JPH11200810A - Labyrinth seal mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a gas leakage amount to the minimum with a simple structure requiring a reduced machining manday and precluding the possibility of generation of contact between a seal fin and a rotary part, or the like. SOLUTION: In a labyrinth seal mechanism to seal leakage gas between an inner circumference of a seal fin 1 and an outer circumferential face 4a of a rotary shaft by facing the seal fin 1 thin-walled and supported to a stationary body to the outer circumferential face 4a of the rotary shaft, and by providing plural number of them along the axial direction of the rotary shaft, a step 5 caved-in from the outer circumferential face 4a opposing to the seal fin 1 toward its shaft center is formed in a position with a fixed distance from the side face of the seal fin 1 toward a gas upperstream.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a labyrinth seal device for a rotary machine such as an axial compressor or a steam turbine.

[0002]

2. Description of the Related Art In a rotary machine such as an axial turbomachine or a steam turbine, a labyrinth seal is often used to seal gas between an outer peripheral surface of a rotating shaft (rotor) and a stationary member such as a casing. .

FIGS. 3 and 4 show an example of a seal portion between a rotor disk and a vane shroud in a low pressure final stage of a steam turbine. FIG. FIG. 4 is an enlarged view of a portion Z in FIG. 3 and 4, reference numeral 2 denotes a rotor that rotates at high speed, and reference numerals 4 and 4 denote low-pressure stage rotor disks fixed to the rotor 2. Reference numeral 6 denotes a low pressure final stage stationary blade, the inner peripheral side of which is fixed to a ring-shaped stationary blade shroud 3. 15 is a moving blade.

Reference numeral 1 denotes a thin annular seal fin formed in the inner periphery of the stationary blade shroud 3, and a labyrinth seal type seal in which a plurality of (three in this example) rows are arranged in the axial direction of the rotor disk 4. Fins.

An appropriate gap B is provided between the outer circumference 4a of the rotor disk 4 and the inner circumference of the seal fin 1, and the gap B is formed between the seal fin 1 and the outer circumference of the rotor disk 4. It is set so as to avoid contact and minimize leakage of gas (steam) 6. In FIG.
Reference numeral 1 denotes a gas vortex in the space between the seal fins 1.

FIGS. 5 to 10 show a conventional example of a labyrinth seal mechanism between the seal fin 1 and the rotor 2 (or the rotor disk 4).

FIG. 5 shows a model similar to that of FIG. 4, in which a plurality of seal fins 1 are provided opposite to each other with a gap B around the outer periphery of a rotor 2.

In FIG. 6, a plurality of annular grooves 2a are engraved on the outer periphery of the rotor 2 and the inner periphery of the seal fin 1 is formed in the grooves 2a.
The gaps B are opposed to the land portions between the seal fins 1 and 1 and the cavity flows 23 and 2 are formed between the seal fins 1 and 1 and in the groove 2a.
4 is formed to reduce the amount of gas leakage.

In FIG. 7, a plurality of seal fins 1 provided on the stationary blade shroud 3 are inclined toward the gas inflow side in the axial direction to reduce the amount of gas leakage.

8 and 9, the seal fin 1 is cut off obliquely to form an inclined surface 1a so as to form a wedge-shaped seal fin 1 as a whole, thereby reducing the amount of leakage through the gap B. ing.

In FIG. 10, a seal fin 2a provided on an outer periphery of a rotor 2 is projected between seal fins 1 and 1 provided on a stationary blade shroud 3 so that gas flows zigzag through gaps B and C. To reduce the amount of gas leakage.

[0012]

However, the conventional labyrinth seal mechanism shown in FIGS. 5 to 10 has the following problems. That is, the structure shown in FIG. 4 has a simple structure and requires a small number of processing steps. However, since the gas leakage flow path is a simple one-way flow path, even if the gap B is minimized, the gas leakage amount is small. Not less, the sealing mechanism is low.

In FIG. 6, since the rotor 2 is provided with the groove 2a, the strength of the rotor 2 is reduced and the groove 2a is formed.
It requires man-hours for processing. 7 shows the rotor 2
Rotate, the leakage amount increases to the same extent as in FIG.

