Abstract:
The invention relates to a guide vane ( 17 ) for a turbomachine ( 1 ), in particular a gas turbine guide vane, in which the platform ( 48 ) has a separating region ( 50 ), which is embodied as a separate component. This has, in particular, advantages with respect to the simplification of cast blade/vane ( 17 ) in terms of manufacturing technology, with respect to the variability of a material selection, the quality of a protective coating to be applied and efficient cooling.

Description:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/EP00/02499 which has an International filing date of Mar. 21, 2000, which designated the United States of America, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a guide blade for a turbomachine, preferably for a turbine and even more preferably a gas turbine, for use, for example, in a power station for generating electricity. The invention also preferably relates to a guide blade ring made up of such guide blades. The invention relates, even more preferably, to a component for bounding a flow duct in a turbomachine. 
     BACKGROUND OF THE INVENTION 
     Such a gas turbine has a shaft or a rotor to which so-called rotor blades are permanently connected. The rotor blades extend in the radial direction into a flow duct of the turbine. A plurality of rotor blades form a rotor blade ring in the peripheral direction of the rotor. A plurality of rotor blade rings are arranged at a distance from one another in the longitudinal direction of the rotor. So-called guide vanes, which extend in the radial direction from, the outside into the flow duct, are arranged on the turbine casing. The guide vanes are likewise arranged in guide vane rings, the individual guide vane rings meshing with the rotor blade rings in the manner of teeth. In contrast to the rotor blades, the guide vanes are solidly and immovably fastened on the casing. 
     The flow duct enclosed between the rotor blades and the guide vanes is bounded by the guide vanes and rotor blades and is sealed toward the outside. For this purpose, both the rotor blades and the guide vanes have, as a rule, a so-called platform in the region of their blade/vane root, with which they are fastened to the rotor or to the casing. This platform extends essentially at right angles to their blade/vane aerofoil, which protrudes radially into the flow duct. 
     Very high temperatures occur, particularly in the case of gas turbines in the field of electricity generation. Efforts are made to achieve continually higher gas temperatures in the course of efficiency increases. This increases the demands made on the materials used and on the cooling, which is generally necessary, of the individual components of the gas turbine. 
     An impingement cooling system for a gas turbine blade/vane is revealed in DE 26 28 807 A1. The gas turbine blade/vane is aligned along a blade/vane axis and has a blade/vane aerofoil and a platform region along the blade/vane axis. In the platform region, the platform extends transverse to the blade/vane axis away from the blade/vane aerofoil outward approximately at right angles. In this way, the platform forms a part of the flow duct for a working fluid (hot gas), which flows through the gas turbine. Due to the very high temperatures in the flow duct, the surface of the platform exposed to the hot gas is subjected to severe thermal effects. In order to cool the platform, a perforated wall element is arranged in front of the surface of the platform facing away from the hot gas. Cooling air enters via the holes in the wall element and meets the surface of the platform facing away from the hot gas. This achieves efficient impingement cooling. 
     WO 97/12125 A1 shows a sealing element for sealing a gap between components of a gas turbine installation. Two blades/vanes directly adjacent to one another in a blade/vane ring have mutually opposite grooves on opposing edges of their platforms. A sealing element is inserted into these grooves. A gap between the platforms is sealed by this sealing element. At the same time, however, the platforms are not rigidly connected to one another so that sufficient clearance remains for thermal expansions in particular. The sealing element has a profiled surface area and this provides an improved sealing effect. 
     In addition to being subjected to thermal effects, the rotor blades must withstand high centrifugal forces during operation because of the rotational speed of the rotor. This applies particularly to turbines which are employed as propulsion engines or propulsion turbines, for example in the aeronautical field. Particularly high rotational speeds are provided for such propulsion turbines. Because of the high centrifugal forces associated with the high rotational speeds, efforts are made to achieve the lowest possible mass of the rotor blades, particularly in the case of these propulsion turbines. For this purpose, U.S. Pat. No. 3,294,364 proposes separating the platform from the individual guide blades, i.e. to dispense with an integral unit, consisting of rotor blades and platform, and its advantages. For the multi-part configuration demands, as compared with the integral unit, increased complexity and therefore increased time and cost requirements during the assembly of the rotor blades in the turbine. The separation between the platform and the actual rotor blade is, for example, known from U.S. Pat. No. 5,244,345. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a guide blade for a turbomachine which can be manufactured simply and at favorable cost. A further object of the invention is to provide a guide blade ring made up of such guide blades and to provide a component for bounding a flow duct in a turbomachine. 
