Patent Publication Number: US-11391166-B2

Title: Dovetail slot for use with rotor assemblies

Description:
BACKGROUND 
     The present disclosure relates generally to a rotor assembly and more particularly relates to a rotor assembly including intentionally frequency mistuned turbine buckets. 
     A turbine bucket, also known as a rotating turbine blade or turbine rotor blade, converts energy from a flowing fluid such as hot combustion gas or steam into mechanical energy by causing a shaft of a turbomachine to rotate. As the turbomachine transitions through various operating modes, the turbine blades are subjected to both mechanical and thermal stresses. 
     Steam turbine buckets are operated in an environment where they are subject to high centrifugal loads and vibratory stresses. In the process of operation, flutter, i.e., self-excited vibrations of turbine buckets, can lead to catastrophic failures in turbine components. Flutter is an aero-elastic instability that results from coupling between aerodynamic and inertial forces. This interaction causes unsteady aerodynamic forces acting on the turbine buckets, which leads to vibrations. The vibrations may cause structural failure. As such, the flow rate and pressure of steam turbine are limited to prevent flutter, which restricts the power output and efficiency of steam turbine. 
     One known method for reducing flutter is to change the natural frequency of turbine buckets by precisely removing material from one of two adjacent turbine buckets, which requires expensive machining of the turbine buckets, results in wasted raw material and reduces the efficiency of the steam turbine. 
     Thus, an improved rotor assembly, for example, a rotor assembly including improved intentionally frequency mistuned turbine buckets, would be desired in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of an exemplary opposed-flow steam turbine according to one embodiment of the present disclosure. 
         FIG. 2  is an illustration of a portion of an exemplary turbine wheel used in the steam turbine of  FIG. 1 , according to one embodiment of the present disclosure. 
         FIG. 3  is a schematic view of an exemplary first dovetail slot according to one embodiment of the present disclosure. 
         FIG. 4  is a schematic view of an exemplary second dovetail slot according to one embodiment of the present disclosure. 
         FIG. 5  is a schematic view of an exemplary second dovetail slot according to another embodiment of the present disclosure. 
         FIG. 6  is an illustration of a portion of an exemplary rotor assembly according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the present disclosure will be described below. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this disclosure belongs. The terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, are not to be limited to the precise value specified. Additionally, when using an expression of “about a first value-a second value,” the about is intended to modify both values. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here, and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
       FIG. 1  is a schematic illustration of an exemplary opposed-flow steam turbine  10 . The steam turbine  10  includes first and second low pressure (LP) sections  12  and  14 . As is known in the art, each of turbine sections  12  and  14  includes a plurality of stages of diaphragms (not shown in  FIG. 1 ). A rotor shaft  16  extends through first and second low pressure (LP) sections  12  and  14 . Each of LP sections  12  and  14  includes a nozzle  18  and  20 . A single outer shell or casing  22  is divided along a horizontal plane and axially into upper and lower half sections  24  and  26 , respectively, and spans both first and second low pressure (LP) sections  12  and  14 . A central section  28  of single outer shell or casing  22  includes a low pressure steam inlet  30 . Within the single outer shell or casing  22 , first and second low pressure (LP) sections  12  and  14  are arranged in a single bearing span supported by journal bearings  32  and  34 . A flow splitter  40  extends between the first and second turbine sections  12  and  14 . 
     During operation, the low pressure steam inlet  30  receives low pressure/intermediate temperature steam  50  from a source, such as, but not limited to, an HP turbine or IP turbine through a cross-over pipe (not shown). The steam  50  is channeled through the inlet  30  wherein the flow splitter  40  splits the steam flow into two opposite flow paths  52  and  54 . More specifically, in the exemplary embodiment, the steam  50  is routed through LP sections  12  and  14  wherein work is extracted from the steam  50  to rotate rotor shaft  16 . The steam  50  exits LP sections  12  and  14  and is routed to a condenser, for example. 
     It should be noted that although  FIG. 1  illustrates an opposed-flow, low pressure turbine, as will be appreciated by one of ordinary skill in the art, the present invention is not limited to being used only with low pressure turbines and can be used with any opposed-flow turbine including, but not limited to intermediate pressure (IP) turbines and/or high pressure (HP) turbines. In addition, the present invention is not limited to only being used with opposed-flow turbines, but rather may also be used with single flow steam turbines as well, for example. 
