JPS62174507A - Exhaust diffuser for axial flow turbo machine - Google Patents

Abstract

PURPOSE:To prevent an inverse flow at a root and improve diffuser efficiency through the removal of a boundary layer and an exfoliating fluids by forming recessed curvature and projected curvature respectively on the wall surface of an exhaust diffuser. CONSTITUTION:The wall surface of the root flow guide 17 of an exhaust diffuser 'DF' is made to have recessed curvature 'R2' for a flow passage, and the wall surface of a bearing cone 18 is so formed as to have projected curvature 'R3' at the intermediate part of a diffuser flow passage. Tip flow guides 19 and 21 fitted to an internal casing 3 are made monolithic with a rib 22 and a jet groove 20 is formed at the intermediate part of the diffuser flow passage for introducing a fluid of a boundary layer developed along the wall surface of the tip flow guide 19 with the exfoliation thereof starting. According to the aforesaid constitution, an inverse flow at a root is prevented and the boundary layer and exfoliating fluid in the diffuser flow passage can be excluded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] [Industrial Field of Application] The present invention relates to an exhaust diffuser for an axial flow turbomachine with improved thermal efficiency and reliability.

[Conventional technology]

Generally, in order to effectively recover the residual velocity energy of the fluid discharged from the final stage of an axial flow turbomachinery as pressure energy, an exhaust diffuser is installed downstream of the final stage to improve thermal efficiency by increasing the exhaust pressure. Improving diffuser efficiency requires a sufficiently long diffuser channel with an optimal area expansion factor. However, increasing the length of the diffuser lengthens the rotor span due to its structure, which causes problems with the stability of rotor rotation due to the increased size, resulting in lower reliability. Furthermore, since it increases costs, in practice diffusers with a curved shaft radius are often used, with the length as short as possible.

However, with this type of diffuser, the fluid discharged from the final stage suddenly turns from the axial direction in a short distance.

Fluid separation within the diffuser flow path tends to cause pressure loss. Therefore, designing the diffuser flow path is difficult, and optimization of the diffuser shape has been pursued through repeated numerous experiments and analyses.

This will be explained using an axial flow turbine as an example with reference to the drawings. Figure 6 is a sectional view showing the structure of a conventional steam turbine exhaust diffuser. The exhaust diffuser DF covers the steam exhausted from the final stage of the turbine and guides it to a condenser (not shown) installed below. External casing upper half■ and
A chip flow guide (e) attached to the internal casing ■ and a chip flow guide (e) attached to the internal casing ■ in the wake of the nine blades ■ and the blade ■ It is configured to form a flow path between the tip flow guide 0, the root flow guide 0 and the bearing cone ■. Pass through an appropriate area expansion channel.

The residual velocity energy of the exhaust steam that has passed through this area-expanding flow path is recovered by effectively increasing the pressure and converting it into energy.

In such an exhaust dip user structure DF.

The steam discharged from the final stage becomes a diffuser flow path up to the area A2 at the trailing end of the chip flow guide 0, but since the length of the diffuser is short, the area expansion rate A, /A1 cannot be increased.6 Therefore, the diffuser The efficiency is low, and the exhaust energy from the final stage cannot be effectively recovered, resulting in a decrease in the thermal efficiency of the turbine, which requires optimization of the diffuser flow path.

Next, examples of conventional exhaust diffuser efficiency improvement measures are shown in FIGS. 7 to 10. In the structural diagrams of FIGS. 7 to 10, which will be explained below, the same members as in FIG. By using technology, the chip flow guide ■ attached to the inner casing ■ has a long curved shape, and at the same time the bearing cone (10) attached to the outer casing ■ has a curved shape, allowing the exhaust steam from the final stage to be smoothly diffused. This figure shows a diffuser shape with a curved shaft radius in which the diffuser efficiency is increased by increasing the diffuser length and area expansion rate A2/A.

This exhaust diffuser has higher efficiency compared to the conventional type shown in Fig. 6, but the chip flow guide (9
) has a convex curvature, and the boundary layer developed on the wall surface tends to separate in the middle of the diffuser flow path, as can be seen from the flow path velocity distribution shown in the figure. It is easy for backflow to occur nearby. Therefore, the actual area expansion rate is considerably smaller than the geometric area expansion rate A, /A, and may be lower than the expected diffuser efficiency.

Figure 8 shows an intermediate flow guide (14) installed on a rib (13) supported by the bearing cone (12) in the diffuser flow path between the chip flow guide (11) and the bearing cone (12). There is a method for preventing peeling that occurs on the wall surface of the chip flow guide (11) in the middle of the diffuser flow path. As this type of device, for example, B r
ovn B overl review? /8-75 is known. Since the diffuser shape has the ribs (13) and the intermediate flow guide (14) in the flow path, friction loss with the fluid occurs. Furthermore, the steam discharged from the final stage may flow non-uniformly and may damage the intermediate flow guide (14), which poses a problem in terms of reliability.

