Abstract:
A turbine blade is provided, comprising a stator-side end located toward a stationary stator cylinder of the turbine, a rotor-side end located toward an axial rotor of the turbine, a leading edge located between the stator-side end and the rotor-side end, a trailing edge located between the stator-side end and the rotor-side end and located down-stream of the leading edge with respect to a fluid flow direction, wherein the rotor-side and stator-side ends have a negative sweep angle as measured between the instantaneous tangent of the blade surface and the fluid flow direction. Also, a turbine blade is provided, comprising a stator-side end located toward a stationary stator cylinder of the turbine, a rotor-side end located toward an axial rotor of the turbine, a delivery side located between the stator-side end and the rotor-side end, a suction side located between the stator-side end and the rotor-side end and located down-stream of the leading edge with respect to a fluid flow direction, wherein the rotor-side end is inclined toward the delivery side and the stator-side end is inclined with respect to a fluid flow direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2004/006624, filed Jun. 18, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 03015496.7 EP filed Jul. 9, 2003, all of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a turbine blade which has a blade height, a rotor-side end and a stator-side end, a leading edge and trailing edge and a suction side and delivery side and which is designed for use in relation to a general direction of flow, and also to a turbomachine which is equipped with such a turbine blade. 
     BACKGROUND OF THE INVENTION 
     In steam turbine construction, for example, curved guide blades are used as an embodiment of turbine blades especially when high three-dimensional flows occur which exhibit pronounced radial differences in the static pressure profile between the rotor side and the stator side, these differences arising due to deflection in the guide blades. In steam turbines, especially in low-pressure turbines with a large outflow cross section, the blade length to hub ratio is relatively high. The flow of a flow medium in the last stage of a low-pressure turbine having a large inflow cross section leads, in the case of a high blade length to hub ratio, to a radial reaction distribution which has an adverse effect on the efficiency of the steam turbine. The reaction distribution is in this case different in the radial direction and is low at the hub and high at the casing, this being felt to be a disadvantage. 
     In a thermal turbomachine, the percentage fraction of the isentropic enthalpy gradient in moving blades in relation to the entire isentropic enthalpy gradient over a stage consisting of a guide blade ring and a moving blade ring is designated as the isentropic reaction degree r. Such a stage in which the reaction degree is r=0 and the highest enthalpy gradient occurs is designated as a straightforward constant-pressure stage. 
     In a conventional excess-pressure stage, the reaction degree is r=0.5, so that the enthalpy gradient in the guide blades is exactly the same as in the moving blades. A reaction degree of r=0.75 is designated as a strong reaction. In steam turbine construction practice, the conventional excess-pressure stage and the constant-pressure stage are predominantly employed. As a rule, however, the latter has a reaction degree somewhat different from zero. 
     A low or even negative reaction of the hub leads to severe impairments and to efficiency losses of the turbine during operation. A high reaction of the casing gives rise to a high attack velocity of the moving blades in the tip region. The high attack velocity has an adverse effect on efficiency, since the behavior of flow losses is squarely proportional to velocity. A reduction in the reaction would remedy this. Moreover, a lower reaction of the casing would lead to a reduction in the gap losses, and the efficiency would thereby be additionally improved. 
     A high reaction in the hub region reduces the gap losses in the guide blade ring and thus leads to improved efficiency. 
     Curved guide blades are in this case used, in particular, in order to optimize the radial reaction distribution. 
     Turbines with guide blades curved only in the circumferential direction are known, for example, from DE 37 43 738. This shows and describes blades, the curvature of which is directed over the blade height toward the delivery side of the guide blade in each case adjacent to the circumferential direction. This publication also discloses blades, the curvature of which is directed over the blade height toward the suction side of the guide blade in each case adjacent to the circumferential direction. 
     Consequently, both radial and circumferentially running boundary layer pressure gradients are to be effectively reduced, and consequently the aerodynamic blade losses are to decrease in size. 
     Turbines with guide blades curved in the direction of flow and in the circumferential direction are known, for example, from DE 42 28 879. 
     Curved guide blades are also known from U.S. Pat. No. 6,099,248. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to specify a turbine blade and turbomachine in which the efficiency is improved. 
     In the turbine blade initially described, this is achieved, according to the invention, by means of the characterizing features as described in the claims. 
     The advantage of the invention is to be seen, inter alia, in that the radial reaction distribution is improved as a result of the improved inflow. 
     Further advantageous refinements are described in the subclaims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are illustrated by means of the figures. In the figures, functionally similar components are designated by the same reference symbols. 
