JPH07133701A - Axial turbine - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce energy loss in an axial flow turbine and improve turbine performance. In an axial-flow turbine stage composed of a turbine vane and a turbine rotor blade, a trailing edge 7 of the turbine vane 3 to a leading edge of the turbine rotor blade 5 extends from the root of the turbine stage to the tip of the turbine stage. 6, the axial flow direction distance L is changed according to the turning angle of the turbine rotor blade, and the larger the turning angle of the turbine rotor blade, the more the turbine rotor blade trailing edge 7 reaches the turbine rotor blade leading edge 6. The distance L in the axial direction is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial flow turbine,
In particular, the present invention relates to an axial flow turbine capable of reducing energy loss generated between a turbine stationary blade and a turbine rotor blade and improving turbine performance.

[0002]

2. Description of the Related Art In recent years, it has been an important subject to improve turbine performance in order to improve the operating economy of a power plant and improve the power generation efficiency. In general, an axial turbine includes a stationary blade 3 fixed by a stationary blade outer ring 1 and a stationary blade inner ring 2, and a moving blade 5 fixed on a rotating shaft 4, as shown in FIG.
This paragraph is formed by combining one or more paragraphs in the axial direction.

FIG. 6 is a view of FIG. 5 seen from the radial direction.
As shown in this figure, in a paragraph in which the blade heights of the stationary blades and the moving blades are relatively small compared to the diameter of the rotating shaft, the stationary blades 3 have substantially the same cross-sectional shape from the root to the tip. On the other hand, the moving blade 5 is geometrically obtained from the outflow speed and the outflow angle of the working fluid flowing out from the stationary blade 3 and the rotational speed in the circumferential direction of the moving blade 5 at an arbitrary sectional height. Corresponding to the relative inflow angle to the blade, the blade has a cross-sectional shape that is continuously twisted from the blade root portion to the blade tip portion. Figure 7 (a)
And FIG.7 (b) shows the turning angle in the front-end | tip part of a moving blade, and the root part of a moving blade, respectively.

As can be seen from both figures, the turning angle εr of the blade root portion is larger than the turning angle εt of the blade tip portion. FIG. 8 shows the turning angle from the root portion of the moving blade to the tip portion of the moving blade, and the turning angle ε of the moving blade continuously decreases from the moving blade root portion to the moving blade tip portion. The blade cross-sectional shape of the moving blade 5 is configured such that the blade cross-sectional area continuously decreases from the moving blade root to the moving blade tip in order to reduce centrifugal stress during turbine operation. Therefore, the position of the leading edge 6 of the moving blade is such that it is continuously located downstream in the axial direction from the moving blade root portion to the moving blade tip portion. On the other hand, the trailing edge 7 of the vane is located at substantially the same position in the axial direction from the vane root portion to the vane tip portion. Therefore, the axial direction distance from the trailing edge 7 of the stationary blade to the leading edge 6 of the moving blade continuously increases from the root portion to the tip portion of the paragraph, as shown in FIG.

Taking the root part of the paragraph and the tip part of the paragraph as an example, the axial flow direction distance from the trailing edge of the stationary blade to the leading edge of the moving blade in the root part of the paragraph where the turning angle of the moving blade is large is Lr. Lt <Lt (1), where Lt is the axial flow distance from the trailing edge of the stationary blade to the leading edge of the moving blade at the tip of the moving blade with a small turning angle. ing.

[0006]

In order to improve turbine performance, it is important to reduce internal energy loss as much as possible in the turbine stage constructed as described above. However, the conventional turbine stage configured as in the formula (1) cannot sufficiently reduce the energy loss generated between the turbine stationary blade and the turbine moving blade.

That is, the energy loss that is affected by the axial distance from the trailing edge of the turbine vane to the leading edge of the turbine vane is increased by the wake from the vane, and the airfoil loss of the vane and the energy loss from the vane are increased. It can be classified as mixing loss due to mixing of wakes.

