Patent Publication Number: US-10767504-B2

Title: Flexible damper for turbine blades

Description:
BACKGROUND 
     1. Field 
     The present invention relates to gas turbine engines, and more specifically to a flexible damper for a turbine blade. 
     2. Description of the Related Art 
     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. 
     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. 
     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. Hot gas path turbine blades may employ some form of damping to manage vibratory excitations during operation. The most common configuration is a straight pin with constant cross-section. 
     The damper pins need to be properly aligned and manufactured within specified tolerances in order to make eventual contact once the turbine blades are rotating at a certain speed. The turbine damper pins are used for the purpose of damping blade mechanical vibrations. The damper pins can work well when the damper pin slot machining tolerances are small for both surface finish and straightness as well as the small relative position tolerance between adjacent blades. When the surface finish is poor, or the slot is not straight, or the adjacent blade position is off, then the damping and sealing functions of the damper pin are diminished. 
     Continuous contact between the damper and slots of the blades is a serious issue for a curved root attached turbine blade. A single piece, solid curved damper has a problem that if it rotates even slightly in its groove it can only contact the blade at its ends and at a point in the middle and can have virtually no contact for most of the length of the damper. The centrifugal forces acting on the curved damper will not be distributed in a straight line, instead, will be distributed around the curvature which can cause the damper to have a tendency to tilt and thereby lose most of its contact with the blades. 
     SUMMARY 
     In one aspect of the present invention, a flexible damper for turbine blades comprises: a plurality of segments positioned together in a substantially linear pattern, each segment comprising a first side, a second side generally opposite the first side, a top side, a bottom side, a length, a width, and a thickness. 
     In another aspect of the present invention, a rotor assembly comprises: a disc comprising a plurality of elongated channels provided therein and spaced along a disc periphery and a plurality of disc posts, each positioned between each channel; a plurality of turbine blade airfoils, each comprising a trailing edge and a leading edge joined by a pressure side and a suction side to provide an outer surface extending from a platform in a radial direction to a tip, wherein each turbine blade airfoil is installed in each of the elongated channels on the disc; and a plurality of flexible dampers each comprising a plurality of segments, each segment comprising a first side, a second side generally opposite the first side, a top side, a bottom side, a length, a width, and a thickness; wherein each damper is removably placed into a slot in between each pair of blades. 
     In another aspect of the present invention, a method for attaching dampers to a rotor assembly comprises: installing a plurality of turbine blades onto a disc comprising a plurality of elongated channels provided therein and spaced along a disc periphery, wherein the plurality of turbine blades each comprises an airfoil, a trailing edge, and a leading edge joined by a pressure side and a suction side to provide an outer surface extending in a radial direction to a tip, wherein a plurality of turbine blades are installed in each of the elongated channels on the disc, removably attaching a plurality of flexible dampers, each damper comprising a plurality of segments, each segment comprising a first side, a second side, a top side, a bottom side, a length, a width, and a thickness. 
     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 
       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. 
         FIG. 1  is a top perspective view of a flexible damper in between two blades; 
         FIG. 2  is a cross-sectional view of a flexible damper in between blades in an embodiment of the invention; 
         FIG. 3  is a perspective view of a flexible damper with embedded wire of an embodiment of the invention; 
         FIG. 4  is a side view of an airfoil assembly according to an exemplary embodiment of the invention; 
         FIG. 5  is a cross-sectional view of a portion of the flexible damper and blades taken along the section line B-B in  FIG. 4 ; 
         FIG. 6  is a side view of an airfoil assembly according to an exemplary embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of a portion of the flexible damper and blades taken along the section line C-C in  FIG. 6 ; 
         FIG. 8  is a cross-sectional view of a portion of the flexible damper taken along the section line D-D in  FIG. 7 ; 
         FIG. 9  is a side view of an airfoil assembly according to an exemplary embodiment of the invention; and 
         FIG. 10  is a cross-sectional view of a portion of the flexible damper and blades taken along the section line E-E in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Broadly, an embodiment of the present invention provides a flexible damper for turbine blades includes a plurality of segments positioned together in a substantially linear pattern, each segment including a first side, a second side, a top side, a bottom side, a length, a width, and a thickness. 
     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. 
