Patent Publication Number: US-2023160310-A1

Title: Inner shroud damper for vibration reduction

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent arises from U.S. Non-Provisional patent application Ser. No. 17/143,851, which was filed on Jan. 7, 2021. U.S. Non-Provisional patent application Ser. No. 17/143,851 is hereby incorporated herein by reference in its entirety. Priority to U.S. Non-Provisional patent application Ser. No. 17/143,851 is hereby claimed. 
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to gas turbines, and, more particularly, to an inner shroud damper for vibration reduction. 
     BACKGROUND 
     A gas turbine engine generally includes, in serial flow order, an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air enters the inlet section and flows to the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section, thereby creating combustion gases. The combustion gases flow from the combustion section through a hot gas path defined within the turbine section and then exit the turbine section via the exhaust section. 
     BRIEF SUMMARY 
     Methods, apparatus, systems, and articles of manufacture to reduce turbine engine vibration are disclosed. 
     Certain examples provide an apparatus including at least one arm including a joint to couple to an inner shroud, the at least one arm having a first side and a second side, and at least one mass damper coupled to the at least one arm. 
     Certain examples provide a gas turbine engine including an inner shroud, a seal box coupled to the inner shroud, and an inner shroud damper including at least one arm disposed inside the seal box, the at least one arm including a joint to couple to the inner shroud and at least one mass damper coupled to the at least one arm. 
     Certain examples provide an apparatus including means for coupling at least one arm to an inner shroud and means for damping engine vibration, the means for damping coupled to the at least one arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example gas turbine engine. 
         FIG.  2    illustrates an example cross-sectional side view of the high pressure compressor of the turbofan shown in  FIG.  1   . 
         FIG.  3    illustrates an example cross-sectional view of a first example inner shroud damper. 
         FIGS.  4 A and  4 B  illustrate an example perspective view of the first example inner shroud damper of  FIG.  3   . 
         FIG.  5 A  illustrates an example cross-sectional view of a second example inner shroud damper. 
         FIG.  5 B  illustrates an example perspective view of the second example inner shroud damper of  FIG.  5 A . 
     
    
    
     The figures are not to scale. Instead, the thickness of the layers or regions may be enlarged in the drawings. Although the figures show layers and regions with clean lines and boundaries, some or all of these lines and/or boundaries may be idealized. In reality, the boundaries and/or lines may be unobservable, blended, and/or irregular. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, region, or plate) is in any way on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. As used herein, connection references (e.g., attached, coupled, connected, and joined) may include intermediate members between the elements referenced by the connection reference and/or relative movement between those elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and/or in fixed relation to each other. As used herein, stating that any part is in “contact” with another part is defined to mean that there is no intermediate part between the two parts. 
     DETAILED DESCRIPTION 
     Engine and component vibration occurs during normal engine operation. For example, forces acting on one or more airfoils (e.g., vanes, blades, etc.) during operation of the engine can cause the one or more airfoils to vibrate an undesirable amount, introducing stress, and eventual wear, on the one or more airfoils. Component vibration mode responses to the engine vibration or other sources include airfoil mode response (e.g., one airfoil is vibrating), soldier mode response (e.g., one or more airfoils attached to the shroud are vibrating together), etc. The vibration mode responses cause eventual wear on the airfoils (e.g., trunnion cracking, trunnion locking, etc.). There is a continuing need to reduce the vibration response of the component. Certain examples provide an inner shroud damper that absorbs relatively high energy and acts anti-mode for certain vibration frequencies, improving durability of the one or more airfoils and associated engines. 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific examples that may be practiced. These examples are described in sufficient detail to enable one skilled in the art to practice the subject matter, and it is to be understood that other examples may be utilized. The following detailed description is therefore, provided to describe an example implementation and not to be taken limiting on the scope of the subject matter described in this disclosure. Certain features from different aspects of the following description may be combined to form yet new aspects of the subject matter discussed below. 
     Descriptors “first,” “second,” “third,” etc. are used herein when identifying multiple elements or components which may be referred to separately. Unless otherwise specified or understood based on their context of use, such descriptors are not intended to impute any meaning of priority, physical order or arrangement in a list, or ordering in time but are merely used as labels for referring to multiple elements or components separately for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for ease of referencing multiple elements or components. 