8 and 9, it is difficult to machine the tip of the seal fin 1. Further, in FIG. 10, the seal fins 1 or 2a are provided on both the rotor 2 and the stationary blade shroud 3, so that a large number of processing steps are required, and the seal fins 1 And 2a may come into contact with each other.

An object of the present invention is to reduce the amount of gas leakage to a minimum by using a structure having a simple structure, a small number of processing steps, and no risk of contact between the seal fin and the rotating part. An object of the present invention is to provide a labyrinth seal mechanism.

[0016]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The gist of the invention is to provide a thin seal fin supported by a stationary object and formed on the outer peripheral surface of a rotating shaft. A labyrinth seal mechanism, which is opposed to and is provided along the axial direction of the rotating shaft, and seals leakage gas between an inner periphery of the seal fin and an outer peripheral surface of the rotating shaft. Is formed at a predetermined distance from the side surface of the seal fin near the upstream side of the leak gas toward the upstream side of the leak gas, the step being depressed toward the axial center from the outer peripheral surface facing the seal fin. The labyrinth seal mechanism is characterized in that it is formed.

In the above means, the distance (S) at which the step is provided is set to be 2 to 15 times the gap (B) between the inner periphery of the seal fin and the outer peripheral surface of the rotating shaft opposed thereto. Is preferred.

According to the above means, the leaked gas flows along the surface of the rotating body, but its boundary layer has a strong rotating component, and when this reaches the step, it forms an outward flow by centrifugal force. . The outward flow is separated into a flow toward the opposite side of the seal fin and a flow to be sucked into the seal fin by the differential pressure, and the seal fin has the above-mentioned separated component toward the rotation center. Flow flows in. Due to the flow toward the rotation center direction, a gap of the flow is generated in the gap at the tip of the seal fin, and the effective cross-sectional area of the flow in the gap decreases,
This reduces the amount of gas leakage.

By setting the position of the step in the axial direction to be at least twice and not more than 15 times the seal fin gap (B), the step is directed toward the center of rotation separated from the outward flow formed by the step. The flow can be reliably formed.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 3 is a cross-sectional view of a main part near a low-pressure final stage of a steam turbine to which the present invention is applied. In FIG.
Reference numeral 4 denotes a low-pressure rotor disk fixed to the rotor 2. Reference numeral 6 denotes a low pressure final stage stationary blade fixed to the ring-shaped stationary blade shroud 3 on the inner peripheral side. 15 is a moving blade.

Reference numeral 1 denotes a thin annular seal fin formed on the inner periphery of the stationary blade shroud 3, and a plurality of (three in this example) labyrinth seal type seals are arranged in the axial direction of the rotor disk 4. Fins.

An appropriate gap B is provided between the outer periphery 4a of the rotor disk 4 and the inner periphery of the seal fin 1, and this gap B is provided for contact between the seal fin 1 and the outer periphery of the rotor disk 4. Is set so that leakage of gas (steam) 6 is minimized. The above configuration is shown in FIG.
Is the same as the conventional one shown in FIG.

In the embodiment of the present invention, the shape of the rotor disk (or rotor) facing the seal fin 1 is improved. That is, in FIGS. 1 and 2, reference numeral 5 denotes an annular step formed on the rotor disk 4. The step 5 is formed by shaving a predetermined depth D from the outer peripheral surface 4a of the rotor disk 4 at a position of a distance S from the side surface of the seal fin 1 on the gas upstream side to the upstream side of the gas, and forming the recess. I have. The position S of the step 5 is defined by the inner periphery of the seal fin 1 and the outer peripheral surface 4 of the rotor disk 4.
It is preferable that the gap is set to be 2 to 15 times the gap B with respect to a.

During operation of the steam turbine provided with the labyrinth seal mechanism configured as described above,
That is, from the outer peripheral side of the rotor disk 4
The gas flowing along the surface of the disk has a strong rotation component in the boundary layer due to the rotation of the rotor disk 4. When the gas having such a rotation component reaches step 5,
The centrifugal force results in an upward flow 15 shown in FIG.