FIG. 9 shows the area A1 of the diffuser flow path formed between the chip flow guide (15) and the bearing cone (16). A2. A3. As shown in Figure 10, the area of A4 is rapidly reduced from A2 to A in the middle of the flow path to increase the speed of the steam, thereby eliminating the boundary layer that has developed on the wall surface of the chip flow guide (15) in the middle of the diffuser flow path. At the same time, turn the flow and increase the area expansion rate A4/1 from the middle of the flow path again.
Pressure recovery is being performed at A. This type of device is known, for example, as published in "Turbo Machinery Vol. 11, No. 8, P 458J.

However, by narrowing down the area from A2 to A, pressure recovery is not effectively achieved in this range, and the pressure is likely to drop, and the pressure rise across the entire diffuser means that the expected diffuser efficiency cannot be obtained. Sometimes.

[Problem that the invention seeks to solve]

Next, using FIGS. 11 and 12, the flow characteristics of the turbine at partial load and the drawbacks of conventional techniques will be explained. In the conventional diffuser shapes shown in Figures 6 to 9, since the slope α° of the root flow guide ■ shown in Figure 11 is a positive value, the steam streamline at the final stage blade outlet root part is It has a concave R curvature with respect to the road. As a result, when the steam flow rate becomes lower than a certain value during partial load operation in a 6-steam turbine where the pressure (Pex shown in the figure) at the final stage outlet route increases, the flow rate at the final stage becomes lower than a certain value as shown by the vortex streamline W in Figure 12. It is known that backflow areas occur in some parts of the road.

Now, when the turbine flow rate is reduced under partial load, the average pressure at the final stage blade outlet is regulated by the condenser pressure and is kept almost constant, while the average pressure at the blade inlet decreases. Backflow begins at the point where the pressure difference across the blade is reversed. Normally, at the inlet of one blade, the pressure at the root is lowest, so the backflow usually starts from the root. Therefore, if the inclination α° of the root flow guide (c) shown in FIG. 11 is positive, there is a drawback that a backflow region is likely to occur. When this backflow occurs, not only does the stage efficiency decrease, but also an exciting force is applied to the rotating blades, which may cause damage.

In this way, the conventional exhaust diffuser flow path shapes shown in Figs. 6 to 9 have a tendency to deteriorate turbine thermal efficiency due to a decrease in diffuser efficiency or a decrease in stage efficiency due to backflow, and to cause frequent troubles due to fluid dynamics. There is a drawback that reliability is impaired.

An object of the present invention is to provide an exhaust diffuser for an axial flow turbomachine that does not impair the thermal efficiency and reliability of the turbine.

[Structure of the invention]

[Means for Solving the Problems] The exhaust diffuser for a commutation turbomachine according to the present invention has a concave R-curvature surface and a convex R-curvature surface with respect to the flow path in the middle of the wall surface forming the exhaust diffuser flow path. It is characterized by having formed the following.

[Function] In the exhaust diffuser for the trickle turbomachine according to the present invention, first, by making the root flow guide wall surface concave, the streamline of the exhaust steam at the outlet of the final stage blade upstream thereof becomes a convex curvature, which increases the pressure. is prevented and reduced. For this reason, the pressure difference before and after the blade root portion increases, making it possible to reduce backflow during partial load operation.

In addition, the concave surface of the root flow guide wall surface allows the curvature of the chip flow guide to be increased, thereby making it possible to reduce the occurrence of a boundary layer or peeling that develops on the wall surface. The convex surface of the bearing cone changes the streamlines of the exhaust steam outward of the flow path, thereby eliminating boundary layers and separation fluids from within the diffuser that would otherwise reduce diffuser efficiency.

〔Example〕

The present invention will be described below with reference to embodiments shown in FIGS. 1 to 5. In each drawing, the same reference numerals as in FIGS. 6 to 11 indicate the same parts, and the explanation thereof will be omitted. First, in the embodiment shown in FIG. 1, the exhaust diffuser DF of the steam turbine according to the present invention has a root flow guide (
17) The wall surface of the bearing cone (18) is formed with a concave R2 curvature relative to the flow path, and the wall surface of the bearing cone (18) is formed with a convex R1 curvature at the middle portion of the diffuser flow path. In addition, the chip flow guides (19) and (21) attached to the internal casing ■ are integrated with a rib (22), and the chip flow guide (1
9) An ejection groove (20) is provided to guide the boundary layer that has developed on the wall surface and the fluid where separation has begun.

Next, the operation of the exhaust diffuser for an axial flow turbomachine according to the present invention will be explained using FIG. First, by making the wall surface of the root flow guide (17) concave, the streamline at the upstream final stage blade outlet section has a convex curvature of R□, and the pressure at the blade exit root section is prevented from increasing and is reduced. the result,
The pressure difference before and after the blade root section increases, making it possible to reduce backflow during partial load operation. Next, the exhaust steam flow Fa from the final stage increases in pressure between 〇 and A2 to the area where the optimal diffuser flow path is formed, but since the root flow guide (17) wall surface is given a concave R2 curvature, Chip flow guide (
It is possible to increase the curvature R4 of 19), and it is possible to reduce the occurrence of a boundary layer or peeling that develops on the wall surface.

