U.S. patent application number 12/415031 was filed with the patent office on 2009-10-29 for fan blade.
This patent application is currently assigned to Rolls-Royce PLC. Invention is credited to Kristofer John Bottome.
Application Number | 20090269189 12/415031 |
Document ID | / |
Family ID | 39494072 |
Filed Date | 2009-10-29 |
United States Patent
Application |
20090269189 |
Kind Code |
A1 |
Bottome; Kristofer John |
October 29, 2009 |
FAN BLADE
Abstract
A fan blade for the fan of a gas turbine engine has a radially
outer tip portion which, in use, is adjacent to a fan case of the
engine. The tip portion includes a movable sealing element for
sealing a gap between the tip portion and the fan case. The sealing
element movably adapts to changes in the spacing of the gap to
maintain a seal between the tip portion and the fan case.
Inventors: |
Bottome; Kristofer John;
(Nottingham, GB) |
Correspondence
Address: |
MCCORMICK, PAULDING & HUBER LLP
CITY PLACE II, 185 ASYLUM STREET
HARTFORD
CT
06103
US
|
Assignee: |
Rolls-Royce PLC
London
GB
|
Family ID: |
39494072 |
Appl. No.: |
12/415031 |
Filed: |
March 31, 2009 |
Current U.S.
Class: |
415/173.3 ;
415/121.2 |
Current CPC
Class: |
F04D 29/164 20130101;
F05D 2220/36 20130101; F05D 2240/307 20130101; F01D 11/12 20130101;
F05D 2220/323 20130101; F05D 2240/55 20130101 |
Class at
Publication: |
415/173.3 ;
415/121.2 |
International
Class: |
F01D 11/08 20060101
F01D011/08; F01D 25/00 20060101 F01D025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2008 |
GB |
0807358.7 |
Claims
1. A fan blade for the fan of a gas turbine engine, the blade
having a radially outer tip portion which, in use, is adjacent to a
fan case of the engine, the tip portion including a movable sealing
element for sealing a gap between the tip portion and the fan case,
wherein the sealing element movably adapts to changes in the
spacing of the gap to maintain a seal between the tip portion and
the fan case.
2. A fan blade according to claim 1, wherein the sealing element is
formed integrally with the blade.
3. A fan blade according to claim 1, wherein the sealing element is
removably attached to the blade.
4. A fan blade according to claim 1, wherein the sealing element is
formed of flexible material which flexes to adapt to changes in the
spacing of the gap.
5. A fan blade according to claim 1, wherein the sealing element
responds to centrifugal loading by extending across the gap.
6. A fan blade according to claim 1, which is configured to promote
air film lubrication of the interface between the sealing element
and the fan case.
7. A gas turbine engine having a fan comprising circumferentially
spaced fan blades according to claim 1.
8. A gas turbine according to claim 7, wherein the fan case has an
acoustic liner at the interface between the sealing element and the
fan case.
9. A gas turbine according to claim 7, wherein the fan case has
debris removal channels at the interface between the sealing
element and the fan case.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is entitled to the benefit of British
Patent Application No. GB 0807358.7, filed on Apr. 23, 2008.
FIELD OF THE INVENTION
[0002] The present invention relates to a fan blade for the fan of
a gas turbine engine.
BACKGROUND OF THE INVENTION
[0003] The fan of a gas turbine engine comprises a cascade of
circumferentially spaced an blades mounted at their radially inward
ends on a disc and extending radially outwardly towards a fan case.
To minimise aerodynamic losses and maintain the performance and
stability of the fan blades, it is important to reduce leakage of
air between the tips of the fan blades and the case. To this end,
it is usual to have a close clearance between the tips and the
case.
[0004] A conventional method of achieving a close clearance is to
use fan track liners. These are positioned outboard of the fan
blades on the fan case, and typically comprise an abradable liner
supported by an aluminium honeycomb structure. The abradable liner
consists of Nomex.TM. (available from DuPont) honeycomb filled with
lightweight epoxy filler. The liner forms an aerodynamic seal
between the fan blades and the case.
[0005] In general, abradable liners seal the tip well at maximum
engine speed, but less so at cruise when centrifugal forces on the
blade are lower, and clearance between the tip and the fan case
increases. This causes an efficiency drop at cruise. Under certain
operating conditions (e.g. manoeuvre loading or abnormal engine
conditions such as red line/over speed) it is acceptable for fan
blades to make rubbing contact with the abradable liner. However,
for every rub event, the efficiency drop at cruise increases.
[0006] Further, such contacts carry the risk of damaging the blade,
and reducing its longevity. This risk can be higher with a blade
formed of composite material, which may be susceptible to
delamination or matrix damage under frictional loading. Ultimately,
damage from excessive rubbing contacts accumulating over time may
cause premature blade failure, particularly in blades formed of
composite material.
