JPH0477123B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a turbine impeller used in a steam turbine, and more particularly to a turbine impeller having a shroud that is integrally or integrally attached to the tip of a rotor blade.

[Technical background of the invention and its problems]

Generally, a steam turbine rotatably accommodates a rotor shaft in a sealed turbine casing, and a plurality of rotor disks are integrally or integrally provided to the rotor shaft by shrink fitting or the like. As shown in FIG. 1, a rotor disk 1 has a large number of turbine blades 2 planted around its outer periphery to form a turbine impeller. in particular,
The turbine blade 2 has a saddle-shaped blade root portion 3, and is implanted by engaging with a groove-shaped blade planting portion 1a formed on the outer periphery of the rotor disk 1. A large number of turbine blades 2 are arranged in the circumferential direction of the rotor disk 1 to form a rotor blade row.

A shroud 4 is provided at the tip of each turbine blade 2. This shroud 4 is a turbine blade 1
This system is installed for the purpose of suppressing vibration and ensuring turbine performance. As shown in FIG. 2, the shroud 4 is provided with an engagement hole 5 in a circumferentially continuous plate.
a, and then caulk the top of the protrusion 2a to fix the plate to the tip of the turbine blade 2 to form a surrounding ring, or as shown in FIG. There is a structure in which the enclosing ring is made by integrally molding the plate by cutting it out.

A plurality of strip-shaped fins 6 are provided on the stationary side of the steam turbine opposite to the shroud 4, as shown in FIG. Specifically, this fin 6 protrudes from the overhang part of the nozzle diaphragm outer ring so as to be continuous in the circumferential direction.
The gap d between the tip and the outer surface of the shroud 4 is made as small as possible to reduce steam leakage from this minute gap d. That is, by providing a plurality of fins 6, the gap between the fins 6 and the shroud 4 is divided into a plurality of annular chambers 7 to reduce the amount of leaked steam and ensure turbine performance. The loss due to leaking steam L from the minute gap d is approximately inversely proportional to the square root of the number of fins 6,
It is proportional to the size of the minute gap d. From this, it can be seen that the minute gap d is the main factor determining the loss due to the leaked steam L, as shown in FIG. 4, and if the gap d is narrowed, the loss will be reduced in proportion to this. Therefore, in the steam turbine, the minute gap d is designed to take the minimum value within a range in which the fin 6 and the shroud 4 do not come into contact with each other during rotation and are damaged.

On the other hand, in a turbine impeller used in a steam turbine, the pitch P between the blades of the turbine blades 2 installed on the rotor disk 1 is not uniform over the entire circumference. In particular, as shown in FIG. 5, in a turbine impeller having a saddle-shaped blade root 3, a notch 8 for installing the turbine blade 2 is formed in the blade planting part 1a of the rotor shaft 1. It is implanted by sequentially inserting it from this notch and sliding it in the circumferential direction.Finally, the special turbine blade 10 or block 11 as shown in FIGS. 6A and 6B is inserted, and the retaining pin ( (not shown)
It is prevented from falling out by placing it in place.

However, the notch 8 formed in the rotor disk 1 is chamfered for convenience in inserting the turbine blades 2 and 10 and for the purpose of alleviating stress concentration at the corners of the notch 8, but the effects of this chamfering etc. Therefore, the width (circumferential length) of the notch 8 is larger than the width of the blade root 3 of the normal turbine blade 2,
For this reason, the pitch P between the blades of the turbine blades 2 and 10 is
becomes larger than other parts.

In addition, the notch 8 of the rotor disk 2 is shown in FIG. 6B.
When block 11 shown in Figure 1 is used, the centrifugal force corresponding to the blade section and shroud of the turbine blade in this part is missing, resulting in an imbalance of centrifugal force in the turbine impeller, which causes shaft vibration. or In order to solve this problem, a method has been adopted in which the pitch P between the blades of the plurality of turbine blades 2 provided at symmetrical positions (diametrically opposed to each other) of the notch 8 is increased to achieve balance.