     The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. As used herein, “vertical” refers to the direction perpendicular to the ground. As used herein, “horizontal” refers to the direction parallel to the centerline of the gas turbine engine  100 . As used herein, “lateral” refers to the direction perpendicular to the axial vertical directions (e.g., into and out of the plane of  FIGS.  1 ,  2   , etc.). 
     Various terms are used herein to describe the orientation of features. As used herein, the orientation of features, forces and moments are described with reference to the axial direction, radial direction, and circumferential direction of the vehicle associated with the features, forces and moments. In general, the attached figures are annotated with a set of axes including the axial axis A, the radial axis R, and the circumferential axis C. 
     “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc. may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, and (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” entity, as used herein, refers to one or more of that entity. The terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., a single unit or processor. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
     Gas turbine engines include rows of vanes, rows of rotor blades, etc. In some examples, the vanes of gas turbine engines are variable stator vanes (“VSV”) which allow individual stator vanes to rotate about their respective axes (e.g., the radial axis). In some prior designs, VSV and shroud assemblies include one 360 degree segment, two 180 degree segments, or other number of segments, which form a single row of stators associated with a particular stage of the compressor. While examples disclosed herein are described with reference to stators in the compressor, the examples disclosed herein can be applied to stators in any section of the gas turbine engine. 
     In some examples, the rotation of the VSVs is controlled by trunnions disposed within the shroud and/or a seal box beneath the shroud and VSV. As used herein, a “trunnion” is a part and/or feature that permits a rotation of a part and/or feature support thereon and/or thereby. In some prior techniques, testing has shown that the trunnions can have unfavorable cracking and fatigue depending on the vibration response mode (e.g., a soldier mode response, etc.). The vibration response during engine operation is based at least in part on conflicting design parameters of the VSVs (e.g., stiffness, durability, etc.) in view of the shroud end mass. Such responses can cause the trunnions to lock (e.g., stop rotating) within the seal box, which decreases engine performance and fatigues the VSV. For example, during particular vibration responses, the cylindrical shape of the trunnion may deform in a manner that causes three points of the trunnion to contact the shroud, which prevents the trunnion from rotating, thereby locking the VSV. Additionally, trunnion locking can cause fatigue and cracking in the cylindrical trunnion. 
     Examples disclosed herein can reduce undesired effects caused by these distortions in the engine based on a reduction of engine vibration. By coupling an inner mass damper to the inner shroud of the gas turbine engine, for example, the vibration response is mitigated. The inner mass damper can include one or more arms, one or more mass dampers, etc. 
     Reference now will be made in detail to examples of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one example can be used with another example to yield a still further example. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG.  1    is a schematic cross-sectional view of a prior art turbofan-type gas turbine engine  100  (“turbofan  100 ”). As shown in  FIG.  1   , the turbofan  100  defines a longitudinal or axial centerline axis  102  extending therethrough for reference. In general, the turbofan  100  may include a core turbine or gas turbine engine  104  disposed downstream from a fan section  106 . 
     The core turbine  104  generally includes a substantially tubular outer casing  108  that defines an annular inlet  110 . The outer casing  108  can be formed from a single casing or multiple casings. The outer casing  108  encloses, in serial flow relationship, a compressor section having a booster or low pressure compressor  112  (“LP compressor  112 ”) and a high pressure compressor  114  (“HP compressor  114 ”), a combustion section  116 , a turbine section having a high pressure turbine  118  (“HP turbine  118 ”) and a low pressure turbine  120  (“LP turbine  120 ”), and an exhaust section  122 . A high pressure shaft or spool  124  (“HP shaft  124 ”) drivingly couples the HP turbine  118  and the HP compressor  114 . A low pressure shaft or spool  126  (“LP shaft  126 ”) drivingly couples the LP turbine  120  and the LP compressor  112 . The LP shaft  126  may also couple to a fan spool or shaft  128  of the fan section  106 . In some examples, the LP shaft  126  may couple directly to the fan shaft  128  (i.e., a direct-drive configuration). In alternative configurations, the LP shaft  126  may couple to the fan shaft  128  via a reduction gear  130  (e.g., an indirect-drive or geared-drive configuration). 
