Abstract:
The invention relates to a turbine blade comprising a vane that runs along a blade axis and a platform region, which is located at the root of the vane having a platform that extends transversally to the blade axis. The aim of the invention is to configure a delimitation of a flow channel of a gas turbine in the simplest possible manner. Therefore, the platform is configured by an elastic sheet metal part that rests on the vane. Said part leads to a gas turbine comprising a flow conduit that runs along an axis of the gas turbine, said conduit having an annular cross-section for a working medium and a second vane stage that is situated downstream of a first vane stage, which runs along the axis.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2005/000223, filed Jan. 12, 2005 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 04001107.4 filed Jan. 20, 2004. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a turbine blade with a blade leaf arranged along a blade axis and with a platform region, which, arranged at the foot of the blade leaf, has a platform extending transversely with respect to the blade axis. The invention applies, furthermore, to a gas turbine with a flow duct extending along an axis of the gas turbine and having an annular cross section for a working medium, and a second blade stage arranged downstream of a first along the axis, a blade stage having a number of annularly arranged turbine blades extending radially into the duct. 
     BACKGROUND OF THE INVENTION 
     In a gas turbine of this type, temperatures which may lie in the range of between 1000° C. and 1400° C. arise in the flow duct after it has been acted upon by hot gas. The platform of the turbine blade, as a result of the annular arrangement of a number of such turbine blades in a blade stage, forms part of the flow duct for a working fluid in the form of hot gas which flows through the gas turbine and thereby drives the axial turbine rotor by the turbine blades. Such high thermal stress on the flow duct boundary formed by the platforms is counter-acted in that a platform is cooled from the rear, that is to say from a turbine blade foot arranged below the platform. For this purpose, the foot and the platform region conventionally have suitable ducting so as to be acted upon by a cooling medium. 
     An impact-cooling system for a turbine blade of the type initially mentioned may be gathered from DE 2 628 807 A1. In DE 2 628 807 A1, for cooling of the platform, a perforated wall element is arranged upstream of that side of the platform which faces away from the hot gas, i.e. downstream of the platform, that is to say between a blade foot and the platform. 
     Cooling air under relatively high pressure impinges through the holes of the wall element onto that side of the platform which faces away from the hot gas, with the result that efficient impact cooling is achieved. 
     EP 1 073 827 B1 discloses a novel way of designing the platform region of cast turbine blades. The platform region is designed as a double platform consisting of two platform walls lying opposite one another. What is achieved thereby is that the platform wall directly exposed to the flow duct and therefore to the hot gas and delimiting the flow duct can be made thin. The design in the form of two platform walls results in functional separation for the platform walls. The platform wall delimiting the flow duct is responsible essentially for the ducting of hot gas. The opposite platform wall not acted upon by the hot gas takes over the absorption of the loads originating from the blade leaf. This functional separation allows the platform wall delimiting the flow duct to be made so thin that the ducting of the hot gas is ensured, without substantial loads in this case having to be absorbed. 
     In the design of the turbine blade of the type initially mentioned, in a parting plane between platforms of turbine blades of the same blade stage which are contiguous or of adjacent turbine blades of blade stages arranged one behind the other, sealing measures are necessary in order to prevent an unwanted and excessive outflow of cooling medium into the flow duct acted upon by hot gas. The measures required for sealing off may lead to difficult situations in structural and cooling terms on a platform wall subjected to high thermal load and constitute an increased potential for the failure of a turbine blade and consequently of a gas turbine. 
     Conventionally, the sealing off of such parting planes is achieved by the installation of special sealing elements. However, on the one hand, these have to be sufficiently flexible to permit simultaneous relative movements of adjacent parts, in particular of adjacent turbine blades and their platforms, and, on the other hand, they must nevertheless maintain a sealing action. The installation of such sealing elements leads to geometrically and structurally complicated components. As a result of this, special cooling measures are necessary so that platform edge regions where access is difficult can be cooled sufficiently. 
