Abstract:
A method for assembling a power system is provided. The method includes coupling a first turbine and second turbine together with a coupling that extends between a first rotor of a first turbine and a second rotor of the second turbine, and such that the first turbine has fluid flow along a first flow path, and the second turbine has fluid flow along a second flow path. The method further includes fixedly coupling an outer wall to the first turbine that directs fluid flow from the first flow path towards the second flow path.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to turbine engines and more particularly to methods and apparatus for improving performance of turbine engines that are axially coupled together.  
           [0002]    At least some known power generating systems include at least two turbines coupled axially together via a coupling. More specifically, the turbines are connected such that their rotor shafts rotatably coupled and such that fluid flow exiting a final stage of an upstream turbine enters the first stage of a downstream turbine through a cavity defined between the turbines.  
           [0003]    The cavity formed between the turbines may facilitate undesirable energy losses between the turbines. For example, because the rotating shaft and coupling are exposed to the flow path, as the shaft is rotated, fluid may become entrained and become ejected into flow path in a condition known as windage loss. In addition, undesirable flow separation losses may occur as the fluid contacts the coupling enroute to the downstream turbine. In addition, if an exit annulus of the upstream turbine has a different height or diameter than the entrance annulus of the downstream turbine, additional energy losses may occur as the fluid flow is channeled through the coupling.  
           [0004]    Some known power generation systems supply additional steam to the coupling region. Additional steam is admitted as required by the thermodynamic cycle so as not to affect the coupling losses. However, the introduction of such steam may cause an undesirable disturbance to the fluid flowing through the coupling.  
           [0005]    As such, other known power generation systems include a generally cylindrical coupling cover which overlies the rotating shaft and coupling and has an axis that is generally coincident with the axis of rotation of the turbines. Although the coupling cover facilitates mitigating losses associated with the rotating shaft and coupling, the additional cover also produces energy losses itself, and does not address recovering energy from the flowpath. Additionally, the coupling cover does not provide a means for retrofitting previously commissioned turbines.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0006]    In one aspect, a method for assembling a power system is provided. The method includes coupling a first turbine and second turbine together with a coupling that extends between a first rotor of a first turbine and a second rotor of the second turbine, and such that the first turbine has fluid flow along a first flow path, and the second turbine has fluid flow along a second flow path. The method further includes fixedly coupling an outer wall to the first turbine that directs fluid flow from the first flow path towards the second flow path.  
           [0007]    In another aspect, a turbine for use in a power system is provided. The turbine includes a first turbine having a first rotor and fluid flow along a first flow path, a second turbine having a second rotor and fluid flow along a second flow path, a coupling extending between said first and second turbines, the coupling for rotatably coupling the first turbine to the second turbine and an outer wall coupled to the first turbine to direct fluid flow from the first flow path to the second flow path.  
           [0008]    In a further aspect, a power system is provided. The power system includes a first turbine including a first rotor and fluid flow along a first flow path, a second turbine comprising a second rotor and fluid flow along a second flow path, a coupling extending between the first and second turbines for rotatably coupling the first and second turbines together and an outer wall fixedly attached to the first turbine such that the outer wall directs fluid flow from the first flow path to the second flow path.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a cross-sectional view of first and second turbines coupled to one another illustrating the coupling and flow path therebetween;  
         [0010]    [0010]FIG. 2 is a side cross-sectional view of an outer wall coupled to a turbine shown in FIG. 1  
         [0011]    [0011]FIG. 3 is a front view of an outer wall coupled to a turbine shown in FIG. 1; and  
         [0012]    [0012]FIG. 4 is a front view of one embodiment of the outer wall coupled to the first turbine shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    Referring to the drawing figures, particularly to FIG. 1, there is illustrated first and second turbines, namely a first or upstream turbine, generally designated  10 , and a downstream turbine, generally designated  12 , axially coupled together along their flow paths such that their rotor shafts are coupled to one another. First turbine  10  includes a plurality of axially spaced rotor wheels  14  mounting buckets  16  which, together with diaphragms  18  mounting partitions  20 , form multiple stages of first turbine  10 . Likewise, second turbine  12  includes a plurality of axially spaced rotor wheels  22  mounting buckets  24  which, in conjunction with diaphragms  26  carrying partitions  28 , form multiple stages of the second turbine  12 .  
         [0014]    A fluid, such as steam, passes generally axially past the various stages of the upstream turbine  10  along a first flow path portion indicated by an arrow  27 , through an intermediate cavity  30  and through a second flow path portion indicated by an arrow  29  comprised of the various stages of the downstream turbine  12 . Thus, flow path portions  27  and  29  and cavity  30  form a flow path through the joined turbines. Additionally, the discrete rotor shafts  34  and  36  of the first and second turbines  10  and  12 , respectively, are joined one to the other by a coupling, generally indicated  38 . The coupling includes flanges  40  on the ends of the respective rotor shafts with bolts  41  interconnecting the flanges and, hence, the shafts to one another. A radial fluid (steam) admission port  45  is provided through a common outer shell  42  for admitting additional fluid (steam) into intermediate cavity  30  to join the fluid in the flow path. The rotating shafts  34  and  36  and the coupling  38  are exposed to the flow path within cavity  30 , with resulting windage loss through turbulent mixing and losses due to flow separation by impact against protuberant surfaces on coupling  38  and other parts.  
