Note: Descriptions are shown in the official language in which they were submitted.
CA 02642777 2008-11-04
225199 (13DV)
BAFFLE SEAL FOR GAS TURBINE ENGINE
THRUST REVERSER
BACKGROUND OF THE INVENTION
This invention relates generally to gas turbine engine thrust reversers and
more
particularly to air seals for such reversers.
A gas turbine engine includes a turbomachinery core having a high pressure
compressor,
combustor, and high pressure turbine in serial flow relationship. The core is
operable in a
known manner to generate a primary flow of propulsive gas. A typical turbofan
engine
adds a low pressure turbine driven by the core exhaust gases which in turn
drives a fan
through a shaft to generate a bypass flow of propulsive gas. In the case of a
high bypass
engine this provides the majority of the total engine thrust.
Aircraft turbofan engines typically employ thrust reversers for ground
deceleration.
Known designs include "target" reversers, blocker-door reversers, and cascade
or
"doorless" reversers. Thrust reversers may be provided for the primary or
bypass flows of
an engine, or both. Each type of thrust reverser includes one or move
components which
are selectively moveable from a stowed position in which they do not affect
engine thrust,
to a deployed position in which some portion of the engine's thrust is turned
or directed
forward in order to slow the aircraft.
Thrust reverser components are relatively large and subject to air loads,
vibration, thermal
gradients, and other varying loads in operation. Accordingly, there is a limit
to how small
gaps and tolerances can be made, and some leakage of fan bypass flow occurs
from the
bypass duct to secondary flowpaths (i.e. inside the reverser). This results in
a mixing
pressure loss in the bypass duct that reduces net thrust, thus undesirably
increasing
specific fuel consumption (SFC).
- 1 -
CA 02642777 2008-11-04
225199 (13DV)
BRIEF SUMMARY OF THE INVENTION
These and other shortcomings of the prior art are addressed by the present
invention,
which provides a thrust reverser seal that reduces unwanted leakage of air
flow, thus
improving SFC of the engine.
According to one aspect, the invention provides a baffle seal for a thrust
reverser of a gas
turbine engine, including a seal body of a resilient material. The seal body
has a
relatively flat central portion having opposed front and back sides; and a
raised sealing
rim extending at least partially around the central portion. An outer
periphery of the
sealing rim extends beyond an outer periphery of the central portion so as to
define an
exposed sealing surface.
According to another aspect of the invention, a transcowl assembly for a gas
turbine
engine thrust reverser includes (a) longitudinally-extending structural beam
having a side
face; (b) an arcuate transcowl segment having an end disposed adjacent the
side face, the
transcowl segment moveable forward and aft along the structure beam between
stowed
and deployed positions. The transcowl segment includes: (i) an outer panel;
(ii) an inner
panel; and (iii) an arcuate cross-section baffle disposed between the inner
and outer
panels. A resilient baffle seal is carried by the structural beam. The baffle
seal is arranged
to engage in sealing contact with an inner surface of the baffle so as to
resist leakage of
air between the baffle and the structural beam.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be best understood by reference to the following description
taken in
conjunction with the accompanying drawing figures in which:
Figure 1 is a schematic side view of a gas turbine engine incorporating a
thrust reverser
constructed according to an aspect of the present invention;
Figure 2 is schematic side view of the gas turbine engine of Figure 1, with a
transcowl
thereof removed to show the internal components of the thrust reverser;
- 2 -
CA 02642777 2008-11-04
225199 (13DV)
=
Figure 3 is a schematic cross-sectional view of an aft portion of the gas
turbine engine
shown in Figure 1;
Figure 4 is half-sectional view taken along lines 4-4 of Figure 3;
Figure 5 is a perspective view of a baffle seal of the thrust reverser;
Figure 6 is a front view of the baffle seal of Figure 5; and
Figure 7 is a side view of the baffle seal of Figure 5.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings wherein identical reference numerals denote the same
elements
throughout the various views, Figure 1 depicts an aircraft turbofan engine 10.
The engine
has a longitudinal axis "A". The engine 10 is enclosed in a nacelle 12 and a
casing or
core nacelle 14 which defines an inner flowpath 16 of a bypass duct 18. A fan
nacelle 20
cooperates with the core nacelle 14 to define the outer flowpath 22 of the
bypass duct 18.
