Title: Blade arrangement for gas turbine engine
Abstract: A blade arrangement for a gas turbine engine includes a plurality of blades mounted for rotation on a disc so as to extend radially therefrom and a retention member, the retention member including an attachment portion which is attached to the disc and an abutment portion for resisting forward axial movement of at least one of the blades relative to the disc. The blade arrangement further comprises restraint means spaced from the attachment portion of the retention member, for substantially preventing radially outward movement of the abutment portion of the retention member when a forward axial force is applied by the blade to the abutment portion.
Patent Number: 6,971,855 Issued on 12/06/2005 to Richards, et al.
| Inventors:
|
Richards; Martyn (Burton on Trent, GB);
Udall; Kenneth F (Derby, GB);
Swift; Andrew (Denstone, GB)
|
| Assignee:
|
Rolls-Royce plc (London, GB)
|
| Appl. No.:
|
724629 |
| Filed:
|
December 2, 2003 |
Foreign Application Priority Data
| Current U.S. Class: |
416/220R; 416/244.R |
| Intern'l Class: |
F01D 005/32 |
| Field of Search: |
416/219 R,220.R,204.A,244.R
|
References Cited [Referenced By]
U.S. Patent Documents
| 3734646 | May., 1973 | Perkins.
| |
| 4207029 | Jun., 1980 | Ivanko.
| |
| Foreign Patent Documents |
| 0 609 979 | Aug., 1994 | EP.
| |
| 2 244 100 | Nov., 1991 | GB.
| |
Primary Examiner: Look; Edward K.
Assistant Examiner: Edgar; Richard A.
Attorney, Agent or Firm: Taltavull; W. Warren, Manelli Denison & Selter PLLC
Claims
1. A blade arrangement for a gas turbine engine, the blade arrangement comprising:
a plurality of blades mounted for rotation on a disc so as to extend radially
outwardly therefrom; and
a retention member, the retention member including an attachment portion which
is attached to the disc and an abutment portion for resisting forward axial movement
of at least one of the blades relative to the disc;
wherein the blade arrangement further comprises restraint means spaced from the
attachment portion of the retention member, for substantially preventing radially
outward movement of the abutment portion of the retention member when a forward
axial force is applied by the blade to the abutment portion wherein the attachment
portion of the retention member is located axially forwardly of the abutment portion
and of the restraint means.
2. A blade arrangement according to claim 1 wherein the retention member includes
an arm portion which extends between the attached portion and the restraint means,
the arm portion being angled at between 40° and 70° to the axial direction
of the blade arrangement.
3. A blade arrangement according to claim 1 wherein the retention member is shaped
such that the abutment portion contacts part of the blade when a forward axial
force is applied to the blade, to resist forward axial movement of the blade.
4. A blade arrangement according to claim 3 wherein the geometry of the blade
arrangement is such that when the blade applies a forward axial force to the abutment
portion of the retention member, a vector representing the resultant force applied
to the retention member passes substantially through the attachment portion of
the retention member.
5. A blade arrangement according to claim 4 wherein the restraint means includes
a part of the retention member which is shaped such that its radial movement is
substantially prevented by an adjacent part of the blade or the disc.
6. A blade arrangement according to claim 1 wherein the restraint means is substantially
cylindrical in shape, and the adjacent part of the fan blade or disc comprises
a substantially cylindrical member, located radially outwardly of and adjacent
to the restraint means, to substantially prevent radially outward movement of the
restraint means.
7. A blade arrangement according to claim 1, wherein the blade arrangement forms
part of a low pressure compressor or fan.
8. A gas turbine engine including a low pressure compressor or fan including
a blade arrangement according to claim 1.
9. A blade arrangement for a gas turbine engine, the blade arrangement comprising:
a plurality of blades mounted for rotation on a disc so as to extend radially
outwardly therefrom; and
a retention member, the retention member including an attachment portion which
is attached to the disc and an abutment portion for resisting forward axial movement
of at least one of the blades relative to the disc;
where in the blade arrangement further comprises restraint means spaced from
the attachment portion of the retention member, for substantially preventing radially
outward movement of the abutment portion of the retention member when a forward
axial force is applied by the blade to the abutment portion wherein the retention
member is shaped such that the abutment portion contacts part of the blade when
a forward axial force is applied to the blade, to resist forward axial movement
of the blade wherein the geometry of the blade arrangement is such that when the
blade applies a forward axial force to the abutment portion of the retention member,
a vector representing the resultant force applied to the retention member passes
substantially through the attachment portion of the retention member wherein the
restraint means includes a part of the retention member which is shared such that
its radial movement is substantially prevented by an adjacent part of the blade
or the disc wherein the said part of the retention member comprises a restraint
member extending from a remainder of the retention member in an axially rearwards
direction, the adjacent part of the blade or disc being located radially outwardly
of the restraint member.
