DE3938356C2 - Pelton cup for high specific speeds - Google Patents

Description

The invention relates to cup shapes for, for example, DE-PS 8 54 328 known Pelton turbine impellers according to the preamble of claim 1 for proportions of beam circle diameter D to beam thickness diameter d ( Fig. 2, Fig. 3), D / d for short, in Extent less than 7 to much less than 5.

To put it graphically, a small ratio D / d means relatively large Pelton cups, which move very close to the center line 2 of the turbine wheel, as clearly shown in FIGS . 2 and 3.

The invention consists in the discovery of interrelated Proportions as specified in claims 1 to 5 for small values D / d and that deviate widely from the usual known values.

In the specialist literature, a ratio D / d of greater than 10 recommended to achieve good efficiencies, the majority executed Pelton wheels have a ratio D / d of 10 to 15. The ratio rarely works D / d down to 8, known exceptions with D / d = 6.5 are known.

The desire to realize small ratios D / d arises when the Pelton turbine is used not only in the traditional application area of large gradients and relatively small amounts of water (technically expressed by small ones) due to its excellent efficiency behavior over wide water volume ranges and because of the possibility of its problem-free, almost non-reactive double regulation specific speeds n _Q <10 per nozzle), but also on low slopes and large amounts of water and this also at the highest possible speeds!

You can use a traditionally designed Pelton wheel with D / d = 10 and highest efficiency, of course, also with good efficiency in the middle of Field of application of a Francis turbine, e.g. B. with a 30 m gradient and 1000 l / s use, but will be a very large expensive wheel with an unfavorable have to accept low speed. It is better to choose a small one Ratio D / d to less than 5 and dealing with the kinematic difficulties of water jet guidance, which then arise.  

These difficulties are the constructive consequences of an overhanging clearance angle -α ₁ at the blade tip P ₁ in FIG. 3, with definition of α ₁ relative to the cup edge plane R and the plus-minus assignment in FIG. 3B.

In the case of strongly negative angles α _1, the conventional design points of view for the construction of Pelton cups fail with acceptable efficiencies. Therefore, there is a recommendation in the literature not to go below 10 with D / d. Values around 8 are seldom realized. That is the state of the art.

Figs. 1 to 5, however, show a Pelton buckets with the fiction, modern characteristics for a D / d ratio = 4.33 and for a specific speed based on the unit volume of 1 m ³ / s, and defines a nozzle for each wheel of n = _Q 15.

This is an unusually high specific speed for a Pelton wheel, defined for one Nozzle per wheel is characterized by the features of claims 1 to 5 according to the invention achieved, which are best explained in connection with the figure description:

Fig. 1 shows an isometric perspective view of the blade illustrated in the further figures for a typical sample value of D / d = 4.33. Fig. 1 shows those external features that, when looked at briefly, stand out as a major difference to known Pelton cups according to the current state of the art: These are the cup halves lying kidney-like, symmetrically obliquely to the central cutting edge M, which are seen radially inside much further apart than radially outside How this is expressed in the wide spacing of the vertices P ₃ and in the strong expansion angle of the contour lines 3 (defined parallel to the cup edge plane R) and 4 (symmetrically starting from the point P ₄ in the cup edge plane R). Furthermore, the very strong inclination of the central cutting edge M with respect to the cup edge plane R in the direction of the cutting tip P _{1 is} striking, which results in a point P ₅ which protrudes high above the cup edge plane. At the same time, one can see from the angles of inclination of the segment-like fastening foot of the cup body 1 that the assembly of such a shaped blade takes place extraordinarily close to the rotational axis of the turbine. The blade attachment in the wheel body - whether individual attachment as shown in all figures or as an integral casting - all blades cast in one piece with the wheel body - has nothing to do with the features of the invention. The next figures show additional optical characteristics, such as their quantitative definition in numerical values.

FIG. 2 shows a view of the Pelton cup according to the invention perpendicular to the cup edge plane R, which is marked in FIG. 3.

The cup 1 rotates at an angular velocity ω about the extraordinarily close axis of rotation 2 . The beam with the diameter d affects the beam circle diameter D with the center on the axis of rotation 2 radially far inward from the prior art at point P ₆ . However, the radial position of the jet with diameter d within the marked radial cup height H is not specified in the claims, since various assumptions are possible as long as there is an effective kinematic clearance angle on the back of the blade.

