Abstract:
A turbine blade includes a first cooling air duct and a second cooling air duct which is separated from the first cooling air duct by a wall and which has a main direction, wherein the first and the second cooling-air duct are connected to one another by a first opening in the wall, wherein the wall has a second opening, to permit an improved cooling air action and thus higher operating temperatures and higher efficiency of the turbine. The second opening is adjoined by a diverting duct, the main direction of which, in the region in which the diverting duct issues into the second cooling air duct, is oriented substantially parallel to the main direction of the second cooling air duct.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2014/065205 filed Jul. 16, 2014, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP13178390 filed Jul. 29, 2013. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a turbine blade with a first cooling air duct and a second cooling air duct, which is separated from the first cooling air duct by a wall, is neighboring the first cooling air duct and has a main direction, wherein the first and second cooling air ducts are connected to one another at their respective end by a first opening in the wall, wherein the wall has a second opening, which separates the wall in a middle region into a first part and a second part. 
       BACKGROUND OF INVENTION 
       [0003]    A turbine is a flow machine, which converts the internal energy (enthalpy) of a flowing fluid (liquid or gas) into rotational energy and ultimately into mechanical drive energy. The laminar flow around the turbine blades, which is as free from turbulence as possible, has the effect of extracting from the stream of fluid some of its internal energy, which passes on to the moving blades of the turbine. These then set the turbine shaft in rotation, and the usable power is delivered to a machine coupled thereto, such as for example a generator. The moving blades and the shaft are parts of the movable rotor of the turbine, which is arranged within a housing. 
         [0004]    Generally a number of blades are mounted on the shaft. Moving blades mounted in a plane respectively form an impeller or rotor. The blades are profiled in a slightly curved manner, similar to an aircraft wing. Upstream of each rotor there is usually a stator. These stationary blades protrude from the housing into the flowing medium and impart a spin to it. The spin generated in the stator (kinetic energy) is used in the subsequent rotor to set the shaft on which the rotor blades are mounted in rotation. The rotor and the stator are together referred to as a stage. Often a number of such stages are connected one behind the other. 
         [0005]    The turbine blades of a turbine are subjected to particular loads. The high loads necessitate materials that are highly load-resistant. Turbine blades are therefore produced from titanium alloys, nickel superalloy or tungsten-molybdenum alloys. The blades are protected by coatings for greater resistance to temperatures and erosion, such as for example pitting, also known as “pitting corrosion”. The heat shielding coating is known as a thermal barrier coating or TBC for short. Further measures for making the blades more heat-resistant comprise ingenious systems of cooling ducts. This technique is used both in the stationary blades and in the moving blades. 
         [0006]    The turbine blades often have cast-in cooling ducts that wend their way through the respective turbine blades in a serpentine or meandering manner, i.e. the wall between two cooling ducts is interrupted at its respective end by an opening through which the cooling air is diverted into the second duct in the opposite direction, i.e. the main direction of the cooling air of the second duct. Such cooling ducts are known for example from EP 1 607 576 A2. It is sometimes necessary here to provide additional openings, known as “cooling air refreshers”, in the wall between the two serpentine passages, which as a partial bypass feed fresher air, i.e. cooler air, into a middle region of the second cooling air duct, in order still to achieve a sufficient cooling effect here. This may however also be necessary for reasons of stability of the cast core. 
         [0007]    The thermal loading of the turbine blades currently restricts the efficiency of the turbine, since the materials only allow a limited operating temperature. High operating temperatures however have a positive effect on the Carnot efficiency. 
       SUMMARY OF INVENTION 
       [0008]    An object of the invention is therefore to provide a turbine blade of the type mentioned at the beginning that allows an improved cooling air effect, and consequently higher operating temperatures and a higher efficiency of the turbine. 
         [0009]    This object is achieved according to the invention by the second opening being adjoined by a diverting duct, the main direction of which in the region in which it enters the second cooling air duct is aligned substantially parallel to the main direction of the second cooling air duct. 
         [0010]    The invention is based here on the idea that the aerodynamic bypass between two cooling air ducts that is formed by the cooling air refreshers can sensitively disturb the cooling air stream, and consequently may lead to problems in the cooling of the turbine blade. It has surprisingly been found that, on account of the in some cases great differences in pressure between neighboring cooling ducts, the cooling air can leave the cooling air refresher at up to 0.8 Ma. This means that the momentum of the cooling air from the cooling air refresher is much greater than the momentum of the other cooling air flowing along the main direction in the cooling air duct. The stream consequently does not go over into the main direction, but impinges on the opposite wall almost unchecked, and is only limitedly available downstream of the cooling air refresher. In order to counteract this, a mechanical diversion of the cooling air stream from the cooling air refresher into the main direction of the second duct should be provided. This can be achieved by the opening of the cooling air refresher being adjoined by a diverting duct that aligns the cooling air parallel to the main direction of the second duct. 
