GB2489222A

GB2489222A - Bladed rotor with annulus filler

Info

Publication number: GB2489222A
Application number: GB1104645.5A
Authority: GB
Inventors: Paul Mason
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2011-03-21
Filing date: 2011-03-21
Publication date: 2012-09-26
Also published as: GB201104645D0

Abstract

A rotor, for example of a gas turbine engine fan, comprises a bladed rotor disc having an annulus filler structure which comprises annulus filler elements 16. Adjacent elements meet along a joint line 44 which is situated between two adjacent blades 8. A region of each element may be located between a blade root 10 and an adjacent disc post. Each element may comprise first and second walls 26, 28 situated on opposite sides of a blade, the walls being connected by a web 30 which extends around the root of the blade. The elements may meet at respective flanges 32 which have respective mating surfaces 36. Each respective flange may have a rib 34, adjacent ribs being accommodated in a channel (40, figure 6) to secure the flanges together.

Description

t V.' INTELLECTUAL ..* PROPERTY OFFICE Application No. GB 1104645.5 RTIVI Date 27 June 2011 The following terms are registered trademarks and should be read as such wherever they occur in this document: Kevlar Intellectual Properly Office is an operating name of the Patent Office www.ipo.gov.uk

A ROTOR HAVING AN ANNULUS FILLER

This invention relates to a rotor comprising a rotor disc having an array of blades and an annulus filler structure which is disposed between adjacent blades. The invention is particularly, although not exclusively, concerned with a rotor in the form of a fan of a turbofan gas turbine engine.

The fan of such an engine typically comprises a rotor disc which has an array of slots at its periphery, which are defined between disc posts and which receive individual fan blades. It is common for annulus fillers to be provided between adjacent blades of the fan in order to provide an airwashed surface which has the desired aerodynamic profile, and provides a transition between forward and aft components such as a spinner fairing and a fan rear seal.

It is known to mount annulus fillers by securing them at their forward and aft ends to the surrounding structure. Annulus fillers are subjected to substantial centrifugal forces as the rotor rotates, and, if they are unsupported between their ends, these centrifugal forces can cause deformation. It is therefore necessary to design the annulus fillers so that they deform under rotation to provide the desired aerodynamic profile.

Furthermore, the stresses imposed on the annulus filler during an operating cycle need to be analysed to ensure that the fatigue life of the component lies within acceptable limits.

The effects of centrifugal forces on the annulus fillers can be mitigated by constructing each annulus filler in the form of a structural beam, for example an I-section beam, so that it is resistant to bending. This increases the bulk, and consequently the weight, of the component. An alternative measure is to provide connections, for example in the form of hooks, between the ends of the annulus filler, which engage cooperating formations on the periphery of the rotor disc. It is possible for annulus fillers with such hook connections to be fitted incorrectly, so that they may become detached in operation. Also, the hook connections can be susceptible to Low Cycle Fatigue cracking which, again, can result in release of the annulus filler. A further disadvantage arises from the need for corresponding profiles on the rotor disc, which increase the diameter and weight of the rotor disc and the forging from which it is machined, and also increase the amount of machining required to form the finished disc. The additional diameter means that the effective depth of the blade-retaining slots is increased, which reduces the stability of the cutting tools required to form the slots.

The provision of hook features on the rotor disc thus increases the cost of the rotor discs.

According to the present invention there is provided a rotor comprising a rotor disc having an array of blades and an annulus filler structure which is disposed between adjacent blades, the annulus filler structure comprising annulus filler elements which meet each other along a joint line which is situated between the adjacent blades.

The joint line may be situated substantially midway between the blades. The annulus filler structure may comprise a pair of the annulus filler elements.

The blades may terminate at blade roots which are accommodated in respective blade slots in the disc, the blade slots being defined between disc posts. Each of the annulus filler elements may have a region which is situated between a respective one of the adjacent blades and the respective disc post.

Each of the annulus filler elements may comprise an airwashed surface which extends in the direction from one of the adjacent blades towards the other. The airwashed surfaces of the pair of annulus filler elements may meet each other at the joint line.

