Abstract:
A blade assembly of a power plant having a modular structure, wherein blade elements include at least one blade airfoil, and at least one footboard mounting part. Blade elements can each have at its one ending a configuration for an interchangeable connection among each other. The connection of the airfoil with respect to other elements can be based on a fixation in radially or quasi-radially extension relative gas turbine axis, wherein the assembling of the blade airfoil in connection with the footboard mounting part is based on a friction-locked bonding actuated by adherence interconnecting, or on use of a metallic and/or ceramic surface fixing blade elements to each other, or on closure configuration with a detachable, permanent or semi-permanent fixation.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a blade assembly for a turbomachine, preferably a gas turbine engine, and refers in particular to a modular blade with one or more removable elements or modules. The term blade is to define in a broad sense. Though the invention preferably refers to rotor blades, the invention is not limited to this category, but additionally relates to guide vanes and similar components of turbomachines. 
         [0002]    Basically, the modular blade assembly of the present invention comprises various interchangeable modules or elements, wherein the mentioned parts being substitutable, semi-substitutable or non-substitutable. 
         [0003]    According to the invention a blade assembly on the basis of a modular structure at least comprises a blade airfoil, a footboard mounting part, wherein the elements of the modular structure of the blade having at its one endings means for the purpose of an interchangeable connection among each other. The connection of the airfoil with respect to the other elements is based on a fixation in radial or quasi-radial direction in relation to the rotor axis of the turbomachine, wherein the assembling of the blade airfoil in connection with the footboard mounting part is based on a friction-locked bonding actuated by adherence interconnecting, or the assembling of the blade airfoil in connection with the footboard mounting part is based on the use of a metallic and/or ceramic surface fixing blade elements to each other, or the assembling of the blade airfoil in connection with the footboard mounting part is based on force closure means with a detachable, permanent or semi-permanent fixation. 
         [0004]    Cooling passages extend inside the blade airfoil for cooling purposes and are supplied with a cooling medium, particularly cooling air, via a feed hole which is arranged on the shank at its side or directly via the blade root portion. 
         [0005]    The detachable or permanent connection between the modules comprising a force-closure means consists of bolts or rivets, or is made by HT brazing, active brazing, soldering etc. 
       BACKGROUND OF THE INVENTION 
       [0006]    According to US 2011/0142684 A1 a rotor blade airfoil is formed by a first process using a first material. A platform is formed by a second process using a second material that may be different from the first material. The mentioned platform is assembled around a shank of the airfoil. One or more pins extend from the platform into holes in the shank. The platform may be formed in two portions and placed around the shank, enclosing it. The two platform portions may be bonded to each other. Alternately, the platform may be cast around the shank using a metal alloy with better castability than that of the blade and shank, which may be specialized for thermal tolerance. The pins bear load from the under section of the airfoil. 
         [0007]    According to US 2011/0142639 A1 a turbine airfoil extends from a shank. A platform brackets or surrounds a first portion of the shank Opposed teeth extend laterally from the platform to engage respective slots in a disk. Opposed teeth extend laterally from a second portion of the shank that extends below the platform to engage other slots in the disk. Thus the platform and the shank independently support their own centrifugal loads via their respective teeth. The platform may be formed in two portions that are bonded to each other at matching end-walls and/or via pins passing through the shank. Coolant channels may pass through the shank beside the pins. 
         [0008]    EP 2 189 626 B1 refers to a rotor blade arrangement, especially for a gas turbine, which rotor blade arrangement can be fastened on a blade carrier and comprises in each case a blade airfoil element and a platform element, wherein the platform elements of a blade row forms a continuous inner shroud. With such a blade arrangement a mechanical decoupling, which extends the service life, is achieved by blade airfoil element and platform element being formed as separate elements and by being able to be fastened in each case separately on the blade carrier. 
         [0009]    US 2011/268582 A1 relates to a blade comprises a blade airfoil which extends in the longitudinal direction of the blade along a longitudinal axis. The blade airfoil, which is delimited by a leading edge and a trailing edge in the flow direction, merges into a shank at the lower end beneath a platform which forms the inner wall of the hot gas passage, the shank terminating in a customary blade root portion with a fir-tree-shaped cross-sectional profile by which the blade can be fastened on a blade carrier, especially on a rotor disk, by inserting into a corresponding axial slot (see, for example, FIG. 1 of U.S. Pat. No. 4,940,388). 
         [0010]    It is notorious and state of the art that a rotor blade having cooling passages which extend inside the blade airfoil for cooling the blade and are supplied with a cooling medium, particularly cooling air. 
         [0011]    Referring to the cited US document cooling passages (not shown) extend inside the blade airfoil for cooling the blade and are supplied with a cooling medium, particularly cooling air, via a feed hole which is arranged on the shank at the side. The shank, similar to the blade airfoil, has a concave and a convex side. The feed hole, which extends obliquely upwards into the interior of the blade airfoil, opens into the outside space on the convex side of the shank. In order to reduce the mechanical stresses which are associated with the mouth of the feed hole and at the same time to positively influence the vibration behaviour of the blade, provision is made around the mouth of the feed hole for a planar or virtually planar-that is to say not formed consistently planar over the entire surface-stiffening element which reaches beyond the direct vicinity of the feed hole, which stiffening is formed integrally on the shank and consists of the same material as the blade. As is to be seen from the cross section of the stiffening element which is shown in  FIG. 3 , the stiffening element is formed as a large-area plateau, and from the opening of the feed hole arranged to the left of the center plane reaches far beyond the center plane of the blade so that the stiffening element is formed symmetrically to the center plane and also encompasses the mouth of the feed hole. 
         [0012]    Referring to US 2013/0089431 A1 a blade airfoil for a turbine system is disclosed. The blade airfoil includes a first body having exterior surfaces defining a first portion of an aerodynamic contour of the blade airfoil and made from a first material. The blade airfoil further includes a second body having exterior surfaces defining a second portion of an aerodynamic contour of the blade airfoil, the second body coupled to the first body and formed from a second material having a different temperature stability compared to the first material. In another embodiment, a nozzle for a turbine section of a turbine system is disclosed. The nozzle includes a blade airfoil having exterior surfaces defining an aerodynamic contour, the aerodynamic contour comprising a pressure side and a suction side extending between a leading edge and a trailing edge. The blade airfoil includes a first body having exterior surfaces defining a first portion of the aerodynamic contour of the blade airfoil and formed from a first material. The blade airfoil further includes a second body having exterior surfaces defining a second portion of the aerodynamic contour of the blade airfoil, the second body is coupled to the first body and formed from a second material having a different temperature stability compared to the first material. The accompanying drawings of this US document, especially  FIGS. 3 through 6 , together with description, illustrate embodiments and explain the principles of this state of the art. 