       FIG. 2  is an illustration of a portion of an exemplary turbine wheel  200  that may be used in the steam turbine  10 . The turbine wheel  200  includes a plurality of first dovetail slots  300  and a plurality of second dovetail slots  100  different from the first dovetail slot  300 . More specifically, the plurality of first dovetail slots  300  and the plurality of second dovetail slots  100  are alternately spaced circumferentially on a radially outer periphery of the turbine wheel  200 , and are shaped and sized to receive an attachment portion therein. 
       FIG. 3  is a schematic view showing the first dovetail slot  300  in greater detail. In the exemplary embodiment, the first dovetail slot  300  is symmetric about a centerline  302 . Alternative embodiments may alter the location of each element described below in relation to the centerline  302 . The first dovetail slot  300  includes a plurality of hook fillets and a plurality of neck fillets. In some embodiments, the first dovetail slot may include three, four, five or more neck fillets and hook fillets. Specifically, in the exemplary embodiment, the first dovetail slot  300  includes a first top hook fillet  310 , a first top neck fillet  320 , a first bottom hook fillet  312 , a first bottom neck fillet  322  and a first bottom flat surface  330  arranged from top to bottom. 
     In the exemplary embodiment, the first top neck fillet  320  is formed with a radius  340 . In the exemplary embodiment, the radius  340  measures between 1.690 millimeters (mm) and 2.706 mm or, more specifically, approximately 2.198 mm. The first bottom neck fillet  322  is formed with a compound radius  342 . In the exemplary embodiment, the compound radius  342  includes two radii  344  and  346 . Specifically, in the exemplary embodiment, the radius  344  measures between 1.69 millimeters (mm) and 2.706 mm or, more specifically, approximately 2.198 mm. The radius  346  measures between 5.776 millimeters (mm) and 10.348 mm or, more specifically, approximately 8.062 mm. In alternative embodiments, the first top neck fillet or first bottom neck fillet may include different radius measurements, or the first bottom neck fillet may include only a single radius. 
     In the exemplary embodiment, the first top hook fillet  310  includes a radius  350  which, in the exemplary embodiment, measures between 1.255 millimeters (mm) and 5.827 mm or, more specifically, approximately 3.541 mm. Alternative embodiments may use a different radius for the first top hook fillet  310 . Radius  350  is designed to facilitate a smooth transition between the first dovetail slot  300  and a turbine wheel surface  304 . The first bottom hook fillet  312  is formed with two identical radii  352  and a flat surface  354  extending therebetween. In the exemplary embodiment, each radius  352  measures between 0.425 millimeters (mm) and 1.441 mm or, more specifically, approximately 0.933 mm. The flat surface  354  measures between 0.500 millimeters (mm) and 3.707 mm or, more specifically, approximately 0.663 mm. Alternative embodiments may use one or more flat surfaces having different lengths. Further, alternative embodiments may use a different radius or may use two different radii. 
     In some embodiments, the first dovetail slot  300  may further include a first middle hook fillet  314  and a first middle neck fillet  324 , arranged from top to bottom between the first top neck fillet  320  and the first bottom hook fillet  312 . The first middle neck fillet  324  is formed with a radius  360 . In the exemplary embodiment, the radius  360  is identical and measures between 1.690 millimeters (mm) and 2.706 mm or, more specifically, approximately 2.198 mm. Alternative embodiments may vary the radius of each neck. The first middle hook fillet  314  is formed with two identical radii  370  and a flat surface  372  extending therebetween. In the exemplary embodiment, each radius  370  measures between 1.604 millimeters (mm) and 2.62 mm or, more specifically, approximately 2.112 mm. The flat surface  372  measures between 0.250 millimeters (mm) and 3.393 mm or, more specifically, approximately 0.853 mm. Alternative embodiments may use one or more flat surfaces having a different length. Further, alternative embodiments may use a different radius or may use two different radii. 
     The second dovetail slot  100  in wheel  200  of  FIG. 2  may be formed in various configurations. For example,  FIG. 4  is a schematic view of an exemplary second dovetail slot  400 , as a specific embodiment of the second dovetail slot  100  in  FIG. 2 . In the exemplary embodiment, the second dovetail slot  400  is symmetric about centerline  402 . Alternative embodiments may alter the location of each element described below in relation to centerline  402 . The second dovetail slot  400  includes a plurality of hook fillets and a plurality of neck fillets. In some embodiments, the second dovetail slot may include three, four, five or more neck fillets and hook fillets. Specifically, in the exemplary embodiment, the second dovetail slot  400  includes a second top hook fillet  410 , a second top neck fillet  420 , a second bottom hook fillet  412 , a second bottom neck fillet  422  and a second bottom flat surface  430  arranged from top to bottom. The second dovetail slot  400  may further include a second middle hook fillet  414  and a second middle neck fillet  424 , the second middle hook fillet  414  and the second middle neck fillet  424  arranged from top to bottom between the second top neck fillet  420  and the second bottom hook fillet  412 . The geometric construction of the second dovetail slot  400  is similar to the first dovetail slot  300 . 
