Abstract:
The invention relates to a turbine blade comprising a profiled vane around which working gas flows. The working gas cross-flows a front edge of the vane and flows away on a rear edge of the vane. The vane has a first and a second channel system for guiding two media separated from the turbine blade. Combustion taking place inside is reduced in a safe manner to maintain the service life of the turbine blade and to prevent damage in the gas turbine, such that a first outlet connected to the first channel system is arranged in the region of the rear edge for blowing out the first media into the working gas and a second outlet connected to the second channel system is arranged in the region of the rear edge for blowing out the second medium.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2007/051403, filed Feb. 13, 2007 and claims the benefit thereof. The International Application claims the benefits of European application No. 0600831.9, filed Apr. 21, 2006, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a turbine blade with a profiled blade airfoil which is exposable to circumflow by an operating gas, which has a leading edge which is exposable to inflow of the operating gas and also a trailing edge on which the operating gas can flow out, and with a first passage system and with a second passage system for the separate guiding of two different media which can be fed separately to the turbine blade, wherein the first passage system leads to at least one first discharge opening, which is arranged in the region of the trailing edge, for blowing out the first medium into the operating gas. 
     BACKGROUND OF THE INVENTION 
     Such a turbine blade is known for example from WO 2005/003517 A1. The blade walls which form the blade airfoil enclose a cavity on the inside in which cooling air can flow. Furthermore, further passages for guiding a second medium, specifically fuel, are provided in the blade wall of the turbine blade. Holes extend through the blade wall of the turbine blade, through which holes the cooling medium which flows inside the turbine blade can discharge outwards into a hot gas space. In order to produce a combustible mixture, connecting passages, which connect the fuel-guiding passages to the through-holes, are provided in the blade wall. As a result, fuel can be mixed with cooling air still inside the through-holes and as a combustible mixture can be blown out into the hot gas which flows around the turbine blade. With such a turbine blade, both the hot gas which flows through the turbine and the cooling air which discharges from the turbine blade can be reheated as a result of the combustion of the mixture, which in general is carried out for increasing the level of performance of the gas turbine, for reducing the pollutant emissions and for improving the efficiency of the gas turbine, and is known as a form of carnotization. 
     Furthermore, a combustion chamber with a multiplicity of porous heat-shield elements is known from WO 99/46540 A1, by means of which a combustible mixture can be subsequently introduced into the combustion chamber of a gas turbine, i.e. outside the burners of the gas turbine. 
     A turbine blade with a multiplicity of internally arranged cooling passages which extend from the blade root towards the blade tip and also formed in a meandering configuration in the process, is known from EP 0 896 127 A2. The cooling passages are connected to altogether three root-side openings for feeding cooling air of different quality. One of the openings is connected to a rectilinear cavity which extends from the blade root to approximately the blade tip. This cavity is directly adjacent to the trailing edge of the blade airfoil of the turbine blade and is in flow communication with the discharge openings which are arranged on the trailing edge. The cooling medium which is fed through the corresponding root-side opening can flow through the cavity and can leave the trailing edge via the discharge openings over the approximately entire length of the trailing edge with a cooling effect in the process. At the same time, the turbine blade has a further cavity, on the blade-tip-side end of which a cooling passage, which extends transversely to the longitudinal extent of the blade airfoil, is provided. This cooling passage leads to the trailing edge only in its blade-tip-side region. 
     Furthermore, it is known from U.S. Pat. No. 6,551,063 to construct the trailing edge of a turbine blade in modules by a plate-like element which covers the trailing edge ribs being soldered on or welded on, in the case of a turbine blade with a so-called “cut-back” trailing edge. 
     It is disadvantageous to the concepts which are also known as “in-situ blade reheat” that, as a result of the mixing of cooling air and fuel in the components, the reaction partners can ignite as a result of self-ignition or flashback. As a result of this, stable combustion processes are possibly formed inside the turbine blade so that the cooling effect of the fuel-air mixture is lost, or the component can be damaged as a result of the combustion which occurs internally. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to provide a turbine blade for a gas turbine in which a combustion which takes place inside is safely avoided for maintaining the service life of the turbine blade and for avoiding damage in the gas turbine. 
     This object is achieved with a turbine blade according to the invention in which the first discharge openings, which are connected to the first passage system, are arranged in the region of the trailing edge, and in which at least one second discharge opening, which is arranged in the region of the trailing edge, for blowing out the second medium is connected to the second passage system. 
