Abstract:
A rotor is provided for an axial-throughflow turbo machine, which carries a plurality of moving blades which are each pushed with a blade root into a rotor groove extending about the axis and are held. The blade root includes a hammer root with a hammerhead and is supported on radial stop faces of the rotor groove which lie further outward in the radial direction, against centrifugal forces acting on the moving blades, and are supported on axial stop faces lying further inward in the radial direction, against axial forces which act on the moving blade. The rotor groove has at its bottom, to reduce thermal stresses, an axially and radially widened bottom region with a continuously curved cross-sectional contour. In such a rotor, an advantageous adaptation of the blading is achieved by the blade root of the moving blades being adapted to the widened bottom region in the radial direction.

Description:
FIELD OF INVENTION 
     The present invention relates to the technological field of axial-throughflow turbomachines. It refers to a rotor for an axial-throughflow turbomachine and to a moving blade for such a rotor. 
     BACKGROUND 
     Stationary gas turbines with a high power output have long been an essential component of power stations, especially combined-cycle power stations.  FIG. 1  shows a perspective, partially sectional view of an example of such a gas turbine which is supplied by the Assignee of the present invention and is known by the type designation GT26®. 
     The gas turbine  10  of  FIG. 1  is equipped with what is known as sequential combustion. It comprises a multistage compressor  12  which sucks in air via an air inlet  15  and compresses it. The compressed air is used, in a following first annular combustion chamber  14   a , partially for the combustion of an injected fuel. The hot gas occurring flows through a first turbine  13   a  and then enters into a second combustion chamber  14   b  where the remaining air is employed for the combustion of a fuel which again is injected. The hot gas stream coming from the second combustion chamber  14   b  is expanded in a second turbine  13   b  so as to perform work and emerges from the gas turbine  10  through an exhaust gas outlet  16 , in order to be discharged outward or, in a combined-cycle power station, in order to be used for the generation of steam. 
     The compressor  12  and the two turbines  13   a ,  13   b  have sets of moving blades which rotate about the axis  30  and which, together with guide vanes fastened to the surrounding stator, form the blading of the machine. All the moving blades are arranged on a common rotor  11  rotatable about the axis and are fastened releasably to the rotor shaft by means of rotor grooves provided for this purpose. Special attention is in this case devoted to the last stages  12   a  of the compressor  12  where the compressed air reaches temperatures of several hundred degrees Celsius. 
     It is known from the prior art (see, for example, WO-A1-2005/054682), according to  FIG. 2 , to provide the moving blades  12  of the last stages  12   a  of the compressor  12  with a blade root  18  designed as a hammerhead root and to push them with the blade root  18  into a rotor groove  19  extending about the axis and hold them there. The blade root  18  is supported on radial stop faces  25  of the rotor groove  19  which lie further outward in the radial direction, against centrifugal forces which act on the moving blade  17 . Said blade root is likewise supported on axial stop faces  20  lying further inward in the radial direction, against axial forces which act on the moving blade  17 . An undercut is in this case provided between each of the radial stop faces  25  and each of the axial stop faces  20 . A spring  22  is provided at the bottom of the rotor groove  19  and fixes the moving blade  17  in the radial direction during assembly. 
     In the course of ongoing discussions about energy and the environment, there is the persistent desire to increase the power, efficiency, combustion temperature and/or mass throughflow of machines of this type. An increase in the power output can be achieved, inter alia, by improving the compressor. 
     An improvement in the gas turbine entails an increase in the mass throughflow through the compressor which leads to a higher gas temperature in the last compressor stages  12   a . The up-to-date, progressive aerodynamic design of the blade leaves for the compressor requires greater axial chord lengths, this leading to a greater distance between the rotor grooves  19 . 
     The two together give rise to markedly increased thermal stresses in the notches at the bottom of the rotor grooves in the rear compressor stages when the machine is being started, because the center of the rotor body is still at a low temperature (T 1  in  FIG. 2 ), whereas the outer region is already exposed to the high full-load temperature (T 2  in  FIG. 2 ), and therefore high thermal stresses occur in the material. 
     In another context, to be precise in moving blades of gas turbines with a dovetail-shaped blade root which bears against oblique stop faces in the rotor groove and because of the friction exerts shear forces on the side walls of the groove, it has been proposed to introduce fillets into the rotor groove below the stop faces in order to break down the friction-induced stresses (see U.S. Pat. No. 5,141,401). Here, however, thermal stresses do not play any part. 
