JPS61145369A - Kaplan turbine - Google Patents

Abstract

PURPOSE:To increase a number of sheets of runner blades and prevent the generation of cavitation with no worsening of water turbine performance, by forming each of the runner blade branching in the peripheral part into plural sheets of branch blade parts. CONSTITUTION:A runner blade 9 is constituted by an internal peripheral blade part 10 connected with a stub 8 and branch blade parts 11, 12 branching into two sheets in the end of said internal peripheral blade part 10. While a Kaplan turbine generates cavitation in its runner blade surface, and the cavitation, first being generated in the peripheral part of the blade, spreads to an internal peripheral side in accordance with a decrease of pressure. Accordingly, if the generation point of time of cavitation in a place excepting the runner blade is considered, the runner blade is preferably formed branching, that is, in double construction in the peripheral side from the center of a flow path width.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a Kaplan water turbine in which the angle of runner blades is variable, and particularly to a Kaplan water turbine suitable for high head.

(Technical precursor to the invention and its problems) Kaplan turbines have movable runner blades, so when the load or head changes and the water flow direction changes, the blade angle can be adjusted accordingly to improve the flow. This suppresses the generation of separation and vortices, prevents a drop in efficiency, and enables quiet operation.

FIG. 4(a) shows a conventional Kaplan water turbine, in which high-pressure water flowing into the casing 1 passes through the Sude vane 2 and the guide vane 3, thereby driving the runner blades 4. These runner blades 4 are attached at equal angular intervals to the outer periphery of a runner boss 6 fixed to the main shaft 5, and are configured to be rotatable in the six directions of arrows by a blade operating mechanism housed within the runner boss 6.

When this Kaplan turbine is used in a hydroelectric power plant with a high head, the flow velocity increases, and cavitation is likely to occur at the runner blade outlet. This cavitation is
As will be explained in detail below, this is more likely to occur on the outer periphery of the runner blade than on the inner periphery. That is, as shown in FIG. 4(b), the radius is 1" and 1" from the center axis of rotation Y-Y, respectively.
The absolute flow velocities vb and vo are almost equal at the inner circumferential end pb and the outer circumferential end PO of the shear runner blade, however, at the outer circumferential end PO
Since the peripheral speed uO of is considerably larger than the peripheral speed ub of the inner peripheral end Pb, the relative flow velocity WO of the outer peripheral end PO is significantly larger than the relative flow velocity wb of the inner peripheral end Pb. Therefore, cavitation tends to occur at the outer peripheral edge of the runner blade.

Figure 5 shows runner blades 4, 4. This is an expanded view of the outermost periphery of... When the pitch of the blade row is t and the H chord length is 1, the relationship between the ratio t/1 of the two and Thoma's initial cavitation coefficient σ0 is shown in the graph in Figure 6 when the specific speed ns of the Kaplan turbine is used as a parameter. As shown, as the ratio t/J decreases, the cavitation coefficient σ
0 also becomes smaller. Therefore, by reducing the ratio t/41, it is possible to suppress the occurrence of cavitation. In order to reduce this comparison t/1, it is possible to increase the chord length ρ or decrease the row pitch t, but since there is a limit to increasing the chord length j due to the structure of the Kaplan turbine, It is necessary to reduce the blade pitch t by increasing the number of runner blades.

However, when the number of runner blades is increased, the blade operation mechanism for rotationally driving these runner blades also becomes complicated, and therefore the diameter of the runner boss that accommodates the runner blades inevitably becomes larger. Increasing the diameter of the runner boss increases the overall size of the Kaplan turbine and reduces the performance of the turbine.

In this way, in Kaplan turbines for high head use, the number of runner blades should be increased in order to prevent cavitation, but this increase inevitably leads to an increase in the diameter of the runner boss, resulting in a decrease in turbine performance. For this reason, the conventional t has normally had a head of less than 80 m and a number of runner blades of less than 8 blades.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a Kaplan water turbine in which the number of runner blades can be increased without reducing the performance of the water turbine.

(Summary of the Invention) In order to achieve this object, the present invention provides a Kaplan water turbine equipped with a plurality of runner blades with variable blade angles, each of which is divided into a plurality of branch blade portions at the outer periphery. - It is characterized by being branched.

[Embodiments of the invention]

An embodiment of a Kaplan water turbine according to the present invention will be described below with reference to FIGS. 1 to 3.

In FIGS. 1(a), (b) and (C), the vane spindle 7 is attached to the runner boss 6 of FIG. 4(a),
A runner blade 9 is integrally fixed to the blade spindle 7 via a stub 8. This runner blade 9 includes an inner peripheral blade part 10 connected to the stub 8 and an inner peripheral blade part 1 connected to the stub 8.
Branching blade part 11.12 which branches into two pieces at the tip of 0
It consists of One branch blade part 11 is located on an almost extension of the inner circumferential blade part 10, and the other branch blade part 12 is a bent part 12a bent at a right angle from the tip of the blade part 10 to the side.
and a blade portion 12b extending therefrom. Further, the length N1 of this branch blade part 11 is set to be longer than the length 12 of the other branch blade part 12.

