JPH09264106A - Exhaust diffuser for turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss within an exhaust diffuser and improve the efficiency of a turbine by providing a plurality of guide vanes protruding into an exhaust gas passage on the inner circumference of the diffuser provided in the downstream of a moving vane group, and specifying the distance for the moving vane rear edge to the guide vane front edge. SOLUTION: A radial turbine has a moving vane 2 provided on a rotating shaft 3 within a casing having a scroll 1 formed therein, the operating gas flowing into the scroll 1 imparts a work to the moving vane 2 by expansion and deflection within the moving vane 2 to rotate it together with the rotating shaft 3, and then flows out through an exhaust diffuser 4. A guide vane 5 is rotatably mounted on the inner wall surface of the exhaust diffuser 4 on the lower stream of the moving vane. A guide vane rotating shaft 54 is rotated from the outside of the casing, whereby the angle of the guide vane 5 to the flow can be regulated. The distance ΔZ measured in the turbine rotating shaft direction from the moving vane rear edge to the guide vane front edge is set to 5% or more of the turbine rotating shaft-directional length of the moving vane.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust diffuser for a gas turbine or a steam turbine.

[0002]

2. Description of the Related Art FIG. 4 is a vertical sectional view of a conventional radial turbine. In the figure, 1 is a scroll (spiral flow passage) formed in a casing 10, 3 is a rotating shaft rotatably supported in the casing, 2 is a rotor blade provided on the rotating shaft, and 4 is an exhaust gas. The diffuser 21 is a shroud around the outer periphery of the moving blade outlet.

In the present apparatus, the working gas flowing into the scroll 1 is given a velocity component in the radial direction by the scroll 1, flows into the moving blade 2, and is expanded and turned in the moving blade 2 to perform work on the moving blade 2. After being given and rotated with the rotating shaft 3, it flows out through the exhaust diffuser 4.

FIG. 5 is a triangular diagram of the average velocity at the outlet of the rotor blade 2 of the turbine. Normally, in order to suppress the loss that occurs when the gas passes through the diffuser 4, the absolute outflow angle α ₄ which is the angle measured from the axial direction of the blade absolute outflow velocity C ₄ (= diffuser inflow velocity) is the design point. It is designed so that the diffuser inflow angle α _{D, OPT} (≈10 ° to 30 °) is almost optimal. However, when the flow at the outlet of the moving blade 2 is examined in detail, as shown in the efficiency distribution in the blade height direction shown in FIG. 6, the efficiency near the wall of the shroud 21 or the diffuser 4 at the outlet of the moving blade 2 is Significantly lower than average efficiency, which results in the outlet shroud 2 of blade 2 of FIG.
As shown by the velocity triangle on the 1st side, in the vicinity of the shroud 21, the value of the absolute outflow angle α ₄ is, for example, + 30 °.
It is a large value such as + 50 ° or more. In such a state, as compared with the case where the absolute outflow angle α ₄ is α _{D, OPT} , the flow of the diffuser 4 before the flow out of the turbine 4
Since the flow distance along the wall surface of the diffuser 4 becomes longer, the wall friction loss increases, and the flow easily separates from the wall surface of the diffuser 4, so the loss is likely to increase due to the separation.

[0005]

In the conventional exhaust diffuser, as described above, the diffuser 4 is also designed.
As the absolute outflow angle α _{4 in the} vicinity of the wall surface of the diffuser 4 becomes large, the loss generated in the vicinity of the wall surface of the diffuser 4 becomes larger than planned, and there is a problem that the turbine efficiency decreases. Further, when the turbine operates at a non-design point, particularly when operating at a smaller flow rate than the design point, the diffuser 4
The value of the absolute outflow angle α _{4 in} the vicinity of the wall surface of the is further deviated from the optimum value α _{D, OPT,} and the decrease of the turbine efficiency due to the increase of the diffuser loss becomes more remarkable.

