Abstract:
A turbine guide blade includes a platform which absorbs thermal loads and a fastening region adjoining the platform for absorbing mechanical loads. The fastening region has such a slim construction that it leaves a cold side of the platform readily accessible.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of copending International Application No. PCT/DE99/02595, filed Aug. 18, 1999, which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a turbine guide blade which is directed along an axis and has a blade profile, a platform and a fastening region. 
     German Published, Non-Prosecuted Patent Application DE 26 28 807 A1 discloses an impingement-cooling system for a gas-turbine blade. The gas-turbine blade is directed along a blade axis and has a blade body and a platform region along the blade axis. A platform extends in the platform region, transversely to the blade axis, radially outwardly away from the blade body. Such a platform forms part of a flow duct for a working fluid that flows through a gas turbine in which the turbine blade is fitted. Very high temperatures occur in that flow duct in a gas turbine. As a result, that surface of the platform which is exposed to the hot gas is subjected to high thermal loading. 
     In order to cool the platform, a perforated wall element is disposed in front of that side of the platform which faces away from the hot gas. Cooling air enters through the holes in the wall element and strikes that side of the platform which faces away from the hot gas. Efficient impingement cooling is thus achieved. 
     A guide-blade segment having closed-circuit steam cooling is described in European Patent Application EP 0 698 723 A2, corresponding to U.S. Pat. Nos. 5,634,766; 5,591,002; and 5,743,708. The guide-blade segment has a platform region which serves to define a hot-gas duct of a gas turbine. The platform region has an outflow-side hook with which it is connected to a casing of a steam turbine in such a way as to absorb loads. The platform region serves both as a hot-gas screen and to absorb loads. 
     A turbine blade disclosed in UK Patent 1 516 757, corresponding to U.S. Pat. Nos. 4,012,167 and 4,017,213, is constructed in a similar manner. There too, a cooled platform region acts through an outflow-side hook connecting it to the casing of a gas turbine to assume the functions of both absorbing loads and providing the hot-gas screen. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a turbine guide blade, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which can be cooled in a simple and efficient manner. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a turbine guide blade, comprising a guide blade axis. A blade profile is disposed along the axis and has a profile contour. A platform follows the blade profile along the axis. The platform has a hot-gas side for defining a hot-gas duct of a turbine and a cold side opposite the hot-gas side. A fastening region follows the platform along the axis, for absorbing most mechanical loads caused by a working medium flowing around the blade profile. The platform has to absorb at most a small portion of the mechanical loads. The fastening region, in a projected view along the axis in a direction from the fastening region toward the blade profile, covers less than three quarters of the cold side. 
     Such a turbine guide blade has a functional separation for thermal loads on one hand and mechanical loads on the other hand. The thermal loads are absorbed in front of the fastening region largely by the platform. The platform screens a working medium flowing around the blade profile from the fastening region and forms part of a flow duct of a turbine in which the turbine blade is fitted. The platform has a comparatively thin construction, so that it can be cooled in an efficient manner. Such a thin construction is made possible due to the fact that most of the mechanical loads which act on the turbine blade due to the working fluid are absorbed by the fastening part. The turbine guide blade can be fastened in a turbine housing through the fastening part. The force acting on the blade profile and being exerted by the working fluid is transmitted to the turbine casing through the fastening part. The platform must therefore absorb at most a small proportion of those forces and can therefore have a comparatively thin construction. The accessibility of the cold side of the platform may be restricted by the fastening part, e.g. when the fastening part has a platform-like construction. The invention removes that disadvantage by providing a slim construction of the fastening part. Thus the fastening part only partly covers the cold side. The cold side is therefore still readily accessible, e.g. for the fitting of an impingement-cooling plate. 
     In accordance with another feature of the invention, the fastening region includes a core which is connected to the cold side and has a core contour running in the same direction as the profile contour; and a planar web which extends along the axis and serves for fastening in a turbine casing. 
     In accordance with a further feature of the invention, the core is connected to the web through a stiffening connecting region. 
     In accordance with an added feature of the invention, a vertical rib preferably connects the core and the web in a stiffening manner along the axis. A horizontal rib preferably connects the core and the web in a stiffening manner perpendicularly to the axis. Furthermore, four vertical ribs and/or four horizontal ribs are preferably provided. 
     Projections or hooks, for example, with which the turbine guide blade is hooked in the turbine casing, are disposed on the web. A robust and yet slim construction of the fastening region is achieved by the construction of the fastening region with a core and a stiffening connection between the core and the web. In particular, the fastening region obtains stiffness which is sufficient for the use of the turbine guide blade, by ribbing through the use of the vertical and/or horizontal ribs. 
     In accordance with an additional feature of the invention, the vertical rib or ribs and/or the horizontal rib or ribs are formed in one piece with the core and with the web. 
     In accordance with yet another feature of the invention, the turbine guide blade is preferably cast and in fact preferably directionally solidified or single-crystalline. 
     In accordance with yet a further feature of the invention, the turbine guide blade has an impingement-cooling plate which is disposed in front of the cold side and in turn has a multiplicity of openings directed toward the cold side. With such an impingement-cooling plate, cooling fluid is directed through the openings perpendicularly onto the cold side. The platform is cooled in an especially efficient manner by such impingement cooling. The impingement-cooling plate can be fitted in a very simple manner due to the easy accessibility of the cold side. In addition, the easy accessibility of the cold side also permits the fitting of a more complex impingement-cooling system. 