         [0013]    U.S. Pat. No. 5,700,131 shows an internally cooled turbine blade for a gas turbine engine that is modified at the leading edge and trailing edge to include a dynamic cooling air radial passageway with an inlet at the root portion and a discharge at the tip feeding a plurality of radially spaced film cooling holes in the blade airfoil surface. Replenishment holes communicating with the serpentine passages radially spaced in the inner wall of the radial passage replenish the cooling air lost to the film cooling holes. The discharge orifice is sized to match the backflow margin to achieve a constant film-hole coverage throughout the radial length. Trip strips may be employed to augment the pressure drop distribution. Also well known by those skilled in this technology is that the engine&#39;s efficiency increases as the pressure ratio of the turbine increases and the weight of the turbine decreases. Needless to say, these parameters have limitations. Increasing the speed of the turbine also increases the blade airfoil loading and, of course, satisfactory operation of the turbine is to stay within given blade airfoil loadings. The blade airfoil loadings are governed by the cross sectional area of the turbine multiplied by the velocity of the tip of the turbine squared, or AN&lt;2&gt;. Obviously, the rotational speed of the turbine has a significant impact on the loadings. The spar/shell construction contemplated by this invention affords the turbine engine designer the option of reducing the amount of cooling air that is required in any given engine design. And in addition, allowing the designer to fabricate the shell from exotic high temperature materials that heretofore could not be cast or forged to define the surface profile of the blade airfoil section. In other words, by virtue of this invention, the shell can be made from Niobium or Molybdenum or their alloys, where the shape is formed by a well-known electric discharge process (EDM) or wire EDM process. In addition, because of the efficacious cooling scheme of this invention, the shell portion could be made from ceramics, or more conventional materials and still present an advantage to the designer because a lesser amount of cooling air would be required. 
         [0014]    EP 2 642 076 shows a connecting system for metal components and CMC components, a turbine blade retaining system and rotating component retaining system are provided. The connecting system includes a retaining pin, a metal foam bushing, a first aperture disposed in the metal component, and a second aperture disposed in the ceramic matrix composite component. The first aperture and the second aperture are configured to form a through-hole when the metal component and the ceramic matrix composite component are engaged. The retaining pin and the metal foam bushing are operably arranged within the through-hole to connect the metal component and the ceramic matrix composite component. 
         [0015]    U.S. Pat. No. 7,972,113 B1 shows an airfoil portion  11 , as seen in  FIG. 2 , having a curvature in which the airfoil portion includes both curvature and twist extending from the platform to the blade tip. The airfoil  11  also can include one or more cooling air passages  15  to provide cooling air for the blade. The cooling air passages  15  can be radial passages or a series of serpentine flow passages. The airfoil root with the dovetail  12  is pinched between two platform halves  21  and  22  to form the blade assembly  10 . Each of the platform halves  21  and  22  includes an opening  25  on the inner surface that forms the slot to receive the dovetail  12  of the airfoil  11  and a top or flow forming surface  23 . As seen in  FIG. 2 , the openings  25  in the platform halves  21  and  22  extend around the airfoil  11  on both the leading edge trailing edges and both the pressure and suction sides. The dovetail  12  in the airfoil  11  also has the shape of the dashed lines in  FIG. 2  that represent the slots  25  formed within the platform halves  21  and  22 . The dovetail  12  and slots  25  are shaped and sized so that the dovetail  12  will fit tightly within the slots  25  between the platform halves  21  and  22  when the platform halves are fastened together. Each platform halve  21  and  22  includes at least one hole  24 , as seen in  FIGS. 1 and 3 , to receive a fastener, such as a threaded bolt and a top or flow forming surface  23 . If a threaded bolt is used to secure the platform halves together, then at least one hole  24  opposite to the bolt head would include threads as well. The openings of the footboard mounting elements ( 120 ,  130 ) do not extend around the airfoil on both the leading edge trailing edges and both the pressure and suction sides, but in the axis of the gas turbine. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention provides a structure or architecture of a blade for a turbomachine, assembled from a plurality of interchangeable modules or elements optimized to the various operation regimes of the turbomachine. 
         [0017]    In a separate process the various modules or elements may be repaired and/or reconditioned. 
         [0018]    On the basis of the claims: 
         [0019]    Especially by using a blade which can be assembled by at least two separate parts, i.e. a separate blade airfoil and footboard mounting part(s), appropriate preconditions can be created to provide interchangeability or repairing and/or reconditioning of the identified separate parts, modules, elements, without replacing the whole blade. 
         [0020]    Usually, the inner platform forms an integral part of the blade. According to the fact that during operations at elevated temperatures thermal stress is induced into the transition element(s) from the blade airfoil to the inner platform of the blade. This means, that thermal stresses developing at the leading edge and the trailing edge of the blade airfoil can produce local failure(s) in the used material or at least increase the reconditioning effort. 
         [0021]    Accordingly, the modular blade assembly on the basis of a modular structure according to the invention comprises substantially heat shield, blade airfoil, inner platform, shank and footboard mounting part(s). The blade airfoil and/or the inner platform and/or the heat shield and/or the shank and/or the footboard mounting part have at its one end means for the purpose of an interchangeable connection of the mentioned modules to each other, wherein the used connection of the blade modules among one another have a permanent or semi-permanent fixation of the blade airfoil in radial or quasi-radial extension with respect to the axis of the turbomachine rotor. The assembling of the blade airfoil in connection with the other modules, especially with respect to the separated inner platform, is based, directly or indirectly, on a friction-locked bonding actuated by adherence interconnecting, or on a force-fit or form-fit connection, or using a shrinking joint. 