     As shown in  FIG.  1   , the fan section  106  includes a plurality of fan blades  132  coupled to and extending radially outwardly from the fan shaft  128 . An annular fan casing or nacelle  134  circumferentially encloses the fan section  106  and/or at least a portion of the core turbine  104 . The nacelle  134  is supported relative to the core turbine  104  by a plurality of circumferentially-spaced apart outlet guide vanes  136 . Furthermore, a downstream section  138  of the nacelle  134  can enclose an outer portion of the core turbine  104  to define a bypass airflow passage  140  therebetween. 
     As illustrated in  FIG.  1   , air  142  enters an inlet portion  144  of the turbofan  100  during operation thereof. A first portion  146  of the air  142  flows into the bypass flow passage  140 , while a second portion  148  of the air  142  flows into the inlet  110  of the LP compressor  112 . One or more sequential stages of LP compressor stator vanes  150  and LP compressor rotor blades  152  coupled to the LP shaft  126  progressively compress the second portion  148  of the air  142  flowing through the LP compressor  112  en route to the HP compressor  114 . Next, one or more sequential stages of HP compressor stator vanes  154  and HP compressor rotor blades  156  coupled to the HP shaft  124  further compress the second portion  148  of the air  142  flowing through the HP compressor  114 . This provides compressed air  158  to the combustion section  116  where it mixes with fuel and burns to provide combustion gases  160 . 
     The combustion gases  160  flow through the HP turbine  118  in which one or more sequential stages of HP turbine stator vanes  162  and HP turbine rotor blades  164  coupled to the HP shaft  124  extract a first portion of kinetic and/or thermal energy from the combustion gases  160 . This energy extraction supports operation of the HP compressor  114 . The combustion gases  160  then flow through the LP turbine  120  where one or more sequential stages of LP turbine stator vanes  166  and LP turbine rotor blades  168  coupled to the LP shaft  126  extract a second portion of thermal and/or kinetic energy therefrom. This energy extraction causes the LP shaft  126  to rotate, thereby supporting operation of the LP compressor  112  and/or rotation of the fan shaft  128 . The combustion gases  160  then exit the core turbine  104  through the exhaust section  122  thereof. 
     Along with the turbofan  100 , the core turbine  104  serves a similar purpose and sees a similar environment in land-based gas turbines, turbojet engines in which the ratio of the first portion  146  of the air  142  to the second portion  148  of the air  142  is less than that of a turbofan, and unducted fan engines in which the fan section  106  is devoid of the nacelle  134 . In each of the turbofan, turbojet, and unducted engines, a speed reduction device (e.g., the reduction gearbox  130 ) may be included between any shafts and spools. For example, the reduction gearbox  130  may be disposed between the LP shaft  126  and the fan shaft  128  of the fan section  106 . 
       FIG.  2    illustrates an example cross-sectional side view of the HP compressor  114  of the turbofan  100  shown in  FIG.  1   . The HP compressor  114  includes one or more sequential stages. The illustrated example of  FIG.  2    includes a first stage  206 , a second stage  208  positioned axially downstream from the first stage  206 , a third stage  210  positioned axially downstream from the second stage  208 , and a fourth stage  212  positioned axially downstream from the third stage  210 . Although, the HP compressor  114  can include more or less stages as is necessary or desired. 
     Each of the stages  206 ,  208 ,  210 ,  212  include a row  214  of the stator vanes  202  and a row  216  of the rotor blades  204 . The stator vanes  202  in the row  214  are circumferentially spaced apart. In examples disclosed herein, the stator vanes  202  are variable stator vanes (“VSVs  202 ”), which can be coupled to one or more synchronization rings or brackets, for example. The synchronization rings or brackets are coupled to an actuator to at least partially rotate the VSVs  202  about the radial axis. For example, the VSVs  202  are coupled to a VSV lever arm  230 . In examples disclosed herein, the VSVs  202  can rotate about an axis in the radial direction R to mitigate compressor stall or surge. Each of the VSVs  202  includes a trunnion  227  to couple with a corresponding inner shroud  226 . In the illustrated example of  FIG.  2   , the trunnion  227  is disposed radially inward from the engine case  232 . In the illustrated example of  FIG.  2   , the inner shroud  226  is coupled to a seal box  228 . 