     In connection with measures for reducing the stresses in the region of the rotor groove, EP-A1-1703080 repeats the critical influence of the cross-sectional contour of the groove upon the stress profile in the rotor. It is suggested there, in this connection, that the groove bottom be given an elliptical cross-sectional contour. 
     A rotor groove designed in this way has at its bottom, in order to reduce thermal stresses, an axially and radially widened bottom region  23  with a continuously curved cross-sectional contour which is distinguished by a large radius of curvature in the region of the mid-plane  33  and is designed to be mirror-symmetrical with respect to the mid-plane  33 . 
     Should the design of the rotor root  18  of the moving blade  17  be preserved in the case of a rotor groove geometry modified in this way, the hammerhead of the blade root  18  according to  FIG. 3  would have to be enlarged by the amount of the additional volume  24  illustrated by hatching, and this would lead to a marked increase in the mass of the moving blade  17  and therefore to a rise in the centrifugal forces acting on the rotor groove  21 . 
     SUMMARY 
     In a first embodiment, the present disclosure is directed to a rotor for an axial-throughflow turbo machine. The rotor carries a plurality of moving blades which are pushed, in each case, with a blade root into a rotor groove extending about an axis and are held there. The blade root includes a hammer root with a hammerhead and is supported on radial stop faces of the rotor groove which lie further out in the radial direction, against centrifugal forces which act on the plurality of moving blades, and is supported on axial stop faces lying further inward in the radial direction, against axial forces which act on the plurality of moving blades. The rotor groove having at a bottom portion, in order to reduce thermal stresses, an axially and radially widened bottom region with a continuously curved cross-sectional contour. The blade root of the plurality of moving blades is adapted to the widened bottom region in a radial direction. 
     In another embodiment, the disclosure is directed to a moving blade ( 26 ) for the above rotor. The moving blade includes a blade root designed as a hammer root with a hammerhead. The blade root is extended in the radial direction below the hammerhead in order to bridge the radial widening of the widened bottom region of the rotor groove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below by means of exemplary embodiments in conjunction with the drawing, in which 
         FIG. 1  shows a perspective, partially sectional view of a gas turbine with sequential combustion, such as is suitable for implementing the invention; 
         FIG. 2  shows the longitudinal section through the rotor of a known gas turbine in the region of the last stages of the compressor with the associated fastening of the moving blades; 
         FIG. 3  shows two adjacent identical rotor grooves with a widened bottom region and a continuously curved cross-sectional contour in an enlarged illustration with the associated dimensions; 
         FIG. 4  shows a possible adaptation of the blade root to the modified rotor groove geometry; 
         FIG. 5  shows the illustration of an adapted moving blade for the changed rotor groove geometry from  FIG. 3  according to an exemplary embodiment of the invention; 
         FIG. 6  shows the adapted moving blade from  FIG. 5  inserted into the rotor groove from  FIG. 3 ; and 
         FIG. 7  shows an illustration of an adapted moving blade for the changed rotor groove geometry from  FIG. 3  in a type of design alternative to that of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Introduction to the Embodiments 
     The object of the invention, therefore, is to design the rotor or the moving blades used on the rotor, such that the advantages of a rotor groove geometry with a widened bottom region and large radius of curvature can be exploited, preferably without disadvantages of any kind. 
     The object is achieved by the whole of the features as set forth in the appended claims. In the embodiments of the invention, the rotor groove has at its bottom, in order to reduce thermal stresses, an axially and radially widened bottom region with a continuously curved cross-sectional contour, and the blade root of the moving blades is adapted in the radial direction to the widened bottom region. 
     According to one embodiment of the invention, the widened bottom region is formed mirror-symmetrically to a mid-plane passing through a rotor groove and standing perpendicularly to the axis, and the radius of curvature of the cross-sectional contour of the bottom region in this case decreases from the mid-plane towards the margin. 
     Another embodiment of the invention is distinguished in that the widened bottom region has a predetermined maximum width in the axial direction, in that the radial stop faces have a predetermined minimum spacing in the axial direction, and in that the ratio of the minimum spacing to the maximum width amounts to between 0.1 and 0.6, that is to say 0.1&lt;d 5 /d 1 &lt;0.6. 
     It is in this case advantageous if the widened bottom region has a predetermined first maximum depth in relation to the radial stop faces, the widened bottom region has a predetermined second maximum depth in relation to the inner edges of the axial stop faces, and the ratio of the second maximum depth to the first maximum depth amounts to between 0.4 and 0.9, that is to say 0.4&lt;d 3 /d 4 &lt;0.9. 