The present invention aims to solve the above-mentioned drawbacks of the prior art and to provide an exhaust diffuser capable of reducing the loss in the diffuser.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above problems and relates to an exhaust diffuser for a turbine having the following characteristics in an exhaust diffuser provided downstream of a moving blade group of a gas turbine or a steam turbine. It is a thing. (1) A plurality of guide vanes protruding into the exhaust gas flow passage are provided on the inner circumference of the exhaust diffuser, and the distance measured from the trailing edge of the moving blade to the leading edge of the guide blade in the turbine rotation axis direction is the turbine of the moving blade. It is set to 5% or more of the length in the rotation axis direction. (2) In the turbine exhaust diffuser according to the above item (1), the guide blade cross-sectional shape is measured from the blade angle of the guide blade to 10 ° at the trailing edge in the blade rotating direction with reference to the turbine rotation axis direction. The angle was 30 °, and the leading edge had a larger angle. (3) In the exhaust diffuser for a turbine according to the above item (1) or (2), to change the guide vane blade angle measured in the rotor blade rotation direction with respect to the turbine rotation axis direction for each guide blade. The rotation axis of the.

[0008]

1 is a diagram of a radial turbine according to a first embodiment of the present invention, in which (a) is a longitudinal sectional view,
(B) is a development view showing the arrangement of the moving blades and the guide blades. In FIG. 1 (a), 5 is a guide vane rotatably provided on the inner wall surface of the exhaust diffuser downstream of the moving blade, and 53 is a mounting plate of the guide vane, which has a disc shape and is provided on the inner wall of the exhaust diffuser. It fits in the circular recess. Reference numeral 54 denotes a guide vane rotating shaft connected to the mounting plate, and the angle of the guide vane with respect to the flow can be adjusted by rotating the rotating shaft from the outside of the casing. h is the protruding height of the guide blade 5 into the flow path, h ₄ is the height of the trailing edge of the moving blade 2,
ΔZ is the distance between the leading edge of the trailing edge of the guide vane 5 blades 2, L _B is the length of the rotor blades 2 rotating axis direction.

In FIG. 1B, 51 is a leading edge of the guide blade 5, 52 is a trailing edge, and 22 is a line connecting the trailing edge of the moving blade 2. α is the blade angle measured in the rotary axis direction of the blade with reference to a line parallel to the axis of the turbine rotation axis, α _LE is the blade angle of the leading edge of the guide blade, and α _TE is the blade angle of the trailing edge. . The structure of the parts other than the above is the same as the conventional one, and corresponding members are designated by the same reference numerals.

In this embodiment, the guide vanes are designed and set as follows. (1) Guide blade leading edge blade angle α _LE = 30 ° to 50 °, (α _LE =
α ₄ ) (2) Guide vane trailing edge blade angle α _TE = 10 ° to 30 °, (α _LE ＞
(α _TE ) (3) Guide vane protruding height h ≦ 0.1 h ₄ to 0.15 h ₄ (4) Distance from the line connecting the trailing edges of the moving blade to the leading edge of the guide vane Δ
Z> 0.05 L _B of the above conditions (1) the reason for the numerical selection guide vane leading edge blade angle alpha _LE terms are as follows. The guide blade leading edge blade angle α _LE is made to coincide with the direction of the flow flowing into the guide blade 5 in order to avoid the occurrence of loss at the inlet of the guide blade 5. As described in the section of the problem, the value of the absolute outflow angle α ₄ of the flow exiting the moving blade 2 near the wall surface of the diffuser 4 is, for example, + 30 ° to + 50 °.
That is the above, and the shape of the guide vanes 5 is designed and set so that α _LE matches this value. That is, α _LE = α ₄ = 30 ° to 50
°. As a result, the flow flowing out from the moving blade 2 smoothly flows into the guide blade 5.

