Abstract:
A blade for a gas turbine includes an airfoil extending in radial direction of the turbine or longitudinal direction of the blade, respectively, between a platform and a blade tip. The airfoil is bordered across the airfoil by a leading edge and a trailing edge and has a suction side and a pressure side. At the trailing edge a first cooling passage runs parallel to the trailing edge from the platform to the blade tip in the interior of the airfoil. The cooling passage is supplied with a cooling air flow from the platform side, and from which cooling air is discharged through a plurality of cooling holes arranged all over the blade. For such a blade the cooling is optimized by providing a first cooling passage, the passage area of which is tapered in radial direction by between 35% and 59%.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2009/063388, which was filed as an International Application on Oct. 14, 2009, designating the U.S., and which claims priority to European Application 08167661.1 filed in Europe on Oct. 27, 2008. The entire contents of these applications are hereby incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    The present disclosure relates to the field of gas turbines, such as a cooled blade for a gas turbine and a method for producing such a blade. 
       BACKGROUND INFORMATION 
       [0003]    The efficiency of gas turbines can depend substantially on the temperature of hot gas that expands in a turbine while performing work. In order to increase efficiency, components (guide vanes, moving blades, heat accumulating segments etc.) exposed to the hot gas can be produced from heat resistant materials and can be cooled as effectively as possible during operation. Different methods have been developed in relation to the cooling of blades, and these can be used alternatively or cumulatively. 
         [0004]    One known method includes conducting a coolant, such as pressurized cooling air from the compressor of the gas turbine, in cooling ducts through an interior of the blades. This coolant is allowed to enter into the cooling duct through cooling bores arranged in a distributed fashion. The cooling ducts can be repeatedly reversed in the interior of the blade in a serpentine fashion. See, for example, WO A1 2005/068783. The heat transfer between the coolant and walls of the blade can be improved in this case by additional turbulence generated in the coolant flow by suitable cooling elements, for example turbulators, or impingement cooling. However, complementary methods can permit the coolant to emerge from the interior of the blade such that there is formed on the blade surface a film of coolant, known as film cooling, that provides the blades additional protection against thermal loads. 
         [0005]    Particular attention can be paid to the cooling of a narrow trailing edge of the blade. It can be advantageous for the efficiency of the turbine if the trailing edge can be designed to be as thin as possible. The trailing edge should be adequately cooled. Moreover, it can be advantageous to have cooling that is uniform in all operating states. It can be advantageous that the use of coolant be restricted to what is required in order not to exert a disadvantageous influence on the efficiency of the machine. 
       SUMMARY 
       [0006]    A blade for a gas turbine is disclosed, including a platform, a blade tip, a leading edge, a trailing edge, and an airfoil extending between the platform and the blade tip, the airfoil being bounded in at least one direction by the leading edge and the trailing edge and having a suction side and a pressure side, wherein in a region of the trailing edge and in a direction running parallel to the trailing edge from the platform up to the blade tip, in an interior of the airfoil, there is a first cooling duct for feeding a coolant flow from the platform and from which coolant is guided to an outside of the airfoil via a multiplicity of holes arranged distributed on the blade, wherein a cross section of the first cooling duct tapers toward the blade tip, the taper being between 35% and 59%. 
         [0007]    A method for producing a blade for a gas turbine, including forming a blade which includes a platform, a blade tip, a leading edge, a trailing edge, and an airfoil extending between the platform and the blade tip, the airfoil being bounded in at least one direction by the leading edge and the trailing edge and having a suction side and a pressure side, wherein in a region of the trailing edge and in a direction running parallel to the trailing edge from the platform up to the blade tip in an interior of the airfoil, there is a first cooling duct for feeding a coolant flow from the platform and from which coolant is guided to an outside of the airfoil via a multiplicity of holes arranged distributed on the blade, and wherein a cross section of the first cooling duct tapers toward the blade tip, the taper being between 35% and 59%, and forming the holes on the blade from outside into the blade as cooling bores with specified geometric tolerance by at least one of EDM (Electro-Discharge Machining) or laser drilling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The disclosure is explained in more detail below with the aid of exemplary embodiments in conjunction with the drawings. All elements that are not essential for directly understanding the disclosure have been omitted. Identical elements are provided with identical reference numerals in the various figures. The flow direction of the media is specified by arrows. In the drawings: 
           [0009]      FIG. 1  shows a perspective, simplified illustration of a cooled gas turbine blade in accordance with an exemplary embodiment of the disclosure, only the cooling bores arranged distributed in the region of the trailing edge being shown; 
           [0010]      FIG. 2  shows the cooling duct running parallel to the trailing edge, together with the cooling bores emanating therefrom from  FIG. 1 ; 
           [0011]      FIG. 2   a  shows an enlarged section from  FIG. 2  for the purpose of explaining the cross sectional dimensions in the cooling duct; and 
           [0012]      FIG. 3  shows, in an illustration comparable to  FIG. 2 , the configuration being composed of cooling duct and cooling bores as seen from another side. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The disclosure relates to a cooled blade for a gas turbine which is distinguished by improved cooling, and a method for producing it. It can be advantageous that in a region of a trailing edge of a blade, and running parallel to the trailing edge from a platform up to a blade tip in an interior of an airfoil, there is a first cooling duct to which a coolant flow is supplied from the platform and from which coolant is guided to an outside via a multiplicity of holes distributed on the blade. The cross section of the first cooling duct tapers toward the blade tip, the taper being between, for example, 35% and 59%. For example, the taper of the blade can be approximately 42% (e.g., ±10%). 
