Title of Invention

"PELTON BUCKET OF A PELTON WHEEL"

Abstract

A Pelton bucket of a pelton wheel comprising a front edge, a rear edge, at least one exit edge (6) extending between the front and rear edges, the at least one exit edge (6) comprising one of at least one partially concavely curved portion and at least one straight portion, wherein the at least one exit edge comprises a portion below an imaginary line extending between the front and the rear edges of the pelton bucket.

Full Text

The present invention relates to a Pelton bucket of a pelton wheel. Poiton buckets have been produced to date with flat exit edges. Preferably In the case of small circular jet ratios, that Is to say when the buckets must be moved closer together to a very small circular et diameter, the exit edges have frequently been leveled downward only at the cup base, since otherwise too little space remains at the cup base between the Peltoh buckets for the water that is to flow off, the result being to reduce the deflection angle of the jet. The flat exit edges necessarily reduce the clear spans between successive buckets, less space therefore remaining for the water that is to flow off. Moreover, the path length required for the deflection is therebyunnecessarily langthened All these disadvantages have a negative effect on the efficiency of the Peiton turbine. It is therefore the object of the present invention to optimize the deflection of the jet by a particularly shaped bucket, and thus to improve the efficiency of the Peiton turbine. 1 he object set is achieved for the Peiton bucket, and the method for producing a Peiton bucket is achieved according to the invention by virtue of the fact that the exit edge of the Peiton bucket of the Pultun wheel is concavely curved at least partially. Owing to this shape of the exit edge, optimum use is made of the kinetic energy of the jet during guidance in the Peiton bucket, and the energy is transferred to the Peiton wheel, resulting in Mliripfdvenisnt in the efficiency or the Peiton turbine. It is possible overall to achieve thereby a gain in efficiency of 0.3 to 0.4%, which signifies a substantial gain given customary performances of a few hundred MW with Peiton turbines. This particular shape arises from an pptimlzation of the deflection of the jet, and ensures that the jet is not guided beyond the path length required for proper deflection. Moreover, the exit angle of the Peiton bucket can be further closed by means of this shape, something which likewise has a favorable effect on the efficiency of the Peiton turbine. An additional effec: of the lowering of the exit edge in the region of the middle of the cup is to create more room for the water flowing past from the cup upstream, resulting therefore iIn an increase in the clear span. As a direct consequence thereof, the exit angles of the Peiton bucket can be further closed in this region in order to preserve the optimum clear spans, and this again has a favorable effect on the efficiency of the Peiton turbine. In an advantageous design, the exit edge of the Peiton bucket is raised in the region of the cup base by comparison with a flat exit edge, it thereby being possible to increase the deflection angle of the jet, and this has a positive effect, in accordance with the law of momentum, on the efficiency of a Pelton turbine. Given small circular jet ratios D^/B2, Di/B2 3.3, the aperture langle at the exit edge should be increased in the region of the cup base at the same time as the exit edge in said region is pulled up, in order to prevent the jet flowing out from grazing the subsequent bucket too strongly. The longer guidance of the jet in the bucket result^, in particular, in a gain in efficiency. A further advantageous embodiment is obtained when the exit edge is raised in the region of the bucket face byl comparison with a flat exit edge, and this additionally permits clearance while optimizing the shape of the Pelton bucket. In order to ensure ithe most fluent possible transitions of the bucket shape, the exit edge is curved, with reference to a radial plane of the Pelton wheel, advantageously at least partially convexly. It is thereby possible for the jet to be deflected during transition and without unnecessary losses in the Pelton bucket, and to emerge from the Pelton bucket. As an alternative to this,; a simplification in the production of a Pelton bucket according to the invention can be achieved when the concavely and/or the convexly curved shape is approximated at le&st partially by a polygon. The efficiency of the Pelton turbine is influenced positively when the outflow angle of the jet at the Pelton bucket is set by the shape of the exit edge such that the radial component of the exit speed of the jet is minimized. An additional improvement in the efficiency can be achieved when the outflow angle of the jet at the Pelton bucket is set by the shape of the exit edge such that thei deflection of the jet is maximized with reference to 180° at least partially. The efficiency canibe yet further improved when the outflow angle at the Pelton bucket is set such that upon exiting from the Pelton bucket the jet only partially grazes the subsequent Pelton bucket. Good optimization results can be achieved when the exit angle profile is firstly calculated, for example with the aid of numerical, fluid dynamic and/or mathematical models, and the fine tuning is carried out in model trials. The invention is described with the aid of the schematic, exemplary and non-restrictive figures 1 to 4, in which: figure 1 shows the outflow of the jet at a Pelton bucket having a flat exit edge, figure 2 shows a comparison of a Pelton bucket having a flat exit edge with Pelton buckets