First, the airfoil loss of the moving blade, which is increased by the wake from the stationary blade, will be described. FIG. 10 is a diagram showing the flow downstream of the stationary blade during the operation of the axial turbine. As shown in the figure, during turbine operation, a velocity region called a wake W having a velocity distribution smaller than the velocity C2 of the main flow is generated at the trailing edge 7 of the stationary blade 3. The moving blade 5 is D in the figure.
Since the rotor blade 5 rotates in the direction indicated by, the rotor blade 5 downstream of the stationary blade 3 rotates so as to cross the wake W. The inflow angle to the rotor blade 5 is usually designed for the velocity C2 of the main flow. That is, the design inflow angle β2 into the rotor blade 5
Is the outflow angle α2 of the fluid from the vane 3 and the velocity C2 of the main flow.
And the rotational speed U in the circumferential direction of the rotor blade 5 are used to obtain the geometrical relationship. However, the wake W from the stationary wings
The working fluid outflow velocity C2 ′, the outflow angle α2 of the fluid outflowing from the stationary blade 3, and the inflow angle β2 ′ into the moving blade 5 geometrically determined from the circumferential rotational speed U of the moving blade 5 are It is significantly different from the design inflow angle β2 into the rotor blade 5 in the mainstream portion. Therefore, the difference Δβ from the design blade inflow angle of the working fluid when the moving blade 5 passes through the wake from the stationary blade is Δβ = β2′−β2 (2) due to the geometrical relationship.

Difference from the design inflow angle of this working fluid Δβ
Greatly affects the airfoil loss in the rotor blade. It is generally known that the airfoil loss increases when the actual working fluid inflow angle differs from the designed airfoil inflow angle. In particular, since the leading edge of the moving blade has a sharp angle, it is significantly increased as compared with the stationary blade. It is also generally known that the larger the turning angle of the fluid from the blade inlet to the blade outlet, the larger the airfoil loss. As can be seen from FIGS. 7A and 7B, the turning angle εr of the blade root portion is larger than the turning angle εt of the blade tip portion. That is, the relationship between the airfoil loss ζb in the moving blade and the difference Δβ between the working fluid and the design blade inflow angle is as shown in FIG. It is larger than the mold loss ζbt. Further, as shown in FIG. 8, the turning angle of the moving blade continuously decreases from the moving blade root portion to the moving blade tip portion, so that between the moving blade root portion and the moving blade tip portion ( Hereinafter, the airfoil loss of the moving blade middle portion) is determined by the blade blade loss ζbr at the blade root portion and the blade blade loss ζbt at the blade tip portion.
It becomes an intermediate value between and. In the following description, the case where the turning angle of the moving blade is largest, that is, the root portion of the moving blade and the turning angle of the moving blade is smallest, that is, the tip portion of the moving blade will be described as an example.

The airfoil loss at the blade root portion and the blade tip portion is the minimum value ζbrmin when Δβ = 0, that is, when the working fluid flows in at each design blade inflow angle β2.
And ζ btmin. 12 (a) and 12
(B) shows a change in the airfoil loss of the moving blade 5 when the moving blade 5 passes through the flow path of one pitch of the stationary blade 3.
As shown in FIG. 12A, the moving blade 5 always crosses the wake W from the stationary blade 3 when passing through the flow path X for one pitch in the circumferential direction of the stationary blade 3. When the moving blade 5 moving in the rotation direction D is at a certain circumferential position, the blade-shaped loss ζbr of the blade root portion and the blade-shaped loss ζbt of the blade tip portion are as shown in FIG. 12 (b). . That is, when the moving blade is in the main flow region, the working fluid flows in at the design blade inflow angle, so Δβ = 0, and as can be seen from FIG. 11, the blade type loss ζbr at the root portion of the moving blade has a minimum value. It becomes equal to ζ brmin, and the airfoil loss ζ bt at the blade tip becomes equal to the minimum value ζ bt min. On the other hand, when the rotor blade enters the area of the wake W, Δβ ≠ 0. Therefore, as can be seen from FIG. 11, the blade type loss ζbr of the rotor blade root portion becomes larger than ζbrmin, and Airfoil loss ζbt at the tip is larger than ζbtmin. As a result, the airfoil loss 1 pitch average value ξbr of the blade root portion becomes larger than ζbrmin, and the blade loss 1 pitch average value ξbt of the blade tip portion becomes larger than ζbtmin. Further, as can be seen from FIG. 8, the turning angle of the moving blade is larger at the root portion of the moving blade than at the tip portion of the moving blade. Therefore, the 1-pitch average value ξbr of the airfoil loss at the root portion of the moving blade is Of the airfoil loss of 1 pitch is larger than ξbt.

