Abstract:
A strip seal arrangement for turbine components employs acoustic damping. A sealing plate having a front face adjacent a combustion chamber and a back face facing away from a combustion chamber configured to have one or more holes of a predefined cross-sectional area. Containers having predefined volumes are attached to the back face of the sealing plate such that the one or more holes are in fluidic communication with the one or more containers thereby creating at least one acoustic damper. The side edges of the sealing plate fit into a slots of burner front panels, creating a seal between the panels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT/EP2013/056229 filed Mar. 25, 2013, which claims priority to European application 12162752.5 filed Mar. 30, 2012, both of which are hereby incorporated in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of gas turbines, and more particularly to gas turbine combustors having one or more tuned damping devices included into combustor seal to suppress high frequency thermo-acoustically induced pressure oscillations. 
       BACKGROUND 
       [0003]    Gas turbine combustors can cause gas pressure (acoustic) and temperature oscillations during operation. These are especially a problem with lean premixed, low emissions combustors. 
         [0004]    These thermo-acoustic combustion oscillations are amplified when the frequency of the oscillations matches an acoustic resonant frequency or frequencies of the combustor volume. These pressure and thermal fluctuations and can cause mechanical and thermal damage to the turbine. They also may limit the usable range of the turbine. 
         [0005]    Such oscillations have been a known problem since the early days of gas turbine development. A possible method to suppress such oscillations consists in attaching damping devices having resonator cavities, or similar devices to the combustors. 
         [0006]    Space Restrictions 
         [0007]    In the past, dampers have been applied to a burner front panel. Since more damping devices increase damping efficiency, there may be several damping devices used. Also, multiple frequencies could be damped. This would also require additional damping devices. Therefore, there may be space restrictions on the front panel. 
         [0008]    Difficult to Install/Replace 
         [0009]    Also, the damping devices have also been installed on the combustor liner segments. Due to their position, these are sometimes difficult to install. Also, if the turbine is significantly modified, the acoustic frequencies produced by the turbine changes. Therefore, in cases such as these, one would like to change the frequencies dampened. Dampers installed on the burner liner and other hard to access locations, are difficult to replace to change the resonant frequencies damped. 
         [0010]    Currently, there is a need for a system for dampening acousto-thermal oscillations in gas turbine combustors that is more compact, can be easily installed or replaced, while still providing efficient performance. 
       SUMMARY 
       [0011]    The technical aim of the present invention is to provide a burner strip seal arrangement for damping desired frequencies that is compact, fits into existing spaces on a conventional burner, is easy to install and replace by which known acoustic frequencies can be damped. 
         [0012]    The design of the present invention of incorporating dampers on seals opens up wider design flexibility as the seals are usually placed at locations where enough space is available. The damping devices on seal segments can therefore increase the high frequency damping potential and increase the number of addressed frequencies. The seal strip arrangements are cheaper and easier to install and replace compared with the prior art designs that were installed on burner front panel or combustor liner segments. 
         [0013]    A strip seal arrangement designed to seal a first sealing surface to a second sealing surface is described. It includes a sealing plate with a front face facing a combustion chamber and a back face facing away from the combustion chamber. The sealing plate has one or more holes of a predefined cross-sectional area extending through a thickness of the sealing plate positioned along a length of the sealing plate. 
         [0014]    One or more containers having predefined volumes are attached to the back face of the sealing plate in fluid communication with the one or more holes to create at least one acoustic damper. The strip seal arrangement seals two components while damping specified the acoustic vibrations. 
         [0015]    The present invention may be described as a method for designing a strip seal arrangement having acoustic damping properties by providing a sealing plate having a front face adjacent a combustion chamber and a back face facing away from a combustion chamber configured to have one or more holes of a predefined cross-sectional area extending from the front face to the back face through a thickness of the sealing plate; and 
