Abstract:
A stage ( 10 ) of stationary vanes ( 12 ) of a gas turbine engine, including: a plurality of stationary vanes disposed in an annular array ( 14 ); and an energy damping system ( 30 ) having a plurality of connection assemblies ( 32 ), each joining respective adjacent stationary vanes. A spring ( 34 ) is configured to circumferentially bias respective adjacent stationary vanes, and a damper ( 36 ) is configured to oppose relative circumferential movement between the respective adjacent stationary vanes. The connection of the overall assembly disclosed herein allows for the oscillating system to decrease its amplitude over the shortest time period no matter the conditions. This reduces wear compared to underdamped arrangements that do not decrease amplitude as quickly.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an energy damping system for stationary vanes and airfoils in a gas turbine engine 
       BACKGROUND OF THE INVENTION 
       [0002]    A stage of stationary vanes in a turbine of a gas turbine engine includes an annular array of stationary vanes. During operation in the turbine, the vanes redirect a flow of combustion gases for delivery at the proper angle to a downstream row of rotating blades. A stage of stationary airfoils in a compressor includes an annular array of stationary airfoils. During operation in the compressor, the airfoils redirect a flow of compressed air. For sake of simplicity, turbine stationary vanes and compressor stationary airfoils are referred to herein as stationary vanes, or simply vanes. A singlet vane includes an inner shroud, an outer shroud, and one airfoil connecting the two, while a vane is generally considered to include an inner shroud, an outer shroud, and one airfoil connecting to an adjacent or multiple adjacent airfoils. Singlets and stationary vanes are referred to herein as vanes. Singlets/vanes may be manufactured by any means. Two or more singlets or vanes may be joined to form a stationary vane sub-assembly. 
         [0003]    The stationary vanes are located upstream and downstream of rotating components. The stationary vanes deal with a multitude of stimulation from their rotating neighbors and variations from suction and pressure surfaces of the airfoil as the flow passes over them. The outer shroud of a stationary vane assembly has a hook feature that slides into a casing groove feature. The outer shroud secures the stationary vanes to the frame casing of the gas turbine. The frame casing is a relatively more rigid body than the vane assembly. The casing can carry singular or multiple stationary vane assemblies. In addition, the outer shroud secures the stationary vanes to the frame of the gas turbine engine, and is relatively more rigid than the airfoil of the vane. At the interface between the airfoil and the outer shroud, where the airfoil meets the relatively more rigid outer shroud, known issues of friction, vibration and wear are common. 
         [0004]    The main locations of the wear is between the vane&#39;s hook to casing grooves and the mating faces of adjacent vanes. As a result, stationary vanes consistently show wear at their mechanical interfaces even though the parts are viewed as stationary components. Consequently, there remains room in the art for improvement 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The invention is explained in the following description in view of the drawings that show: 
           [0006]      FIG. 1  is a front view of an exemplary embodiment of a compressor vane stage of a gas turbine engine 
           [0007]      FIG. 2  is a cross sectional view along line A-A of an exemplary embodiment of the stationary vane of  FIG. 1   
           [0008]      FIG. 3  is a rear view of an alternate exemplary embodiment of the spring. 
           [0009]      FIG. 4  is a partial perspective view of an exemplary embodiment of the outer shrouds of  FIG. 1 . 
           [0010]      FIG. 5  is a partial perspective view of an exemplary embodiment of the outer shrouds of  FIG. 1 . 