By the way, the working fluid of the wake is mixed with the working fluid of the mainstream portion as it goes away from the trailing edge 7 of S1, S2 and S3 and the stationary blade 3 in the downstream direction as shown in FIG. That is, the velocity C2 'of the wake W approaches the velocity C2 of the main flow as it moves away from the trailing edge 7 of the stationary blade 5 in the downstream direction. Therefore, as shown in the figure, the difference Δβ between the working fluid and the set moving blade inflow angle becomes smaller as the distance from the trailing edge 7 of the stationary blade 5 becomes further downstream.

From the above, the one-pitch average value ξ of the axial flow direction distance L from the trailing edge of the stationary blade to the leading edge of the moving blade and the airfoil loss of the moving blade
The relationship with b is as shown in FIG. Figure 12 (b)
As can be seen from the above, the one-pitch average value ξbr of the blade type loss at the root portion of the blade is larger than the one-pitch average value ξbt of the blade type loss at the blade tip portion. When the axial flow direction distance L from the trailing edge of the stationary blade to the leading edge of the moving blade becomes large, one pitch average value ξbr of the airfoil loss at the root portion of the moving blade and one pitch of the airfoil loss at the tip portion of the moving blade. The average value ξbt is ζbr
Asymptotically approach min and ζbtmin.

Next, the mixing loss due to the mixing of the wakes from the stationary blade will be described. As described above, during the period from the trailing edge of the vane to the leading edge of the rotor blade, the fluid of the wake is mixed with the working fluid in the main stream, so heat is generated based on the viscosity of the working fluid, and the energy of the fluid is generated. Is lost and mixing loss occurs. In FIG. 15, the vertical axis represents the average value of mixing loss for one pitch ξm
As the distance L in the axial flow direction from the trailing edge of the stationary blade to the leading edge of the moving blade to the leading edge of the moving blade increases along the horizontal axis, wake mixing is promoted, and mixing loss of 1 The average pitch value ξm also increases.

From the above-described two losses, a comprehensive evaluation of the energy loss affected by the axial flow direction distance from the turbine vane trailing edge to the turbine rotor blade leading edge is shown in FIG. In this figure, the vertical axis represents the energy loss ζ (=, which is influenced by the axial flow distance from the stationary blade trailing edge to the moving blade leading edge.
ξ b + ξ m) and the horizontal axis represents the axial flow direction distance L from the trailing edge of the stationary blade to the leading edge of the moving blade. From this figure, in the axial flow direction distance L from the trailing edge of the stationary blade to the leading edge of the moving blade, the energy loss ζr, (= ξbr + ξm) and ζt (= ξbt + ξ
It can be seen that there is an axial distance from the trailing edge of the vane to the leading edge of the blade, where m) is the smallest.

At the axial flow direction distance L from the trailing edge of the same vane to the leading edge of the moving blade, the blade shape loss ξbr of the moving blade at the root portion of the moving blade having a large turning angle is the moving blade having a small turning angle. It is larger than the airfoil loss ξbt of the blade at the tip. In addition, the axial distance in the axial direction from the trailing edge of the stationary blade to the leading edge of the blade until the airfoil loss ξbr near the blade root approaches a certain value, the ξbt at the blade tip approaches a certain value. Is greater than the axial distance from the trailing edge of the stationary blade to the leading edge of the moving blade. Therefore, the axial distance in the axial direction from the trailing edge of the stationary blade to the leading edge of the moving blade in the root portion of the paragraph where the energy loss ζ is the minimum (hereinafter, referred to as the optimum axial distance in the root portion of the paragraph) is Lro, and the tip of the paragraph If the distance in the axial direction from the trailing edge of the stationary blade to the leading edge of the moving blade (hereinafter referred to as the optimum axial flow distance at the tip of the paragraph) is Lto, then the relationship of Lro> Lto (3) is established. .

The root portion of the moving blade has been described as an example when the turning angle of the moving blade is large, and the tip portion of the moving blade has been described as an example when the turning angle of the moving blade is small. Exists in the axial direction distance from the trailing edge of the stationary blade to the leading edge of the moving blade that minimizes the energy loss. As described above, the blade airfoil loss in the moving blade middle portion becomes a value between the blade root loss portion and the blade tip loss portion, so that the energy in the moving blade middle portion is The optimum axial flow distance that minimizes loss is from the optimum axial flow distance Lro at the root of the paragraph to the optimum axial flow distance Lto at the tip of the paragraph.
Changes continuously until. FIG. 17 shows the height position of the moving blade,
It shows the relationship of the optimum axial flow distance. As can be seen from this figure, the greater the height position of the moving blade, the smaller the optimum axial flow distance.

