Patent Publication Number: US-9885243-B2

Title: Turbine bucket having outlet path in shroud

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to turbines. Specifically, the subject matter disclosed herein relates to buckets in gas turbines. 
     Gas turbines include static blade assemblies that direct flow of a working fluid (e.g., gas) into turbine buckets connected to a rotating rotor. These buckets are designed to withstand the high-temperature, high-pressure environment within the turbine. Some conventional shrouded turbine buckets (e.g., gas turbine buckets), have radial cooling holes which allow for passage of cooling fluid (i.e., high-pressure air flow from the compressor stage) to cool those buckets. However, this cooling fluid is conventionally ejected from the body of the bucket at the radial tip, and can end up contributing to mixing losses in that radial space. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Various embodiments of the disclosure include a turbine bucket having: a base; a blade coupled to the base and extending radially outward from the base, the blade including: a body having: a pressure side; a suction side opposing the pressure side; a leading edge between the pressure side and the suction side; and a trailing edge between the pressure side and the suction side on a side opposing the leading edge; and a plurality of radially extending cooling passageways within the body; and a shroud coupled to the blade radially outboard of the blade, the shroud including: a plurality of radially extending outlet passageways fluidly connected with a first set of the plurality of radially extending cooling passageways within the body; and an outlet path extending at least partially circumferentially through the shroud and fluidly connected with all of a second, distinct set of the plurality of radially extending cooling passageways within the body. 
     A first aspect of the disclosure includes: a turbine bucket having: a base; a blade coupled to the base and extending radially outward from the base, the blade including: a body having: a pressure side; a suction side opposing the pressure side; a leading edge between the pressure side and the suction side; and a trailing edge between the pressure side and the suction side on a side opposing the leading edge; and a plurality of radially extending cooling passageways within the body; and a shroud coupled to the blade radially outboard of the blade, the shroud including: a plurality of radially extending outlet passageways fluidly connected with a first set of the plurality of radially extending cooling passageways within the body; and an outlet path extending at least partially circumferentially through the shroud and fluidly connected with all of a second, distinct set of the plurality of radially extending cooling passageways within the body. 
     A second aspect of the disclosure includes: a turbine bucket having: a base; a blade coupled to the base and extending radially outward from the base, the blade including: a body having: a pressure side; a suction side opposing the pressure side; a leading edge between the pressure side and the suction side; and a trailing edge between the pressure side and the suction side on a side opposing the leading edge; a plurality of radially extending cooling passageways within the body; and at least one bleed aperture fluidly coupled with a first set of the plurality of radially extending cooling passageways, the at least one bleed aperture extending through the body at the trailing edge; and a shroud coupled to the blade radially outboard of the blade, the shroud including an outlet path extending at least partially circumferentially through the shroud and fluidly connected with all of a second, distinct set of the plurality of radially extending cooling passageways within the body. 
     A third aspect of the disclosure includes: a turbine having: a stator; and a rotor contained within the stator, the rotor having: a spindle; and a plurality of buckets extending radially from the spindle, at least one of the plurality of buckets including: a base; a blade coupled to the base and extending radially outward from the base, the blade including: a body having: a pressure side; a suction side opposing the pressure side; a leading edge between the pressure side and the suction side; and a trailing edge between the pressure side and the suction side on a side opposing the leading edge; and a plurality of radially extending cooling passageways within the body; and a shroud coupled to the blade radially outboard of the blade, the shroud including: a plurality of radially extending outlet passageways fluidly connected with a first set of the plurality of radially extending cooling passageways within the body; and an outlet path extending at least partially circumferentially through the shroud and fluidly connected with all of a second, distinct set of the plurality of radially extending cooling passageways within the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 disclosure, in which: 
         FIG. 1  shows a side schematic view of a turbine bucket according to various embodiments. 
         FIG. 2  shows a close-up cross-sectional view of the bucket of  FIG. 1  according to various embodiments. 
         FIG. 3  shows a partially transparent three-dimensional perspective view of the bucket of  FIG. 1  and  FIG. 2 . 
         FIG. 4  shows a close-up cross-sectional view of a bucket according to various additional embodiments. 
         FIG. 5  shows a partially transparent three-dimensional perspective view of the bucket of  FIG. 4 . 
         FIG. 6  shows a close-up schematic cross-sectional depiction of an additional bucket according to various embodiments. 
