JPH03107504A - Fluid leak preventing device for axial flow turbine - Google Patents

Abstract

PURPOSE:To reduce a leak loss so as to enhance turbine stage efficiency by leading fluid in the inlet of a stationary blade to the vicinity of the downstream end in a peripheral axial direction of a bucket cover to eject the fluid toward the upstream in the axial direction. CONSTITUTION:Static diaphragm outer and inner rings 3 and 4 hold a stationary blade 2. A bucket 1 is disposed downstream of the corresponding stationary blade 2. A bucket cover 5 is attached to the tip end of the bucket 1. A seal fin 7 is embedded in the diaphragm outer ring 3 located outside of the bucket cover 5. With this arrangement, a passage 9 communicated from the upstream of the stationary blade 2 toward the outlet of the bucket 1 is formed in the diaphragm outer ring 3. An annular nozzle 10 is interposed between the disphragm outer ring 3 and a cover 8. High pressure steam is ejected from the annular nozzle 10 toward the seal fin 7, thereby preventing any lead of fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a leakage prevention device for a radial gap between the outer peripheral surface of a bucket cover and the inner surface of a diaphragm outer ring of an axial fluid machine.

[Conventional technology]

A turbine performs useful work when the flow that has passed through multiple stator blades attached to a diaphragm passes through multiple moving blades attached to a rotor. An annular bucket cover is attached to the circumferential direction of the tip. This bucket cover has an opening into which a tenon provided at the tip of each rotor blade is fitted, and after fitting, each canon passing through the opening is fixed by hammering out each canon with a hammer. The bucket cover also forces a radial flow of accelerated flow within the rotor blades, so that a portion of the turbine working fluid passes through the flow path defined by the rotor blades and the packet cover. Instead, after passing through the stationary blades, the leakage flow flows in the radial direction and flows in the axial direction on the outer circumferential surface of the bucket cover. This leakage flow is a flow that does not perform useful work, and in the turbine structure, in order to increase turbine efficiency,
A labyrinth seal structure is used to suppress leakage from around the radial tips of rotor blades in turbines.
Nowadays, means to minimize leakage are constantly being sought. However, although the labyrinth seal structure can reduce the amount of leakage, it is impossible to eliminate it.

As a method to improve this, Soviet Patent No. 5U1188
As described in No. 337-A, a passage is provided that connects the diaphragm outer periphery of the stator blade flow to the diaphragm outer periphery of the stator blade outlet (rotor blade inlet), and the high pressure fluid upstream of the stator blade is directed to the rotor blade inlet side. A method is used to reduce the leakage flow that flows in the axial direction on the outer circumference of the bucket cover by guiding it onto the outer circumference of the bucket cover.

[Problem to be solved by the invention]

The above conventional technology reduces the leakage flow that flows in the radial direction after passing through the stator blades without passing through the flow path defined by the rotor blades and the bucket cover, and flows in the axial direction around the outer circumference of the bucket cover. However, it has not yet been possible to eliminate the leakage flow that flows in the axial direction on the outer circumference of the bucket cover, including the fluid led from the first flow of the stator blade.

An object of the present invention is to provide an axial flow turbine that uses leakage flow flowing axially downstream on the outer periphery of a bucket cover to relatively increase the flow rate into the packet to perform effective work and improve turbine efficiency. An object of the present invention is to provide a fluid leakage prevention device.

[Means to solve the problem]

In order to achieve the above objective, a flow path is provided that communicates from the outer periphery of the diaphragm upstream of the stator blade to the outer periphery of the diaphragm at the outlet of the rotor blade, and an annular nozzle is formed at the outlet end of this flow path to allow the high-pressure fluid upstream of the stator blade to flow. is ejected from an annular nozzle into the seal fin gap so that the fluid flows over the outer circumference of the bucket cover from the downstream side to the upstream side.

[Effect]

In an axial flow turbine, when the working fluid passes through the stationary blades, the pressure is converted into velocity energy, which increases the speed and performs impulse work on the rotor blades.As it passes through the rotor blades, the pressure further decreases, increasing the speed. It flows out and does reaction work. Therefore, the pressure of the working fluid is highest at the inlet of the stator blade, and becomes lower at the outlet of the stator blade and the rotor blade. -4- On the other hand, if high-pressure steam at the stator blade inlet flows out as a jet to the rotor blade outlet through the bypass passage, the static pressure becomes equal to the rotor blade outlet pressure, but the total pressure is not doing work inside the rotor blade, so , even if friction loss in the bypass flow path is taken into consideration, the pressure will be higher than the stator blade outlet pressure. Therefore, when this jet is ejected into the gap between the outer peripheral surface of the bucket 1 cover and the seal fin, it overcomes the pressure at the stator blade outlet and moves the seal fin part from the downstream side of the rotor blade outlet to the upstream side of the stator blade outlet. It is possible to flow in the opposite direction to the main flow inside the wing.

This makes it possible to almost eliminate leakage flowing downstream in the axial direction without applying any work to the outer circumferential surface of the bucket cover.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a sectional view showing a main part of the embodiment, in which a stationary diaphragm outer ring 3 and an inner shaft 4 hold two plurality of stationary blades arranged in the circumferential direction.

A plurality of rotatable rotor blades 1 are arranged downstream of the corresponding stationary blades 2 in the flow direction.