The guide blade trailing edge blade angle α _{TE of} item (2) of the above conditions
The reason for selecting the numerical value of is as follows. FIG. 2 schematically shows the relationship between the inflow angle α _D and the diffuser loss in the vicinity of the wall surface of the diffuser 4. When α _D is too large, the distance that the flow flows along the wall surface of the diffuser 4 by the time it flows out from the turbine (diffuser 4) becomes long, so that the wall friction loss increases and the flow separates from the wall surface of the diffuser 4. Diffuser loss increases due to the increased ease. When α _D is too small, the flow distance along the wall surface of the diffuser 4 becomes too short before the flow flows out from the turbine (diffuser 4), and the flow force is not pressed against the wall surface of the diffuser 4 by centrifugal force. , The flow becomes easy to separate, and the diffuser loss increases. From the above, the optimum diffuser inflow angle α that minimizes the diffuser loss
_{D and OPT} exist. The value of α _{D, OPT} varies depending on the shape of the diffuser 4 and the state of the flow flowing into the diffuser 4, and is in the range of about 10 ° to 30 °. In this embodiment, in order to minimize the diffuser loss after leaving the guide vanes 5, the guide vane trailing edge vane angle α
Optimum turbine diffuser inflow angle α assuming _TE
Matching _{D and OPT} , α _TE = α _{D, OPT} , but the value of α _{D, OPT} varies depending on the turbine design and is approximately 10 ° to 30 °.
Since it is a value of the order of magnitude, there is a range in the value of α _TE . That is, α _TE = α _{D, OPT} = 10 ° to 30 °. This makes it possible to minimize the losses generated in the diffuser 4 after the flow leaves the guide vanes 5.

The reason for selecting the numerical value of the projecting height (hereinafter referred to as "blade height") h of the guide vane into the flow path in the above condition (3) is as follows.

[0013] guide vanes 5, the efficiency is turning left region (alpha ₄ is large, see FIG. 7, the portion of Δh of Figure 6) lower optimal diffuser inflow angle by forcibly guides the direction of flow of the Since the aim is to minimize the diffuser loss that occurs downstream of the guide vanes 5 in accordance with α _{D, OPT} , the height of the problem area is basically Δh.
The blade height h is adjusted to (h = Δh), but the value of Δh also depends on the turbine design, and according to the measurement, it is approximately h ₄
Values in the range of 5% to 20%.

If the blade height h is designed excessively, the guide vanes 5 become a flow resistance, additional loss occurs, and there is a high possibility that the efficiency of the turbine is rather lowered by the setting of the guide vanes 5. Conversely speaking, the design of the guide vanes 5 becomes difficult. In some cases, the flow rate may be restricted by the guide vanes 5. Further, the fluid force acting on the guide vanes 5 increases, and problems such as vibration and breakage are likely to occur. From the above, h ≦ (0.1 to 0.
15) h ₄ This makes it possible to control the range in which the absolute outflow angle α ₄ increases.

The reason for selecting the numerical value of the distance ΔZ from the trailing edge of the moving blade to the leading edge of the guide blade in the above-mentioned condition (4) is as follows. In order to prevent the guide blade 5 from vibrating and breaking due to the wake of the moving blade 2, it is necessary to set the above distance ΔZ to a certain level or more. At present, the minimum limit is an empirical value based on an analogy from the structure of a similar machine. If the distance ΔZ is too large, the merit of providing the guide vanes 5 is lost. No upper limit is specified, but ΔZ
By setting ΔZ to a small value in the range of> 0.05 L _B , it is possible to reduce / prevent vibration / breakage of the guide blade 5 due to wake of the moving blade 2.

By providing a plurality of guide blades 5 under the above conditions on the wall surface of the diffuser 4 so as to project downstream of the moving blade 2 into the flow path, the diffuser out of the flow flowing out from the moving blade 2 is diffused. The flow direction (absolute flow angle α) near the wall surface of 4 can be controlled by the guide vanes 5.

If the leading edge angle is adjusted in the above embodiment, the trailing edge angle also changes accordingly.
It is apt to be considered to deviate from the optimum value. For example, at the design point, the blade leading edge angle α _{LE, D} = shroud blade outflow angle α
₄ = + 50 °, blade trailing edge angle α _{TE , D} = optimum diffuser inflow angle α _{D, OPT} = + 20 °, the operating conditions change, and when α ₄ changes ± 10 °, blade leading edge angle α _{If TE} coincides with α ₄ , the blade trailing edge angle α _TE deviates ± 10 ° from α _{D, OPT} (points a and b in Fig. 2), but the amount of change in diffuser loss near α _{D, OPT} is gentle. Therefore, the increase in diffuser loss is small, and the diffuser loss is smaller than when the guide vanes are not provided (point c in FIG. 2). That is, the effect of slight deviation from the optimum value is small, and the merit of the guide vanes is very large.