           [0011]      FIGS. 6-7  are rear views along B-B of  FIG. 4  showing exemplary embodiments of the dampers of  FIG. 4   
           [0012]      FIGS. 8-12  are top views showing various exemplary embodiments of the dampers of  FIG. 4   
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The present inventor has recognized that wear, friction and cracks may be forming at the interfaces between the outer shrouds of the vane and the casing groove that retains the vane assembly used in a gas turbine engine. The inventor has further recognized that this is because the airfoil of the vane is relatively less rigid and relatively free to vibrate, while the outer shroud of the vane is relatively rigid and relatively less free to vibrate due to being secured to a frame of the gas turbine engine. In addition, the present inventor has recognized that wear may be forming at the interfaces between the shrouds of the vanes and adjacent vane segment mating faces for similar reasons. The energy in the vibrating vane is thus directed into the mechanical interfaces of adjacent vanes, assembly anti-rotation features, and the casing frame groove interface. The vane mating faces that interface with adjacent vanes and the outer shroud hook to the casing frame groove have various mechanical interface geometries which lead to wear, friction and cracks. In some stationary vane configurations the airfoil is welded to the outer shroud at an interface, further aggravating the potential for crack formation and propagation at the weld. Further, the inventor recognizes that this problem may be exacerbated over time as gas turbine engine demand for power requires an airfoil and count change to achieve higher pressure ratios and increased mass flow. The arrangement disclosed herein is a system that addresses dampened and simple harmonic motion of singular bodies and assemblies. 
         [0014]    Conventional practice to reduce wear, friction, and cracks has been to increase the amount of material in the shrouds and to design thicker airfoils to decrease freedom between the outer shroud and its interface with the gas turbine engine. For example, in configurations where the outer shroud resides in an annular groove, the outer shroud is made more structurally substantial, and the over-designed outer shroud is held in place tightly in the groove. The airfoils may also be thickened to handle the stresses. The airfoils, if retaining thicker overall profiles, will reduce vibratory motion, however, this will affect performance. Of note, all airfoils are designed to handle the steady and peak stresses with a safety factor. In addition, airfoils are tuned to stay away from certain driver wakes from upstream and downstream blades. However, disclosed herein is an arrangement that enables the shrouds with a certain Young&#39;s Modulus and mass to dampen out the vibrational energy coming from the airfoils. In essence, the flow energy across each airfoil causes a reaction to move outwards and onwards to the shroud hooks. The airfoil is stuck between two fixed points causing those connections points to dissipate that excess energy that the airfoil cannot. At the hooks the mechanical interfaces oscillate at certain frequencies causing friction and heat thereby creating wear. 
         [0015]    The inventor has taken an innovative approach to reduce vibration and stress and associated wear and crack formation at the interfaces by reducing the motion inside of the mechanical interface between the outer shroud and the groove in which it resides. This permits vibrations originating in the airfoil to pass through into the shrouds which, in turn, dissipate the motion to a controlled and limited freedom. The inventor further proposes an energy damping system that damps the redirected vibrational energy. Accordingly, the energy from the vibrations is permitted to travel to the shrouds, where it is harmlessly dissipated via the energy damping system. This reduces the need to increase component mass to overcome excess energy, which, in turn, enables a thinning of the airfoil, resulting in an increase in aerodynamic efficiency and longer component life span. 
         [0016]    The energy damping system proposed includes connection assemblies that secure adjacent stationary vanes together. Each stationary vane may include an inner shroud, and outer shroud, and one airfoil connecting the two, (i.e. a singlet) and there may be a connection assembly between each adjacent singlet. Alternately, the energy damping system may secure adjacent stationary vanes together, where each adjacent stationary vane is part of a different vane sub-assembly. For example, two stationary vane sub-assemblies, each having an inner shroud, and outer shroud, and two airfoils may be secured together. In this instance, where a first vane sub-assembly is adjacent a second vane sub-assembly, one of the stationary vanes in the first vane sub-assembly is secured to one of the stationary vanes in the second vane sub-assembly. For this reason, while the figures depict singlet stationary vanes, the discussion and the principles apply equally to adjacent singlet stationary vanes and to adjacent vane sub-assemblies. As such, the discussion focuses on adjacent stationary vanes, which applies whether singlets or vane sub-assemblies are being considered. The singlets/segments may be assembled, or cast, forged, or otherwise manufactured as is known in the art. When a vane is cast, deleterious effects of porosity, inclusions and micro-fissure near and surrounding weld joints may be rendered moot. When forged, deleterious effects will not appear, but grain control at adverse locations cannot be controlled allowing for higher stresses vs. cast components. 