     A damper may be introduced in between blades in order to help with damping vibrations of the blades and sealing leakage flows between blades. Damping is an important benefit that a damper may provide for a turbine blade. The damping occurs when there is direct contact and relative movement between adjacent blades and the damper. An aspect of the level of damping is a contact surface. The contact surface is the area of contact between each component. Another phenomena that occurs once the blades are at a certain rotational speed, is that there is radial growth of the airfoil as well as an untwisting at operating conditions. During this process the leakage flow between adjacent blade surfaces needs to be limited. A damper, in this case, may also provide a sealing function for the blades. 
     Continuous contact between the damper and blades is a serious issue for a curved root attached turbine blade. A single piece, solid curved damper has a problem that if it rotates even slightly in its groove it can only contact the blade at its ends and at a point in the middle and can have virtually no contact for most of the length of the damper. The centrifugal forces acting on the curved damper will not be uniformly distributed in a straight line, instead, will be distributed around the curvature which can cause the damper to have a tendency to tilt and thereby lose most of its contact with the blades. 
     The traditional solid damper will not stay in contact with a curved root blade and will be ineffective. An increase in contact with all components is desirable. Embodiments of the present invention provide a segmented damper that is flexible. The flexible damper, as will be discussed in detail below, will provide improved contact between blades with increased contact along the length of the damper providing increased dampening and sealing features. 
     As is shown in  FIGS. 1 through 10 , 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  28  in a radial direction to a tip (not shown). A damper  24  may be a separate component that may be removably inserted between adjacent blades  10  in an assembled wheel (not shown), with the wheel having a plurality of removably inserted blades. The wheel may include a disc having a plurality of elongated channels spread along the disc periphery. The blades are inserted within these channels. In between the plurality of channels may be a plurality of disc posts  26 . A slot  60  may be formed by adjacent blade platforms  28  and the disc post  26  positioned between the blades  10 . 
     Each turbine blade includes the platform  28 , the airfoil, and the blade root. In certain embodiments, the blade  10  may have a curved root. In other embodiments, the blade  10  may have a conventional straight root. The airfoil extends outward in a first direction from the platform  28  forming the leading edge  12 , the trailing edge  14 , the pressure side  16 , and the suction side  18 . Each turbine blade  10  is then installed in the turbine disc, with the airfoil extending outward away from the platform  28 . The pressure side  16  spans between the leading edge  12  and the trailing edge  14  with a concave shape. The suction side  18  is opposite the pressure side  16  and spans between the leading edge  12  and the trailing edge  14  with a convex shape. 
     The damper  24  includes a plurality of segments  32 . The flexibly of the damper may be provided by the plurality of segments  32  strung together piece-wise in substantially linear segments. Each segment  32  may include a first side  46 , a second side  48 , a top side  50 , a bottom side  52 , a length  56 , a thickness  58 , and a width  54 . The plurality of segments may be placed into a slot  60  that is formed between two adjacent blade platforms  28  and a disc post  26 . In certain embodiments, each segment  32  may include an inter-segment ( 32 ) linkage mechanism  22 . The linkage mechanism  22  may be at least one embedded wire  30 , a radial pin connector  38  and a radial loose fit hole  40 , an axial pin connector  42  and an axial loose fit hole  44 , or the like. In certain embodiments, multiple parallel embedded wires  30  may be used to connect each segment  32  as is shown in  FIGS. 4 and 5 . The linkage mechanism  22  may further connect and provide sealing functions in between each segment  32  within the slot  60 . 
     Each segment may also include in certain embodiments an extended portion  34  along one side and a cutout portion  36  along the same side on an opposite end, wherein the extended portion  34  of one segment  32  overlaps the cutout portion  36  of a next connected segment  32 . 
     The plurality of segments  32  may have one of several different shapes in order to fit an application. The plurality of segments  32  may have a predominately rectangular shape, have both straight edges and curves, tubular, or the like. The size and shape of each segment  32  may be determined by mechanical and aerodynamic requirements such as the size of the slot  60 , the contact surface for damping, and the airfoil radial growth and untwist at operating conditions. The plurality of segments  32  is shown with several different shapes throughout the Figures listed. The cross-section of the damper  24  is circular in  FIG. 2 , however, the damper  24  can be any shape that may be required for the slot geometry and damping characteristics. 