     Similarly, the rotor blades  204  in the row  216  are also circumferentially spaced apart. In the example shown in  FIG.  2   , the row  216  of rotor blades  204  is positioned axially downstream from the row  214  of stator vanes  202 . Each of the rotor blades  204  includes a connection portion  234  (not labeled with respect to the rotor blades  204  of the stages  208 ,  210 ,  212 ) extending radially inward from the engine case  232  for coupling with a corresponding rotor disc  218 . The connection portion can include an axial dovetail, a circumferential dovetail, a fir tree, or other connection portion shape. 
     The rows  214  of the stator vanes  202  and the rows  216  of the rotor blades  204  of each of the stages  206 ,  208 ,  210 ,  212  collectively define a compressed gas path  222  through which the second portion  148  of the air  142  flows. In particular, the stator vanes  202  direct the second portion  222  of the air  142  onto the rotor blades  204 , which impart kinetic energy into the second portion  148  of the air  142 . In this respect, the rotor blades  204  convert the second portion  148  of the air  142  flowing through the HP compressor  114  into the compressed air  158 . Outlet guide vanes, if included, direct the flow of compressed air  158  into the combustion section  116 . 
     A coupling, such as a labyrinth seal  224 , is positioned between each adjacent pair of rotor discs  218 . In the example shown in  FIG.  2   , for example, a first labyrinth seal  224  is positioned between the rotor discs  218  of the first and the second stages  206 ,  208 . A second labyrinth seal  224  is positioned between the rotor discs  218  of the second and the third stages  208 ,  210 . A third labyrinth seal  224  is positioned between the rotor discs  218  of the third and the fourth stages  210 ,  212 . A fourth labyrinth seal  224  is positioned axially downstream of the rotor discs  218  of the fourth stage  212 . The labyrinth seals  224  prevent interstage leakage of the second portion  148  of the air  142  across the compressor stages  206 ,  208 ,  210 ,  212 . Furthermore, the labyrinth seals  224  permit relative rotation between each of the rows  214  of stator vanes  202  and the adjacent rotor discs  218 . This allows the rotor blades  204  to rotate, while the stator vanes  202  remain stationary. In other examples, the coupling may be a brush seal (not shown) or any type of suitable seal. In this respect, all of the rotor discs  218  rotate in unison when the HP turbine  118  drives the HP shaft  124 . Furthermore, each of the labyrinth seals  224  in combination with each corresponding adjacent pair of rotor discs  218  coupled thereby define a rotor disc space  220 . 
       FIG.  3    illustrates an example cross-sectional view of an example first inner shroud damper  300 . The illustrated example of  FIG.  3    includes a perspective view of the cross-sectional side view of the HP compressor  114  shown in  FIGS.  1  and  2   . The HP compressor  114  includes a VSV  202  of the row  214  of the second stage  208 . However, the rows  214  of the stages  206 ,  210 ,  212  can additionally or alternatively be included. While only one VSV  202  is illustrated in  FIG.  3   , it is to be understood that one or more VSVs  202  can be included. The HP compressor  114  includes the inner shroud  226  and the seal box  228 , including the inner shroud damper  300 . 
     The inner shroud damper  300  includes a first carrier  302 , a second carrier  304 , and a mass damper  306 . In examples disclosed herein, the first carrier  302  and the second carrier  304  act as a carrier to the mass damper  306 . For example, the carriers  302 ,  304  act as an interface between the mass damper  306  and the inner shroud  226 . The carriers  302 ,  304  can be arms, segments, etc. However, other constructions and/or methods can be used to couple the mass damper  306  to the inner shroud  226 . The carriers  302 ,  304  are disposed inside the inner shroud  226  and the seal box  228 . In some examples, the carriers  302 ,  304  are curved beam structures such that they run through the seal housing (e.g., the seal box  228 ) of the inner shroud  226  circumferentially. However, the carriers  302 ,  304  can be other shapes that integrate with the inner shroud  226 . The carriers  302 ,  304  can be cantilever bolted arms coupled to the inner shroud  226 . The carrier, as illustrated by the carriers  302 ,  304 , can be any material suitable for the environment and compatible within the shroud and damping systems. In some examples, the carriers  302 ,  304  are steel. However, the carriers  302 ,  304  can additionally or alternatively be alloys of titanium, iron, nickel with adequate strength, fatigue, and/or other material characteristics, etc. for vibration damping. 