according to the invention, figure 3 shows the outflow of the jet at an inventive Pelton bucket, and figure 4 shows a plan view of an inventive Pelton bucket. Rotating about an axis of rotation in a housing is a Pelton turbine to which a medium, mostly water, is applied from a pressure pipeline via a jet 2, or simultaneously via a plurality of jets, in a fashion tangential to a mean circular jet diameter D1 The medium moving in a translatory fashion enters the rotating Pelton bucket 1 through a cutout in the bucket face, is bifurcated at the bucket blade 5, deflected in the two cups of the Pelton bucket 1 , and leaves the Pelton bucket i to both sides over the outer bucket rim, as illustrated schematically in figure 1 and figure 2. According to the law of momentum, the force F on a stationary Pelton bucket 1 is yielded as Here, £3 is the outflow angle with reference to the entrance axis of the jet 2, p is the density of the medium, c th? jet speed and A the jet cross section. As may be seen from the relationship for the! force, the force is maximized when e3 vanishes, that is to say when the medium is deflected by 180°. Since the Pelton wheel rotates with the Pelton buckets 1, in the j case of conventional Pelton wheels, that is to say with a flat exit edge 3, deflection angles of between approximately 130° to 180° in terms of phase result with reference to the entrance axis. According the Euler turbine equation, P-pQ(u3c:iu - the performance P1 of the Pelton turbine is at a maximum when the medium flows out of the impeller in the circumferential direction (index u), that is to say when there is no radial component (index r) of the jet speed cand it holds that c3r = 0 => c3 = c3u. p in this case again denotes the density of the medium, O the volumetric flow and u the I circumferential spewed of the bucket. The index 0 relates to the entrance of the jet into the Pelton bucket 1, and the index 3 to the exit from the Pelton bucket 1. Thus, for optimum operation of a Pe|ton turbine the deflection angle should be maximized during the entire deflection phase With reference to 180°, and at the same time the exit speed c3 should have only a circumferential component c3u. Indicated in figure! 1 is a Pelton wheel that has two conventional Pelton buckets 1 and to which a jet 2 is applied. The jet 2 is bifurcated at the bucket blade 5, is deflected in the cups and exits at the outflow angle £3 from the Pelton bucket 1 . In conventional Pelton buckets, the "outflow angle e3 is approximately 40° to 50°. The exit angle profile caused by the flat exit edge 3, results in an exit speed c3, which has a radial component c3r, with the disadvantages known from the above discussion. In order to prevent the outflowing water from grazing the subsequent Pelton; bucket 1 too strongly, which would have a negative effect on the performance of the Pelton turbine, a beveled exit edge 4 is often provided in the region of the cup base. Consequently, although upon exiting the water does graze the outside of the subsequent Pelton bucket 1 less, the outflow angles £3S are increased even more, and the resulting exit speed c3S therefore has a still larger radial component. It is directly evident on the basis of the above discussion that the efficiency of the Pelton turbine is thereby degraded. A single conventional Pelton bucket 1 having a flat exit edge 3 is illustrated in figure 2, a). Contrasting in figures 2, b) and c) with this conventional Pelton bucket 1 are inventive Pelton buckets 1 in which! a flat exit edge 3 is indicated as a comparison in each case. It can be seen in figure 2, b) that the exit edge 6 of the inventive Pelton bucket has a concave curvature. A concave curvature is understood here by definition as a curvature whose center of curvature in a side view of the Pelton bucket 1 according to figure 2, a) comes to lie above the exit edge. A convex exit edge consequently has a center of curvature below the exit edge 6, that is to say in the Pelton bucket body itself, for example. Furthermore, the exit edge 6 is lowered in the region of the middle of the cup, that is to say around the circular jet diameter D(, by comparison with the flat exit edge 3, and is raised in the region of the cup base by comparison with the flat exit edge 3, the overall result being a running, concavely curved exit edge 6. In particular, in the case of this exemplary embodiment, a contour is thus produced with reference to a radial plane of the Pelton wheel which has a running, convexly curved shape at the bucket face and then goes over into a running, concavely curved shape up to the cup face. Other shapes are of course also conceivable and possible. This shape is yielded from an optimization with regard to the minimization of the radial component o$r of the exit speed c3, advantageously c3r = 0. Further factors featuring in the optimization are the minimization of the outflow angle e3, with regard to a maximum deflection angle with reference to 180°,: and the path length required for the proper deflection of the jet 2 in the Pelton bucket 1. The optimization of the curved exit edge is carried out with the aid of computational models, for example numerical, fluid dynamic or mathematical models, and verified in subsequent model trials and/or simulations. Of course, it is also possible to optimize the shape only by means of model trials. The following value ranges have proved to be advantageous in practice for this purpose. Figure 2, d) shows two points X1 and X2 that result from the point of intersection of the curved exit edge 6 and the inside of a cup. The basic circle with the radius RG about the Pelton wheel axis ;is then yielded as the circle that is tangent to the extension of the line X1- *X2. As