       In the figures: 
         FIG. 1  shows a side view of a final stage, equipped with a turbine blade, of a turbomachine; 
         FIG. 2  shows a view of a guide blade in the direction of flow of a flow medium; 
         FIG. 3  shows a blade with an illustration of a reaction distribution according to the prior art and of a turbine blade according to the invention, shown in  FIG. 1 ; 
         FIG. 4  shows a diagrammatic and perspective illustration of the turbine blade of  FIG. 1  at a rotor-side end; 
         FIG. 5  shows a diagrammatic and perspective illustration of the turbine blade of  FIG. 1  at a stator-side end; 
         FIG. 6  shows a perspective view of a turbine blade. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the steam turbine final stage shown diagrammatically in a side view in  FIG. 1 , the walls delimiting a throughflow duct  1  are, on the one hand, a rotor-side duct wall  3  and, on the other hand, a stator-side duct wall  5 . The stator-side duct wall  5  belongs to an inner casing  6 . A final stage consists of a row of guide blades and a row of moving blades, of which in each case only one guide blade  10  and one moving blade  11  is shown in  FIG. 1  for the sake of clarity. The guide blades are fastened to the inner casing  6  in a way not illustrated. 
     The moving blades are fastened in the rotor  2  in a way not illustrated. 
     The guide blade  10  has a stator-side end  7 , a middle region  8  and a rotor-side end  9 . A flow medium can flow through the duct  1  in the direction of flow  4 . The direction of flow  4  is essentially parallel to an axis of rotation  12  of the rotor  2 . The guide blade  10  has a leading edge  13  and a trailing edge  14  which are formed over the entire blade height. 
     The moving blade  11  likewise has a leading edge  15  and a trailing edge  16 . 
     As illustrated in  FIG. 6 , the disposition of the turbine blade  10  is described by means of a turbine blade form curve  39 . The turbine blade  10  is divided into cylinder surfaces  40 . For the sake of clarity, only six cylinder surfaces  40  are illustrated in  FIG. 6 . The turbine blade form curve  39  describes the disposition more accurately, the more cylinder surfaces  40  are formed. For each cylinder surface  40 , its mass center of gravity  41  is determined. The turbine blade form curve  39  is formed by connecting the mass centers of gravity  41  from a turbine blade root  42  to the turbine blade tip  43 . 
     As is evident from  FIG. 1 , the turbine blade form curve  39  terminates in each case at the rotor-side end  9  and at the stator-side end  7  of the turbine blade  10 . The statements refer below to a turbine blade designed as a guide blade  10 . 
     The turbine blade form curve  39  is considered at its rotor-side end  9 , and the three-dimensional form of the turbine blade form curve  39  is depicted by a tangent which is to be understood as the mathematical derivation of the turbine blade form curve  39  in a curve direction. The tangent or mathematical derivation is designated at the rotor-side end  9  of the turbine blade form curve  39  as an auxiliary tangent  17 . In other words: the three-dimensional form or the disposition of the turbine blade  10  at the rotor-side end  9  is illustrated by the auxiliary tangent  17 . 
     The guide blade  10  is shaped at its rotor-side end  9  in such a way that it has a negative sweep in the direction of flow  4 . Of course, the auxiliary tangent  17  likewise has a negative sweep with respect to the direction of flow  4 . 
     The disposition of the stator-side end  7  of the guide blade  10  is illustrated by a second auxiliary tangent  18 . In this case, the turbine blade form curve  39  is considered at its stator-side end  7 , and the three-dimensional form of the turbine blade form curve  39  is depicted by a tangent which is to be understood as a mathematical derivation of the turbine blade form curve  39  in a curve direction. 
     The guide blade  10  is shaped at its stator-side end  7  in such a way that it has a negative sweep in the direction of flow  4 . Of course, the auxiliary tangent  18  likewise has a negative sweep with respect to the direction of flow  4 . 
     The disposition of the guide blade  10  is described in the center, in the middle region  8 , essentially by an auxiliary tangent  65 . In this case, the turbine blade form curve  39  is considered in its middle region  8 , and the three-dimensional form of the turbine blade form curve  39  is depicted by the auxiliary tangent  65  which is to be understood as a mathematical derivation of the turbine blade form curve  39  in a curve direction. This starts from a point of the guide blade form curve  39  which lies in the middle region  8  and at this point forms a tangent or derivation produced as an auxiliary tangent  65 . 
     The guide blade  10  is shaped in its middle region  8  in such a way that it has a positive sweep in the direction of flow  4 . Of course, the auxiliary tangent  65  likewise has a positive sweep with respect to the direction of flow  4 . 