     According to the invention, the object directed towards the guide blade is achieved by means of a guide blade for a turbomachine, which guide blade is aligned along a blade/vane axis and has a blade/vane aerofoil arrangement, a fastening region and a platform region arranged between the blade/vane aerofoil region and the fastening region. The platform region is preferably designed to receive a separating region which can be separated non-destructively from the guide blade. The separating region is preferably part of a platform, which is associated with the platform region, for bounding a flow duct in the turbomachine. 
     The guide blade is therefore no longer configured integrally, as was previously usual in the case of guide blades, but has a platform region which can be separated—the separating region. This multi-part design therefore initiates a new way of constructing guide blades. In contrast to the rotor blades for aircraft turbines, for which such a multi-part construction is known, the construction does not appear to be appropriate for guide blades of a gas turbine in the field of electricity generation. On the one hand, there are of course no centrifugal forces in the case of the guide blades and, on the other, the assembly complexity and therefore the expenditure of time and cost are disadvantageously influenced by the multi-part construction. 
     In a surprising manner, however, the multi-part design leads to a marked simplification of the manufacturing process for the guide blade per se. Particularly in the case of one-piece cast guide blades, this is due to the casting process being very much simpler because at least part of the platform, which usually protrudes at right angles to the blade/vane axis, does not have to be cast at the same time. This results in a casting mold which is very much simpler to handle and manufacture. This simplification of the casting process is important, particularly in the case of single-crystal or directionally solidified guide blades. Such guide blades have very good material properties. Because attempts are made to achieve continually higher operating temperatures for gas turbines in the field of electricity generation, it is usually only possible to employ such high-quality guide blades. 
     A further essential advantage of the multi-part configuration for the manufacturing process may be seen in the fact that the individual parts have clearly simplified geometry as compared with the integral configuration. This permits the application of a high-quality coating which protects the turbine guide blades from damage, in particular from thermal damage due to the desired high temperatures. In the case of the integral configuration, a high-quality and enduring coating is only possible with great difficulty in the transition region between the blade/vane aerofoil and the platform extending essentially at right angles to it because, in this transition region, it is almost impossible to achieve a uniform coating, such as is possible in the case of a simple geometry, in particular in the case of a flat shape. 
     Material pairing is, furthermore, at best only possible in a very limited manner in the case of an integral design. For both reasons, cost and the different, in particular thermal, demands made on the various blade/vane regions, however, it can be advantageous to use different materials for various regions of the blade/vane. This applies particularly to the platform. Because of the independent embodiment of at least a part of the platform as a separating region, this separating region can be manufactured from a material which is different from the rest of the blade/vane material. Manufacture with an independent separating region is of particular advantage in the case of a guide blade, in which the platform has to receive, at most, a small part of loads which occur during an employment of the guide blades in a turbomachine. The fastening region is then advantageously configured in such a way that it receives the essential part of these loads. Because of this, no particular measures have to be taken for a particularly stable and permanent connection when attaching the separating region at the platform region. 
     The separating region can be advantageously attached by means of a blading-side edge, with the platform region and the blading-side edge being configured in such a way that they mesh together, in particular over the complete length of the blading-side edge, when the separating region is attached. 
     Such meshing together achieves good fixing of the separating region on the platform region. In addition, meshing together seals the separating region and the platform region against a working medium or against a cooling medium. The working medium, in particular hot gas, is guided within the flow duct of the turbomachine whereas the cooling medium for cooling the platform flows onto the platform on the surface remote from the flow duct surface. 
     In addition, the blading-side edge and the platform region preferably mesh together as groove and tongue. This is particularly simple from the point of view of manufacturing technology and also permits simple installation of the blade/vane in the turbomachine. 
     An intermediate piece can be advantageously introduced between the platform region and the blading-side edge, which intermediate piece seals a gap, which remains between the separating region and the platform region after the attachment of the separating region. A gap remaining between the platform region and the separating region is therefore sealed, by means of such an intermediate piece, against entry of the working medium flowing in the flow duct. The intermediate piece can also, however, reduce or prevent entry of a cooling medium into the flow duct. In addition, a mechanical fixing of the separating region on the platform region can also be achieved by means of the intermediate piece. This is preferably achieved by both the blading-side edge and the platform region having a groove. These grooves are located opposite to one another during an attachment of the separating region. The intermediate piece can be laid in the grooves, in particular over the complete groove length. When the separating region is attached, therefore, the two opposing grooves form a channel into which the intermediate piece is introduced. This corresponds to the arrangement of the sealing element between the platforms of two adjacent blades/vanes, as follows from WO 97/12125 A1 cited further above. 