     The invention is based on the knowledge that it is primarily necessary to feed the reaction partners, i.e. the two media, separately inside the turbine blade and to avoid a mixing inside the volume of the component in order to safely prevent an unwanted combustion which may possibly take place inside the turbine blade. A flashback into the component, which the pressure which prevails in the operating gas and possibly also the flow direction of the operating gas may bring about, also has to be safely avoided. For this reason, the discharge openings, from which on the one hand the first medium, for example cooling air, discharges, and on the other hand from which the second medium, for example fuel, discharges, are not opened transversely or towards the flow direction of the operating gas but are arranged on the trailing edge of the turbine blade so that the outflowing media have at least one flow component acting in the same direction in three-dimensional space as the operating gas. 
     Since the two media are blown out of the component on the trailing edge and are blown into the operating gas, the reaction partners can only be mixed to form a possibly combustible mixture outside the turbine blade. The proposed solution, furthermore, enables quick mixing of a first medium with a second medium, the mixture which results in this way being admixed in turn with the operating gas of the turbine. The risk of flashbacks of a perhaps combustible mixture is therefore effectively prevented since no combustible mixture consisting of a first and second medium occurs inside the turbine blade or, on account of the pressure in the operating gas and/or on account of its flow direction, can be blown back into the turbine blade. Consequently, with the disclosed invention an especially reliable turbine blade can be disclosed in which a combustible mixture consisting of a first medium and second medium cannot be fed back. Self-ignition of the mixture inside the turbine blade can be safely avoided, maintaining the service life of the turbine blade. In a turbine which is equipped with the turbine blade according to the invention, the operating gas which flows in the turbine can be reheated reliably and without risk with regard to a fire taking place inside the turbine blade. 
     Flashback safety is ensured above all by the fact that the fuel is injected close to the trailing edge in the region of the directed operating gas flow, i.e. with two identical flow direction components and without forming backflow zones. Therefore, residence time distributions, which are caused by flow vortices and which can bring about a combustion inside the turbine blade, do not occur. 
     Naturally, the proposed turbine blade can also be used for the addition of other fluid media as fuel or air inside a turbine, regardless of whether it is a gas or steam turbine. 
     An exceptionally efficient low-emissions combustion of the fuel in the operating gas can be achieved if the trailing edge extends along a blade airfoil principal axis from a root region of the blade airfoil to a tip region which lies opposite said root region, wherein the second discharge opening is arranged at least partially at the same height as the first discharge opening, as seen along the blade airfoil principal axis. Therefore, for the first time it is possible for both fuel and combustion air to be injected at the same time into the operating gas through the trailing edge at a radial height of the annular passage-shaped operating gas space of the gas turbine in order to achieve an especially efficient combustion. Consequently, the first discharge opening and the second discharge opening do not lie one behind the other but next to each other in an overlapping manner, as seen in the direction of the blade airfoil principal axis. 
     In this case, it is particularly advantageous for combustion of the fuel in the operating gas if the trailing edge extends along a blade airfoil principal axis from a root region of the blade airfoil to a tip region which lies opposite said root region, wherein the second discharge opening is arranged at least partially at the same height as the first discharge opening, as seen along the blade airfoil principal axis. Therefore, for the first time it is possible for both fuel and combustion air to be injected at the same time into the operating gas through the trailing edge at a radial height of the annular passage-shaped operating gas space of the gas turbine in order to achieve an especially efficient combustion. Consequently, the first discharge opening and the second discharge opening do not lie one behind the other but next to each other in an overlapping manner, as seen in the direction of the blade airfoil principal axis. 
     In order to inject quantities of first and second medium which are particularly well matched to each other into the operating gas within a comparatively narrow section of the trailing edge, one of the first discharge openings in each case with one of the second discharge openings in each case forms an overlapping pair of openings, as seen along the blade airfoil principal axis. The configuration of a turbine blade according to the invention, in which a plurality of pairs of openings which are arranged next to each other follow each other along the trailing edge so that the parallel blowing out of the two media can be carried out over the entire height of the blade airfoil of the turbine blade, is especially preferred in this case. In order to achieve this, the first and the second discharge openings, alternatively to the aforementioned solution, can also extend in each case over the entire height of the trailing edge. 
     In a first development, it is proposed that in the region of the trailing edge means are provided which bring about a mixing of the first medium with the second medium directly downstream of the discharge openings. The blowing out of the two media is carried out in a manner which gives rise to an extremely quick mixing after their entry into the operating gas space within a very short distance and within a very short time. As a result, it is ensured that in the operating gas space an exceptionally homogeneous mixing of the two media is first carried out, and then subsequent to this, for reheating the operating gas which flows through the turbine, the mixture is mixed with this operating gas and automatically ignited on account of the temperature which prevails in the operating gas. This enables an especially low-emissions combustion of the combustible mixture, which is produced in the first mixing step, by means of premix flames. 