     The mass dampers  306  are disposed between the first carrier  302  and the second carrier  304 . In examples disclosed herein, the mass dampers  306  are bolted, brazed, and/or retained to the carriers  302 ,  304 . For example, the mass dampers  306  are integrally brazed or otherwise retained to the carriers  302 ,  304 . In some examples, the mass dampers  306  and the carriers  302 ,  304  are integrally brazed to the inner shroud  226 . In some examples, the mass dampers  306  are honeycomb structures (e.g., an array of hollow cells formed between walls). In some examples, the mass dampers  306  include one or more layers of the honeycomb structures. However, the mass dampers  306  are additionally or alternatively an inertial mass, a viscoelastic material (e.g., rubber, silicone, etc.), etc. 
     In examples disclosed herein, the mass dampers  306  provide mass damping behavior during engine operation. For example, the mass dampers  306  absorb energy (e.g., vibrational energy) during engine operation and act anti-mode to certain vibration responses. That is, the VSVs  202  vibrate at a first frequency during normal engine operation based on the design parameters of the VSVs  202  (e.g., durability, stiffness, etc.). The mass dampers  306  can be tuned (e.g., designed to have a certain durability, stiffness, weight, etc.) to vibrate at a second frequency during normal engine operation such that the second frequency interferes with the first frequency. That is, the mass dampers  306  can be tuned to act anti-mode to the vibration of the gas turbine engine  100 . For example, the gas turbine engine  100  may vibrate at a first frequency of 10 Hz. The mass dampers  306  can be tuned to vibrate at a second frequency that is non-integral to the system response, such as 13 Hz or 14 Hz. The vibration of the mass dampers  306  interferes with the vibration of the VSVs  202 , and, thus, dampens the vibration of the VSVs  202 . 
       FIG.  4 A  illustrates an example perspective view of the first inner shroud damper  300  of  FIG.  3   . The inner shroud damper  300  includes a first joint  402  and a second joint  404 . For example, the first carrier  302  is coupled to the inner shroud  226  via the first joint  402  and the second carrier  304  is coupled to the inner shroud  226  via the second joint  404 . However, other constructions and/or methods can be used to couple the inner shroud damper  300  to the inner shroud  226 . In some examples, the joints  402 ,  404  can be used to form a means for coupling at least one carrier (e.g., the first carrier  302 , the second carrier  304 ) to an inner shroud (e.g., the inner shroud  226 ). In some examples, the joints  402 ,  404  are bolts. However, the joints  402 ,  404  can be screws, pins, etc. 
     In the illustrated example of  FIG.  4 A , the inner shroud damper  300  includes three mass dampers  306 . However, the inner shroud damper  300  can include additional or fewer mass dampers  306 . For example, the inner shroud damper  300  includes a first mass damper  406 , a second mass damper  408 , and a third mass damper  410 . In the illustrated example of  FIG.  4 A , the first carrier  302  has a first side  412  and a second side  414  and the second carrier  304  has a first side  416  and a second side  418 . The mass dampers  406 ,  408 ,  410  are coupled to the second side  414  of the first carrier  302  and the first side  416  of the second carrier  304 . In some examples, the number of mass dampers  306  corresponds to the number of VSVs  202  (e.g., a one to one ratio, a two to one ratio, etc.). The mass dampers  306  (e.g., the mass dampers  406 ,  408 ,  410 ) are circumferentially spaced apart. At least the mass dampers  306  (e.g., the first mass damper  406 , the second mass damper  408 , the third mass damper  410 , etc.) can be used to implement a means for damping engine vibration. 
       FIG.  4 B  illustrates an example perspective view of the joint  404 . For example, the second carrier  304  is disposed in the seal box  228 . The joint  404  of the second carrier  304  can couple the second carrier  304  to the inner shroud  226  (not illustrated). 
