Patent Publication Number: US-8967968-B2

Title: Turbine rotor blade

Description:
TECHNICAL FIELD 
     The present invention relates to a turbine blade provided with a platform in which a cooling channel is formed. 
     BACKGROUND ART 
     An aerofoil portion of the turbine blade and the platform are heated to high temperature by high-temperature combustion gas flowing in a gas turbine. This causes the aerofoil portion and the platform to thermally expand outward in a radial direction of a rotor. As the aerofoil portion and the platform thermally expand at different rates, the heat elongation of the aerofoil portion and the platform causes heat stress between a hub of the aerofoil portion and the platform connected to the hub. The heat stress acts intensively on a trailing-edge end of the hub, which tends to cause a crack in the trailing-edge end. Therefore, it is necessary to reduce the heat stress while suppressing the temperature increase in the aerofoil portion and the platform. 
     JP2001-271603A proposes, as shown in  FIG. 10 , to provide cooling channels  61  through  64  in the aerofoil portion  12  and the platform  60  and to form a concave  20  in a trailing-edge end part  22  of the platform  60  along a circumferential direction of the rotor (in a direction of passing through a plane of paper of  FIG. 10 ). In the aerofoil portion  12 , the cooling channels  61  to  63  are formed along the radial direction of the rotor from a base portion  2  through the aerofoil portion  12 . In the platform  60 , the cooling channel  64  is formed along the axial direction of the rotor from the trailing-edge end surface  18  to a leading-edge end portion of the platform  60 . By streaming cooling air in the aerofoil portion  12  and the platform  60 , the temperature increase of the aerofoil portion  12  and the platform  60  is prevented. 
     Further, in response to the heat elongation of the aerofoil portion  12  expanding outwardly in the radial direction of the rotor, the trailing-edge end surface  18  disposed outside of the concave  20  in the radial direction of the rotor, expands outwardly in the radial direction of the rotor. By this, concentration of the heat stress on the trailing edge end portion  22  of the hub  13  is prevented. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     
         
         JP2001-271603A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the method described in JP2001-271603A, the cooling channel of large diameter is formed in the platform  60  along the axial direction of the rotor to improve the cooling effect for the platform  60 . However, this requires the trailing-edge end surface  18  disposed outward from the concave  20  in the radial direction of the rotor. By increasing the thickness of the end surface  18 , it becomes difficult for the trailing-edge end  22  of the platform  60  to deform, thereby not being able to achieve sufficient reduction of the heat stress. In view of this, instead of increasing the thickness of the end surface  18 , the diameter of the cooling channel is increased as show in  FIG. 11 . In  FIG. 11 , only an upper half  66  of the cooling channel  65  is formed in the end surface  18  and a lower half is exposed. The cooling air reaching near the trailing-edge end  22  disperses from an opening  67 . As a result, the function of cooling the end surface significantly declines. 
     Therefore, it is an object of the present invention to provide a turbine blade equipped with a platform, which is capable of reducing the heat stress acting between the hub and the platform and also capable of efficiently cooling the platform. 
     Solution to Problem 
     To solve the above issues, a turbine blade of the present invention may include, but is not limited to: 
     a base portion which is fixed to a rotor; 
     an aerofoil portion which extends in a radial direction of the rotor and which includes a blade surface on a pressure side and a suction side, the blade surface forming an aerofoil profile between a leading ledge and a trailing edge; and 
     a platform which is provided between the base portion and the aerofoil portion and which has a concave formed in a trailing-edge end portion of the platform along a circumferential direction of the rotor and a cooling channel formed inside the platform with an opening to an end surface disposed outward from the concave in a radial direction of the rotor, and 
     the end surface may be formed thicker in the radial direction of the rotor at the opening of the cooling channel opening to the end surface than at a position which corresponds to a trailing-edge end of a hub of the aerofoil portion at which the aerofoil portion is connected to the platform. 