         [0022]    Thus, the structure of the blade includes substantially a blade airfoil, an inner platform, a fir-tree-shaped cross-sectional profile by which the blade can be fastened on a blade carrier or directly on a rotor disk as main modules with additional sub-modules, especially an intermediate shank between the inner platform and the footboard mounting part(s), also called root portion, having preferentially a fir-tree-shaped cross-sectional profile. As an additional sub-module of the blade airfoil the tip comprises a heat shield with seal means. 
         [0023]    Main-modules of the separated inner platform and blade airfoil are assembled by joining at least two parts of the inner platform with placing the blade airfoil between them before mounting the fir-tree root portion. The modules may be sealed to each other by ceramic, seal ropes or similar embodiments. 
         [0024]    The blade platform is separated in axial direction. In contrast, the state of the art suggests a separation of the platform into a pressure side portion and a suction side portion. 
         [0025]    In particular this embodiment in accordance with the state of the art, namely US 2011/0142639 A1, is designed so that the blade assembly, including a blade or blade airfoil, has a pressure side, a suction side, a shank, a platform, having a pressure side portion and a suction side portion, each comprising a root portion with at least one laterally extending tooth that engages into the rotor disk. After assembly, the platform surrounds or brackets a first portion of the shank. A second portion of the shank extends outside the platform, or radially inward of the platform when mounted in a turbine disk. The part of the shank outside the platform has at least two opposed laterally extending teeth that engage into the rotor disk. 
         [0026]    The identified embodiment comprises pins on one or both platform portions that pass through pin holes inside of the shank. The pins may be bonded to the opposite platform portion after assembly. The pins connect the two platform portions. The pins may fill the holes and thus provide load sharing between the shank and the platform. 
         [0027]    Thus, the separation of the platform in axial direction in accordance with the present invention bears their loads and airfoil bears its loads and involves a completely new philosophy in connection with the modular structure of a blade. 
         [0028]    In accordance with the present invention, the blade shank under-structure consists, in radial direction of the airfoil, of an elongated and relatively slim formed portion. The elongated portion extends over the entire height of the footboard mounting part(s), wherein the foot-side end of the elongated portion has, with respect to both sides of the axial expanse of the elongated portion, a shape of teeth configuration, and the bottom of the elongated portion of the shank under-structure may be formed as the final part of the fir-tree-shaped cross-sectional profile. The teeth of the elongated portion of the shank under structure may align with the recesses of two-folded footboard mounting elements to provide room for the teeth of the elongated portion. 
         [0029]    The term “radial” or “radially” as used herein, is intended to mean radial to the gas turbine rotor axis, when the blade assembly is installed in its operational position. 
         [0030]    Moreover, the footboard mounting parts have axially opposite cracks or clutches corresponding to the axially extending contour of the elongated portion of the shank under-structure for the reciprocal axial coupling. 
         [0031]    Additional geometric features, such as grooves, may be provided on the elongated portion of the shank under-structure for interlocking with the both footboard mounting elements. 
         [0032]    The assembling of mentioned elements is based generally on a friction-locked bonding actuated by adherence interconnecting, or is based on the use of a metallic and/or ceramic surface fixing blade elements to each other, or is based on force-fit or form-fit or shrinking joint connection, or is based on force closure means with a detachable or permanent connection. Additionally, one or more mechanical fixing means may be inserted into the connection area, wherein the mechanical fixing means are provided as separate parts and they can be cast into the connection area with a perfect fit connection. 
         [0033]    Another aspect of the invention regards supplement means for a sealing structure, wherein the sealing structure must be designed preferably as joining without force transmission between blade airfoil and platform element(s), wherein the platform element(s) comprise additional sub-modules. Different types of sealing structure come into consideration: 
         [0034]    1. A “rope seal” as is described for example in U.S. Pat. No. 7,347,424 B2. In this case, there are leakage losses, however. 
         [0035]    2. A “brush seal” Also in this case, leakage losses have to be taken into consideration. 
         [0036]    3. A temperature-resistant filing material for ensuring a 100%-sealing without leakage losses with simultaneous avoidance of force transmission, for example by means of superplastic material. 
         [0037]    4. Other seals are also conceivable, which are suitable for this application purpose. 
         [0038]    Especially by using a blade which can be assembled by at least two separate parts, i.e. blade airfoil comprising an elongated portion of the shank under-structure on the one hand, and separated coupling footboard mounting elements on the other hand, preconditions are created to provide an interchangeability or repairing and/or reconditioning of the identified separate parts, modules, elements, without replacing the whole blade. 
         [0039]    Basically, it is also possible to parcel out blades in various separate elements or modules, i.e. with respect to heat shield, blade airfoil, inner platform and footboard mounting part(s). If the blade comprises an intermediate shank between inner platform and footboard mounting part(s) the same implementation can be applied. 
         [0040]    Significant thermal stress concentration can be avoided by decoupling the separated coupling footboard mounting parts in axially direction from the blade airfoil and elongated portion of blade shank under structure. 
         [0041]    In addition, with decoupling these parts also different degrading mechanism can be separated, like oxidation of the inner platform from the low cycle fatigue of the blade airfoil portion. By decoupling the parts from each other, both have to carry themselves in corresponding carrier. The same proceeding can be adopted with respect to the heat shield. 
         [0042]    In case of a fixed position of the blade, by at least one fixing means at the inner end of the blade airfoil, the blade airfoil stays in close contact or is connected in one piece with the inner platform, which borders the hot gas flow through the turbine stage towards the inner diameter of the hot gas flow channel of the turbine stage. On the other hand, the inner platform, which is directly or indirectly connected with the blade airfoil in a flush manner, is manufactured in one piece with the blade airfoil and borders the hot gas flow channel radially outwards. 
         [0043]    Alternatively, the assembling of the blade airfoil in connection with the mentioned interdependent modules is based on the use of a metallic and/or ceramic surface fixing the blade modules to each other. Further alternatively, the assembling of the blade airfoil in connection with the other modules based on force-fit or form-fit or shrinking joint, or force closure means with a detachable or permanent connection, wherein at least one blade airfoil comprises at least one outer hot gas path liner, hereinafter called shell, encasing at least one part of the blade airfoil. 