         [0016]    attaching one or more containers having predefined volumes to the back face of the sealing plate such that the one or more holes are in fluidic communication with the one or more containers thereby creating at least one acoustic damper. 
         [0017]    The present invention may also be described as a method for creating a seal between turbine components that damps desired acoustic frequencies using a strip seal arrangement, by providing a sealing plate having a front face and a back face, 
         [0018]    calculating at least one cross-sectional area and at least one container volume to create a Helmholtz damper to damp said desired acoustic frequencies, 
         [0019]    forming one or more holes of the calculated cross-sectional area through a thickness of the sealing plate extending from the front face to the back face, 
         [0020]    attaching one or more containers having the calculated volumes to the sealing plate such that holes formed through the sealing plate are fluidically coupled to the containers, and 
         [0021]    attaching the sealing plate between two turbine components thereby creating a seal between them. 
         [0022]    According to one embodiment the seals can be used for retrofit into an existing turbine component. The method to retrofitting a seal with a damping comprising the step of removing an existing seal between turbine components to provide space for attaching the seal having acoustic damping properties between two turbine components and inserting the seal having holes and attached containers thereby creating a seal between said turbine components. 
         [0023]    Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this 5 description, be within the scope of the present invention, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. The invention will now be described in more detail with reference to the appended drawings in which: 
           [0025]      FIG. 1  is a diagram illustrating the classical Helmholtz acoustic damper. 
           [0026]      FIG. 2  is a diagram illustrating a classical Helmholtz acoustic damper and an additional Helmholtz damper installed on the backside of the first one. 
           [0027]      FIG. 3  is a graph of amplitude and phase of the reflection coefficient vs. normalized frequency plotted for a Strouhal coefficient of 0.3, 0.5 and 1.0. 
           [0028]      FIG. 4  is a perspective view of a burner assembly of a turbine showing a conventional sealing strip intended to be replaced with a seal strip arrangement according to one embodiment of the present invention. 
           [0029]      FIG. 5  shows a perspective view of the seal strip arrangement having two dampers partially fitting inside of the slot of front panel. 
           [0030]      FIG. 6  is a side elevational view of the seal strip arrangement having two damping devices partially fitting within a slot of the front panel. 
           [0031]      FIG. 7  is a perspective view of the seal strip arrangement of the present invention employing six damping devices, and an enlarged partially cut-away portion of the dampers. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Theory 
         [0033]    There are several types of acoustic dampers such as quarter wave tubes, Helmholtz dampers or acoustic screens. We will focus on Helmholtz dampers. 
         [0034]    When air is forced into a cavity, the pressure inside the cavity increases. When the external force pushing the air into the cavity is removed, the higher-pressure air inside will flow out. The cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time. 
         [0035]    The air in the port (the neck of the chamber) has mass. Since it is in motion, it possesses some momentum. A longer port would make for a larger mass, and vice-versa. The cross-sectional diameter of the port is related to the mass of air and the volume of the chamber. A port that is too small in area for the chamber volume will “choke” the flow while one that is too large in area for the chamber volume tends to reduce the momentum of the air in the port. 
         [0036]    For example,  FIG. 1  shows a classical Helmholtz damper. It includes a resonator  1  having a volume V, with an acoustic neck  2  that leads to an opening  3 , usually opening to a chamber, such as a combustion chamber  7  having acoustic oscillations desired to be damped. 
         [0037]    The main parameters, like the volume V of resonator the cross-sectional area of the acoustic neck  2  (here, represented by the diameter D) and the length L of the acoustic neck  2  are highlighted. 
         [0038]    The design parameters of the Helmholtz damper are chosen in such a way, that the resonator frequency f H  of the damper corresponds to the frequency of the combustor oscillations. 
         [0039]    It can be shown that the angular frequency (corresponding to the resonant frequency (f H ) is given by: 
         [0000]    
       