     It would be desirable to have a gas turbine in which the boundary of the flow duct is configured as simply as possible and at the same time can be cooled effectively and is sealed off. 
     SUMMARY OF THE INVENTION 
     This is where the invention comes in, the object of which is to specify a turbine blade with a platform, which at the same time is configured in a simple way and also advantageously satisfies the geometrically structural and cooling requirements within the framework of a flow duct boundary of a gas turbine. Furthermore, the sealing off of the parting planes between adjacent turbine blades is to take place particularly simply and cost-effectively. 
     As regards the turbine blade, the object is achieved by the invention by means of the turbine blade initially mentioned, in which, according to the invention, the platform is formed at least partially by a first resilient elastic sheet metal part which is fixed to the blade leaf and which can be laid against an adjacent turbine blade. 
     The invention proceeds from the consideration that the use of a platform which is not load-bearing for forming the boundary of a flow duct, acted upon by hot gas, of a gas turbine is fundamentally suitable for cooling the platform and consequently the boundary of the flow duct as effectively as possible. Beyond this, the essential recognition of the invention is that it is possible to equip the platform itself with an increased sealing action, specifically in that the platform is made thin-walled such that it is formed by a resilient elastic sheet metal part lying against the blade leaf. 
     To be precise, the platform, as a part delimiting the flow duct acted upon by hot gas, consequently fulfills all the requirements in terms of cooling and also of a sealing element. By resilient elastic sheet metal part being fixed to the blade leaf, to be precise, the platform as such is sufficiently flexible to permit simultaneous relative movements of adjacent blade leaves and of other parts, and nevertheless maintains the sealing action. This avoids the need for a special sealing element. This simplifies the configuration and cooling of the flow duct boundary. 
     According to the invention, the first resilient elastic sheet metal part is provided as a platform wall which is not load-bearing, which at least partially delimits the flow duct acted upon by hot gas. A load-bearing platform wall provided in EP 1 073 827 B1, which would be arranged downstream of the first resilient elastic sheet metal part, may largely be dispensed with. The platform therefore consists at least partially of the first resilient elastic sheet metal part fixed to the blade leaf. 
     The sealing element necessary hitherto between platforms of adjacent turbine blades may be dispensed with, since the first resilient elastic sheet metal part of one turbine blade lies sealingly against the other adjacent turbine blade. 
     The advantages as regards the cooling and sealing action of the first resilient elastic sheet metal part for the platform and consequently the flow duct boundary are preserved. 
     Advantageous developments of the invention can be gathered from the subclaims and specify in detail advantageous possibilities, in particular, for developing the platform in terms of the above object. 
     According to a particularly preferred development of the invention, there is provision for the platform to be formed by the first resilient elastic sheet metal part fixed to a first abutment on one side of the blade leaf and to be formed by a second sheet metal part fixed to a second abutment on the other side of the blade leaf. Consequently, two sheet metal parts are expediently provided, which form the platform and which therefore extend on both sides transversely with respect to the blade axis on one side of the blade leaf and the other. 
     Expediently, the second sheet metal part lying against the blade leaf assumes the function of a first platform wall not bearing the load of the blade leaf, and, furthermore, the platform has a second platform wall bearing the load of the blade leaf. In this refinement, appropriate cooling space for acting upon by cooling medium is formed between the first platform wall which is not load-bearing and which consists of the second sheet metal part and the second thicker load-bearing platform wall, as a special load-bearing structure. 
     According to a development of the invention, each abutment may be designed in the form of a groove or edge. This allows a particularly reliable and fluidically beneficial fastening of the sheet metal part to the foot of the blade leaf. 
     Within the scope of a preferred development of the invention, it has proved expedient for the sheet metal parts, in particular the first, to be held at a further abutment of an adjacent turbine blade. Expediently, this further abutment may be in the form of a bearing support. 
