Abstract:
A turbine guide vane having an aerodynamically bent vane airfoil with a channel system equipped with a throttle element is provided herein. The channel system includes channel sections for the guidance of coolant. In order to provide an alternative turbine guide vane by means of which both a partial coolant flow flowing in the interior and a partial coolant flow guided out of the turbine guide vane are adjustable; therefore, in an embodiment, the throttle element is designed for the removal of coolant.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2012/075256 filed Dec. 12, 2012, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP12155394 filed Feb. 14, 2012. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention relates to a turbine guide vane with an aerodynamically curved vane airfoil, which has a system of channels comprising channel sections for conducting coolant and equipped with a throttle element. 
     BACKGROUND OF INVENTION 
     Such a turbine vane is known for example from WO 01/36790 A1. The throttling of the cooling air consumption of the known turbine vane takes place with the aid of a plug, which is provided in the turbine guide vane from the outside, at a point of reversal of the cooling channel. Depending on the depth of penetration of the plug, the cross section of the point of reversal through which flow can pass, and consequently the throughflow of cooling air, can be set to a predetermined degree in a simple manner. Casting-dependent dimensional differences that result from the production of the turbine vane can be compensated with the aid of the plug, whereby excessive consumption of cooling air can be avoided. 
     Furthermore, it is known that, instead of a throttle, an opening may also be situated at the point of reversal for the removal of cooling air. In this case, the use of a throttle has not so far been possible at this position. 
     SUMMARY OF INVENTION 
     An object of the invention is to provide an alternative turbine guide vane with which subsequent throttling is possible in spite of an opening being present at the point of reversal for conducting coolant out from the turbine vane. 
     An object directed at the turbine guide vane is achieved by such a vane according to the features of the independent claims. Advantageous designs are specified in the subclaims. Its features may be combined with one another in any way desired. 
     An embodiment of the invention is based on the realization that, in the case of a turbine guide vane with an aerodynamically curved vane airfoil, which has a system of channels comprising channel sections for conducting coolant and equipped with a throttle element, the throttle element should be designed in such a way that it also allows the removal of coolant. Consequently, it should be equipped with an inflow opening, an outflow opening and a channel connecting the two openings. To this extent, the throttle element thus serves not just for throttling. It is at the same time also used as a diverter for dividing the coolant into two separate partial streams of coolant. The first of the two partial streams of coolant flows further within the turbine guide vane and is used for cooling the vane airfoil and the trailing edge thereof. The other of the two partial streams of coolant is conducted directly out from the turbine guide vane. The latter is of advantage in particular when further gas turbine components that either have to be cooled or with which the turbine guide vane (or other components) form gaps into which a hot gas of the gas turbine could penetrate are arranged at that end at which the coolant is conducted out from the turbine guide vane. By providing the coolant at these gas turbine components, the gaps concerned are blocked by coolant flowing out, so that the penetration of hot gas can be avoided with certainty. Both the cooling of the further gas turbine components and the blocking of the gaps to prevent hot gas from being drawn in prevent premature aging of the components as a result of inadmissibly high material temperatures, and consequently prolong their service life. 
     According to a first advantageous development, the throttle element is fitted in the turbine guide vane and is designed in the form of a cup with a circumferentially arranged inflow opening for coolant, the cup opening of the throttle element being arranged in the outer surface of the turbine guide vane. In this case, the cup opening represents the outflow opening for the partial stream of coolant flowing into the throttle element. With the aid of this design, a comparatively simple construction of a flow diverter is provided, the other of the two partial streams of coolant being produced by the incoming coolant flow flowing past the throttle element—to be more precise past the inflow opening of the throttle element—and continuing into the downstream channel sections of the system of channels. A further advantage of this construction is that the division of the incoming coolant flow into two partial streams can take place with a single component fitted into the cast turbine guide vane—the throttle element. The division of the stream of coolant depends on the size of the outflow opening and on the remaining throughflow cross section at the throttling point in the system of channels. 
     This design has the further advantage that operationally stressed turbine guide vanes already existing in the field can be equipped with such a throttling device, if appropriate retrofitted, without the turbine guide vanes having to be machined, modified or prepared for this purpose. 