         [0044]    The shell itself represents the aero profile of the blade airfoil and consists of an interchangeable module with various variants in cooling and/or material configurations and/or corporal compounding adapted to the different operating regimes of the turbomachine, e.g. gas turbine. 
         [0045]    Accordingly, the blade comprises a blade airfoil, having at its one end radial or quasi-radial means for inserting it into a recess and/or boost of an inner platform for the purpose of a detachable or semi-detachable or permanent or quasi-permanent connection resp. fixation, being independent on the elongated portion of the shank under-structure and footboard mounting part(s). 
         [0046]    This fixation can be made by means of a friction-locking actuated by adherence or through the use of a metallic and/or ceramic surface coating, or by a force closure means consisting of bolts or rivets, or made by HT brazing, active brazing or soldering. 
         [0047]    The same proceeding is also applied to the blade airfoil with respect to the heat shield, wherein the inner and outer modules can be consisted of one piece or a composite structure. 
         [0048]    According to individual operative requirements or individual operating regimes of a turbomachine, e.g. a gas turbine, particularly the footboard mounting part(s), the inner platform, or the footboard mounting part(s) include an integrated inner platform, blade airfoil, heat shield comprising additional means and/or inserts, which are able to withstand the thermal and physical stress, wherein the mentioned means and inserts are holistically or on their part interchangeable. 
         [0049]    However, it must be ensured that the inner platform and the heat shield of the blade of the first row are aligned adjacent to each other in circumferential direction limiting an annular hot gas flow in the region of the inlet of the turbine stage. 
         [0050]    In case of a solely detachable fixation between the inner end of the blade airfoil and inner platform, as mentioned before in connection with a preferred embodiment, the inner platform provides at least one recess for the insertion of the hook like extension or lug of the blade airfoil at its radially end(s) so that the blade airfoil is fixed at least in axial and circumferential direction of the turbine stage. Also in such a case the axial coupling between both footboard mounting parts and the elongated portion of the shank can be installed. 
         [0051]    Additional geometric features, namely variously designed grooves, may be provided on the elongated portion of the shank under-structure for interlocking with both footboard mounting parts. 
         [0052]    The hook like extension has a cross like cross section which is adapted to a groove inside the inner platform. The recess inside the inner platform provides at least one position for insertion or removal at which the recess provides an opening through which the hook like extension of the blade airfoil can be inserted completely only by radial movement. The shape of the extension of the blade airfoil and the recess in the inner platform is preferably adapted to each other like a spring nut connection. 
         [0053]    For insertion or removal purpose it is possible to handle the blade airfoil only at its radially outwardly directed end which is a remarkable feature for performing maintenance work at the turbine stage. 
         [0054]    It is feasible that the inner platform is detachably mounted to an intermediate piece, for example to a shank, or directly to the footboard mounting part which is also detachably mounted to the inner structure respectively inner component of the turbine stage. Hereto, the intermediate piece provides at least one recess for insertion a hook like extension of the inner platform for axially, radially and circumferentially fixation of the inner platform. 
         [0055]    The mentioned intermediate piece may be structured for an axially directed coupling like the coupling of both footboard mounting parts. 
         [0056]    Basically, the intermediate piece allows some movement of the inner platform in axial, circumferential and radial direction. There are some axial, circumferential and radial stop mechanisms in the intermediate piece to prevent the inner platform from unrestrained movements. With the axial and circumferential stop mechanism the blade airfoil of the blade is not cantilevered but supported at the outer and inner platform. An additional spring type feature presses the inner platform against a radial stop mechanism within the intermediate piece, so that the blade airfoil can be mounted into the outer and inner platform by sliding the blade airfoil radially inwards from a space above the heat shield liner. 
         [0057]    Furthermore, a manner of attaching the blade airfoil and outer shell or outer shell portions to the inner platform respectively heat shield consisting of a recess provided in the heat shield. 
         [0058]    Likewise, the radial end of the blade airfoil can be introduced in a recess of the inner platform. The mentioned recesses can be substantially blade-airfoil shaped, corresponding to the outer contour of the blade airfoil or blade airfoil assembly. Thus, the blade airfoil and blade airfoil assembly include at least one outer shell arrangement which can be trapped between the inner platform and the heat shield. 
         [0059]    Moreover, existing solutions according to the mentioned state of the art under section “Background of the Invention” cover only parts of the object of the present invention. A further important feature of the invention in connection with the operating aspects of the blade airfoil comprises at least one outer shell and, if necessary, at least one no flow-applied intermediate shell for modular alternatives of the original blade airfoil. 
         [0060]    The function of the blade airfoil carrier pertains to carrying mechanical load from the blade airfoil module. In order to protect the blade airfoil carrier with respect to the high temperature and separate thermal deformation from the blade airfoil module, an outer and, additionally, an intermediate hot gas path shell, also called intermediate shell, may be introduced. 
         [0061]    Accordingly, the intermediate shell is in any case optional in relation to the operating aspect of the blade. It may be required as compensator for potentially different thermal expansion of outer shell and spar understructure and/or cooling shirt for additional protection of the spar. The outer shell is joined to the optional intermediate shell or spar generally by interference fit or force-fit or form-fit, and the intermediate shell is also joined to the spar by interference fit, force-fit, form-fit or using a shrinking joint. 
         [0062]    The spar, including the tip cap, is manufactured by additive manufacturing methods, and includes a cooling configuration which additionally cools the spar. 
         [0063]    Furthermore, the intermediate shell provides, additionally, a protection to the spar understructure or airfoil contour in case of damage of the outer shell. Basically, the intermediate shell is an interchangeable module with many variations referring to cooling methods and/or material configurations, with the aim that the shell(s) is adapted to the different operating regimes of the gas turbine. 
         [0064]    If several superimposed shells are provided, they may be built with or without spaces between them. 
         [0065]    The internal cooling of the shells can be individually provided, or the cooling being operatively connected with the inner cooling of the blade airfoil. 
         [0066]    The mentioned shells may consist of at least two segments. Preferably, the segments, forming the shell, are connected together so as to permit assembly and disassembly of shell, shell components, blade airfoil and various other components of the blade. 
         [0067]    Fundamentally, the complete shell includes a leading edge and a trailing edge in conformity with the structure and aero profile of the blade airfoil. 
