JPS6375362A - Francis turbine - Google Patents

Abstract

PURPOSE:To hold down wear and efficiency lowering in a runner vane, by making an inlet angle proximate to a joint between a crown of the runner vane and a shroud smaller. CONSTITUTION:Each section of a runner vane 1 is regulated of the inlet angle at a band 3 and a crown 2. And, a blade angle nearby the band 3 and the crown 2 is made smaller. Therefore, a delay flow proximate to upper and lower covers at the runner upstream flows into the runner vane 1, so that even if an inflow angle to a runner at the part becomes smaller than a main flow part, the blade angle of the runner is made to be smaller, whereby separation of the flow at that part is in no case produced, thus wear and efficiency lower in the runner vane are preventable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Francis turbine, and more particularly to the structure of a runner for a Francis turbine.

[Conventional technology]

The structure of a conventional Francis turbine is shown in Figures 2 and 3. Second
The figure is a meridional sectional view of the water turbine, and Figure 3 is the vane 1 of Figure 2.
They are conical cross-sectional views near the crown <(aa' cross section) and near the band <(bb' cross section).

FIG. 4 shows the entrance angle (α) distribution from the band to the crown. As can be seen from the figure, the entrance angle of conventional water turbines changes almost uniformly from the band to the crown.

On the other hand, FIG. 5 shows the flow at the runner inlet. C is the velocity vector of the absolute flow at the outlet of the guide vane, U is the velocity pertle in the circumferential direction at the outer circumference of the runner vane, and W is the velocity vector of the flow relative to the runner vane. As shown in this figure, the direction of the relative velocity vector and the entrance angle of the vane almost match in the main flow part, that is, in the part sufficiently far from the upper and lower covers. however,
Near the upper and lower covers, the speed slows down due to the frictional force generated between the wall surface and the flow, as shown by C' in the figure. Therefore, the direction of the relative velocity vector W' to the runner is different from the velocity vector W of the main flow section, and the relative inflow angle β' to the vane becomes small. If the relative inflow angle to the lamp becomes small, it will no longer match the vane inlet angle, resulting in flow separation on the pressure side of the vane, as shown in FIG. When separation occurs in this manner, in rivers containing a large amount of sediment, the vortices generated at the separation portion increase the number of times the sediment collides with the vane, which has the disadvantage that the vane is worn out by the sediment.

In addition, as literature on soil abrasion, there is a periodical, Wat
er Power & Dam Con5tructi
"Action ex" published in the August 1985 issue of on
erted on reactionturbine
by sandflow", but there is no description of the present invention.

[Problem that the invention seeks to solve]

The above conventional technology does not take into account changes in the relative flow angle near the crown and shroud, and has drawbacks such as wear of the runner vanes and reduced efficiency.

An object of the present invention is to provide a Francis water turbine in which wear and efficiency reduction at the roots of runner vane crowns and shrouds are suppressed.

[Means for solving problems]

The above objectives are achieved by reducing the entrance angle of the runner vane near its junction with the crown and shroud.

[Effect]

The runner vane of the present invention has a reduced angle near the junction with the crown and shroud. Therefore, even if the slow flow near the upper and lower covers upstream of the runner flows into the runner vane and the inflow angle into the runner in that part becomes smaller than that in the main flow part, the flow in that part is reduced because the runner blade angle is made small. It does not cause peeling of the material, and prevents abrasion caused by earth and sand and a decrease in efficiency.

〔Example〕

Figure 1 shows the meridional cross section of the runner, each section B in Figure 7.
This is a diagram drawn by matching the inlet radius and the circumferential direction angle θ on the plan view at the inlet end of -g.

In the figure, the solid lines in the aa' and gg' sections indicate the embodiment of the present invention, and the dotted lines indicate the conventional example. FIG. 8 shows the band-to-crown distribution of the runner vane entrance angle α according to the embodiment of the present invention.

As shown in Figure 2, the water given a swirl by the guide vanes flows into the runners and does work. The relative inflow angle to the runner is determined by the combination of the absolute velocity vector C and the circumferential velocity vector U, as shown in FIG. On the other hand, near the upper cover 4 and lower cover 5, the absolute velocity becomes small as shown by C' in the figure due to the boundary layer of the wall surface (an area where the velocity is slow due to friction with the wall surface). Experimental results show that this absolute speed is slow.

The range is approximately 10% of the runner vane height from the wall surface.
is within the range of Furthermore, when the influence of the slow speed is converted into a relative inflow angle to the runner, it is about 5 degrees to 20 degrees.

According to experiments, the higher the head, the larger this angle becomes. For this reason, in this embodiment, as shown in FIG. 8, the runner vane angle near the crown and band is reduced by at most 10 degrees.

In this way, in the present invention, the blade angle near the band and crown is made small, so the flow angle and the blade angle match,
Separation of the flow is eliminated, and it is possible to reduce the wear of earth and sand that occurs when the earth and sand hits the vane due to the vortices generated by the separation flow, and it is also possible to improve the efficiency of the rerunner with less loss due to the separation flow.

〔Effect of the invention〕

According to the present invention, it is possible to suppress the flow separation phenomenon near the crown or band at the runner inlet, so it is possible to suppress earth and sand abrasion and a decrease in efficiency.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of various parts of a runner vane according to an embodiment of the present invention, Fig. 2 is a meridional sectional view of a water turbine, Fig. 3 is a sectional view aa' and bb' of Fig. 2, and Fig. 4 is a sectional view of each part of a runner vane according to an embodiment of the present invention. FIG. 5 is a flow vector diagram at the runner vane inlet, FIG. 6 is a route diagram showing the flow state at the runner vane inlet, FIG. 7 is a meridional cross-section of the runner of the present invention, and FIG. FIG. 8 is a vane entrance angle distribution diagram of the present invention. 1... Vane, 2... Crown, 3... Band,
4... Upper cover, 5... Lower cover, 6... Guide vane.

Claims (1)

[Claims] 1. In a Francis turbine runner consisting of a band, a crown, and a vane, the inlet angle of the vane at the runner inlet is set near the joint of the band and the crown, and the other part becomes closer to the joint of the band and the crown. The Francis turbine is characterized by being smaller than the . 2. In the invention of item 1, when the height of the vane at the runner inlet is set, the inlet angle at the junction with the band and crown is greater than the inlet angle at a distance of 0.1 h from the band and crown, respectively. , a Francis turbine characterized by a 5 to 20 degree reduction.