GB2408296A

GB2408296A - Compressor blade root retainer with integral sealing means to reduce axial leakage

Info

Publication number: GB2408296A
Application number: GB0327252A
Authority: GB
Inventors: Tony David Pheaton
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-11-22
Filing date: 2003-11-22
Publication date: 2005-05-25
Also published as: GB0327252D0

Abstract

A retainer device 20 for locking a blade 26, preferably a compressor blade, into a rotor disc 28 of a gas turbine engine (10, fig 1) locatable in the cavity 22 formed therebetween. The retainer includes a first end 30, having a retaining feature 32, which may lock a retaining ring 33 in place, wherein the retaining feature 32 may be bent from a co-planar formation to enclose the ring 33. At the second end 34 there includes means 36 for sealing the end of the cavity 22, so as to reduce axial leakage of working fluid between stages. The sealing means 36 may comprise a lip feature 44, which may be deformable. A plurality of devices 20 (and 120, fig 5) of varying masses may be used with a plurality of blades in order to improve balance of the overall arrangement.

Description

Retainer Devices The present invention relates to retainer devices for use

in blade mounting cavities of a gas turbine engine, and more particularly but not exclusively to blade assemblies for a gas turbine engine.

A compressor of a gas turbine engine conventionally comprises a plurality of rotor blades mounted in a blade mounting disc. Each blade includes a blade root which locates in a correspondingly shaped recess in the disc, and respective blade mounting cavities are formed between each blade root and the disc. A retaining ring is used to retain the blades in the disc, and retainer devices, also known as Jockstraps, are inserted into each respective blade mounting cavity to hold the retaining ring in position.

Conventional retainer devices do not close the blade mounting cavities and this can result in leakage of air through the cavities against the direction of airflow during operation of the compressor. This may cause a reduction in compressor efficiency and may also cause increased wear.

According to a first aspect of the present invention, there is provided a retainer device for use in a blade mounting cavity of a gas turbine engine, the device comprising first and second ends, the first end including an interference retainer for retaining a blade in a mounting disc and the second end including a closure for the cavity.

The retainer may extend in a first direction and the closure may extend in a second direction, and the first direction may be substantially opposite to the second direction.

The closure may be locatable by deflection in the cavity. The device may include an upper surface for abutment with the blade root. The closure may extend centrally to the major axis of the device, and may comprise a lip extending from the second end of the device. The device may have first and second side edges and the closure may extend between said side edges. The closure and device may be a unitary component, and the device may be in the form of a retaining strap. The closure may comprise a sealing arrangement for greater sealing, in use, of the cavity between the blade root and the disc.

The interference retainer may comprise a retainer projection. The retainer projection may extend from the first end of the device to allow lateral distortion for retention. The retainer projection and the device may be unitary. The retainer projection may be co-operable, in use, with a blade retaining ring for retaining a plurality of blades in a blade mounting disc.

A plurality of retainer devices may be used for rotationally balancing a plurality of blades mounted in a blade mounting disc.

According to a second aspect of the present invention, there is provided a blade assembly for a gas turbine engine, the assembly comprising; a blade mounting disc; a plurality of blades, each having a blade root and being mounted in said disc by said blade root, a cavity being defined between each blade root and the disc; a blade retaining ring for retaining the plurality of blades in the blade mounting disc; and a plurality of blade retainer devices, each retainer device being located in a respective cavity and comprising first and second ends, the first end including an interference retainer co-operable with the blade retaining ring, and the second end including a closure for a respective cavity.

Each blade retainer device may be as described above.

Respective blade retainer devices may be of different masses to allow rotational balance of the blade assembly.

According to a third aspect of the present invention, there is provided a gas turbine engine including a blade assembly as described above.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic cross-sectional view of part of a gas turbine engine; Fig. 2 is a diagrammatic cross-sectional view of part of a blade assembly including a retainer device according to the invention; Fig. 3 is a view in the direction of arrow A of Fig. 2; Fig. 4 is a diagrammatic perspective view of a retainer device; and Fig. 5 is a diagrammatic perspective view of a modified retainer device.

Referring to Fig. 1, a gas turbine engine is generally indicated at 10 and comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high pressure compressor 14, combustion equipment 15, a high pressure turbine 16, an intermediate pressure turbine 17, a low pressure turbine 18 and an exhaust nozzle 19.