         [0015]    Common outer shell  42  mounts radial fluid (steam) admission port  45  for admitting fluid (steam) into intermediate cavity  30  for joining with the fluid (steam) exiting an exit annulus  47  of upstream turbine  10  and flowing to entrance annulus  49  of downstream turbine  12 .  
         [0016]    A diffuser, generally designated  50 , forming part of the cavity  30  intermediate first and second turbines  10  and  12 , respectively. The diffuser  50  recovers kinetic energy from the fluid (steam), leaving upstream turbine  10  prior to entry into downstream turbine  12 . To form diffuser  50 , as well as to minimize or eliminate both windage loss and spinning loss, there is provided an inner cover  52  in the form of a surface of revolution, preferably a frustoconical section having an axis coincident with the axis of rotation of combined shafts  34  and  36 . Inner cover  52  having an outer surface  53  defines an inner margin of the flow path exiting exit annulus  47  of upstream turbine  10  to entrance annulus  49  of downstream turbine  12 . That is, inner cover  52  extends from adjacent the root radius of the buckets forming the final stage of upstream turbine  10  to the inner band of the first stage of downstream turbine. Cover  52  is supported by the first stage diaphragm of the downstream turbine  12 . The flow path through intermediate cavity  30  is thus substantially sealed from coupling  38  between the shafts.  
         [0017]    Also defining diffuser  50  is an outer wall  54  which forms a generally axially downstream extension of the upstream turbine  10 . Outer wall  54  in the form of a surface of revolution, preferably a frustoconical section having an axis coincident with the axis of rotation of combined shafts  34  and  36 . The outer wall has an outer wall surface  55  and an inner wall surface  56 . Inner wall surface  56  of outer wall  54  in part defines the outer margin of the flow exiting upstream turbine  10 . Outer surface  53  of inner cover  52  and inner wall surface  56  thus define an annulus about the flow path whose area increases in a downstream direction toward downstream turbine  12 , i.e., form a diffuser. The surfaces of revolution which define the diffuser, i.e., cover  52  and wall  56 , may have any annular configuration provided the flow area increases in a downstream direction and the flow path between the exit annulus of the upstream turbine effects a smooth flow transition therebetween.  
         [0018]    Outer wall  54  has a flange  58  mounted on its smaller diameter. In one embodiment, flange  58  is mounted along the length of outer wall  54 . The flange is welded to the smaller diameter of the frustum and holes are drilled parallel to the axis of rotation through the flange. Although the device is described as being made of steel, it may be made of any material capable of withstanding the environment and mechanical constraints of the application. The outer is fixedly secured to a turbine casing  60  as shown in FIGS. 2 and 3. To apply the outer wall to the turbine casing, holes are drilled in turbine casing  60  and tapped to receive fasteners  62 , such as a bolt, through the flange. In one embodiment, the device may be cut into sections to ease installation and may be omitted over sectors of the casing cavity where it would otherwise adversely disturb fluid flow as shown in FIG. 4.  
         [0019]    Inlet port  45  provides for radial admission of fluid (steam) into intermediate cavity  30 . Inlet port  45  forms part of outer shell  42  common to both the upstream and downstream turbines. Inlet port  45  is configured to turn the generally radially inwardly directed flow as it encounters outer wall surface  55  of outer wall  54  and turns the flow axially and circumferentially before the flow enters coupling cavity  30 . Thus, where the inlet flow path meets the axial flow path from the upstream turbine, the velocity of the flow is sufficiently reduced such that mixing losses are reduced.  
         [0020]    Diffuser  50  substantially minimizes or eliminates the spinning and windage losses. Moreover, the flow path between the exit annulus of the upstream turbine and the entry annulus of the downstream turbine effects a smooth flow transition therebetween, notwithstanding differences in heights and/or diameters of the exit and entrance annuli  47  and  49 , respectively.  
         [0021]    The above-described outer wall is cost-effective and time saving. The outer wall includes a flange that facilitates securing the outer wall to a turbine, thus allowing retrofitting previously commissioned turbines. Because the turbine can be drilled and tapped to receive a fastener passing through the flange, installed turbines can be retrofitted with the outer wall. As a result, the outer wall significantly improves the performance of the turbine in a cost-effective and a time-saving manner.  
         [0022]    Exemplary embodiments of outer wall are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each outer wall may be utilized independently and separately from other components described herein. Each outer wall component can also be used in combination with other outer wall and turbine components.  
         [0023]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.