Patent Publication Number: US-2015071771-A1

Title: Inter-stage seal for a turbomachine

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to the art of turbomachines and, more particularly, to an inter-stage seal for a turbine portion of a turbomachine. 
     Turbomachines include a compressor portion linked to a turbine portion through a common compressor/turbine shaft and a combustor assembly. An inlet airflow is passed through an air intake toward the compressor portion. In the compressor portion, the inlet airflow is compressed through a number of sequential stages toward the combustor assembly. In the combustor assembly, the compressed airflow mixes with a fuel to form a combustible mixture. The combustible mixture is combusted in the combustor assembly to form hot gases. The hot gases are guided along a hot gas path of the turbine portion through a transition piece. The hot gases expand through a number of turbine stages acting upon turbine buckets mounted on wheels to create work that is output, for example, to power a generator, a pump, or to provide power to a vehicle. Exhaust gases from the turbine portion are often times passed to a heat recovery steam generator which creates a steam flow that is passed to a steam turbine portion. 
     Additional gases, in the form of compressor air, may pass into the turbine portion, or in the form of lower temperature air, may enter wheel spaces in turbine portion to cool a rotor and/or a wheel. In a steam turbine, lower temperature steam may be fed into wheel spaces of early stages to cool the rotor that supports rotating buckets. In either case, inter-stage seals substantially isolate the hot gases, or working fluids, flowing along the hot gas path and the fluids used for cooling purposes. The inter-stage seals typically include axial outwardly extending arms that cooperate with turbine blade angel wings to reduce leakage. Typical angel wing seals involve a rotating seal tooth or sealing face mating with a stationary counterpart. There typically exists a clearance between a rotating component and a stationary component to reduce contact or rubbing. The clearance may allow leakage to flow between the rotating component and the stationary component. The leakage flow may increase cooling requirements that may negatively impact turbomachine efficiency. Reducing working fluid leakage increases turbomachine efficiency. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the exemplary embodiment, an inter-stage seal for a turbomachine includes a sealing member extending from a first end to a second end through an intermediate portion having a sealing surface, a first mounting member extending from a first end portion coupled to the sealing member adjacent the first end to a second, cantilevered end portion having a first rotor mounting element, and a second mounting member extending from a first end portion coupled to the sealing member adjacent the second end to a second, cantilevered end portion having a second rotor mounting element. 
     According to another aspect of the exemplary embodiment, a turbomachine includes a turbine portion having a first stage rotor supporting a plurality of first stage turbine blades and a second stage rotor supporting a plurality of second stage turbine blades. At least one inter-stage seal extends between the first and second stage rotors. The at least one inter-stage seal includes a sealing member extending from a first end to a second end through an intermediate portion having a sealing surface, a first mounting member extending from a first end portion coupled to the sealing member adjacent the first end to a second, cantilevered end portion having a first rotor mounting element connected to the first stage rotor, and a second mounting member extending from a first end portion coupled to the sealing member adjacent the second end to a second, cantilevered end portion having a second rotor mounting element connected to the second stage rotor. 
     According to yet another aspect of the exemplary embodiment, a method of sealing between adjacent stages in a turbomachine includes positioning an inter-stage seal across a rotor, axially shifting the inter-stage seal across the rotor, arranging a sealing member of the inter-stage seal across a gap extending between the rotor and an adjacent rotor, connecting a first mounting member extending from a first end of the sealing member with the rotor, and connecting a second mounting member extending from a second end of the sealing member to the another rotor. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional side view of a turbomachine including an inter-stage seal, in accordance with an exemplary embodiment; 
         FIG. 2  is a partial plan view of a turbine portion of the turbomachine of  FIG. 1 ; 
         FIG. 3  is a perspective view of the inter-stage seal of  FIG. 1 ; 
         FIG. 4  is a plan view of an inter-stage seal being positioned across a rotor of the turbomachine of  FIG. 1 ; 
         FIG. 5  is a plan view of the inter-stage seal straddling the rotor of  FIG. 4 ; 
         FIG. 6  is a plan view of the inter-stage seal axially shifting toward another rotor of the turbomachine; and 
         FIG. 7  is a plan view of the inter-stage seal connected to the rotor and the another rotor, in accordance with an exemplary embodiment. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A turbomachine, in accordance with an exemplary embodiment, is indicated generally at  2 , in  FIG. 1 . Turbomachine  2  takes the form of a turbine portion  4  having a housing  5  that surrounds a plurality of turbine stages  6 . Turbine stages  6  include a first stage  8 . First stage  8  includes a plurality of first stage vanes or nozzles, one of which is indicated at  10 , and a plurality of first stage axial entry buckets or blades, one of which is indicated at  12 . Blades  12  are mounted to a first stage rotor  14  through a plurality of dovetail slots  15 . First stage rotor  14  includes one or more axial locking members  16  that constrain axial movement of blades  12 . 
     Plurality of turbine stages  6  also include a second stage  18  arranged downstream of first stage  8 . Second stage  18  includes a plurality of second stage vanes or nozzles, one of which is indicated at  20 , and a plurality of second stage axial entry buckets or blades, one of which is indicated at  22 . Blades  22  are mounted to a second stage rotor  24  through a plurality of dovetail slots  25 . Second stage rotor  20  includes one or more axial locking members  26  that constrain axial movement of blades  22 . A third stage  28  is arranged downstream of second stage  18 . Third stage  28  includes a plurality of third stage vanes or nozzles, one of which is indicated at  30 , and a plurality of third stage axial entry buckets or blades, one of which is indicated at  32 . Blades  32  are mounted to a third stage rotor  34  through a plurality of dovetail slots  35 . Third stage rotor  34  includes one or more axial locking members  36  that constrain axial movement of blades  32 . Blades  12 ,  22 , and  32  extend along a hot gas path  37  of turbine portion  8 . 