     According to the above turbine blade, the end surface may be formed thinner at a portion corresponding to the trailing-edge end of the hub of the aerofoil portion than other portions of the end surface. Thus, the portion near the trailing-edge end portion of the platform where the trailing-edge end of the hub is connected can deform easily in response to the heat elongation of the aerofoil portion and thus, it is possible to suppress the heat stress generated near the trailing-edge end portion of the platform. 
     Further, it is possible to form the cooling channel having a large diameter. As a result, the cooling performance for the platform is enhanced and it becomes possible to apply the present invention to the turbine used under high temperature. 
     In the above turbine blade, the end surface of the platform on a trailing edge side may gradually decrease in a thickness of the end surface in the radial direction of the rotor from the suction side of the aerofoil portion toward the trailing-edge end of the hub. 
     In this manner, the end surface of the platform on the trailing edge side gradually decreases in a thickness of the end surface in the radial direction of the rotor from the suction side of the aerofoil portion toward the trailing-edge end of the hub and the end surface of the platform is formed thickest on the trailing edge side. As a result, the cooling channel can be formed along the axial direction of the rotor on the suction side, thereby improving the cooling performance for the platform on the suction side. 
     In the above turbine blade, a plurality of the cooling channels may be formed in the platform along the axial direction of the rotor next to each other, and among the plurality of the cooling channels, a cooling channel that is arranged on the pressure side of the aerofoil portion may have a smaller diameter than a cooling channel that is arranged on the suction side of the aerofoil portion. 
     In this manner, among the plurality of the cooling channels formed next to each other, a cooling channel that is arranged on the pressure side of the aerofoil portion may have a smaller diameter than a cooling channel that is arranged on the suction side of the aerofoil portion. As a result, a plurality of the cooling channels can be formed in the platform. 
     Further, by forming a plurality of the cooling channels in the platform, the cooling effect of the platform can be significantly improved. 
     In the above turbine blade, the thickness of the end surface of the platform on the trailing edge side may gradually decrease in the end surface in the radial direction of the rotor from the suction side of the aerofoil portion toward the trailing-edge end of the hub and from the pressure side of the aerofoil portion toward the trailing-edge end of the hub. 
     In this manner, the thickness of the end surface of the platform on the trailing edge side gradually decreases in the end surface in the radial direction of the rotor from the suction side of the aerofoil portion toward the trailing-edge end of the hub and from the pressure side of the aerofoil portion toward the trailing-edge end of the hub. As a result, the cooling channels having a large diameter can be formed on both sides of the trailing edge end of the hub in the circumferential direction of the rotor. By this, the cooling effect for the platform can be significantly improved. 
     In the above turbine blade, a plurality of the cooling channels may be formed in the platform along the axial direction of the rotor next to each other, and among the plurality of the cooling channels, a cooling channel that is arranged closer to the trailing-edge end of the hub may have a smaller diameter than a cooling channel that is arranged farther from the trailing-edge end of the hub. 
     In this manner, among the plurality of the cooling channels formed next to each other, a cooling channel that is arranged closer to the trailing-edge end of the hub has a smaller diameter than a cooling channel that is arranged farther from the trailing-edge end of the hub. As a result, a plurality of the cooling channels can be formed in the platform. 
     Further, by forming a plurality of the cooling channels in the platform, the cooling effect for the platform can be significantly improved. 
     In the above turbine blade, the plurality of the cooling channels may include a cooling channel which is formed in the trailing-edge end portion of the platform along a shape of a trailing edge side of the blade surface on the suction side. 
     In this manner, the cooling channel is formed in the trailing-edge end portion of the platform along a shape of a trailing edge side of the blade surface on the suction side. As a result, it is possible to positively cool the trailing-edge end portion of the platform. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to efficiently cool the platform and to reduce stress acting between the hub and the platform. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an oblique perspective view of a turbine blade regarding a first embodiment of the present invention. 