     As a result of the mixing within a short reaction distance and reaction time, the effect is achieved, furthermore, of the mixture being combusted before leaving the annular passage-shaped operating gas space, since the energy increase of the operating gas which takes place as a result of the reheating of the operating gas is only for power increase and efficiency increase of the turbine when the reheated operating gas flows past the rotor blades of the turbine for converting the flow energy into mechanical energy. 
     As a result of the short reaction distance, the overall length of the turbine can also be shortened. Therefore, an especially compact and inexpensively producible gas turbine, which is equipped with the turbine blades according to the invention, can also be disclosed by the invention. 
     Furthermore, it is proposed that the means create a backflow-free mixing of the first medium with the second medium by at least one of the two media, or both of the two media, being blown out at least approximately on a sharp edge. As a result of the sharp edge, backflow-free vortices are created which, on account of their flow direction, prevent the mixture flowing back into the turbine blade. Furthermore, feeding back of the mixture which is present in the operating gas space should be avoided anyway as a result of pressure ratios in which the pressure which prevails in the two media at the discharge opening is greater than the pressure of the operating gas. A combustion process of the mixture which may possibly take place inside the turbine blade can therefore be effectively avoided, which maintains the service life of the turbine blade. 
     It is also proposed that the means which are arranged in the trailing edge of the blade airfoil comprise at least one connecting passage which connects at least one the two passage systems to the discharge opening which is associated with it, wherein the connecting passage is shaped such that this imparts an eddy or vortex to the medium which flows through it. The connecting passage which connects the passage system to the corresponding discharge opening therefore has a spatial shape which imparts an eddy or vortex to the medium which flows through it, which is continued after discharging from the discharge opening. The directions of the eddy or of vortex are selected so that, directly after being discharged from the discharge opening, the two media flow into each other and so bring about their effective mixing. This leads to an especially homogeneous mixture and to its especially efficient and low-emissions combustion as a result of a self-ignited premix flame. Consequently, the pollutant loading which is created by the gas turbine, especially the NOx emissions, can be minimized. 
     The connecting passages for example are spiralled in the manner of a corkscrew so that the media which discharge through the discharge openings try to maintain this helical movement, i.e. its flow direction, after discharging. With suitable connecting passages, i.e. with an offset arrangement of the connecting passages which are shaped like a corkscrew in the manner of a double-thread screw, an eddy can therefore be imparted in each case to the two media, which enables them to mix through with each other particularly efficiently after their discharge from the connecting passages. 
     In a further advantageous development, it is proposed that the means are provided in the discharge openings. Consequently, in the discharge openings themselves and not only in the upstream connecting passages, turbulators, dimples or the like can be provided as the means which impart an eddy or backflow-free vortex to the medium which flows out through them. A nozzle with a star-like encompassing contour is preferably inserted in a circular opening as a separating element for the two media. One of the two media can flow out from the center of the nozzle, and the other of the two media can flow out from the cross-sectional area between the circular opening and the star-like contour. This nozzle-shaped configuration brings about a further improved mixing through of the two outflowing media. 
     In addition, it is proposed by the invention that the means for mixing the first medium with the second medium are provided on an inner side of the suction-side trailing edge wall of the blade airfoil, and/or on an inner side of the pressure-side trailing edge wall, which trailing edge wall or walls is or are exposable to circumflow by the operating gas. 
     The means which are provided in the discharge openings can also be a freely oscillating tongue which is clamped at one end and which, as a result of its flow-induced oscillations, mixes the two media with each other particularly efficiently. 
     If the blowing out of the two media is carried out essentially or approximately parallel to the flow direction of the operating gas, a mixing through of the two media can take place just marginally inside the turbine blade in the region of the trailing edge without compromising the flashback safety of the component. The mixing through of the two media for example can be achieved by means of a field of pins and/or by means of turbulators. 
     It is also proposed that the blade airfoil is cast, and the means for mixing the two media are fastened in the blade airfoil as a separately produced insert. The structural features of the turbine blade which are proposed by the invention in the casting method must customarily be produced in an especially costly manner. Therefore, the invention proposes to prefabricate these structures as a separately produced insert and then to fasten the insert in the cast blade airfoil. As a result of this, an especially inexpensive turbine blade can be disclosed. 
