U.S. patent application number 13/604722 was filed with the patent office on 2014-03-06 for rub tolerant fan case.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is Michael Edward Eriksen, Gerald Alexander Pauley, Daniel Thomas Scorse. Invention is credited to Michael Edward Eriksen, Gerald Alexander Pauley, Daniel Thomas Scorse.
Application Number | 20140064938 13/604722 |
Document ID | / |
Family ID | 49001051 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140064938 |
Kind Code |
A1 |
Eriksen; Michael Edward ; et
al. |
March 6, 2014 |
RUB TOLERANT FAN CASE
Abstract
A case apparatus for a gas turbine engine includes an annular
case having an interior surface with annular recess formed therein;
and an annular bumper disposed in the recess, the bumper comprising
a frangible material and having a low-friction contact surface,
wherein the bumper is configured to permit elastic radial
deflection in response to applied forces below a predetermined
threshold.
Inventors: |
Eriksen; Michael Edward;
(Cincinnati, OH) ; Pauley; Gerald Alexander;
(Hamilton, OH) ; Scorse; Daniel Thomas;
(Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Eriksen; Michael Edward
Pauley; Gerald Alexander
Scorse; Daniel Thomas |
Cincinnati
Hamilton
Cincinnati |
OH
OH
OH |
US
US
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
49001051 |
Appl. No.: |
13/604722 |
Filed: |
September 6, 2012 |
Current U.S.
Class: |
415/173.3 ;
415/173.4 |
Current CPC
Class: |
F01D 25/24 20130101;
Y02T 50/672 20130101; Y02T 50/60 20130101; F01D 21/045
20130101 |
Class at
Publication: |
415/173.3 ;
415/173.4 |
International
Class: |
F01D 11/08 20060101
F01D011/08; F01D 11/12 20060101 F01D011/12 |
Claims
1. A case apparatus for a gas turbine engine, comprising: an
annular case having an interior surface with annular recess formed
therein; and an annular bumper disposed in the recess, the bumper
comprising a frangible material and having a low-friction contact
surface, wherein the bumper is configured to permit elastic
deflection in response to applied forces below a predetermined
threshold.
2. The apparatus of claim 1 wherein the bumper includes a web
defining the contact surface, and a pair of spaced-apart parallel
legs extending from the web, wherein the web and the legs
cooperatively define a channel.
3. The apparatus of claim 2 wherein the web is convex-curved.
4. The apparatus of claim 2 wherein the bumper includes a pair of
flanges extending in opposite directions from distal ends of the
legs.
5. The apparatus of claim 1 wherein the bumper comprises
carbon-epoxy composite.
6. The apparatus of claim 5 wherein the composite includes at least
one layer of glass fiber at the contact surface.
7. The apparatus of claim 2 further comprising a filler disposed in
the channel of the bumper.
8. The apparatus of claim 7 wherein the filler comprises a
honeycomb structure.
9. The apparatus of claim 1 further comprising an abradable
material disposed in the recess adjacent the bumper, such that the
abradable material, the contact surface, and the interior surface
cooperatively define a flowpath surface.
10. The apparatus of claim 9 wherein the abradable material
comprises a phenolic resin.
11. A fan apparatus for a gas turbine engine comprising: an annular
fan case having an interior surface with annular recess formed
therein; and an annular bumper disposed in the recess, the bumper
comprising a frangible material and having a low-friction contact
surface; and a rotor carrying an array of blades mounted for
rotation within the case such that the bumper is in axial alignment
with tips of the blades, wherein the bumper is configured to permit
elastic radial deflection in response to contact between the blades
and the bumper generating applied forces below a predetermined
threshold.
12. The apparatus of claim 11 wherein the bumper includes a web
defining the contact surface, and a pair of spaced-apart parallel
legs extending from the web, wherein the web and the legs
cooperatively define a channel.
13. The apparatus of claim 12 wherein the web is convex-curved.
14. The apparatus of claim 12 wherein the bumper includes a pair of
flanges extending in opposite directions from distal ends of the
legs.
15. The apparatus of claim 11 wherein the bumper comprises
carbon-epoxy composite.
16. The apparatus of claim 15 wherein the composite includes at
least one layer of glass fiber.
17. The apparatus of claim 12 further comprising a filler disposed
in the channel of the bumper.
18. The apparatus of claim 17 wherein the filler comprises a
honeycomb structure.
19. The apparatus of claim 11 further comprising an abradable
material disposed in the recess adjacent the bumper, such that the
abradable material, the contact surface, and the interior surface
cooperatively define a flowpath surface.
20. The apparatus of claim 19 wherein the abradable material
comprises a phenolic resin.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to gas turbine engines and
more particularly to a containment structure for a fan of a gas
turbine engine.
