Abstract:
An axial flow gas turbine ( 20 ) includes a rotor ( 13 ) and a stator, and a hot gas path through which hot gas passes. The rotor ( 13 ) includes a rotor shaft ( 15 ) with axial slots for receiving a plurality of blades (B 1 -B 3 ) arranged in a series of blade rows, with rotor heat shields (R 1 , R 2 ) interposed between adjacent blade rows. The rotor shaft ( 15 ) is configured to axially conduct a main flow of cooling air along the rotor heat shields (R 1 , R 2 ) and the lower parts of the blades (B 1 -B 3 ), and the rotor shaft ( 15 ) supplies the interior of the blades (B 1 -B 3 ) with cooling air ( 18 ). Stable and predictable cooling air parameters at any blade row inlet are secured by providing air-tight cooling channels ( 21 ), which extend axially through the rotor shaft ( 15 ) separate from the main flow of cooling air ( 17 ), and supply the blades (B 1 -B 3 ) with cooling air ( 18 ).

Description:
This application claims priority under 35 U.S.C. §119 to Russian Federation application no. 2010148730, filed 29 Nov. 2010, the entirety of which is incorporated by reference herein. 
     BACKGROUND 
     1. Field of Endeavor 
     The present invention relates to the technology of gas turbines, and more specifically to a gas turbine of the axial flow type. 
     2. Brief Description of the Related Art 
     A gas turbine is composed of a stator and a rotor. The stator constitutes a casing with stator heat shields and vanes installed in it. The turbine rotor, arranged coaxially within the stator casing, includes a rotating shaft with axial slots of fir-tree type used to install blades. Several blade rows and rotor heat shields are installed therein, alternating. Hot gas formed in a combustion chamber passes through profiled channels between the vanes, and, when striking against the blades, makes the turbine rotor rotate. 
     For the gas turbine to operate with a sufficient efficiency it is essential to work with a very high hot gas temperature. Accordingly, the components of the hot gas channel, especially the blades, vanes and heat shields, of the turbine experience a very high thermal load. Furthermore, the blades are at the same time subject to a very high mechanical stress caused by the centrifugal forces at high rotational speeds of the rotor. 
     Therefore, it is of essential importance to cool the thermally loaded components of the hot gas channel of the gas turbine. 
     In the prior art, it has been proposed to provide channels for a blade cooling medium within the rotor shaft itself (see for example EP 909 878 A2 or EP 1 098 067 A2 or U.S. Pat. No. 6,860,110 B2). However, such a cooling configuration requires the complex and costly machining of the rotor or rotor disks. 
     A different cooling scheme according to the prior art is shown in  FIG. 1 . The gas turbine  10  of  FIG. 1  includes a plurality of stages the first three of which are shown in the Figure. The gas turbine  10  includes a rotor  13 , which rotates around a central machine axis, not shown. The rotor  13  has a rotor shaft  15  with axial slots of the fir-tree type used to install a plurality of blades B 1 , B 2  and B 3 . The blades B 1 , B 2  and B 3  of  FIG. 1  are arranged in three blade rows. Interposed between adjacent blade rows are rotor heat shields R 1  and R 2 . The blades B 1 , B 2 , B 3  and the rotor heat shields are evenly distributed around the circumference of the rotor shaft  15 . Each of the blades B 1 , B 2  and B 3  has an inner platform, which—together with the respective platforms of the other blades of the same row—constitutes a closed ring around the machine axis. 
     The inner platforms of blades B 1 , B 2  and B 3  in combination with the rotor heat shields R 1  and R 2  form an inner outline of the turbine flow path or hot gas path  12 . At the outer side, the hot gas path  12  is bordered by the surrounding stator  11  with its stator heat shields  51 , S 2  and S 3  and vanes V 1 , V 2  and V 3 . The inner outline separates a rotor cooling air transit cavity, which conducts a main flow of cooling air  17 , from the hot gas flow within the hot gas path  12 . To improve tightness of the cooling air flow path, sealing plates  19  are installed between adjacent blades B 1 -B 3  and rotor heat shields R 1 , R 2 . 
