Abstract:
Embodiments of the invention relate generally to rotor cooling and, more particularly, to a stator member having at least one passage for the delivery of cooling steam to a bucket root. In one embodiment, the invention provides a turbine comprising: a rotor including a first bucket root; and a stator member having: a rotor bore within which at least a portion of the rotor is disposed; a facing end adjacent to the first bucket root of the rotor; a plurality of seals within the rotor bore for sealing against the rotor, the plurality of seals including a first seal nearest the facing end and a second seal adjacent to the first seal; and a plurality of passages, each extending from a surface of the rotor bore at a point between the first seal and the second seal and extending through the facing end.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Cooling of the first wheelspace adjacent to a rotor bucket has been employed in many turbomachines, including steam turbines. Typically, such cooling employs the diversion of steam from a later stage of a high-pressure section to the first wheelspace of an intermediate-pressure section. It has now been discovered, however, that, in an operative state, the swirl ratio of the cooling flow—defined as the circumferential speed of the cooling steam divided by the speed of the rotor—is important in providing efficient cooling and extending rotor life. Also important is the pressure drop between the source of the cooling steam and a point at which it is released to the wheelspace. Embodiments of the invention describe the improvement and/or interaction of both swirl ratio and pressure drop to provide more efficient cooling flow. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0002]    In one embodiment, the invention provides a turbine comprising: a rotor including a first bucket root; and a stator member having: a rotor bore within which at least a portion of the rotor is disposed; a facing end adjacent to the first bucket root of the rotor; a plurality of seals within the rotor bore for sealing against the rotor, the plurality of seals including a first seal nearest the facing end and a second seal adjacent to the first seal; and a plurality of passages, each passage extending from a surface of the rotor bore at a point between the first seal and the second seal and extending through the facing end. 
         [0003]    In another embodiment, the invention provides a stator member for a turbine, the stator member comprising: an elongate body; a rotor bore within and along a longitudinal axis of the elongate body; at least one passage having a first opening on a surface of the rotor bore and extending through the elongate body to a second opening on a facing end of the elongate body, the facing end lying along a plane substantially perpendicular to the longitudinal axis of the elongate body; and a first recess along the surface of the rotor bore for containing a sealing device, the first recess being disposed between the facing end and the first opening of the at least one passage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
           [0005]      FIG. 1  shows a schematic cross-sectional side view of a portion of a turbine according to an embodiment of the invention. 
           [0006]      FIG. 2  shows a schematic cross-sectional side view of a portion of a turbine according to another embodiment of the invention. 
           [0007]      FIG. 3  shows a facing view of an inducer plate according to an embodiment of the invention. 
           [0008]      FIG. 4  shows a side view of the inducer plate of  FIG. 3 . 
           [0009]      FIG. 5  shows a schematic cross-sectional side view of a portion of a turbine according to another embodiment of the invention. 
           [0010]      FIG. 6  shows a schematic cross-sectional side view of a portion of a turbine according to another embodiment of the invention. 
           [0011]      FIG. 7  shows a graphical representation of relative heat exchange and pressure difference as a function of swirl ratio according to various embodiments of the invention. 
       
    
    
       [0012]    It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  shows a schematic cross-sectional side view of a portion of a turbine  100  according to one embodiment of the invention. In  FIG. 1 , a rotor  40  resides within a rotor bore  20  of a stator member  10 . A first wheelspace  60  exists between a facing end  12  of stator  10  and a first bucket root  70  of bucket  50 . As can be seen in  FIG. 1 , bucket  50  is one of a plurality of buckets  50 ,  52  affixed to rotor  40 , which alternate a plurality of non-rotating nozzles  60 ,  62 , as is typical of turbomachines such as turbine  100 . Those with knowledge in the art understand that the term “blade” is usually used for aviation turbines, while the term “bucket” is typically used when describing the same type of component for land-based turbines. For simplicity, however, the term “bucket” shall be used herein to collectively refer to buckets or blades. 
         [0014]    A plurality of seals  26 ,  28  reside within seal cavities  16 ,  18 , respectively, of stator  10  and act to seal rotor  40  against stator  10 . As shown in  FIG. 1 , first seal  26  is a brush seal while second seal  28  is a packing ring. Other seal configurations and combinations are possible, of course, and are within the scope of the invention. 
