Abstract:
A rotor shaft, particularly for a gas turbine, includes a cooling air supply disposed inside the rotor shaft and a plurality of cooling air ducts connected to the cooling air supply and extending essentially radially outward toward an outside of the shaft, wherein each of the cooling air ducts has an elliptic cross section.

Description:
[0001]     Priority is claimed to Swiss Patent Application No. CH 00504/05, filed on Mar. 23, 2005, the entire disclosure of which is incorporated by reference herein.  
         [0002]     The present invention relates to the field of rotating machines. It refers to a rotor shaft, in particular for a gas turbine.  
       BACKGROUND  
       [0003]     Where machines subjected to high thermal and mechanical load are concerned, such as for example, compressors, gas turbines or steam turbines, it is desirable to reduce mechanical stresses by means of a suitable design of the individual machine and plant parts.  
         [0004]     Thus, from the prior art, it is known, for example (see EP-A1-0 945 594 or U.S. Pat. No. 6,478,539 B1), in the moving blades of gas turbines, to design the transition from the blade leaf to the adjoining blade platform lying beneath it with a predetermined, preferably elliptic curvature contour, the major axis running in the radial direction and the minor axis being oriented parallel to the surface of the platform.  
         [0005]     Furthermore, it is known from U.S. Pat. No. 6,237,558 B1 to provide specific locations of the crankcase of an internal combustion engine which are critical in terms of mechanical stresses with a curvature which follows a conic section (ellipse, hyperbola, parabola).  
         [0006]     Not only the moving blades of turbines are exposed to high mechanical loads on account of the high rotational speeds, but also the rotor shaft itself. Critical locations are in this case, above all, the grooves in the rotor shaft which are arranged on the outer circumference and which, running in the axial direction or running around annularly, may be provided, for example, for receiving the blade roots of the moving blades or as part of a shaft seal. Where such grooves are concerned, the stresses arising in the groove depend critically on the cross-sectional contour. GB-A-2 265 671 or U.S. Pat. No. 4,818,182 discloses grooves running around annularly for the fastening of moving blades, said grooves having a rounded cross-sectional contour. No information is given on the nature of the curvature profile or on the influence of the contour on the stresses in the groove.  
         [0007]     In the rotor parts subjected to particularly high thermal load, the turbine part, additional cooling measures are often provided, in order, at the high hot-gas temperatures, to achieve a sufficient service life of the material used. Cooling measures of this kind include cooling air ducts which run approximately in the radial direction from the inside outward through the rotor shaft and lead cooling air from an inner cooling air supply to the surface of the rotor shaft. Cooling air ducts of this type, however, constitute mechanical weakenings of the rotor shaft which may have an adverse effect in the case of the high temperatures and centrifugal forces and under the changing loads.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide such a rotor shaft equipped with radial cooling air ducts, in such a way that the weakenings of the rotor shaft due to the cooling air ducts are minimized or at least markedly reduced.  
         [0009]     The present invention provides a rotor shaft, in particular for a gas turbine, in which cooling air ducts are provided, which run from the inside outward essentially in the radial direction and are connected to a cooling air supply present inside the rotor shaft, characterized in that the cooling air ducts have an elliptic cross section for the reduction of mechanical stresses.  
         [0010]     A refinement of the invention is characterized in that the cooling air ducts are arranged so as to be distributed over the circumference of the rotor shaft, and in that the elliptic cross section of the cooling air ducts is in each case oriented such that the major axis is oriented in the circumferential direction and the minor axis is oriented in the axial direction.  
         [0011]     Preferably, the rotor shaft has a compressor part and a turbine part, and the cooling air ducts are arranged in the turbine part.  
         [0012]     Another refinement of the invention is distinguished in that the turbine part has a plurality of rotor disks arranged one behind the other in the axial direction, for the fastening of moving blades, and in that the cooling air ducts are arranged between adjacent rotor disks.  