By the way, the minute gap d between the fin 6 and the shroud 4 is determined by taking into account the deformation of the shroud 4 due to the centrifugal force effect due to rotation during turbine operation, but the pitch between the blades of the turbine blades 2 is determined over the entire circumference. It is not uniform, and the amount of deformation of the shroud 4 due to centrifugal force is proportional to the fourth power of the pitch P between the blades. Therefore, the deformation of the shroud 4 during turbine operation is represented by the broken line BL in FIG. 7. That is, in the part P ₁ where the blade pitch P is narrow, the shroud 4 is deflected radially outward by E ₁ under the action of centrifugal force during turbine operation, and the shroud 4 in the wide blade pitch part P ₂ is deflected by E _{2 .} only bends. Here, the relationship is E ₂ = E ₁・(P ₂ /P ₁ ) ⁴ ...(1), and the amount of deformation of the wide part P ₂ of the pitch between the blades is greater than that of the narrow pitch part P ₁ of the blades. Very large.

For this reason, in conventional steam turbines, the outermost shape of the turbine impeller during turbine operation is determined based on the amount of deformation of the shroud 4 at the wide part _P2 of the pitch P between blades, and the outermost shape of the turbine impeller is determined based on this. The gap d with the fin 6 is determined.

However, the part _P2 of the turbine blade 2 where the pitch P between the blades is large is a part of the entire turbine impeller, and most of the remaining part is planted so that the pitch between the blades is constant (small) _P1 . ing. Furthermore, the gap d between the shroud 4 and the fin 6 is determined based on a turbine blade having a large interblade pitch P. Therefore, the minute gap d becomes an unnecessarily large gap by the difference in the amount of deflection (E ₂ - _{E 1} ) based on the difference in the pitch P between the blades, and the amount of leaked steam that does not do work increases by that amount, There were problems such as hindering improvements in turbine efficiency.

[Object of the Invention] Taking the above-mentioned points into consideration, the present invention maintains the gap between the shroud and the fin at an optimal minute gap during turbine operation, reduces the amount of steam leaking from that part, and reliably improves turbine efficiency. It is an object of the present invention to provide a turbine impeller that can be obtained.

[Summary of the invention]

In order to achieve the above-mentioned object, a turbine impeller according to the present invention has a plurality of turbine blades circumferentially implanted in a rotor disk, and a shroud is integrally or integrally provided at the tips of the implanted turbine blades. and the turbine blade is configured such that at least one part of the blade pitch is different from the blade pitch of the remaining turbine blades,
At least the tip of the turbine blade where the pitch between the blades is large is located radially inward from the tips of the remaining turbine blades by at least the difference in the amount of deformation of the shroud due to the centrifugal force generated due to the difference in the pitch between the blades. This is what I did.

[Embodiments of the invention]

Hereinafter, preferred embodiments of a turbine impeller according to the present invention will be described with reference to the accompanying drawings.

In explaining the turbine impeller of this invention,
The same members as in the conventional turbine impeller are given the same reference numerals, and their explanations will be omitted.

The turbine blades 2 installed on a rotor disk (not shown) are constructed as shown in _FIG .
The tip of A (the length from the center of the rotor shaft to the tip of the turbine blade) is located radially inward from the tip of the turbine blade 2 having an inter-blade pitch _P1 . The pitch between the blades of most of the turbine blades 2 installed on the rotor disk is _P1 , and the pitch between the blades _P1 is smaller than the pitch between the blades _P2 . The difference Δ in the radial direction between the blade tips of the turbine blade 2A and the normal turbine blade 2 is based on the difference in the outward expansion in the radial direction due to the centrifugal force of the shroud 4, which is integrally or integrally attached to the tip of the turbine blade 2. be. Specifically, the amount of radial outward expansion (deformation) of the pitch P ₂ between the blades due to the action of centrifugal force at the rated rotation of the turbine is E ₂ , and the amount of deformation of the pitch P ₁ between the blades is E ₁ Then, the difference Δ in the radial direction is Δ
≧E ₂ -E ₁ , and the shroud 4 is installed so as to satisfy this condition.