In addition, between the diffuser flow paths A and A, by changing the streamline outward of the flow path by the R3 curvature of the convex surface of the bearing cone (18), a part of the flow Fb is transferred to the tip flow guide (19). The flow Fc is ejected from the ejection groove (20) formed between and (21), and the boundary layer and separation fluid that cause a decrease in diffuser efficiency are extinguished from inside the diffuser. Areas A2 and A of this diffuser flow path
, are almost the same value.

As a result, the pressure drop in this section can be suppressed as much as possible. Moreover, in the flow paths A3 to A4, the area expansion ratio is set to an appropriate value, and the pressure can be recovered again.

This control function from A2 to A□ separates the axial flow flowing out from the final stage and the radial flow of Fe from the flow Fd, and creates a two-stage diffuser of an axial flow diffuser and a radial flow diffuser each having an optimal shape. It is formed.

FIG. 3 is an example showing a comparison of area enlargement ratios between the present invention and the prior art. The area magnification ratio of the present invention can be made larger than that of the prior art because loss due to separation is less likely to occur within the diffuser flow path. To explain the relationship between area expansion rate and diffuser efficiency: 1 Normally, assuming that there is no loss in the diffuser flow path, the pressure recovery coefficient Cp [(outlet pressure car population pressure)/dynamic Expressed in terms of pressure), it is as follows.

That is, if a loss-free shape is possible in the diffuser flow path, the pressure recovery coefficient Cp will be larger if the outlet area is larger than the inlet area, which means that the diffuser efficiency will be better. Figure 4 is a well-known diffuser performance curve.

It is clear that the pressure recovery coefficient of the present invention is greater than that of the prior art.

FIG. 5 shows another embodiment of the present invention, which is an axial flow exhaust type diffuser in an axial flow turbomachine.

Root flow guide (22) and tip flow guide (2)
In the diffuser flow path formed in 3) and (25), the root flow guide has a concave R2 curvature at the diffuser inlet and a convex R3 curvature wall at the intermediate portion. Further, a jetting groove (24) is provided in the middle part of the chip flow guides (23) and (25). This type of exhaust diffuser flow path shape has the same effect as that shown in FIG. 2 described above.

〔Effect of the invention〕

As described above, the present invention prevents backflow at the root by installing the concave surface R on the root flow guide wall that forms the exhaust diffuser flow path, and prevents the boundary layer and separation fluid by installing the convex surface R on the bearing cone wall. can be excluded. Therefore, it is possible to increase the diffuser efficiency and reduce the backflow area in the flow path during partial load operation, and it is possible to obtain an excellent axial flow turbomachine with high thermal efficiency and reliability.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of the exhaust diffuser for a trickle turbomachine according to the present invention, FIG. 2 is a cross-sectional view showing the function of the exhaust diffuser of the present invention, FIG. 4 is a diffuser performance curve diagram, FIG. 5 is a sectional view of a trickle exhaust type diffuser showing another embodiment of the present invention, FIG. 6 is a sectional view showing the structure of a conventional exhaust diffuser, and 7. 8th. Fig. 9 is a sectional view showing different conventional exhaust diffusers, Fig. 10 is a characteristic diagram showing area changes of the exhaust diffuser in Fig. 9, and Figs. 11 and 12 are flow characteristics of the steam turbine at partial load. FIG. 3 is a schematic configuration diagram for explaining the generation of vortex streamlines. 1... Upper half of external casing 2... Rotor 3...
・Internal casing 4... Nozzle 5... Vane 6
, 9.11.15...Chip flow guide 7.10
, 12.16... Bearing cone 8... Root flow guide 13... Rib 14... Intermediate flow guide 17... Root flow guide 18... Bearing cone 19.21, 23.25...・Chip flow guide 20
．． 24...Furomizo 22...Rib DF...Exhaust diffuser agent Patent attorney Yoshiaki Inomata (and 1 other person) Figure 8 Chief''! L/H Figure 4 Figure 6 Figure 9 ω

Claims (4)

[Claims] (1) In the middle of the wall that forms the exhaust diffuser flow path,
An exhaust diffuser for an axial flow turbomachine, characterized in that a concave R-curvature surface and a convex R-curvature surface are formed with respect to a flow path. (2) A concave R-curvature surface is formed on the wall surface of the root flow guide forming the exhaust diffuser flow path, and a convex R-curvature surface is formed on the wall surface of the bearing cone. axial flow turbomachinery exhaust diffuser. (3) The axial flow turbo according to claim 1, characterized in that a concave R-curvature surface and a convex R-curvature surface are formed in tandem on the wall surface of the root flow guide forming the exhaust diffuser flow path. Mechanical exhaust diffuser. (4) Claim 1, characterized in that an ejection groove for eliminating a boundary layer or separation fluid is provided in the middle of the flow path of a chip flow guide that forms an exhaust diffuser flow path facing the root flow guide. Exhaust diffuser for axial flow turbomachinery as described.