[0002] A turbofan engine typically includes a fan, a booster, a
high pressure compressor, a combustor, a high pressure turbine, and
a low pressure turbine in serial axial flow relationship about a
longitudinal centerline axis of the engine. The high pressure
turbine is drivingly connected to the high pressure compressor via
a first rotor shaft, and the low pressure turbine is drivingly
connected to both the fan and booster via a second rotor shaft. The
fan includes an annular disk and a plurality of radially extending
blades mounted to the disk, wherein the disk and the blades are
rotatable about the longitudinal centerline of the engine. Such
fans are surrounded by a fan case which is specifically designed to
be capable of containing a fan blade in the event that the fan
blade is released from its disk during operation. This prevents or
minimizes the structural damage to the engine and aircraft should
one or more fan blades be released from the disk due to a
catastrophic failure of one or more blades, ingestion of debris, or
other cause.
[0003] The fan case also serves as the outer flowpath boundary
through the fan rotor and closely circumscribes the tips of the fan
blades in order to minimize leakage past the fan blades. Prior art
fan cases are typically lined with a sacrificial abradable material
in order to protect the fan blades during contact between the fan
blades and the fan case (referred to as "rub.") While sacrificial
wearing away of the abradable prevents damage to costly fan blades,
it also opens up the radial clearance at the blade tips, resulting
in loss of engine thrust.
[0004] Some engines are subject to unavoidable fan blade rubs in
operation, for example during aircraft maneuvers or transient fan
unbalance. In these cases the use of an abradable material alone
could result in unacceptable thrust loss.
[0005] Accordingly, there is a need for a fan casing that tolerates
fan blade rubs while maintaining intended clearances.
BRIEF DESCRIPTION OF THE INVENTION
[0006] This need is addressed by the present invention, which
provides a fan casing incorporating a frangible, rub-tolerant
bumper.
[0007] According to one aspect of the invention, a case apparatus
for a gas turbine engine includes an annular case having an
interior surface with annular recess formed therein; and an annular
bumper disposed in the recess, the bumper comprising a frangible
material and having a low-friction contact surface, wherein the
bumper is configured to permit elastic deflection in response to
applied forces below a predetermined threshold.
[0008] According to another aspect of the invention, a fan
apparatus includes: an annular fan case having an interior surface
with annular recess formed therein; an annular bumper disposed in
the recess, the bumper comprising a frangible material and having a
low-friction contact surface; and a rotor carrying an array of
blades mounted for rotation within the case such that the bumper is
in axial alignment with tips of the blades, wherein the bumper is
configured to permit elastic radial deflection in response to
contact between the blades and the bumper generating applied forces
below a predetermined threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention may be best understood by reference to the
following description taken in conjunction with the accompanying
drawing figures in which:
[0010] FIG. 1 is a schematic half-sectional view of a fan section
of a gas turbine engine incorporating a fan case constructed
according to an aspect of the present invention; and
[0011] FIG. 2 is an enlarged view of a portion of a fan case shown
in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Referring to the drawings wherein identical reference
numerals denote the same elements throughout the various views,
FIG. 1 shows a portion of an exemplary fan section 10 of a turbofan
gas turbine engine used for powering an aircraft in flight. The fan
section 10 includes a fan 12 which is rotated about a central
longitudinal axis "A" by a conventional fan shaft 14 powered by a
conventional low pressure turbine (not shown). The fan 12 includes
a rotor disk 16 from which extends radially outwardly an array of
airfoil-shaped fan blades 18 (only one shown in FIG. 1). The rotor
disk 16 and the fan blades 18 may be separable from each other or
they may be part of an integrally-bladed rotor or "blisk." Each fan
blade 18 has a leading edge 20, a trailing edge 22, a root 24, and
a tip 26. Disposed downstream of the fan 12 is an array of
airfoil-shaped outlet guide vanes ("OGVs") 27. While the invention
is described in the context of a fan and fan case, it will be
understood that the principles of the present invention are equally
applicable to casings surrounding other types of rotating
components.
[0013] An annular fan case 28 surrounds the fan 12. As used herein,
the term "annular" refers to a structure with a closed perimeter
that is generally ring-shaped and includes both circular and
non-circular shapes. The fan case 28 has forward and aft ends 30
and 32. A forward flange 34 mates with a nacelle (not shown) and an
aft flange 36 mates with a flange 38 of a downstream engine casing
component 40. The fan case 28 has an outer surface 42 and an
opposed interior surface 44. The interior surface 44 cooperates
with other components, described in more detail below, to define a
flowpath surface "F" configured to closely surround the tip 26 of
the fan blades 18.
[0014] In accordance with known practices, the fan case 28 is sized
and shaped so as to be able to withstand expected operating loads
such as gas pressure loads, body loads, and maneuvering loads. The
fan case 28 is also configured to serve as a containment member, or
in other words to resist penetration if it should be struck by a
fan blade 18 released from the rotor disk 16. A blade release would
typically be the result of a foreign object being ingested by the
fan 12 during engine operation and is commonly referred to as a
"blade-out" event. In the illustrated example, the fan case 28 is
of monolithic construction and is made from an alloy such as
aluminum, titanium, or steel. Fan cases may be made from composite
materials as well. As used herein, the term "axial alignment"
implies a common or overlapping position of two components as
measured along the central longitudinal axis A.