Each annulus filler element may comprise first and second outer walls which are situated on opposite sides of the respective blade. In embodiments in which the blades comprise blade roots accommodated in blade slots, the outer walls of each annulus filler element may be interconnected by a connecting web which extends around the root of the respective blade. The annulus filler element may comprise side walls which extend between the respective first and second outer walls and the connecting web.

Each of the annulus filler elements thus provides part of each of the annulus filler structures on opposite sides of the blade.

The annulus filler elements may abut each other at the joint line at respective mating surfaces which extend radially of the disc. The mating surfaces may be provided on edge flanges of the annulus filler elements.

Securing means may be provided for securing the edge flanges together. The securing means may comprise a locking element having a channel in which the edge flanges are received. The edge flanges may have ribs which project away from the joint line and which are accommodated within the channel. The locking element may extend over substantially the full extent of the joint line.

The rotor may comprise a fan rotor of a gas turbine engine.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a section of a rotor comprising a rotor disc fitted with fan blades and an annulus filler structure; Figure 2 is a view of an annulus filler element of the annulus filler structure of Figure 1, taken from the forward end; Figure 3 is a view of the annulus filler element of Figure 2, taken from the aft end; Figure 4 corresponds to Figure 1, but shows a subassembly comprising the annulus filler structure and the fan blades; Figure 5 is a radial sectional view of the rotor of Figure 1; and Figure 6 is an enlarged view of part of Figure 5.

Figure 1 shows a rotor disc 2 of a fan rotor of a gas turbine engine. It will be appreciated that the rotor disc is in the form of an annulus, only part of which is shown in Figure 1. The rotor disc 2 has a circumferential array of blade slots 4, only two of which are shown in Figure 1. The slots 4 are defined by disc posts 6.

An array of fan blades 8 is distributed around the disc 2, of which two are shown in Figure 1. Each blade 8 is shown truncated for clarity, and comprises a blade root 10 which is accommodated in a respective one of the blade slots 4.

An annulus filler structure 12 is assembled with the disc 2 and the blades 8 to provide platforms 14 extending between each pair of adjacent blades 8. The annulus filler structure 12 is made up of a series of annulus filler elements 16, one of which is shown in Figures 2 and 3.

The annulus filler element 16 shown in Figures 2 and 3 comprises two outer walls 18, which are spaced apart by a gap 22 corresponding to the local profile of the blade 8 which extends through the gap 22 as shown in Figure 1. The outer walls 18, 20 each have an airwashed surface 24, i.e. a surface over which passes the main flow through the fan. Side walls 26, 28 extend inwardly from the inner surfaces of the respective outer walls 18, 20. The side walls 18 extend substantially radially with respect to the central axis of the disc 2, and meet a connecting web 30 at their radially inner ends.

The connecting web 30 is profiled to fit the root 10 of the respective blade, as shown more clearly in Figure 5. The connecting web 30 extends over the full axial length of the annulus filler element 16, although it has a cut-out or recess 31 at a position between its ends.

In some embodiments, the side walls 26, 28 may be inclined to the radial direction where required by geometrical constraints imposed by surrounding structures.

Each of the outer walls 18, 20 terminates, at its edge away from the gap 22, at a radially inwardly projecting edge flange 32. Each edge flange 32 itself terminates at a rib 34 which is directed back towards the gap 22. The edge flanges 32 have flat, radially extending, mating surfaces 36.

As will be appreciated from Figures 4 and 5, the root 10 of each blade 8 can be slid into the connecting web 30 of the respective annulus filler element 16, with the result that the outer walls 18, 20 of the annulus filler element 16 are situated one on each side of the blade 8. The outer walls 18, 20 project towards the blade 8 beyond the respective side walls 26, 28, to form lips 38. Sealing means (not shown) may be provided to form a seal between the blade 8 and the lips 38. In some embodiments, stub platforms may project from the blade 8 towards the lips 38.