     In an alternative embodiment, the middle region  8  may also have a negative sweep or even be perpendicular to the direction of flow  4 . 
     Negative and positive sweeps are defined here as follows: 
     negative sweep: the direction of flow  4  must be rotated through an acute angle in a mathematically negative direction (clockwise) with respect to the auxiliary tangent  17  or to the auxiliary tangent  18 , in order to achieve a coincidence of the direction of flow  4  with the auxiliary tangent  17  or  18 . 
     Positive sweep: the direction of flow  4  must be rotated through an acute angle in a mathematically positive direction (counterclockwise) with respect to the auxiliary tangent  65 , in order to achieve a coincidence of the direction of flow  4  with the auxiliary tangent  65 . 
     The distance between the trailing edge  14  of the guide blade  10  and the leading edge  15  of the adjacent moving blade  11  is constant at the rotor-side end  9  and in the middle region  8 . 
     In an alternative embodiment, the distance between the trailing edge  14  of the guide blade  10  and the trailing edge  15  of the adjacent moving blade  11  may be different. 
     The rotor-side end  9  and the stator-side end  7  lie essentially one above the other in the direction of flow  4 . 
     A view in the direction of flow  4  is illustrated in  FIG. 2 . The guide blade  10  lies between a delivery side  21  and a suction side  22 . The middle line, shown in  FIG. 2 , between the delivery side  21  and the suction side  22  constitutes the leading edge  13 . The direction of flow  4  runs essentially perpendicularly with respect to the drawing plane. The flow medium in this case flows along the direction of flow  4  and impinges first onto the leading edge  13  of the guide blade  10 . 
     The rotor-side end  9  of the guide blade  10  is inclined in the direction of the delivery side  21 . The stator-side end  7  is likewise inclined toward the delivery side  21 . 
     In the middle region  8  of the guide blade  10 , the guide blade  10  is inclined toward the suction side  22 . 
     In an alternative embodiment, the middle region  8  may also be inclined toward the delivery side  21 . In a further alternative embodiment, the middle region may be inclined neither toward the delivery side  21  nor toward the suction side  22 . 
     However, in an alternative exemplary embodiment of the turbine blade, the middle region may also be oriented in a radial direction  34 . 
     The leading edge  13  is positioned essentially upstream of the trailing edge  14  at the rotor-side end  9  of the guide blade  10 . 
     The leading edge  13  is positioned essentially upstream of the trailing edge  14  in the direction of flow  4  at the stator-side end  7  of the guide blade  10 . 
     In the middle region, the trailing edge  14  is displaced toward the delivery side  21  with respect to the leading edge  13 . 
     The stator-side end  7  of the guide blade  10  is displaced in the radial direction  34  toward the delivery side  21  with respect to the rotor-side end  9 . 
     In  FIG. 4 , a diagrammatic and perspective illustration of the turbine blade  10 ,  11  at the rotor-side end  9  can be seen and serves for a more detailed explanation of the position of the auxiliary tangent  17  and of angles α and γ which are related to this. 
     The three-dimensional form of the turbine blade  10  has not been illustrated for the sake of clarity. The turbine blade  10  is illustrated at the rotor-side end  9  by the auxiliary tangent  17 . 
     The auxiliary tangent  17  would, if prolonged in the direction of the rotor  2 , touch the rotor  2  at a point  44 . A first auxiliary axis  20  intersects the axis of rotation  12  perpendicularly and runs through the point  44 . 
     A second auxiliary axis  23  intersects the first auxiliary axis  20  at the point  44  and runs essentially parallel to the direction of flow  4  which, in this exemplary embodiment, is parallel to the axis of rotation  12 . 
     A third auxiliary axis  24  intersects the first auxiliary axis  20  at the point  44  and runs perpendicularly with respect to the first auxiliary axis  20  and perpendicularly with respect to the second auxiliary axis  23 . 
     The first auxiliary axis  20  and the second auxiliary axis  23  form a first projection plane  45 . The first auxiliary axis  20  and the third auxiliary axis  24  form a second projection plane  46 . 
     The auxiliary tangent  17  is projected onto the first projection plane  45 , in that each point of the auxiliary tangent  17  is projected onto the first projection plane  45  in the direction of the third auxiliary axis  24 . 
     This is explained, by way of example, with reference to a point  47  of the auxiliary tangent  17 . The point  47  is projected along a first projection straight line  48 , in a direction running parallel to the third auxiliary axis  24 , onto a first projection point  49  lying in the first projection plane  45 . A first projection straight line  17 ′ is thus projected onto the first projection plane  45 . 
     The first projection straight line  17 ′ is inclined at an angle α with respect to the second auxiliary axis  23 . 