     The invention also proposes a gas turbine which is equipped with a turbine blade according to the invention, wherein the advantages which are associated with the turbine blade can also be transferred to the gas turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features are to be gathered from the following description of exemplary embodiments. Elements which are essentially the same are identified with the same designations. In addition, reference is made to the description for the exemplary embodiment with regard to like features and functions. In the drawing: 
         FIG. 1  shows a schematic view of a turbine blade with a feed pipe for fuel, 
         FIG. 2   a  shows a cross section through the blade airfoil of the turbine blade with a passage system, cast in a blade wall, for guiding a second medium, 
         FIG. 2   b  shows a cross section through the blade airfoil of the turbine blade with a passage system, which is formed by a tube-like insert, for guiding the second medium, 
         FIG. 2   c  shows a cross section through the blade airfoil of the turbine blade with a passage system, which is enclosed by an impingement cooling plate, for guiding the second medium, 
         FIG. 3  shows a perspective view of the trailing edge of the blade airfoil of the turbine blade, 
         FIG. 4  shows the cross section through the blade trailing edge according to  FIG. 3 , 
         FIG. 5  shows the cross section through the trailing edge of the turbine blade with connecting passages which wind around each other in the manner of a double helix, 
         FIG. 6  shows the cross section through the trailing edge of the turbine blade with a movable element which is fastened in the trailing edge, 
         FIG. 7  shows the perspective view of the trailing edge of the turbine blade with nozzles which are arranged in the region of the trailing edge, 
         FIG. 8  shows the cross section through the trailing edge of the turbine blade according to  FIG. 7  with the nozzle-shaped discharge opening arranged thereupon, 
         FIG. 9  shows the nozzle which can be fastened in the trailing edge of the turbine blade according to  FIG. 7 , in perspective view, 
         FIG. 10  shows the cross section through the trailing edge of the turbine blade with a corrugated insert, 
         FIG. 11  shows the trailing edge of the turbine blade with the corrugated insert, 
         FIG. 12  shows the corrugated insert for a turbine blade according to  FIG. 11 , 
         FIG. 13  shows a cross section through the trailing edge of the turbine blade with a field consisting of pins which is arranged in the trailing edge, 
         FIG. 14  shows the longitudinal section through the turbine blade according to  FIG. 13  in the region of the trailing edge, 
         FIG. 15  shows, in perspective view, the trailing edge of the turbine blade with a crosswise blowing out, 
         FIG. 16  shows the cross section through the trailing edge of the turbine blade with a crosswise blowing out according to  FIG. 15 , 
         FIG. 17  shows the insert which can be inserted in the region of the trailing edge for producing the crosswise blowing out, in a perspective view, and 
         FIG. 18  shows an insert for producing counter-flowing vortices in the region of the trailing edge of the turbine blade. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic view of a turbine blade as is used for example in one of the front stages of the turbine of for example a stationary axial gas turbine. The turbine blade  10  is represented as a stator blade and, with regard to its installed position in the gas turbine, comprises an inner platform  12 , an outer platform  14  and a blade airfoil  16  which extends between the platforms in the radial direction of the gas turbine. The outer platform  14  in this case represents a root region  13  upon which the turbine blade  10 , for example on a stator blade carrier, can be fastened. A tip region  15 , which lies opposite the root region  13 , in this case comprises the inner platform  12 . 
     The blade airfoil  16 , as  FIG. 2   a  to  FIG. 2   c  show, is curved in cross section in the shape of a droplet and extends from a leading edge  18  to a trailing edge  20 . A blade airfoil principal axis  21  in this case extends essentially parallel to the trailing edge  21  or along the radial direction of the gas turbine. During operation of the gas turbine, the blade airfoil  16 , which has a height H, is exposed to circumflow by an operating gas  22  which first flows onto the turbine blade  10  at the leading edge  18  and after flowing round the blade airfoil  16  leaves at the trailing edge  20 . In the meantime, it flows along an annular passage-shaped operating gas space  24  which is at least partially delimited radially inwardly by the inner platforms  12  and radially outwardly by the outer platforms  14  of the turbine blades  10 . 
     The blade airfoil  16  is formed with its inside being hollow and inside this has at least one first passage system  30  and a second passage system  40  which are formed separately from each other. A medium M 1  or M 2  can therefore be guided separately in each passage system  30 ,  40 . The first medium M 1  for example is fed through the casing of the turbine from radially outside to the first passage system  30 . The second medium M 2 , which preferably is not to be mixed with the first medium M 1  inside the turbine blade  10 , is fed via a separate feed pipe  32  to the turbine blade  10 . For this purpose, the turbine blade  10  has a connector  34  to which the feed pipe  32  is connected in a gastight manner, for example by means of a seal  36  which is known from steam cooling. For further guiding of the second medium M 2  in the blade airfoil  16 , a pipe system  37  branches out from the connector  34  on the inside. 