         [0014]    In an exemplary embodiment of the disclosure, a cross-sectional area of the first cooling duct has a height in a circumferential direction of the turbine, and a width in an axial direction of the turbine. The height/width side ratio diminishes toward the blade tip. The height/width side ratio diminishes toward the blade tip at, for example, 5% to 14%; for example, the height/width side ratio diminishes toward the blade tip by approximately 9%. 
         [0015]    The holes arranged distributed on the blade can be designed as elongated cooling bores that can be produced with low geometric tolerance, for example, by EDM (Electro-Discharge Machining) or laser drilling. 
         [0016]    In another exemplary embodiment of the disclosure, first cooling bores can be arranged distributed along the trailing edge. Second cooling bores can be arranged distributed on the blade tip, and the first and second cooling bores open into the exterior on a pressure side of the blade or have been introduced into the blade from the pressure side. 
         [0017]    The inlets of the first cooling bores can be arranged substantively on a centerline of the first cooling duct. 
         [0018]    The first cooling bores can have a cylindrical shape in that the ratio of a length to diameter of the first cooling bores can be between, for example, 20 and 35. The spacing of neighboring first cooling bores in a radial direction can be, for example, 2 to 5 times, for example, 3.5 times their diameter. The first cooling bores can enclose with the horizontal an angle of, for example, 20°-40°; for example, approximately 30°. The angle of the first cooling bores to the surface of the blade can be between, for example, 8° and 15°; for example, approximately 10°. 
         [0019]    In accordance with an exemplary embodiment of the disclosure, at the transition between the platform and airfoil, the first cooling bores can be aligned with the centerline of the airfoil such that the coolant air is ejected centrally through these cooling bores at the intersection point between the centerline and the profile of the trailing edge. 
         [0020]    In an exemplary embodiment the first cooling bores can merge uniformly at the blade tip into the second cooling bores. The second cooling bores can have a cylindrical shape. The ratio of length to diameter of the second cooling bores can be between, for example, 4 and 15. The spacing of neighboring second cooling bores can be, for example, 4 to 6 times; for example, 5 times their diameter. The angle of the second cooling bores to the surface of the blade can be between, for example, 25° and 35°; for example, approximately 30°. 
         [0021]    In an exemplary embodiment for the cooling of the blades, third and fourth cooling bores can run through the platform, and the third cooling bores open into an exterior on a suction side of the blade, and the fourth cooling bores open into the exterior on the pressure side of the blade. 
         [0022]    The fourth cooling bores can have a cylindrical shape and enclose different angles with the edge of the platform. The spacing of neighboring fourth cooling bores on the outside of the platform can be, for example, 5 to 8 times; for example, approximately 6 times their diameter. The ratio of length to diameter of the fourth cooling bores can be between, for example, 25 and 35. A proportion of the fourth cooling bores exit from the first cooling channel on its side facing the pressure side of the blade. 
         [0023]    The third cooling bores can have a cylindrical shape and enclose different angles with the edge of the platform. The spacing on neighboring third cooling bores on the outside of the platform can be, for example, 6 to 8 times; for example, approximately 6.5 times their diameter. The ratio of length to diameter of the third cooling bores can be between, for example, 30 and 45. The third cooling bores can emerge from the first cooling duct on its side facing the suction side of the blade. 
