DESCRIPTION

The invention relates to a turbine rotor blade comprising a blade root, the blade root having, with respect to a direc ^¬ tion of flow of a work medium circulating around the turbine rotor blade, a front end face and a rear end face.

Moreover, the invention relates to a turbine rotor arrange ^¬ ment comprising at least one rotor disk and at least one ro ^¬ tor blade fixed to said rotor disk and radially extending from said rotor disk.

Furthermore, the invention relates to a method for manufac ^¬ turing a turbine rotor blade with a blade root, wherein the blade root is formed, with respect to a direction of flow of a work medium circulating around the turbine rotor blade, with a front end face and a rear end face.

A rotor of a turbine, such as a steam turbine or a gas tur ^¬ bine, conventionally comprises several rotor disks connected torque proof with each other and each carrying several rotor blades extending radially from said rotor disk, respectively. Each rotor blade comprises an airfoil portion getting in contact with a work medium and a blade root for fixing the rotor blade to a rotor disk. For this purpose, a rotor disk comprises several circumferentially displaces rotor disk slots which each can accommodate a blade root of a rotor blade in order to have a positive connection in the radial direction between the rotor blade and the rotor disk.

During operation of a corresponding turbine, a rotor disk re- ceives forces from rotor blades carried by this rotor disk caused by a transmission of forces from the respective blade root to the respective rotor disk slot. Therefore, the dura ^¬ bility of a rotor disk, and thus the durability of a turbine rotor, strongly depends on the way the force transmission takes place and on the magnitude of the force to be absorbed by the rotor disk. High stress particularly occurs, with respect to a direction of flow of a work medium circulating around the turbine rotor blade, in a rear contact area be ^¬ tween a blade root and a rotor disk slot.

EP 0 906 514 Bl discloses a rotor for a turbomachine, having blades which can be fitted into slots. At least one blade root has at least two regions of different rigidity which are adapted to different regions of the rigidity of the slot into which the blade root can be fitted. The blade root has two opposite end faces, namely, with respect to a direction of flow of a work medium circulating around the blade, a front end face and a rear end face. A material reduction reducing the rigidity is provided in the region of the end faces. By this, stress acting on the slot in the region of the end fac ^¬ es of the blade root can be reduced. It is an object of the invention to enhance durability of a turbine rotor.

This object is solved by the independent claims. Advantageous embodiments are disclosed in the description, the dependent claims and in the figures, wherein these embodiments either taken alone or in any combination with each other may relate to an advantageous or preferred aspect of the invention.

A turbine rotor blade according to the invention comprises a blade root, the blade root having, with respect to a direc ^¬ tion of flow of a work medium circulating around the turbine rotor blade, a front end face and a rear end face, wherein at least one of the front end face and the rear end face com ^¬ prises at least one recess located at a distance to an edge of the respective end face.

According to the invention, the rigidity of the blade root is selectively and locally reduced at the front end region and/or the rear end region of the blade root by providing at least one recess at the respective end face of the blade root. The rigidity of the respective end region of the blade root is reduced by the recess so that forces transmitted in this end region from the rotor blade to the rotor disk are correspondingly reduced. At the same time, higher forces are transmitted from the rotor blade to the rotor disk in a mid ^¬ dle region of the blade root and the accommodating slot, wherein this middle region is less susceptible to deteriorate under stress than the end regions of the blade root. There ^¬ fore, the forces transmitted from the rotor blade to the ro ^¬ tor disk are partly and selectively displaced from at least one end region of the blade root to a middle region of the blade root to thereby partly unload the respective end re- gion. Through this, durability of the rotor disk, and there ^¬ fore of the turbine rotor, is enhanced.

The at least one recess can be formed at an end face of the blade root without amending the remaining design of the blade root. Through this, the mechanical interface between the blade root and the rotor slot of a rotor disk is not nega ^¬ tively affected by the recess according to the invention.

