Compressor Blade Root Seal

Abstract

A sealing device for restricting leakage across the stages of an axial coessor through the clearances around the root fittings of replaceable blades. A compliant dished annulus is attached on the high pressure side of each compressor stage at its inside radius. The combination of centrifugal force and pressure differential across each compressor stage deforms the sealing device against the blade root fittings thereby restricting the leakage.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in axial compressors, and more particularly to a sealing device for restricting blade root fitting leakage in compressor rotor stages having removable blades.

Axial gas turbine compressor rotors commonly use dovetail broached slots for the attachment of the blades to the rotor disk. This attachment technique is used for the purpose of facilitating blade replacement. Consequently in order to accommodate the normal manufacturing tolerances of the blade root fitting a clearance is necessary in each slot. The result is that some of the compressed gas behind each compressor stage leaks back through these clearances into the preceding stage reducing substantially the overall efficiency of the gas turbine power plant. In particular where the pressure increment across the stage is large the leakage rate becomes significant, thus degradation of compressor efficiency is not minimized by staging optimization.

Various techniques of providing blade root sealing have been developed within the prior art to limit this leakage. Most of these techniques provide individual sealing devices attached at each blade root, thereby multiplying the number of components in a compressor with the attendant problems of reliability and weight.

SUMMARY OF THE INVENTION

Accordingly, it is the general purpose and object of the present invention to provide a blade root seal integrally formed as one unit. Other objects are to provide a blade root seal that is durable, replaceable and minimally affecting the existing compressor disc parameters.

These and other objects are accomplished according to the present invention by providing an annular seal generally dished to conform with the convolutions of the blade attachment rim of the compressor disc attached on the high pressure side thereof. The seal is formed from a compliant material such as metal foil and is pressed into sealing contact by the combination of the pressure differential across the stage and the centrifugal force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall side view of an axial compressor shown partly in cross section illustrating a three stage compressor;

FIG. 2 is a plan view of a fragment of a compressor disc assembly as viewed from the high pressure side along section 2--2 of FIG. 1; and

FIG. 3 is an enlarged fragmentary view in cross section of the compressor disc assembly taken along section 2--2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 an axial compressor section 25 of a gas turbine is contained within the compressor housing 26. A rotor unit consisting of three compressor disc assemblies 10 mounted on a rotor shaft is enclosed by the housing 26 having stator rings 27 mounted to the housing 26 interspaced between adjacent assemblies 10. Each compressor disc assembly 10 includes blades 16 peripherally mounted on a disc 15 having an annular seal 11 covering the high pressure side of the blade mounting interface according to the present invention.

As shown in more detail in FIG. 2 each compressor disc assembly 10 includes a plurality of removable blades 16 radially extending from mounting slots 12 formed in a peripheral flange 14 of a disc 15. Each blade 16 includes a root end fitting 17 formed to engage in locking arrangement the convolutions of the slot 12. A locking device 19 commonly engages each blade 16 to disc 15. Each blade root fitting 17 is shown in partial contact with the convolutions of the slot 12 generally in the areas of radial stress force transfer path being placed in abutment therewith either by the centrifugal force generated by the rotation of disc 15 or by the locking mechanism 19. Thus the blade 16 is located in the slot 12 in a manner that produces the highest leakage rates if clearances exist between the convolutions of the slot 12 and the blade root fitting 17. As illustrated each blade root end fitting 17 is dimensionally limited to allow for clearances 18 as is necessary to accommodate various manufacturing tolerances. The total area of clearances 18, which typically accumulates to an order of magnitude of approximately 1 to 2 square inches in a medium sized jet power plant, is a primary source of unwanted pressure leakage across the compressor disc. To limit this leakage a thin foil annular seal 11 is installed according to the present invention extending outwardly from rim 14.