     The platform advantageously has an area extension, the separating region having a proportion more than 70% of this area extension. In consequence, a major part of the platform is configured in the form of the separating region. More than 90% of the platform is preferably configured as the separating region. The platform is therefore an independent component to a major or even almost complete extent. 
     A stiffening rib preferably extends from the separating region, in particular approximately at right angles to an area extent of the separating region. This stiffening rib is connected to the fastening region when the separating region is attached. Such a stiffening rib serves to provide an additional mechanical stabilization of the platform in the turbomachine. The stiffening rib preferably meshes into the fastening region, and in particular—as described for the separating region and the platform region—by means of a groove and tongue configuration or by means of an intermediate piece introduced into the opposing grooves. By this means, the separating region is also fixed to the fastening region in addition to being fixed on the platform region. An extension approximately at right angles of the stiffening rib relative to the area extension of the separating region provides mechanical fixing in a direction approximately at right angles to the fixing direction in the platform region. 
     The guide blade is preferably designed as a gas turbine guide blade of a gas turbine in a power station for generating electricity. As already mentioned, the gas turbine guide blade is subjected to particularly severe thermal effects due to the hot gas flowing in the flow duct, i.e. the hot gas duct. The platform, too, is subject to these severe thermal effects. The at least partially separate design of the platform as an independent component, the separating region, immediately achieves several advantages, of which the essential ones are briefly summarized once again: 
     1. The separating region can be manufactured from a material which is different from the material of the rest of the guide blade because it does not have to be cast together with the rest of the guide blade. As an example, the separating region can be manufactured from a ceramic material. The separating region can also include a metallic material, or an alloy, which is different from the material of the rest of the guide blade. 
     2. Gas turbine guide blades are frequently provided with a coating system for protection against oxidation and/or corrosion and for protection against overheating. Due to the separate embodiment of the separating region, a different coating system can be provided for the separating region and for the rest of the vane to match different thermal effects. In addition, this coating can be applied more simply and with a higher quality because the blade/vane and the separating region can be respectively coated separately. Particularly in the case of plasma spraying, it is important to align the surface to be coated as nearly as possible at right angles to the plasma beam. In the case of oblique spraying, increased porosity occurs on the coating and, therefore, increased susceptibility to flaking. The separate embodiment of guide blade and platform by means of the separating region makes it possible to place both the guide blade and the separating region substantially at right angles to the plasma jet during the coating operation. 
     3. The platform cooling is frequently effected by arranging impingement cooling sheets on the side of the platform remote from the hot gas duct. Such sheets have openings by means of which the cooling air is fed at right angles onto the platform surface to be cooled. In the case of a guide vane with a completely integral configuration, it can be difficult to apply such impingement cooling sheets. Problems particularly occur when a double platform is provided. In the double platform, a platform part on the hot gas side undertakes the screening from the hot gas whereas a load-carrying platform part opposite, in the radial direction, to this platform part on the hot gas side undertakes the receiving of the load. In such a double-platform concept, relatively little space remains between the platform parts so that welding on platform cooling sheets is complex and difficult. In the case of a separating region which is separate, these difficulties do not arise because the separating region can be provided with impingement cooling sheets or further means, for example turbulators or ribs, in a simple manner and independently of the rest of the blade/vane. 
     4. The transition region between the blade/vane aerofoil and the platform is a critical region with respect to the thermal effects because radiusing, and therefore an accumulation of material, occurs in this region. This transition region is difficult to cool and, because of the accumulation of material, is subjected to particularly severe thermal stresses at the same time. Due to the separate embodiment of the separating region, this transition region can now be cooled effectively and in a simple manner. This takes place by feeding cooling air through a gap between the separating region and the platform region. The cooling air therefore flows through this gap directly past the critical transition region and cools the latter in the process. 
     According to the invention, the object directed toward a guide blade ring is achieved by means of a guide blade ring with guide blades according to one of the above embodiments, the separating region respectively associated with a guide blade being arranged between two guide blades immediately adjacent to one another. 
