JPH04214905A - Honeycomb-shaped labyrinth seal for steam turbine - Google Patents

Abstract

PURPOSE: To allow an exhaust water passage for the water gathered by a seal to direct the water stream at the outlet not in the axial direction but outward in the radial direction. CONSTITUTION: A honeycomb-shaped labyrinth seal 3 is equipped with a lowermost downstream row of honeycomb cells 9 extending beyond the outlet edge 20 of the base part 7, and each of the cells in the lowermost understream row is partially overhung from the base part 7 in an amount approx. equal to half the width of a drain passage 11 formed in the base part 7.

Description

[Detailed description of the invention]

0001

[Background of the invention]

FIELD OF THE INVENTION This invention relates to honeycomb labyrinth seals, and more particularly to improved seals for use in low pressure steam turbines.

0002

2. Description of the Related Art A grooved honeycomb labyrinth seal for a steam turbine is described in U.S. Pat. No. 4,416,457.

Referring to FIGS. 1 and 2 in the accompanying drawings,
The honeycomb labyrinth seal 3 described in the above-mentioned US patent includes a base portion 7 and a plurality of honeycombs extending radially inwardly from the base portion 7 and each opening adjacent to a wing 1. It is formed from a plurality of arc-shaped segments including rows of shaped cells 9. The plurality of passages or grooves 11 are arranged such that each cell 9 communicates with at least one groove 11 and the majority of cells communicate with two grooves 11. In the figure, the left groove 11
are open to the upstream side, while the groove 11 on the right side in the figure is open to the downstream side, and there is an interconnection between the groove 11 and the cell 9, which allows the steam and its entrained moisture is allowed to flow from the upstream side of the seal across the base portion 7 of the seal to the downstream side of the seal. Cell 9 has a generally hexagonal shape with six walls, some of which form a common wall for adjacent cells.

Axial gaps 13 are provided between circumferentially adjacent segments of the honeycomb labyrinth seal, which allow water collected in the grooves 11 to drain therefrom. be able to. The blade ring 5 is also provided with a suitable drain (not shown) in order to drain water from the seal groove 4 formed in the blade ring 5.

FIG. 3 shows a typical arrangement for existing honeycomb seal structures in steam turbine blade rows. A radial step is formed between the outer diameter of the downstream stationary blade 16 and the inner diameter of the seal. Radial passages are formed between surfaces 12 and 12a for the purpose of removing steam and moisture from the flow in the blade rows. It is difficult to achieve efficient swirling of the fluid leaving the tip region of the rotor (located on the underside of the seal) and therefore it is difficult for moisture to flow into the moisture removal and extraction slot 14. Therefore, turbulent flow conditions may occur in the above-mentioned region.

It is naturally conceivable that the moisture discharged from the seal follows a flow path in the approximately axial direction and is mixed into the main steam flow on the downstream side via the stationary vane 16 and is accompanied by it. Moisture erosion damage can occur on rotor blades or blades.

As a result of observing the flow field behavior and moisture erosion characteristics downstream of a typical honeycomb seal installation location, it was found that It has been found that turbulent flow patterns (standing eddies) can exist in conjunction with radial steps. Also, the moisture collected by the seal cannot flow into the moisture removal or extraction slot on the swirl side as expected. These two phenomena can be attributed to the sharp 90° corner at the exit edge of the seal, which limits the ability to jump over it to extract steam and divert moisture flow. It will be done.

[0008]

SUMMARY OF THE INVENTION One object of the present invention is to provide an improved honeycomb labyrinth seal in which a drainage passage for moisture collected by the seal directs water flow at the outlet in a radially outward direction rather than in an axial direction. It is about providing.

Another object of the present invention is to utilize the centrifugal force effect of the rotor blades to promote radially outward flow of steam and condensate from the blade tip region near the outlet edge. An object of the present invention is to provide a honeycomb labyrinth seal with an improved structure.

The foregoing and other objects of the present invention provide a honeycomb labyrinth seal associated with a rotatable steam turbine blade, comprising: a base portion having an inlet edge and an outlet edge; a plurality of rows of honeycomb-like cells extending radially inwardly from the base portion, each cell being open adjacent the wing; each cell being connected to at least one passageway; opens upstream of the row of honeycomb cells, and at least one passage opens downstream of the row of honeycomb cells, such that steam passes through the passages and cells from the upstream side of the honeycomb labyrinth seal to the downstream side of the honeycomb labyrinth seal. a plurality of said passageways arranged such that the downstream-most row of honeycomb cells extends beyond an outlet edge of said base portion or an outlet of a rotor; This is achieved by providing a honeycomb labyrinth seal whose edges extend beyond the honeycomb labyrinth seal.

The above objects and advantages of the honeycomb labyrinth seal of the present invention will become more apparent upon reference to the following detailed description and accompanying drawings.

0012

[Detailed description of the preferred embodiment]

4-7, the honeycomb labyrinth seal 3 is connected via the base portion 7 to the seal support ring 5a by conventional means. A moisture removal and extraction slot opening 14 is formed adjacent to the upstream stator vane 18 and between the downstream stator vane 16 and the seal support ring 5a. The rotor blades 1 rotate in a direction perpendicular to the flow direction.

A plurality of passages are provided in the base portion 7 by grooves 11 . Each labyrinth seal 3 includes a base portion 7 and a plurality of rows of honeycomb-like cells 9 extending radially inwardly from the base portion 7 and each opening adjacent to the rotor blade 1 . It is formed from arc-shaped segments. Each cell 9 is connected to at least one passageway 11.