         FIG. 2  is a fragmentary view taken in a direction of an arrow A of  FIG. 1 , showing an enlarged view around a trailing-edge end portion of a platform. 
         FIG. 3  is a cross-sectional view taken along a line B-B of  FIG. 1 . 
         FIG. 4  is a cross-sectional view of a gas turbine, showing a flow of cooling air near the turbine blade. 
         FIG. 5  is another example of the cooling channel formed in the platform. 
         FIG. 6  is yet another example of the cooling channel formed in the platform. 
         FIG. 7  is a perspective view of the turbine blade taken from a trailing edge side in relation to a second embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of the platform regarding a third embodiment of the present invention. 
         FIG. 9  is a perspective view of the turbine blade taken from a trailing edge side in relation to a fourth embodiment of the present invention. 
         FIG. 10  is a vertical cross-sectional view of a conventional turbine blade. 
         FIG. 11  is an oblique perspective view showing a trailing-edge end portion of the platform. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of a turbine blade regarding the present invention will now be described in detail with reference to the accompanying drawings. In the detailed explanation, the turbine blade is applied to a gas turbine. However, this is not limitative and the present invention can be applied to a steam turbine as well. Further, it is intended that unless particularly specified, dimensions, materials, shape, its relative positions and the like shall be interpreted as illustrative only and not limitative of the scope of the present invention. 
       FIG. 1  is an oblique perspective view of a turbine blade regarding a first embodiment of the present invention.  FIG. 2  is a fragmentary view taken in a direction of an arrow A of  FIG. 1 , showing an enlarged view around a trailing-edge end portion of a platform. 
     As shown in  FIG. 1  and  FIG. 2 , in the first embodiment of the present invention, a cooling channel  14  is formed in the platform  16  on a suction side of an aerofoil portion  12  to reduce heat stress of the platform on the suction side. 
     The turbine blade  1  of the gas turbine includes a base portion  2  fixed to a rotor, the aerofoil portion  12  extending in a radial direction of the rotor and including a blade surface  8  on a pressure side and the suction side between a leading edge  4  and a trailing edge  6 , and the platform  16  provided between the base portion  2  and the aerofoil portion  12  and having the cooling channel  14  for streaming cooling air. 
     At a trailing-edge end portion  22  of the platform, a concave  20  is formed along the circumferential direction of the rotor. The concave  20  is a so-called relief portion. The cooling channel  14  has an opening  15  opening to a trailing-edge end surface  18  disposed outward from the concave  20  in the radial direction of the rotor. 
     The thickness L of the trailing-edge end surface  18  in the radial direction of the rotor gradually decreases from the suction side of the aerofoil portion  12  toward the trailing-edge end of the hub. In other words, the thickness L of the end surface  18  in the radial direction of the rotor decrease gradually from L 1  near the opening  15  of the cooling channel  14  to L 2  immediately below the trailing-edge end of the hub  13 . 
     In the embodiment, there is no cooling channel provided on the pressure side in the platform  16  along the axial direction of the rotor. Thus, the end surface  18  may be formed thinner or with the same thickness between immediately below the trailing edge end of the hub  13  and an end on the pressure side. 
     The thickness L 2  of the end surface  18  immediately below a connection point where the trailing-edge end of the hub  13  is connected to the platform  16  in the circumferential direction of the rotor, is deformable in response to heat elongation of the aerofoil portion  12 . This is substantially the same as the thickness L 3  of the end surface  18  of the conventional platform  60  described in JP2001-271603A (see  FIG. 11 ). Thus, the thickness L 1  of the end surface  18  at the opening  15  of the cooling channel  14  formed along the axial direction of the rotor is greater than the thickness L 3  of the end surface  18  of the conventional platform  60  of JP2001-271603A. By this, the cooling channel  14  can have an opening of a greater diameter than the cooling channel  64  formed in the conventional platform  60 . 