     In accordance with a concomitant feature of the invention, the turbine guide blade is constructed as a gas-turbine guide blade. In particular in a stationary gas turbine, very high temperatures for the gas flowing through the gas turbine are achieved. There is thus a need for very efficient cooling of the platform of a gas-turbine guide blade. Very effective cooling is achieved with the concept of a comparatively thin platform which is readily accessible from the cold side, since the production of the gas-turbine guide blade at the same time turns out to be very simple. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a turbine guide blade, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, perspective view of a gas-turbine guide blade as seen from a first direction of view; 
     FIG. 2 is a perspective view of the gas-turbine blade of FIG. 1 as seen from a second direction of view; and 
     FIG. 3 is a plan view of a fastening region of a gas-turbine guide blade. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail to the figures of the drawings, in which the same reference numerals have the same meaning, and first, particularly, to FIG. 1 thereof, there is seen a gas-turbine guide blade  1 . A head region  5 , a blade profile  7  with a profile contour  8 , a platform  9  and a fastening region  11  extend along an axis  3 . The head region  5  serves to define and seal a non-illustrated hot-gas duct of a gas turbine on the shaft side. The gas-turbine guide blade  1  can be fitted in the gas turbine. In the fitted state, the blade profile  7  is disposed in the hot-gas duct. The platform  9  serves to define and seal the hot-gas duct on the casing side. The platform  9  has a hot-gas side  9 B directed toward the blade profile  7  and a cold side  9 A opposite the hot-gas side  9   b . The platform  9  is stiffened by an encircling strut  10 . The fastening region  11  serves to fasten the gas-turbine guide blade  1  in a turbine casing. The fastening region  11  includes a core  13  with a core contour  14 . The core  13  is disposed on the cold side  9 A and the core contour  14  thereof geometrically constitutes an extension of the blade profile  7 . A cavity  15  passes through the core  13  as well as through the blade profile  7 . Cooling air for cooling the gas-turbine guide blade  1  can be directed into this cavity  15 . 
     Two planar webs  17 A,  17 B directed along the axis  3  are disposed on the cold side  9 A. In particular, an incident-flow-side web  17 A is disposed on the side of a leading edge  7 A of the blade profile  7 . An outflow-side web  17 B is disposed on the side of a trailing edge  7 B of the blade profile  7 . The core  13  lies between the webs  17 A,  17 B. The incident-flow-side web  17 A has an L-shaped projection  19 A at its end. The outflow-side web  17 B has a parallelepiped-shaped projection  19 B at its end. The gas-turbine guide blade  1  is hooked in a turbine casing through the use of the projections  19 A,  19 B. The core  13  is connected to the webs  17 A and  17 B in a connecting region  18  in a stiffening and rounded-off manner. Four horizontal ribs  21  which stiffen the fastening region  11  perpendicularly to the axis  3 , are also provided. Two respective horizontal ribs  21  are disposed between each web  17 A and  17 B and the core  13 . In addition, four vertical ribs  23  are provided between the platform  9  and the horizontal ribs  21 , specifically one vertical rib  23  for each horizontal rib  21 . These vertical ribs  23  connect the core  13  to the webs  17 A,  17 B in a stiffening manner. Therefore, stiffening along the axis  3  is obtained. 
     Due to this construction of the fastening region  11  with the core  13 , the webs  17 A,  17 B and the horizontal and vertical ribs  21 ,  23 , a very robust configuration of the fastening region  11  is obtained. At the same time, however, the fastening region  11  only partly covers the cold side  9 A, as is seen in FIG.  3 . As a result, the cold side  9 A is still readily accessible. In this way, structural measures for cooling the platform  9  can be taken in a simple manner, from the production point of view. In particular, an impingement-cooling plate seen in FIG. 3 can be attached in front of the cold side  9 A in a simple manner. Furthermore, a considerable saving in weight is obtained for the turbine guide blade, a factor which is of particular interest for an aircraft engine. 
     FIG. 2 shows the gas-turbine guide blade  1  of FIG. 1 in a direction of view facing toward the trailing edge  7 B. The vertical ribbing on the incident-flow side of the fastening region  11  can be seen in this direction of view. This vertical ribbing corresponds to the outflow-side vertical ribbing provided by the vertical ribs  23 . 
     FIG. 3 shows a projected view of the gas-turbine guide blade  1  of FIG. 1 along the axis  3  in the direction from the fastening part  11  toward the blade profile  7 . It becomes clear in this view that the fastening region  11  only partly covers the cold side  9 A. Preferably, more than one quarter of the cold side  9 A remains visible, i.e. readily accessible. Preferably, more than 60% of the region of the cold side  9 A without the portion of the core  13  remains visible. An impingement-cooling plate  31  is disposed in front of the cold side  9 A. A number of openings  33  are made in this impingement-cooling plate  31 . Cooling air passes through these openings  33  perpendicularly onto the cold side  9 A. As a result, the cold side  9 A is efficiently cooled by impingement cooling. The mounting of the impingement-cooling plate  31  or of another, possibly more complex, cooling configuration turns out to be very simple due to the easy accessibility of the cold side  9 A.