         [0011]    In an advantageous configuration, the second cooling air duct is delimited by an outer wall of the turbine blade that has a plurality of cooling air outlet openings. This is so because, in particular in the case of cooling air ducts that are directly adjacent the outer wall of the blade and have outlet openings for film cooling, such as for example at the profile tip, there is the problem that the cooling air emerging at great momentum from the cooling air refresher impinges directly on the opposite outlet openings and flows out there. Consequently, scarcely any fresh cooling air is available downstream of the cooling air refresher. Therefore, the described diversion is particularly advantageous here. 
         [0012]    In a further advantageous configuration, a delimitation of the cooling air duct is formed by a part of the wall adjoining the second opening. In other words: the diverting duct runs parallel to the wall, so that the wall forms a delimitation between the first cooling air duct and the diverting duct. This makes particularly easy shaping possible during the casting process, since the corresponding wall can be configured as straight throughout. 
         [0013]    In yet a further advantageous configuration, a delimitation of the cooling air duct is formed by parallel parts of the wall that are offset with respect to one another. The two parts of the wall, on the near side and the far side of the opening, are therefore extended beyond the opening in a parallel-offset manner, and consequently partially overlap. As a result, the diverting duct may be formed by simple extension of the parts of the wall, without additional walls. 
         [0014]    In a first advantageous configuration of the turbine blade, the offset of the wall is in this case brought back outside the region of the cooling air duct in such a way that the wall runs in a straight line outside the region of the cooling air duct. In other words: the wall runs along a straight line, wherein part of the wall on one side of the opening is deflected and taken parallel to the other part of the wall on the other side of the wall. This part therefore describes an S shape in the region of the opening, whereby the diverting duct is formed. 
         [0015]    In a second, alternative advantageous configuration, the parts of the wall differing by the second opening and lying outside the region of the cooling air duct run on parallel straight lines that are at a distance from one another. This means that the two parts of the wall, on the near side and the far side of the opening, run parallel to one another, but do not lie on one straight line. They respectively form a straight line, wherein the two straight lines overlap in the region of the cooling air refresher and thus form the diverting duct for the cooling air. 
         [0016]    In this case, the length of the cooling air duct is advantageously greater than its width. The length is in this case taken to be the distance along which the two parts of the wall run parallel to one another, while the width is formed by the distance between the two parts of the wall. This ensures that a sufficient diversion of the momentum of the cooling air takes place and the component of the momentum that extends perpendicularly to the main direction is largely eliminated. 
         [0017]    A stator or rotor for a turbine advantageously comprises such a turbine blade as a stationary or moving blade. 
         [0018]    A turbine advantageously comprises such a stator and/or rotor. 
         [0019]    The turbine is in this case advantageously designed as a gas turbine. Specifically in gas turbines, the thermal and mechanical loads are particularly high, so that the described configuration of the turbine blade offers particular advantages with regard to the cooling, and consequently also the efficiency. 
         [0020]    A power generating plant advantageously comprises such a turbine. 
         [0021]    The advantages achieved by the invention are in particular that a more uniform cooling is achieved, in particular at the profile tip of a turbine blade, by the specific diversion of the cooling air in a cooling air refresher into the direction of flow of the intended cooling duct. There is no crossing of the cooling air stream, as a result of which the number of cooling air refreshers can also be increased, which in turn increases the stability of the cast core, and consequently brings advantages in the production of the turbine blade. Improved conduction of the cooling air has the effect that the cooling effect is improved and at the same time the consumption of cooling air is reduced. This increases the efficiency of the turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Exemplary embodiments of the invention are explained in more detail on the basis of a drawing, in which: 
           [0023]      FIG. 1  shows a partial longitudinal section through a gas turbine, 
           [0024]      FIG. 2  shows the profile of a moving blade, 
           [0025]      FIG. 3  shows a longitudinal section through the moving blade, 
           [0026]      FIG. 4  shows a cooling air refresher in a first embodiment, and 
           [0027]      FIG. 5  shows a cooling air refresher in a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0028]    The same parts are provided with the same designations in all of the figures. 
         [0029]      FIG. 1  shows a turbine  100 , here a gas turbine, in a longitudinal partial section. The gas turbine  100  has inside a rotor  103 , which is rotatably mounted about an axis of rotation  102  (axial direction) and is also referred to as a turbine rotor. Following one another along the rotor  103  are an intake housing  104 , a compressor  105 , a toroidal combustion chamber  110 , in particular an annular combustion chamber  106 , with a number of coaxially arranged burners  107 , a turbine  108  and the exhaust housing  109 . 
         [0030]    The annular combustion chamber  106  communicates with an annular hot gas duct  111 . There, for example four series-connected turbine stages  112  form the turbine  108 . Each turbine stage  112  is formed from two blade rings. As seen in the direction of flow of a working medium  113 , in the hot gas duct  111  a row of stationary blades  115  is followed by a row  125  formed from moving blades  120 . 
         [0031]    The stationary blades  130  are in this case secured to the stator  143 , whereas the moving blades  120  of a row  125  are fitted to the rotor  103  by means of a turbine disk  133 . The moving blades  120  consequently form component parts of the rotor  103 . Coupled to the rotor  103  is a generator or a machine (not represented). 
