Note: Descriptions are shown in the official language in which they were submitted.
¦ ~092/12854 PCT/GB92/00118
`
2~92~1~
Structural_Cellular com~onent
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; The present in~ention relates to structural cellular
components and is particularly although not exclusively
concerned with a structural cellular component for a
noise attenuation panel for use in the attenuation of
noise in aero engines.
In patent application publication No. GB-A-2223448 a
noise attenuation panel is disclosed having a backing
sheet, a facing sheet and a cellular core having a
multiplicity of opened ended juxtaposed cells. The
backing sheet extends across the open ends of the cells
at the rear of the core and the ~acing sheet extends
across the open ends of the cells at the front of the
core. In the panel disclosed, the facing sheet is made
~of a porous permeable thermoplastics material preferably
produced by a powder sintering process and the backing
sheet is imperforate and impermeabls.
The noise attenuation panel disclosed in GB-A-2223448 is
proposed for use in reducing turbine engine noise and is
formed as an integral part of an aero engine structure.
For example, it is proposed that the panels form part of ~ -
a cowling surrounding a turbine engine inlet duct or be
placed; adjacent a high tùrbulence region of the fan of a ~ -~
turbofan engine.
' The cellular core in the panel specifically disclosed in
3 GB22234~A is furthermore formed by cells having wall
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~ ' portions which extend paxallel to each other and
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l perpendicular to the backing and facing sheets.
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While the panel specifically disclosed in GB-A-?223448
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W092/t2854 PCT/GB92/00118_ 1
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has been found to be successful for use in aero engine
environments, drawbacks may be found in the use of a
cellular core in which the cells are formed as described,
that is to say, with the wall portions extending parallel
to each other and perpendicular to the backing and facing
sheets.
According to a first aspect of the present invention
there is provided a structural cellular component for a
noise attenuation panel, the component comprising wall
portions which provide bounding surfaces for an array of
cells and which terminate at opposite fac~s of the
component, characterised in that the wall portions or
predetermined ones of the wall portions forming the cells
extend to at least one of the faces of the component at
an angle or angles inclined to the normal to that face.
There is currently a trend towards the development of
ultra high bypass (UHB) ratio t:urbofan engines giving
rise to associated low blade passage frequencies of the
fan. In order to provide for r-oise attenuation at these
low frequencies the depth of the cells of the cellular
core of the previously proposed panel of GB 2223448A
needs to be increased, giving rise an increase in the
depth of the panel. This increase in panel depth is
however found to be undesirable for the environments in
.~ .
which the panel is used.
Accordingly there is a need to provide a structural
cellular component for a noise attenuation panel which is
effective to attenuate noise at the lower frequenc,es
generated in the large diameter UHB ratio turbofan
engines without requiring an undesirable increase in
panel depth.
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A first embodiment of the first aspect of the present
invention is characterised in that the wall portions of
the cellular component provide bounding surfaces for an
array of juxtaposed cells which terminate in open ends at
one of the faces of the component with the wall portions
extending to that face at angles inclined to the normal
to that face.
In the first embodiment of the invention hereinafter to
be descri~ed, the cells also terminate in open ends at
the opposite face of the component with the wall portions
extending to the opposite face at angles inclined to the
normal to that face.
Preferably, the wall portions extend to the face or faces
of the component along lines which are parallel to each
other.
.
In preferred embodiments of the invention hereinafter to
be described the angle at which the wall portions are
inclined to the normal to the or each face of the
component is in excess of 20.
In the embodiments of the invention hereinafter to be
described, the cells are of constant cross-section with
the lateral edges of each cell lying along lines parallel
to each other. In the embodiments described the cells
are of hexagonal cross-section but in alternative
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embodiments of the invention the cells may conform to an
isogrid or ortho~rid pattern.
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In alternative embodiments of the invention not
~; illustrated by the drawings the wall portions or
predetermined ones of the wall portions extend to the
face or each face of the component along lines which are
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W092/12854 PCT/GB92/00118_
9~
not parallel to each other. In these embodiments, the
cells may be of pyramidal form or in the form of
truncated pyramids.