     That part of the platform which is located in each case between two adjacent guide blades is therefore configured as a separating region. The complete guide blade ring is therefore built up from guide blades with separating regions introduced separately between them. The advantages of such an assembly follow in a manner corresponding to the above statements with respect to the advantages of the guide blades. 
     Two guide blades immediately adjacent to one another are preferably associated respectively with a single, common separating region. In consequence, each of the two guide blades share a separating region located between them. In other words, each two guide blades have a common platform region which is located between them. This results, in particular, in a simplification with respect to manufacture technology because the number of components is reduced. 
     According to the invention, the object directed toward a component is achieved by a component for bounding a flow duct in a turbomachine, which component can be introduced between two immediately adjacent guide blades of a guide blade ring and can be connected to these guide blades. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiment examples of the invention are explained in more detail using the drawing. In this, diagrammatically in part and not to scale: 
     FIG. 1 shows a gas turbine, 
     FIG. 2 shows a part of a gas turbine guide blade in perspective view, 
     FIG. 3 shows another embodiment of a gas turbine guide blade in perspective view, 
     FIG. 4 shows an excerpt from a connection location between a separating region and a platform region, and 
     FIG. 5 shows an end view onto a guide blade ring of a gas turbine. 
    
    
     SIMILAR DESIGNATIONS HAVE THE SAME SIGNIFICANCE IN THE VARIOUS FIGURES. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a gas turbine  1  such, for example, as is employed in the field of electricity generation in a power station. A compressor  5 , a combustion chamber  7  and a turbine part  9  are arranged sequentially along a turbine center line  3 . The compressor  5  and the turbine part  9  are arranged on a common shaft  11 . In the case of a power station, the shaft  11  is connected to a generator (not shown here) for generating electrical energy. A flow duct  12  is provided in the turbine part  9 . Guide blade rings  13  and rotor blade rings  15 , of which only one ring is shown as an example in each case, are arranged alternately in sequence in the flow duct  12  along the turbine center line  3 . Each guide blade ring  13  is built up from gas turbine guide blades  17 . Each rotor blade ring  13  is built up of gas turbine rotor blades  19 . 
     During operation of the gas turbine  1 , ambient air  21  is compressed in the compressor  5  and supplied to the combustion chamber  7 . There, it is burnt along with fuel being supplied. The resulting hot exhaust gas  23  (also designated as hot gas) is led through the flow duct  12 . A reduction in pressure occurs during this procedure. The potential energy released in the process is transferred as kinetic energy via the guide blades  17  and the rotor blades  19  to the shaft  11 , which is provided with a rotational motion. The components in the flow duct  12 , in particular the gas turbine guide blades  17  and the gas turbine rotor blades  19 , are subjected to severe thermal effects due to the hot exhaust gas  23 . 
     FIG. 2 shows, in perspective view, a part of a gas turbine guide blade  17 . A blade/vane aerofoil region  34 , a platform region  36  and a fastening region  38  are arranged sequentially along a blade/vane axis  32 . When the gas turbine guide blade  17  is installed in a gas turbine  1 , the blade/vane aerofoil region  34  protrudes into the flow duct  12 . The fastening region  38  is used for fastening the gas turbine guide blade  17  in the gas turbine  1 . The blade/vane aerofoil region  34  has a suction surface  40  and a pressure surface  42 . The blade/vane aerofoil region  34  merges into the platform region  36  in a radiused transition region  44 . 
     The platform region  36  includes a platform  48 , which extends at right angles to the blade/vane axis  32  and which, when the gas turbine guide blade  17  is installed in the gas turbine  1 , partially bounds the flow duct  12 . The platform  48  is essentially configured as a separate component, namely as a separating region  50 . In the platform region  36 , a groove  46  extends approximately at right angles to the blade/vane axis  32  and so that it follows the contour of the blade/vane aerofoil region  34 . Matching this groove  46 , a tongue  52 , i.e. a protrusion  52  which extends along the blading-side edge  51  and which can be introduced as an accurate fit into the groove  46 , is arranged on a blading-side edge  51  of the separating region  50 . Groove and tongue can also be exchanged, i.e. the separating region  50  has the groove  46  and the platform region  36  has the tongue  52 . 