The gas turbine engine 10 works in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 which produces two air flows: a first air flow into the intermediate pressure compressor 13 and a second air flow which provides propulsive thrust. The intermediate pressure compressor 13 compresses the air flow directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines 16, 17 and 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low pressure turbines 16, 17 and 18 respectively drive the high and intermediate pressure compressors 14 and 13, and the fan 12 by suitable interconnecting shafts.

Figs. 2 to 4 show generally a retainer device 20, commonly referred to as a Jockstrap or retaining strap, according to the invention for use in a blade mounting cavity 22 of the gas turbine engine 10, the cavity 22 being defined between a root 24 of a blade 26 and correspondingly shaped recess in a blade mounting disc 28. The retainer device 20 comprises a first end 30 which includes an interference retainer 32 co-operable with a blade retaining ring 33. The retaining ring 33 securely retains each blade 26 in its corresponding cavity 22 and the interference retainer 32 holds the retaining ring 33 in position. The retainer device 20 also comprises a second end 34 including a closure 36 for the cavity 22. The device 20, interference retainer 32 and closure 36 are of unitary construction.

In more detail, the device 20 comprises a blade root abutment portion 38 in the form of a substantially flat metallic strip having a major axis extending between the first and second ends 30, 34 and having upper and lower surfaces 40, 42. The interference retainer 32 extends from the first end 30 of the device 20 and when the device 20 is not in use is co- planar with the abutment portion 38, as shown in dotted lines. This enables the device 20 to be inserted into and extracted from a blade mounting cavity 22, as described below. The interference retainer 32 is in the form of a tang or prong which is substantially smaller in width than the abutment portion 38 to enable it to be distorted, in use, by bending upwardly to a retaining position shown in solid lines in Fig. 4. When in the retaining position, the interference retainer 32 extends in an upward direction substantially perpendicular to the abutment portion 38 which corresponds to the radially outward direction of the disc 28.

The closure 36 is in the form of a lip 44 extending from the second end 34 of the device 20 in a downward direction which, when the device 20 is in location in a cavity 22, corresponds substantially to the radially inward direction of the disc 28. The lip 44 includes a gently curved edge 46 which extends between first and second side edges 48, 50 of the device 20. The curvature of the lip 44 corresponds substantially to the circumferential curvature of the base of the blade mounting cavity 22.

An aperture 52 is provided at the second end 34 of the device 20 to receive an extraction tool to assist with extraction of the device 20 from a cavity 22, as described later.

Fig. 5 illustrates a modified retainer device 120 according to the invention, in which corresponding elements are given corresponding reference numerals. The device 120 differs from the device 20 in that material has been removed from the blade root abutment portion 38 to reduce the mass of the device for the purpose of assisting with rotational balancing of a blade assembly. As shown, the abutment portion 38 comprises a central abutment portion 54 with first and second laterally extending portions 56, 58.

In use, a blade assembly is formed by mounting a plurality of blades 26 in corresponding recesses of a blade mounting disc 28. A blade retaining ring 33 is located in abutment with the roots 24 of the blades 26. Once the blades 26 and ring 33 are in position, a blade retainer device 20, 120 is inserted into each blade mounting cavity 22 by locating the interference retainer 32 in a first end of the cavity 22 and pushing the device 20, 120 into the cavity 22 until the retainer 32 projects from a second end 62 of the cavity 22. When the device 20, 120 is in the correct position, the interference retainer 32 is then bent upwardly so as to contact the blade retaining ring 33 and secure it in position.

When the device 20, 120 is in location in a blade mounting cavity 22, the blade root abutment portion 38 abuts the root 24 of a respective blade 26. The lip 44 then extends away from the root 24 in a radially inward direction towards the disc 28 and thereby closes the cavity 22.

After insertion of each blade retainer device 20, 120 into a respective cavity 22, the blade assembly is subjected to rotational balance testing. If there is rotational imbalance in the assembly, selected retainer devices 20, 120, for example devices 120 as shown in Fig. 5, can be removed and replaced with devices of different mass, for example heavier devices 20 as shown in Fig. 4.