     The angle α may in this case assume values of between 0° and 90°, in particular the value of the angle α lies between 50° and 80°. 
     The auxiliary tangent  17  is also projected onto the second projection plane  46 , in that each point of the auxiliary tangent  17  is moved in the direction of the second auxiliary axis  23  onto the second projection plane  46  until this is touched. 
     This is explained by way of example, with reference to the point  47  of the auxiliary tangent  17 . The point  47  is projected along a second projection straight line  51 , in a direction running parallel to the second auxiliary axis  23 , onto a second projection point  52  lying in the second projection plane  46 . A second projection straight line  17 ″ is thus formed on the second projection plane  46 . 
     The second projection straight line  17 ″ is inclined at an angle γ with respect to the first auxiliary axis  20 . 
     The angle γ may assume values which lie between 0° and 90°, in particular the angle γ lies at 70°. 
     The rotor-side end face of the turbine blade  10  is indicated by a dashed line run  54 . 
     In  FIG. 5 , a diagrammatic and perspective illustration of the turbine blade  10  of the stator-side end  7  can be seen and serves for a more detailed explanation of the positions of the auxiliary tangent  18  and of angles β, δ and ξ which are related to this. 
     The three-dimensional form of the turbine blade  10  has not been illustrated for the sake of clarity. The turbine blade  10  is illustrated at the stator-side end  7  by the auxiliary tangent  18 . 
     The auxiliary tangent  18  would, in its prolongation in the direction of the inner casing  6 , touch the inner casing  6  at a point  55 . 
     A fourth auxiliary axis  26  intersects the axis of rotation  12  perpendicularly and runs through the point  55 . A fifth auxiliary axis  27  intersects the fourth auxiliary axis  26  at the point  55  and runs parallel to a surface of the inner casing at the point  55 . A sixth auxiliary axis  28  intersects the fourth auxiliary axis  26  perpendicularly at the point  55  and runs perpendicularly with respect to the fifth auxiliary axis  27 . 
     The fourth auxiliary axis  26  and the fifth auxiliary axis  27  form a third projection plane  56 . The fourth auxiliary axis  26  and the sixth auxiliary axis  28  form a fourth projection plane  57 . 
     The auxiliary tangent  18  is projected onto the third projection plane  56 , in that each point of the auxiliary tangent  18  is moved in the direction of the sixth auxiliary axis  28  onto the third projection plane  56  until it touches the latter. 
     This is explained, by way of example, by means of a point  58  of the auxiliary tangent  18 . The point  58  is projected along a third projection straight line  59 , in a direction running parallel to the sixth auxiliary axis  28 , onto a third projection point  60  lying in the third projection plane  56 . A third projection tangent  18 ′ is thus projected onto the third projection plane  56 . 
     The projection tangent  18 ′ is inclined at an angle ξ with respect to the fifth auxiliary axis  27 . The angle ξ lies between 0° and 180°. 
     The projection tangent  18 ′ is also inclined at an angle β with respect to the axis of rotation  12 . The angle β may assume essentially values of between 0° and 90°. 
     The auxiliary tangent  18  is also projected onto the fourth projection plane  57 , in that each point of the auxiliary tangent  18  is moved in the direction of the fifth auxiliary axis  27  onto the fourth projection plane  57  until it touches the latter. 
     This is explained, by way of example, by means of the point  58  of the auxiliary tangent  18 . The point  58  is projected along a fourth projection straight line  62 , in a direction running parallel to the fifth auxiliary axis  27 , onto a fourth projection point  63  lying in the fourth projection plane  57 . A fourth projection tangent  18 ″ is thus projected onto the fourth projection plane  57 . 
     The projection tangent  18 ″ is inclined at an angle δ with respect to the sixth auxiliary axis  28 . The angle δ lies between 0° and 90°, preferably the angle δ is 75°. 
       FIG. 3  illustrates, as a graph, a reaction distribution as a function of a blade height. The X-axis  35  in this case represents the reaction distribution in arbitrary units. The Y-axis  36  in this case represents the distance from a hub. The dashed line  37  shows the profile of the reaction distribution according to the previous prior art. The unbroken line  38  shows the profile of the reaction distribution when the guide blades are designed according to the invention illustrated here. 
     As mentioned initially, it is a disadvantage if the reaction distribution in the radial direction  34  is different. The dashed line  37 , which illustrates the reaction distribution according to the previous prior art, shows the abovementioned behavior which is felt to be a disadvantage. According to this, the reaction distribution from the hub to the casing is different. The unbroken line  38  shows an improved reaction distribution, as compared with the dashed line  37 .