10. A blade arrangement according to claim 9 wherein the abutment portion and
the restraint member together comprise a portion of the restraint member which
is generally L-shaped in section.
11. A blade arrangement according to claim 9 wherein the attachment portion of
the retention member is located axially forwardly of the abutment portion and of
the restraint means.
12. A blade arrangement according to claim 11 wherein the disc also includes
an attachment portion, to which the retention member is attached, via a bolt arrangement,
the bolt extending in the axial direction, and passing through both respective
attachment portions of the retention member and the disc.
13. A blade arrangement according to claim 12 wherein the restraint means includes
an arm portion which extends between the attachment portion and the restraint member,
the arm portion being angled at between 40° and 70° to the axial direction
of the blade arrangement.
14. A blade arrangement according to claim 13 wherein the arm portion includes
an undercut shoulder, which is generally L-shaped in section, and of complementary
shaped to a radially outer corner of the attachment portion.
15. A blade arrangement according to claim 13 wherein the arm portion is substantially
frustoconical in shape.
16. A blade arrangement for a gas turbine engine, the blade arrangement comprising:
a plurality of blades mounted for rotation on a disc so as to extend radially
outwardly therefrom; and
a retention member, the retention member including an attachment portion which
is attached to the disc and an abutment portion for resisting forward axial movement
of at least one of the blades relative to the disc;
where in the blade arrangement further comprises restraint means spaced from
the attachment portion of the retention member, for substantially preventing radially
outward movement of the abutment portion of the retention member when a forward
axial force is applied by the blade to the abutment portion wherein the restraint
means comprises an elongate finger, located between the disc and the blade, the
finger extending rearwardly from a remainder of the retention member, in the axial direction.
17. A blade arrangement according to claim 16 wherein the retention member includes
a plurality of elongate fingers each located between a blade and the disc, an elongate
finger being located between each blade and the disc.
Description
FIELD OF THE INVENTION
The invention relates to a blade arrangement for a gas turbine engine, particularly
but not exclusively for a low pressure compressor or fan.
BACKGROUND OF THE INVENTION
A blade arrangement for a gas turbine engine fan includes a plurality of fan
blades
mounted for rotation on a fan disc so as to extend radially outwardly from the
disc. Each blade is mounted on the disc via a root portion of the blade which fits
into a complementary slot in the disc. The root portion may for example be "dovetail"
shaped. The blade arrangement is conventionally contained within a fan case, a
small clearance being provided between radially outer tips of the blades and the
fan case.
If a single fan blade of the blade arrangement becomes detached from the disc,
this produces a very large forward axial force on the adjacent blade. Large forward
axial forces are also imposed on the other remaining blades because the loss of
a single blade results in the distortion or ovality of the fan case. The more the
casing distorts, the heavier the contact between the casing inner surface and the
remaining blade tips, leading to increased forward force on each remaining blade
as it rotates past the distortions in the casing. There is consequently a requirement
to restrain the remaining blades in the axial direction, to prevent further blade loss.
Conventionally, axial restraint has been provided by a thrust ring.
This consists of a generally annular member which is attached to the disc and which
includes an abutment portion located axially forward of the blades. When an axially
forward force is exerted on a blade, the blade abuts against the thrust ring and
is retained in place on the disc.
As engines have increased in size, the magnitudes of the forces exerted on the
blades in the event of a single blade being lost have increased. A larger, heavier
blade can cause increased distortion of the fan case leading to increased forward
forces on the remaining blades as they rotate past the distortions in the casing.
There is thus a desire to provide an improved thrust ring.
SUMMARY OF THE INVENTION
According to the invention there is provided a blade arrangement for a
gas turbine engine, the blade arrangement comprising:
a plurality of blades mounted for rotation on a disc so as to extend radially
outwardly
therefrom; and
a retention member, the retention member including an attachment portion which
is attached to the disc and an abutment portion for resisting forward axial movement
of at least one of the blades relative to the disc;
the blade arrangement further comprising restraint means spaced from the attachment
portion of the retention member, for substantially preventing radially outward
movement of the abutment portion of the retention member when a forward axial force
is applied by the blade to the abutment portion.
Where the term "forward" is used throughout this specification it refers to
a direction towards the front of the engine in normal use.