is known to persons skilled in the art, for Pelton wheels the radius is to be RG = (0.25 to 0.85)B2 in the case of circular jet ratios D1B2 ~ 6, while the radius is RG = (0.55 to 1,2)B2 in the case of D1/B2~ :3. The depth TBR of the curved exit edge 6 in the region of the circular jet diameter DT should ithen be in the range of TBR = (0.03 to 0.17)B2. B2 in this case denotes the width of the Pelton bucket 1, as illustrated in figure 4. The curved exit edge has been approximated by a polygon 7 in figure 2, c). It can further be seen that, in addition, the exit edge 7 is further raised in the region of the bucket face by comparison with the flat exit edge 3. This brazing is, of course, also possible with curved exit edges 6. Figure 3 shows a: Pelton wheel, which is indicated by two Pelton buckets 1 having a concavely curved exit edge 6, and to which a jet 2 is applied. The outflow angle £3 resulting from the deflection- is yielded in this exemplary embodiment in such a way that the radial component c3r of the exit speed 03 optimally vanishes, and it is only the circumferential component that continues to remain, and so it holds that c3 = c3u. As a comparison, the exit speed Css of a conventional Pelton bucket 1 is indicated and has a radial component on the basis of the larger ^xit angle £3S. The exit angle profile over the Pelton bucket length BL is indicated in figure 4 at three points by the respective ejxit angle β2 The exit angles β2 are set such that the deflected jet does not graze the outer suijface of the subsequent Pelton bucket too strongly. An optimum exit angle profile exits in this case for each circular jet ratio Di/B2. This exit angle profile can be calculated and/or simulated with the aid of numerical, fluid dynamic and/or mathematical models, or is determined in model trials. Of course, any desired combination of the methods for determining the! optimum exit angle profile can also be applied. WE CLAIM: 1. A Pelton bucket of a pelton wheel comprising: a front edge; a rear edge; at least one exit edge (6) extending between the front and rear edges; characterised in that the at least one exit edge (6) comprising one of: at least one partially concavely curved portion; and at least one straight portion, wherein the at least one exit edge comprises a portion below an imaginary line extending between the front and the rear edges of the pelton bucket. 2. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge having the at least one straight portion and wherein the at least one straight portion has a plurality of straight portions. 3. The Pelton bucket as claimed in claim 2, wherein one of the plurality of straight portions is arranged at an angle to another of the plurality of straight portions. 4. The Pelton bucket as claimed in claim 1, wherein a portion of the at least one exit edge in the region of a bucket base is arranged above the imaginary line extending between the front and the rear edges of the pelton bucket. 5. The Pelton bucket as claimed in claim 1, wherein a portion of the at least one exit edge in a region of mean circular jet diameter is arranged below the imaginary line extending between the front and the rear edges of the Pelton bucket. 6. The Pelton bucket as claimed in claim 1, wherein the at lest one exit edge having the at least one partially concavely curved portion and wherein the front edge is arranged on a bucket face and arranged at a greater distance from a lower most part of an inner surface of the pelton bucket than a lower most part of the at least partially concavely curved portion. 7. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge having the at least one partially concavely curved portion and wherein the front edge is arranged on a bucket face, wherein the at least partially concavely curved portion extends to a region of the front edge, whereby in the region, a part of the at least partially concavely curved portion is arranged at a greater distance from a lower most part of an inner surface of the pelton bucket than a lower most part of the at least partially concavely curved portion. 8. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge having at least one partially convexly curved portion. 9. The Pelton bucket as claimed in claim 1, wherein the pelton bucket having two exit edges which extend to the front edge of a bucket face of the pelton bucket and wherein at least one of the two exit edges having one of at least one partially concavely curved portion and at least one straight portion, wherein the at least one of the two exit edges has a portion that is arranged below the imaginary line extending between the front and the rear edges of the pelton bucket. 10. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge having the at least one straight portion and wherein the at least one straight portion forms part of a polygonal shaped exit edge. 11. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge is adapted to produce a jet outflow angle having a minimum jet exit speed radial component. 12. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge has a shape that is adapted to produce a jet outflow angle having a maximum deflection relative to 180 degree. 13. The Pelton bucket as claimed in claim 1, wherein the at least one exit edge is adapted to produce a flow having an optimal angular profile. 14. The Pelton bucket as claimed in claim 1, wherein a contour of the at least one exit edge has an outflow angle which minimizes a radial component of an exit speed. 15. The Pelton bucket as claimed in claim 1, wherein a portion of the at least one exit edge in the region of a bucket face is arranged above the imaginary line extending between the front and the rear edges of the pelton bucket.