     For example, such a bearing support may be formed by a step integrally formed between the blade foot and the foot of the blade leaf. The first sheet metal part of a first turbine blade engages sealingly behind the bearing support of the turbine blade adjacent to this. The second sheet metal part may advantageously engage behind the bearing support arranged on the same turbine blade or, additionally or alternatively, may be attached to the step. 
     Expediently, in the state of rest, the first resilient elastic sheet metal part lies loosely against the further abutment of the adjacent turbine blade. In this case, a sufficient fastening, yet to be explained, of the sheet metal part arises from the movement or fluidic tie-up of the turbine blade in the operating state of a gas turbine. 
     The sealing action of the first resilient elastic sheet metal part on the further abutment may be further improved if the first resilient elastic sheet metal part lies against the further abutment under a self-generated prestress. 
     Furthermore, to achieve the object, the invention applies to a gas turbine mentioned initially, a blade stage having a number of annularly arranged turbine blades extending radially into the flow duct, in accordance with the invention a turbine blade being designed according to an abovementioned type. 
     Advantageous developments of the gas turbine may be gathered from the further subclaims and specify in detail advantageous possibilities, in particular, for designing the flow duct boundary and the function of the turbine blade within the framework of the flow duct boundary in accordance with the above object. 
     Within the framework of a first development, the turbine blade is a moving blade. Such a moving blade is fastened to an axially extending turbine rotor and rotates together with the turbine rotor during operation of the gas turbine. During the rotary operation of a turbine blade in the form of a moving blade on the turbine rotor, a centrifugal force acting from the foot of the blade leaf in the direction of the blade leaf is generated as a result of rotation. In this case, according to the development, the first resilient elastic sheet metal part achieves a sufficient sealing action between two mutually contiguous sheet metal parts of two adjacent moving blades. As a result of the centrifugal force, the first resilient elastic sheet metal part of a first moving blade is pressed against a further abutment of the second moving blade and is thereby laid in place, fastened by centrifugal force. That is to say, even in the event that the first resilient elastic sheet metal part lies loosely against the further abutment in the state of rest of the moving blade, the centrifugal force ensures that the resilient elastic sheet metal part lies sealingly against the moving blade in the operating state. When the moving blade of the gas turbine is in operation, the first resilient elastic sheet metal part thus also has the function of a sealing element. In this case, the lying surface of the first resilient elastic sheet metal part against the further abutment of the adjacent moving blade in the form of a bearing support advantageously acts as a sealing abutment for the first metal part. The penetration of hot gas flowing through the turbine through the gap formed hitherto between two platforms of adjacent moving blades can be avoided on account of the effective seal, as can an undesirably high leakage of coolant through the gap into the hot-gas space. 
     According to an alternative development of the gas turbine, the turbine blade is provided as a guide blade on the peripheral turbine casing. During the operation of a turbine blade in the form of a guide blade on the turbine casing, a pressure drop is generated by a cooling medium from the foot of the blade leaf in the direction of the blade leaf. In this case, the alternative development provides for the first resilient elastic sheet metal part of a first guide blade to be pressed due to the pressure drop against the further abutment of a second guide blade and thereby to be fastened by pressure. The pressure drop is thus generated in that the first resilient elastic sheet metal part is acted upon from the rear by cooling medium and is thereby pressed against the further abutment. For a guide blade, the pressure drop is sufficiently high, so that this not only suffices for a pressure fastening of the first resilient elastic sheet metal part against the further abutment, but, furthermore, when the guide blade in the gas turbine is in operation, the first resilient elastic sheet metal part has the function of a sealing element. The lying surfaces of the first resilient elastic sheet metal part act as sufficient sealing surfaces at an abutment explained above, and the abutment acts as an abutment for the first resilient elastic sheet metal part. 