         [0017]    These connection assemblies unite the adjacent stationary vanes to form a unified full or semi annulus of stationary vanes capable of damping vibrations introduced by one or more of the airfoils. Further, the energy damping system includes individually replaceable and/or tunable springs, dampers, and/or connectors. This permits individual selection and/adjustment of each component so that each connection assembly can be tuned to accommodate conditions local to the respective adjacent stationary vanes. Such tuning may occur initially, and may recur periodically throughout a life of the gas turbine engine to accommodate changes, such as engine wear etc. The connection assemblies may be part of a compressor or a turbine. 
         [0018]    Consequently, a final design for the stage of vane sub-assemblies will be a balance. At one end of the spectrum singlets may be used. This would permit maximum energy damping and the greatest local tuning freedom, but may cost more to implement and maintain. At the other end of the spectrum vane sub-assemblies may be used to define the array. As the number of stationary vane sub-assemblies decreases so would the energy damping and local tuning freedom, but so also may the cost to implement and maintain 
         [0019]      FIG. 1  shows a stage  10  of stationary vanes  12  arranged in an annular array  14  about a longitudinal axis  16  of a gas turbine engine (not shown). The stationary vanes  12  shown are singlets  18  secured together side-to-side to form the annular array  14 , each singlet  18  having an inner shroud  20 , an outer shroud  22 , and one airfoil  24  connecting the inner shroud  20  to the outer shroud  22 . An energy damping system  30  includes a plurality of connection assemblies  32  disposed between adjacent stationary vanes  12 . Each connection assembly  32  includes at least one spring  34 , at least one damper,  36 , and optionally an inner connecting element  38 . 
         [0020]    The springs  34  may be in compression and therefore tend to bias the stationary vanes  12  apart in a circumferential direction  40 . Alternately, the springs  34  may be in tension and bias the stationary vanes  12  together in the circumferential direction  40 . Accordingly, together the springs  34  create a load path  42  through the annular array  14 , where the load path  42  may be compressive or tensile. The annular array  14  may be composed of two or more discrete semi-annular arrays  50 , each mounted separately from the other and not connected to the other. In such an exemplary embodiment a respective load path  42  would exist within each semi-annular array  50 . 
         [0021]    In an exemplary embodiment, there may be a top semi-annular array  52  and a bottom semi-annular array  54 , each having a semi-annular shape and each comprising vane sub-assemblies (not shown) or singlets  18 . A base singlet  56  of the top semi-annular array  52  may be rigidly or loosely mounted to a mount  58  (partly shown) of the gas turbine engine at a specified angular position  60  of, for example, 270 degrees. The mount  58  may be an annular groove (not shown) configured to receive the outer shroud  22 . The outer shrouds  22  of a remainder of the singlets  18  may also be positioned in the annular groove. In an exemplary embodiment when the base singlet  56  is rigidly mounted, the remaining singlets  18  may have slightly more freedom than the base singlet  56 . In such an exemplary embodiment the outer shroud  22  of the base singlet  56  is not permitted to move axially, circumferentially, radially, or to rotate about a radial  62  of the singlet  18 , and thereby acts as a fixed anchor for a remainder of the singlets  18  in the top semi-annular array  52 , which are permitted limited movement in at least one of those directions, if not all. Alternately, the mount  58  may be mounted with limited freedom to move in at least one of those directions, in which case the remaining singlets  18  may float with the permitted movement of the base singlet  56 . Alternately, the base singlet  56  may experience periods where it is rigidly mounted and periods when limited movement is permitted due to relative thermal growth and transient engine operating conditions etc. 