This flow 15 is separated into a flow 12 going in the opposite direction of the seal fin 1 and a flow 13 that is about to be sucked into the seal fin 1 by a differential pressure. It flows in as a component toward the rotation center (downward). Due to the generation of the flow 13 directed toward the center of rotation, a flow gap is formed at the tip of the seal fin 1 in the gap B on the inner periphery of the seal fin 1, the effective cross-sectional area of the flow in the gap B is reduced, and the gas The leakage flow is reduced.

This phenomenon occurs because the centrifugal force of the gas increases and the gas flow velocity increases as the rotation speed of the rotor disk 4 increases, so that the reduction amount of the effective area increases and the gas leakage increases. The effect of reducing the amount is obtained.

The reason that the distance S is set to be 2 to 15 times the gap B is that the outer circumferential flow 15 formed in the step 5 is separated from the vortex 12 to form the center flow 13. Requires a distance that is at least twice as large as the gap B, and if this distance S is greater than 15 times B above, no flow toward the center occurs after the above separation, and the flow becomes parallel to the axis. This is because the effect of reducing the effective area is lost.

In the step 5, when the seal fin 1 is provided on the stationary blade shroud 3, as in this embodiment,
Although provided on the rotor disk 4 or the rotor 2, the seal fins 1 can be provided on all the labyrinth seal mechanisms that seal the gas by providing the seal fins 1 on a stationary object facing the outer periphery of the rotating body.

[0029]

The present invention is configured as described above.
According to the present invention, the outward flow of the leakage gas is formed by the steps provided on the outer periphery of the rotating body,
A flow toward the center of rotation separated from the outward flow is formed in the seal fin gap, and the effective passage area of the seal fin gap through which this flow flows is reduced. As a result, the amount of gas leaking through the seal fin gap is reduced.

Therefore, according to the present invention, the amount of gas leakage is reduced as compared with the conventional one by means of providing a step on the outer periphery of the rotating body, which has a very simple structure and does not increase the number of processing steps. A labyrinth seal mechanism can be obtained.

If the installation position of the step is set as in claim 2, a flow from the outward flow toward the center of rotation can be surely formed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a labyrinth seal mechanism of a steam turbine according to an embodiment of the present invention.

FIG. 2 is an operation explanatory view in the embodiment.

FIG. 3 is a sectional view of a main part in the vicinity of the last stage of the steam turbine low pressure.

FIG. 4 is an enlarged sectional view of a portion Z in FIG. 3;

FIG. 5 is a sectional view of a main part showing a first example of a conventional labyrinth seal mechanism.

FIG. 6 is a sectional view of a main part showing a second example of a conventional labyrinth seal mechanism.

FIG. 7 is a sectional view of a main part showing a third example of a conventional labyrinth seal mechanism.

FIG. 8 is a sectional view showing a main part of a fourth example of a conventional labyrinth seal mechanism.

FIG. 9 is an enlarged view of a portion W in FIG. 8;

FIG. 10 is a sectional view showing a main part of a fifth example of a conventional labyrinth seal mechanism.

[Explanation of symbols]

 Reference Signs List 1 seal fin 2 rotor 3 stationary blade shroud 4 rotor disk 4a outer peripheral surface 5 step 15 rotor blade

Claims (2)

[Claims] A thin seal fin supported by a stationary object and formed in a thin-walled shape is opposed to an outer peripheral surface of a rotating shaft, and is provided in plural numbers along an axial direction of the rotating shaft. And a labyrinth seal mechanism configured to seal the leak gas between the outer peripheral surface of the rotary shaft and the outer peripheral surface of the rotary shaft. A labyrinth seal mechanism, wherein a step depressed toward an axial center side from an outer peripheral surface facing the seal fin is formed at a position at a fixed distance. 2. A distance (S) at which the step is provided is configured to be twice to 15 times a gap (B) between an inner periphery of the seal fin and an outer peripheral surface of a rotating shaft opposed thereto. 2. The labyrinth seal mechanism according to 1.