         [0068]    It is possible to compensate or reduce local differences in flow-applied and incoming flow onto the individual blade on the basis of a particular positioning of the respective blade row. It is in this way possible, inter alia, to reduce the excitation of oscillations in the blade region. 
         [0069]    In any damage event the repair of the flow-applied outer shell involves the replacement of the single damaged subcomponents, but not the entire replacement of the blade airfoil. The modular design facilitates the use of various materials in the shell, including materials with different physical values. Thus, suitable materials can be selected within the shell components to optimize component life, cooling air usage, aerodynamic performance, and costs. 
         [0070]    The flow-applied shell assembly can further include a seal provided between a recess and at least one of the radial ending of the shell and the outer peripheral surface of the blade airfoil proximate the radial end. As a result, hot gas infiltration or cooling air leakage, except when an effusion cooling is provided, can be excluded, if the shell segments can be brazed or welded along their radial interface at or near the outer peripheral surface so as to close the gaps. Alternatively, the gaps can be filled with a compliant insert or other seal (rope seal, tongue and groove seal, sliding dovetail, etc.) to prevent hot gas ingress and migration through the gaps. In all cases, the interchangeability or repairing and/or reconditioning of the single shell or shell components is to be maintained. 
         [0071]    The gap or groove of the radial interface of the single shell components can be filled with a ceramic rope and/or a cement mixture can be used. An alternative consists of a shrinking shell or shell components on the blade airfoil. If in such a case the interchangeability or repairing and/or reconditioning of the shell or shell components are not guaranteed, it must be ensured that the entire blade airfoil arrangement can be replaced. 
         [0072]    Both, inner platform and heat shield can be formed similar to components or subcomponents of the blade airfoil. 
         [0073]    Especially, the mentioned inner platform can consist of at least two segments. Preferably, the components forming the inner platform are connected together or to the blade airfoil and/or shell components, so as to permit assembly and disassembly of this inner platform. 
         [0074]    The hot gas loaded (flow-applied) side of platforms is equipped with one or more fixed or removable inserts. The insert equipment forming an integral coverage or capping with respect to the hot gas loaded area. 
         [0075]    The mentioned insert equipment has a coating surface, which is able to resist the thermal and physical stresses, wherein the mentioned equipment comprises inserts that are holistically or on their part interchangeable. 
         [0076]    The gap or groove of the axial and or radial interface of the single inserts within the outer and inner platform can be filled with a ceramic rope and/or a cement mixture can be used. An alternative consists of shrinking capping components on the mentioned platforms. If in such a case the interchangeability or repairing and/or reconditioning of inserts are not guaranteed, it must be ensured that the entire platform can be replaced. 
         [0077]    Regardless of the specific manner in which the blade airfoil or shells are attached to the inner platform and heat shield, the hot gases in the turbine must be prevented from infiltrating into any spaces between the recesses in the mentioned elements and blade airfoil resp. blade airfoil shells, so as to prevent undesired thermal inputs and to minimize flow losses. 
         [0078]    If the blade airfoil is internally cooled with a cooling medium at a higher pressure than the hot combustion gases, excessive cooling medium leakage into the hot gas path can occur. To minimize such concerns, one or more additional seals can be provided in connection with the shell arrangement. The seal means can comprise one rope seals, W-shaped seals, C-shaped seals, E-shaped seals, a flat plate, or labyrinth seals. The seal means can consist of various materials including, for example, metals and/or ceramics. 
         [0079]    Additionally, a thermal insulating material or a thermal barrier coating (TBC) can be applied to various portions of the blade assembly. 
         [0080]    The main advantages and features of the present invention being as follows:
       Thermo-mechanical decoupling of modules improves part lifetime compared to integral design.   Modules with different variants in cooling and/or material configuration can be selected to best fit to the different operating regimes of the gas turbine respectively power plant.   It is possible to introduce an inner spar comprising an extension from the root portion of the blade to the tip of the blade airfoil, and can be secured the inner spar to the attachment at the root portion by various connection means.   It is possible to introduce an inner spar comprising an extension from the root portion of the blade to the tip of the blade airfoil, wherein the spar having in the region of the shank a special contour in accordance with the contour of opposite cracks or clutches of footboard mounting parts.   The blade shank under-structure consisting, in radially direction of the airfoil, of an elongated and relatively slim formed portion. The elongated portion extends over the entire height of the footboard mounting part(s), wherein the foot-side end of the elongated portion having, along both sides of the axial expanse of this elongated portion, shapes of teeth, and the bottom of the elongated portion may be formed as a fir-tree-shaped cross-sectional profile. The teeth of the elongated portion may align with the recesses of two-piece footboard mounting parts to provide room for the teeth of the elongated portion. The footboard mounting parts having axially opposite cracks or clutches corresponding to the axially extending contour of the elongated portion for the reciprocal axial coupling.   The blade airfoil comprising a single outer shell, or interdependent shell, or intermediate shell components which can be selected in a manner to optimize component life, cooling usage, aerodynamic performance, and to increase the capabilities of resistance against high temperature stresses and thermal deformation.   The shells are segmented in various alternatives, wherein the individual part may be consisted in appropriate materials.   The capping or introduction of various inserts in connection with the inner platform and heat shield can be selected in a manner to optimize component life, cooling usage, aerodynamic performance, and to increase the capability of resistance against high temperature stresses and thermal deformations.   Root portion, inner platform, blade airfoil, heat shield and additional integrated elements can be completed with a selected thermal insulating material or a thermal barrier coating.   The spar having various passageways to supply a cooling medium through the blade.   The cooling of all above mentioned elements/modules of the blade consists mainly of a convective cooling, with selected impingement and/or effusion cooling.   The interchangeability or repairing and/or reconditioning of all elements/modules to one another are given as a matter of principle.   The fixation of the various elements/modules to one another can be consisted in means of a friction-locked connection actuated by adherence or through the use of a metallic and/or ceramic surface coating, or by bolts or rivets, or by HT brazing, active brazing or soldering.   The platforms may be composed of individual parts, which being on the one hand actively connected to the blade airfoil and shell elements and on the other hand being actively connected to rotor and stator.   The modular design of the blade airfoil facilitates the use of various materials in the structure of the shell, including materials which are dissimilar, in accordance with the different operating regimes of the gas turbine respectively power plant.   The modular blade assembly consisting of replaceable and non-replaceable elements, and besides the modular blade assembly comprising substitutable and/or non-substitutable elements.       