     Moreover, the cup opening may also have a collar, the diameter of which is greater than the opening in which the throttle element is fitted. This prevents the throttle element from being able to fall into the channel sections, and thus be lost, when it is fitted. 
     The turbine guide vane is usually a cast component that is to the greatest extent or completely of a monolithic design. The turbine guide vane expediently comprises a root region and a head region for fastening. The two regions are arranged at the two ends of the vane airfoil. The throttle element may be arranged in the root region and/or in the head region. The root region of the turbine guide vane serves for the fastening of the turbine guide vane to an annular guide vane carrier. Extending radially inwardly from the root region is the vane airfoil, the inner end of which is adjoined by the head region. The root region and the head region generally each comprise what is known as a platform for the local, radial delimitation of the hot gas channel of the gas turbine. Provided on the side of the inner platform that is facing away from the hot gas channel are hooks, which are part of the head region and to which a ring known as a U ring is generally fastened. With this U ring, the turbine guide vanes or else turbine guide vane segments of a guide vane ring of the gas turbine are coupled to one another. Since these U rings may possibly have to be cooled and the gaps formed by these components with the rotor have to be blocked to prevent penetration of hot gas, it is of particular advantage if the coolant that is usually conducted through the turbine guide vane can be removed again at the head-side end of the turbine guide vane by the throttle element and used there on the hub side. 
     Also advantageous is that development in which two cooling channel sections arranged approximately parallel in relation to one another are connected to one another in terms of flow in the vane airfoil by way of a deflecting region arranged on the root side or on the head side and the throttle element protrudes into the deflecting region transversely with respect to the local throughflow direction of the coolant in said deflecting region. In this case there is between the two channel sections arranged parallel to one another a separating wall, which ends at the deflecting region, so that, depending on the depth of penetration, the throttle element can end closer to or further away from the end of this separating wall. To this extent, said separating wall is part of the throttling device, so that elements that are already present in a turbine guide vane assume a further function, for which they were not originally intended, if the throttle element is retrofitted. Coolant can be removed by the throttle element with little loss of pressure if the inflow opening is facing the incoming coolant flow. 
     In order to avoid areas known as dead water areas in the coolant flow or in the system of channels directly downstream from the throttle element, and consequently poorly cooled vane walls, it is preferably provided that at least one further circumferentially arranged throughflow opening is provided in the throttle element. In this case, the cross-sectional area of all the throughflow openings is preferably significantly smaller than the cross-sectional area of the inflow opening. The throughflow openings preferably lie opposite the inflow opening, and consequently on that side of the throttle element on which the partial stream of coolant that initially remains in the turbine guide vane flows away. It is even conceivable that such throughflow openings themselves are situated in the throttle element if the latter is not designed for the removal of cooling air—that is to say is not of a tubular design—but is of a solid design. 
     It is unimportant for the invention whether the feeding of coolant takes place here on the root side or on the head side. However, in one embodiment the throttle element is arranged in that region that is opposite from the feed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features of the invention are explained in more detail on the basis of the drawing that follows, in which: 
         FIG. 1  shows a turbine guide vane in a perspective representation with a cut-open vane airfoil and a throttle element fitted on the head side and 
         FIG. 2  shows a hub-side cross section through the vane airfoil of the turbine guide vane with the throttle element located therein. 
         FIG. 3  shows a turbine guide vane in a perspective representation with a cut-open vane airfoil and a throttle element fitted on the root side. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     A turbine guide vane  10  for a stationary gas turbine is perspectively represented in  FIG. 1 . The turbine guide vane  10  comprises a root region  12 , an aerodynamically curved main airfoil  14  and a head region  16 , which follow one another along a longitudinal axis  18 . In the fitted position in a gas turbine, the root region  12  is situated radially on the outside and the head region  16  is situated radially on the inside. Both the root region  12  and the head region  16  each comprises a platform  20 , respectively forming the local, radial delimitation of the annular hot gas path of the gas turbine in the region of the turbine guide vane  10  concerned. To this extent, the vane airfoil  14  extends through the annular hot gas channel  22 . Both the root region  12  and the head region  16  have on their sides facing away from the hot gas channel  22  a number of hooks  24  for fastening. The hooks  24  provided at the root region  12  serve for fastening the turbine guide vane  10  to an annular turbine guide vane carrier that is not represented. On the other hand, the hooks situated in the head region  16  serve for fastening a ring known as a U ring, which is also not represented any further here. 