         [0024]    In order to generate and/or reinforce a turbulent cooling air flow, obliquely positioned ribs can be arranged in the first cooling duct. In the region of the platform, the first cooling duct can be connected via a bend to a parallel running second cooling duct. An outwardly guiding particle hole of relatively large diameter can be provided in the blade tip at the end of the first cooling duct. 
         [0025]    In an exemplary embodiment of a method for producing the blade, holes arranged distributed on the blade are introduced from outside into the blade in the form of cooling bores with low geometric tolerance by, for example, EDM (Electro-Discharge Machining) or laser drilling. 
         [0026]    The disclosure can be applied advantageously in a gas turbine having a multiplicity of moving blades fitted on a rotor and of guide vanes fitted in the housing surrounding the rotor. This can be done by using blades according to the disclosure as moving blades and/or guide blades. 
         [0027]      FIG. 1  shows a perspective, simplified illustration of a cooled gas turbine blade in accordance with an exemplary embodiment of the disclosure. The blade  10 , which can be a moving blade rotating with the rotor about the machine axis, or a guide blade mounted in stationary fashion on the housing, includes an airfoil  11  that extends in a longitudinal direction of the blade or in a radial direction of the gas turbine and terminates at the free end in a blade tip  14 . Adjoining the other end of the airfoil  11  is a platform  12  that bounds the hot gas duct and below which there is integrally formed a blade root  13  for mounting the blade  10  in a groove, provided for the purpose, in the rotor. The airfoil is bounded in the direction transverse to the longitudinal axis, that is to say in the flow direction of the hot gas of the turbine, upstream by a leading edge  15 , and downstream by a trailing edge  16 . The airfoil  11  has a cross sectional profile of a wing, the convexly curved side being the suction side  17  and the concavely curved side being the pressure side  18 . 
         [0028]    In an interior a number of cooling ducts are provided that run parallel in the longitudinal direction, and are connected in a serpentine fashion. The figures show only a last cooling duct  25 , arranged in the region of a trailing edge  16 , and a portion of a cooling duct  26  arranged upstream thereof ( FIG. 2 ). The two cooling ducts  25  and  26  can be interconnected by a bend  28  conforming to the flow ( FIG. 2 ). In order to cool the blade  10 , there can be applied to the cooling ducts  25 ,  26  a cooling air flow  21  that (as indicated by a dashed and dotted arrow in  FIG. 1 ) can be guided up from below through the blade root  13  and the platform  12  from a plenum with compressed air of the gas turbine. 
         [0029]    The trailing edge  16 , the platform  12  and the blade tip  14  of the blade can be penetrated by a multiplicity of long cooling bores  19 ,  20 ,  22  and  23  through which cooling air moves outward out of the cooling ducts  25 ,  26 , and in the process cools the regions of the blade  10  which are flowed through. The cooling bores  19 ,  20 ,  22  and  23  can be produced, for example, by EDM (Electro-Discharge Machining; spark erosion) and/or laser drilling, it thereby being possible to effect narrow geometric tolerances in the bores. 
         [0030]    All the cooling bores  22  and  23  of the airfoil  11  and of the blade tip  14  can open outward on the pressure side  18  of the blade  10 . The cooling bores  19  and  20  and  20   a, b  running through the platform  12  can open into the exterior on the suction side  17  of the blade (cooling bores  19 ) or on the pressure side  18  of the blade (cooling bores  20  and  20   a, b ). All the cooling bores of the cooling channels  25  (cooling bores  19 ,  20   a ,  22 ,  23 ) and  26  (cooling bores  20   b ) can emerge in the interior of the blade  10 . 
         [0031]    In order to permit the cooling air guided in the cooling ducts  25 ,  26  to emerge at predetermined rates through all the cooling bores  19 ,  20 ,  22 ,  23  on the trailing edge  16 , the blade tip  14  and the platform  12 , the cooling duct  25  at the trailing edge can be dimensional with regard to flow cross section and side ratio (H/W in  FIG. 2   a ). This can ensure that the cooling air pressure in the cooling duct  25  assumes and maintains a predetermined value in all operating states of the machine. In particular, the dependence of the flow cross sections and side ratios in the cooling ducts  25  on the blade height (spatial coordinates in blade longitudinal direction) is arranged. The flow cross section of the cooling duct  25  can taper conically toward the blade tip  14 , by, for example, 35% to 59%; for example, approximately 42%. The ratio H/W of duct height H in a circumferential direction and duct width W in an axial direction (see  FIG. 2   a ) can diminish toward the blade tip  14  by, for example, 5% to 40%; for example, by approximately 9%. 