         FIG. 7  shows a schematic partial cross-sectional depiction of a turbine according to various embodiments 
     
    
    
     It is noted that the drawings of the invention are not necessarily 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 between the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As noted herein, the subject matter disclosed relates to turbines. Specifically, the subject matter disclosed herein relates to cooling fluid flow in gas turbines. 
     In contrast to conventional approaches, various embodiments of the disclosure include gas turbomachine (or, turbine) buckets having a shroud including an outlet path. The outlet path can be fluidly connected with a plurality of radially extending cooling passageways in the blade, and can direct outlet of cooling fluid from a set (e.g., two or more) of those cooling passageways to a location radially outboard of the shroud, and proximate the trailing edge of the bucket. 
     As denoted in these Figures, the “A” axis represents axial orientation (along the axis of the turbine rotor, omitted for clarity). As used herein, the terms “axial” and/or “axially” refer to the relative position/direction of objects along axis A, which is substantially parallel with the axis of rotation of the turbomachine (in particular, the rotor section). As further used herein, the terms “radial” and/or “radially” refer to the relative position/direction of objects along axis (r), which is substantially perpendicular with axis A and intersects axis A at only one location. Additionally, the terms “circumferential” and/or “circumferentially” refer to the relative position/direction of objects along a circumference (c) which surrounds axis A but does not intersect the axis A at any location. It is further understood that common numbering between FIGURES can denote substantially identical components in the FIGURES. 
     In order to cool buckets in a gas turbine, cooling flow should have a significant velocity as it travels through the cooling passageways within the airfoil. This velocity can be achieved by supplying the higher pressure air at bucket base/root relative to pressure of fluid/hot gas in the radially outer region of the bucket. Cooling flow exiting at the radially outer region at a high velocity is associated with high kinetic energy. In conventional bucket designs with cooling outlets ejecting this high kinetic energy cooling flow in radially outer region, most of this energy not only goes waste, but also creates additional mixing losses in the radially outer region (while it mixes with tip leakage flow coming from gap between the tip rail and adjacent casing). 
     Turning to  FIG. 1 , a side schematic view of a turbine bucket  2  (e.g., a gas turbine blade) is shown according to various embodiments.  FIG. 2  shows a close-up cross-sectional view of bucket  2 , with particular focus on the radial tip section  4  shown generally in  FIG. 1 . Reference is made to  FIGS. 1 and 2  simultaneously. As shown, bucket  2  can include a base  6 , a blade  8  coupled to base  6  (and extending radially outward from base  6 , and a shroud  10  coupled to the blade  8  radially outboard of blade  8 . As is known in the art, base  6 , blade  8  and shroud  10  may each be formed of one or more metals (e.g., steel, alloys of steel, etc.) and can be formed (e.g., cast, forged or otherwise machined) according to conventional approaches. Base  6 , blade  8  and shroud  10  may be integrally formed (e.g., cast, forged, three-dimensionally printed, etc.), or may be formed as separate components which are subsequently joined (e.g., via welding, brazing, bonding or other coupling mechanism). 
     In particular,  FIG. 2  shows blade  8  which includes a body  12 , e.g., an outer casing or shell. The body  12  ( FIGS. 1-2 ) has a pressure side  14  and a suction side  16  opposing pressure side  14  (suction side  16  obstructed in  FIG. 2 ). Body  12  also includes a leading edge  18  between pressure side  14  and suction side  16 , as well as a trailing edge  20  between pressure side  14  and suction side  16  on a side opposing leading edge  18 . As seen in  FIG. 2 , bucket  2  also includes a plurality of radially extending cooling passageways  22  within body  12 . These radially extending cooling passageways  22  can allow cooling fluid (e.g., air) to flow from a radially inner location (e.g., proximate base  6 ) to a radially outer location (e.g., proximate shroud  10 ). The radially extending cooling passageways  22  can be fabricated along with body  12 , e.g., as channels or conduits during casting, forging, three-dimensional (3D) printing, or other conventional manufacturing technique. 