Referring to FIG. 3 the peripheral rim 14 of disc 15 typically increases in cross section with increasing radius in order to most effectively transmit the bearing forces generated by the angular motion of the blades 16 within corresponding slots 12. Accordingly, the seal 11 placed across the slots 12 will be pressed against the blade roots 17 by centrifugal force C.F. Seal 11 is formed out of thin metal sheet stock of a thickness sufficient to straddle the clearances 18, attached by diffusion bonding at the inside radius thereof to the inside radius of the peripheral flange of disc 15, being preformed in the shape of a concave annulus to generally mate with the convolutions of the flange and is placed in sealing contact therewith by the centrifugal force C.F. and pressure differential .DELTA.P. The outer radius of seal 11 is formed to provide a sealing lip 20 thereby increasing the centrifugal mass on the exterior radius of the seal and providing an easily deformable localized bearing surface.

In operation each compressor disc assembly 10 comprises one stage within a multistage axial compressor. Each stage progressively compresses the intake air, thus the radial dimension of the disc 15 and the size of blades 16 are adjusted to conform with the theoretical volumetric decrease of the gas upon compression. Accordingly, the leakage rate for the same mass flow rate within any stage increases with the pressure differential across that stage since the leakage area is generally constant. The present invention utilizes this pressure differential .DELTA.P across the compressor stage in order to provide sealing. The inventive seal 11 is formed from a metallic foil in the order to 2 to 3 mills thick attached by diffusion bonding at the inside radius thereof to the peripheral flange 14 of disc 15. Although other methods of bonding are possible within the scope of the present invention diffusion bonding offers the best compromise of durability and weight. The installation of blade locks 19 can be performed through the open side of the disc, however, in the case where blade lock insertion is necessarily from the sealed side appropriate openings, where necessary, are provided in the seal. Blade replacement is not restricted by the seal since the installation can be from either side in view of the flexibility of seal 11.

Some of the many advantages of the present invention should now be readily apparent. The inventive seal reduces leakage across the compressor stages of a gas turbine engine, characteristically a major concern in the development of gas turbines, without affecting the critical design parameters of the compressor disc itself such as stress distribution, changing of disc modes and disc loading. Thus the seal is adaptable to be installed on existing compressors without entailing large expenses in disc alteration. Above features are possible in view of the advantageous utilization of centrifugal forces and pressure differentials by the invention allowing for a seal structure which minimally affects the critical parameters of the disc.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

What is claimed is:

1. In a multistage axial compressor having replaceable blades mounted in transverse slots around the periphery of each disc, the improvement comprising:

annular sealing means concentrically disposed near the periphery of each disc on the high pressure side occluding the exposed ends of the slots for preventing fluid leakage therethrough, said sealing means compliantly mating with the disc and attached adjacent to the disc along the inside edge by diffusion bonding, the outer edge extending outwardly to be urged into sealing contact across the slots when subjected to a centrifugal force and pressure differential, said sealing means further being formed of a metallic foil in the order of 2 to 3 mills thickness and having a deformable bead at the outer edge thereof adjacent to the disc.

2. A rotor, comprising:

a disc including a peripheral rim with axial-facing surfaces increasing in cross section radially outwardly, and having a plurality of convoluted transverse slots about the rim formed to receive removable blades;

blades having root sections with axial-facing surfaces coplanar with the rim surfaces inserted in each of the slots; and

a continuous annular seal concentrically attached near the inner edge thereof to the side of the disc occluding the exposed ends of the slots.

3. A rotor according to claim 2, further comprising:

said annular seal being flexible and compliantly mating with the rim and attached adjacent to the rim along the inside edge, the outer edge extending outwardly to be urged into sealing contact across the slots when subjected to a centrifugal force and pressure differential.

4. A rotor according to claim 3 further comprising:

said annular seal being formed of a metallic foil in the order of 2 to 3 mills thickness and attached to the disc by diffusion bonding.

5. A rotor according to claim 4, further comprising:

said annular seal having a deformable bead at the outer edge thereof adjacent to the disc.

6. A rotor according to claim 5, further comprising:

a plurality of key means respectively interposed between said blades and said disc for retaining said blades to said disc; and

cutouts formed in said seal for permitting installation of said keys.