The blade arrangement may form part of a low pressure compressor or fan.
Preferably the retention member is shaped such that the abutment portion
contacts part of the blade when a forward axial force is applied to the blade,
to resist forward axial movement of the blade.
Preferably the geometry of the blade arrangement is such that when the
blade applies a forward axial force to the abutment portion of the retention member,
a vector representing the resultant force applied to the retention member passes
substantially through the attachment portion of the retention member.
Preferably the restraint means includes a part of the retention member
which is shaped such that its radial movement is substantially prevented by an
adjacent part of the blade or the disc. Where a part of the blade or disc is referred
to this is intended to include any additional member attached to the blade or disc.
The said part of the retention member may comprise a restraint member extending
from a remainder of the retention member in an axially rearwards direction. Preferably
the adjacent part of the blade or disc is located radially outwardly of the restraint
member. A small radial gap may be provided between the restraint member and the
adjacent part of the blade or disc. Preferably this gap is between up to 5 mm in width.
The attachment portion of the retention member is preferably located axially
forwardly of the abutment portion and of the restraint means. The attachment portion
is preferably attached to the disc by attachment means. The disc may also include
an attachment portion, to which the retention member is attached. The attachment
means preferably includes a bolt arrangement, the bolt extending in the axial direction,
and passing through both respective attachment portions of the retention member
and the disc.
Preferably the retention member includes an arm portion which extends
between the attachment portion and the restraint member. Preferably the arm portion
is angled at between 10° and 80° to the axial direction of the blade
arrangement. The arm portion may be angled at between 20° and 50° to
the axial direction.
Preferably the arm portion is substantially frustoconical in shape.
The restraint member may be substantially cylindrical in shape. Preferably the
cylinder is generally co-axial with the disc. The adjacent part of the fan blade
or disc may comprise a substantially cylindrical member provided on the blade,
located radially outwardly of and adjacent to the restraint member, to substantially
prevent radially outward movement of the restraint member.
Alternatively the restraint member may comprise an elongate finger,
located between the disc and the blade. Preferably the finger extends rearwardly
from a remainder of the retention member, in the axial direction. Preferably the
retention member includes a plurality of elongate fingers each located between
a blade and the disc. Preferably an elongate finger is located between each blade
and the disc.
According to the invention there is further provided a gas turbine engine
including a blade arrangement according to any of the preceding definitions. The
blade arrangement may form part of a low pressure compressor or fan of the gas
turbine engine.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be described for the purpose of illustration
only, with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic sectional view showing the general arrangement of a
known gas turbine engine.
FIG. 2 is a diagrammatic perspective view of part of a known blade arrangement
for a gas turbine engine fan, showing a lost blade;
FIG. 3 is a diagrammatic sectional view of part of a blade arrangement incorporating
a known thrust ring;
FIG. 4 is a diagrammatic sectional view of part of a blade arrangement according
to a first embodiment of the invention;
FIG. 5 is a diagrammatic sectional view of part of a blade arrangement according
to a second embodiment of the invention;
FIG. 6 is a diagrammatic sectional view of part of a blade arrangement according
to a third embodiment of the invention; and
FIG. 7 is a diagrammatic sectional view of part of a blade arrangement according
to a fourth embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1 a ducted fan gas turbine engine generally indicated
at
10 comprises, in axial flow series, an air intake
12, a propulsive
fan
14, an intermediate pressure compressor
16, a high pressure compressor
18, combustion equipment
20, a high pressure turbine
22, an
intermediate pressure turbine
24, a low pressure turbine
26 and an
exhaust nozzle
28.
The gas turbine engine
10 works in the conventional manner so that air
entering the intake
12 is accelerated by the fan
14 to produce two
air flows, a first air flow into the intermediate pressure compressor
16
and a second airflow of "bypass air" which provides propulsive thrust. The intermediate
pressure compressor
16 compresses the air flow directed into it before delivering
the air to the high pressure compressor
18 where further compression takes place.
The compressed air exhausted from the high pressure compressor
18 is directed
into the combustion equipment
20 where it is mixed with fuel and the mixture
combusted. The resultant hot combustion products then expand through and thereby
drive the high, intermediate and low pressure turbines
22,
24 and
26 before being exhausted through the nozzle
28 to provide additional
propulsive thrust. The high, intermediate and low pressure turbines
22,
24 and
26 respectively drive the high and intermediate pressure compressors
16 and
18 and the fan
14 by suitable interconnecting shafts.