SUMMARY OF THE INVENTION
[0007] Thus, in a first aspect, the present invention provides a
fan blade for the fan of a gas turbine engine, the blade having a
radially outer tip portion which, in use, is adjacent to a fan case
of the engine, the tip portion including a movable sealing element
for sealing a gap between the tip portion and the fan case, wherein
the sealing element movably adapts to changes in the spacing of the
gap to maintain a seal between the tip portion and the fan
case.
[0008] In this way, sealing functionality is transferred from the
fan case to the fan blade, and the use of an abradable liner on the
fan case can be avoided. This reduces engine weight, as well as
helping to avoid rubbing contact damage to the fan blade.
[0009] The fan blade can have one sealing element, typically
running the length of the radially outer edge of the blade.
Alternatively, the blade can have a plurality of sealing elements,
for example in an overlapping arrangement, and again typically
running along the radially outer edge of the blade.
[0010] The sealing element can be formed integrally with the blade.
However, preferably, the sealing element is removably attached to
the blade. For example, the blade can have a keyway slot or slots
for slidingly receiving the sealing element(s). A removably
attached sealing element can, advantageously, be easily replaced if
it becomes damaged.
[0011] The sealing element may be formed of flexible material,
which flexes to adapt to changes in the spacing of the gap. For
example, the element can be formed as a strip e.g. of flexible
plastic or rubber. Or the element can be formed as brush, with the
fibres of the brush, in use, extending across the gap. The fibres
of a brush sealing element may be formed of carbon fibre.
[0012] Preferably, the sealing element responds to centrifugal
loading by extending across the gap. For example, the element may
have a curved or bent cross-section that straightens out under
centrifugal loading to extend across the gap.
[0013] The fan blade may be configured to promote air film
lubrication of the interface between the sealing element and the
fan case. This can reduce the wear on the sealing element and, to a
lesser extent, on the fan case.
[0014] A further aspect of the present invention provides a gas
turbine engine having a fan comprising circumferentially spaced fan
blades according to the previous aspect.
[0015] The fan case may have an acoustic liner at the interface
between the sealing element and the fan case. This can reduce
engine noise, and is possible because an abradable liner at this
position is not needed.
[0016] The fan case may have debris removal channels at the
interface between the sealing element and the fan case.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows schematically the tip of a fan blade;
[0018] FIGS. 2(a) and (b) show schematically the operation of a
sealing element of the fan blade of FIG. 1;
[0019] FIGS. 3(a) and (b) show schematic end-on views of further
sealing elements;
[0020] FIGS. 4(a) and (b) show schematic end-on views of a further
sealing element;
[0021] FIG. 5 shows a schematic end-on view of a further sealing
element;
[0022] FIG. 6 shows schematically (a) a transverse cross-section
and (b) a plan view of a fan case; and
[0023] FIGS. 7(a), (b) and (c) show schematic end-on views of three
fan blades.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] FIG. 1 shows schematically the tip of a fan blade 1. Slotted
into a keyway 2 which runs along the radially outer edge of the
blade is a strip sealing element 3 formed of a flexible material,
such as plastic, rubber (e.g. silicone rubber) or coated metal
foil. The sealing element can be removably replaceable when worn or
damaged.
[0025] The keyway 2 can be formed in the body of a composite or a
metallic blade, or can be formed by a separate part, e.g. facing
side plates, attached to the tip of such a blade.
[0026] FIGS. 2(a) and (b) show schematically the operation of the
sealing element 3. In
[0027] FIG. 2(a), the engine is stationary. Sealing element 3 has a
curved cross-section profile, and there is a relatively large cold
build clearance 5 between the radially outer edge of the sealing
member 3 and the fan case 4. In FIG. 2(b), the blade is now
rotating in the direction indicated by the curved arrow. A
centrifugal force (CF) straightens out the profile of the sealing
element so that it extends to achieve a close clearance 6 with the
fan case.
[0028] The sealing element can be configured so that, under the
pressure differential produced during operation, an air film is
generated which lubricates the space between the sealing element
and the case. In this way, excessive wear of the element can be
avoided.
[0029] Instead of being attached via keyway 2, the sealing element
can be adhesively bonded, or mechanically fastened in other ways to
the tip of the blade. Preferably, the element is attached in such a
way as to allow extraction and replacement during overhaul.
However, particularly with a composite blade, the sealing element
can be integrated with the blade, for example by moulding or
co-moulding.