     The second passage system  40  which is provided inside the blade airfoil  16  for guiding the second medium M 2  can be configured in different ways. 
     The blade airfoil  16  which is shown in cross section in  FIG. 2   a  has a central cavity  38  which, as part of the first passage system  30 , is provided for guiding the first medium. The first passage system  30 , in the example which is shown, comprises the entire cavity  38  of the turbine blade  10 . Alternative configurations are conceivable, in which the cavity  38  can be divided into a plurality of regions by for example a rib  45  extending from the pressure-side wall  44  to the suction-side wall  42 . This rib  45  is indicated in  FIG. 2   a  by means of broken lines in the region of the leading edge  18 . 
     The first medium M 1 , preferably cooling air, which flows inside the first passage system  30  serves for cooling the turbine blade  10 , and after cooling has been carried out is blown out from the trailing edge  20  of the turbine blade  10  in the manner of open cooling and so is blown into the operating gas  22  flowing approximately parallel. For this purpose, the turbine blade  10  has a first connecting passage  46  which leads to the first discharge opening  48  which is provided in the region of the trailing edge  20 . In  FIGS. 2   a ,  2   b  and  2   c  which are shown the cavity  38  merges in a stepless manner into the first connecting passage  46  and this merges into the first discharge opening  48 . 
     According to  FIG. 2   a , the second passage system  40 , which is provided for the further guiding of the second medium M 2 , comprises a cavity  40  which is provided in the suction-side blade wall  42 . The second passage system  40 , by means of a suitable casting core, was also produced directly when casting the blade airfoil  16  and is fluidically connected to second discharge openings  52  via second connecting passages  50 . 
     The first passage system  30  and also the second passage system  40  extend in each case over the height H of the blade airfoil  16  which extends in the radial direction of the gas turbine. A first discharge opening  48  for the first medium M 1 , which extends over the entire height H of the blade airfoil  16 , and a plurality of second discharge openings  52  for the second medium M 2 , which are evenly distributed along the height H, are provided on the trailing edge  20  of the turbine blade  10 . It is also conceivable that a plurality of first discharge openings  48  and/or only one second discharge opening  52  are, or is, provided. It is important for this and for the subsequently described developments that both first and second discharge openings  48 ,  52  lie at least partially at the same radial height of the trailing edge  20  and therefore overlap in order that the two media M 1 , M 2  are blown out as close as possible to each other. 
       FIG. 2   b  shows an alternative development of the turbine blade  10  in cross section, in which the second passage system  40  for guiding the second medium M 2  comprises a tube  60  which is inserted in the cavity  38  of the turbine blade  10 . The tube  60  is connected over the height H of the blade airfoil  16  to the inner side  74  of the suction-side blade wall  42 . The connecting passages, which are not shown in  FIG. 2   b , have already also been produced when casting, or drilled subsequently, for blowing out the medium M 2  in the suction-side blade wall  42 , in a similar way to the turbine blade  10  which is shown in  FIG. 2   a , and on the one hand lead to the tube  60  and on the other hand lead to the discharge opening  52 . 
       FIG. 2   c  shows a further variant. An impingement cooling insert  62 , which is required for impingement cooling of the blade walls  42 ,  44 , is at a distance from the inner side  74  of the blade airfoil  16  by means of spacers  66  and in cross section is formed so that inside the cavity  38  this insert contributes both to the forming of the first passage system  30  and of the second passage system  40 , and hermetically separates the passages  30 ,  40  from each other in the process. 
     The second connecting passages  50  may have also been cast in the suction-side blade wall  42  of the turbine blade  10  in a similar way to  FIG. 2   b.    
     Fuel guiding is carried out in the case of the previously described developments in such a way that parts of the second passage system  40 , which can also be referred to as a fuel passage system, penetrate the turbine blade  10  in the radial direction, and in this case is formed either as a passage which is cast in the blade wall  42 ,  44  ( FIG. 2   a ), as a separately constructed single-wall or multi-wall tube ( FIG. 2   b ) or as a separate fuel passage from the impingement cooling insert ( FIG. 2   c ). Each of the proposed developments enables a guiding of fuel close to the trailing edge  20  so that a constructionally simple injection of fuel into a region of directed operating gas flow is possible. 