     In the illustrated example as shown in  FIGS. 3 &amp; 4 , a top hook opening width difference between a minimum opening width  380  of the first top hook fillet  310  and a minimum opening width  480  of the second top hook fillet  410  being linear to a bottom hook opening width difference between a minimum opening width  382  of the first bottom hook fillet  312  and a minimum opening width  482  of the second bottom hook fillet  412 . In some embodiments, the top hook opening width difference is linear to a middle hook opening width difference between a minimum opening width  384  of the first middle hook fillet  314  and a minimum opening width  484  of the second middle hook fillet  414 . 
     In some embodiments, a top neck opening width difference between a maximum opening width  390  of the first top neck fillet  320  and a maximum opening width  490  of the second top neck fillet  420  is linear to a bottom neck opening width difference between a maximum opening width  392  of the first bottom neck fillet  322  and a maximum opening width  492  of the second bottom neck fillet  422 . In some embodiments, the top neck opening width difference is linear to a middle neck opening width difference between a maximum opening width  394  of the first middle neck fillet  324  and a maximum opening width  494  of the second middle neck fillet  424 . 
     In some embodiments, the hook opening width difference is linear to the top neck opening width difference. 
     In some embodiments, the top hook opening width difference is linear to a bottom surface width difference between a width of the first bottom flat surface  330  and a width of the second bottom flat surface  430 . 
     In the exemplary embodiment, the top hook opening width difference, the middle hook opening width difference and the bottom hook opening width difference are equal. In some embodiments, the top neck opening width difference, the middle neck opening width difference, and the bottom neck opening width difference are equal. 
     Further, two of the top hook opening width difference, the middle hook opening width difference, the bottom hook opening width difference, the top neck opening width difference, the middle neck opening width difference, the bottom neck opening width difference and the bottom surface width difference may be equal in some embodiments. In the exemplary embodiment, all the differences are between 2 millimeters (mm) and 20 mm or, more specifically, approximately 10 mm, or approximately 5 mm. 
       FIG. 5  is a schematic view of an exemplary second dovetail slot  500 , as another specific embodiment of the second dovetail slot  100  in  FIG. 2 . In the exemplary embodiment, the second dovetail slot  500  is symmetric about centerline  502 . Alternative embodiments may alter the location of each element described below in relation to centerline  502 . The second dovetail slot  500  includes a plurality of hook fillets and a plurality of neck fillets. In some embodiments, the second dovetail slot may include three, four, five or more neck fillets and hook fillets. Specifically, in the exemplary embodiment, the second dovetail slot  500  includes a second top hook fillet  510 , a second top neck fillet  520 , and a second bottom portion  540  arranged from top to bottom, the second bottom portion  540  comprising a second bottom hook fillet  512 , a second bottom neck fillet  522  and a second bottom flat surface  530  arranged from top to bottom. The geometric construction of the second dovetail slot  500  is similar to the first dovetail slot  300 . 
     In the illustrated example as shown in  FIGS. 3 &amp; 5 , the second bottom portion  540  being geometrically substantially same as the bottom portion of the first dovetail slot  300 , and the second top hook fillet  510  being geometrically difference from the first top hook fillet  310  of the first dovetail slot  300 . In some embodiments, a minimum opening width  380  of the first top hook fillet  310  is difference from the minimum opening width  580  of the second top hook fillet  510 . In some embodiments, a height  396  of the first top hook fillet  310  is difference from a height  596  of the second top hook fillet  510 . 
       FIG. 6  is an illustration of a portion of an exemplary rotor assembly  600  that may be used with the turbine wheel  200 , a plurality of first turbine buckets  700  and a plurality of second turbine buckets  800 . The first turbine buckets and the second turbine buckets may be free-standing buckets. The first turbine bucket  700  includes a first dovetail, a first airfoil portion and a first root extending between the first airfoil portion and the first root, the first turbine bucket  700  is coupled within the first dovetail slot  300 . The second turbine bucket  800  includes a second dovetail, a second airfoil portion and a second root extending between the second airfoil portion and the second root, the second turbine bucket  800  is coupled within the second dovetail slot  100 . 
     This written description uses examples to describe the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure 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. Various aspects and embodiments of the present invention will now be defined by the following numbered clauses: 
     1. A turbine wheel ( 200 ), comprising: 
     a plurality of first dovetail slots ( 300 ), at least one of the plurality of first dovetail slots ( 300 ) comprising a first top hook fillet ( 310 ), a first top neck fillet ( 320 ), a first bottom hook fillet ( 312 ), a first bottom neck fillet ( 322 ) and a first bottom flat surface ( 330 ) arranged from top to bottom; and
 