In contrast, the measure disclosed in EP 0 906 514 Bl affects the mechanical interface between the blade root and the rotor slot of the rotor disk. Since the material reduction of EP 0 906 514 Bl reducing the rigidity is also present at the re ^¬ spective end face of the blade root, the axial fixation of the rotor blade by an axially locking plate is negatively af- fected. Moreover, in case the rotor blade is cooled by a cooling medium flowing through the rotor blade, the sealing between the rotor blade and the axial locking plate is nega ^¬ tively affected producing a leakage of cooling medium out of the rotor slot. These disadvantages are not related with the present invention.

The blade root of the inventive rotor blade may have any de ^¬ sired cross-section. With respect to a direction of flow of a work medium, such as steam or gas, circulating around the turbine rotor blade, the blade root has an upstream front end face and a downstream rear end face. That the recess is located at a distance to the edge of the respective end face of the blade root particularly means that the recess does not extend to the bottom edge of the respec ^¬ tive end face. Preferably, the recess does not extend to any part of the surrounding edge of the respective end face. The recess may have a polygonal, circular, oval or elliptical cross-section. Since the stress in the region of the rear end portion of the blade root is typically higher than in other regions of the blade root, the recess is preferably located at the rear end face of the blade root. The depth of the re- cess can be simply adapted to the respective application case. It is possible that two or more recesses are provided at one end face of the blade root. Moreover, one, two or more recesses may be provided at each end face of the blade root. In the latter case the end faces may differ in their respec- tive number of recesses.

The turbine in which the rotor blade may be employed can be a steam turbine or a gas turbine. Preferably, a contour of the recess is at least partly adapted to a contour of the edge of the respective end face. Tests have showed that this embodiment of the recess and its location has the best effects on the desired stress reduction in the respective end region of the blade root. Preferential- ly, a distance between the contour of the recess and the con ^¬ tour of the edge of the respective end face is at least par ^¬ tially constant, especially in lateral regions of the blade root . The blade root preferably comprises a fir-tree-shape in cross-section with a convex bottom portion and at least one further convex portion located closer to an airfoil portion of the turbine rotor blade than the convex bottom portion, wherein the recess is mostly or completely located at the convex bottom portion. Typically, the highest stress acts on the convex bottom portion of a blade root having a fir-tree- shape cross-section. Therefore, the reduction of the rigidity of the blade root in the region of the convex bottom portion by providing the recess mostly or completely at the convex bottom portion leads to an optimal stress reduction to there ^¬ by further enhance durability of the rotor disk. Preferably, the recess is formed as a slot. Depending on the shape of the recess, in particular its geometry, depth, etc., the flow conditions in a cavity formed by the turbine rotor and the turbine stator might induce a swirl in the rim cavity by the drag of the recess. This could increase the tempera- ture in the cavity. By forming the recess like a slot the in ^¬ crease in temperature in the rim cavity can be minimized. The rim cavity air is only marginally influenced by the slot-like recess, i. e., by the respective slotted end face of the blade root.

Preferably, the turbine rotor blade further comprises at least one cooling channel passing through the blade root for conducting a cooling medium through the turbine rotor blade. The cooling medium, such as a cooling gas, can be supplied to the cooling channel through the rotor slot of a rotor disk, wherein the rotor slot forms a duct segment of a cooling me ^¬ dium supply. The turbine rotor blade can also have two or more cooling channels. The depth of the at least one recess at the respective end face of the blade root can be adapted to the position and run of an adjacent cooling channel of the turbine rotor blade to maintain a necessary minimal material thickness between the bottom of the recess and the cooling channel . A turbine rotor arrangement according to the invention comprises at least one rotor disk and at least one rotor blade fixed to said rotor disk and radially extending from said ro ^¬ tor disk, wherein the rotor blade is constructed according to any one of the aforementioned embodiments or to any combina ^¬ tion of at least two embodiments of the aforementioned embod ^¬ iments . Advantages mentioned above with respect to the turbine rotor blade are correspondingly connected with this turbine rotor arrangement. The rotor disk may comprise several circumferen- tially displaced rotor slots each accommodating a blade root of a separate rotor blade, wherein each rotor blade may be constructed according to any one of the aforementioned embod ^¬ iments or to any combination of at least two embodiments of the aforementioned embodiments.