     The separating region  50  has an area extension F. Ribs  56  are arranged on the lower surface of the separating region  50  and approximately at right angles to this area extension F. When the separating region  50  is attached to the platform region  36 , the blading-side edge  51  of the separating region  50  meshes, by means of the tongue  52 , with the groove  46 . This attachment of the separating region  50  is represented by the arrows  58 . At the same time, the ribs  56  come into coincidence with grooves  49  in the fastening region  38  and are connected in the fastening region  38  with an appropriate connector (not shown in any more detail). Such a connector can, for example, be an intermediate piece  82  described in more detail by means of FIG.  4 . Additional stiffening of the connection between separating region  50  and platform region  36  is achieved by means of the ribs  56 . The fastening region  38  is configured in such a way that it receives the essential part of the forces which are exerted on the gas turbine guide blade  17  during operation of the gas turbine  1 . Essentially, therefore, the separating region  50  is used only for screening from the hot exhaust gas  23  in the flow duct  12 , i.e. for bounding the flow duct  12 . 
     The separated embodiment of the separating region  50  as a separate component provides substantial simplification from the point of view of manufacturing technology, particularly in the case of a cast gas turbine guide blade  17 , because a platform  48  which protrudes at right angles makes the casting process more complicated and more expensive. In addition, the separating region  50  can be embodied in an arbitrary material matched to the requirements at the platform  48  independently of the rest of the gas turbine guide blade  17 . In addition, the separating region  50  can be provided with a coating which may differ from the coating of the rest of the gas turbine guide blade  17 . Furthermore, this coating can be applied, for example in the case of plasma spraying, in a high-quality manner because the separating region  50  can be oriented in an optimum manner during the coating process independently of the rest of the gas turbine guide blade  17 . In addition, the transition region  44  between the blade/vane aerofoil region  34  and the platform region  36  can be effectively cooled because cooling air can be led between the separating region  50  and the platform region  36  through the groove  46  and past the edge  52  to the transition region  44 , where it effectively cools the transition region  44 . It is precisely the transition region  44  which, because of material thickening, presents a critical location with respect to thermal stresses. 
     FIG. 3 shows, in perspective view, a further design of a gas turbine guide blade  17 . In this representation, it can be seen that the gas turbine guide blade  17  has a hollow space  60  which extends through the gas turbine guide blade  17  and along the blade/vane center line  32 . Stiffening ribs  62  are arranged within the hollow space  60 . The fastening region  38  has mutually opposed hook-on edges  63   a  and  63 b. These hook-on edges  63   a  and  63   b  are used to fasten the gas turbine guide blade  17  in the gas turbine  1 . The hook-on edges  63   a  and  63   b  are stiffened by means of stiffening ribs  64 . A separating region  50  forming the platform  48  can, as already described in FIG. 2, be connected to the rest of the gas turbine guide blade  17 . The separating region  50  has, on the cold side  69  opposite to the hot-gas side (and visible in this representation), impingement cooling pockets  68  over which is arranged an impingement cooling sheet  70  with impingement cooling openings  72 . These cooling means can be applied particularly simply due to the separate embodiment of the separating region  50 . A groove  66 , which extends approximately at right angles to the blading-side edge  51  in an end region  67  of the separating region  50  is used, corresponding to the fastening of the separating region  50  in the platform region  36 , for fastening the separating region  50  onto a further component (not shown here in any more detail) of the gas turbine  1 . 
     FIG. 4 shows, in perspective and as excerpt, a further possibility for the mechanical fixing of the separating region  50  on the platform region  36 . In contrast to fixing in accordance with the groove and tongue principle, such as is represented in FIGS. 2 and 3, FIG. 4 shows fastening by way of an intermediate piece  82 , which is laid both in a groove  80  of the separating region  50  on the blading-side edge  51  and in the groove  46  of the platform region  36 . The intermediate piece  82  has, in addition, a profiled surface  84  through which a sealing effect is increased. Such a sealing effect is used for sealing a gap between the separating region  50  and the platform region  38  against the hot exhaust gas  23  in the flow duct  12 . This is represented in more detail in FIG.  5 . 
     FIG. 5 shows, in a plan view, an excerpt from a guide blade ring  13 . Each two gas turbine guide blades  17  directly adjacent to one another share a separating region  50  located between them in the peripheral direction of the guide blade ring  13 . A gap  86  is located between the separating regions  50  and the platform regions  36  of the respective gas turbine guide vanes  17 . This is sealed against penetration of the hot exhaust gas  23  from the flow duct  12  by the intermediate piece  82 , as shown in FIG.  4 . The embodiment of the separating region  50  as a common separating region  50  for each two blades reduces the number of components and, by this means, achieves a further simplification from the point of view of manufacturing technology. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.