While not illustrated, it will be understood that the nacelle 12 encloses
conventional
components including a fan, a low pressure compressor or "booster" and a low
pressure
turbine ("LPT"), collectively referred to as a "low pressure system", and a
high pressure
compressor ("HPC"), a combustor, and a high pressure turbine ("HPT"),
collectively
referred to as a "gas generator" or "core". Together, the high and low
pressure systems are
operable in a known manner to generate a primary or core flow as well as a fan
flow or
bypass flow. The present invention is described and illustrated in the context
of a high-
bypass turbofan engine. However, the principles described herein are equally
applicable
to fan reversers for low-bypass engines, to turbine reversers, or to turbojet
engines.
The engine 10 includes a thrust reverser 24 of the type having a pair of
opposed, generally
semicircular cowlings referred to as "transcowls" 26. In the illustrated
example, the
reverser includes "left" and "right" transcowls. Only the left transcowl 26 is
shown in
Figure 1, it being understood that the right transcowl 26 is generally a
mirror image
thereof. The present invention is equally applicable to other configurations
which may
use transcowls positioned in a different orientation (e.g. upper and lower),
or a single
- 3 -
CA 02642777 2008-11-04
225199 (13DV)
larger transcowl. The transcowls 26 are supported at their terminal ends by
spaced-apart
upper and lower beams 28 and 30, respectively, via rails or tracks 32, so that
the
transcowls 26 can translate forward and aft in a direction generally parallel
to axis A,
powered by a known type of actuator (not shown). As with prior art thrust
reversers, the
reverser halves may be mounted so that they can swing open about a
longitudinal axis for
inspection or servicing. Accordingly, the upper beam 28 may also be referred
to as a
"hinge beam" and the lower beam 30 may be referred to as a "latch beam".
Figure 2 shows the engine 10 with the transcowl 26 removed to expose the
internal
components of the thrust reverser 24. A semicircular torque box 34 supports
then upper
and lower beams 28 and 30. A semicircular assembly of cascade boxes 36
containing
reversing vanes 38 extends from the upper beam 28 to the lower beam 30 and is
structurally attached to the upper and lower beams 28 and 30 and to the torque
box 34. A
mirror-image torque box and cascade boxes (not shown) are carried on the
opposite side
of the engine 10. An inner reverser fairing 40 cooperates with the core
nacelle 14 to form
a part of the bypass duct inner flowpath 16.
Figure 3 shows in more detail the cross-section of the thrust reverser 24 in a
forward-most
or "stowed" position. The transcowl 26 includes an outer wall 42, an inner
wall 44 which
forms a part of the outer flowpath 22, and a forward-facing baffle 46 having
an arcuate
cross-section. A radially inner end of the baffle 46 carries a forward seal 48
which rides
in close proximity to the aft end of the torque box 34.
For various reasons it is impractical to make a complete seal between the
torque box 34
and the baffle 46 using the forward seal 48. Accordingly, there exists an open
leakage
path which allows air to flow from the bypass duct 18 through the forward seal
48 in a
generally radially outward direction into the space between the torque box 34
and the
baffle 46, then circumferentially around to the upper beam 28 and the lower
beam 30,
and then longitudinally aft back into the bypass duct 18. Diversion of the fan
flow
through this leakage path results in a mixing pressure loss which reduces net
thrust of the
engine 10, which in turn increases SFC.
- 4 -
CA 02642777 2008-11-04
225199 (13DV)
To reduce or prevent this leakage, one or more baffle seals 50 are provided,
as shown in
Figure 4, which is a forward-looking aft (FLA) view. Upper and lower baffle
seals 50A
and 50B are attached to the side faces 52A and 52B of the upper and lower
beams 28 and
30, respectively, in alignment with the upper and lower ends 54A and 54B of
the baffle
46. Only the right-side (i.e. aircraft starboard side) baffle seals 50 are
shown in Figure 4,
with the understanding that another pair of baffle seals 50 would be installed
on the left-
side (i.e. aircraft port) faces of the upper and lower beams 28 and 30.
Figures 5-7 illustrate a baffle seal 50 in more detail. The specific baffle
seal 50 illustrated
is the upper right-hand unit, which is identical to a lower left-hand unit
(not shown). In
this example, the upper left-hand and lower right-hand baffle seals 50 would
have mirror-
image configurations to that of the illustrated baffle seal 50, but otherwise
the baffle seal
50 is representative of all of the baffle seals 50.