     It is especially beneficial if a plurality of identical rotor grooves are provided, offset at a predetermined distance, in the axial direction, and the ratio of the maximum width to the distance amounts to between 0.5 and 0.8, that is to say 0.5&lt;d 1 /d 2 &lt;0.8. 
     According to a further embodiment of the invention, the blade root is lengthened in the radial direction below the hammerhead in order to bridge the radial widening of the widened bottom region. 
     Preferably, to lengthen the blade root, a lengthening bolt extending radially is provided. The comparatively slender lengthening bolt bridges the distance, without any mass being needlessly added to the moving blade. 
     It is in this case advantageous in production terms if the lengthening bolt is integrally formed on the hammerhead. 
     Furthermore, it is advantageous if a curved transitional face is provided at the transition between the lengthening bolt and the hammerhead in order to ensure a continuous transition. 
     Alternatively, there may be provision for producing the lengthening bolt as a separate part and for connecting this to the hammerhead. 
     It is proved advantageous, in this case, to fasten the lengthening bolt to the hammerhead by screwing or welding. 
     Furthermore, the mass of the moving blade may be further reduced if mass-reducing recesses are provided in the blade root. 
     Preferably, the recesses extend over the hammerhead and the lengthening bolt. 
     Although preferably running in the circumferential direction, these recesses may also extend in another, for example radial direction. 
     In a refinement of the rotor according to the invention, an interspace remains free between the lower end of the lengthening bolt and the bottom of the widened bottom region, and the free interspace has arranged in it a spring which presses the moving blade with the blade root against the radial stop faces in the radial direction. 
     In another refinement, the hammerhead has a predetermined height, the lengthening bolt has a predetermined radial length, and the ratio of height to length is between 0.2 and 0.8, that is to say 0.2&lt;d 2 /d 1 &lt;0.8. 
     A further refinement is distinguished in that the hammerhead has a predetermined first axial width, in that the lengthening bolt has a predetermined second axial width, and in that the ratio of the second to the first axial width is between 0.2 and 0.6, that is to say 0.2&lt;d 4 /d 3 &lt;0.6. 
     DETAILED DESCRIPTION 
       FIG. 4  shows the longitudinal section, comparable to  FIG. 2 , through the rotor  11  of a gas turbine in the region of the last stages of the compressor according to the invention. A comparison of  FIGS. 2 and 4  shows that the upper portion of the rotor groove  21  remains unchanged, as compared with the known rotor groove geometry from  FIG. 2 . The radial and axial stop faces  25  and  20  correspondingly remain virtually unchanged. Consequently, the proven design can be adopted in this region. 
     What is novel, however, is the widened bottom region  23  of the rotor groove  21 . In the widened bottom region, a cross-sectional contour of the bottom region  23  is continuously curved, and the radius of curvature of the cross-sectional contour of the bottom region  23  is very large in the region of the mid-plane and decreases sharply from the mid-plane towards the margin. The cross-sectional contour is mirror-symmetrical to the mid-plane. 
     The widened bottom region  23  widens directly below the axial stop faces  20 , on both sides, in the axial direction in the manner of a relief. It has, as shown in  FIG. 3 , a predetermined maximum width d 1  in the axial direction, while the radial stop faces  25  have a predetermined minimum spacing d 5  in the axial direction. It is especially beneficial if the ratio of the minimum spacing d 5  to the maximum width d 1  amounts to between 0.1 and 0.6, that is to say the inequality 0.1&lt;d 5 /d 1 &lt;0.6 is true. 
     The widened bottom region  23  has a predetermined first maximum depth d 4  in relation to the radial stop faces  25 . It has a predetermined second maximum depth d 3  in relation to the inner edges of the axial stop faces  20 . It is especially beneficial if the ratio of the second maximum depth d 3  to the first maximum depth d 4  amounts to between 0.4 and 0.9, that is to say if the inequality 0.4&lt;d 3 /d 4 &lt;0.9 is true. 
     A further inequality relates to the offset of the rotor grooves with respect to one another. If a plurality of identical rotor grooves  21  are provided, offset at a predetermined distance d 2  with respect to one another, in the axial direction, it is advantageous if the ratio of the maximum width d 1  to the distance d 2  amounts to between 0.5 and 0.8, that is to say the inequality 0.5&lt;d 1 /d 2 &lt;0.8 is true. 