Preferably, the turbine rotor arrangement further comprises at least one axial locking plate, wherein a bar is formed be ^¬ tween a bottom edge of the respective end face and a bottom edge of the recess, and wherein the bar comprises a slot opening radially inwards and encompassing a radially outside portion of the axial locking plate. If the rotor blade is cooled by a cooling medium flowing through at least one cooling channel of the rotor blade, the sealing between the rotor blade and the axial locking plate is obtained through encom ^¬ passing the radially outside portion of the axial locking plate by the bar or rather the slot of the bar. Thus, accord- ing to this embodiment, a leakage of cooling medium out of the rotor slot is securely prevented, although the rigidity of the respective end region of the blade root is reduced by the recess. In a method according to the invention for manufacturing a turbine rotor blade with a blade root, the blade root is formed, with respect to a direction of flow of a work medium circulating around the turbine rotor blade, with a front end face and a rear end face, wherein at least one recess is formed on at least one of the front end face and the rear end face, such that the recess is located at a distance to an edge of the respective end face. Advantages mentioned above with respect to the turbine rotor blade are correspondingly connected with this method. In par ^¬ ticular, the turbine rotor blade according to any one of the aforementioned embodiments or to any combination of at least two embodiments of the aforementioned embodiments may be man ^¬ ufactured using the inventive method.

Preferably, the recess is formed using a casting process and/or a machining process. Therefore, the recess can be simply formed, especially by integrating the manufacture of the recess in a conventional process for manufacturing a tur ^¬ bine rotor blade. Using a casting process for forming the recess allows for simultaneously manufacturing of the recess and the remaining turbine rotor blade. Using a machining pro- cess makes it possible to finish a conventionally manufac ^¬ tured turbine rotor blade to have a turbine rotor blade with at least one inventive recess.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned attributes and other features and ad ^¬ vantages of the invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein

FIG. 1 shows a schematic cross-section of a detail of a tur ^¬ bine rotor arrangement according to an embodiment of the in- vention,

FIG. 2 shows a schematic front view of the turbine rotor ar ^¬ rangement shown in FIG. 1, FIG. 3 shows a schematic perspective view of a detail of a turbine rotor blade according to a further embodiment of the invention, FIG. 4 shows another schematic perspective view of the tur ^¬ bine rotor blade shown in FIG. 3, and

FIG. 5 shows a schematic front view of a detail of a turbine rotor blade according to a further embodiment of the invention .

DETAILED DESCRIPTION OF EMBODIMENTS Figure 1 shows a schematic cross-section of a detail of a turbine rotor arrangement 1 according to an embodiment of the invention .

The turbine rotor arrangement 1 comprises at least one rotor disk 2 and at least one rotor blade 3 fixed to said rotor disk 2 and radially extending from said rotor disk 2.

The turbine rotor blade 3 comprises a blade root 4. The blade root 4 comprises, with respect to a direction 5 of flow of a work medium circulating around the turbine rotor blade 3, a front end face 6 and a rear end face 7. The blade root 4 is accommodated in a rotor disk slot 8 of the rotor disk 2.

The blade root 4 may comprise a fir-tree-shape in cross sec- tion with a convex bottom portion (not shown in FIG. 1) and at least one further convex portion (not shown in FIG. 1) lo ^¬ cated closer to an airfoil portion (not shown) of the turbine rotor blade 3 than the convex bottom portion. The turbine rotor blade 3 further comprises two radially ex ^¬ tending cooling channels 9 and 10 passing through the blade root 4 for conducting a cooling medium according to the arrows 11 through the turbine rotor blade 3. The cooling chan ^¬ nels 9 and 10 are supplied with the cooling medium flowing through the ground of the rotor disk slot 8.

The turbine rotor arrangement 1 further comprises at least one axial locking plate 12, wherein a radially inside portion of the axial locking plate 12 is accommodated in a radially outwards opening slot 13 of the rotor disk 2.