FIG. 2 illustrates in more detail a part of a blade arrangement in the form
of a fan
14 for the gas turbine engine
10. The fan
14 includes
a plurality of fan blades
30 extending radially outwardly from a disc
32.
Each blade
30 includes a dovetail root portion
34 fitting into a
complementary slot
36 in the disc
32. A fan case
38 (see FIG.
1) surrounds the blades
30, a small clearance being provided between radially
outer tips of the blades
30 and the fan case
38.
Referring again to FIG. 2, a single fan blade
30a has been
lost from the disc
32, along a release plane
39. The released blade
30a initially impacts an adjacent trailing blade
30b at
an impact point
40, exerting a substantial forward axial force on that blade.
A forward axial force is also exerted on the remaining blades by the distortion
of the fan case
38, as explained previously.
Referring to FIG. 3, it is known to use a thrust ring
42 to provide
axial restraint for the blades
30, when a single blade is released. FIG.
3 shows a blade
30 mounted on a disc
32, an annulus filler
44
also being visible. The annulus filler
44 fits between adjacent blades and
provides a smooth surface for airflow between the blades.
The thrust ring
42 is generally annular in overall shape and includes
a ring shaped attachment portion
46, which is attached by means of axially
extending bolts
48 to an adjacent ring shaped attachment portion
50
of the disc
32.
The thrust ring further includes an abutment portion
52 which is located
axially forwardly of a stop lug
54 attached to the blade root portion
34.
The abutment portion
52 thereby restrains axially forward movement of the
blade
30.
Referring to FIG. 4, there is illustrated in section a part of an improved
blade arrangement in the form of a fan
14.
The fan
14 includes a plurality of fan blades
30 (only one of which
is visible in FIG. 4) mounted on a disc
32, as previously described. The
fan arrangement further includes a retention member in the form of a thrust ring
42.
The thrust ring
42 is generally annular, being shown in section in FIG.
4, and includes an attachment portion
46 which is generally ring shaped.
The attachment portion
46 forms a radially inner part of the thrust ring
42, and is located at its axially forward end. The attachment portion
46
is affixed to a generally ring shaped attachment portion
50 of the disc
32, by attachment means in the form of bolts
48, just one of which
is visible and indicated schematically in FIG. 4. The bolts
48 extend axially
through the attachment portions
46 and
50 and hold the thrust ring
42 to the disc
32, preventing relative axial movement therebetween.
An attachment point
56 is defined where the bolts
48 intersect the
plane where the attachment portions
46 and
50 meet.
The thrust ring
42 further includes an arm portion
46 and which
is generally frustoconical in shape (and therefore straight and sloping in section
as illustrated in FIG. 4). The arm portion
58 in this embodiment slopes
at an angle of about 55° to the axial direction.
At its axially forward and radially inner end, the arm portion
58 includes
an undercut shoulder
59, which is generally L-shaped in section, and of
complementary shape to a right angled radially outer corner
61 of the attachment
portion
50.
At an axially rearward and radially outward end of the arm portion
58,
the thrust ring
42 includes restraint means in the form of a restraint member
60. The restraint member
60 is generally cylindrical in shape, extending
backwards from the arm portion
58 in the axial direction.
The thrust ring
42 further includes an abutment portion
52 which
extends radially outwardly from the arm portion
58. The abutment portion
52 is generally ring shaped, and is located rearwardly of the attachment
portion
46, and hence of the attachment point
56.
The blade
30 is formed with a post member
62 which in normal operation
touches or nearly touches the restraint member
60 and the abutment portion
52 of the thrust ring
42. The post member
62 extends in the
axially forward direction from the remainder of the blade
30 and lies radially
outwardly of the abutment portion
52 of the thrust ring
42. Although
just one post member
62 is illustrated in FIG. 4, each fan blade
30
would include a post member.
The thrust ring
42 functions as follows. If a blade is lost from the disc
32 a large rearward force is exerted on the remainder of the blades, including
the blade
30 illustrated in FIG. 4. The initial force is in the direction
of the arrow X. This force causes the post member
62 to abut against the
abutment portion
52 of the thrust ring
42. Because the thrust ring
42 is affixed to the disc
32 via the bolts
48, at the point
of attachment
56, the axially directed force causes a bending moment about
the bolts
48. The applicant has appreciated that in prior art designs of
thrust ring this force results in a rolling moment which causes a slight radially
outward movement of the abutment portion
52 of the thrust ring. This causes
the generally frustoconical shape of the thrust ring
42 to open out slightly
causing bending about the bolts
48 and possible weakening of the bolts
48.