         [0013]     In particular, it is conceivable that cavities are formed, concentrically with respect to the rotor axis, inside the rotor shaft, and that the cooling air ducts emanate from at least one of the cavities and are connected to the cooling air supply via this cavity. It is then especially beneficial that the cavities have, at least partially, an elliptic cross-sectional contour on the outer circumference for the reduction of mechanical stresses, preferably the cross-sectional contour on the outer circumference being composed of two elliptic segments of two ellipses which are tilted with respect to one another and the major axes of which are oriented approximately in the radial direction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention will be explained in more detail below by means of exemplary embodiments in conjunction with the drawings, in which:  
         [0015]      FIG. 1  shows a perspective side view of a rotor shaft (without blading) with cooling air ducts in the turbine part according to an exemplary embodiment of the present invention;  
         [0016]      FIG. 2  shows a longitudinal section through the rotor shaft from  FIG. 1  in the region of the turbine part;  
         [0017]      FIG. 3  shows a view of the turbine part of a rotor shaft, said turbine part being equipped with conventional cooling air ducts;  
         [0018]      FIG. 4  shows an illustration, comparable to  FIG. 3 , of a rotor shaft according to an exemplary embodiment of the invention; and  
         [0019]      FIG. 5  shows, in longitudinal section, a rotor shaft with inner cavities which, according to another exemplary embodiment of the invention, are provided on the outer circumference with a partially elliptic cross-sectional contour. 
     
    
     DETAILED DESCRIPTION  
       [0020]      FIG. 1  reproduces a perspective side view of a rotor shaft  10  (without blading) of a gas turbine. The rotor shaft  10 , rotationally symmetric with respect to the rotor axis ( 17  in  FIG. 2 ), is subdivided into a compressor part  11  and a turbine part  12 . Between the two parts  11  and  12 , inside the gas turbine, the combustion chamber is arranged, into which the air compressed in the compressor part  11  is introduced and out of which the hot gas flows through the turbine part  12 . The turbine part  12  has, arranged one behind the other in the axial direction, a plurality of rotor disks  13 , in which, according to  FIG. 3, 4 , axially oriented reception slots  21  for the reception of corresponding moving blades are formed so as to be distributed over the circumference. The blade roots are held in the reception slots  21  in the customary way by positive connection by means of a pinetree-like cross-sectional contour. According to  FIG. 5 , in the compressor part  1   1 , circumferential grooves  18  running around are provided, in which the blading of the compressor part is fastened.  
         [0021]     In the turbine part  12  subjected to high thermal load, a multiplicity of cooling air ducts  14  are provided, distributed over the circumference, between adjacent rotor disks, which cooling air ducts emanate approximately radially outward from a cavity  15  formed inside the rotor shaft  10  and issue into the outside space on the surface of the rotor shaft  10  ( FIG. 2 ). The cavity  15  is connected to a central cooling air supply  16  running in the axial direction. Whereas, in earlier designs ( FIG. 3 ), the cooling air ducts ( 14 ′) had a circular cross section, in the novel configuration of  FIG. 4  the cooling air ducts  14  have an elliptic cross section for reasons of mechanical stability. The elliptic cross section of the cooling air ducts  14  may be predetermined even during the casting of the rotor shaft. It is also conceivable, however, to introduce such a cross section into the rotor shaft  10  by means of special machining methods, such as erosion.  
         [0022]     As can be seen clearly in  FIG. 4 , the ellipses of the duct cross section of the cooling air ducts  14  are oriented such that the major axes are oriented in the circumferential direction, while the minor axes lie parallel to the rotor axis  17 . A maximum reduction of the mechanical stresses is thereby achieved. It goes without saying that the advantages of an elliptic cross section are not restricted to cooling air ducts in the rotor shaft itself, but also apply to cooling air ducts which are arranged on other parts of the rotor, such as moving blades or the like.  
         [0023]     The cavity  15  formed concentrically with respect to the rotor axis  17  is likewise optimized in its cross-sectional profile in terms of the mechanical stresses which arise. The optimization of the cross-sectional profile takes place in the way illustrated in  FIG. 5  in further cavities  19 ,  20  in the compressor part  11 , in such a way that the edge contour on the outer circumference of the cavity  15 ,  19 ,  20  is at least partially of elliptic design. In particular, as is illustrated for the cavity  20  in  FIG. 5 , the cross-sectional contour on the outer circumference is composed of two elliptic segments of two ellipses E 1 , E 2  (depicted by dashes in  FIG. 5 ) which are tilted with respect to one another and the major axes of which are oriented approximately in the radial direction. Such a shaping of the cavities present inside the rotor shaft  10  is not only advantageous in connection with the cooling air ducts  14  in the turbine part, but may also be used in other cavities  19 ,  20  which are located, for example, in the compressor part  11  of the rotor shaft  10 .