Water turbine

Details Water turbine Water turbine

1999-10-13

2002-01-01

Verdier, Christopher (Department: 3745)

Rotary kinetic fluid motors or pumps

Selectively adjustable vane or working fluid control means

Upstream of runner

C415S164000

Reexamination Certificate

active

06334757

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a water turbine provided with guide vanes and, more particularly, to a water turbine with three-dimensional vane type guide vanes. A vane construction, in which an outer profile and/or position in section perpendicular to the rotational axis thereof, of each vane forming the guide vanes changes to a direction of a rotation axis thereof, is referred to as the three-dimensional vane type.
A conventional water turbine will be explained hereunder, referring to FIGS.
20
(
a
) and
20
(
b
). FIG.
20
(
a
) is a horizontal sectional view of the conventional water turbine and FIG.
20
(
b
) is a sectional view taken along a line A—A of FIG.
20
(
a
). The water turbine is formed of a casing
1
, stay vanes
2
, guide vanes
3
, a runner
4
, etc. Water enters the casing
1
and then flows in the runner through the stay vanes
2
and the guide vanes
3
. The water flowed in the runner
4
rotates the runner
4
in a rotation direction
11
. Upper and lower sides of the runner
4
are fixed to a band
8
and a crown
10
, respectively. The crown
10
is fixed to a rotating shaft
14
and the runner
4
rotates about the center of the rotating shaft
14
. Each vane of the guide vanes
3
rotates about the center of a rotating shaft
7
.
All vanes of the guide vanes
3
are opened and closed at the same phase. The opening and closing of the vanes are effected by rotation of a guide ring
24
connected to the rotating shaft
7
by arms
25
a
,
25
b
. For the guides vanes
3
, it is necessary to fully shutdown water when the operation is stopped. Therefore, usually, each vane of the guide vanes
3
has a shape of two-dimensional vane type. A vane construction in which the outer profile and position in each section perpendicular to the rotating shaft
7
each are the same as those in the other sections is referred to as the two-dimensional vane type.
One of subjects which are important to the performance of a water turbine is to prevent cavitation. Occurrence of cavitation inside the runner
4
causes problems such as reduction in efficiency, occurrence of vibration or noises, etc. In the case where cavitation is remarkable, the runner
4
is damaged and its exchange may be required in some cases. In the case of the water turbine in FIGS.
20
(
a
),
20
(
b
), since the curvature of the runner
4
on the side of the band
8
is large, the flow in this region is accelerated, whereby the pressure is lowered. Therefore, it is important to prevent cavitation from occurring at the inlet of the runner
4
on the side of the band
8
.
As a first prior art concerning prevention of cavitation, there is JP A 59-82580 which discloses a construction in which a leading edge portion
9
of the runner
4
is inclined against a rotation direction
11
from the crown
10
side to the band
8
side.
As a second prior art concerning prevention of cavitation, there are JP A 51-72846, JP A 52-98841 and JP A 61-43977, each of which discloses three-dimensional vane type guide vanes each having a side shape of a parallelogram or a trapezoid. A construction in which a trailing edge of a sectional shape of an upper side of the guide vane
4
extends toward the runner
4
also is disclosed.
As a third prior art concerning prevention of cavitation, there is JP A 60-182361 which discloses a guide vane constructed so that an angle between a peripheral direction of the runner and a straight line connecting a rotation axis of the guide vane and a trailing edge becomes smaller on a lower side.
SUMMARY OF THE INVENTION
In the case of the first prior art, cavitation on the suction surface side of blade of the runner
4
can be prevented when a water level of a dam is high, that is, in a high head. However, cavitation on a pressure surface side of blade of the runner
4
when the water level is low, that is, in a low head can not be prevented. Therefore, it is difficult to take countermeasures in the case where operation conditions change due to lowering in water level of the dam. Further, in order to prevent cavitation on an existing water turbine, it is necessary to exchange a runner
4
of a high manufacturing cost. Further, since the runner
4
is a large-sized structural component, much time is needed for conveying and installing the runner, which is a cause of rising in cost.
In the case of the second prior art, the guide vanes
3
can not shutdown a water flow path.
In the case of the third prior art, the design becomes difficult because it is necessary to change a vane shape of the guide vane from an upper side to a lower side.
An object of the present invention is to provide a water turbine which is provided with guide vanes each having a shape of three-dimensional vane type easy to design and is able to shutdown and which is able to prevent cavitation occurrence at a low cost.
First of all, a cause that cavitation occurs at the inlet of a runner will be explained, referring to FIG.
21
. Cu, Cv and Cw in
FIG. 21
denote a rotating speed of the runner, an absolute speed of water flow and a relative water flow speed to the runner, respectively. A triangle formed by those three speed vectors is called a speed triangle at the inlet of the runner. FIGS.
21
(
a
), (
b
) and (
c
) show speed triangles at time of low head, at time of rated operation head and at time of high head, respectively.
As shown in
FIG. 21
, at time of any heads other than (b) of rated speed operation head, an angle of water flowing in the runner does not meet an angle of a leading edge (tip portion) of blade of the runner
4
. Therefore, there is the possibility that cavitation occurs. At time of low head in FIG.
21
(
a
), cavitation is likely to occur on the pressure surface side
13
of blade of the runner
4
. At time of high head in FIG.
21
(
c
), cavitation is likely to occur on suction surface side
12
of blade of the runner. Such a change in angle of water flowing in the runner is known to occur generally in water turbines.
Usually, the possibility of cavitation occurrence is larger at time of high head in which a load to the runner becomes larger. However, there is also some possibility of cavitation occurrence at a time of a low head, according to design. In general, it is required for cavitation not to occur within a range of operation head of the water turbine. Therefore, for design of runner, it is required to prevent cavitation from occurring at a head at which the cavitation is most likely to occur.
By the way, an inflow angle of water to the runner is an average inflow angle in a peripheral direction of the runner. Precisely, in the vicinity of blade of the runner and at the other place, the inflow angle changes in the peripheral direction. The reason will be explained, referring to FIG.
22
. Generally, as blades generating lift, wings of an air plane, runner blades of a water turbine, etc. are known. At tips of those blades or wings, as shown in
FIG. 22
, a direction of fluid flow changes so that the fluid flows in from the pressure surface side. This is because a kind of eddy layer called circulation is formed around the blade, and the direction of flow is bent, receiving induction speed from the eddy layer.
In this manner, in the case where a blade generating lift is inside the flow, the inflow angle of fluid changes, with an upstream side being influenced by the blade. In the case of runner of a water turbine, also, as shown in
FIG. 23
, there is a tendency that water is flowed in from the pressure surface side
13
in the vicinity of the leading edge (tip end)
4
a
of blade of the runner
4
. From the above-mentioned matters, also, it is found that cavitation is likely to occur on the suction surface side
12
of blade of the runner at time of high head. As shown in the same figure, a water flow at a place separate from the leading edge
4
a
of blade of the runner
4
is almost an average relative speed Cw.
An object of the present invention is to control a magnitude of the effect which blades of a water turbine runner generating lift impart to an upstream

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