When the blade operating mechanism in the runner boss drives the blade spindle 7, the runner blade has a blade angle within a range between the minimum blade angle shown in FIG. 2(a) and the maximum blade angle shown in FIG. 2(b). It is possible to take the optimum shift depending on the direction of water flow.

In addition, the relationship between the length ρ1°N12 of both branch separate root parts 11 and 12 and the distance d between the drawing root parts is as shown in FIG. 2(a). 11 and the lower branched blade portion 12 of the adjacent runner blade are preferably selected so that they are aligned substantially in a straight line, and the outlet end T1 of the former and the inlet end T2 of the runner blade 112 are very close to each other.

Furthermore, the positions of the branch blade portions 11 and 12 of the runner blade 9 are as follows:
For the reasons described below, it is desirable that the channel width S is located on the outer circumferential side from the center of the channel width S shown in Fig. 4 (a).In other words, cavitation that occurs on the runner blade surface of a Kaplan turbine first occurs on the outer circumference of the blade as described above. However, by the time the cavity spreads to the center of the flow path width S, it spreads to the inner circumferential side as the pressure decreases. Therefore, considering the point at which cavitation occurs at locations other than the runner blades, branching or duplication of the runner blades should be performed on the outer periphery side from the center of the flow path width. desirable.

When the outer peripheral part of the runner blade is branched to form two blades as in the present invention, the force of two blades acts on the blade spindle 7, and the spindle diameter d1 in FIG. , it is necessary to increase the blade thickness at the blade root in FIG. 3(b) accordingly.

However, even if the blades are doubled, the spindle diameter d1
It is sufficient to increase the thickness of the blade root by approximately 1.3 times, not twice. To explain this in detail, even if twice the torsional moment is required to open and close the blades, the torsional strength of the spindle is proportional to the cube of the diameter d1, so if the spindle receives twice the torsional moment with the same stress as before, In other words, it is sufficient to increase the spindle diameter 3□ dl by 42 1.26 times.

Furthermore, when considering the influence of the bending moment exerted on the runner blade by water pressure, we find that the connection between the stub 8 and the inner peripheral part 10 of the runner blade (double hatched area) is shown in FIG. 3(b). When the length of is bl and the thickness of the blade there is h, the stress at the root of the runner blade due to the above bending moment is proportional to bh2. Therefore, when the bending moment is doubled due to double blades, even if this is to be borne by the blade thickness h alone, it is sufficient to multiply the thickness h by J2 1.41, and in reality, as described above, When the spindle diameter d1 is multiplied by 1.26, the diameter d2 and length b of the stub 8 are also multiplied by 1.26 times the blade thickness h.

In this way, even if the blades are doubled, the spindle diameter can be reduced to 1.2
Since it is sufficient to multiply by 6, it is possible to prevent the runner boss from increasing in diameter.

In the above embodiment, the outer circumferential portion of the runner blade has two blades, but it may of course have three or more blades as required.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, since the runner blade is branched into a plurality of branch blade portions at the outer peripheral portion, it is possible to suppress the occurrence of cavitation at the outer peripheral portion of the runner blade. Therefore, if the number of runner blades on the inner circumference is the same as that of the conventional one, there will be no substantial deterioration in the performance of the turbine. When used for this purpose, the number of runners on the inner circumference can be reduced and the runner boss diameter can be reduced.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1(a), (b), and (c) are plan views showing an embodiment of a runner blade for a Kaplan water turbine according to the present invention, respectively;
Side view and sectional view, Figures 2(a) and (b) are developed views showing the outer circumference of the runner blade during minimum blade angle operation and minimum blade angle operation, respectively, and Figures 3(a) and (b) FIG.
). (b) is a cross-sectional view showing a conventional Kaplan turbine, a diagram showing the velocity triangle at the innermost point and outermost point of the runner blade outlet, and Fig. 5 shows the pitch of the conventional runner blade. The developed diagram shown in FIG. 6 is a graph showing the relationship between the pitch of the runner blade in FIG. , 9... runner blade, 10...
...Inner circumferential blade part, 11... Branch blade part, 12... Branch blade part, S... Channel width. Applicant's agent Inomata Kiyomoto 2 Figure 44 Inokomaki 5 Author - 6 Ward 4 Ri

Claims (1)

[Scope of Claims] 1. A Kaplan water turbine equipped with a plurality of runner blades whose blade angles are variable, characterized in that each of the runner blades branches into a plurality of branch blade portions at an outer peripheral portion. Kaplan water wheel. 2. The Kaplan water turbine according to claim 1, wherein the branching blade portion is two in number, and is branched outward from the center of the channel width.