     Within the framework of a refinement of the gas turbine, it proves advantageous that a flow duct boundary is continuously formed, between a first turbine blade and an adjacent second turbine blade of the same blade stage, by a first resilient elastic sheet metal part of the first turbine blade and by a second sheet metal part of the second turbine blade. Within a blade stage, a continuous radial boundary of the flow duct is thereby advantageously formed. 
     Within the framework of a further refinement of the gas turbine, it proves advantageous, furthermore, that a flow duct boundary is continuously formed, between a first turbine blade of the first blade stage and a second turbine blade of the second blade stage axially adjacent to the first turbine blade with respect to the rotor, by a first resilient elastic sheet metal part of the first turbine blade and by a second sheet metal part of the second turbine blade. A continuous boundary of the flow duct is thereby advantageously formed. Advantageously, the blade stages are guide blade stages and the turbine blades are guide blades. 
     Because of, the abovementioned types of continuous boundary, the parting planes, otherwise to be sealed off in the case of conventional boundaries of a flow duct of a gas turbine, and the then additionally required sealing elements are expended. The problems arising in connection with sealing elements are eliminated entirely on account of the continuous delimitation of the flow duct by means of the first resilient elastic sheet metal part and the second sheet metal part. 
     In this case, it proves expedient that a first resilient elastic sheet metal part arranged on a first turbine blade and a second sheet metal part arranged on a second turbine blade are held jointly at the further abutment of the first turbine blade. Details are explained in connection with the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A particularly preferred exemplary embodiment of the invention is described below with reference to the drawing. This is not intended to illustrate the exemplary embodiment true to scale, on the contrary the drawing, where appropriate for an explanation, is in diagrammatic and/or slightly distorted form. As regards additions to the teachings which can be seen directly from the drawing, reference is made to the relevant prior art. In particular, in the drawing: 
         FIG. 1  shows a particularly preferred embodiment of a gas turbine with a flow duct and with a preferred version of the guide and moving blading in diagrammatic form in a cross-sectional view; 
         FIG. 2  shows a platform region of a particularly preferred embodiment of a first turbine blade of a first blade stage and of a second turbine blade, axially adjacent to the first turbine blade, of a second blade stage, in a perspective view. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a gas turbine  1  with a flow duct  5  extending along an axis  3  and having an annular cross section for a working medium M. A number of blade stages are arranged in the flow duct  5 . In particular, a second guide blade stage  9  is arranged downstream of a first guide blade stage  7  along the axis  3 . Furthermore, a second moving blade stage  13  is arranged downstream of a first moving blade stage  11 . The guide blade stages  7 ,  9  in this case have a number of guide blades  21  arranged annularly on a peripheral turbine casing  15  and extending radially into the flow duct  5 . A moving blade stage  11 ,  13  in this case has a number of moving blades  23  arranged annularly on an axial turbine rotor  19  and extending radially into the flow duct  5 . The flow of a working medium M is in this case generated in the form of a hot gas by a burner  17 . Correspondingly to the annular cross section of the flow duct  5 , a number of such burners  17  are arranged around the axis  3  in an annular space not shown in the cross-sectional drawing of  FIG. 1 . 
     A guide blade  21  and a moving blade  23  are shown diagrammatically in  FIG. 1 . A guide blade  21  has a blade tip  27  arranged along a blade axis  25 , a blade leaf  29  and a platform region  31 . The platform region  31  has a platform  33  extending transversely with respect to the blade axis  25  and a blade foot  35 . 
     A moving blade  23  has a blade tip  37  arranged along a blade axis, a blade leaf  39  and a platform region  41 . The platform region  41  has a platform  43  extended transversely with respect to the blade axis  45  and a blade foot  47 . 
     The platform  33  of a guide blade  21  and the platform  43  of a moving blade  23  thus form in each case part of a boundary  49 ,  51  of the flow duct  5  for the working medium M which flows through the gas turbine  1 . The peripheral boundary  49  is in this case part of the peripheral turbine casing  15 . The rotor-side boundary  51  is in this case part of the turbine rotor  19  rotating when the gas turbine  1  is in the operating state. 