         [0015]    In the embodiment of  FIG. 1 , a first passage  30  extends from a first opening  32  between first seal  26  and second seal  28 , through a second passage  38  and stator  10 , to a second opening  34  on facing end  12  of stator  10 . Cooling steam is thereby allowed to pass from between first seal  26  and second seal  28  to first wheelspace  60 , thereby cooling first bucket root  70 . As will be described in greater detail below, second passage  38  is angled tangentially (circumferentially) with respect to a longitudinal axis of stator  10 , such that cooling steam contacts first bucket root  70  at an angle. However, first passage  30  may also optionally be angled tangentially with respect to a longitudinal axis of stator  10 . Typically, such an angle will be in the direction of rotation of rotor  40 , such that the swirl ratio of the cooling steam and the attendant heat extraction efficiency are increased. Second passage  38  may comprise or include a convergent or a convergent-divergent section to accelerate the flow exiting opening  34 . 
         [0016]    As shown in  FIG. 1 , an optional additional passage  90  may be provided in first bucket root  70 , such that cooling steam directed into first wheelspace  60  may continue to flow through bucket root  70  and into second wheelspace  61  between first bucket root  70  and second bucket root  72 . Again, additional passage  90  and/or its opening  92  into second wheelspace  61  may be angled with respect to a longitudinal axis of stator  10 . Such angling may be, for example, in the direction of rotation of rotor  40 . 
         [0017]    An additional advantage of the introduction of cooling steam into first wheelspace  60 , particularly where a significant increase in pressure is achieved within first wheelspace  60 , is a reduction in leakage of operating hot steam from steam path  66  into first wheelspace  60 , which would act to heat bucket root  70 . 
         [0018]      FIG. 2  shows a schematic cross-sectional side view of a portion of a turbine  200  according to another embodiment of the invention. Here, an inducer plate  180  has been attached to facing end  112  of stator  110 . According to some embodiments of the invention, inducer plate  180  is non-fixedly attached to facing end  112 , such that it can be replaced. According to some embodiments of the invention, first passage  130  and second passage  138  may not be tangentially angled for ease of manufacture. In such a case, inducer passage  136  may be angled tangentially with respect to the longitudinal axis of stator  110 , providing substantially the same angling of cooling steam as it exits inducer plate  180  as if first passage  130  and/or second passage  138  were angled. Again, inducer passage  136  may include a convergent or a convergent-divergent section to accelerate the flow exiting opening  134 . 
         [0019]      FIGS. 3 and 4  show, respectively, facing and side views of one embodiment of inducer plate  180  in which passages  182 ,  184 ,  186  are so angled tangentially (circumferentially). Although only three passages  182 ,  184 ,  186  are labeled in  FIGS. 3 and 4  and shown in  FIG. 4 , this is merely for the sake of simplicity of illustration. In addition, it should be appreciated that any number of passages of any size or of varying sizes may be employed, depending on the requirements of the situation in which inducer plate  180  will be employed. 
         [0020]    In the embodiment shown in  FIGS. 3 and 4 , inducer plate  180  comprises a body  182  having a first face  182 A and a second face  182 B and a plurality of passages  184 ,  186 ,  188  passing from first face  182 A to second face  182 B. Either first face  182 A or second face  182 B is placed in contact with facing end  112  ( FIG. 2 ) of stator  110  ( FIG. 2 ), such that passages  182 ,  184 ,  186  are in communication with second passage  138 . As shown in  FIG. 4 , each passage  184 ,  186 ,  188  is angled at angle a with respect to a longitudinal axis A of stator  110 , i.e., a line substantially perpendicular to first face  182 A and/or second face  182 B. For passage  186 , for example, opening  185  on face  182 A and opening  187  on face  182 B are labeled. Inducer plate  180  may be attached to facing end  112  using any known or later-developed device or method, including, for example, bolts, screws, or other fasteners, welding, etc. 
         [0021]    The angle a to which passages  184 ,  186 ,  188  are angled tangentially with respect to longitudinal axis A of stator  110  ( FIG. 2 ) will vary, of course, depending on the desired effect of such angling. Typically, however, angle a is between about 45° and about 90° from longitudinal axis A of stator  110 , e.g., between about 60° and about 85°, or about 80°. As noted above, Applicants have discovered that the swirl ratio of the cooling steam—defined as the circumferential speed of the cooling steam divided by the speed of the rotor—is important in providing efficient cooling and extending rotor life. More specifically, Applicants have discovered that a swirl ratio of about 1.7 or greater results in a higher heat transfer rate. Angles between about 45° and about 90° from the longitudinal axis of stator  110  have been found to achieve such swirl ratios. 