         [0032]    The first cooling bores  22  of the blade  10  can be introduced into the airfoil  11  from the pressure side  18 . They open in the interior of the blade  10  into the cooling duct  25 , specifically such that their holes can lie directly on the centerline (dashed and dotted line  30  in  FIG. 2 ) of the cooling duct cross section. 
         [0033]    The first cooling bores  22  can be aligned in this case such that they enclose an angle between, for example, 20° and 40°; for example, approximately 30° with the horizontal. The angle between the first cooling bores  22  and the surface of the airfoil  11  can be between, for example, 8° and 15°; for example, approximately 10°. The spacing between neighboring first cooling bores  22  in a radial direction can correspond to 2 to 5 times, for example, approximately 3.5 times the bore diameter. The ratio of the length of the first cooling bores  22  to the diameter can vary along the blade heights in the region between  20  and  35 . The first cooling bores  22  can all have a cylindrical shape. 
         [0034]    At the transition between the platform  12  and the airfoil (at the lower end of the cooling duct  25  at the transition to the bend  28 ), the first cooling bores  22  there can be aligned along or substantially along the chord line  29  of the airfoil  11  (dashed and dotted line in  FIG. 1 ) such that the cooling air can be ejected centrally through these first cooling bores  22  at the intersection point between the chord line  29  and the profile of the trailing edge  16 . 
         [0035]    The first cooling bores  22  can merge uniformly into shorter second cooling bores  23  on the blade tip  14 . The second cooling bores  23  can have a cylindrical shape. The ratio of length to diameter of the second cooling bores  23  can be between, for example, 4 and 15. The spacing of neighboring second cooling bores  23  can be, for example, 4 to 6 times; for example, 5 times their diameter. The angle of the second cooling bores  23  to the surface of the blade  10  can be between, for example, 25° and 35°, for example; approximately 30°. 
         [0036]    As described above, third and fourth cooling bores  19  and  20 ,  20   a, b  run through the platform  12 , the third cooling bores  19  open into the exterior on the suction side  17  of the blade  10 , and the fourth cooling bores  20 ,  20   a, b  open into the exterior on the pressure side  18  of the blade  10 . The fourth cooling bores  20 ,  20   a, b  also have a cylindrical shape. They enclose various angles with the edge of the platform  12  (spreading). The spacing on neighboring fourth cooling bores  20 ;  20   a, b  on the outside of the platform  12  is, for example, 5 to 8 times; for example, approximately 6 times their diameter. The ratio of length to diameter of the fourth cooling bores  20 ,  20   a, b  is between, for example,  25  and  35 . A proportion ( 20   a ) of the fourth cooling bores can exit from the first cooling channel  25  on its side facing the pressure side  18  of the blade  10 . Another portion ( 20   b ) can exit from the second cooling duct  26  at its side facing the pressure side  18  of the blade  10 . 
         [0037]    The third cooling bores  19  can also have a cylindrical shape and enclose different angles with the edge of the platform  12 . The spacing of neighboring third cooling bores  19  on the outside of the platform  12  is, for example, 6 to 8 times; for example, approximately 6.5 times their diameter. A ratio of length to diameter of the third cooling bores  19  lies between, for example,  30  and  45 . The third cooling bores  19  can exit from the first cooling duct  25  at its side facing the suction side  17  of the blade  10 . 
         [0038]    In order to generate and/or reinforce a turbulent cooling air flow, obliquely positioned ribs  27  can be arranged in the first cooling duct  25 . It is possible to provide in the blade tip  14 , at the end of the first cooling duct  25 , a dust hole  24  of larger diameter that leads outward and is known per se, for example, from EP A2 1 882 817 and can contribute to preventing accumulation of dust in the cooling duct  25 . 
         [0039]    Thus, it will be appreciated by those having ordinary skill in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10  Blade (gas turbine) 
           11  Airfoil 
           12  Platform 
           13  Blade root 
           14  Blade tip 
           15  Leading edge 
           16  Trailing edge 
           17  Suction side 
           18  Pressure side 
           19 ,  20 ,  20   a,b  Cooling hole 
           22 ,  23  Cooling hole 
           21  Cooling air flow 
           24  Dust hole 
           25 , 26  Cooling passage 
           27  Rib 
           28  Bend 
           29  Chord line (airfoil) 
           30  Centerline (cooling passage  25 )