JPH03903A - Nozzle diaphragm of axial-flow turbine - Google Patents

Abstract

PURPOSE:To decrease the loss due to mixing the flow near a wall surface with a main flow by forming the inlet angle of plural guide vanes disposed in the peripheral direction so that they may be directed toward the center of a flow passage from the wall surface side of a nozzle diaphragm and change from the peripheral direction to the axial direction. CONSTITUTION:In the outer race 3 and the inner race 4 of a nozzle diaphragm, respective guide vanes 7, 8 are disposed on the upstream side of a nozzle blade 5, whereas the respective guide vanes 7, 8 are formed into a blade shape and are arranged at the inner race 4 and the outer race 3 at regular intervals in the peripheral direction, and an outlet portion is positioned parallel to a turbine rotating shaft. The inlet angle of respective guide vanes 7, 8 is formed so that they may be directed toward the center of a flow passage from the wall surface side of the nozzle diaphragm and change from the peripheral direction to the axial direction. It is thus possible to change the flow with large turning angle near the wall surface in the axial direction by the respective guide vanes, decreasing the loss due to mixing with a main flow.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in nozzle diaphragms for axial flow turbines.

[Conventional technology]

In an axial flow turbine, a nozzle diaphragm is provided to effectively and safely guide high temperature, high pressure fluid to a low temperature, low pressure state to the rotor blades. FIG. 7 shows a schematic structure of the nozzle diaphragm section. The nozzle diaphragm 1 consists of a nozzle diaphragm outer shaft 3 supported at a predetermined position in a casing 2, an inner ring 4 of the nozzle diaphragm arranged on the inner circumference side, and an inner and outer space of the nozzle diaphragm @3°4. The working fluid passes through the flow path formed between the nozzle blades 5 of the nozzle diaphragm 1, as shown by the arrow, and is moved. It is guided by the blades 6 and rotates the rotor 7.

By the way, a general axial flow turbine is designed so that the absolute outflow direction of the fluid at the outlet of the five-stroke X6 is axial. However, near the inner and outer wall surfaces of the flow path, the relative outflow velocity at the outlet of the rotor blade 6 decreases due to secondary flow loss in the nozzle blade 5 and the blade cascade flow path of the rotor blade 6, as shown in FIG. As shown by the broken line, the flow becomes a swirling flow with a large circumferential component.

The flows near the wall and in the center of the channel, which have greatly different speeds in the outflow direction, are mixed as they move downstream, causing a mixing loss. In particular, if the inner circumferential wall surface of the nozzle diaphragm outer ring 3 widens rapidly along the direction of fluid flow as shown in Figure 7, the distance to the inlet of the nozzle blade in the next stage becomes long, resulting in a mixing loss. becomes larger. For this reason, sometimes peeling occurs on the wall surface before flowing into the nozzle blade 5.

Therefore, in the past, for example,
As in Publication No. 1, partition plates are sunk individually at the root and in front of the tips of the nozzle blades, and the flow of wax generated from the trailing edges of these partition plates is used to improve mixing. is being carried out.

[Problem to be solved by the invention]

Although peeling on the wall surface can be prevented by the prior art described in Section 2, consideration has not been given to reducing mixing loss.

An object of the present invention is to reduce the mixing loss near the wall surfaces of the inner and outer rings of the nozzle diaphragm and to improve the performance of the turbine.

[Means to solve the problem]

In order to achieve the above object, the swirling flow near the wall surface is made to flow in the same direction as the main flow using guide vanes.

[Effect]

As shown in FIG. 8, the relative outflow velocity of the fluid at the outlet of the rotor blade 6 is slower than U in the mainstream to U' near the wall surfaces of the inner and outer rings of the nozzle diaphragm. However, the absolute outflow velocity is V' in the vicinity of the wall compared to V in the mainstream, which is faster than in the mainstream.