         [0022]    Individual tailoring of the spring  34  and the damper  36  may result in relatively strong connection assembly  32  between the base singlet  56  and the adjacent stationary vane  12  because the base singlet  56  experiences the accumulated excess energy of all of the other stationary vanes  12  in that semi-annular array  50 . The connection assembly  32  may become relatively weaker the farther it is located from the base singlet  56 . The relatively weakest connection assembly  32  may be at the last stationary vane  12  and the adjacent stationary vane  100  (second to last), because it only needs to dissipate excess energy from the last two stationary vanes  12 . The damping ratio between adjacent stationary vanes  12  may be underdamped (ζ&lt;1) while a damping ratio of the semi-annular array  50  may be critically damped (ζ=1). The connection assembly  32  may be tuned to prevent certain high and/or low frequencies, such as those known to result from fluid flow and/or those known to result from mechanical motion such as rotating blades etc. 
         [0023]    Likewise, a base singlet  66  of the bottom semi-annular array  54  may be mounted to the mount  58  at a specified angular position  70  of, for example, 90 degrees. The base singlet  66  of the bottom semi-annular array  54  may be rigidly or loosely mounted to the mount  58  at a specified angular position  60  of, for example, 90 degrees. The outer shrouds  22  of a remainder of the singlets  18  may also be in the annular groove. In an exemplary embodiment when the base singlet  66  is rigidly mounted, the remaining singlets  18  may have slightly more freedom than the base singlet  66 . In such an exemplary embodiment the outer shroud  22  of the base singlet  66  is not permitted to move axially, circumferentially, radially, or to rotate about a radial  62  of the singlet  18 , and thereby acts as a fixed anchor for a remainder of the singlets  18  the bottom semi-annular array  54 , which are permitted limited movement in at least one of those directions. Alternately, the mount  58  may be mounted with limited freedom to move in at least one of those directions, in which case the remaining singlets  18  may float with the permitted movement of the base singlet  66 . Alternately, the base singlet  66  may experience periods where it is rigidly mounted and periods when limited movement is permitted due to relative thermal growth and transient engine operating conditions etc. As was the case for the top semi-annular array  52 , the bottom semi-annular array  54  may also be tuned. 
         [0024]    While two semi-annular arrays of singlets  18  are disclosed, any number of less-than-fully-annular arrays may be used, each having its own base singlet, (or base vane segment), to fully compose the annular array and the above principles would apply. In addition, the less-than-fully-annular arrays need not be axisymmetric. For example, there may be one or more arrays that differ in the portion of the full annulus they occupy. There may be, for example, one semi-annular array, and two quarter-annulus arrays. The number of the less-than-fully-annular arrays and arc-length of each less-than-fully-annular array may be chosen based on any number of factors, including field assembly and disassembly considerations etc. 
         [0025]      FIG. 2  shows a side view of a singlet  18  along line A-A of  FIG. 1 , showing a mateface  80  (side surface) of the stationary vane  12  that abuts an adjacent mateface (not shown) of an adjacent stationary vane. There may be one or more recesses  82  in the mateface  80 , and a spring  34  may reside in a respective recess  82 . The spring  34  may be a coil spring or a compressible and/or an expandable material or arrangement etc. capable of imparting the requisite bias. The adjacent mateface may or may not have a recess  82  to coincide with the recess  82  in which a spring  34  resides. In the case where there is a recess  82  in the mateface  80  and a corresponding recess  82  in the adjacent mateface, both ends of the spring will reside in respective recesses  82 . In the case where there is a recess  82  in one mateface  80  but not in the other, one end of the spring  34  may reside in the mateface and the other may simply rest on the adjacent mateface. There may be one spring  34  or more than one spring  34  between adjacent stationary vanes  12 . The spring  34  may be located in the inner shroud  20 , in the outer shroud  22 , or when more than one spring  34  is used they may be in either or both the inner shroud  20  and the outer shroud  22 . Any number of springs  34  may be used in any location as necessary and all may have the same spring constant or its own spring constant as necessary to tune the springs  34  for the respective adjacent stationary vanes  12 . In addition, the springs  34  may be positioned farther upstream or downstream in an axial direction  84  as necessary. 