As shown in Figures 5 and 6, when the blade 8, carrying the annulus filler element 16, is installed in its blade slot 4, each edge flange 32 abuts the edge flange 32 of a neighbouring annulus filler element 16, with their mating faces 36 in contact with each other. The edge flanges 32, and consequently the annulus filler elements 16, are secured together by securing means in the form of a locking element 40. As shown in Figure 6, the locking element is in the form of a strip which extends the full length of the abutting edge flanges 32. The locking strip 40 has a channel-shaped cross-section having inturned edges 42. The ribs 34 on the edge flanges 32 are accommodated within the channel so as to retain the edge flanges 32 in secure face-to-face contact with each other. An end stop (not shown) may be provided on one or both of the annulus filler elements 16 to locate the locking strip 40 in the axial direction.

When fully assembled, the side-by-side outer walls 18, 20 of adjacent annulus filler elements 16 combine to provide the platform 14 of the annulus filler structure 12 between each pair of blades 8. The outer walls 18, 20 meet each other along a joint line 44 formed by the abutting mating faces 36. As shown, for example, in Figure 4, this joint line 44 runs between the adjacent blades 8 from the forward end to the aft end of the annulus filler structure 12, and in particular the platform 14. The joint line 44 runs substantially midway between the blades 8. However, it will be appreciated that, owing to the aerofoil shape of the blades 8, the joint line 44 may deviated from a line situated precisely between the opposing faces of the blades 8. Also, in some embodiments, it may be necessary or desirable for the joint line 44 to be closer to one of the blades 8 on each side of it than the other.

The blade roots 10 and the posts 6 on the disc 2 may be provided with recesses or passages (not shown) for receiving shear keys. Such shear keys may, if fitted, extend through the cut-outs 31 to maintain the axial alignment between the annulus filler element 16 and the respective blade 8.

The edge flanges 32 have a significant depth in the radial direction, and are secured together by the locking strip 40 at their radially inner ends. The locking strip 40 provides additional stiffness to the platform 14. The geometry shown in Figure 6 affords substantial resistance to deflection of the outer walls 18, 20 under centrifugal loading, and so maintains the desired external profile of the platform 14. In particular, the locking together of the edge flanges 32 at their mating faces 36 reduces the tendency of the outer walls 18, 20 to roll against each other under centrifugal loading.

Furthermore, the locking strip 40 secures the outer walls 18, 20 relatively to each other in the radial direction, so maintaining a continuous airwashed profile across the joint line 44.

It will be apparent from Figures 1 to 4 that the annulus filler element 16 is curved in order to conform to the profile of the blade root 10. Figures 2 and 3 also shows weight-saving apertures 46 provided in the side walls 26, 28 in order to reduce the weight of the annulus filler element.

The annulus filler elements 16 may be made from any suitable material such as an aerospace metallic alloy or a composite material. The configuration of the annulus filler elements lends itself particularly to manufacture from a composite material, for example by lay-up using pre-impregnated pre-forms, or dry pre-forms impregnated with resin in a resin transfer moulding process, or using automated fibre placement techniques. The composite material may comprise carbon fibre, glass fibre, or Kevlar reinforcements. If carbon fibre is used, provision for protection against galvanic corrosion will be required where the annulus filler elements 16 interface with aluminium alloy components.

The annulus filler elements 16 could alternatively be manufactured by an extrusion operation followed by pultruding or hydroforming to shape, or by injection moulding.

Suitable surface treatments such as coatings may be applied to regions of the annulus filler elements 16, for example to avoid erosion of the airwashed surfaces 24, or to avoid fretting at contact regions, such as the regions of the elements that contact the blade root 10 or the posts 6.

An annulus filler structure 12 as described above is locked firmly with respect to the disc on assembly of the complete fan rotor by means of the blade roots 10 accommodated in the blade slots 4. Radial loading on the annulus filler elements 16 is distributed over the full axial length of the disc posts 6, so reducing stresses in the annulus filler elements 16 and enabling significant weight savings. As shown in Figure 5, the side walls 18 extend radially of the disc 2, with the result that the side walls 18 are able to withstand centrifugal forces without bending stresses, further enabling weight reduction.