       FIG. 3  is a cross-sectional view taken along a line B-B of  FIG. 1 . As shown in  FIG. 3 , one end of the cooling channel  14  communicates with a cooling channel  24  on the leading edge side. The cooling channel  24  is in communication with the base portion  2  and the aerofoil portion  12  of the turbine blade  1 . Further, the cooling channel  14  extends from the cooling channel  24  toward a front lower end of the platform  16  (left bottom in  FIG. 3 ), and bends near the front lower end of the platform toward the trailing edge side and extends along the axial direction of the rotor. 
     A portion of the cooling air flowing in the cooling channel  24  enters the cooling channel  14 . The cooling air having entered the cooling channel  14  flows through the cooling channel  14  and exits from the opening  15  on the trailing edge side. 
     At a position where the hub  13  comes closest to the end surface  18  on the trailing edge side, a binding force from the platform having high rigidity is large and thus, the heat stress acting on the aerofoil portion  12  and the hub tends to increase near the trailing edge. Therefore, to reduce the heat stress, the concave  20  (the relief portion) is formed in the trailing-edge end portion  22 . In other words, the position where the hub  13  comes closest to the end surface  18  on the trailing edge side, is immediately below the connection point where the trailing-edge end of the hub is connected to the platform  16 . It is necessary to release the binding from platform side in the vicinity of the connection point. Specifically, as shown in  FIG. 3 , a point A is described at the end surface by drawing a line parallel with the axial direction of the rotor from a trailing edge  6 . In a vicinity of the point A, the hub  13  comes closest to the end surface  18  on the trailing edge side. In other words, when the trailing-edge end surface  18  of the platform  16  on the suction side and the pressure side has the opening  15  of the cooling channel  14  formed along the axial direction of the rotor, it is necessary to form the end surface  18  the thinnest in the radial direction of the rotor near the point A so as to achieve high relief effect. 
       FIG. 4  is a cross-sectional view of a gas turbine, showing a flow of the cooling air near the turbine blade  1 . 
     As shown in  FIG. 4 , the cooling air supplied from a turbine casing enters a disc cavity  31  in the rotor  30 , passes through a radial hole  33  formed in a rotor disc  32  to the cooling channel  24  formed in the base portion  2 . On the way to the aerofoil portion  12 , a portion of the cooling air enters the cooling channel  14  formed in the platform  16 . 
     A supply system for supplying the cooing air to the cooling channel  14  may not be limited by this and another system may be used. 
     As described above, according to the turbine blade of the present embodiment, the thickness L (L 1 ) at the opening  15  of the cooling channel  14  of the end surface  18  of the platform  16  in the radial direction of the rotor is greater than at the position immediately below the trailing edge end of the hub  13  of the aerofoil portion  12 , L 2  (near the point A of  FIG. 3 ). By this, it is possible to enhance the cooling capacity for the platform  16 . 
     On the other hand, the thickness L 2  of the end surface  18  immediately below the trailing-edge end of the hub  13  is smaller than the thickness L 1  of the end surface at the opening  15  of the cooling channel  14 . Thus, a portion of the end surface  18  near the connection point of the trailing-edge end of the hub  13  can deform easily in response to the heat elongation of the aerofoil portion  12 , and it is possible to suppress the heat stress generated near the trailing-edge end portion  22  of the platform  16 . 
     Further, it is now possible to form the cooling channel  14  having a large diameter in the platform  16  on the suction side of the aerofoil portion  12 . As a result, the cooling capacity for the platform is improved, making it applicable to the turbine used at high temperature. 
     The end surface  18  gradually decreases in a thickness L of the end surface  18  in the radial direction of the rotor from the suction side of the aerofoil portion  12  toward the trailing-edge end of the hub  13 , thereby improving the cooling capacity for the platform  16  on the suction side of the aerofoil portion  12  which is under high heat load. It is easy to process the end surface  18  so as to gradually reduce the thickness L of the end surface  18  in the radial direction of the rotor from the suction side of the aerofoil portion  12  toward the trailing-edge end of the hub  13  without increase in labor hours or the cost. 
