JPH0151671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a once-through water turbine, and particularly to a shape of a runner vane that improves performance.

[Background of the invention]

First, a typical structure of a conventional once-through water turbine will be explained using FIG. A runner 2 is rotatably supported within the casing 1 by a rotating shaft 3 and a bearing (not shown), and a runner vane 4 is coupled to the outer periphery of the runner 2. Water flows into the runner 2 through the inlet pipe 5 as shown by the solid arrow in the figure, and passes through two inlet channels 9 and 9' formed by the guide vane 6 and the upper and upper sewer walls 7 and 8.
After applying rotational power to the runner 2, it is discharged onto the water surface 11 formed in the suction pipe 10.

Next, FIG. 2 is a three-dimensional drawing of the once-through turbine in FIG. 1, but the guide vane 6 and runner 2 are
have the same ratio in the axial direction (1/3:2/
3). In addition, since each part 6' and 6'' of the divided guide vane 6 can be opened and closed independently of each other, each part 2' and 2'' of the runner 2 can be opened and closed independently of each other, so that each part 2' and 2'' of the runner 2 can be opened and closed independently of each other. It is possible to introduce water flow into both or just one side.

FIG. 3 is an explanatory diagram showing the relationship between flow rate and efficiency in this case. The solid line, broken line, and dashed-dotted line in the figure indicate the efficiency for the combination of each part 2' and 2'' of the runner 2 where water flow is introduced, and the cases where the water flow is introduced only into 2'' and only 2', respectively. It shows.

In the conventional once-through turbine configured in this way, even when the flow rate decreases, the guide vane 6'
Or by fully closing guide vane 6″,
As shown in the curve with three peaks at the bottom of the figure, it has the advantage of preventing a decline in efficiency.
This is the reason why once-through turbines are said to have good light load characteristics despite their simple structure.

Now, factors that influence the performance of a once-through water turbine are considered to be the shape of the introduction water turbines 9, 9' and the shape of the runner vane. Among these, the present invention examines the relationship between runner shape and water turbine performance.

As already shown in Figure 1, the characteristics of the water flow in a once-through turbine are (1) that the water flow is two-dimensional; (2)
The water stream flows through the runner and performs work in two stages: as it enters the runner and as it exits the runner. FIG. 4 shows the velocity triangle at each of these stages, and its efficiency η is given by the Euler equation below.

Here, g: gravitational acceleration, H: effective head, and
v _ui is the circumferential component of Ci and is given by the following formula.

v _ui = u _i + w _i cosβ _i i=1~4 ...(2) Here, the inclination angle β _i of the runner vane shown in Fig. 4, the clearance between adjacent runner vanes at the inlet and outlet Δ ₁ , Δ ₂ , by using the runner vane outer diameter D ₁ and inner diameter D ₂ and substituting equation (2), equation (1) becomes as follows.

ηgH=u ₁ (w ₁ + w ₄ ) (cosβ ₁ −D ₂ /D ₁ Δ ₁ /Δ ₂ cosβ ₂ ) ...(3) As seen in this equation, the efficiency η depends on the runner vane shape (inlet angle β ₁ , Exit angle β ₂ , inner/outer diameter ratio D ₂ /D ₁ , inlet,
It is a function of the exit clearance ratio Δ ₁ /Δ ₂ ) and the velocity component (inlet circumferential velocity u ₁ , relative speeds w ₁ and w ₄ of the first stage entrance and second stage exit), but the exit β ₂ and Δ ₂ , which indicate the shape of , are not very essential parameters. The reason for this will be explained below.

First, _the exit angle β ₂ is usually designed to be 90 degrees. Now, considering the case where β ₂ <90°, as shown by the upper solid line in Fig. 5, the water flow from the outlet of the first stage toward the center of the runner is approximately β ₂ with respect to the vane inner diameter. It can be bent at an angle. The main water flow again flows into the runner vane section from the inlet of the second stage, but since the inclination angle of the runner vane in this section is still _β2 , there is little collision loss due to the difference between the direction of the water flow and the vane inclination angle. On the other hand, the broken line in the same figure shows the case where β ₂ >90°, but in this case as well, the collision loss at the second stage entrance is small. From the above explanation, it can be seen that if β ₂ is a value near 90 degrees, it will not affect performance much.

Next, regarding the exit clearance Δ ₂ , if β ₂ is a value near 90 degrees as described above, this value is uniquely determined by the number of blades Z, so it can be considered as a constant. Generally, the value of Z is often determined from vane strength calculations, and is usually designed to be 24 to 36 vanes. Furthermore, the runner vane inner and outer diameter ratio D ₂ /
The value of D ₁ is usually designed to be 2/3.

As can be seen from the above explanation, the performance of a once-through turbine is mainly determined by the shape parameters β ₁ and Δ ₁ of the runner base inlet, and the winding angle γ of the runner vane, which affects the relative speed w ₄ (see Figure 4). It can be decided.