According to a second aspect of the present invention
there is provided a noise attenuation panel comprising a
cellular component part in the form of a component
according to the first aspect of the invention, a backing
component part extending across one face of the cellular
component part at the rear thereof and a facing component
part extending across the oth0r face of the cellular
component part at the front thereof.
In a preferred embodiment of the invention according to
its second aspect, the facing component part comprises or
includes an outer facing sheet which is made of a porous
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permeable thermoplastics material. Preferably, the
porous permeable thermoplastics material for the outer
facing sheet is produced by powder sintering a
thermoplastics material.
In an embodiment of the invention hereinafter to be
described the facing component part further includes an
inner facing sheet made from an open square weave fabric
having apertures constituted by the openings between
ad~acent warp and weft threads of the fabric.
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In yet another embodiment of the invention hereinafter to
be described the cellular component part comprises an
upper cellular element in the form of a component
according to the first aspect of the invention, a lower
cellular element in the form of a component according to
the first aspect of the invention and positioned beneath
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the upper cellular element and a septum sheet which
extends across the lower cellular element at an upper
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~092/12854 PCT/GB92/00118
2~9~
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face thereof and across the upper cellular element at the
lower face thereof.
In an embodiment of the invention hereinafter to be
described the upper and lower cellular elements comprise
identical arrays of cells inclined to the normal to the
panel. In one such embodiment the upper and lower
cellular elements are arranged one above the other and
the cells of the one are inclined to the normal to the
panel in the same direction as the cells of the other.
In an embodiment of the invention hereinafter to be
described the two cellular elements are so positioned and
arranged that the upper open ends of the cells of the
upper cellular element are in registration with the open
upper ends of the cells of the lower cellular element,
whereby the lower open ends of the cells of the upper
element are out of registxation with the upper open ends
of the cells of the lower element.
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`~ In an alternative embodiment of the invention not
illustrated the two cellular elements are so arranged
that the lower open ends of the cells of the upper
, cellular element are in registration with the upper open
`, ends of the cells of the lower cellular element, whereby
the cells of the lower cellular element form a
continuation of the cells of the uppex cellular element.
,
In yet another embodiment of the invention hereinafter to
be described, the upper and lower cellular elements are
so positioned and arranged one above the other that the
cells of the one element are inclined to the normal to
the panel in a direction opposite to that of the cells of
the other element.
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W092/12854 ~ PCT/GB92/0011~_
The septum sheet may be constructed from a porous
permeable thermoplastics material or alternatively made
of a stainless steel fabric. The upper cellular element
or the lower cellular element or both may be made from an
impermeable material or from a porous permeable
thermoplastics material.
,
According to a third aspect of the present invention,
there is provided an aero engine having a surface
subjected to the passage across it of gaseous flow and a
noise attenuation panel according to the second aspect of
the invention so positioned that its front face forms the
surface or part of the surface subjected to passagQ of
" the gaseous flow across it.
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Embodiments of the invention will now be described by way
of example with referenre to the accompanying drawings in
which.-
Fig. 1 is a schematic isometric view from above of a
; noise attenuation panel embodying a structural cellular
component according to a first embodiment of the
invention;
Fig. 2 is a schematic cross section of an end region of
i the panel shown in Fig. 1, secured to a supporting
channel member;
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Figs. 3, 4 and 5 are schematic cross sectional scrap-
views of noise attenuation panels according to three
further embodiments of the invention; and
Fig 6 is a schematic cross-section of an aero engine
embodying noise attenuation panels according to the
invention.
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~92/12854 PCT/CB92/00118
2Q924~ ~
Referring first to Figs. 1 and 2, the noise attenuation
panel 10 comprises a backing sheet 11, a cellular core 12
and inner and outer facing sheets 13 and 14.
The cellular core 12 comprises a multiplicity of open-
ended juxtaposed cells 15 of hexagonal cross section ~o
provide a honeycomb configuration in which the lateral
edges 16 are (i) parallel to each other, (ii) lie in
planes which are perpendicular to the backing sheet 11
and parallel to the edge 111 of the sheet 11 and (iii)
lie on lines which are inclined to the normal to the
backing sheet, whereby the length of the cells 15 between
the backing sheet 11 and the inner facing sheet 13 is
greater than the distance of separation of the two sheets
11 and 13.