a plurality of second dovetail slots ( 100 ,  400 ,  500 ), at least one of the plurality of second dovetail slots ( 100 ,  400 ,  500 ) comprising a second top hook fillet ( 410 ,  510 ), a second top neck fillet ( 420 ,  520 ), a second bottom hook fillet ( 412 ,  512 ), a second bottom neck fillet ( 422 ,  522 ) and a second bottom flat surface ( 430 ,  530 ) arranged from top to bottom; wherein the plurality of first dovetail slots ( 300 ) and the plurality of second dovetail slots ( 100 ,  400 ,  500 ) are alternately spaced circumferentially on a radially outer periphery of the turbine wheel ( 200 ), and a top hook opening width difference between a minimum opening width ( 380 ) of the first top hook fillet ( 310 ) and a minimum opening width ( 480 ,  580 ) of the second top hook fillet ( 410 ,  510 ) being linear to a bottom hook opening width difference between a minimum opening width ( 382 ) of the first bottom hook fillet ( 312 ) and a minimum opening width ( 482 ) of the second bottom hook fillet ( 412 ,  512 ).
 
2. The turbine wheel ( 200 ) of clause  1 , wherein at least one of the plurality of first dovetail slots ( 300 ) further comprising a first middle hook fillet ( 314 ) and a first middle neck fillet ( 324 ), the first middle hook fillet ( 314 ) and the first middle neck fillet ( 324 ) arranged from top to bottom between the first top neck fillet ( 320 ) and the first bottom hook fillet ( 312 ).
 
3. The turbine wheel ( 200 ) of clause  2 , wherein at least one of the plurality of second dovetail slots ( 100 ,  400 ,  500 ) further comprising a second middle hook fillet ( 414 ) and a second middle neck fillet ( 424 ), the second middle hook fillet ( 414 ) and the second middle neck fillet ( 424 ) arranged from top to bottom between the second top neck fillet ( 420 ,  520 ) and the second bottom hook fillet ( 412 ,  512 ).
 