 
         [0097]    In addition, the following summaries form an integral part of this description:
       First summary: The blade airfoil has a pronounced or swirled aerodynamic profile in radially direction, is cast, machined or forged comprising additionally additive features with internal local web structure for cooling or stiffness improvements. Furthermore, the blade airfoil may be coated and comprising flexible cooling configurations for adjustment to operation requirements like, base-load, peak-mode, partial load of the gas turbine respectively power plant.   Second summary: Referring to the blade airfoil a preferred solution of this invention has a blade shank under-structure consisting, in radial direction of the airfoil, of an elongated and relatively slim formed portion. The elongated portion extends over the entire height of the footboard mounting part(s), wherein the foot-side end of the elongated portion having, along both sides of the axial expansion of the elongated portion, shapes of teeth, and the bottom of the elongated portion of the shank under-structure may be formed as a final part of the fir-tree-shaped cross-sectional profile. The teeth of the elongated portion of the shank under-structure may align with the recesses of two-piece footboard mounting parts to provide room for the teeth of the elongated portion.   Third summary: The inner platform is cast, forged or manufactured in metal sheet or plates. The inner platform is consumable in relation to predetermined cycles and replaced frequently as specified maintenance period and may be decoupled under other mechanical provisions from blade airfoil, wherein, supplementary, the inner platform may be mechanically connected to airfoil carrier using closure elements, namely bolts or rivets. The inner platform may be coated with CMC or ceramic materials.   Fourth summary, the shank is cast, forged or manufactured in metal sheet or plate. The shank is normally not consumable in relation to predetermined cycles and replaced as specified maintenance period and may be under other mechanically decoupled from blade airfoil, wherein the shank may be supplementary mechanically connected to airfoil using closure elements, namely bolts or rivets. The inner platform may be coated with CMC or ceramic materials.   Fifth summary: The footboard mounting parts consist essentially of inner platform, shank and fir-tree-shaped-shaped cross sectional portion having axially opposite cracks or clutches corresponding to the axially extending contour of the elongated portion of the shank under-structure for the reciprocal axial coupling.   Sixth summary: The assembly of the modules according to second and fifth summary is as follows: Separated footboard mounting parts (see fifth summary) and elongated blade airfoil (see second summary) are assembled by joining two correspond pieces of the footboard mounting parts with placing the underside elongated portion of the rotor blade airfoil between them before mounting the assembly to the rotor fir-tree recess. The modules may be sealed against each other by ceramic seal means or similar.   Seventh summary: If the blade airfoil is provided with an outer platform on the side of stator, this element is cast, forged or manufactured in metal sheet or plate. The outer platform is consumable in relation to predetermined cycles and replaced frequently as specified maintenance period and may be under other mechanically decoupled from the blade airfoil, wherein, supplementary, the outer platform may be mechanically connected to blade airfoil using closure elements, namely bolts or rivets. The outer platform may be coated with CMC or ceramic materials.   Eighth summary: The spar as under-structure of the flow-applied blade airfoil operating directly as under structure of the shell assembly, which is interchangeable, pre-fabricated or manufactured, in being single or multi-piece, uncooled or cooled, if cooled using convective and/or film and/or effusion and/or impingement cooling structure, having a web structure for cooling or stiffness improvement.   Ninth summary: The outer shell is an optional embodiment and represents the aero profile of the blade airfoil. The outer shell is interchangeable, consumable, pre-fabricated, using single or multi-piece with radial or circumferential patches and comprising variants in cooling and/or material configurations adapted to the different operating regimes of the gas turbine respectively power plant. The outer shell is joined to the intermediate shell or spar, may be used a shrinking assembly.   Tenth summary: The intermediate shell is an optional embodiment and may be required as compensator for potentially different thermal expansion of outer shell and spar and/or as cooling shirt for additional thermal protection of the spar. Also it provides additional protection of the spar in case the outer shell suffers damage by encumbrances, mechanical or thermal stresses or oxidation. The intermediate shell is interchangeable, consumable, pre-fabricated, using single or multi-piece with radial or circumferential patches and comprising variants in cooling and/or material configurations adapted to the different operating regimes of the gas turbine respectively power plant. The intermediate shell is joined to the spar, and may be used a shrinking assembly.   Eleventh summary: The insert elements and/or mechanical interlock are inserted at least in a force-fitting manner into appropriately designed recesses in the space of/or within a module of the blade, in the manner of a push loading drawer comprising additional fixing means, wherein the upper surface of the insert and/or mechanical interlock forming the respective flow-applied zone and may provide thermal protection of the modules.   Twelfth summary: The optional closing pieces may be crimped or welded on the various modules to secure assembly of all parts and may potentially provide thermal protection of the involved modules.       
 
         [0110]    The foregoing and other features of the present invention will become more apparent from the following description and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0111]    The invention shall subsequently be explained in more detail based on exemplary embodiments in conjunction with the drawing. In the drawing: 
           [0112]      FIG. 1  shows an axial assembly of the rotor blade; 
           [0113]      FIG. 2  shows a plan view according to  FIG. 1 ; 
           [0114]      FIG. 2 a    shows a three-dimensional view of the footboard mounting parts or elements 
           [0115]      FIG. 2 b    shows a further three-dimensional view of the footboard mounting parts or elements 
           [0116]      FIG. 3  shows an exemplary assembled rotor blade; 
           [0117]      FIG. 4  shows a longitudinal section through the assembled rotor blade; 
           [0118]      FIG. 5  shows a partial longitudinal section through the upper end of the rotor blade airfoil; 
           [0119]      FIG. 6  shows a partial longitudinal section through the root portion of the rotor blade; 
           [0120]      FIG. 7  shows a cross section through the rotor blade airfoil. 
           [0121]      FIG. 8  shows a platform with inserts or mechanical interlocks optionally sealed by HT ceramics. 
           [0122]      FIG. 9  shows a joining technology in the range of the tip of the rotor blade airfoil. 