     A working fluid, in the form of hot gases that may include products of combustion or steam, expands through turbine stages  6  to an outlet (not separately labeled) acting upon the first, second, and third stage blades  12 ,  22 , and  32 . The force of the hot gases impacting the first, second, and third stage blades  12 ,  22  and  32  is transmitted to first, second, and third stage rotors  14 ,  24  and  34  which rotate. Rotational energy from the first, second, and third stage rotors  14 ,  24 , and  34  is transmitted to a load (not shown) through a shaft (not separately labeled). In addition to the working fluid, a cooling fluid is passed through a wheelspace portion  38  of turbine portion  4 . Wheelspace portion  38  may include inter-rotor spaces between adjacent rotors  14 ,  24  and  24 ,  34  such as shown at  38   a  and  38   b  respectively. Wheelspace portion  38  may also include a portion  39  that exists between stationary components (not separately labeled) and rotor  14 . 
     In order to limit hot gas ingestion into spaces  38   a  and  38   b  and other inter-wheel spaces (not shown), and to reduce leakage of the cooling fluid, turbine portion  4  includes a first inter-stage seal  40  arranged between first and second rotors  14  and  24  in stages  8  and  18  respectively, and a second inter-stage seal  44  arranged between rotors  24  and  44  in second and third stages  18  and  28 , respectively. In accordance with an aspect of the invention, a conventional angel wing seal (not shown) may be placed on an upstream side (not separately labeled) of first stage rotor  14 . Of course it should be understood that other types of seals, including an inter-stage seal  40  could be used. At this point it should be understood that the number of stages and inter-stage seals may vary. 
     Reference will now be made to  FIGS. 2-3  in describing first inter-stage seal  40 , in accordance with an exemplary embodiment, with an understanding that second inter-stage seal  44  may include similar structure. First inter-stage seal  40  includes a sealing member  60  that extends from a first end  62  to a second end  63  through an intermediate portion  65 . Intermediate portion  65  includes a sealing surface  67  and an opposing, cooling surface  69 . Sealing surface  67  includes one or more radially outwardly projecting sealing elements  72 . When installed, sealing elements  72  extend toward a bottom surface of, for example, second stage nozzles  20 . 
     Inter-stage seal  40  also includes a first mounting member  81  that interfaces with first stage rotor  14  and a second mounting member  84  that interfaces with second stage rotor  24 , as will be detailed more fully below. First mounting member  81  extends from a first end portion  90  to a second, cantilevered, end portion  91 . First end portion  90  extends from first end  62  and second end portion  91  includes a first rotor mounting element  94 . First rotor mounting element  94  takes the form of a dovetail member  96  that is configured to slidingly engage with dovetail slot  15 . Second mounting member  84  extends from a first end portion  104  to a second, cantilevered, end portion  105 . First end portion  104  extends from second end  63  and second end portion  105  includes a second rotor mounting element  108 . Second rotor mounting element  108  takes the form of a dovetail member  110  that is configured to slidingly engage with dovetail slot  25 . In the exemplary embodiment, first and second rotor mounting elements  94  and  108  are shown as complete dovetails. It should be readily understood that first and second rotor mounting elements  94  and  108  can also take the form of partial or whole form dovetails having various geometries that structurally match dovetail slots on the rotor. First and second ends  62  and  63  abut, or nearly abut, base portions (not separately labeled) of corresponding ones of first stage blades  12  and second stage blades  22 . In accordance with an aspect of the exemplary embodiment, inter-stage seal  40  rotates together with first and second stage blades  12  and  22 . Accordingly, gaps between abutting surfaces may be set to very small dimensions that effectively fluidically separate inter-rotor spaces  38   a  and  38   b  from hot gas path  37 . 
     Reference will now be made to  FIGS. 4-7  in describing a method of installing inter-stage seal  40 , in accordance with an aspect of the exemplary embodiment. As shown in  FIG. 4 , inter-stage seal  40  is positioned at first stage rotor  14  prior to the installation of first stage blades  12 . Inter-stage seal  40  is moved into position such that first and second mounting members  81  and  84  straddle first stage rotor  14 , as shown in  FIG. 5 . Inter-stage seal  40  is axially shifted causing dovetail member  96  to pass into dovetail slot  15 , as shown in  FIG. 6 . Inter-stage seal  40  is further axially shifted until dovetail member  110  enters dovetail slot  25  in second rotor  24 , as shown in  FIG. 7 . At this point, additional inter-stage seals may be mounted to first stage rotor  14 , or first stage rotor blades  12  may be installed and locked into position. In the exemplary embodiment, each rotor wheel may include balance holes  120 ,  122 , and  124  formed in first, second, and third stage rotors  14 ,  24 , and  34 . Balance holes  120 ,  122 , and  124 may pass cooling flow between inter-rotor spaces  38   a  and  38   b  and the like. 
     At this point it should be understood that the exemplary embodiments describe an inter-stage seal for a turbine. The inter-stage seal joins adjacent rotors doing away with the need for turbine wheels and corresponding seals. The particular shape of the inter-stage seal also removes the need for angel wings provided on the rotor blades for sealing purposes. The inter-stage seal, in accordance with the exemplary embodiment, contributes to an overall reduction in axial length of a turbine while maintaining a desired separation between working fluid and cooling fluid flows. At this point it should be understood that the inter-stage seal, in accordance with exemplary embodiment, may be employed in a gas turbine or a steam turbine. It should be further understood that the particular geometry of the inter-stage seal may vary and should not be limited to the geometries shown. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.