However, in the conventional axial flow turbine paragraph,
As shown in FIG. 8, from the root part of the paragraph where the turning angle of the rotor blade is large to the tip of the paragraph where the turning angle of the rotor blade is small,
Since the axial distance in the axial direction from the trailing edge of the stationary blade to the leading edge of the moving blade is large, the axial distance in the axial direction from the trailing edge of the stationary blade to the leading edge of the moving blade extends from the root of the paragraph to the leading edge of the paragraph. It is impossible to achieve the optimum axial flow distance, and there is a problem that the energy loss is not minimized.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an axial flow turbine capable of reducing the energy loss in the axial flow turbine and improving the turbine performance.

[0019]

In order to achieve the above object, the present invention relates to an axial flow turbine stage constituted by a turbine vane and a turbine rotor blade, from the root part of the turbine stage to the tip part of the turbine stage. , The axial flow direction distance from the trailing edge of the turbine blade to the leading edge of the turbine blade is changed according to the turning angle of the turbine blade, and the larger the turning angle of the turbine blade is, It is characterized in that the axial distance from the edge to the leading edge of the turbine rotor blade is increased.

[0020]

[Function] Energy loss from the trailing edge of the turbine vane to the leading edge of the turbine blade from the root to the leading edge of the paragraph is affected by energy loss (= blade airfoil loss increased by wake from the vane) (Mixing loss due to the mixing of wakes from the vanes) can be minimized, and the turbine performance can be significantly improved as compared with the conventional axial flow turbine.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Further, the same reference numerals are given to the same members. Figure 1
FIG. 3 is a sectional view showing a paragraph of an axial flow turbine according to the present invention. In this figure, a stationary blade 3 is fixed by a stationary vane outer ring 1 and a stationary vane inner ring 2, and a moving blade 5 fixed to a rotating shaft 4. In this embodiment, the stationary blade 3 is similar to that of the prior art, and the position of the front edge 6 of the moving blade 5 in the axial flow direction extends from the tip of the paragraph to the root of the paragraph.
The axial distance from the rotor to the leading edge 7 of the rotor blade 5 is from Lt to Lr.
It is arranged so that it continuously increases.

FIG. 2 shows a practical relationship between the turning angle of the moving blade and the optimum axial flow distance. From the experimental results and the like, when the turning angle ε of the moving blade is in the range of 50 degrees to 150 degrees, L is empirically calculated between the turning angle ε of the moving blade and the optimum axial flow distance Lopt.
The relationship of opt / te = a · ε + b is established. Where t
e is the thickness of the trailing edge of the vane, and is a parameter related to the size of the wake generated from the trailing edge of the vane. In the range of the turning angle ε of the moving blade, if the constant a is 0.29 and the constant b is selected in the range of -4.6 to +3.3, it is suitable for application to an actual machine. If the axial flow direction distance from the stationary blade trailing edge to the moving blade leading edge at any blade height position within the range shown in this figure is selected according to the turning angle at that blade height position, From the root to the tip of the paragraph, the energy loss affected by the axial flow distance from the turbine vane trailing edge to the turbine blade leading edge (= blade airfoil loss that increases due to wake from the vane + (Mixing loss due to wake mixing from the vane) can be minimized at any height in the paragraph, and the axial flow distance from the turbine vane trailing edge to the turbine blade leading edge affects the overall paragraph. The resulting energy loss can be reduced.

FIG. 3 is a sectional view of a turbine showing another embodiment of the present invention. In this embodiment, the moving blade 5 is similar to that of the prior art, and the trailing edge 7 of the stationary blade 3 extends from the front end of the paragraph to the root portion of the rear edge 7 of the stationary blade 3.
The axial distance from the rotor to the leading edge 6 of the rotor blade 5 is from Lt to Lr.
It is arranged so that it continuously increases. FIG. 4 is a sectional view of a turbine showing another embodiment of the present invention. In this embodiment, the positions of the trailing edge 7 of the stationary blade 3 and the leading edge 6 of the moving blade 5 in the axial direction are set from the tip of the paragraph to the root of the paragraph, and the trailing edge 7 of the stationary blade 3 to the leading edge of the moving blade 5 are arranged. It is arranged by changing from the conventional axial flow turbine stage so that the axial flow distance to 6 continuously increases from Lt to Lr.