           [0123]      FIG. 10  shows a further joining technology in the range of the tip of the rotor blade airfoil. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0124]      FIG. 1  shows a rotor blade assembly  100 , comprising an airfoil  110  having a pressure side and a suction side and a rotor blade shank under structure consisting, in radially direction of the airfoil, of an elongated and relatively slim formed portion  150 . The elongated portion  150  extends over the entire height of the footboard mounting part comprising inner platform  122 / 132 , shank portion  123 / 133  and a root portion  160  with a fir-tree-shaped cross-sectional profile, which subject to the invention, namely the footboard mounting part is divided into at least two-folded footboard mounting elements  120 ,  130 . The footboard mounting part may be consisted of several elements. 
         [0125]    The foot-side end of the elongated portion  150  has opposed extending teeth  152 , and the bottom of the elongated portion of the shank under structure may be formed as the final part  151  of the fir-tree-shaped cross-sectional profile  160 . The teeth  152  of the elongated portion  150  of the shank under structure may align with the recesses of both separate footboard mounting elements  120 ,  130  to provide room for the teeth of the elongated portion  150 . 
         [0126]    According to  FIG. 2  the footboard mounting elements  120 ,  130  having axially opposite cracks or clutches  121 ,  131  corresponding to the axially extending contour of the elongated portion of the shank under structure  150  for the reciprocal axial coupling  140 ,  141 . Additional geometric features such as grooves may be provided on the elongated portion of the shank under structure for interlocking with the both footboard mounting elements. 
         [0127]    A further improvement in connection with the assembly of footboard mounting elements  120 ,  130  referring to the sealing structure, wherein the sealing must be designed preferably as joining without force transmission between rotor blade airfoil and footboard mounting parts elements  120 ,  130 . In this context, reference is made to  FIGS. 2 a  and 2 b   , from which emerges for a person skilled in the art the geometry of these parts. 
         [0128]    Different types of seal come into question, namely:
       a rope seal,   a brush seal,   a temperature-resistant filing material for ensuring a 100%-sealing without leakage losses with simultaneous avoidance of force transmission, for example by means of superplastic material,   other seals are also conceivable, which are suitable for this application purpose.       
 
         [0133]    In  FIG. 3  an assembled rotor blade  100  according to an exemplary embodiment of the invention is reproduced. The rotor blade  100  comprises a blade airfoil  110  which extends in the longitudinal direction of the rotor blade along a longitudinal axis  111 . 
         [0134]    The blade airfoil  110 , which is delimited by a leading edge  112  and a trailing edge  113  in the flow direction, merges into a shank  120 / 130  at the lower end beneath an inner platform  122 / 132  which forms the inner wall of the hot gas passage, the shank terminating in a customary blade root portion  160  with a so called fir-tree-shaped cross-sectional profile by which the rotor blade  100  can be fastened on a blade carrier, especially on a rotor disk, by inserting into a corresponding axial slot. 
         [0135]    The inner platform abuts the platforms of neighbouring blades to help define a gas passage inner wall for the turbine. An outer not specially shown heat shield at the tip of the blade airfoil  114  cooperates again with its neighbours in the manner shown to help define the outer wall of the turbine&#39;s gas passage. 
         [0136]    Cooling passages, which are not shown, extend inside the blade airfoil  110  for cooling the rotor blade  100  and are supplied with a cooling medium, particularly cooling air, also via a feed hole  124  which is arranged on the shank  123  at the side (see  FIG. 4 ). The shank  123 / 133  may consist of a concave and a convex side, similar to the blade airfoil  110 . In  FIG. 3  the convex side faces the viewer. The feed hole  124 , which extends obliquely upwards into the interior of the blade airfoil  110 , opens into the outside space on the convex side of the shank  120 . 
         [0137]      FIG. 4  shows a section taken from sectional lines IV-IV of  FIG. 3 . The embodiment of the rotor blade  100 , generally illustrated with reference numeral  200 , comprising outer shell assembly  220 , intermediate shell  230 , and generally elliptical shaped spar  210 . The spar  210  extending longitudinally or in the radial direction from a root portion  160  to a tip embodiment  240  with a downwardly extending first portion  211  and a second portion  212  that fair into a rectangular shaped projection  213  that is adapted to fit into an attachment which is anchored in a final complementary portion  214  with the same outer contour compared to the fir-tree-shaped cross-sectional profile  160 . 
         [0138]    The shank  120 / 130  may be formed with the inner platform  122 / 132  may be formed separately and joined thereto and projects in a circumferential direction to abut against the inner platform in the adjacent rotor blade in the turbine disk (not shown). A seal (not shown) may be mounted between platforms of adjacent rotor blades to minimize or eliminate leakage around the individual rotor blades. 
         [0139]    The tip  114  of the rotor blade  100  may be sealed by an embodiment  240  that may be formed integrally with the spar  210 , or may be a separate piece that is suitably joined to the top end of the spar  210 . The outer shell  220  extends over the surface of the spar  210  and is located in the central portion  221  and spaced from the outer surface of the spar  210 . 
         [0140]    The outer shell  220  defines a pressure side (see  FIG. 7 ), a suction side (see  FIG. 7 ), a leading edge  112  and a trailing edge  113  (see also  FIG. 3 ). As mentioned above the outer shell  220  may be consisted of different materials depending on the different operating regimes of the gas turbine. The outer shell  220  can consist of a single unit or be divided into various parts along the longitudinal axis  111  (see  FIG. 3 ), similar to the spar  210 . 
         [0141]    As shown in  FIG. 4 , the cooling air  215  is additionally (see numeral  124 ) admitted through an inlet  216 , the central opening formed at the ingress in the final complementary portion  214  and, subsequently, in the spar  210 , and flows in a straight passage or interior cavity  217  in radially or quasi-radially direction. 
         [0142]    According to  FIG. 4  an intermediate shell  230  may be introduced. The intermediate shell  230  constitutes one of the important features of the invention. It may be required as a compensator for potentially different thermal expansion of outer shell  220  and spar  210  and/or cooling shirt for additional protection of the spar. The outer shell  220  is joined to the intermediate shell  230  or generally to the spar  210  by interference fit, wherein the intermediate shell  230  is also joined to the spar by interference fit, or generally by a shrinking joint. 