A striking feature when looking closely at the view in FIG. 2 perpendicular to the cup rim plane R is the course of the bottom crest line S symmetrical to the cup center plane mm: This bottom crest line S is defined as the connection of the lowest points under the cup rim plane R, for example in plane parallel sections perpendicular to R and parallel to the axis of rotation 2 represented by typical cuts BB, CC and EE in FIG. 2, shown in detail in FIGS. 3A, 4 and 5, which likewise contribute to clarifying the definition of the apex line S. The radially outer end points P _{2 of} this apex line have the axial distance b ₁ from one another, which is substantially less than the axial distance b _{2 of} the radially inner end points P ₃ .

This ratio b ₂ / b ₁ is given in claim 2 for the blade according to the invention with 1.7 to 2.5, preferably 2 to 2.3, while constructions according to the prior art are clearly between 1 and 1.4. What is essential in claim 2 is not only the large ratio b ₂ / b ₁ visible in FIG. 2, but the course of the curvature of the bottom apex line S expressed by the initial tangent angle B ₂ at point P ₂ in the view in FIG. 2: This angle is in the blade according to the invention, in deviation from the prior art, is extremely small and is specified in claim 2 with 5 ° to 48 °, preferably 5 ° to 20 °, which characterizes the strong bell-like extension of the lines S in FIG. 2. In the case of Pelton cups according to the prior art, the angle B ₂ defined in this way is almost 90 °, rarely does it go down to values from 70 °, but never to values as low as 5 ° to 20 ° as can be seen in FIG 2 is set.

Fig. 2 also illustrates the claim 3: The angle β _{4 of} a height line parallel to the cup edge R (defined in Fig. 3) at a depth t ₀ , which is dimensioned (seen in Fig. 3) that the plane of this height layer line also includes the axis of rotation 2 of the Pelton wheel (clearly visible in FIG. 3), measured radially between the planes of the cuts EE at a distance of 0.55 H and CC at a distance of 0.81 H ( FIG. 2) is 12 ° to 50 °, preferably 12 ° to 40 °. In the example shown in FIG. 2, this angle is β ₄ = 36 °.

In the case of examples according to the prior art, this angle β ₄ thus hardly reaches the value of 8 ° and usually only moves by 5 °.

This extraordinarily large angle β ₄ is a consequence of the guidance of the bottom apex line S defined in claim 2 and the large ratio b ₂ / b _{1 defined there} .

Another consequence of the cup halves arranged obliquely symmetrically to the central plane mm is the tangent angle β _{7 of} the cup edge R (marked in FIGS. 1 and 3) at the height of the typical section EE at a distance of 0.55 H from the apex line through the points P ₃ : According to claim 5, this angle marked in FIG. 2 is 8 ° to 18 °. In the case of examples according to the prior art, the angle β ₇ thus defined is not 8 ° to 18 °, but only 0 ° to 5 °.

FIG. 2 also shows the level line 4 in the plane of the cup edge R on the slope of the protruding central cutting edge M with the highest point P ₅ above the cup edge plane R.

FIG. 3 shows the section AA, the guidance of which along the bottom apex line S is defined in FIG. 2 and partly parallel to the central plane mm in FIG. 2. Claim 3 discussed above under FIG. 2 also becomes partly in FIG. 3 Illustrated: An immediate consequence of the exceptionally large angle β ₄ described under FIG. 2 is an equally exceptionally steep angle α _{4 of} the central cutting edge M with respect to the cup edge plane R, which can be 18 ° to 50 ° in the blade according to the invention. In the example in FIG. 3, α ₄ = 35 °. In the case of examples carried out according to the prior art, this angle is at most 10 °.

The steep angle α ₄ in FIG. 3 also means a starting point P _{5 of} the central cutting edge M, which protrudes high above the cup edge plane, expressed by the coordinate ratio T ₅ / t ₂ , which assumes values from 0.3 to even 1. The example according to the invention shown in the figures has a ratio of T ₅ / t ₂ of 0.71.

T ₅ is the height of point P ₅ above the cup rim plane R. "t ₂ " is the greatest depth of a cup half compared to R.

In the case of examples carried out according to the prior art, the value for T ₅ / t _{2 is} very much less, namely 0 to 0.15 and is sometimes also negative, in the case of a central cutting edge entirely below the cup edge plane R.