     As can be seen from  FIG. 1 , air cools the rotor shaft  15  when flowing in the axial direction along the common flow path between blade necks of blades B 1 -B 3  and rotor heat shields R 1 , R 2 ; this air passes consecutively through the inner cavity of the blade B 1 , then in turn through blade B 2  and blade B 3  cavities. 
     However, blades contained in modern turbines operate under heavier conditions than vanes because they are, in addition to the effects of high temperatures and gas forces, subject to loads caused by centrifugal forces. To create an efficient blade having large life span, one should solve an intricate complex technical problem. 
     To solve this problem successfully, one should know the cooling air pressure at the blade inner cavity inlet as precisely as possible. Therefore a serious shortcoming of the rotor design presented in  FIG. 1  is that the cooling air pressure loss increases in an unpredictable way as this air passes from the first stage blade B 1  to the third stage blade B 3 . This is caused by air leakages into the turbine flow path  12  through slits between adjacent blades and rotor heat shields. This disadvantage prevents effectively cooled blades from being designed since total cross section area of the above-mentioned slits depends on a scatter of part manufacturing tolerances and on doubtful effectiveness of sealing plates  19 . 
     SUMMARY 
     One of numerous aspects of the present invention includes a gas turbine which can eliminate the aforementioned shortcomings and secures in a simple way stable and predictable cooling air parameters at any blade row inlet. 
     A gas turbine embodying principles of the present invention is of the axial flow type and comprises a rotor and a stator, which stator constitutes a casing surrounding the rotor, thereby providing a hot gas path, through which hot gas formed in a combustion chamber passes, whereby the rotor comprises a rotor shaft with axial slots, especially of the fir-tree type, for receiving a plurality of blades, which are arranged in a series of blade rows, with rotor heat shields interposed between adjacent blade rows, thereby forming an inner outline of the hot gas path, and whereby the rotor shaft is configured to conduct a main flow of cooling air in an axial direction along the rotor heat shields and the lower parts of the blades, and whereby the rotor shaft supplies the blades with cooling air entering the interior of the blades. 
     According to another aspect, air-tight cooling channels are provided which extend axially through the rotor shaft separate from the main flow of cooling air, and supply the blades with cooling air. 
     According to an exemplary embodiment, the stator comprises a vane carrier, wherein stator heat shields and vanes are installed, with the stator heat shields lying opposite to the blades and the vanes lying opposite to the rotor heat shields. 
     According to another exemplary embodiment, each blade row comprises the same definite number of blades in the same angular arrangement, and there is at least one air-tight cooling channel provided for one angular blade position of the blade rows, which air-tight cooling channel extends through the respective blades of all blade rows being arranged at the same angular position. 
     According to another exemplary embodiment, the air-tight cooling channels are established by coaxial cylindrical openings passing in the axial direction through the rotor heat shields and the lower parts of the blades, and by sleeves, which connect the openings of adjacent blades and rotor heat shields in an air-tight fashion. 
     Especially, air-tight cooling channels are closed at their ends by a plug. 
     According to another exemplary embodiment, the connecting sleeves are configured to allow a relative displacement of the parts being connected without losing air-tightness of the connection. 
     Especially, the connecting sleeves have at each end a spherical section on their outside, which allows the swiveling of the sleeves within a cylindrical opening similar to a ball joint. 
     According to another exemplary embodiment, the connecting sleeves are of reduced mass without sacrificing their stiffness by providing a plurality of circumferentially distributed axial ribs. 
     The axial ribs may be provided at the inner side of the connecting sleeves. 
     Alternatively, the axial ribs may be provided at the outer side of the connecting sleeves, whereby the radial height of the ribs is smaller than the radial height of the spherical sections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings. 