     As indicated diagrammatically in  FIG. 1  and shown in detail in  FIG. 2 , in this case the platform  33  of a guide blade  21  and the platform  43  of a moving blade  23  are formed by sheet metal parts fixed to the blade leaf  29 ,  39 . 
       FIG. 2  shows, to represent a platform region  31 ,  41 , a platform region  61 . The first turbine blade  63  and second turbine blade  65 , shown in  FIG. 2 , in this case represents a first guide blade  21  of a first guide blade stage  7  and a second guide blade  21 , arranged directly axially downstream of this, of a second guide blade stage  9 . The first turbine blade  63  and the second turbine blade  65  also represent a first moving blade  23 , shown in  FIG. 1 , of the first moving blade stage  11  and a second moving blade  23 , directly arranged axially downstream of this, of the second moving blade stage  13 . Preferably, however, the turbine blades  63 ,  65  are guide blades. 
     The first turbine blade  63  has a blade leaf  69  depicted in truncated form. The second turbine blade  65  in this case has a blade leaf  67  depicted in truncated form. In the case of the first turbine blade  63  and of the second turbine blade  65 , the platform region  61  has formed in it, at the foot of the blade leaf  67 ,  69 , a platform  71  which extends transversely with respect to the blade axis  73 ,  75 . In this case, the platform  71  is formed, on the one hand, by a first resilient elastic sheet metal part  79  shown in the first blade  63  and, on the other hand, by a second sheet metal part  77  shown in the second blade  65 . The first resilient elastic sheet metal part  79  is fastened to a first abutment  83  on one side of the blade leaf  69 , this side being shown in the case of the first turbine blade  63 . The second resilient elastic sheet metal part  77  is fastened to a second abutment  81  on the other side of the blade leaf  67 , this side being shown in the case of the second turbine blade  65 . The fastening may take place, for example, by welding or soldering and is in this case leak tight. The first abutment  83  and the second abutment  81  are in each case designed in the form of a groove, into which in each case the first resilient sheet metal part  79  and the second sheet metal part  77  butts in each case with its edge ending at the blade leaf  69  or at the blade leaf  67 . Furthermore, the second resilient elastic sheet metal part  77  is held at a further abutment  85  of the second turbine blade  65 . In the present embodiment, the second sheet metal part  77  is attached to the abutment  85 . Alternatively or additionally, the second sheet metal part  77  could also engage behind the further abutment  85 . The latter case applies to the first resilient elastic sheet metal part  79  of the first turbine blade  63 , which sheet metal part is held jointly with the second sheet metal part  77  at the further abutment  85  of the second turbine blade  67 . For this purpose, the first resilient elastic sheet metal part  79  engages loosely behind the further abutment  85 . The further abutment  85  is designed in the form of a bearing support for holding the second sheet metal part  77  and the first resilient elastic sheet metal part  79  and thus forms, on its side facing the first resilient elastic sheet metal part  79 , a sealing surface which serves as an abutment for the first resilient elastic sheet metal part  79 . 
     A boundary  87  of the flow duct  5  is formed in the way outlined above between the first turbine blade  63  and the second turbine blade  65  by the first resilient elastic sheet metal part  79  of the first turbine blade  63  and by the second sheet metal part  77  of the second turbine blade  65 , the boundary  87  being continuous. Thus, the use of a thin-walled platform  71  which is not load-bearing for producing the boundary  87  in the form of a second sheet metal part  77  and of a first resilient elastic sheet metal part  79  makes it possible at the same time for the sheet metal parts  77 ,  79  to act as a sealing element. A sealing element of this type is at the same time sufficiently flexible to allow relative movement of the adjacent first turbine blade  63  and second turbine blade  65 , and nevertheless has a sufficient sealing action. This avoids the need for a sealing element, such as would have been necessary for the sealing off of parting planes in the case of hitherto conventional platforms lying opposite one another. Potentially high-risk, structurally and thermally unfavorable reception structures of such a sealing element are consequently avoided. 
