U.S. patent application number 11/232992 was filed with the patent office on 2006-03-30 for damped assembly.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Andrew Motherwell, Mark Thomas.
Application Number | 20060067817 11/232992 |
Document ID | / |
Family ID | 33397419 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060067817 |
Kind Code |
A1 |
Motherwell; Andrew ; et
al. |
March 30, 2006 |
Damped assembly
Abstract
In a nozzle guide vane assembly for a compressor or fan stage of
a gas turbine engine each of the guide vanes is held in position
between an outer casing and an annular inner ring by means of a
rubber boot or collar at each end of the vane. Operational
experience has shown potential for these assemblies to resonate
within the engine, the cause of which is traced to the stiffness of
the rubber collar. The present invention proposes as a solution a
modified form of collar in which a stiffening plate is either
bonded to the surface of the rubber or is incorporated into the
construction during the rubber vulcanisation process. Alternatively
or in addition the properties of the material from which the boots
are moulded may be modified by the inclusion of chopped fibres of a
range of materials.
Inventors: |
Motherwell; Andrew;
(Bristol, GB) ; Thomas; Mark; (Bristol,
GB) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
ROLLS-ROYCE PLC
London
GB
|
Family ID: |
33397419 |
Appl. No.: |
11/232992 |
Filed: |
September 23, 2005 |
Current U.S.
Class: |
415/191 |
Current CPC
Class: |
F05D 2260/96 20130101;
F01D 9/042 20130101; F04D 29/023 20130101; F05D 2300/611 20130101;
F05D 2220/36 20130101; F05D 2300/431 20130101; F04D 29/542
20130101; F05D 2300/603 20130101; F05D 2300/614 20130101; F04D
29/668 20130101 |
Class at
Publication: |
415/191 |
International
Class: |
F01D 9/00 20060101
F01D009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2004 |
GB |
0421588.5 |
Claims
1. A damped assembly comprising at least one member carried in a
supporting structure by at least one end of the member located in a
socket formed in the supporting structure with an intermediate
collar of resilient material interposed therebetween wherein the
collar of resilient material includes stiffening means.
2. A damped assembly as claimed in claim 1 wherein the stiffening
means includes a metal plate.
3. A damped assembly as claimed in claim 2 wherein the metal plate
is bonded to a surface of the collar.
4. A damped assembly as claimed in claim 2 wherein the stiffening
means and the collar are formed as a unitary member.
5. A damped assembly as claimed in claim 1 wherein the properties
of the resilient material of which the intermediate collar is
comprised are modified by the inclusion of a further material to
increase the stiffness of the resilient material.
6. A damped assembly as claimed in claim 5 wherein the further
material is selected from the group of materials including carbon
fibre, glass fibre Kevlar fibre and glass micro-spheres.
Description
[0001] The invention relates to a damped assembly.
[0002] In particular it concerns a nozzle guide vane assembly for a
compressor or fan stage of a gas turbine engine in which the guide
vanes are held in position in an annular ring by means of an
intermediate damping medium.
[0003] In known nozzle guide vane assemblies individual vanes are
held in place between concentric rings by means of inserts of a
resilient material such as silicone rubber material. The inserts of
resilient material contribute some damping to the assembly as a
result of its inherent energy absorbing properties. However, such
an arrangement suffers the drawback that the due to the nature of
the resilient material the overall assembly can have poor
stiffness. This can lead to movement of the vanes relative to their
supporting structure allowing vibration and resonant frequencies
within the engine running range. This is generally undesirable and
in the extreme can lead to structural failure. The invention is
intended to overcome this drawback.
[0004] According to the broadest aspect of the invention there is
provided a damped assembly comprising at least one member carried
in a supporting structure by at least one end of the member located
in a socket formed in the supporting structure with an intermediate
collar of resilient material interposed therebetween.
[0005] The invention and how it may be carried into practice will
now described by way of example with reference to the accompanying
drawing in which:
[0006] FIG. 1 shows a nozzle guide vane assembly for a gas turbine
engine in which the vanes are located using a resilient collar;
[0007] FIG. 2 shows a detailed view of the resilient collar of FIG.
1; and
[0008] FIG. 3 shows a section through the collar seated in position
over a vane in the assembly of FIG. 1.
[0009] Referring firstly to FIG. 1 of the drawings there is shown a
segment 2 of an annular nozzle guide vane assembly for a gas
turbine engine including at 4 two nozzle guide vanes. The vanes 4
have a hollow interior cavity 6 and are mounted in a supporting
structure comprising an annular, radially outer casing, a portion
of which is shown at 8, and a concentric inner ring, a portion of
which is shown at 10. The overall assembly includes a multiplicity
of the vanes 4 spaced apart equidistantly around the rings 8 and
10.