Conventionally, in determining these parameters,
For reasons such as ease of manufacture and simple structure, it has been common to design the vane shape as a single circular arc. In this case, as shown in FIG. 6, it can be seen that the values of the winding angle γ and the inlet clearance Δ ₁ are uniquely determined with respect to the inlet angle β ₁ . As a result, as shown in Fig. 7, the efficiency η obtained by the experiment also becomes
It was determined almost entirely by the value of β ₁ , and its maximum value η _nax was about 83% at most. This value is several percent lower than the efficiency of other types of water turbines, and while this gives good light-load characteristics, this is considered to be the biggest drawback of once-through water turbines.

[Purpose of the invention]

The present invention has been made to improve the above-mentioned drawbacks, and its purpose is to obtain a highly efficient once-through water turbine.

[Summary of the invention]

In view of the fact that the reason for the low efficiency of conventional once-through water turbines is that the runner vane shape was not optimized, the present invention experimentally confirmed the influence of the inlet clearance and winding angle of adjacent runner vanes, It is based on finding the appropriate value for each.

That is, the feature of the present invention is that a once-through water turbine has a runner having two or more circular diameter side plates and a plurality of runner vanes fixed near the outer periphery of the side plate, and the runner is rotatably provided in a casing. , the distance between the arcuate curve connecting the front and rear edges of the runner vane and the front edge of another runner vane adjacent to the back of this runner vane to the closest curve of the arcuate curve is defined as the runner vane inlet gap _Δ1 . , the runner outer diameter is D ₁ and the number of runner vanes is Z
When Δ ₁ /D ₁ is 1.440/Z−0.008≦Δ ₁ /D ₁
≦1.896/Z−0.0122, and the angle γ between the straight line from the runner center to the leading edge of the runner vane and the straight line from the runner center to the trailing edge of the runner vane is 18°≦γ≦24°. It is in.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings, which is the same as the conventional example except for the shape of the runner vane. First, FIG. 8 defines the related shape parameters of the runner vane 4. Here, the entrance angle β ₁ is the tangent at point A of the circular arc passing through point A on the leading edge of runner vane 4 and points B and C in its vicinity, and A
Defined as the angle formed by the tangent to the runner outer diameter line at a point. Note that points B and C are the intersections of the center line of the runner vane 4 and the radius that forms 5 degrees and 10 degrees with the radius OA.

Next, the winding angle γ is the angle formed by the radius OD passing through point D of the trailing edge of the runner vane 4 and the aforementioned OA. moreover,
The inlet clearance Δ ₁ is defined as the closest distance between a point A' on the leading edge of the runner vane adjacent to the downstream side and an arc passing through A, B, and C mentioned above.

Here, in the following explanation, γ,
Parameters other than Δ ₁ and β ₁ are fixed to the following values, and it is assumed that the runner outer diameter D ₁ =φ250 mm.

Inside/outside diameter ratio D ₂ /D ₁ = 2/3 Number of blades Z = 30 blades Outlet angle β ₂ = 90 degrees... (4) Now, the present invention deals with the winding angle γ and the inlet which have an essential influence on the performance of the water turbine. The point is that the clearance Δ ₁ is defined in the following range.

(a) Winding angle γ = 18 degrees to 24 degrees ……(5) (b) Inlet clearance Δ ₁ = 10 to 12.8 mm ……(6) In equation (6), Δ ₁ is the runner outer diameter D ₁ When it is made into a non-deletion element, Δ ₁ /D ₂ =0.040~0.0512...(6)′.

Next, the basis for defining equations (5) and (6) above will be explained based on experimental results. First, FIG. 9 shows the results of an experiment in which a plurality of arcs of the runner vane 4 were connected and the entrance angle β ₁ was varied, with the winding angle γ being taken as the horizontal axis. The numbers in the figure indicate the inlet clearance _Δ1 . The following points are clear from this figure.

(1) For any value of Δ ₁ , the peak of efficiency η is near γ≒21 degrees.

(2) This value of γ is larger than γ=16 degrees when the entrance angle β ₁ =20 degrees in the conventional single arc vane, as shown in FIG.

That is, in the present invention, for any inlet clearance Δ ₁ , the relatively efficient γ = 18 to 24
The reason for choosing the degree range is as follows. γ is 18
When it is smaller, the flow path length of water flowing along the runner vane 4 is short, water flows quickly along the runner vane 4, the amount of angular operation given to the runner vane 4 is small, and efficiency cannot be improved. Moreover, when γ is larger than 24, the flow path length becomes long, the loss due to water flow path resistance increases, and the inlet clearance Δ ₁ becomes narrow.
Efficiency deteriorates due to such factors. Therefore, γ=18~
If the angle is within the range of 24 degrees, the length of the water flowing along the runner vane 4 will be appropriate without causing the above-mentioned drawbacks, and angular momentum will be easily imparted to the runner vane 4, thereby increasing efficiency.

Then, when γ is within the above range, the inlet clearance Δ ₁ may be selected as follows.

That is, FIG. 10 organizes the experimental results with the inlet clearance Δ ₁ plotted on the horizontal axis, and the parameter is the winding angle γ. The following points are clear from this figure.