     In the embodiment shown here, the platform  71  largely manages on its rear side  89  without a supporting structure or a load-bearing platform wall arrangement. Instead, on the rear side  89 , a first cooling space  93  and a second cooling space  91  are formed, which make it possible to cool the platform  71  optimally in the region between the second turbine blade  65  and the first turbine blade  63 . Thus, a platform edge design which is otherwise normally complicated to configure can, in connection with the further abutment  85 , have a simpler configuration without any thermally high-risk region. To assist the cooling in the cooling spaces  91 ,  93 , the carrying structure  95 ,  97  of the turbine blades  65 ,  63  which starts from the foot of the blade leaf  67 ,  69  is continued with an optimized configuration toward the blade foot  35 ,  47  in  FIG. 1 . 
     The sealing action, provided particularly at the further abutment  85 , of the second sheet metal part  77  and of the first resilient elastic sheet metal part  79  arises, depending on the type of operation of the first turbine blade  63  and of the second turbine blade  65 , preferably in the form of a guide blade  21  shown in  FIG. 1  or, if appropriate, also in the form of a moving blade  23  shown in  FIG. 1 . 
     During the rotary operation of a turbine blade  65 ,  63  in the form of a moving blade  23  on a turbine rotor  19 , to be precise, a centrifugal force acting from the foot of the blade leaf  67 ,  69  in the direction  99  of the blade leaf  67 ,  69  is generated as a result of rotation. A pressure drop, in the case of a guide blade  21 , also occurs in addition. It is also conceivable that the first resilient elastic sheet metal part  79  lies sealingly against the further abutment  85  by means of a prestress self-generated by the first resilient elastic sheet metal part  79 . The pressing force generated by the pressure drop can thereby be intensified. 
     During the operation of a turbine blade  65 ,  63  in the form of a guide blade  21 , shown in  FIG. 1 , on a peripheral turbine casing  15 , a pressure drop from the foot of the blade leaf  67 ,  69  in the direction  99  of the blade leaf  67 ,  69  is generated from the rear side  89  of a platform  71  by a cooling medium. The direction  99  of an abovementioned centrifugal force for a moving blade  23  also the direction  99  of the pressure drop for a guide blade  21  are identified in  FIG. 2  by an arrow. Depending on the design of the turbine blade  67 ,  69  as a moving blade  23  or as a guide blade  21 , therefore, the platform  71  in the form of the resilient elastic sheet metal parts  77 ,  79  is pressed against the further abutment  85  by means of the centrifugal force or by means of the pressure drop. In this way, the sheet metal parts  77 ,  79  of the platform  71  are fastened by centrifugal force or fastened by pressure and at the same time deploy their sealing action and separating action between the flow duct  5 , acted upon by hot gas, and the rear side  89 , acted upon by cooling medium, of the platform  71 . 
     In summary, in order to configure a boundary  87  of a flow duct  5  of a gas turbine  1  as simply as possible, in the case of a turbine blade  63 ,  65  with a blade leaf  67 ,  69  arranged along a blade axis  73 ,  75  and with a platform region  61  which, arranged at the foot of the blade leaf 
       67 ,  69 , has a platform  71  extending transversely with respect to the blade axis  73 ,  75 , it is proposed that the platform  71  be formed by a sheet metal part  77 ,  79  fixed to the blade leaf  67 , 69 . This also applies to a gas turbine  1  with a flow duct  5  extending along an axis  3  of the gas turbine  1  and having an annular cross section for a working medium M, and with a second blade stage  9 ,  13  arranged downstream of a first  7 ,  11  along the axis  3 , a blade stage  7 ,  9 ,  11 ,  13  having a number of annularly arranged turbine blades  63 ,  65  extending radially into the duct  5 , according to the above concept.