       FIG.  5 A  illustrates an example cross-sectional view of a second example inner shroud damper  500 . The illustrated example of  FIG.  5 A  includes a portion of a VSV  202  and the labyrinth seal  224 . The inner shroud damper  500  includes a carrier  502 , a first mass damper  504 , and a second mass damper  506 . The carrier  502  is a curved beam structure such that the carrier  502  runs through the seal housing (e.g., the seal box  228 ) of the inner shroud  226  circumferentially. However, the carrier  502  can be other shapes that integrate with the inner shroud  226 . The carrier  502  can be a cantilever bolted arm coupled to the inner shroud  226 , for example. In the illustrated example of  FIG.  5 A , the carrier  502  is disposed between the mass dampers  504 ,  506 . The carrier, as illustrated by the carriers  302 ,  304 , can be any material suitable for the environment and compatible within the shroud and damping systems. For example, the carrier  502  is steel. However, the carrier  502  can additionally or alternatively be titanium alloys, iron or nickel alloys with adequate strength, fatigue, and/or other material characteristics, etc., for vibration damping. 
       FIG.  5 B  illustrates an example perspective view of the second example inner shroud damper  500  of  FIG.  5 A . The illustrated example of  FIG.  5 B  includes the carrier  502 , the first mass damper  504 , the second mass damper  506 , and a joint  508 . However, other constructions and/or methods can be used to couple the inner shroud damper  500  to the inner shroud  226 . The carrier  502  is coupled to the inner shroud  226  via the joint  508 . In some examples, the joint  508  is a bolt. However, the joint  508  can be a screw, a pin, etc. 
     The illustrated example of  FIG.  5 B  includes a pair of mass dampers (e.g., the first mass damper  504  and the second mass damper  506  are aligned). However, the inner shroud damper  500  can include additional or fewer mass dampers (e.g., the mass dampers  504 ,  506 ) and/or mass damper pairs. The carrier  502  has a first side  510  and a second side  512 . The first mass damper  504  is bolted, brazed, and/or retained to the first side  510  of the carrier  502 . The second mass damper  506  is bolted, brazed, and/or retained to the second side  512  of the carrier  502 . For example, the mass dampers  504 ,  506  are integrally brazed or otherwise retained to the carrier  502 . In some examples, the mass dampers  504 ,  506  and the carrier  502  are integrally brazed to the inner shroud  226 . In some examples, the mass dampers  504 ,  506  are honeycomb structures (e.g., an array of hollow cells formed between walls). However, the mass dampers  504 ,  506  can be inertial masses, a viscoelastic material (e.g., rubber, silicone, etc.), etc. In examples disclosed herein, the mass dampers  504 ,  506  provide mass damping behavior during engine operation. For example, the mass dampers  504 ,  506  absorb energy (e.g., vibrational energy) during engine operation and act anti-mode to certain vibration responses. That is, the VSVs  202  vibrate at a first frequency during normal engine operation based on the design parameters of the VSVs  202  (e.g., durability, stiffness, etc.). The mass dampers  504 ,  506  can be tuned (e.g., designed to have a certain durability, stiffness, weight, etc.) to vibrate at a second frequency during normal engine operation such that the second frequency interferes with the first frequency. 
     In examples disclosed herein, the second inner shroud damper  500  can include one or more pairs of mass dampers. In some examples, the number of mass damper pairs correspond to the number of VSVs  202  (e.g., a one to one ratio, a two to one ratio, etc.). The pairs of mass dampers are spaced circumferentially. In the illustrated example of  FIG.  5 B , the pair of mass dampers  504 ,  506  are aligned relative to each other. In some examples, the first mass damper  504  and the second mass damper  506  are not paired (e.g., the second mass damper  506  is offset with respect to the first mass damper  504 ). 
     The inner shroud damper  300  and/or the inner shroud damper  500  can prevent and/or reduce strain caused by engine vibration of the VSVs  202  during normal engine operation. The reduction/prevention of engine vibration increases the reliability of the VSVs  202  and the durability of the VSVs  202 . The improved reliability/durability of the VSVs  202  can reduce the risk of stall due to vane locking, for example. Additionally or alternatively, the inner shroud damper  300  and/or the inner shroud damper  500  reduces the weight, cost, etc., of the gas turbine engine  100 . 