     The developments which are shown in  FIG. 2   a  to  FIG. 2   c  make it possible to guide the fuel in the turbine for carrying out the “in-situ blade reheat” process and to add this fuel to the operating gas  22  which flows there, without the cooling, the strength or the aerodynamics of the turbine blade  10  being negatively influenced, wherein on account of the hermetically separated guiding of the two media M 1 , M 2  a mixing inside the turbine blade  10  is always reliably prevented. 
       FIG. 3  shows the perspective view of the trailing edge  20  of the blade airfoil  16 , blanking out the outer and the inner platform. The cavity  38 , which is arranged inside the turbine blade  10 , as part of the first passage system  30  merges into the first connecting passage  46  which in its turn merges in a stepless manner into the first discharge opening  48  which is arranged in the trailing edge  22  of the turbine blade  10 . 
     Cast-in second passages  40  are provided in each case both in the suction-side blade wall  42  and in the pressure-side blade wall  44  and extend over the height of the blade airfoil  16 . The second passages  40  are connected via second connecting passages  50  to the second discharge openings  52 . 
     Due to the development which is shown, mixing of the two media M 1 , M 2  inside the turbine blade  10  is effectively avoided. 
     Means are provided in the region of the trailing edge  20  which effect an eddying or swirling of the two media M 1 , M 2  which flow out of the turbine blade  10 . The means which are shown in  FIG. 3  are so-called mixing inserts  70  for improved mixing of the two outflowing media M 1 , M 2 . The mixing inserts  70  are formed in the shape of a pyramid, as wedges or also as tetrahedrons  72 , in the rear, i.e. downstream, triangular surface of which the second discharge opening  52  is provided in each case. Two tetrahedrons  72   a ,  72   c , the free points of which face the inner side  76  of the pressure-side blade wall  44 , for example are provided on the inner side  74  of the suction-side blade wall  42 . A further tetrahedron  72   b  is provided between the two tetrahedrons  72   a ,  72   c  but arranged on the inner side  76  of the pressure-side blade wall  44  so that for the first discharge opening  48  a meander-shaped gap is created along the trailing edge  20  from the outer end to the inner end. 
     Inside the turbine blade  10  the first medium M 1 , preferably cooling air, can flow in the cavity  38  in a known manner, for example meander-like, in order to protect in the meantime the material which forms the blade airfoil  16  against thermal overloading. From there, the first medium reaches the first discharge opening  48  via the first connecting passages  46 . Similarly to this, the second medium M 2 , preferably fuel, which is fed to the second passages  40 , is guided to the second discharge openings  52 . 
     On account of the mixing inserts  70  which are sharp-edged in their contour, especially the angular tetrahedrons  72 , a backflow-free swirling of the cooling air which flows out through the first discharge opening  48  can be achieved. The fuel which in the meantime flows into the swirled cooling air is then mixed with the cooling air in a particularly efficient manner. 
     Despite the separated feed of the two media M 1 , M 2 , it is possible in this way to achieve efficient mixing with a short mixing time and a short mixing distance in order to combust the self-igniting mixture with low emissions, forming small premix flames. As a result of this, the overall length of the turbine can also be reduced. Furthermore, on account of the selected outflow directions of the media M 1 , M 2  which leave the turbine blade  10 , it can be ensured that a backflow of the mixture into the discharge openings  48 ,  50  is safely avoided. Accordingly a fire cannot occur inside in the passages  30 ,  40 ,  46 ,  50  of the turbine blade  10  so that the service life of the turbine blade  10  is maintained. 
       FIG. 4  shows the cross section through the development of a turbine blade according to  FIG. 3 , in which the tetrahedrons  72  which lie opposite each other in an offset manner, the suction-side blade wall  42 , the pressure-side blade wall  44 , the two first passages  30  and also the two second passages  40  are shown. Instead of the tetrahedrons  72 , other geometric shapes are also conceivable as mixing inserts  70 . 
       FIG. 5  shows an alternative development of the invention, in which the cavity  38  which is provided inside the turbine blade  10  is provided for guiding cooling air as the first medium M 1 . The second passage  40  for guiding the second medium M 2  is provided in the pressure-side blade wall  42 . Discharge openings  48 ,  52 , which are distributed in each case over the height of the turbine blade  10 , are provided in pairs on the trailing edge  20 . Each first and each second discharge opening  48 ,  52  is connected in each case to the associated passage system  30 ,  40  via the helical connecting passage  50 ,  46  which is associated with it. In this case two connecting passages  46 ,  50  are always entwined with each other in the manner of a double helix. The media M 1 , M 2 , which flow through the helically winding connecting passages  46 ,  50 , on account of the helical shape also continue to flow with the consequently imparted eddy after leaving the turbine blade  10 . The connecting passages  46 ,  50  are oriented to each other so that after the discharging of the two media M 1 , M 2  from the discharge openings  48 ,  52  these flow into each other and so bring about a particularly efficient mixing within an especially short mixing distance and short mixing time. This particularly efficient mixing is a precondition for the low-emissions combusting of the mixture with short complete combustion duration after self-ignition has been carried out on account of the temperature which prevails in the operating gas  22 . As a result of the combustion of the mixture, the operating gas  22  or the cooling air which flows into the turbine is reheated, as a result of which its energy content is increased and can be used as mechanical energy which is provided by the turbine. The efficiency of the turbine is also increased as a result. 