     The vane airfoil  14  comprises a leading edge  17  and a trailing edge  19 , between which there extend a pressure-side vane airfoil wall  40  and a suction-side vane airfoil wall  42 . The vane airfoil  14  represented in  FIG. 1  is not shown completely perspectively, but partly in longitudinal section. As a result, the channel sections  26  of a system of channels  28  that are present in the interior of the vane airfoil  14  are represented. Consequently, the system of channels  28  with the channel sections  26  is arranged between the two walls  40 ,  42  ( FIG. 2 ). The system of channels  28  is designed for conducting coolant, which can be fed to the turbine guide vane  10  via an opening  29  arranged on the root side. In the embodiment shown, three channel sections  26  arranged parallel to one another are provided, two of which are connected to one another in terms of flow at the head region by way of a deflecting region  30 . In this deflecting region  30 , the turbine guide vane  10  has an opening  31 , in which a throttle element  32  is inserted from the outside. In order to secure the turbine guide vane  10  against losing the throttle element, the throttle element  32  may be welded or brazed to the cast turbine guide vane  10  at isolated points or else around the periphery. 
     The throttle element  32  is in the form of a cup, with a cylindrical casing and a cup base  34 , which lies opposite a separating wall  36  separating the two channel sections  26 , thereby forming a gap. 
     Identical features are provided with the same designations in all of the figures. Consequently,  FIG. 2  shows the turbine guide vane  10  according to section II-II in  FIG. 1  with the head region  16  and the hooks  24  arranged thereupon in a perspective representation. The throttle element  32  fitted into the turbine guide vane  10  from the outside on the head side is perspectively represented and has an inflow opening  37 , which is facing one ( 26   a ) of the channel sections  26 . Through the inflow opening  37 , a cup opening  38  can be seen. The cup base  34  lies opposite the head-side end  39  ( FIG. 1 ) of the separating wall  36 , thereby forming a gap. 
     In the exemplary embodiment shown, the throttle element  32  is formed cylindrically with a constant diameter. The throttle element may also be designed cylindrically with diameters differing from section to section or may have a conically shaped design. 
     The inner surfaces of the vane airfoil walls  40 ,  42  are spaced apart laterally from the throttle element  32 , so that the incoming coolant flow from the channel section  26   a , usually cooling air, flows either into the inflow opening  37  or into the gaps between the inner surfaces of the vane walls or the separating wall  36  and the throttle element  32  for being divided into two streams of cooling air. The latter partial stream subsequently flows through the channel section  26   b  and remains initially in the turbine guide vane  10 . The partial stream flowing into the inflow opening  37  flows out through the cup opening  38  and can be used on the hub side for cooling the components situated there or for blocking gaps to prevent hot gas from being drawn in. 
     To avoid coolant flow areas with a low flow rate, one or more throughflow openings  41  may also be provided in the throttle element. 
     It is of particular advantage that, with the aid of the throttle element  32 , the entire amount of cooling air of the turbine guide vane  10  on the one hand and the ratio of the division of the two partial streams of coolant on the other hand can be set, even after the turbine guide vane  10  has been cast. By saving cooling air, a gas turbine equipped with the turbine guide vanes  10  according to the invention has an improved efficiency. At the same time, it is possible to retrofit already operationally stressed turbine guide vanes  10  with a throttle element  32  without any need in principle for them to be machined, as long as the turbine guide vane  10  has an opening for the removal of coolant flowing in it. It is also possible with the aid of the throttle element  32  to make turbine guide vanes  10  that are as new but do not conform to specifications fit for use in a gas turbine. This allows the reject rate of components to be reduced, which minimizes costs. 
     Altogether, embodiments of the invention relate to a turbine guide vane  10  with an aerodynamically curved vane airfoil  14 , which has a system of channels  28  comprising channel sections  26  for conducting coolant and equipped with a throttle element  32 . In order to provide an alternative turbine guide vane  10 , with which both a partial stream of coolant flowing in the interior and a partial stream of coolant conducted out again from the turbine guide vane  10  can be set, it is proposed that the throttle element  32  is designed for the removal of coolant.