     In the above embodiment, one cooling channel  14  is formed on the suction side of the aerofoil portion  12 . This is, however, not limitative and the number or the size of the opening of the cooling channel  14  may be freely determined depending on the heat load of the platform and the generated heat stress. For instance, as shown in  FIG. 5  and  FIG. 6 , the thickness L of the end surface  18  may be constant between immediately below the trailing-edge end of the hub  13  and the pressure-side end which is the end of the end surface  18  on the pressure side of the aerofoil portion  12 , and a plurality of cooling channels  14  and  26  may be formed on the suction side of the aerofoil portion  12  and a cooling channel  28  may be formed on the pressure side of the aerofoil portion  12 . In this case, the openings of the cooling channels  14 ,  26 ,  28  may decrease in the diameters of the openings gradually from the suction side to the pressure side of the aerofoil portion  12 . 
     In this manner, by making the diameters of the cooling channels  26  and  28  smaller than that of the cooling channel  14 , it is still possible to form the cooling channels  26  and  28  even where the thickness L of the end surface  18  in the radial direction of the rotor is small. 
     By forming a plurality of the cooling channels  14 ,  26  and  28  in the platform  16 , it is possible to significantly enhance the cooling effect for the platform. 
     Other embodiments of the turbine blade  1  are explained hereinafter. In the following embodiments, components already described in the first embodiment are denoted by the same reference numerals, and thus detailed description thereof will be hereinafter omitted and mainly the differences are explained. 
       FIG. 7  is a perspective view of a turbine blade  41  taken from the trailing edge side in relation to a second embodiment of the present invention. 
     As shown in  FIG. 7 , to reduce the heat stress of the platform on both the suction side and the pressure side, the cooling channels  14 ,  26  and  44  are formed in a platform  42  on both the suction side and the pressure side. The shape of the concave  20  (the relief portion) is modified in correspondence to the positions of the cooling channels  14 ,  26  and  44 . 
     In the platform  42  of the turbine blade  41 , a plurality of the cooling channels  14 ,  26  and  44  are formed. And, the openings  15 ,  27  and  45  of the cooling channels  14 ,  26  and  44  respectively are formed in the trailing-edge end surface  18 . Specifically, the openings  15  and  27  corresponding to the cooling channels  14  and  26  are formed in the end surface  18  on the suction side and the opening  45  corresponding to the cooling channel  44  is formed in the end surface  18  on the pressure side. 
       FIG. 7  shows one example of the shape of the concave (the relief portion)  20  formed in correspondence to the positions of the cooling channels  14 ,  26  and  44 . The position immediately below the connection point where the trailing-edge end of the hub  13  is connected to the platform, is indicated as the point A. The lower point of the trailing-edge end at the position is indicated as a point D. In this manner, the shape of the concave  20  is determined by a line B-C-D-E-F. In other words, the concave  20  is formed into a mountain-shape as a whole with the point D at the top such that the a ceiling portion is formed by a linear line C-D-E having a constant height L 0  in the radial direction of the rotor, the point D being in middle and by gradual slopes formed on both sides of the linear line toward the suction-side end and the trailing-edge end. 
     In the case of the concave  20  having the shape described above, the thickness L of the end surface  18  in the radial direction of the rotor is the smallest at the position with the thickness L 0  (between the points A and D) immediately below the connection point where the trailing-edge end of the hub  13  is connected to the platform  16  In other words, the thickness L 4 , L 5 , L 6  of the end surface  18  at each of the openings  15 ,  27  and  45  of the cooling channels  14 ,  26  and  44  respectively formed along the axial direction of the rotor is greater than the thickness L 0  immediately below the connection point of the trailing-edge end of the hub  13  in the circumferential direction of the rotor. 