         [0026]    Further, the location of the springs may vary from one set of adjacent stationary vanes  12  to another circumferentially. For example, if the stationary vane  12  shown in  FIG. 1  were locally subject to a force that tended to separate an aft end  86  from an adjacent aft end (not shown), the springs (in compression) could be installed more toward a fore end  88  in the local area. Similarly, if a torque about the radial  62  is imparted by the flow being redirected by the stationary vane  12 , then the springs  34  (in compression) could be angled fore-to-aft between the adjacent stationary vanes to counter the induced torque. (See  FIG. 4 .) For example, if the redirecting torque tended to rotate the aft end  86  toward the reader, one end of the spring  34  could be installed so that it contacts the stationary vane  12  more toward the aft end  86 , and the other end of the spring  34  could be installed so that it contacts the adjacent stationary vane  12  (located out of the page and closer to the reader) more toward the fore end  88  of the adjacent stationary vane. In such an arrangement the spring would couple opposing torques that would cancel the torques induced by the redirected flow. 
         [0027]    Also visible are an inner shroud connecting arrangement  90  including a fastener  92 , a securing spring  94 , and an inner connecting element  38  such as a bar that spans circumferentially from one inner shroud  20  to an adjacent inner shroud. The inner connecting element  38  may have a spring constant and the spring constant may be selected to meet damping requirements as desired. There may be one inner shroud connecting element  90  for each pair of adjacent stationary vanes  12 , meaning there may be two fasteners  92  and two securing springs  94  in each inner shroud  20 . The inner shroud connecting arrangement  90  is shown partially disposed in an inner shroud recess  98 , clear of any nearby components like a rotor shaft (not shown). The inner connecting element  38  may be relatively stiff to overcome any bias felt at the inner shrouds  20  and exerted by the springs  34 . The securing spring  94  will permit slight relative movement between the fastener  92  and the inner connecting element  38 . This permits slight movement of the inner shroud  20  while also attempting to dampen movement from an equilibrium position. Either or both of the springs  34  and the inner shroud connecting arrangement  90  may be present at the inner shroud  20 . 
         [0028]      FIG. 3  shows is a rear view of the stationary vane  12  of  FIG. 2  and an adjacent stationary vane  100 , showing an alternate exemplary embodiment of a spring  34  including a fixed fastener  102 , a spring connecting element  104  that may be relatively inflexible, and a flexible fastener  106  such as a bolt with a flexible shank  108 . The flexible fastener  106  may be pre-flexed in either direction and then tightened onto the spring connecting element  104  to provide the desired bias, and flex of the flexible shank  108  would provide the desired spring constant during operation. 
         [0029]      FIG. 4  is a partial perspective view of an exemplary embodiment of the outer shrouds  22  of the stationary vane  12  and the adjacent stationary vane  100 , with dampers connecting the two. There may be one or more dampers  36  for each set of adjacent stationary vanes  12 . They may or may not align circumferentially and they may or may not stagger their circumferential locations on an outer surface  110  of the outer shrouds  22  as shown. Each damper  36  may include a damper connecting element  112  and a damper post  114 . Between the damper post  114  and the damper connecting element  112  there may be a damping element (not visible) effective to damp vibrational motion between the stationary vane  12  and the adjacent stationary vane  100 . Also visible in  FIG. 4  are angled recesses  82  in which the springs  34  may reside and in a configuration (when in compression) effective to overcome a clockwise torque  120  (as seen from above the outer surface  110 ) induced by the combustion gases turned by the airfoil  24 . 
         [0030]      FIG. 5  is a partial perspective view of an alternate exemplary embodiment of the outer shrouds  22  of the stationary vane  12  and the adjacent stationary vane  100 , with dampers  36  connecting the two. In this alternate exemplary embodiment, instead of being secured to the outer surface  110  of the outer shroud  22 , the damper connecting elements  112  may instead be secured to pillars  122 . The pillars  122  may align circumferentially as shown, and/or there may be more than one circumferential row of pillars so that more than one damper  36  can span adjacent stationary vanes  12 , and/or there may be differing means for connecting the damper connecting element  112  to the respective pillar  122  to avoid interference with other damper connecting elements  112 . Also visible are recesses  82  and a spring  34  with both ends disposed in cooperating recesses  82  in adjacent stationary vanes  12 . 