Incorrect fitting of the annulus filler elements 16 is difficult and, if mis-fitting occurs, is visually noticeable.

The geometry of the annulus filler structure 12 described above is relatively simple compared with known annulus filler components, and consequently manufacturing costs can be reduced. Similarly, the elimination of any requirement for projecting features at the periphery of the fan disc 2 reduces the diameter of the fan disc forging, and reduces the time required for machining complex features such as retaining hooks.

Where a shear key is provided, the absence of any hook feature provides greater freedom for the positioning of the shear key slot 54, since it is not necessary to avoid alignment of the shear key slot with the hook features.

As mentioned above, the annulus filler elements 16 need not be straight, but could be arcuate, provided that the general cross-section of the blade slots 10 is substantially constant over its full length. The local flexibility of the annulus filler can be controlled by varying the thickness of the cross-sections of the outer walls 18, 20, the side walls 26, 28 and the connecting web 30 in order to accommodate blade rock. Flexibility can also be adjusted by varying the geometry and thickness of the edge flanges 32.

Appropriate formations may be provided on the annulus filler elements 16, such as pips, bumps or ridges, in order to avoid water retention and to mitigate contact fretting.

Although the annulus filler elements 16 are described above as being secured together by means of the locking strip 40, other securing mechanisms can be used.

The locking mechanism described with reference to Figure 6 is shown in conjunction with the annulus filling elements 16 which are separate components from the blades 8.

Some bladed rotors comprise blades with integral platforms which abut one another in the intervals between the blades. Locking mechanisms similar to those shown in Figure 6 could be employed for securing together the abutting platforms.

Claims

CLAIMS1 A rotor comprising a rotor disc having an array of blades and an annulus filler structure which is disposed between adjacent blades, the annulus filler structure comprising annulus filler elements which meet each other along a joint line which is situated between the adjacent blades.
2 A rotor as claimed in claim 1, in which the joint line is situated substantially midway between the adjacent blades.
3 A rotor as claimed in claim I or 2, in which the annulus filler structure comprises a pair of the annulus filler elements.
4 A rotor as claimed in any one of the preceding claims, in which the blades comprise blade roots accommodated in respective blade slots in the disc, the blade slots being defined between respective disc posts.
A rotor as claimed in claim 4, in which each of the annulus filler elements has a region which is situated between a respective one of the blade roots and the respective disc post.
6 A rotor as claimed in any one of the preceding claims, in which each of the annulus filler elements comprises an airwashed surface which extends in the direction from one of the adjacent blades towards the other.
7 A rotor as claimed in claim 6, in which the airwashed surfaces of the pair of annulus filler elements meet each other at the joint line.
8 A rotor as claimed in any one of the preceding claims, in which the annulus filler elements comprise first and second outer walls situated on opposite sides of the respective blade.
9 A rotor as claimed in claim 8, in which the outer walls of each annulus filler element are interconnected by a connecting web which extends around the root of the respective blade.
A rotor as claimed in claim 9, in which each annulus filler element comprises side walls which extend between the respective first and second outer walls and the connecting web.
11 A rotor as claimed in any one of the preceding claims, in which the annulus filler elements abut each other at the joint line at respective mating surfaces which extend radially of the disc.
12 A rotor as claimed in claim 11, in which the mating surfaces are provided on edge flanges of the annulus filler elements.
13 A rotor as claimed in claim 12, in which securing means is provided for securing the edge flanges of adjacent annulus filler elements together.
14 A rotor as claimed in claim 13, in which the securing means comprises a locking element having a channel in which the edge flanges are received.
A rotor as claimed in claim 14, in which the edge flanges are provided with ribs which are accommodated within the channel.
16 A rotor as claimed in claim 14 or 15, in which the locking element extends over the full extent of the joint line. -11 -
17 A rotor as claimed in any one of the preceding claims, which is a fan rotor of a gas turbine engine.
18 A rotor substantially as described herein with reference to, and as shown in, the accompanying drawings.
19 An annulus filler element for use in a rotor in accordance with any one of the preceding claims.