Figs. 3 also serves to illustrate in claim 1: This requirement makes a statement about the coordinates ratio t ₁ / t ₂ and α over the tangent angle _2, where t ₁ is the depth of the starting point P ₂ of the bottom apex line S is below the cup rim plane R. The bottom crest line S has already been explained under FIG. 2 and can be seen in FIG. 2. Point P ₂ lies on the cup cutout. This ratio t ₁ to the greatest cup depth t ₂ takes unusually high values in the blade according to the invention, namely up to 1.0. A value of 1.0 for the ratio t ₁ / t _{2 also} means an angle α ₂ = 0, where α _{2 is defined} as the tangent angle at point P ₂ with respect to a direction parallel to the cup edge plane R.

In examples according to the prior art, the coordinate ratio t ₁ / t ₂ thus defined is in the range between 0.55 and 0.8, but never against 1.0.

FIG. 3 also shows the partial section AX with a thick dash-dotted line, which is defined in FIG. 2 parallel to the central plane mm. The tangent angle α ₂ at point P ₂ for the section AA projected on mm along the bottom apex line S can, as can be seen, also become zero for the partial section AX or, as in the example shown for AX in FIG. 3, also slightly negative in the sense of the plus-minus definition for the angle α ₁ in FIG. 3B. Because of the proximity and parallelism of AX to mm, the direction of AX is already clearly similar to the direction of the free-face apex line F in FIG. 3, which shows the connection of all back apexes F - typically shown in the sections BB ( FIG. 3A), CC ( Fig. 4) and EE ( Fig. 5) - represents. This free-area apex line defined in this way ends radially on the outside at the cutting point P ₁ and there has, according to known kinematic laws of beam engagement, the overhanging clearance angle -α ₁ with respect to the cup edge plane R, which in the example shown is coincidentally -17 °. The plus-minus definition for α _{1 is} shown in Fig. 3B.

The Fig. 3 also shows the inclination angle β ₅ of the cup rim plane R with respect to a radial reference plane passing through the Peltonraddrehachse 2 and through the axis of intersection P _7, represented by the point P ₇ of this reference plane. Point P ₇ is defined on the jet circle diameter D, which is the circle to which the water jets from one or more nozzles touch. In the projection view of FIG. 2 perpendicular to the cup edge plane R, the radial beam position is given by the point P ₆ , which in FIG. 3 lies in a radial plane parallel to the cup edge plane R. The thus defined angle of inclination β _{5 of} the cup edge plane backwards, in the direction of rotation, moves in the blade according to the invention within the usual limits of 8 ° to 15 ° and is therefore not mentioned in the claims.

However, it should be expressly pointed out that the large clearance angles at the rear of the blade which are required for kinematic reasons, with such a low ratio of D / d = 4.33, as is shown in the figures as a typical example, not to be simply tilted backwards of the cup can be achieved, as is often observed in the examples carried out and which leads to a loss of deflection angles. Thanks to the features of the blade according to the invention, this strong backward tilting is not necessary, expressed by a small angle β ₅ .

Fig. 3B shows the plus-minus definition for the angle α. ₁

FIG. 3A shows the section BB perpendicular to the cup edge plane R marked in FIG. 2 at a distance of 0.87 H from the apex line through the points P ₃ and also marked in FIG. 3.

This cut is almost on the cup cutout. He shows the dots S the bottom crest line S and the point F the crest line of the open area on the blade surface, which has a clearly visible elliptical contour. Would you also represent the water jet in the blade cut, so would he appears as a distorted ellipse of a circular cylinder to which the elliptical contour on both sides of the points F is approximately an equidistant.

Fig. 4 shows in a definition analogous to Fig. 3A, the section CC at a distance of 0.81 H from the apex line through the points P ₃ , marked in Fig. 2 and is intended to the strong lifting of the central cutting edge and the strong axial outward migration of the Illustrate vertices S.

Fig. 5 shows the section EE perpendicular to the plane of the cup rim R in the radial distance of 0.55 H of the apex line through the points P _3, marked in Fig. 2 and Fig. 3.

Fig. 5 illustrates claim 4, according to which the cutting angle β _{6 is} very large in the blade according to the invention very large deviations from conventional designs, 32 ° to 60 °, preferably 40 ° to 55 °.

