Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Radial flow devices
Reexamination Certificate
2001-10-10
2004-10-05
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Radial flow devices
Reexamination Certificate
active
06799948
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a blade, of a gas turbine, having a wide turning angle and suitable to a heavy duty and high load gas turbine.
BACKGROUND OF THE INVENTION
General blades of a gas turbine will be explained by referring to
FIG. 7
to
FIG. 12. A
gas turbine generally comprises plural stages of stationary blades disposed annularly in a casing (blade ring or chamber), and plural stages of moving blades
1
disposed annularly in a rotor (hub or base). Two adjacent moving blades
1
are shown in FIG.
7
.
The moving blade
1
is composed, as shown in
FIG. 7
, of a front edge
2
, a rear edge
3
, and a belly (or a belly side)
4
and a back (or a back side)
5
linking the front edge
2
and rear edge
3
. Combustion gases G
1
, G
2
, as shown in
FIG. 7
, flow in a passage
6
between the belly
4
and back
5
of two adjacent moving blades
1
at an influent angle &agr;
1
(G
1
), and turn and flow out at an effluent angle &agr;
2
(G
2
). By the flow of combustion gases G
1
, G
2
, the rotor rotates in a direction of blank arrow U through the moving blades
1
.
The width of the passage
6
(“passage width”) of the moving blades
1
in which the combustion gases G
1
, G
2
flow gradually decreases from the front edge
2
to the rear edge
3
as indicated by solid line curve in FIG.
8
. At the rear end
3
, the width is minimum, that is, throat O. Thus, by narrowing the passage width between the moving blades
1
, along the direction of flow of the combustion gases G
1
and G
2
, the combustion gases G
1
and G
2
are expanded and accelerated, and the turbine efficiency is enhanced.
Recently, in the field of gas turbine, the mainstream is the gas turbine of high load with the pressure ratio of 20 or more and the turbine inlet gas temperature of 1400 degree centigrade or more.
As the gas turbine of high load, the following two types are known. One is a high load gas turbine in which there are a large number, for example, from four to five, of blades. The other is a high load gas turbine in which the work of each blade of each stage is increased without increasing the number of stages of blades, for example, remaining at four stages. Of these two high load gas turbines, the latter high load gas turbine is superior in the aspect of the cost performance.
To increase the work &Dgr;H of each blade in each stage, it is required to increase the blade turning angle &Dgr;&agr; as shown in FIG.
9
and
FIG. 10
, and equations (1) and (2).
&Dgr;
H=U×&Dgr;V&thgr;
(1)
&Dgr;
V&thgr;=V
&thgr;1
+V
&thgr;2 (2)
In equations (1) and (2), only the peripheral speed component V&thgr; is defined in the absolute system, and the other peripheral speed components are defined in the relative system.
More specifically, symbol U denotes the peripheral speed of moving blade
1
. The peripheral speed U of moving blade
1
is almost constant, being determined by the distance from the center of rotation of the rotor and the tip of the moving blade
1
, and the rotating speed of the rotor and moving blade
1
. Accordingly, to increase the work &Dgr;H of each blade in each stage, it is first required to increase the difference &Dgr;V&thgr; between the peripheral speed components near the inlet of the combustion gas G
1
and outlet of the combustion gas G
2
.
To increase the difference &Dgr;V&thgr; between the peripheral speed components, it is required to increase the peripheral speed component V&thgr;
1
near the inlet of the combustion gas G
1
, and the peripheral speed component V&thgr;
2
near the outlet of the combustion gas G
2
.
When the peripheral speed component V&thgr;
1
near the inlet of the combustion gas G
1
is increased, the influent angle &agr;
1
becomes larger. When the peripheral speed component V&thgr;
2
near the outlet of the combustion gas G
2
is increased, the effluent angle &agr;
2
becomes larger. When the influent angle &agr;
1
and effluent angle &agr;
2
become larger, the turning angle &Dgr;&agr; becomes larger (see FIG.
10
). As a result, when the turning angle &Dgr;&agr; is increased, the work &Dgr;H of each blade in each stage becomes larger.
Accordingly, as shown in FIG.
11
and
FIG. 12
, by setting the influent angle &agr;
3
and effluent angle &agr;
4
larger than the influent angle &agr;
1
and effluent angle &agr;
2
shown in
FIG. 7
, it may be considered to increase the turning angle &Dgr;&agr;
1
larger than the turning angle &Dgr;&agr; shown in FIG.
10
.
However, the following problems occurs when only the influent angle &agr;
3
and effluent angle &agr;
4
are set larger. That is, the passage width becomes the passage width as indicated by single dot chain line curve shown in FIG.
8
.
As a result, as shown in
FIG. 8
, a maximum width
7
occurs at a position behind the front edge
2
, and a minimum width
8
occurs at a position ahead of the rear edge
3
, that is, a width smaller than throat O is formed. Therefore, as indicated by single dot chain line curve, a deceleration passage (diffuser passage) is formed from the front edge
2
to the maximum width
7
, and from the minimum width
8
to the rear edge
3
. Accordingly, the flow of the combustion gases G
1
, G
2
is decelerated, and the turbine efficiency loss increases.
Thus, if only the blade turning angle is increased, the gas turbine with such blades is not suited to the heavy duty and high load. The problem is the same in the stationary blades as well as in the moving blades
1
.
SUMMARY OF THE INVENTION
It is an object of the invention to present a blade, of a gas turbine, having a wide turning angle and suitable to a heavy duty and high load gas turbine.
The blade, according to the present invention, has such a shape that the diameters of circles inscribing the belly and back sides at different positions of adjacent blades decreases as one goes from the front edge to the rear edge. Since the blade has such a shape, even if the influent angle and effluent angle of gases are increased, a deceleration passage is not formed in the passage between the adjacent moving blades.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.
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patent: 3140042 (1964-07-01), Noriyoshi
patent: 3192719 (1965-07-01), Kronogard
patent: 4165950 (1979-08-01), Masai et al.
patent: 4626174 (1986-12-01), Sato et al.
patent: 4786233 (1988-11-01), Shizuya et al.
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patent: 0 937 862 (1999-08-01), None
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patent: 11-200802 (1999-07-01), None
Ito Eisaku
Uematsu Kazuo
Kershteyn Igor
Look Edward K.
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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