         [0143]    Furthermore, the intermediate shell  230  provides additional protection to the spar  210  in case of damage of the outer shell  220 . Basically, the intermediate shell  230  is an interchangeable module with variants in cooling and/or material configurations adapted to the different operating regimes of the gas turbine. If several superimposed shells are provided, they may be built with or without spaces between each other. 
         [0144]    The internal cooling of the shells may be individually provided, or the cooling being operatively connected with the inner cooling of the blade airfoil. 
         [0145]    Additionally, referring to  FIG. 4 , it can be introduced an additional retaining sleeve (not expressly shown) in the rectangular shaped projection  213 . 
         [0146]      FIG. 5  shows a partial longitudinal section through the upper end of the blade airfoil. The tip  114  of the rotor blade  100  may be sealed by an embodiment  240  that may be formed integrally with the spar  210 , or may be a separate piece that is suitably joined to the top end of the spar  210 . The outer shell  220  extends over the surface of the spar  210 . According to  FIG. 5  an intermediate shell  230  may be made. The intermediate shell  230  constitutes one of the important features of the invention. It may be required as compensator for potentially different thermal expansion of outer shell  220  and spar  210  and/or cooling shirt for additional protection of the spar. The outer shell  220  is joined to the intermediate shell  230  or generally to the spar  210  by interference fit, wherein the intermediate shell  230  is also joined to the spar by interference fit. 
         [0147]    Additionally,  FIG. 5  shows different configurations of cooling holes  251 ,  252  through the elements of the rotor blade airfoil in partially or integrally manner. Furthermore,  FIG. 5  shows a feeding cavity  260  in the intermediate shell  230 . The spar  210  and the various shells  220 ,  230  are provided in the flow and peripheral directions with a number of regularly or irregularly distributed cooling holes  251 ,  252  having the most varied cross-sections and directions compared to the flow direction of the cooling medium. Through the cooling holes  251 ,  252  a cooling medium quantity flows outside of the rotor blade and an increase in the velocity being induced along the surface of the rotor blade. 
         [0148]      FIG. 6  shows a partial longitudinal section through the root portion of the rotor blade. The interior cavity of the rotor blade airfoil (see  FIG. 4 , item  217 ) is integrally or partially filled with an appropriate filling material  270  which can exert various functions. 
         [0149]      FIG. 7  shows a cross section through the rotor blade airfoil, comprising inner platform  122 / 123 , pressure side  280 , suction side  290 , leading edge  112 , trailing edge  113 , outer shell  220  (a detailed intermediate shell is shown in  FIGS. 4 and 5 ), spar, filling material  270  (see also  FIG. 6 ), feeding cavities  260 ,  261 , rib  271  situated in the region of the trailing edge  113  of the rotor blade airfoil  110 . 
         [0150]      FIG. 8  shows a platform  122 / 123  of a rotor blade assembly with inserts and/or mechanical interlocks  301 - 303  optionally sealed by HT ceramics. This arrangement may involve inner and/or outer platform, and/or airfoil, and/or outer hot gas path liner, and are disposed along or within the caloric stress areas, namely the flow-applied zone of the rotor blade. The insert element and/or mechanical interlock forming the respective flow-applied zone are inserted at least in a force-fitting manner into appropriately designed recesses or in the manner of a push loading drawer with additional fixing means  304 . Additionally, the insert element and/or mechanical interlock may be sealed by HT ceramics. 
         [0151]      FIG. 9  shows a joining technology in the range of the tip of the rotor blade airfoil. Specifically,  FIG. 8  shows the connection between the spar  210  and the outer shell  220 . The mentioned elements  210 ,  220  are assembled with the aid of a force F acting metallic clamp  310  in axial direction. A spring  311  results actively connected to the metallic clamp  310  and the spar  210 , and indirectly to the outer shell  220 . 
         [0152]      FIG. 10  shows a further joining technology in the range of the tip of the rotor blade. The assembly in connection with the outer shell  401  with respect to the spar  600  comprising a spring  312  and metallic cover element  313 . 
         [0153]    Important aspects of the shown joining in connection with  FIGS. 9 and 10  are as follows: CMC or metallic outer shell is necessary to protect the sensitive metallic spar. Avoid point mechanical load, especially on the CMC, reduce risk of failure. Generally, good mechanical behaviour is waiting referring to CMC under compression on wide surface. With respect to fixing the CMC or metallic outer shell by brazing, soldering or using HT ceramic adhesives. The concept involves an interference fit with ceramic bush an compensator (spring) and fixation of CMC or metallic shell with metallic clamp and spring ( FIG. 9 ) or by spring and metallic cover ( FIG. 10 ). 
         [0154]    Although this invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention. 
       LIST OF REFERENCES NUMEROUS 
       [0000]    
       
           100  Rotor blade 
           110  Rotor blade airfoil 
           111  Longitudinal axis 
           112  Leading edge of the blade airfoil 
           113  Trailing edge of the blade airfoil 
           114  Tip of the blade airfoil 
           120  Footboard mounting element 
           121  Crack or clutches 
           122  Inner Platform 
           123  Shank portion 
           124  Feed hole 
           130  Footboard mounting element 
           131  Crack or clutches 
           132  Inner Platform 
           133  Shank portion 
           140  Reciprocal axial coupling 
           141  Reciprocal axial coupling 
           150  Elongated portion of the rotor blade airfoil 
           152  Opposed extending teeth 
           160  Root portion with a fir-tree-shaped cross-sectional profile 
           200  Embodiments of the rotor blade 
           210  Spar 
           211  Downwardly extending first portion 
           212  Downwardly extending second portion 
           213  Rectangular shaped portion 
           214  Final complementary portion 
           215  Cooling air or cooling medium 
           216  Inlet 
           217  Interior cavity 
           220  Outer shell 
           221  Central portion 
           230  Intermediate shell 
           240  Tip 
           251  Cooling holes 
           252  Cooling holes 
           260  Feeding cavity 
           261  Feeding cavity 
           270  Filling material 
           271  Rib 
           280  Pressure side 
           290  Suction side 
           301  Insert, mechanical interlock 
           302  Insert, mechanical interlock 
           303  Insert, mechanical interlock 
           304  Fixing means 
           310  Metallic clamp 
           311  Spring 
           312  Spring 
           313  Cover element