[0015] As best seen in FIG. 2, an annular recess 46 is formed in a
portion of the interior surface 44 and a bumper 48 is disposed in
the recess. The bumper 48 may be an annular component having a
contact surface 50 positioned in axial alignment with the fan
blades 18. As discussed in more detail below, the bumper 48 is
configured so as to have low friction at the contact surface 50, to
permit elastic radial deflection with linear stress-strain behavior
during blade contact under relatively low loads, and to be
frangible during blade contact under relatively high loads. As used
herein, the term "low friction" is relative and refers to a
generally hard, smooth condition without a rough finish. In the
illustrated example, the bumper 48 has a "hat section" shape
including a generally axially-aligned web 52, a pair of
spaced-apart, radially-extending legs 54, and optionally a pair of
flanges 56 extending axially forward and aft from the distal ends
of the legs 54. The flanges 56 are shaped to fit against the
interior of the recess 46. The web 52 of the bumper 48 defines the
contact surface 50 and is slightly crowned or convex-curved
relative to the fan blades 18. The bumper 48 is sized and shaped
such that it does not require any change in the recess 46 or the
fan case 28 as compared to a prior art fan case design. It use
therefore has no significant effect on the containment function of
the fan case 28.
[0016] The bumper 48 is constructed so as to be frangible during a
blade impact. As used herein, the term "frangible" refers to a
material that will essentially disintegrate into very small,
low-mass particles upon failure, i.e. it will experience brittle
failure rather than ductile failure. In the illustrated example the
bumper 48 is made from a composite system, for example
intermediate-modulus graphite fibers in a toughened epoxy matrix.
The radially-inboard surface of the bumper 48 may incorporate a
glass fiber layer to minimize damage to the blade tips 26 in case
of contact. The bumper 48 may be secured in position in the recess
46 with a known adhesive.
[0017] An optional filler 58 is disposed in the annular channel
defined by the shape of the bumper 48. The purpose of the filler 58
is to permit control of the bumper's harmonics by providing
stiffness and/or damping to the bumper 48. Materials such as
composite honeycomb (e.g. incorporating an aramid fiber such as
NOMEX) or elastomers may be used for this purpose. The filler 58
may be provided as one piece or as multiple pieces, and may be
bonded to the bumper 48 and/or the recess 46 using a known
adhesive.
[0018] An abradable material 60 of a known type may be disposed in
the recess 46 in the spaces forward and aft of the bumper 48. In
the illustrated example the abradable material 60 comprises a
phenolic resin embedded with glass microspheres. The exposed
surface of the abradable material 60 cooperates with the bumper 48
and the interior surface 44 of the fan case 28 to define the
flowpath surface F. During manufacture, some or all of the interior
surface 44, the abradable material 60, and the bumper 48 may be
machined in one or more process steps to form the contours of the
flowpath surface F.
[0019] In operation, there normally will be no contact between the
bumper 48 and the fan blades 18. Occasionally the fan 12 may
experience a minor unbalanced condition causing it to deflect
radially from a nominal position (i.e. to whirl or gyrate instead
of purely rotating). As a result the tips 36 of the fan blades 18
may deflect radially and contact the bumper 48, specifically the
web 52. The contact surface 50 of the web 52 is low-friction,
allowing the fan blade 18 to skate or skid along its surface, while
the legs 54 permit linear elastic deflection of the bumper 48 in
the radial direction when the applied forces are below a
predetermined threshold. The bumper 48 may thus be considered a
"rub tolerant" structure. The action of the bumper 48 prevents the
fan blade tip 36 from contacting the abradable material 60. This is
desirable as contact with the abradable material 60 causes the
radial clearance between the flowpath surface F and the fan blades
18 to open up, and can lead to unacceptable loss of engine
thrust.
[0020] In contrast, if a fan blade out event occurs, which is an
event generating significantly higher forces than a blade rub, the
bumper 48 will act as a frangible fuse. Upon blade contact the
bumper 48 will essentially be crushed or disintegrate into very
small, low-mass particles. This avoids affecting the fan blade out
loads or causing secondary damage. As an example, the load at which
the bumper 48 will fuse may be on the order of 40-50% greater than
the load expected during occasional rubs. The characteristics of
the bumper 48 may be adjusted for a particular application by
selection of the dimensions of the web 52 and legs 54 as well as
the type of composite material, and the number, size, and
orientation of plies.
[0021] Testing of a fan case constructed as described above has
demonstrated the bumper's ability to provide needed linear elastic
behavior under rub loads while crushing under higher loads as
required so as to not affect fan blade out loads. Testing has also
demonstrated that the bumper 48 prevents thrust loss after reacting
rub loads without crush or delamination.
[0022] The foregoing has described a fan case with a rub tolerant
bumper. While specific embodiments of the present invention have
been described, it will be apparent to those skilled in the art
that various modifications thereto can be made without departing
from the spirit and scope of the invention. Accordingly, the
foregoing description of the preferred embodiment of the invention
and the best mode for practicing the invention are provided for the
purpose of illustration only and not for the purpose of limitation,
the invention being defined by the claims.
* * * * *