In the above formula for the radial difference Δ, the inequality sign is
This takes design errors into consideration, and when the blade tip of the turbine blade 2A with a large interblade pitch is positioned radially inward from the tip of the turbine blade ₂ with a normal blade pitch P2, the blade tip with a large interblade pitch The blade tips of the turbine blades 2A are positioned radially inward from the blade tips of the remaining turbine blades 2 by an amount equal to the radial difference Δ plus a design error.

Therefore, in the turbine impeller having the above-mentioned configuration, during operation of the turbine, the shroud of the narrow pitch _P1 between the blades extends outward in the radial direction by a broken line _E1 .
It deflects as shown by BL, and the shroud at the wide pitch _P2 between the wings deflects by _E2 . In this bent state, the outermost diameter of the shroud 4 runs approximately on the same circle c. From this, we can calculate that the radius (rotational radius) of the tip of the shroud 4 in the wide interblade pitch _P2 portion formed in a part of the circumferential direction of the turbine impeller during turbine operation (rotation radius) is the radius of the remaining majority of the shroud 4. It can be equal to or less than. Therefore, Shroud 4
The gap d between the blade tip and the tip of the fin provided at the stationary part of the steam turbine can be determined based on the amount of deflection E ₁ of the shroud 4 in the narrow pitch P ₁ between the blades. The gap d between the blade and the stationary part (fin) can be set to the minimum value during operation over the entire blade row or most of the blades, and the amount of steam leakage can be kept to a minimum. Therefore, there is less leakage steam that does not do any work,
The operating efficiency of the turbine is definitely increased and the turbine performance is improved.

In addition, in Fig. 8, the wide pitch between the blades P ₂
Although an example has been described in which the portion has one turbine blade, the wide pitch portion may be applied to a blade row formed of a plurality of turbine blades.

Next, a modification of this invention will be described with reference to FIG.

The turbine impeller shown in FIG. 9 is formed integrally with the turbine blade 20 by cutting out a shroud 21 provided at the tip of the turbine blade 20.

The turbine impeller shown in this variant has turbine blades 20 located in a wide interblade pitch _P2 .
At the tip of A, a shroud 21A having a length L ₂ to the free end is provided in the form of a cantilever, so this shroud 21A is bent by E ₂ under the action of centrifugal force. In addition, at the tip of the turbine blade 20 located at the narrow pitch _P1 between the blades, there is a length to the free end.
Since the shroud 21 of _L2 is provided in the form of a cantilever, it is deflected by _E1 due to the action of centrifugal force.

The deflection amounts E ₁ and E ₂ of both shrouds 20 and 21A have the following relationship: E ₁ =E ₁ ·(L ₂ /L ₁ ) ⁴ (2). Therefore, by making the tip radius of the turbine blade 21A having the shroud 21A with the length L ₂ smaller than the tip radius of most of the remaining turbine blades 21 by the radial difference Δ, the result shown in FIG. It has the same effect as the turbine impeller shown.

Here, Δ≧E ₂ −E ₁ ...(3).