         [0031]      FIG. 6  is a rear view along B-B of  FIG. 4  showing an exemplary embodiment of the damper  36 , the damper connecting element  112 , and the damper post  114  spanning a gap  124  between the stationary vane  12  and the adjacent stationary vane  100 . The gap  124  is defined by the mateface  80  and the adjacent mateface  126 . In the exemplary embodiment shown the damping element  130  may be positioned between the damper connecting element  112  and one or both damper posts  114 . The damper may be, for example, a viscoelastic material or any other damper known to those in the art. Likewise, the configuration shown represents only one of many possible configurations known to those of ordinary skill in the art. A damper post  114  having a damping element  130  may be adjustable to control an amount of force pressing the damper connecting element  112  and the damping element  130  together. This may be used to control an amount of damping. Alternatively, a size (e.g. thickness) of the damping element  130  may be controlled to control the amount of damping.  FIG. 7  is a rear view along B-B of  FIG. 4  showing an alternate exemplary embodiment of the damper  36 . In this configuration a turnbuckle  132  may be used to control an amount of preload between the adjacent stationary vanes  12 . 
         [0032]      FIGS. 8-12  show various exemplary embodiments of the damper  36 .  FIG. 8  shows an exemplary embodiment where the damper  36  includes two damper connecting elements  112  between the stationary vane  12  and the adjacent stationary vane  100 . Each damper connecting element  112  is secured by a set of damper posts  114 . For each set of damper posts  114  there may be one or two damped damper posts  134 , which is a damper post  114  with a damping element  130 . Such an arrangement may simply provide redundancy, or it may allow the individual components to be selected with each other in mind to perform a particular tailoring of the relationship between the stationary vane  12  and the adjacent stationary vane  100 . An offset connection  136  may be used to prevent the damper connecting elements  112  from interfering with each other. 
         [0033]      FIG. 9  shows an alternate exemplary embodiment where the damper connecting element  112  is a shock absorber  140 . In this configuration there would be no need for a separate damping element  130  between the damper post  114  and the damper connecting element  112 . In any of the exemplary embodiments shown herein, in addition or instead of being disposed in the recess  82 , the spring  34  may be disposed between the damper posts  114 , or between dedicated spring posts (not shown).  FIG. 10  shows an alternate exemplary embodiment where the damper connecting element  112  is a rigid element and where both damper posts  114  are damped damper posts  134 .  FIG. 11  shows an alternate exemplary embodiment where the damper connecting element  112  comprises a material having a desired spring constant.  FIG. 12  shows an alternate exemplary embodiment where the damper connecting element  112  comprises a composite material having a desired spring constant. 
         [0034]    Other configurations consistent with the principles disclosed herein are considered to be within the scope of this disclosure. For each connection assembly  32  there may be one or more springs located between the stationary vanes  12  and/or on the outer shroud  22 . Likewise, for each connection assembly  32  there may be one or more dampers  36 , and in some embodiments both elements may be secured between damper posts  114  and/or in the recesses  82 . For example, a damping element  130  may be disposed inside a coil spring, and the coil spring with the damping element  130  inside may be positioned in the recess  82 . Each of these components can be individually replaceable, and each may be characterized by its own parameters. This allows tailoring of the spring constants and damping ratios between respective stationary vanes  12 . Further, the springs  34  and the dampers  36  can be tuned radially and/or axially within each spring, damper, and connector assembly to accommodate radial and/or axial variations within a respective gap  124 . Consequently, each connection assembly  32  may be the same as the others in any or all of construction, material, and/or parameters, each may be completely unique, or some may be the same and some unique in the same annular array  14 . 
         [0035]    From the foregoing it can be seen that the inventor has recognized the cause of crack formation and has innovatively departed from convention when devising the solution. Once the new approach became known to the inventor the solution was made possible using readily available components, thereby reducing the cost and complexity of implementation. Consequently, this represents an improvement in the art. 
         [0036]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.