         [0032]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107  and is mixed there with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot gas duct  111  past the stationary blades  130  and the moving blades  120 . The working medium  113  expands at the moving blades  120 , imparting its momentum, so that the moving blades  120  drive the rotor  103  and the latter drives the machine coupled to it. 
         [0033]    While the gas turbine  100  is operating, the components which are exposed to the hot working medium  113  are subjected to thermal stresses. The stationary blades  130  and moving blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , together with the heat shield elements which line the annular combustion chamber  106 , are subjected to the highest thermal stresses. To be able to withstand the temperatures which prevail there, they are cooled by means of a coolant. Similarly, the blades  120 ,  130  may have coatings against corrosion (MCrAlX; M=Fe, Co, Ni, rare earths) and heat (thermal barrier coating, for example ZrO 2 , Y 2 O 4 —ZrO 2 ). 
         [0034]    Each stationary blade  130  has a stationary blade root (not represented here), facing the housing  138  of the turbine  108 , and a stationary blade head, at the opposite end from the stationary blade root. The stationary blade head faces the rotor  103  and is fixed to a sealing ring  140  of the stator  143 . Each sealing ring  140  thereby encloses the shaft of the rotor  103 . 
         [0035]    In  FIG. 2 , the profile of a moving blade  120  is shown by way of example. The profile resembles that of an aircraft wing. It has a rounded profile tip  144  and a trailing profile edge  146 . Between the profile tip  144  and the trailing profile edge  146  there extend the pressure side  148  and the suction side  150  of the moving blade. Incorporated between the pressure side  148  and the suction side  150  are cooling air ducts  152 , which extend along the main direction of extent of the moving blade  120 , leading into  FIG. 2 , and are delimited from one another by walls  154 . 
         [0036]    Provided here in the region of the profile tip  144  are cooling air outlet openings  156 , through which cooling air can emerge, and thus form a protective cooling film on the outer side of the moving blade  120 . Additionally arranged in the cooling air duct  152  adjacent the trailing profile edge  146  are pin-like cooling bodies  158 , known as “pin fins”, which improve the heat transfer from the cooling air into the moving blade  120  by their surface located in the cross section of the cooling air. 
         [0037]      FIG. 3  shows the moving blade  120  in longitudinal section. It can be seen here that the three parallel cooling ducts  152  adjoining the profile tip  144  are connected via openings  160  at their respective ends in such a way that they form a meandering common duct. Cooling air K enters at the lower end of  FIG. 3  and at the end of the duct is respectively diverted into the opposite direction at each opening  160 , and continues to flow in this way along the duct until it finally emerges at the cooling air outlet openings  156 . 
         [0038]    In the said three cooling air ducts  152 , arranged on the flat outer side of the moving blade  120  are cooling ribs  162 , which act as turbolators and thus improve the cooling effect. By contrast, the cooling air duct  152  facing the trailing profile edge  146  is connected separately and, as described, has cooling bodies  158 . It can be seen in  FIG. 3  that the cooling bodies  158  form a grid. 
         [0039]    The cooling structure described has been explained on the basis of the example of a moving blade  120 . Similar cooling structures may also be provided correspondingly in stationary blades  130 . The configuration described below of a wall  154  between two cooling air ducts  154  may be similarly realized there. 
         [0040]      FIG. 4  and  FIG. 5  respectively show the wall  154  between the cooling duct  152  adjacent the profile tip  144  and the cooling duct  152  neighboring it. On account of the emergence of the cooling air K through the cooling air outlet openings  156 , it is required here to provide what are known as cooling air refreshers at various points in the middle region of the wall  152 , i.e. away from the end of the cooling ducts  152 . These cooling air refreshers substantially comprise an opening  164  in the middle region in the wall  152 , so that the latter is divided into a first part  166  and a second part  168 . 
         [0041]    As a result of the considerable difference in pressure between the cooling air ducts  152 , cooling air K emerges at great momentum through the opening  164  into the cooling air duct  152  adjacent the profile tip  144 . By analogy with  FIG. 3 , its main direction of flow of the cooling air K points upward in  FIGS. 4 and 5 . In order that this cooling air K does not flow directly perpendicularly to the main direction into the cooling outlet openings  156  opposite the opening  164 , in the exemplary embodiments of  FIGS. 4 and 5  there respectively adjoins a diverting duct  170 , which is aligned parallel to the main direction. The cooling air K in the diverting duct  170  consequently flows parallel to the cooling air K in the cooling air duct  152  adjacent the profile tip  144 . 
         [0042]    In the exemplary embodiment of  FIG. 4 , this is realized by the second part  168  of the wall  154  being offset in an S-shaped manner in the region of the opening  164  and running with an offset parallel to the first part  166 . Outside the region of the diverting duct  170 , the two parts  166 ,  168  run on one line. 
         [0043]    In the exemplary embodiment of  FIG. 5 , the two parts  166 ,  168  do not run on one line, but are offset parallel to one another. Only by a straight overlap do they form the diverting duct  170 . 
         [0044]    In both exemplary embodiments, the length of the diverting duct  170  is greater than its width, so that a reliable diversion of the cooling air K is ensured.