         FIG. 1  shows the first three stages of a known gas turbine, wherein the cooling air entering the blades is directly taken from the main flow of cooling air flowing along the rotor shaft; 
         FIG. 2  shows, in a drawing, which is equivalent to  FIG. 1 , a blade cooling configuration according to an embodiment of the invention; 
         FIG. 3  shows a perspective picture of the blade cooling configuration according to  FIG. 2 ; 
         FIG. 4  shows a magnified detail of the blade cooling configuration according to  FIG. 2 ; 
         FIG. 5  shows, in a reduced version of  FIG. 4 , the cutting plane A-A, along which the cross sections of  FIG. 6  and  FIG. 7  have been taken; 
         FIG. 6  shows a first cross section along the cutting plane A-A in  FIG. 5 ; 
         FIG. 7  shows a second cross section along the cutting plane A-A in  FIG. 5 ; 
         FIG. 8  shows two different views (a) and (b) of a first embodiment of the sleeve according to  FIG. 2-5 ; and 
         FIG. 9  shows a cross-sectional view of a second embodiment of the sleeve according to  FIG. 2-5 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 2  and  FIG. 3  show a gas turbine with a blade cooling configuration according to an exemplary embodiment of the invention. The gas turbine  20  of  FIG. 2  includes a plurality of stages, the first three of which are shown in the Figure. Similar to  FIG. 1 , the gas turbine  20  includes a rotor  13  with a rotor shaft  15  and the blades B 1 , B 2  and B 3 . The blades B 1 , B 2  and B 3  are again arranged in three blade rows. Interposed between adjacent blade rows are rotor heat shields R 1  and R 2 . The blades B 1 , B 2 , B 3  and the rotor heat shields are evenly distributed around the circumference of the rotor shaft  15 . Each of the blades B 1 , B 2  and B 3  has an inner platform, which—together with the respective platforms of the other blades of the same row—constitutes a closed ring around the machine axis. 
     The inner platforms of blades B 1 , B 2  and B 3 , in combination with the rotor heat shields R 1  and R 2 , form an inner outline of the turbine flow path or hot gas path  12 . Opposite to the rotor heat shields R 1  and R 2  are rows of vanes V 2  and V 3 . A first row of vanes V 1  is arranged at the entrance of the hot gas path, which is entered by the hot gas  16 . The inner outline separates a rotor cooling air transit cavity, which again conducts a main flow of cooling air  17 , from the hot gas flow within the hot gas path  12 . To improve tightness of the cooling air flow path, sealing plates  19  are installed between adjacent blades B 1 -B 3  and rotor heat shields R 1 , R 2 . 
     The basic difference and advantage of the proposed design according to  FIG. 2  is the availability of air-tight cooling channels  21  separated from the main cooling air flow  17  passing along the shaft  15 . The number of these cooling channels  21  corresponds to the number of blades B 1 , B 2  and B 3  in the circumferential direction in each of the blade rows. For this reason, the number of blades and the circumferential distribution of the blades is the same in each turbine stage or blade row (see  FIGS. 6 and 7 ). 
     The cooling channels  21  are used to separately supply the blades B 1 , B 2  and B 3  with cooling air. They are formed by providing coaxial cylindrical openings  28  passing through the blade B 1 , rotor heat shield R 1 , blade B 2 , rotor heat shield R 2 , and blade B 3 . Each channel  21  is terminated with a plug  24  mounted at the end of the corresponding opening  28  of blade B 3 . Air-tightness of channels  21  is reached by cylindrical sleeves  22 ,  23  (see  FIGS. 4 ,  5 ), which are each installed with one of its ends in a recess of a corresponding blade, and—with its other end—in a recess of the corresponding adjacent rotor heat shield. The sleeves  22 ,  23  are shaped so that they do not prevent adjacent parts from mutual radial and axial displacements (see  FIG. 4 ). 
     The openings  28  in blades B 1 -B 3  and rotor heat shields R 1 , R 2  are cylindrical. They are shaped so to provide minimum clearance within the contact zone between the recess and the cylindrical sleeves  22 ,  23  by machining. Thus, both overflow and mixing between main flow  17  and the flow in a channel  21  are prevented by a nearly zero clearance within the contact zones between sleeves  22 ,  23  on the one side, and blades B 1 -B 3  and rotor heat shields R 1 , R 2  on the another side. 
     Taking into consideration the above, the following advantages of the proposed design can be recognized: 
     1. No air leakages from blade cooling air supply channels  21  into the turbine flow path  12 . 
     2. Air from supplying channel  21  does not leak away and does not mix with the main cooling air flow  17  passing along the rotor shaft  15 . 