4. The turbine wheel ( 200 ) of clause  3 , wherein the top hook opening width difference is linear to a middle hook opening width difference between a minimum opening width ( 384 ) of the first middle hook fillet ( 314 ) and a minimum opening width ( 484 ) of the second middle hook fillet ( 414 ).
 
5. The turbine wheel ( 200 ) of clause  1 , wherein a top neck opening width difference between a maximum opening width ( 390 ) of the first top neck fillet ( 320 ) and a maximum opening width ( 490 ) of the second top neck fillet ( 420 ,  520 ) is linear to a bottom neck opening width difference between a maximum opening width ( 392 ) of the first bottom neck fillet ( 322 ) and a maximum opening width ( 492 ) of the second bottom neck fillet ( 422 ,  522 ).
 
6. The turbine wheel ( 200 ) of clause  3 , wherein a top neck opening width difference between a maximum opening width ( 390 ) of the first top neck fillet ( 320 ) and a maximum opening width ( 490 ) of the second top neck fillet ( 420 ,  520 ) is linear to a middle neck opening width difference between a maximum opening width ( 394 ) of the first middle neck fillet ( 324 ) and a maximum opening width ( 494 ) of the second middle neck fillet ( 424 ).
 
7. The turbine wheel ( 200 ) of clause  1 , wherein the top hook opening width difference is linear to a top neck opening width difference between a maximum opening width ( 390 ) of the first top neck fillet ( 320 ) and a maximum opening width ( 490 ) of the second top neck fillet ( 420 ,  520 ).
 
8. The turbine wheel ( 200 ) of clause  1 , wherein the top hook opening width difference is linear to a bottom surface width difference between a width of the first bottom flat surface ( 330 ) and a width of the second bottom flat surface ( 430 ,  530 ).
 
9. The turbine wheel ( 200 ) of clause  4 , wherein the top hook opening width difference, the middle hook opening width difference and the bottom hook opening width difference are equal.
 
10. The turbine wheel ( 200 ) of clause  1 , wherein the turbine wheel ( 200 ) is in a steam turbine ( 10 ).
 
11. A rotor assembly ( 600 ), comprising:
 
a plurality of first turbine buckets ( 700 ), at least one of the plurality of first turbine buckets ( 700 ) comprising a first dovetail, a first airfoil portion and a first root extending between the first airfoil portion and the first root;
 
a plurality of second turbine buckets ( 800 ), at least one of the plurality of second turbine buckets ( 800 ) comprising a second dovetail, a second airfoil portion and a second root extending between the second airfoil portion and the second root;
 
a turbine wheel ( 200 ) for use with the turbine buckets ( 700 ,  800 ), the turbine wheel ( 200 ) comprising:
 
a plurality of first dovetail slots ( 300 ), at least one of the plurality of first dovetail slots ( 300 ) comprising a first top hook fillet ( 310 ), a first top neck fillet ( 320 ), a first bottom hook fillet ( 312 ), a first bottom neck fillet ( 322 ) and a first bottom flat surface ( 330 ) arranged from top to bottom; and
 
a plurality of second dovetail slots ( 100 ,  400 ,  500 ), at least one of the plurality of second dovetail slots ( 100 ,  400 ,  500 ) comprising a second top hook fillet ( 410 ,  510 ), a second top neck fillet ( 420 ,  520 ), a second bottom hook fillet ( 412 ,  512 ), a second bottom neck fillet ( 422 ,  522 ) and a second bottom flat surface ( 430 ,  530 ) arranged from top to bottom; wherein the plurality of first dovetail slots ( 300 ) and the plurality of second dovetail slots ( 100 ,  400 ,  500 ) are alternately spaced circumferentially on a radially outer periphery of the turbine wheel ( 200 ), and a top hook opening width difference between a minimum opening width ( 380 ) of the first top hook fillet ( 310 ) and a minimum opening width ( 480 ,  580 ) of the second top hook fillet ( 410 ,  510 ) being linear to a bottom hook opening width difference between a minimum opening width ( 382 ) of the first bottom hook fillet ( 312 ) and a minimum opening width ( 482 ) of the second bottom hook fillet ( 412 ,  512 );
 
wherein the first turbine bucket ( 700 ) is coupled within the first dovetail slot ( 300 ), and the second turbine bucket ( 800 ) is coupled within the second dovetail slot ( 100 ,  400 ,  500 ).
 