         
           
             
               ω 
               H 
             
             = 
             
               
                 
                   γ 
                    
                   
                     
                       
                         A 
                         2 
                       
                        
                       
                         P 
                         0 
                       
                     
                     
                       m 
                        
                       
                           
                       
                        
                       
                         V 
                         0 
                       
                     
                   
                 
               
                
               in 
                
               
                   
               
                
               radians 
                
               
                 / 
               
                
               
                 second 
                 . 
               
             
           
         
       
     
         [0040]    where 
         [0041]    251658240γ(gamma) is the adiabatic index or ratio of specific heats. This value is usually 1.4 for air and diatomic gases. 
         [0042]    A is the cross-sectional area of the neck 
         [0043]    251658240m is the mass in the neck 
         [0044]    P 0  is the static pressure in the cavity 
         [0045]    V 0  is the static volume of the cavity 
         [0046]    For necks with a constant cross sectional area, the area is: 
         [0000]    
       
      
       A=V 
       n 
       /L  
      
     
       Where: 
       [0047]    L is the length of the neck, and V n  is the volume of the neck. 
         [0048]    Thus: 
         [0000]    
       
         
           
             
               ω 
               H 
             
             = 
             
               
                 γ 
                  
                 
                   
                     
                       AV 
                       n 
                     
                      
                     
                       P 
                       0 
                     
                   
                   
                     mLV 
                     0 
                   
                 
               
             
           
         
       
     
         [0049]    By the definition of density: 
         [0000]    
       
         
           
             
               
                 
                   V 
                   n 
                 
                 m 
               
               = 
               
                 1 
                 ρ 
               
             
             , 
           
         
       
     
         [0000]    thus: 
         [0000]    
       
         
           
             
               ω 
               H 
             
             = 
             
               
                 γ 
                  
                 
                   
                     
                       P 
                       0 
                     
                      
                     A 
                   
                   
                     ρ 
                      
                     
                         
                     
                      
                     
                       V 
                       0 
                     
                      
                     L 
                   
                 
               
             
           
         
       
       
         
           and 
         
       
       
         
           
             
               f 
               H 
             
             = 
             
               
                 ω 
                  
                 
                     
                 
                  
                 H 
               
               
                 2 
                  
                 π 
               
             
           
         
       
     
         [0050]    where: f H  is the resonant frequency (Hz). 
         [0051]    The speed of sound in a gas is given by: 
         [0000]    
       
         
           
             υ 
             = 
             
               
                 γ 
                  
                 
                   
                     P 
                     0 
                   
                   ρ 
                 
               
             
           
         
       
     
         [0052]    Thus, the frequency of resonance is: 
         [0000]    
       
         
           
             
               f 
               H 
             
             = 
             
               
                 v 
                 
                   2 
                    
                   π 
                 
               
                
               
                 
                   A 
                   
                     
                       V 
                       0 
                     
                      
                     L 
                   
                 
               
             
           
         
       