[0010] At each of the vane locations an aperture 12 is formed in
the outer ring 8 opposite a corresponding aperture 14 in the inner
ring 10, both apertures conforming to the cross section of the
vanes 4 plus a small gap to receive a collar 16. Into each said
aperture there is fitted a collar or boot 16 made of resilient
material to the shape of the vane cross-section to form a socket
into which one end of the vane 4 is received. Thus, there is a
collar or boot 16 of resilient material interposed between
adjoining metal parts 8 and 4, or 10 and 4. In engine operation,
the rubber collars 16 act to damp relative movement of the metal
parts. Each of the collars 16 is formed in an aerofoil shape so
that there is an aperture 17 through its middle through which
access to the interior 6 of the aerofoil 4 is provided, for example
for the passage of cooling air.
[0011] Experience in the gas turbine environment has shown that due
to the nature of the resilient material the overall system has
relatively poor stiffness. This can result in increased axial
deflection of the inner ring 10 if the whole assembly is supported
by means of cantilevered mounting of the outer casing annulus 8.
The extent to which the modal vibration frequencies of the
aerofoils can be tuned, to avoid resonances in the engine running
range, is limited by the resilient material of which the collars or
boots 16 are made.
[0012] According to the present invention this drawback is solved
by the arrangement illustrated in FIG. 2 in which the collar or
boot 16 is modified by the addition of stiffening means. In one
embodiment of the invention this stiffening means is in the form of
a thin metal plate 18 attached to an end face of the collar. In
this example the collar 16 was stiffened by the addition of a metal
plate 18 formed of 0.5 mm thick stainless steel bonded to an end
surface 20 of the collar 16. The inner and outer peripheries of the
plate 18 were formed in the outline shape of an aerofoil
cross-section. The dimensions of the aperture 22, defined by the
inner periphery of the plate 18 were slightly larger than the
corresponding external dimensions of the aerofoil vane 4 and of the
end face 20 of the collar 16. Also the external dimensions of the
plate 18 were slightly smaller than the corresponding dimensions of
the collar face 20. The plate 18 was then bonded to the end surface
20 of the collar 16 in a position to leave a small clearance gap
all round the aerofoil 4 after assembly.
[0013] The plate 18 was bonded to the collar 16 during a
vulcanisation process to cure the silicone rubber material from
which it was moulded. The plate 18 was coated with a suitable
primer and placed in the mould (not shown) on the uncured silicone
rubber. Upon completion of the curing process the stiffening plate
18 and the collar 16 were bonded together well enough to survive
intact the mechanical stresses of assembly and use in which the
assembly is subject to thermal cycles and simultaneous mechanical
stresses.
[0014] The stiffness of this collar assembly 16, 18 is influenced
by several factors, including thickness of the plate 18, the plate
material and the width of overlap with the end face 20 of the
rubber collar. These variables may be selected to produce a desired
stiffness in the final assembly. The in-plane and bending stiffness
of the assembly will be increased by the high in-plane stiffness of
the plate 18. Therefore the stiffness of the assembly can be
determined by selection of the plate material ie its modulus,
thickness and width. The transverse stiffness of the collar
assembly is also influenced by all the above factors but is
primarily determined by the width of plate overlap, or rather by
the clearance between the plate 18 and the vane 4. Lack of
clearance acts to constrain local shear deformation of the rubber
collar material adjacent to the vane surface ie reducing the width
of overlap reduces the transverse stiffness of the collar 16.
[0015] In the case of the illustrated example the plate 18 was
bonded to one end surface 20 of the collar 16. In another example
(not shown) the stiffening means, ie the plate 18 and the collar 16
were formed as a unitary member. The plate 18, was primed on both
sides, and was placed in the mould when only partially filled with
uncured silicone rubber, so that when filling was complete the
plate 18 was fully embedded in the collar 16 with rubber on both
sides. The vulcanisation procedure was then carried out as
normal.
[0016] In further embodiments the inherent properties of the rubber
material from which the collar was moulded were modified by
inclusions within the body of the silicone rubber. Examples of
stiffening materials used are chopped fibres of carbon, glass, and
Kevlar (p-phenylene terphthalamide) (Kevlar is a registered trade
mark) or glass micro-spheres, ie minute (sub-millimetre) spheres of
glass. Such inclusions modify the way and degree to which the
rubber deforms when subject to external mechanical stress. Such
modified material may be used in addition to a stiffening plate as
described above or as an alternative thereto. The thickness and
length of the fibres used is dependent upon the design of the
rubber boot, the inherent properties of the basic rubber material
and the degree of modification of the resilient properties
desired.
* * * * *