     Basically, the previous moving blades with their blade roots  18  can be taken over unchanged and used in the widened rotor grooves  21 . However, because of the widened bottom region  23 , the blade root  18  would then have to be provided with an additional volume  24 , as shown in  FIG. 4 , which would lead to undesirable secondary effects. 
     An adaptation of the blade root to the changed rotor groove geometry is therefore preferred, this being reproduced by way of example in  FIGS. 5 ,  6  and  7 . The moving blade  26  of  FIGS. 5 and 6  has a blade root  27  which in the upper portion, which reaches as far as the axial stop faces, is designed in essentially the same way as the blade root  18  from  FIG. 2 . However, by contrast differs in the radial downward prolongation, starting at the hammerhead  32 , by means of a lengthening bolt  29  which is integrally formed onto the hammerhead  32  and which is narrower (width d 9 ) than the hammerhead  32  (width d 8 ). The radial length (d 6 ) of the lengthening bolt ( 29 ) is markedly greater than the height (d 7 ) of the hammerhead  32 . 
     If the lengthening bolt  29  is integrally formed directly on the hammerhead  32 , a curved transitional face  28  is preferably provided at a transition between the lengthening bolt  29  and the hammerhead  32  in order to ensure a continuous transition. 
     As a cost-effective alternative for the axial lengthening of the blade root  18 , it is appropriate to produce the lengthening bolt  29  as a separate part and to connect it to the hammerhead  32 . Screwing or welding has in this case proved to be a method of connection which satisfies the requirements of practical operation. Thus, the hammerhead  32  may be equipped on the bottom  34 , in the region of the mid-plane  33 , with a threaded bore  35 . With the aid of an integrally formed threaded bolt  36 , the lengthening bolt  29  is screwed into the blade root  18 , as outlined by way of example in  FIG. 7 . 
     Furthermore, one or more mass-reducing recesses  31  are provided in the blade root  18 ,  27  and may be designed as a circular, elliptical or otherwise shaped hole or slot in a single or multiple version. The recess or recesses  31  extends or extend in the radial direction preferably over the hammerhead  32  and the lengthening bolt  29 . In this case, this recess or these recesses  31  preferably, but not necessarily, runs or run in the circumferential direction, as illustrated in  FIGS. 5 ,  6  and  7 . Other suitable directional runs and embodiments of mass-reducing recesses  31  may likewise be envisaged, however, such as, for example, in the form of bores introduced radially into the blade root  27 . 
     The ratio of the height (d 7 ) of the hammerhead  32  to the length (d 6 ) of the lengthening bolt  29  is preferably between 0.2 and 0.8, that is to say the inequality 0.2&lt;d 7 /d 6 &lt;0.8 is applicable. 
     The ratio of the axial width (d 9 ) of the lengthening bolt  29  to the axial width (d 8 ) of the hammerhead  32  is preferably between 0.2 and 0.6, that is to say the inequality 0.2&lt;d 9 /d 8 &lt;0.6 is applicable. 
     The invention includes the following features and advantages: The blade root comprises as a radial prolongation a lengthening bolt having the dimensions 0.2&lt;d 7 /d 6 &lt;0.8 and 0.2&lt;d 9 /d 8 &lt;0.6, so that the spring  22  can be used for assembly. The lengthening bolt  29  may be chamfered at the margins in order to save additional weight. The transitional faces between the lengthening bolt and the hammerhead are preferably curved in order to reduce mechanical stresses. In the region of the hammerhead and of the lengthening bolt, recesses, in particular holes or slots are provided, in order to reduce the weight or mass. 
     LIST OF REFERENCE SYMBOLS 
     
         
           10  Gas turbine 
           11  Rotor 
           12  Compressor 
           12   a  Last compressor stages 
           13   a ,  13   b  Turbine (HP, LP) 
           14   a ,  14   b  Combustion chamber 
           15  Air inlet 
           16  Exhaust gas outlet 
           17 ,  26  Moving blade, moving blade leaf 
           18 ,  27  Blade root 
           19 ,  21  Rotor groove 
           20  Stop face (axial) 
           22  Spring 
           23  Bottom region (widened) 
           24  Additional volume 
           25  Stop face (radial) 
           28  Transitional face (curved) 
           29  Lengthening bolt 
           30  Rotor axis 
           31  Recess 
           32  Hammerhead 
           33  Mid-plane 
           34  Blade root bottom 
           35  Threaded bore 
           36  Threaded bolt 
         d 1 , . . . , d 4  Distance