     In the second embodiment, the thickness L 0  of the end surface  18  immediately below the connection point of the trailing edge end of the hub  13  is approximately the same as the thickness L 3  of the end surface  18  of the conventional platform  60  described in JP2001-271603A. This is the same as the first embodiment. The thickness L 4 , L 5  and L 6  at the openings  15 ,  27  and  45  of the cooling channels  14 ,  26  and  44  respectively disposed in the circumferential direction of the rotor are greater than the thickness L 3  of the end surface  18  of the conventional platform  60 . Thus, it is possible to form the cooling channels  14 ,  26  and  44  whose diameters are greater than that of the cooling channel formed in the conventional platform  60 . 
     As described above, according to the turbine blade  41  of the present invention, in addition to the effects achieved in the first embodiment, it is possible to significantly enhance the cooling effect for the platform  16  by providing the cooling channels  14 ,  27  and  44  whose diameters are greater than that of the cooling channel formed in the conventional platform  60 . 
     Next, a third embodiment of the turbine blade is explained. The third embodiment of the present invention is different from the first embodiment in that a cooling channel  54  is further provided. The cooling channel  54  is formed in the platform  16  along a shape of the trailing edge side of the blade surface  8  on the suction side of the aerofoil portion  12 . 
       FIG. 8  is a cross-sectional view of the platform regarding a third embodiment of the present invention. 
     As shown in  FIG. 8 , the cooling channel  54  is formed in the platform  16  on the suction side of the aerofoil portion  12  along a shape of the trailing edge side of the blade surface  10 . 
     The cooling channel  54  has an opening  55  at one end and another opening  56  at the other end. The opening  55  opens to the trailing-edge end surface  18  of the platform  16 . The cooling channel  54  has a diameter smaller than that of the cooling channel  14 . The opening  56  opens to a surface of the platform  16  which is on the base portion side. 
     The flow of the cooling air from the rotor  30  to the cooling channel  54  is now explained. 
     As shown in  FIG. 4 , the cooling air passes through a seal disk  34  and a disc cavity  35  that are formed in the rotor  30  and enters a platform cavity  36 . Then, the cooling air enters the cooling channel  54  from the opening  56  formed on the surface of the platform  16  on the base portion side. The cooling air having entered the cooling channel  54  cools the platform  16  and then exits from the opening  55  on the trailing edge side. 
     The supply system for supplying the cooing air may not be limited by this and another system may be used. For instance, the other end of the cooling channel  54  may be connected to the cooling channel  24  which communicates with the aerofoil portion  12  to branch from the cooling channel  24 . The cooling channel  24  is already described in the first embodiment. 
     Further, in third embodiment, the cooling channel  54  is formed in the platform  16  of the first embodiment. However, this is not limitative and the cooling channel  54  is applicable to the platform  42  of the second embodiment as well. 
     As described above, according to the turbine blade  51  of the third embodiment, in addition to the effects achieved in the first and second embodiments, by providing the cooling channel  54 , it is possible to significantly improve the cooling capacity for the trailing-edge end portion  22  of the platform  16 . 
     A turbine blade of a fourth embodiment of the present invention is explained in reference to  FIG. 8 . The fourth embodiment of the present invention is substantially the same as the first embodiment except that the thickness of the end surface  18  of the platform  16  in the radial direction of the rotor is different from that of the first embodiment. 
     As shown in  FIG. 9 , in the fourth embodiment, the end surface  18  of the platform  16  changes the thickness in the radial direction of the rotor. Specifically, the end surface  18  may be formed with the thickness L 1  near the opening  15  of the cooling channel formed in the platform  16  on the suction side along the axial direction of the rotor so that the opening  15  can be arranged, and with the constant thickness L 2  past the thickness L 1  through immediately below the trailing-edge end to the suction-side end such that the thickness L 2  is smaller than the thickness L 2 . According to the fourth embodiment, the same operations and effects as the first embodiment can be achieved.