In the case of blades according to the prior art, this angle is significantly smaller, namely 12 ° to a maximum of 30 °. "β ₆ " is tangent angle in M. The ratio b / B 1 in the typical section EE at a radial distance of 0.55 H from the apexes P ₃ is large in the blade according to the invention from conventional designs, namely 0.65 to 0 , 85, while executed Pelton cups have a defined ratio of only 0.45 to a maximum of 0.6, namely in the radial range 0.3 H to 0.6 H away from the apex line through the points P ₃ , as in FIG. 2 is defined. The exceptionally wide spacing of the vertices S in the blade b according to the invention in the distance b in relation to the cup width B 1 causes intentionally steeper outer flanks of the cup sections between S and the outlet angle β ₁ , which has usual values, compared to the flatter inner flanks of the cutting edge M go out.

Stiffening ribs 5 can be seen not only in Fig. 5, but also in Fig. 3 and as invisible on the back also shown in dashed lines in Fig. 2, where you can see the useful fork-like arrangement.

Claims (5)

1. Pelton cup for ratio proportions "beam circle diameter to beam thickness (D / d)" ( Fig. 2) from values less than 7 down to 4, characterized in that the cutting edge back clearance angle (α ₁ ) values in the range of plus 10 ° to overhanging minus 25 ° ( FIG. 3B), the ratio of the coordinates (t ₁ / t ₂ ) ( FIG. 3) assumes values from 0.82 to 1, preferably 0.85 to 0.95, during that on the median plane (mm) projected angle (α ₂ ) ( Fig. 3) of the section (AA) ( Fig. 2) is 0 ° to 25 °, preferably 5 ° to 20 °. 2. Pelton cup for ratio proportions "beam circle diameter to beam thickness (D / d)" ( Fig. 2) from values less than 7 down to 4, characterized in that the cutting back clearance angle (α ₁ ) values in the range from plus 10 ° to overhanging minus 25 ° ( Fig. 3B) and with such a guide by connecting the lowest points under the cup edge plane (R), for example in flat parallel sections perpendicular to (R) and parallel to the axis of rotation ( 2 ) of a Pelton cup according to the invention provided turbine wheel defined bottom vertex line (S) is that the ratio of the axial distances of the end points (P ₂ ) and (P ₁ ) ( Fig. 2) of the vertex line (S), expressed by (b ₂ / b ₁ ) ( Fig. 2), assumes values from 1.7 to 2.5, preferably 2 to 2.3, while at the same time the initial tangent angle (β ₂ ) at points (P ₂ ) in a view perpendicular to the cup edge plane (R) ( FIG. 2) Values from 5 ° to 48 °, preferably from n assumes 5 ° to 20 °. 3. Pelton cup according to claims 1 or 2 with a special design of the central cutting edge (M) ( Fig. 2, Fig. 3), characterized in that the angle β ₄ of tangents to a contour line ( 3 ) in a plane parallel to the cup edge plane R in a depth (t ₀ ) below R, so that this plane also includes the axis of rotation ( 2 ), where β _{4 is} measured radially at a distance (0.81 H), where the section (CC) is also marked, that is this angle β ₄ covers a range from 12 ° to 50 ° ( FIG. 2), preferably 12 ° to 40 °, while at the same time the angle of inclination (α ₄ ) ( FIG. 3) is at least 50% of the length of the central cutting edge (M) 18 ° to 50 °, preferably 20 ° to 40 °. The coordinate ratio (T ₅ / t ₂ ) ( FIG. 3) is 0.3 to 1.0, preferably 0.4 to 0.8. 4. Pelton cup according to claims 2 and 3 with a typical shape of cuts perpendicular to the cup edge plane (R) in the radial range from (0.3 H) to (0.6 H), measured radially from the apex line through the points (P ₃ ) outside, these cuts also being perpendicular to the central plane (mm) ( Fig. 2, Fig. 5), characterized in that the ratio (b / B 1) ( Fig. 5) is 0.65 to 0.85, preferably 0.65 to 0.75, while the cutting edge angle (β ₆ ) ( FIG. 5) associated with these proportions, defined as the tangent angle starting from (M), is 32 ° to 60 °. 5. Pelton cup according to one of claims 1 to 4 with kidney-like shape of the view perpendicular to the cup edge plane (R) ( Fig. 2), characterized in that the edge tangent angle (β ₇ ) ( Fig. 2) in the cup edge plane in the radial distance ( 0.55 H) of the section (EE), measured in relation to a parallel to the central plane (mm), is 8 ° to 18 °, preferably 9 ° to 12 °.