Also in the embodiment shown in FIGS. 3 and 4, if the axial flow direction distance from the trailing edge of the stationary blade to the leading edge of the moving blade is selected within the range shown in FIG. Up to this point, the energy loss affected by the axial flow distance from the turbine vane trailing edge to the turbine blade leading edge can be minimized at any height position in the paragraph. It is possible to reduce the energy loss that is influenced by the axial distance from the turbine to the turbine rotor blade leading edge.

[0025]

As described above, according to the present invention, the axial distance in the axial direction from the trailing edge of the turbine vane to the leading edge of the turbine rotor blade is measured from the root portion of the turbine stage to the tip portion of the turbine stage. It was changed according to the turning angle of the turbine rotor blade, and the larger the turning angle of the turbine rotor blade, the greater the axial distance from the trailing edge of the turbine stator blade to the leading edge of the turbine rotor blade. Therefore, the energy loss affected by the axial flow direction distance from the turbine vane trailing edge to the turbine blade leading edge from the root portion to the tip portion of the paragraph (= airfoil loss of the blade that increases due to wake from the vane + (Mixing loss due to mixing of wakes from the vanes) can be minimized, and turbine performance can be significantly improved over prior art axial flow turbines.

[Brief description of drawings]

FIG. 1 is a sectional view of an axial flow turbine showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a turning angle of a moving blade and an optimum axial flow direction distance.

FIG. 3 is a sectional view of an axial flow turbine showing another embodiment of the present invention.

FIG. 4 is a sectional view of an axial flow turbine showing still another embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional axial flow turbine.

FIG. 6 is a view of a conventional axial flow turbine as viewed from a radial direction.

7A and 7B are explanatory views of turning angles of moving blades.

FIG. 8 is an explanatory view of a turning angle change of a moving blade.

FIG. 9 is a diagram showing a relationship between a moving blade height position of a conventional axial flow turbine and an axial flow direction distance from a stationary blade trailing edge to a moving blade leading edge.

FIG. 10 is a diagram for explaining that the inflow angle of the fluid into the moving blade changes due to the wake of the stationary blade.

FIG. 11 is a diagram for explaining airfoil loss of a moving blade.

12A and 12B are views for explaining that the airfoil loss of the moving blade changes due to the wake of the stationary blade.

FIG. 13 is a diagram for explaining a change of the wake from the stationary blade.

FIG. 14 is a diagram for explaining that the airfoil loss of the moving blade changes depending on the axial flow direction distance from the trailing edge of the stationary blade to the leading edge of the moving blade.

FIG. 15 is a diagram for explaining wake mixing loss from the stationary blade.

FIG. 16 is an explanatory diagram of loss from the trailing edge of the stationary blade to the leading edge of the moving blade.

FIG. 17 is a diagram showing a relationship between a blade height position and an optimum axial flow direction distance.

[Explanation of symbols]

1 stationary vane outer ring 2 stationary vane inner ring 3 stationary vane 5 moving blade 6 leading edge of moving blade 7 stationary blade trailing edge L axial distance from trailing edge of stationary blade to leading edge of moving blade Lr paragraph root part Axial distance from the trailing edge of the stationary blade to the leading edge of the moving blade Lt Axial distance from the trailing edge of the stationary blade to the leading edge of the moving blade

Claims (3)

[Claims] 1. In an axial flow turbine stage composed of a turbine vane and a turbine rotor blade, from the root of the turbine stage to the tip of the turbine stage, from the trailing edge of the turbine vane to the leading edge of the turbine rotor. Axial flow direction distance is changed according to the turning angle of the turbine blade,
An axial flow turbine characterized in that the axial flow direction distance from the trailing edge of the turbine stationary blade to the leading edge of the turbine moving blade increases as the turning angle of the turbine moving blade increases. 2. The axial flow direction distance L from the trailing edge of the turbine vane to the leading edge of the turbine blade, the thickness of the trailing edge of the turbine vane is t, and the turning angle of the turbine blade is ε. Then, the axial flow turbine according to claim 1, characterized in that L / t = a · ε + b (a and b are constants). 3. The constant a is 0.29 and the constant b is -4.6.
To +3.3 are selected in the range.
The described axial flow turbine.