Therefore, if the flow near the wall surface is diverted in the same direction as the mainstream flow by the guide vane, the difference in momentum between the two flows will be reduced, and the mixing loss caused by the change in momentum can be reduced.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 4.

In the axial flow turbine according to this embodiment, the nozzle diaphragm outer ring 3. and the nozzle diaphragm inner ring 4,
Guide vanes 7 and 8 are installed upstream of the nozzle X5, respectively. In this case, the guide vanes 7 and 8 have a wing wall shape, as shown in FIG. At the same time, the guide vane outlet portion is installed approximately parallel to the turbine rotation axis. Furthermore, the height of the exit portion of the guide vanes 7 and 8 is up to the point where δ shown in FIG. be. FIG. 3 is a perspective view of the guide vane 8, in which the inlet end recedes from the root to the tip.

That is, FIG. 4 (a) to (e) show the IV-IV cross section of FIG. 3 in order from the root side. - The entrance angle α of the guide vane 8 is the largest at the root, and becomes smaller toward the tip, corresponding to δ in FIG.

Next, the present invention will be explained in detail. Guide vane 7 of wing wall cross section
, 8 are the nozzle diaphragm outer ring 3 and the nozzle diaphragm outer ring 3;
When attached to the diaphragm inner ring 4, as shown in FIG. 9, the flow having a large turning angle (-δ) near the wall surface is efficiently diverted in the axial direction by the guide vanes 7 and 8. This causes the flow to flow in the same direction as the mainstream, reducing mixing with the mainstream.

Loss near the wall is reduced. Moreover, as the position of the guide vane 7°8 changes from the root side to the tip side, the inlet end of the guide vane moves to the downstream side and the chord length of the guide vane becomes smaller, so the loss due to the guide vane is less than necessary. It doesn't get bigger.

As a modification of the present invention, as shown in FIGS. 5 and 6, a guide vane is made of a steel plate, and only the inlet angle of the guide vane changes, but the inlet end does not change toward the downstream side. Both methods can achieve the intended effects of the present invention.

〔Effect of the invention〕

According to the present invention, guide vanes having an airfoil cross section are attached to the outer shaft of the nozzle diaphragm and the inner ring of the nozzle diaphragm of an axial flow turbine at equal intervals in the circumferential direction, so that the swirling flow near the wall surface is diverted in the same direction as the turbine rotation axis as the main stream. However, mixing with the main stream is reduced and turbine performance can be improved.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of one embodiment of the present invention, Fig. 2 is a view from the ■-■ arrow in Fig. 1, Fig. 3 is a perspective view of the guide vane, and Fig. 4 is the IV-TV shown in Fig. 3. 5 and 6 are cross-sectional views of guide vanes of modified examples. FIG. 7 is a cross-sectional view of a general example of an axial flow turbine.
The figure is a velocity triangle diagram representing the flow state at the rotor blade outlet.
The figure is a radial distribution diagram of the absolute outflow angle at the rotor blade outlet. Figure 2 Figure 3 ■ Figure 4 +(L+ +a+ +(,1 +d+ el (YU) (8) (Sub) Figure 6 (■) (f, + fQ) Figure 7 Figure 8

Claims (1)

[Claims] 1. A pair of nozzle diaphragms In an axial flow turbine nozzle diaphragm in which guide vanes are individually provided at the root and forward ends of nozzle blades held by an inner ring and an outer ring, a plurality of guide vanes are provided in the circumferential direction. A nozzle diaphragm for an axial flow turbine, characterized in that the inlet angle of the arranged guide vanes is formed so as to change from the circumferential direction to the axial direction from the wall side of the nozzle diaphragm toward the center of the flow path. 2. The nozzle diaphragm for an axial flow turbine according to claim 1, wherein the exit angle of the guide vane is formed in the axial direction. 3. The axial flow according to claim 1, wherein the inlet end of the guide vane is retreated from the wall side of the nozzle diaphragm toward the center of the flow path toward the downstream side of the flow path. Turbine nozzle diaphragm.