Gas turbine engine casing
An annular fan casing of a gas turbine engine includes a plurality of fan track liner panels, secured to the radially inner surface of the fan casing. The panels are secured using mechanical fasteners, which are secured into non-load-bearing regions of the fan casing so as not to compromise the load-carrying or containment functions of the fan casing.
This invention relates to gas turbine engines, and more particularly to fan casings for such engines.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor, enclosed by a generally cylindrical or frustoconical fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades, enclosed by a generally cylindrical or frustoconical casing.
There is a remote possibility with such engines that part or all of a fan blade or a turbine blade could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as a result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical or frustoconical, relatively thick, metallic containment rings. It is also known to provide generally cylindrical or frustoconical, locally thickened, isogrid metallic containment rings. Furthermore, it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above-mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
There is a requirement to provide a fan track liner within the fan casing. Conventionally the fan track liner is attached within the fan casing by mechanical fasteners passing through the liner and secured into or through the fan casing, or by adhesive.
Conventional mechanical attachment of fan track liners uses fasteners extending radially through reinforced regions of the liner panel. These fasteners produce steps and gaps, which interfere with the aerodynamic flow over the liner panel. The presence of the reinforced regions increases the weight and cost of the liner panels. Furthermore, the fasteners must be secured into or through the fan casing, which weakens the casing and may interfere with its ability to contain a detached fan blade.
Adhesive bonding of the fan track liner to the fan casing must be performed under controlled conditions. If a liner has to be replaced in service it may be difficult to control the bonding conditions, and this can result in unsatisfactory attachment of the liner to the casing. It can be difficult to remove a damaged liner without also damaging the fan casing. The design of fan casings has to include an allowance for possible weakening caused by such damage. This increases the cost and weight of the fan casing.
Accordingly, this invention seeks to provide a novel fan track liner for a gas turbine engine which overcomes the above-mentioned problems.
The invention will be more fully described, by way of example, with reference to the following drawings in which:
A layer of polysulphide sealant is applied to the outer surface of the liner tray 30. This prevents frettage between the liner tray and the fan casing 212 and damps vibration, and will also help to prevent rotation of the liner panels around the casing 212, in case of heavy rubbing of the fan blade tips on the attrition liner 34.
The same means of securing the forward part of the liner panel may be applied to the embodiment of
Referring still to
Although particular embodiments of the invention have been described, it will be apparent to a skilled person that various changes and modifications can be made without departing from the spirit of the invention. Some examples of possible changes and modifications are set out below, though these are not intended to be exhaustive.
The liner tray 30 may be pressed metal, or composite, or laser cut from metal sheet. The liner tray 30 may extend around any convenient arc of the circumference, so that a full set of fan track liner panels 28 consists of fewer or more panels than are described in the embodiments above. It is envisaged that the minimum arc for each panel 28 would be of the order of 100 (a full set consisting of 36 panels), and the maximum arc would be of the order of 90° (a full set consisting of four panels).
The numbers of screws (42, 44), hooks (48, 66) and anti-rotation features (62, 70, 78) provided on each panel 28 may be any suitable number.
The O-ring seal 52, 58 may be replaced by a seal of another type, or may be dispensed with altogether.
The polysulphide sealant may be replaced by an equivalent sealant of different chemical composition.
The locating recesses 64 may be machined or moulded, according to the material from which the liner tray 730 is made, and may be of a different shape from that shown in
A different number of cutouts 68 may be provided, and they may be of a different shape from that described. Cutouts may also be provided in the liner trays of the other embodiments described. Likewise, the different types of anti-rotation features described in the several embodiments may be freely interchanged between those embodiments.
Claims
1. A casing for a gas turbine engine, the casing comprising a generally cylindrical or frustoconical annulus, at least one liner panel being positioned radially inward of the casing, the or each liner panel being removably securable on the casing by at least one mechanical fastener which in use passes through the liner panel, characterised in that the or each mechanical fastener is not secured to the annulus of the casing.
2. A casing as in claim 1, in which the annulus has a first flange and a second flange axially spaced apart, and in which in use the annulus provides a load path at least between the first flange and the second flange.
3. A casing as in claim 2, in which the or each mechanical fastener is not secured to the annulus of the casing between the first flange and the second flange.
4. A casing as in any preceding claim, in which the annulus forms part of a containment system.
5. A casing as in any preceding claim, in which the casing further comprises a member extending generally radially inwards from the annulus, and in which in use at least one mechanical fastener is secured to the member.
6. A casing as in any of claims 1 to 4, in which the casing further comprises a first member and a second member each extending generally radially inwards from the annulus, the first and second members being axially spaced apart.
7. A casing as in claim 6, in which in use at least one mechanical fastener is secured to at least one of the first and second members.
8. A casing as in claim 6, in which the or each liner panel comprises at least one hook, and in which in use at least one mechanical fastener is secured to either the first or the second member, and the hook or hooks engage with the other of the first and second members.
9. A casing as in claim 8, in which a seal is provided between the hook or hooks and the member with which the hook or hooks engage.
10. A casing as in claim 9, in which the seal is an O-ring seal.
11. A casing as in any of claims 8 to 10, in which the hook or hooks include at least one anti-rotation feature which in use engages with a corresponding feature on the casing.
12. A casing as in any preceding claim, in which a layer of sealant is provided on at least part of the radially outer surface of the or each liner panel, to inhibit fretting and vibration.
13. A casing as in claim 12, in which the sealant is a polysulphide.
14. A casing as in any preceding claim, in which the or each mechanical fastener is a threaded fastener.
15. A casing for a gas turbine engine substantially as described in this specification, with reference to and as shown in FIGS. 2 to 13 of the accompanying drawings.
Type: Application
Filed: May 22, 2007
Publication Date: Mar 20, 2008
Inventors: Cedric Harper (Derby), Ian Martindale (Derby)
Application Number: 11/802,324
International Classification: F01D 25/24 (20060101);