         [0022]      FIGS. 5 and 6  show schematic cross-sectional side views of portions of turbines  300 ,  400  according to other embodiments of the invention. In  FIG. 5 , first seal  226  is a packing ring rather than a brush seal, as in  FIG. 1 . In  FIG. 6 , optional inducer plate  380  has been attached to facing end  312  of stator  310 . 
         [0023]    In addition, Applicants have found that limiting the size and/or number of points at which cooling steam is delivered to first wheelspace  60  ( FIG. 1 ) improves heat transfer and, in some cases, also increases the swirl ratio. For example, by limiting the size and/or number of passages  30  ( FIG. 1 ) or the size and/or number of second openings  34  ( FIG. 1 ) into first wheelspace  60 , to achieve a pressure difference of 50 psid (pounds per square inch differential) or more, which accelerates the cooling steam, Applicants have found that heat transfer can be greatly improved. In some cases, the improvement in heat transfer is as much as 80%. In some embodiments, the pressure difference is up to 80 psid. 
         [0024]    In some embodiments of the invention, improvements in heat transfer are achieved through a combination of angling passages  184 ,  186 ,  188  and increasing a pressure difference of the cooling steam to accelerate the flow. It should be noted, however, that, in other embodiments of the invention, angle a may be at or near 0°, such that passages  184 ,  186 ,  188  are oriented substantially parallel to or at a shallow angle relative to first face  182 A and second face  182 B of inducer plate  180 , with heat transfer improvement achieved primarily by increasing the pressure difference of the cooling steam. In still other embodiments, heat transfer improvement is achieved primarily by angling passages  184 ,  186 ,  188 , with no deliberate or significant increase in the pressure difference of the cooling steam, i.e., the pressure difference being less than about 50 psid. 
         [0025]      FIG. 7  shows a graphical representation of relative heat exchange and pressure difference as a function of swirl ratio, based on results observed by Applicants according to various embodiments of the invention. As can be seen in  FIG. 7 , relative heat exchange initially decreases along portion A as swirl ratio increases toward 1.0, at which point relative heat transfer reaches its minimum. This is understandable, since at a swirl ratio of 1.0 the speed of the cooling steam is equal to the speed of the rotor, i.e., the rotor is essentially bathed in the cooling steam with no additional heat transfer achieved via the relative movement of the cooling steam with respect to the rotor. The relative heat exchange values along portion A are those achievable using cooling steam without employing the angled passages  30 ,  38  ( FIG. 1 ) and/or inducer plates  180  ( FIG. 2 ) according to various embodiments of the invention. 
         [0026]    Still referring to  FIG. 7 , as the swirl ratio increases above 1.0, as may be achieved according to various embodiments of the invention, the relative heat exchange increases along portion B until, at about 1.7, the relative heat exchange is equal to the maximum relative heat exchange achievable without the invention, i.e., with a swirl ratio less than 1.0. Swirl ratios above about 1.7 result in relative heat exchange greater than the maximum that can be achieved by a swirl ratio less than 1.0. As can be seen in  FIG. 7 , at a swirl ratio of about 2.5, the relative heat exchange is about twice the maximum achievable with a swirl ratio less than 1.0. 
         [0027]    Portion C of  FIG. 7  shows the pressure difference needed to generate the corresponding swirl ratio. As can be seen, a pressure difference of about 50 psid is needed to achieve a swirl ratio of about 1.7. From that point, pressure difference increases result in further increases of swirl ratio, leading to higher relative heat exchange. This reflects the fact that the relative heat exchange includes a component corresponding to the pressure difference shown in portion C as well as a component corresponding to the angling of the cooling steam achieved using the angled passages and/or inducer plates according to various embodiments of the invention. It also demonstrates the function of the first seal  26  in  FIG. 1  in building the needed pressure to drive cooling flow through angled passage and achieve desirable swirl ratio. 
         [0028]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0029]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any related or incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.