     As shown in  FIG. 2 , in some cases, shroud  10  includes a plurality of outlet passageways  30  extending from body  12  to radially outer region  28 . Outlet passageways  30  are each fluidly coupled with a first set  200  of the radially extending cooling passageway  22 , such that cooling fluid flowing through corresponding radially extending cooling passageway(s)  22  (in first set  200 ) exits body  12  through outlet passageways  30  extending through shroud  10 . In various embodiments, as shown in  FIG. 2 , outlet passageways  30  are fluidly isolated from a second set  210  (distinct from first set  200 ) of radially extending cooling passageways  22 . That is, as shown in  FIG. 2 , in various embodiments, shroud  10  includes and outlet path  220  extending at least partially circumferentially through shroud  10  and fluidly connected with all of second set  210  of radially extending cooling passageways  22  in body  12 . Shroud  10  includes outlet path  220  which provides an outlet for a plurality (e.g., 2 or more, forming second set  210 ) of radially extending cooling passageways  22 , and provides a fluid pathway isolated from radially extending cooling passageways  22  in first set  200 . 
     As seen in  FIGS. 1 and 2 , shroud  10  can include a rail  230  delineating an approximate mid-point between a leading half  240  and a trailing half  250  of shroud  10 . In various embodiments, an entirety of cooling fluid passing through second set  210  of radially extending cooling passageways  22  exits body  12  through outlet path  220 . In various embodiment, first set  200  of radially extending cooling passageways  22  and outlet path  220  outlet to location  28  radially outboard of shroud  10 . In some cases, outlet path  220  is fluidly connected with a pocket  260  within body  12  of blade  8 , where pocket  260  provides a fluid passageway between second set  210  of radially extending cooling passageways  22  and outlet path  220  in shroud  10 . 
       FIG. 3  shows a partially transparent three-dimensional perspective view of bucket  2 , depicting various features. It is understood, and more clearly illustrated in  FIG. 3 , that outlet path  220 , which is part of shroud  10 , is fluidly connected with pocket  260 , such that pocket  260  may be considered an extension of outlet path  220 , or vice versa. Further, pocket  260  and outlet path  220  may be formed as a single component (e.g., via conventional manufacturing techniques). It is further understood that the portion of shroud  10  at leading half  240  may have a greater thickness (measured radially) than the portion of shroud  10  at trailing half  250 , for example, in order to accommodate for outlet path  220 . 
     According to various additional embodiments described herein and shown in  FIG. 4 , a bucket  302  can further include a plenum  36  within body  12 , where plenum  36  is fluidly connected with the first set  200  of plurality of radially extending cooling passageways  22  and, at least one bleed aperture(s)  24 . Plenum  36  can provide a mixing location for cooling flow from first set  200  of radially extending cooling passageways  22 , and may outlet to trailing edge  20  through bleed apertures  24 . Plenum  36  can fluidly isolate first set  200  of radially extending cooling passageways  22  from second set  210  of radially extending cooling passageways  22 , thus isolating first set  200  from outlet path  220 . In some cases, as shown in  FIG. 4 , plenum  36  can have a trapezoidal cross-sectional shape within body  12  (when cross-section is taken through pressure side face), such that it has a longer side at the trailing edge  20  than at an interior, parallel side. According to various embodiments, plenum  36  extends approximately 3 percent to approximately 30 percent of a length of trailing edge  20 . Bleed apertures  24  in bucket  302  (several shown), as noted herein, can extend through body  12  at trailing edge  20 , and fluidly couple first set  200  of radially extending cooling passageways  22  with an exterior region  26  proximate trailing edge  20 . In additional contrast to conventional buckets, bucket  302  includes bleed apertures  24  which extend through body  12  at trailing edge  20 , in a location proximate (e.g., adjacent) shroud  10  (but radially inboard of shroud  10 ). In various embodiments, bleed apertures  24  extend along approximately 3 percent to approximately 30 percent of trailing edge  20  toward base  6 , as measured from the junction of blade  8  and shroud  10  at trailing edge  20 . 
       FIG. 5  shows a partially transparent three-dimensional perspective view of bucket  302 , depicting various features. It is understood, and more clearly illustrated in  FIG. 5 , that outlet path  220 , which is part of shroud  10 , is fluidly connected with pocket  260 , such that pocket  260  may be considered an extension of outlet path  220 , or vice versa. Further, pocket  260  and outlet path  220  may be formed as a single component (e.g., via conventional manufacturing techniques). It is further understood that the portion of shroud  10  at leading half  240  may have a greater thickness (measured radially) than the portion of shroud  10  at trailing half  250 , for example, in order to accommodate for outlet path  220 . 