     A further variant for creating a particularly efficient mixing of the two media M 1 , M 2  which are guided separately in the turbine blade  10  is shown in  FIG. 6 , which shows a cross section through the trailing edge  20  of a modified turbine blade  10 . 
     The means for creating a particularly efficient mixing is a movable plate element  80  which is clamped in a fixed manner at one end, with a free end  82  opposite the fixed end. The plate element  80  is fastened either on the inner side  76  of the pressure-side blade wall  44  or on the inner side  74  of the suction-side wall  42 , for example by welding or soldering, and during operation, on account of the media M 1 , M 2  which flow along it, periodically oscillates back and forth between the two opposite inner sides  74 ,  76  of the pressure-side blade wall  44  and suction-side blade wall  42 , so that the discharge openings  48  and  52  become mutually larger and smaller. In doing so, the outflowing media M 1 , M 2  swirl so that downstream of the plate element  80  a particularly efficient mixing of the two media M 1 , M 2  takes place, achieving the aforementioned advantages. According to  FIG. 6 , the free end  82  of the plate element  80  is slightly thickened in cross section so that it has an increased mass at this point. This makes the maintaining of the oscillation of the plate element  80  easier on the one hand, and on the other hand serves for making the creation of vortices easier, for example for the creation of Kármán vortices. It is not necessary for the free end  82  of the plate element  80  to come to lie on the inner sides  74 ,  76  of the blade walls  42 ,  44  during the oscillating process. 
     A further advantage of the development which is shown in  FIG. 6  is that if outflowing of the medium M 2  is prevented, the passage system  40  can be isolated from the operating gas space  24  since the pressure which prevails in the operating gas  22  or in the medium M 1  presses the plate element  80  onto the inner side  74  of the suction-side blade wall  42 . The counter-pressure which is otherwise caused by the medium M 2  is absent in this case. The discharge opening  52  is then closed and is therefore protected against entry of operating gas. 
       FIG. 7  to  FIG. 9  show in different views the trailing edge  20  of the turbine blade  10  with discharge openings  48 ,  52  which are formed upon it in the shape of nozzles. Openings  92  with a circular contour  93 , which extend parallel to the flow direction of the operating gas  22  and in which a star-shaped insert  90  is inserted in each case as means for creating vortices in the outflowing media M 1 , M 2 , are distributed along the trailing edge  20 . The insert  90 , as shown in  FIG. 9 , has an encompassing contour  96  in the manner of a star on the outflow side with regard to the flow direction of the two media M 1 , M 2 . On the inflow side, a considerably simpler contour  98 , for example that of a rectangle, is provided. 
     Inserted in the opening  92 , the area which is enclosed by the star-shaped encompassing contour  96  of the insert  90  forms the first discharge opening  48 . The area which lies between the circular contour  93  of the opening  92  and the area which lies outside the star-shaped contour  96  then forms the second discharge opening  52 . 
     As long as the turbine blade  10  in the region of the trailing edge  20  according to  FIG. 8  is provided with two second passages  40  which are provided in each case in the blade walls  42 ,  44 , and also is provided with the opening  92  integrated in the trailing edge (cf.  FIG. 7 ), an especially simple swirling of the two media M 1 , M 2  which flow out at the trailing edge  20  of the turbine blade  10  can be achieved with an insert  90  which is configured according to  FIG. 9  and inserted in the opening  92 . The first medium M 1 , preferably cooling air, then flows through the rectangular cross-sectional area in the inside of the insert  90  and, on account of the contour of the insert  90  which changes along the flow direction, is guided in accordance to this. The outflow-side contour  96  of the insert  90  with fingers  94  which project in the shape of a star determines that the medium M 2 , which is fed from the second connecting passages  50 , can flow into the spaces  99  which lie between the fingers  94 . With a trailing edge  20  with a plurality of nozzle-like discharge openings  48 ,  52 , the advantages which are associated with the invention can also be achieved. This development, which is also referred to as a bloom mixer, has exceptionally intensive mixing rates, moreover. 
