turbine blade (114) according to claim 1.

8. The mid-span shroud (150) is located outside the outer half of the airfoil body (138) in the radial direction from the platform (136). The turbine blade (114) according to claim 1.

9. The second opening (182) opens into the first opening (160). The turbine blade (114) according to claim 1.

10. An airfoil body (138) having an outer end (148) and a platform (136), A mid-span shroud (150) located between the outer end (148) of the airfoil body (138) and the platform (136) and having a first opening (160) with a first inner surface (162), A first elongated vibration damping element (176) disposed within the first opening (160) and engaging the first inner surface (162) with friction to damp vibrations by friction, A second elongated vibration damping element (178) disposed radially within a second opening (182) of the airfoil body (138), having a radially inner end (180) coupled to the first elongated vibration damping element (176), and a free radially outer end (184) for damping vibrations by colliding with a second inner surface (166) of the second opening (182) An article comprising.

11. The second opening (164) has a dimension larger than the corresponding outer dimension of the second elongated vibration damping element (178), and allows a limited range of motion within the second opening (164) for damping vibrations by collision of the second elongated vibration damping element (178) with the second inner surface (166) of the second opening (164), the article according to claim 10.

12. The airfoil body (138) includes an inner wall (169) defining an elongated internal cavity (170) extending from the outer end (148) of the airfoil body (138), and the second opening (182) extends radially within the inner wall (169), the article according to claim 10.

13. The first elongated vibration damping element (176) and the second elongated vibration damping element (178) collectively have an upside-down T-shape in the airfoil body (138), the article according to claim 10.

14. The radially inner end (180) of the second elongated vibration damping element (178) is coupled by screwing to the opening (182) of the first elongated vibration damping element (176), the article according to claim 10.

15. The mid-span shroud (150) is located outside the radially outer half of the airfoil body (138) from the platform (136), the article according to claim 10.

Images