     In operation, the inner shroud damper(s) (e.g., the inner shroud damper  300  and/or the inner shroud damper  500 ) coupled to the inner shroud  226  within the seal box  228  provides damping to act anti-mode to vibrations generated by the gas turbine engine  100 . That is, the examples disclosed herein increase reliability/durability of gas turbine engines by decreasing vibration of the gas turbine engines (e.g., vibration of one or more airfoils, etc.). In some examples, the inner shroud damper(s) prevent engine vibration, which reduces the distortions and/or strain caused by gas turbine operation. 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 
     Example methods, apparatus, systems, and articles of manufacture to reduce vibration are disclosed herein. 
     Further aspects of the invention are provided by the subject matter of the following clauses. Example 1 includes an inner shroud damper for a gas turbine engine, the inner shroud damper comprising at least one carrier including a joint to couple to an inner shroud, the at least one carrier having a first side and a second side, and at least one mass damper coupled to the at least one carrier. 
     Example 2 includes the inner shroud damper of any preceding clause, wherein the at least one carrier is a curved beam structure. 
     Example 3 includes the inner shroud damper of any preceding clause, wherein the at least one carrier is disposed inside a seal box, the seal box coupled to the inner shroud. 
     Example 4 includes the inner shroud damper of any preceding clause, wherein the joint is a bolt. 
     Example 5 includes the inner shroud damper of any preceding clause, wherein the at least one mass damper is tuned to act anti-mode to engine vibration based on at least one of durability, stiffness, or weight. 
     Example 6 includes the inner shroud damper of any preceding clause, wherein the at least one mass damper is a honeycomb structure. 
     Example 7 includes the inner shroud damper of any preceding clause, wherein the at least one carrier is a first carrier and the joint is a first joint, further including a second carrier including a second joint to couple to the inner shroud, the second carrier having a first side and a second side. 
     Example 8 includes the inner shroud damper of any preceding clause, wherein the at least one mass damper is coupled to the second side of the first carrier and the first side of the second carrier. 
     Example 9 includes the inner shroud damper of any preceding clause, wherein the at least one mass damper is a first mass damper, further including a second mass damper coupled to the second side of the first carrier and the first side of the second carrier, the second mass damper spaced circumferentially apart from the first mass damper. 
     Example 10 includes the inner shroud damper of any preceding clause, wherein the at least one mass damper is a first mass damper coupled to the first side of the at least one carrier, further including a second mass damper coupled to the second side of the at least one carrier. 
     Example 11 includes the inner shroud damper of any preceding clause, wherein the first mass damper and the second mass damper are aligned. 
     Example 12 includes the inner shroud damper of any preceding clause, wherein the first mass damper is offset from the second mass damper. 
     Example 13 includes a gas turbine engine comprising an inner shroud, a seal box coupled to the inner shroud, and an inner shroud damper including at least one carrier disposed inside the seal box, the at least one carrier including a joint to couple to the inner shroud and at least one mass damper coupled to the at least one carrier. 
     Example 14 includes the gas turbine engine of any preceding clause, wherein the at least one carrier is a curved beam structure. 
     Example 15 includes the gas turbine engine of any preceding clause, wherein the at least one mass damper is tuned to act anti-mode to engine vibration based on at least one of durability, stiffness, or weight. 
     Example 16 includes the gas turbine engine of any preceding clause, wherein the at least one mass damper is a honeycomb structure. 
     Example 17 includes the gas turbine engine of any preceding clause, wherein the at least one carrier is a first carrier and the joint is a first joint, further including a second carrier including a second joint to couple to the inner shroud, the second carrier having a first side and a second side. 
     Example 18 includes the gas turbine engine of any preceding clause, wherein the at least one mass damper is coupled to the second side of the first carrier and the first side of the second carrier. 
     Example 19 includes the gas turbine engine of any preceding clause, wherein the at least one mass damper is a first mass damper coupled to the first side of the at least one carrier, further including a second mass damper coupled to the second side of the at least one carrier. 
     Example 20 includes an inner shroud damper for a gas turbine engine, the inner shroud damper comprising means for coupling at least one carrier to an inner shroud, and means for damping engine vibration, the means for damping coupled to the at least one carrier. 
     The following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.