The tip of the moving blade 1 is inclined because the diameter on the outlet side is large, and a bucket cover 5 is provided at this inclined tip.
This connects the plurality of rotor blades 1. That is, the bucket 1 to the cover 5 have a plurality of openings in the circumferential direction,
After the tenons 6 protruding from the outer ends of the rotor blades 1 pass through these openings and project outwards, the tenons 6 are pinched.

The bucket cover 5 has a radius of -
A flat portion 11 having a similar shape is formed. A seal fin 7 is embedded in the outer diaphragm ring on the outer periphery. Further, the diaphragm outer ring 3 is provided with a flow path 9 communicating from the upstream side of the stationary blade 2 to the rotor blade outlet, and furthermore, an annular nozzle 10 is formed between the cover 8 and the diaphragm outer ring 3.

FIG. 2 shows an enlarged view of the seal portion in FIG. 1. In this diagram,
The width 1 of the annular nozzle 1o formed by the cover 8 and the diaphragm outer ring 3 is slightly smaller than the gap 8 formed by the flat part 11 on the outer periphery of the packet cover and the seal fin 7. On the other hand, the jet stream is formed inward.

As a result, the high-pressure steam at the inlet of the stationary blade is guided to the annular nozzle 10 through the flow path 9, and is ejected from the annular nozzle 1o toward the gap between the reseal fins 7.

The ejected steam passes through the gap δ between the seal fins 7 and flows toward the rotor blade inlet side as indicated by the streamlines of arrows.

Here, the pressure on the upstream side (rotor blade inlet side) of the seal fin 7 is higher than the pressure at the outlet part of the annular nozzle 10 (rotor blade outlet side), but the total pressure of the jet is higher than that on the first flow side of the seal fin 7. Therefore, the jet can be guided to the upstream side of the seal fin 7 by the kinetic energy of the jet. As a result, fluid leakage can be prevented from the upstream side of the seal fins 7 where the pressure is high to the downstream side of the seal fins 7 where the pressure is low.

FIG. 3 is an expansion diagram for explaining the effects of this implementation. First, fluid leaking from the tip of a conventional rotor blade expands as shown by the chain line. That is, the fluid at the tip inlet of the stator vane 2 is at a zero point with a pressure PO, and is accelerated within the stator vane and reaches a state at a' point with a pressure PN. Since the leakage flow is diverted from the main stream and guided to the seal fin inlet, the kinetic energy held at the stationary blade outlet becomes thermal energy, resulting in the state at point b. Furthermore, the jet flow expands to the pressure PB on the rotor blade outlet side in the gap between the seal fins 7 and reaches the state C', but this jet becomes a vortex at the seal fin outlet and reaches the state at point d. Therefore, the leaking fluid does not perform any work, resulting in a loss of LE' due to the heat drop.

On the other hand, in this embodiment, expansion is performed as shown by the solid line. The fluid at the 0 point at the tip inlet of the stationary blade 2 flows through the annular nozzle 10.
The state at point a is reached at the exit. This jet flow passes through the seal fin gap and flows upstream of the seal fin, and the pressure is restored to PN, resulting in the state at point b. This bypass flow flows inside the rotor blade together with the main flow and reaches a zero point state.
Only the heat drop UE works. Therefore, the loss is the heat drop LE
Therefore, compared to the conventional structure, the loss due to the thermal drop can be reduced by the UE. From this result, the present invention has a large effect in the stage where the degree of reaction at the tip of the rotor blade is high, as in a low-pressure steam turbine.

FIG. 4 shows another embodiment of the present invention, in which the sealing parakeet 3
The tip of the nozzle is inclined, forming an oblique annular nozzle 14 between the cover 12 and the cover 12. In this embodiment, since the jet stream is inclined with respect to the outer peripheral surface of the cover 5, the leakage prevention force is slightly reduced.
Although it is smaller, it is effective for a stage where the degree of recoil is slightly lower than that of the embodiments shown in FIGS. 1 and 2.

[Effects of the Invention] The present invention provides a device for preventing fluid leakage from the outer periphery of the cover to the bucket 1 by guiding the fluid on the inlet side of the stator blade to the vicinity of the downstream end of the outer periphery of the bucket cover in the axial direction and ejecting it to the upstream side in the axial direction. , reduce leakage loss, and increase the turbine stage efficiency from 1 to 1, especially in low-pressure steam turbines with high rotor blade tip reaction.
It can be improved by 2%.

[Brief explanation of drawings]

Fig. 1 is a partial sectional view of an embodiment of the fluid leakage prevention device of the present invention, Fig. 2 is a partially enlarged view of Fig. 1, Fig. 3 is an expansion line diagram explaining the present invention in detail, and Fig. 4. FIG. 3 is a partial cross-sectional view of another embodiment of the present invention. 1. Moving blade, 2. Stationary blade, 3. Diaphragm outer ring, 5.
・・Bucket cover, 7.・Seal fin, ・Cover

Claims (1)

[Scope of Claims] 1. In a fluid leakage prevention device for an axial flow turbine that includes a seal fin on the wall surface of a diaphragm outer ring located outside a bucket cover, an annular nozzle is formed at the downstream end of the outer periphery of the bucket cover in the axial direction. A fluid leakage prevention device for an axial turbine, characterized in that a flow path communicating between a stator blade inlet and the annular nozzle is provided in the diaphragm outer ring. 2. The axial flow turbine according to claim 1, wherein fluid flows from the downstream side to the upstream side of the axial flow turbine at an outer periphery of the bucket cover corresponding to the seal fin. Fluid leak prevention device.