In the thrust ring
42 of FIG. 4, any radially outward movement of the
abutment
portion
52 is prevented by the engagement of the restraint member
60
against the post member
62 on the blade
30. Because the point of
attachment
56 and the bolts
48 are located forwardly of the abutment
portion
52, the angle of the arm portion
58 relative to the axial
direction cannot increase without the restraint member
60 moving radially
outwardly, this being prevented by the post member
62.
The geometry of the restraint member
60, abutment portion
52 and
the post member
62 on the blade
30 is such that when the blade
30
exerts an axially forward force on the restraint member
60 and the abutment
portion
52, a vector representing the resultant force applied to the thrust
ring extends in the direction of the arrow Y, i.e. down the arm portion
58
of the thrust ring
42, via the shoulder
59 generally through the
bolts
48, and preferably substantially through the point of attachment
56.
There is therefore substantially no bending moment about the point of attachment
56. The bolts
48 are strong under direct non-bending forces and the
performance of the bolts
48 is therefore improved. The above effect is caused
by the triangulation of the thrust ring geometry which, under forward thrust loading,
produces a resultant force vector extending generally through the point of attachment
56.
Referring to FIG. 5, there is illustrated an alternative embodiment of
the invention, in which corresponding parts are indicated with the same reference
numerals as in FIG. 4. The thrust ring
42 of the FIG. 5 embodiment is of
generally similar shape to that of the FIG. 4 embodiment, including an attachment
portion
46 which is affixed via bolts
48 to an attachment portion
50 of the disc
32. The thrust ring
42 further includes a sloping
arm portion
58 (having an undercut L-shaped shoulder portion
59)
and a restraint member
60, as in the previous embodiment. In the FIG. 5
embodiment however, the arm portion
58 is shorter and the restraint member
60 locates in an undercut portion
64 of the disc
32. The undercut
portion
64 defines a shoulder
66 of the disc, the shoulder
66
being generally annular and adjacent to and radially outwards of the restraint
member
60.
The thrust ring
42 further includes an abutment portion
52 which
is generally ring shaped and which extends radially outwardly from a remainder
of the thrust ring
42. As in the previous embodiment, the abutment portion
52 is located axially forwardly of a part of the blade
30 and resists
forward axial movement of the blade.
The embodiment of FIG. 5 works in a similar way to that described with reference
to the FIG. 4 embodiment, except that the restraint member
60 is prevented
from radially outward movement by the shoulder
66 of the disc
32
rather than by the post member
62 of the blade
30.
Referring to FIG. 6, there is illustrated an alternative embodiment of
the invention, in which corresponding reference numerals are again used. The thrust
ring
42 of FIG. 6 is generally similar to that of FIG. 4 except that the
restraint member
60 is replaced by a plurality of restraint means in the
form of restraint fingers
68. The fingers
68 are elongate and extend
axially backwards from the remainder of the thrust ring
42. A restraint
finger
68 is located between the disc
32 and a restraining base part
69 of each individual fan blade
30 and functions in a similar manner
to the restraint member
60 of the previous embodiments.
FIG. 7 (which shows just part of the retention member
42) illustrates
a variation of the FIG. 6 embodiment. The restraint fingers
68′ are
smaller than restraint fingers
68 and fit between a chuck
70 and
the blade
30. Dowels
72 are provided to prevent relative axial movement
of the blade
30 and the chuck
70.
There are thus provided various embodiments of a blade arrangement wherein
axial forces on the thrust ring
42 are resolved into forces which are directed
generally through the point of attachment
56 of the thrust ring
42
to the disc
32. This triangulation of the thrust ring geometry produces
direct loads on the attachment bolts
48 and avoids rolling moments which
tends to overload the bolts.
Various modifications may be made to the above described embodiment without
departing from the scope of the invention. For example, a small clearance may be
provided between the restraint member
60 of the thrust ring
42 and
the part of the blade
30 or disc
32 against which it abuts, this
allowing some deflection to absorb shock loading. The precise geometry may be varied
and the section lengths, thicknesses and angles may be optimised by use of computer
optimisation techniques. In the described embodiments the restraint member/restraint
fingers abut against a part of the blade
30 or disc
32. They could
of course abut against a further part attached to the blade or disc.
Whilst endeavouring in the foregoing specification to draw attention to those
features of the invention believed to be of particular importance it should be
understood that the Applicant claims protection in respect of any patentable feature
or combination of features hereinbefore referred to and/or shown in the drawings
whether or not particular emphasis has been placed thereon.
*