     
         [0053]    Therefore, the resonant frequency f H  can be selected by selecting the proper cross sectional area A of the acoustic neck  2 , the length L of the acoustic neck  2  and the volume V 0  of the resonator  1 . (Please note that this equation holds for the cross-sectional area of the opening being the same as the cross-sectional area of the acoustic neck. It also applies for an acoustic neck  2  of constant cross sectional area. Further adjustments must be made to these equations if the cross-sectional area of the opening  3  is a different size from that of the acoustic neck  2 , or if the acoustic neck  2  does not have a constant cross-sectional area.) 
         [0054]    Helmholtz dampers are further described in U.S. patent application Ser. No. 2011/0179796, published Jul. 28, 2011, owned by the present applicant and hereby incorporated by reference. 
         [0055]    The damping efficiency of Helmholtz damper in state of the art gas turbines is usually increased by the increase of the damping volume V (see  FIG. 1 ) and/or by increasing the number of single Helmholtz dampers in the combustor. 
         [0056]      FIG. 2  shows an arrangement by means of a serial connection of damping devices. It consists of the basic Helmholtz damper, described above, which has an additional Helmholtz damper installed on the backside of the first one. Therefore, second resonator  4  having a volume V2 has a second neck  5  with a second diameter D2 and second length L2 that leads to a second opening  6 . 
         [0057]    By selecting the proper volume V2, diameter D2 and length L2, the second damper will damp a second desired frequency. Continuing with this arrangement, several frequencies may be dampened in a controlled way, depending on the number of dampers involved, at the same location. 
         [0058]      FIG. 3  is a graph of amplitude and phase of the reflection coefficient vs. normalized frequency. The reflection coefficient is the ratio of air passing out of a resonator to the air passing into the resonator. This is plotted for a Strouhal coefficient of 0.3, 0.5 and 1.0. The Strouhal coefficient (St) is defined by (frequency * diameter of the acoustic neck/velocity of the fluid). 
         [0059]    As is indicated, when the normalized frequency is approximately=1, there is a minimum absolute value of the reflection coefficient. This indicated the point of maximum damping. 
         [0060]      FIG. 4  is a perspective view of a burner assembly  10  of a turbine showing a conventional sealing strip  50  intended to be replaced with a seal strip arrangement  100  according to one embodiment of the present invention. 
         [0061]    The burner assembly  10  has a front panel  20  and a burner throat  40 . The front panel  20  at its top edge  21  and its bottom edge  23  are secured to a portion of the turbine housing (not shown here). The left edge  25  and the right edge  29  of front panel  20  have a slot  31 . The seal strip assembly  100  is intended to seal the front panel  20  to another front panel of an adjacent burner assembly. 
         [0062]    Typically, there is space behind the front panel on either side of the burner assembly  10  that will receive the seal strip arrangement  100 . 
         [0063]    In the prior art arrangement, a left side of the conventional seal strip  50  fit into the slot  31  on a right edge  29  of front panel  20 . Typically, the right side of conventional seal strip  50  fit into a slot of the front panel of a second, adjacent burner assembly (not shown). Alternatively, it could fit into a turbine housing member. 
         [0064]    The conventional seal strip  50  was intended to provide a seal between two components of a gas turbine. This may be between the burner assembly  10  and a second burner assembly, or between the burner assembly  10  and a housing member of the turbine. 
         [0065]    The seal strip arrangement  100  according to the present invention is intended to replace the conventional seal strip  50 . As with the conventional seal strip  50 , it is also intended to provide a seal between two components of a gas turbine. 
         [0066]    As shown here there are six dampers  150  incorporated into the seal strip arrangement  100 . Since this seal strip arrangement  100  does not entirely fit into the slot  31 , but has a portion exposing the holes ( 151  of  FIGS. 5 ,  6 , and  7 ) of the dampers  150 . The holes are allowed to fluidically interact with the combustion chamber of the turbine. 
         [0067]      FIG. 5  shows a perspective view of the seal strip arrangement  100  having two dampers  150  fitting inside of the slot of front panel  20 . 
         [0068]      FIG. 6  is a side elevational view of the seal strip arrangement  100  having two dampers  150  fitting within a slot of the front panel  20 . 
         [0069]      FIG. 7  is a perspective view of the seal strip arrangement  100  of the present invention employing six dampers  150 , and an enlarged partially cut-away portion of the dampers  155 . 
         [0070]    The present invention will further be described in connection with  FIGS. 5 ,  6  and  7 . The seal strip arrangement  100  includes dampers  150  attached to a sealing plate  110 . The sealing plate  110  has a first distal end  111 , a second distal end  113  a left edge  115  and a right edge  117 . The width is from the left edge  115  to the right edge  117 . The length is measured from the first distal end  111  to the second distal end  113 . The thickness of the strip is from a front face  119  to a back face  121 . 
         [0071]    The hole  151  is shown opening in the front face  119  and passing into the neck  153 . Neck  153  passes through the thickness of the sealing plate  110  and into container  155 . The hole  151 , neck  153  and container  155  make up the damper  150 . The hole  151  can have the same cross-sectional area as the neck  153  thereby creating one passageway of continuous cross sectional diameter. 
         [0072]    As indicated above, the dimensions and volumes of the damper  150  are determined to dampen a desired acoustic frequency. 
         [0073]    In an alternative embodiment, additional dampers (as indicated in  FIG. 2  and the associated description above) may be attached to those shown in  FIGS. 5-7  to increase efficiency or to dampen additional acoustic frequencies. 
         [0074]    It is understood that the invention that the resonator and acoustic neck are not limited to the shapes shown here. These may incorporate other shapes as long as they satisfy the assumptions and equations above. 
         [0075]    While the invention has been described with reference to a number of preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. 
         [0076]    Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. 
         [0077]    Exemplary embodiments of the present disclosure are now described with references to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosure. However, the present disclosure may be practiced without these specific details, and is not limited to the exemplary embodiment disclosed herein.