Each baffle seal 50 comprises a seal body 56, optionally provided with a
backing plate
58 and a retainer 60. The seal body 56 is generally three-sided in plan view
with an
arcuate forward edge 62 contoured to the shape of the torque box 34. The seal
body 56
may be generally triangular or may have more of a "D"-shape in plan view,
depending on
the particular application. The seal body 56 has a relatively flat central
portion 64 with
opposed front and back sides 66 and 68. The upper and lower edges of the seal
body 56
are formed into a hollow tube-like sealing rim 70 formed by a closed wall 72,
which in
this case has an elongated cross-section with rounded ends. Other cross-
sectional shapes
may be used as well. For example, instead of a tube-like geometry, the sealing
rim 70 ma
be a flange or "flapper" shape. The outer periphery of the sealing rim 70
defines a sealing
surface 74 which extends beyond the outer periphery of the central portion.
The sealing
rim 70 is generally V- or C- shaped with elongated legs 70A and 70B connected
at their
proximal ends by a curved segment 70C. When installed, the distal ends of the
legs 70A
and 70B butt up against other components of the thrust reverser 24 and may be
closed off
with a sealant, such as room-temperature vulcanizing (RTV) silicone. At least
one vent
opening 76 is formed in the sealing rim 70 to allow it to equalize its
internal pressure with
the ambient pressure (e.g. when atmospheric pressure changes during flight, or
when the
sealing rim 70 is compressed during stowage of the transcowl 26). A portion of
the
- 5 -
CA 02642777 2008-11-04
225199 (13DV)
periphery of the seal body 56 extends outwardly from the central portion 64 to
form an
edge bead 78.
The seal body 56 is formed from a resilient material such as silicone rubber.
The outer
surface of the baffle seal 50 may be covered with a flexible, abrasion-
resistant material to
avoid damage from rubbing. One example of a suitable material is DACRON
polyester
fabric.
The backing plate 58 is made of a relatively rigid material such as aluminum
sheet. It is
generally triangular in plan view with an arcuate forward edge and has a
curved lip 80
formed around its periphery (or a portion thereof) which serves to receive the
edge bead
78 of the baffle seal 50.
The retainer 60 is also made of a relatively rigid material such as aluminum
sheet. It is
generally triangular in plan view with an arcuate forward edge. It has flanges
82 formed
along its upper and lower edges which bear against the inside surfaces of the
baffle seal
50, near the junction between the central portion 64 and the sealing rim 70.
In the illustrated example the baffle seal 50 is secured to the upper beam 28
with rivets 84
extending through the retainer 60, baffle seal 50, backing plate 58, and the
upper beam
28. However it will be understood that the baffle seal 50 could be attached
with other
types of fasteners (e.g. bolts, machine screws), or by methods such as welding
or
adhesives. The backing plate 58 restrains the outer periphery of the seal body
56 against
the upper beam 28 so as to avoid "dishing" or curling. The seal body 56 is
further
restrained in the desired shape by the retainer, which presses the sealing
surface 74 into
place as well as spreading out the load of the metallic rivets 84 to hold the
seal body 56 in
place without tearing.
When the transcowl 26 is stowed, as shown in Figures 5 and 6, the interior
surface 86 of
the baffle 46 engages the baffle seal 50. Because the transcowl 26 moves in
the direction
of the arrow "T" when being stowed or deployed, the interaction with the
baffle seal 50 is
a combination of sliding and compression. This minimizes any loads placed on
the
actuating equipment by the presence of the baffle seal 50.
- 6 -
CA 02642777 2013-09-05
225199 (13DV)
In operation, flow in the bypass duct 18 will initially tend to leak past the
forward seal
48 as with a prior art thrust reverser and will flow circumferentially inside
the leak
path. However, the air is blocked or substantially prevented from exiting the
leak path
by the baffle seal 50. This tends to cause the pressure to equalize between
the leak
path and the bypass duct 18. Without a substantial pressure differential to
drive flow
into the leak path, further leakage is greatly reduced. It is estimated that
this leakage
reduction can improve SFC by about 0.05% in certain applications.
The foregoing has described a baffle seal for a gas turbine engine thrust
reverser.
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 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.
- 7 -