       FIG. 6  shows a close-up schematic cross-sectional depiction of an additional bucket  602  according to various embodiments. Bucket  602  can include outlet passageways  30  located on both circumferential sides of outlet path  220 , that is, outlet path  220  is located between adjacent outlet passageways  30  in shroud  10 . In this configuration, shroud  10  can include a second rail  630 , located within leading half  240  of shroud. Outlet path  220  can extend from second rail  630  to rail  230 , and exit at trailing half  250  of shroud proximate outlet passageways  30  at trailing half  250 . 
     In contrast to conventional buckets, buckets  2 ,  302 ,  602  having outlet path  220  allow for high-velocity cooling fluid to be ejected from shroud  10  beyond rail  230  (circumferentially past rail  230 , or, downstream of rail  230 ), aligning with the direction of hot gasses flowing proximate trailing edge  12 . Similar to the hot gasses, the reaction force of cooling flow ejecting from shroud  10  (via outlet path  220 ) can generate a reaction force on bucket  2 ,  302 ,  602 . This reaction force can increase the overall torque on bucket  2 ,  302 ,  602 , and increase the mechanical shaft power of a turbine employing bucket  2 ,  302 ,  602 . In the radially outboard region of shroud  10 , static pressure is always lower in trailing half region  250  than leading half region  240 . The cooling fluid pressure ratio is defined as a ratio of delivery pressure of cooling fluid at base  6  to the ejection pressure at the hot gas path proximate radially outboard location  28  (referred to as “sink pressure”). While there are specific cooling fluid pressure ratio requirements for buckets in gas turbines, reduction in the sink pressure can reduce the requirement for higher-pressure cooling fluid at the inlet proximate base  6 . Bucket  2 ,  302 ,  602 , including outlet path  220  can reduce sink pressure when compared with conventional buckets, thus requiring a lower supply pressure from the compressor to maintain a same pressure ratio. This reduces the work required by the compressor (to compress cooling fluid), and improves efficiency in a gas turbine employing bucket  2 ,  302 ,  602  relative to conventional buckets. Even further, buckets  2 ,  302 ,  602  can aid in reducing mixing losses in a turbine employing such buckets. For example mixing losses in radially outer region  28  that are associated with mixing of cooling flow and tip leakage flow that exist in conventional configurations are greatly reduced by the directional flow of cooling fluid exiting outlet path  220 . Further, cooling fluid exiting outlet path  220  is aligned with the direction of hot gas flow, reducing mixing losses between cold/hot fluid flow. Outlet path  220  can further aid in reducing mixing of cooling fluid with leading edge hot gas flows (when compared with conventional buckets), where rail  230  acts as a curtain-like mechanism. Outlet path  220  can circulate the cooling fluid through the tip shroud  10 , thereby reducing neighboring metal temperatures when compared with conventional buckets. With the continuous drive to increase firing temperatures in gas turbines, buckets  2 ,  302 ,  602  can enhance cooling in turbines employing such buckets, allowing for increased firing temperatures and greater turbine output. 
       FIG. 7  shows a schematic partial cross-sectional depiction of a turbine  400 , e.g., a gas turbine, according to various embodiments. Turbine  400  includes a stator  402  (shown within casing  404 ) and a rotor  406  within stator  402 , as is known in the art. Rotor  406  can include a spindle  408 , along with a plurality of buckets (e.g., buckets  2 ,  302  and/or  602 ) extending radially from spindle  408 . It is understood that buckets (e.g., buckets  2 ,  302  and/or  602 ) within each stage of turbine  400  can be substantially a same type of bucket (e.g., bucket  2 ). In some cases, buckets (e.g., buckets  2 ,  302  and/or  602 ) can be located in a mid-stage within turbine  400 . That is, where turbine  400  includes four (4) stages (axially dispersed along spindle  408 , as is known in the art), buckets (e.g., buckets  2 ,  302  and/or  602 ) can be located in a second stage (stage  2 ), third stage (stage  3 ) or fourth stage (stage  4 ) within turbine  400 , or, where turbine  400  includes five (5) stages (axially dispersed along spindle  408 ), buckets (e.g., buckets  2 ,  302  and/or  602 ) can be located in a third stage (stage  3 ) within turbine  400 . 
     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. 
     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 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 languages of the claims.