     3. There is a possibility for having influence on parameters of the cooling air supply for the blades B 1 -B 3  through variation of the inner diameter of the sleeves  22 ,  23 . 
     4. There is a possibility for having influence on the thermal state of the rotor shaft  15  due to control over air mass flow passing between blade necks of blades B 1 -B 3  and the rotor heat shields R 1 , R 2  (i.e., the main flow  17 , see  FIG. 2 ) regardless of intensity of the air flow passing along the blade supply channel  21 . Adjustment of the main air flow  17  can be implemented due to variation of both blade necks and rotor heat shield geometry in any blade row or ring of rotor heat shields (see  FIGS. 5-7 , where  FIG. 6  shows maximum area for the main flow  17  of cooling air and  FIG. 7  shows minimum area for the main flow  17  of cooling air). 
     Thus, the combination of blades B 1 -B 3  and rotor heat shields R 1 , R 2  with through channels (openings  28 ) and with sealing sleeves  22 ,  23  allows a modern high performance gas turbine to be created. 
     The proposed rotor design with longitudinal cooling air supply to blades B 1 -B 3  through a separate channel  21  according to  FIG. 2  has also an advantage as compared with the typical known design ( FIG. 1 ) because, with regard to point  4  above, it can be even used without mounting the sleeves  22 ,  23 . 
       FIG. 4  shows embodiments of sleeves, which provide a way for organization of a nearly air-tight channel  21  for cooling air transportation between the rotor parts. 
     Tightness of the channel  21  is attained by cylindrically shaped sockets made at the ends of openings  28  in adjacent rotor heat shields and blades. The cylindrical shape of the sockets has been chosen because such a socket can be manufactured by machining with high accuracy in the simplest manner. 
     When sockets made in adjacent parts are mutually displaced due to manufacturing inaccuracy or because of thermal displacements of the rotor heat shields and blades during turbine operation, spherical sections  25  at both ends of the sleeves  22 ,  23  make it possible to keep the channels  21  air-tight even when the sockets go out of alignment in both circumferential and radial directions. The spherical sections  25  at the ends of the sleeves  22 ,  23  can also be machined with high accuracy. 
     As distinct from stator parts of such type, the sleeves  22 ,  23  are subject to high centrifugal forces during turbine operation. Therefore it is advisable to reduce their weight since otherwise the respective sockets may be worn out gradually when being in contact with other parts during operation. To either reduce the weight without reducing stiffness or improve stiffness without increasing the weight, stiffness ribs may be provided at those sleeves. According to  FIG. 8 , those ribs  26  may be provided on the inner surface of the sleeves  22 ′. According to  FIG. 9 , such ribs  27  can be also arranged on the outer surface of the sleeves  23 ′. In this case the spherical sections  25  should have a greater radial height than the ribs  27 . 
     Merits of the proposed design may be summarized once again: 
     1. Freedom from air leaks out of blade supply channels into the turbine flow path. 
     2. No leaks and no mixing between that air which is fed into the channel with main cooling air flow passing along the rotor. 
     3. Through area of the cooling air transportation channel can be adjusted due to variation of inner diameters of the connecting sleeves. 
     4. The proposed sleeve design allows cooling air leaks to be reduced, and turbine efficiency to be improved. 
     List of Reference Numerals 
       10 , 20  gas turbine 
       11  stator 
       12  hot gas path 
       13  rotor 
       14  vane carrier 
       15  rotor shaft 
       16  hot gas 
       17  cooling air (main flow) 
       18  cooling air (entering blade) 
       19  sealing plate 
       21  cooling channel (air-tight) 
       22 , 22 ′ sleeve (connecting piece) 
       23 , 23 ′ sleeve (connecting piece) 
       24  plug 
       25  spherical section 
       26 , 27  rib 
       28  opening (coaxial, cylindrical) 
     B 1 -B 3  blade 
     R 1 ,R 2  rotor heat shield 
     S 1 -S 3  stator heat shield 
     V 1 -V 3  vane 
     While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.