[0014] The base part 7 has an outlet edge 20. In this connection, in the case of the known seals described with reference to FIGS. 1 to 3, the corresponding outlet edges 20 project beyond the honeycomb cells, the most downstream row of the honeycomb cells being the most The cells were aligned on the downstream grooves 11 and supported on the base portion 7 with their most downstream sides.

In contrast, according to the invention, the most downstream row 9a of the honeycomb cells 9 is aligned above the strip 7a of the base part on the outlet side, which strip 7a is substantially equal to the width of the groove 11. ), so that column 9
A portion of the cell in a extends from the base portion 7. This arrangement reduces the internal drainage for these alternating cell groups with cell wall elements aligned and circumferentially arranged above the drainage channels 11. In this way,
The outlet side wastewater flow is directed radially as it leaves the honeycomb cells from the outlet side. A radial drainage channel is defined between the outlet edge 20 of the base portion 7 and the outermost wall 22 of the cells 9 in the row 9a (FIG. 6). The stream of water droplets ejected outwardly by centrifugal force from the tips of the rotor blades and impinging on the open surfaces of the honeycomb cells 9 promotes a radially outward flow relative to the drainage stream on the exit side of the seal.

FIG. 7 is a diagram illustrating circumferential-axial drainage connections for all cell groups adjacent to the cells shown in FIG. 6.

In general, the desired internal drainage characteristics for seal 3 include the inlet-outlet pressure drop across the rotor row and the outward flow generated by water droplets leaving the blade tips and entering the open faces of the honeycomb-like cell structure. Determined by pressure.

Preferably, the most downstream or outlet row of honeycomb cells protrudes or extends beyond the outlet edge 20 of the base portion 7 by approximately one half of the channel width.

Referring to FIG. 4, the wing 1 is shown in FIGS. 1 and 2.
Advantageously, it extends beyond the seal 3, rather than being aligned with the underside of the seal as in the known seal shown in FIG. Furthermore, the amount of extension is determined by the cross-sectional width of the tip, and the optimum amount of extension of the blade 1 is advantageously determined in relation to the width of the throat opening. The overhang of the exit edge of the rotor blade enhances the effectiveness of the seal exit drainage channel in the radially outward direction due to the pressure from the centrifuged water droplet stream leaving the blade tip. The edge flare on the exit side of the rotor blade also promotes radial expansion of the steam flow immediately downstream of the seal 3. This tends to direct the flow in the direction of the moisture removal/extraction slot 14, and near the large diameter surface at the inlet there is a flow condition that exhibits good behavior (low loss) for the downstream stator blade row. occurs.

According to the present invention, the width of the downstream moisture removal/extraction slot can be increased, or alternatively, if the moisture removal/extraction slot is an important constraining factor,
Due to the upstream displacement of the exit edge 20 of the seal to the rotor blade and the exit surface 12 of the blade ring (FIG. 4), the axial spacing of the blade row can be reduced.

Numerous variations and adaptations of the invention will occur to those skilled in the art. Therefore, it is noted that all such modifications and adaptations are encompassed by the scope of the present invention as long as they do not depart from the scope and spirit of the present invention.

[Brief explanation of the drawing]

1 is a partial cross-sectional view of a known honeycomb labyrinth seal located in a section of a steam turbine along line II--I in FIG. 2;

FIG. 2 is a plan view of the labyrinth seal of FIG. 1;

FIG. 3 is a partially cutaway side view showing a honeycomb labyrinth seal used before the present invention.

FIG. 4 is a partially cutaway side view of a honeycomb labyrinth seal according to a preferred embodiment of the present invention.

FIG. 5 is an enlarged top view showing a portion of the labyrinth seal of FIG. 4;

FIG. 6 is a cross-sectional view taken along line V-V in FIG. 5;

FIG. 7 is a cross-sectional view taken along line VI-VI in FIG. 5;

[Explanation of symbols]

1 Rotating blade or moving blade (steam turbine blade) 3 Honeycomb labyrinth seal 7
Base portion 9 Honeycomb-shaped cells 9a Downstream cell row 11 Groove (passage) 20 Outlet edge

Claims (2)

[Claims] 1. A honeycomb labyrinth seal associated with a rotatable steam turbine blade, comprising: a base portion having an inlet edge and an outlet edge; a plurality of rows of honeycomb-shaped cells extending in a direction, each cell being open adjacent the wing; and a plurality of passageways, each cell connected to at least one passageway, the at least one passageway being connected to the wing; open upstream of the honeycomb row of cells, and at least one passageway opens downstream of the honeycomb row of cells, such that steam passes through the passageways and cells from the upstream side of the honeycomb labyrinth seal to the downstream side of the honeycomb labyrinth seal. said plurality of passages arranged to permit flow of gas, said plurality of passages being arranged to permit flow of gas, said plurality of passages being arranged to permit said flow, said downstream-most row of honeycomb cells extending beyond an outlet edge of said base portion. Honeycomb labyrinth seal. 2. A honeycomb labyrinth seal associated with a rotatable steam turbine blade, comprising: a base portion having an inlet edge and an outlet edge; and a base portion having an inlet edge and an outlet edge; a plurality of rows of honeycomb-like cells extending inwardly, each cell being open adjacent the wing; and a plurality of passageways, each cell connected to at least one passageway; opens upstream of the array of honeycomb cells, and at least one passage opens downstream of the array of honeycomb cells, such that steam passes through the passages and cells from the upstream side of the honeycomb labyrinth seal to the downstream side of the honeycomb labyrinth seal. said plurality of passages arranged to permit the flow of steam, each rotor having an outlet edge extending beyond the most downstream row of honeycomb cells. Honeycomb labyrinth seal for turbines.