One or more devices 20, 120 is removed from a respective blade mounting cavity 22 by bending the interference retainer 32 so that it is substantially coplanar with the abutment portion 38. An extraction tool (not shown) is then inserted into the aperture 52 and the device 20, 120 is pulled out of the cavity 22.

The retainer device 20, 120 according to the invention is formed by stamping a metal sheet, for example steel, titanium or nickel. The lip 44 is then formed by carrying out a suitable bending operation on the stamped sheet.

The provision of a closure 36 in the form of a lip 44 provides for greater sealing, in use, of the blade mounting cavity 22 than conventional retainer devices. This provides a reduction in air leakage through the compressor and results in improved compressor efficiency. The device 20, also provides for both blade retention and closure of the blade mounting cavity 22 using a single unitary device.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that various modifications to the examples given may be made without departing from the scope of the invention as claimed. For example, the closure 36 may be in a form other than a lip 44. The closure 36 may be of any configuration provided that it closes, or at least substantially closes, the blade mounting cavity 22 when in use. The closure 36 may be a separate component from the device 20. The closure 36 may comprise any suitable sealing or packing material. The device 20 may be formed from a material other than metal, and may be formed by a process or method other than stamping and bending, for example machining. The device 20, is not limited for use in the blade assembly of a compressor. The device 20, 120 may be inserted into the blade cavity 22 so that, in use, the closure 36 is located at the first end 56 of the cavity.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings, whether or not particular emphasis has been placed thereon.

Claims

Claims 1. A retainer device for use in a blade mounting cavity of a gas

turbine engine, the device comprising first and second ends, the first end including an interference retainer for retaining a blade in a mounting disc and the second end including a closure for the cavity.
2. A device according to claim 1, wherein the interference retainer extends in a first direction and the closure extends in a second direction.
3. A device according to claim 2, wherein the first direction is substantially opposite to the second direction.
4. A device according to any of the preceding claims, wherein the closure is locatable by deflection in the cavity.
5. A device according to any of the preceding claims, wherein the device includes an upper surface for abutment with the blade root.
6. A device according to claim 5, wherein the closure extends centrally to the major axis of the device.
7. A device according to any of the preceding claims, wherein the closure comprises a lip extending from the second end of the device.
8. A device according to any of the preceding claims, wherein the device has first and second side edges and the closure extends between said side edges.
9. A device according to any of the preceding claims, wherein the closure and device are a unitary component.
10. A device according to any of the preceding claims, wherein the device is in the form of a retaining strap.
11. A device according to any of the preceding claims, wherein the closure comprises a sealing arrangement for greater sealing, in use, of the cavity between the blade root and the disc.
12. A device according to any of the preceding claims, wherein the retainer comprises a retainer projection.
13. A device according to claim 12, wherein the retainer projection extends from the first end of the device to allow lateral distortion for retention.
14. A device according to claim 12 or claim 13, wherein the retainer projection and the device are unitary.
15. A device according to any of claims 12 to 14, wherein the retainer projection is co-operable, in use, with a blade retaining ring for retaining a plurality of blades in a blade mounting disc.
16. A device according to any of the preceding claims, wherein a plurality of said devices is used for rotationally balancing a plurality of blades mounted in a blade mounting disc.
17. A retainer device substantially as hereinbefore described with reference to the accompanying drawings.
18. A blade assembly for a gas turbine engine, the assembly comprising; a blade mounting disc; a plurality of blades, each having a blade root and being mounted in said disc by said blade root, a cavity being defined between each blade root and the disc; a blade retaining ring for retaining the plurality of blades in the blade mounting disc; and a plurality of blade retainer devices, each retainer device being located in a respective cavity and comprising first and second ends, the first end including an interference retainer co-operable with the blade retaining ring, and the second end including a closure for a respective cavity.
19. An assembly according to claim 18, wherein each blade retainer device is as defined in any of claims 2 to 17.
20. An assembly according to claim 18 or claim 19, wherein respective blade retainer devices are of different masses to allow rotational balance of the blade assembly.
21. A gas turbine engine including a blade assembly as defined in any of claims 18 to 20.
22. A blade assembly substantially as hereinbefore described with reference to the accompanying drawings.
23. A gas turbine engine including a blade assembly substantially as hereinbefore described with reference to the accompanying drawings.
24. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.