[0030] Other configurations of the flexible sealing element are
possible. For example, instead of an element formed as a strip
running along the radially outer edge of the blade, a brush sealing
element could be adopted, in which a plurality of fibres extend
from the blade tip towards the casing. These can be bonded in place
or mechanically attached via side plates. For example, the fibres
can be embedded at their radially inner ends in a retaining head,
which itself can be held in a keyway at the radially outer edge of
the blade. When the blade is formed from fibre-reinforced composite
material, the fibres of the composite can themselves extend out of
the matrix of composite at the blade tip to form the brush sealing
element.
[0031] A brush sealing element may be constructed from pure carbon
fibres. Break up of the carbon then produces lubrication on the fan
case.
[0032] The strip sealing element of FIG. 2 has a curved C-shaped
profile. The fibres of a brush sealing element can be similarly
curved so that on centrifugal loading, they straighten out to
achieve a close clearance with the fan case.
[0033] Other shapes are possible, however. For example, the
flexible sealing element may have one or more kinks serving as
hinges about which the portion of the flexible sealing element
radially outward of the kink rotates under centrifugal loading to
straighten the element. FIG. 3(a) shows a schematic end-on view of
a sealing element with one such kink, and FIG. 3(b) shows a
schematic end-on view of a sealing element with two kinks.
[0034] Further embodiments of the sealing element do not rely on
the intrinsic flexibility of a strip or brush, to achieve some or
all of the movability to adapt to changes in the spacing between
the fan blade and the casing.
[0035] For example, FIG. 4(a) shows a schematic end-on view of a
sealing element in which a flexible portion 7 of the element (e.g.
a strip or brush) is fixed to the blade at a mechanical pivot 8,
such as a pin or shaft. The engine is stationary and there is a
large clearance between the sealing element and the fan case 4.
However, as shown in FIG. 4(b), when the engine rotates, the
flexible portion 7 rotates about the pivot 8 by centrifugal force,
and makes air-lubricated contact with the fan case.
[0036] FIG. 5 shows a schematic end-on view of another sealing
element, in which a spring 9 supports a tip portion 10. The spring
is biased towards the blade so that when the engine is stationary
there is a large clearance between the tip portion and the fan case
4. However, when the engine rotates, centrifugal force extends the
spring and the tip portion makes air-lubricated contact with the
fan case. The spring can be formed of e.g. carbon, glass or metal,
and be bonded or mechanically fixed to the tip of the blade. The
tip portion can be formed of e.g. metal, plastic, composite or
ceramic, although a carbon tip is preferred.
[0037] The sealing element of any of the above embodiments may have
a portion formed of relatively low friction material at its
radially outer edge. For example, the low friction material portion
can be of carbon, PTFE or PEEK. It may be applied as a coating to
the sealing element. The material may be reapplied at intervals to
regain efficiency losses.
[0038] FIG. 6 shows schematically (a) a transverse cross-section
and (b) a plan view of the fan case 4. In order to avoid blocking
or damage, the fan case can have grooves 11 to allow any debris
from the sealing element to be pushed away from the fan tip.
[0039] FIGS. 7(a), (b) and (c) show schematic end-on views of three
fan blades. In FIG. 7(a), the blade has a plurality of sealing
elements distributed in an overlapping pattern along the radially
outer edge of the blade to provide an efficient seal. In FIG. 7(b),
the blade has a single sealing element which follows the curved
profile of the radially outer edge of the blade. In FIG. 7(c), the
blade again has a single sealing element which follows the curved
profile of the radially outer edge of the blade, but in this case
the element is contoured or shaped in the direction along the edge
of the blade to increase its stiffness.
[0040] As well as the improvement in engine performance that can be
achieved with the sealing element, for composite blades there is
also a reduced risk of blade delamination due to tip rubs. Further,
the sealing element can accommodate casing distortions.
Additionally, eliminating the abradable liner from the fan case can
reduce engine weight (providing further performance improvements)
and allows an acoustic fan track liner to be provided with the
potential to significantly reduce engine noise.
[0041] Because the sealing element has a relatively large clearance
to the casing when the engine is stationary, the procedure for
mounting fan blades onto the engine is facilitated. Further, once
mounted, the ability of the sealing element to tolerate variation
in blade length can reduce the amount of blade adjustment/shimming
that has to be performed. Also, abradable liners need to be
machined on engine when installed to provide the required fit, but
with the sealing element this requirement is removed.
[0042] While the invention has been described in conjunction with
the exemplary embodiments described above, many equivalent
modifications and variations will be apparent to those skilled in
the art when given this disclosure. Accordingly, the exemplary
embodiments of the invention set forth above are considered to be
illustrative and not limiting. Various changes to the described
embodiments may be made without departing from the spirit and scope
of the invention.
* * * * *