       FIG. 10  to  FIG. 12  show a further development of the invention, in which a corrugated insert  100  for creating vortices in the outflowing media M 1 , M 2  is provided in the region of the trailing edge  20  over its height H. For this purpose, the trailing edge  20  has a rectangular slot  102  which extends over its height H and which is divided into two sections over its height by means of an insert  100  which is inserted therein. The insert  100  is at a distance from the two inner sides  74 ,  76  of the blade walls  42 ,  44 , wherein the distance between each inner wall  74 ,  76  and insert  10  periodically increases and decreases on account of the corrugated shape of the insert  100 , as seen along the trailing edge  20 . The front  104  of the corrugations of the insert  100  which is provided as means for creating vortices is inclined to the flow direction of the media M 1 , M 2  so that the media M 1 , M 2  which are guided on both sides of the insert  100  flow transversely across the corrugations of the insert  100  and are swirled by these so that a homogeneous mixing of the two media M 1 , M 2  downstream of the insert  100  is carried out. The resulting mixture reheats the operating gas  22 , or can also serve for emissions treatment of the operating gas  22 . 
       FIG. 13  and  FIG. 14  show an alternative development, in which only the first medium M 1  which is guided through the first connecting passages  46  is swirled on account of pins  110  which are arranged in an offset manner and which extend from the inner side  76  of the pressure-side blade wall  44  to the inner side  74  of the suction-side blade wall  42 , forming a series of vortex streets. For particularly efficient mixing, the blowing out of the second medium M 2  from the turbine blade  10  into the first medium M 1 , which flows in a swirled manner, is carried out by means of second discharge openings  52  which are provided on the trailing edge  20  and the second upstream connecting passages  50  of which extend in a straight line but are inclined towards the outer or inner platform. Therefore, the means for creating vortices in the medium M 1  is the field of pins  110  which is provided in the first connecting passage  46 . Instead of pins  110 , dimples, turbulators or grooves can also be provided on the inner sides  74 ,  76 . 
     A further development of the invention is shown in  FIG. 15  to  FIG. 17 , in which an insert  120 , which is essentially solid and rectangular in its dimensions, is inserted into a slot  122  which is provided in the trailing edge  20  of the turbine blade  10  and with which the swirling of the two media M 1 , M 2  which flow out at this point is brought about. The insert  120  which is shown in  FIG. 17  in perspective view is equipped with a plurality of first connecting passages  46  which extend parallel to each other and which extend transversely to the second connecting passages  50 . First and second connecting passages  46 ,  50  cross each other without being connected to each other at the crossing points and lead to discharge openings  48 ,  52  which coincide in pairs, where the mixing of the two media M 1 , M 2  takes place. As a result of the outflow directions of the two media M 1 , M 2  which lie at an angle to each other, said media are efficiently swirled and mixed with each other within a short mixing distance. 
     Swirl elements in the form of grooves or dimples, which additionally swirl the operating gas  22 , can also be provided parallel to the connecting passages  46 ,  50 , which are inclined outwardly and inwardly to the platforms, on the surface of the blade walls  42 ,  44  which faces the operating gas  22 , preferably in the region of the trailing edge  20 . 
       FIG. 18  shows in perspective view a tubular insert  130  which is rectangular in cross section and which on the inside has means for creating kidney-shaped vortices  132 . The medium which is introduced into the kidney-shaped vortex flow is mixed especially evenly with the other medium on account of the swirling. 
     Instead of the subsequent inserting of inserts  90 ,  100 ,  120 ,  130  into a cast blade airfoil  16 , and their soldering or welding, these can also be cast in the turbine blade  10  as a component part of a casting core which remains behind in the blade airfoil  16 . 
     A turbine which is equipped with such a turbine blade is suited in a particular way to manipulate the operating medium which flows into it by feeding additional media. For example, the energy content of the operating medium can be increased by means of “in-situ blade reheat”, or the emissions loading of the operating medium can be lowered by the addition of additives. 
     In all, a trailing edge of a turbine blade is proposed by the invention by means of which two media, which are guided separately inside the turbine blade, are added to the operating gas in such a way that these media are first of all mixed with each other before the mixture or one of the media reacts only partially with the operating gas. In order to achieve particularly efficient mixing of the two media within a short mixing distance, means are provided for swirling or eddying the flows, as a result of which, in the case of a combustible mixture, an especially low-emissions combustion of the mixture for reheating the operating gas can be achieved in sufficient time before leaving the turbine, on account of an especially short mixing distance and a short mixing time.