(1) For any value of γ, the peak value of efficiency η is near Δ ₁ =11.5 mm (Δ ₁ /D ₁ =0.046).

(2) The value of Δ ₁ is the value of Δ ₁ when the entrance angle β ₁ = 20 degrees for a single arc vane as shown in Figure 6.
= 13.3mm.

Now, the fact that η has a peak in a relatively small value of Δ ₁ corresponds to the fact that η has a peak in a range where γ is relatively large, as described above. That is, an increase in γ increases the inclination angle of the runner vane 4, but this increase in the inclination angle decreases the inter-vane clearance at the inlet of the runner vane 4 even if the number Z of blades remains the same. In addition, there is a lower limit to the value of Δ ₁ that provides high efficiency because if Δ ₁ is too small, β ₁ is correspondingly too small, and as a result, the inlet collision loss of the water flow into the runner is reduced. This is thought to be due to an increase in For this reason, the present invention specifies Δ ₁ =10 to 12.8 mm, where the efficiency η is relatively high for any γ.

Note that the above-mentioned regulation of Δ ₁ was for the number of blades Z = 30, but since the value of Δ ₁ is influenced by Z, this will be discussed below. Figure 11 shows
The runner outer diameter _D1 remains φ250mm as before.
The upper and lower limits of Δ ₁ when changing the number of blades Z were determined using the same method as in FIG. 10.
This can be expressed mathematically as follows.

³⁶⁰ _Z −2.0≦Δ ₁ ≦ ⁴⁷⁴ _Z −3.0 (7) Furthermore, considering that the value of Δ ₁ is proportional to the runner outer diameter D ₁ and taking the ratio of the two, the following formula is obtained.

1.440/Z−0.008≦Δ ₁ /D ₁ ≦1.896/Z−0.012……(
7)' This formula is a general formula for the appropriate value of the inlet clearance Δ ₁ for the runner outer diameter D ₁ and the number of blades Z.
In addition, if the wall thickness T of the runner vane (see FIG. 8) is taken into account, it can be seen that the actual inlet clearance δ ₁ is expressed by the following formula.

δ ₁ = Δ ₁ −T (8) As mentioned above, in the present invention, the winding angle γ and the inlet clearance Δ ₁ , which essentially affect the efficiency of a once-through turbine, are determined based on experiments conducted by removing the single-arc vane condition. is set to the value. In this way, if the value of the inlet clearance Δ ₁ is calculated using the above equation (7)′, even if the winding angle γ = 18° to 24° is selected, the clearance Δ ₁ between the vanes at the inlet of the runner vane 4 will be Since the flow rate is not reduced, a constant flow rate can be passed to the runner vane 4. As a result,
Compared to the case of conventional single arc vanes, the absolute value of efficiency η is improved, and by considering the inlet clearance Δ ₁ , η _nax = 85%, and by considering the wrap angle γ, η _nax = 86.5%. It became possible to obtain it.

〔Effect of the invention〕

According to the present invention, it is possible to provide a high-performance once-through water turbine in addition to the inherent advantages of a once-through water turbine, such as higher efficiency and better light load characteristics than conventional runners.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of a conventional once-through water turbine, Figure 2 is a three-dimensional view of the once-through water turbine shown in Figure 1, Figure 3 is an explanatory diagram showing the relationship between flow rate and efficiency, and Figure 4 is a speed triangle of a once-through water turbine. Fig. 5 is an explanatory drawing showing the direction of water flow in the runner, Fig. 6 is a diagram showing the winding angle and inlet clearance values of the conventional example, and Fig. 7 is a diagram showing the efficiency and inlet angle of the conventional example. FIG. 8 is an explanatory diagram showing the definition of the shape parameters of the present invention, FIGS. 9 and 10 are diagrams of experimental results showing the basis of the regulations of the present invention, and FIG. 11 is a diagram showing the definition of the shape parameters of the present invention. FIG. 3 is a diagram showing the relationship between the inlet clearance and the number of blades according to the invention. 1...Casing, 2...Runner, 3...Rotating shaft, 4
...Runner vane, 5...Inlet pipe, 6...Guide vane, 7, 8...Waterway wall, 9,9'...Introduction channel, 10
...Suction pipe, 11...Water surface.

Claims (1)

[Claims] 1. In a once-through water turbine that has two or more side plates with a circular diameter and a runner with a plurality of runner vanes fixed near the outer periphery of the side plate, and the runner is rotatably installed in a casing, the leading edge and rear edge of the runner vane The distance from the front edge of another runner vane adjacent to the back surface of this runner vane to the closest position and curve of the arcuate curve connecting the edges is defined as runner vane inlet gap Δ ₁ , and the runner outer diameter is D ₁ And when the number of runner vanes is Z, Δ ₁ /D ₁ is
1.440/Z-0.008≦Δ ₁ /D ₁ ≦0.896/Z-0.0122, and the angle γ formed by the straight line from the runner center to the leading edge of the runner vane and the straight line from the runner center to the trailing edge of the runner vane is 18° ≤ A runner vane for a once-through water turbine characterized by being formed so that γ≦24°.