Further, in the guide blade arrangement, in order to avoid destruction of the guide blades due to resonance with the rotor blades in relation to the pitch of the rotor blades, the number of guide blades is [number of rotor blades / integer], or It is better to avoid the number of blades x integer].

3A and 3B are views of a radial turbine according to a second embodiment of the present invention. FIG. 3A is a vertical sectional view and FIG. 3B is a development view showing the arrangement of moving blades and guide blades. In some turbo gas expander turbines for power generation and cooling, the turbine operating conditions do not change much. In such a case, the guide vane 5 can be designed according to the design point and fixed to the wall surface of the diffuser 4 as shown in the figure. In addition, it may be detachable in consideration of maintenance. The reference numerals of the respective parts of the present embodiment are the same as those described in the description of the first embodiment, and the operation and effect are also the same as those of the first embodiment, and therefore detailed description will be omitted.

[0020]

In the exhaust diffuser of the turbine of the present invention, a plurality of guide vanes projecting into the exhaust gas flow passage are provided on the inner periphery, and the guide blade extends from the trailing edge of the moving blade to the leading edge of the guide vane in the turbine rotation axis direction. The measured distance is set to 5% or more of the length of the rotor blade in the turbine rotation axis direction, or the guide blade cross-sectional shape is measured by measuring the blade angle of the guide blade in the rotor blade rotation direction with reference to the turbine rotation axis direction. Rotation for changing the guide vane blade angle measured in the blade rotating direction with reference to the turbine rotating shaft direction, with an angle of 10 ° to 30 ° at the edge and a larger angle at the leading edge. Since the shaft is provided, the loss in the diffuser can be reduced and the efficiency of the turbine can be improved.

[Brief description of drawings]

1A and 1B are diagrams of a radial turbine according to a first embodiment of the present invention, in which FIG. 1A is a longitudinal sectional view and FIG. 1B is a development view showing an arrangement of a moving blade and a guide blade.

FIG. 2 is a relationship diagram of an inflow angle α _D and a diffuser loss near a diffuser wall surface.

3A and 3B are diagrams of a radial turbine according to a second embodiment of the present invention, FIG. 3A is a longitudinal sectional view, and FIG. 3B is a development view showing an arrangement of moving blades and guide blades.

FIG. 4 is a vertical sectional view of a conventional radial turbine.

FIG. 5 is a triangular diagram of average velocity at a rotor blade outlet of a conventional radial turbine.

FIG. 6 is an efficiency distribution diagram in a blade height direction of a conventional radial turbine.

FIG. 7 is a velocity triangle diagram on the shroud side of a rotor blade outlet of a conventional radial turbine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 scroll 2 rotor blade 21 shroud 22 rotor blade trailing edge 3 rotating shaft 4 exhaust diffuser 5 guide blade 51 guide blade leading edge 52 guide blade trailing edge 53 guide blade mounting plate 54 guide blade rotating shaft

Claims (3)

[Claims] 1. An exhaust diffuser provided downstream of a moving blade group of a gas turbine or a steam turbine, wherein a plurality of guide blades projecting into an exhaust gas flow passage are provided on an inner circumference of the exhaust diffuser, and a moving blade trailing edge. An exhaust diffuser for a turbine, characterized in that the distance measured from the guide blade to the leading edge of the guide blade in the turbine rotation axis direction is 5% or more of the length of the rotor blade in the turbine rotation axis direction. 2. The guide vane cross-sectional shape, the blade angle of the guide vane measured in the rotor rotating direction with reference to the turbine rotating shaft direction, is 10 ° to 30 ° at the trailing edge and larger than that at the leading edge. The exhaust diffuser for a turbine according to claim 1, wherein: 3. A guide shaft, wherein each of the guide vanes is provided with a rotating shaft for changing a guide vane blade angle measured in a rotor blade rotating direction with reference to a turbine rotating shaft direction. 2. An exhaust diffuser for a turbine according to 2.