The rear end face 7 of the blade root 4 comprises a recess 14 located at a distance to an edge of the rear end face 7. A contour of the recess 14 may at least partly be adapted to a contour of the edge of the rear end face 7. The recess 14 may be mostly or completely located at the convex bottom portion of the blade root 3.

A bar 15 is formed between a bottom edge of the rear end face 7 and a bottom edge of the recess 14. The bar 15 comprises a slot 16 opening radially inwards and encompassing a radially outside portion of the axial locking plate 12 to seal the ro- tor disk slot 8 at the rear end side of the turbine rotor ar ^¬ rangement 1.

Figure 2 shows a schematic front view of the turbine rotor arrangement 1 shown in Figure 1.

Figure 2 shows that the blade root 4 comprises a fir-tree- shape in cross section with a convex bottom portion 17 and two further convex portions 18 und 19 located closer to an airfoil portion (not shown) of the turbine rotor blade 3 than the convex bottom portion 17.

Moreover, Figure 2 shows that the recess 14 is located at a distance to an edge of the rear end face 7 surrounding the recess 14. The recess 14 is mostly located at the convex bot- torn portion 17 of the blade root 3. The contour of the recess 14 is partly adapted to a lateral contour of the edge of the rear end face 7.

Figure 3 shows a schematic perspective view of a detail turbine rotor blade 20 according to a further embodiment the invention. The turbine rotor blade 20 comprises a blade root 21 and an airfoil portion (not shown) . The blade root 21 comprises, with respect to a direction 5 of flow of a work medium circulating around the turbine rotor blade 20, a front end face 22 and a rear end face 23. The blade root 21 comprises a fir- tree-shape in cross-section with a convex bottom portion 24 and one further convex portion 25 located closer to the air ^¬ foil portion of the turbine rotor blade 20 than the convex bottom portion 24.

The rear end face 23 comprises a recess 26 located at a dis ^¬ tance to an edge of the rear end face 23. A contour of the recess 26 is partly adapted to a contour of the edge of the rear end face 23. The recess 26 is mostly located at the con- vex bottom portion 24.

The turbine rotor blade 20 further may comprise at least one cooling channel (not shown in FIG. 3) passing through the blade root 21 for conducting a cooling medium through the turbine rotor blade 20.

A bar 27 is formed between a bottom edge of the rear end face 23 and a bottom edge of the recess 26. The bar 27 comprises a radially inwardly projecting projection 28 which may posi- tively be connected with a cover plate (not shown) or axial locking plate (not shown) of a turbine rotor arrangement (not shown) .

Figure 4 shows another schematic perspective view of the tur- bine rotor blade 20 shown in Figure 3. A repeated description is omitted.

Figure 5 shows a schematic front view of a detail of a tur ^¬ bine rotor blade 29 according to a further embodiment of the invention.

The turbine rotor blade 29 comprises a blade root 30 and an airfoil portion (not shown) . The blade root 30 comprises, with respect to a direction 5 of flow of a work medium circulating around the turbine rotor blade 29, a front end face (not shown) and a rear end face 31. The blade root 30 com ^¬ prises a fir-tree-shape in cross-section with a convex bottom portion 32 and one further convex portion 33 located closer to the airfoil portion of the turbine rotor blade 29 than the convex bottom portion 32.

The rear end face 31 comprises two recesses 34 and 35 located at a distance to an edge of the rear end face 31, respective ^¬ ly. A contour of each recess 34, 35 is partly adapted to a contour of the edge of the rear end face 31. Each recess 34, 35 is completely located at the convex bottom portion 32. Each recess 34, 35 is formed as an angled slot.

The turbine rotor blade 20 further may comprise at least one cooling channel (not shown in FIG. 5) passing through the blade root 30 for conducting a cooling medium through the turbine rotor blade 29.

Although the invention has been explained and described in detail in connection with the preferred embodiments it is noted that the invention is not limited to the disclosed em ^¬ bodiments. A person skilled in the art can derive from these embodiments other variations without leaving the scope of protection of the invention.