In addition, in the turbine impeller shown in FIG. 8 and FIG. 9, an example was explained in which the tip radius of the turbine blade in the wide inter-blade pitch portion is reduced, but if a problem arises in the shroud assembly work, , as shown in Fig. 10, the pitch between the wings is wide P ₂
The tip radius of a plurality of turbine blades 2 adjacent to the partial turbine blade 2A may be changed in stages. In this case, the blade tip of the turbine blade 2A having a large interblade pitch is displaced by a required amount inward in the radial direction from the blade tip of a normal turbine blade 2, and the blade tip of the turbine blade 2A is moved circumferentially adjacent to the turbine blade 2A. This is a method in which the blade tips of multiple turbine blades 2 are sequentially changed in stages, and is effective when the difference Δ between the amount of deflection in the part _P2 with a large pitch between the blades and the amount of deflection in the part _P1 with a large pitch between the blades is large. It is. In addition, when forming a rotor blade group by integrally connecting the tips of several turbine blades with a shroud, the tip radius of all turbine blades in the rotor blade group with a wide blade pitch should be It may be smaller than the tip radius of the group of turbine blades by Δ≧E ₂ −E ₁ .

Furthermore, if the pitch between the blades is not only different in two stages but also varies, the amount of radial outward deformation of the shroud due to the action of centrifugal force at the maximum pitch between the blades is taken as _E2 . If the amount of deformation of the shroud for each pitch between blades is adjusted so that the maximum radius of the shroud during turbine operation is set to be uniform over the entire circumference, the same effect as described above can be obtained.

〔Effect of the invention〕

As described above, in the turbine impeller according to the present invention, at least the tips of the turbine blades in the large part of the blade pitch are at least as large as the amount of deformation of the shroud due to the centrifugal force caused by the difference in the blade pitch. Since the difference is located radially inward from the tips of the remaining turbine blades, the outer diameter of the turbine impeller can be made uniform or almost uniform during turbine operation, and the gap between the stationary side fin and the shroud can be reduced. can be minimized.
Therefore, the amount of steam leaking through this gap that does not do any work can be kept to a minimum and work can be done effectively, so the turbine efficiency can be increased and the turbine performance can be reliably improved. .

[Brief explanation of the drawing]

Fig. 1 is a partial perspective view of a turbine impeller incorporated into a conventional steam turbine, Fig. 2 is an exploded perspective view partially showing a turbine impeller with an assembled shroud, and Fig. 3 is a machined integrally formed FIG. 4 is a partial perspective view of a turbine impeller having a type shroud; FIG.
and a diagram showing the mutual arrangement relationship of stationary side fins,
FIG. 5 is a diagram partially showing the mounting relationship in which a turbine blade having a saddle-shaped blade root is installed in a rotor disk, and FIGS. 6A and B show a turbine blade and a block installed in a notch in the rotor disk. FIG. 7 is a perspective view showing the deformation of the shroud of a conventional turbine impeller during turbine operation; FIG. 8 is a partial view showing an embodiment of the turbine impeller according to the present invention; FIG. The figure shows a first modification of the invention, and FIG. 10 shows a second modification of the invention. 1...Rotor disk, 2, 2A, 10, 2
0,20A...Turbine blade, 3...Blade root,
4, 21, 21A... Shroud, 6... Fin, 8... Notch, 11... Block.

Claims (1)

[Scope of Claims] 1. A plurality of turbine blades are installed in the circumferential direction on a rotor disk, and a shroud is integrally or integrally provided at the tips of the installed turbine blades, and the turbine blade has at least one part of the blades. In a turbine impeller configured to have a blade pitch different from that of the remaining turbine blades, at least the tips of the turbine blades where the blade pitch is large are subject to centrifugal force generated due to the difference in blade pitch. A turbine impeller characterized in that the shroud is located radially inward from the tips of the remaining turbine blades by at least the difference in the amount of deformation of the shroud. 2. A plurality of turbine blades circumferentially adjacent to a turbine blade located in a large part of the blade pitch are:
The turbine impeller according to claim 1, wherein the tip thereof is positioned radially outward in stages. 3 Several turbine blades are connected by a shroud to form a rotor blade group, while in a rotor blade group that has turbine blades with a large pitch between the blades, the tips of the turbine blades connect to the turbines of the remaining rotor blade groups. The turbine impeller according to claim 1, which is formed to be located radially inward from the tip of the blade.