12. The rotor assembly ( 600 ) of clause  11 , wherein at least one of the plurality of first dovetail slots ( 300 ) further comprising a first middle hook fillet ( 314 ) and a first middle neck fillet ( 324 ), the first middle hook fillet ( 314 ) and the first middle neck fillet ( 324 ) arranged from top to bottom between the first top neck fillet ( 320 ) and the first bottom hook fillet ( 312 ).
 
13. The rotor assembly ( 600 ) of clause  11 , wherein at least one of the plurality of second dovetail slots ( 100 ,  400 ,  500 ) further comprising a second middle hook fillet ( 414 ) and a second middle neck fillet ( 424 ), the second middle hook fillet ( 414 ) and the second middle neck fillet ( 424 ) arranged from top to bottom between the second top neck fillet ( 420 ,  520 ) and the second bottom hook fillet ( 412 ,  512 ).
 
14. The rotor assembly ( 600 ) of clause  13 , wherein the top hook opening width difference is linear to a middle hook opening width difference between a minimum opening width ( 384 ) of the first middle hook fillet ( 314 ) and a minimum opening width ( 484 ) of the second middle hook fillet ( 414 ).
 
15. The rotor assembly ( 600 ) of clause  11 , wherein the top hook opening width difference, the bottom hook opening width difference and a middle hook opening width difference between a minimum opening width ( 384 ) of the first middle hook fillet ( 314 ) and a minimum opening width ( 484 ) of the second middle hook fillet ( 414 ) are equal.
 
16. The rotor assembly ( 600 ) of clause  11 , wherein the first turbine buckets ( 700 ) and the second turbine buckets ( 800 ) are free-standing buckets.
 
17. The rotor assembly ( 600 ) of clause  11 , wherein the rotor assembly ( 600 ) is in a steam turbine ( 10 ).
 
18. A turbine wheel ( 200 ), comprising:
 
a plurality of first dovetail slots ( 300 ), at least one of the plurality of first dovetail slots ( 300 ) comprising a first top hook fillet ( 310 ), a first top neck fillet ( 320 ), and a first bottom portion arranged from top to bottom, the first bottom portion comprising a first bottom hook fillet ( 312 ), a first bottom neck fillet ( 322 ) and a first bottom flat surface ( 330 ) arranged from top to bottom; and
 
a plurality of second dovetail slots ( 100 ,  400 ,  500 ), at least one of the plurality of second dovetail slots ( 100 ,  400 ,  500 ) comprising a second top hook fillet ( 410 ,  510 ), a second top neck fillet ( 420 ,  520 ), and a second bottom portion ( 540 ) arranged from top to bottom, the second bottom portion ( 540 ) comprising a second bottom hook fillet ( 412 ,  512 ), a second bottom neck fillet ( 422 ,  522 ) and a second bottom flat surface ( 430 ,  530 ) arranged from top to bottom;
 
wherein the plurality of first dovetail slots ( 300 ) and the plurality of second dovetail slots ( 100 ,  400 ,  500 ) are alternately spaced circumferentially on a radially outer periphery of the turbine wheel ( 200 ), the first bottom portion being geometrically substantially same as the second bottom portion ( 540 ), and the a first top hook fillet ( 310 ) being geometrically difference from the second top hook fillet ( 410 ,  510 ).
 
19. The turbine wheel ( 200 ) of clause  18 , wherein a minimum opening width ( 380 ) of the first top hook fillet ( 310 ) is difference from a minimum opening width ( 480 ,  580 ) of the second top hook fillet ( 410 ,  510 ).
 
20. The turbine wheel ( 200 ) of clause  18 , wherein a height of the first top hook fillet ( 310 ) is difference from a height of the second top hook fillet ( 410 ,  510 ).