Documents:

01701-delnp-2003-abstract.pdf

01701-delnp-2003-claims.pdf

01701-delnp-2003-correspondence-others.pdf

01701-delnp-2003-description (complete)-16-10-2008.pdf

01701-delnp-2003-description (complete)-22-08-2008.pdf

01701-delnp-2003-description (complete).pdf

01701-delnp-2003-drawings.pdf

01701-delnp-2003-form-1.pdf

01701-delnp-2003-form-18.pdf

01701-delnp-2003-form-2.pdf

01701-delnp-2003-form-3.pdf

01701-delnp-2003-gpa.pdf

01701-delnp-2003-pct-210.pdf

01701-delnp-2003-pct-409.pdf

1701-DELNP-2003-Abstract-(16-10-2008).pdf

1701-DELNP-2003-Abstract-(22-08-2008).pdf

1701-DELNP-2003-Claims-(16-10-2008).pdf

1701-DELNP-2003-Claims-(22-08-2008).pdf

1701-delnp-2003-complete specification (granded).pdf

1701-DELNP-2003-Correspondence-Others-(06-10-2008).pdf

1701-DELNP-2003-Correspondence-Others-(22-08-2008).pdf

1701-DELNP-2003-Drawings-(16-10-2008).pdf

1701-DELNP-2003-Drawings-(22-08-2008).pdf

1701-DELNP-2003-Form-1-(06-10-2008).pdf

1701-DELNP-2003-Form-1-(16-10-2008).pdf

1701-DELNP-2003-Form-1-(22-08-2008).pdf

1701-delnp-2003-form-13-(06-10-2008).pdf

1701-DELNP-2003-Form-18-(06-10-2008).pdf

1701-DELNP-2003-Form-2-(06-10-2008).pdf

1701-DELNP-2003-Form-2-(16-10-2008).pdf

1701-DELNP-2003-Form-2-(22-08-2008).pdf

1701-DELNP-2003-Form-3-(06-10-2008).pdf

1701-DELNP-2003-Form-3-(22-08-2008).pdf

1701-DELNP-2003-Form-5-(06-10-2008).pdf

1701-DELNP-2003-Form-5-(16-10-2008).pdf

1701-DELNP-2003-Form-5-(22-08-2008).pdf

1701-DELNP-2003-GPA-(22-08-2008).pdf

1701-DELNP-2003-Petition-137-(06-10-2008).pdf

1701-DELNP-2003-Petition-137-(22-08-2008).pdf

1701-DELNP-2003-Petition-138-(22-08-2008).pdf