     As mentioned above, the plurality of blades  10 , may be placed and installed on the wheel. The wheel may include a rotating disc. The disc may include a plurality of elongated channels provided therein and spaced along a disc periphery. Each of the blades  10  may be installed in each of the elongated channels on the disc. In between the plurality of blades  10  may define a slot  60 , having a slot length and a slot width between each blade  10 . The disc post  26  may be positioned between each blade  10 . The disc post  26  may sit underneath the platform  28  of each blade  10 . The damper  24  may be supported by the slot  60  formed by the disc post  26  and the blades  10 . The damper  24  may have a variable length  56 , a variable thickness  58 , and a variable width  54  in the slot  60  along a circumferential direction. The damper  24  may have a variable tangential camber within the slot  60 . The plurality of segments may each be of different length  56 , a different width  54  or different thickness  58  along the slot  60  depending on the shape of the blades  10 . The damper thickness  58 , damper length  56  and damper width  54  are within the slot width and slot length as defined by the space between the blades  10  and disc post  26 . 
     With each damper  24 , there may be a clearance gap  66  to prevent binding during blade movement such as untwist and radial growth. The blade  10  may be allowed to be free to untwist and grow radially without any restriction, or binding, from the damper  24 . 
     In all embodiments, blade  10  to blade  10  contact is maintained for all operating speeds. There is no need for special tools in order to properly set and assemble the plurality of dampers  24  in place for proper contact. The plurality of blades  10  may be placed in the wheel, and each damper  24  may be placed into each damper slot  60 . Once each damper  24  is placed into damper slot  60 , there is blade  10  to blade  10  contact. The blade  10  to blade  10  contact may be maintained at all operating speeds. Therefore, damping may be available at all operating speeds. This is especially true for curved root attached turbine blades. 
     Servicing of the blades  10  and damper  24  may improve with the ability to change out the removably attached segments  32 . Differently shaped segments  32  may be placed in service to update or improve performance of the turbine. A flexible damper  24  with the plurality of segments  32  can replace a standard damper in an existing design. The easy replacement of segments  32  may allow for an increase in damping and sealing of the blades  10 . Additionally, each segment  32  may have a different cross-section in order to optimize the damping along the curved path. 
     The damper  24  may slide into the slot  60  in certain embodiments. In certain embodiments, the damper  24  may be loaded in with a blade  10  and then the next blade  10  may be loaded. In certain embodiments, the damper  24  may be loaded once both adjacent blades  10  have been loaded. The damper  24  may also be loaded prior to the blades  10  being loaded. In more well defined slots  60 , there may be no need to include a linkage mechanism  22  such as wiring of the plurality of segments  32 . The slot  60  can be of any shape. The damper  24  may be of any shape to conform best with the slot shape. 
     A flexible damper  24  may have the ability to manage variation in slot machining tolerances, surface finish, and blade-to-blade positioning. The slot machining tolerances need not be small for the damper  24  to fit within the slot  60 . However, a damper  24  with a plurality of segments  32  may be able to be positioned within a slot  60  without linkage mechanisms  22  and function properly if the slot is well enough defined. The damper  24  may be improved with the linkage mechanisms  22  in place along the plurality of segments  32 . The plurality of segments  32  may be able to locally fit and adjust along the length of the slot  60  to provide the contact against the blades  10  as well as provide sealing against leakage. The segment shapes may be retrofitted into existing designs. The flexible damper  24  may increase the ability to damp and seal curved root attached turbine blades  10 . 
     The plurality of segments  32  may be capable of managing the pathway of the slot  60  and positional tolerances in a conventional straight slot as well as the curved slot required by a curved root attached blade  10 . 
     As mentioned above, the size and shape of each damper  24  may be determined by mechanical and aerodynamic requirements. The cross sectional width or diameter of the damper  24  may be sized to provide more (or less) contact surface or more (or less) weight which provides more (or less) centrifugal force/damping friction. Since the damper  24  is in a plurality of segments  32  it is possible for the damper  24  to have different cross sectional dimensions at different locations along its length so that more (or less) damping may be achieved at different locations so the damping may be tailored to meet the needs of the application. An example may be if after an engine run it is discovered that more damping is needed at the leading edge  12  but not at the trailing edge  14 . The contact surface for damping and sealing may be increased with the flexible damper  24  able to conform to the spacing of the damper slot. 
     Optimization may occur with proper testing of the turbine. A flexible damper may provide multiple methods to dampen during operation and seal between blade surfaces. There may be two or more segment  32  configurations distributed in the slot  60  in order to interfere with coupled blade-to-blade vibration. 
     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.