The backing sheet 11 is unperforated and made from an
imperme~ble sheet material, as shown in Fig. 2, and is
secured by an epoxy resin adhesive El to the lower face
of the cellular core 12.
.
The inner facing sheet 13 is made from an open square
weave fabric formed from a carbon fibre/resin matrix
composite material and the weave is such as to provide
apertures constituted by the openings between adjacent
warp and weft threads of the fabric. The fabric is
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prefexably so woven as to produce a proportion of open
aperture area reIative to the total surface area of the
sheet of around 30%. At the same time, the fabric is so
woven that a relatively large number of its apertures are
contained within the bounds of each cell 15 of the
cellular core 12.
The outer facing ~heet 14 comprises a sheet of a porous
permeable thermoplastics material-produced by powder
sintering the thermoplastic. Examples of suitable
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WO92/12854 PCT/GB92/0011~_
thermoplastics materials include polyether ketone,
polyether ether ketone, polyaromatic ketone,
polyphenylene sulphide, polyamide-imide, thermoplastic
polyimide, polyether-imide, polyurethane and
polyethylene.
The outer facing sheet 14 is bonded to the inner facing
sheet 13 and the inner facing sheet 13 is, as shown in
Fig.2, secured to the upper face of the cellular core 12
by means of an epoxy resin adhesi.ve E2.
,
During manufacture of the panel lO, it may be found
advantageous to form the inner woven facing sheet 13 in a
part cured condition and to bring the outer facing sheet
.~ 14 into contact with it during a final curing step so
that the resin serves to bond the two sheets together.
` The combined sheets 13 and 14 may then be secured to the
~;- upper face of the cellular core 12 using the epoxy resin
~ adhesive E2.
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The epoxy adhesives E1 and E2 may for example be obtained
~.` from Ciba-Geigy Plastics & Additives Company Limited of
`:~ Cambridge, England. Adhesives and rasins need not
~ however be epoxy resin adhesives, but could for example
.~l be a phenolic, polyimide or thermoplastics resin.
: The backing sheet 11 is imperforate and made of a non-
`` porous impermeable material and may be made of any of the
following materials:-
(i) A carbon/thermoplastic composite
where for example the thermoplastic is
polyether ether ketone, the-material being
automatically tape wound or hand laid.
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~92/128~4 2 o 9 ~ PCT/CB92/00118
(ii) A carbon/epoxy resin.
(iii) An aluminium alloy.
The cellular core 12 in the embodiment of the invention
illustrated is made from a non-porous impermeable sheet
of any of the following materials:-
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(i) A thermoplastic such as
~` polyether ether ketone.
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(ii) A polyester fabric/phenolic
~ resin.
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(iii) A fibreglass/phenolic resin.
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` ( lV) A NOMEX/phenolic resin (NOMEX
being a registered trade mark for an
~ aramid fibre paper impregnated with
-~v various resins 1o produce a structural
material. By "aramid is meant an aromatic
polyami~e polymer.
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~! . (V) An aluminium alloy.
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The cellular core 12 may however if desired be made of a
i porous permeable thermoplastics material and may be in
the same form as the outer facing sheet 14.
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The panel l0 is of arcuate form, possibly of double
curvature, and is embodied as a .structural part of a duct
of a nose cowl of a turbofan aero engine, the panel lO
being one of several arcuate panels disposed just
upstream of the fan of the engine. It is, of course, of
vital importance that the panel does not deteriorate in
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WO92/128~4 PCT/CB92/0011~
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use and, in particular, that no part of it becomes
detached from its supporting structure. The structure
will usually include supporting channel members of which
only one member 17 is shown in Fig. 2. The panel 10 is
secured to the member 17 by bonding the inner facing
sheet 13 to an outer face of a flange 18 of the channel
member 17 using a carbon bond 19 and by bonding the
backing sheet 11 to the outer face of a flange 20 of the
channel member 17 using a carbon to carbon bond 21. The
gap between the panel 10 and the base 22 of the channel
member 17 may be sealed or closed by use of a mastic 23.
,
A panel having an outer facing sheet 14 made of a porous
thermoplastics material as described with reference to
Figs. l and 2 has been found to give rise to several
advantages over the panels of the prior proposals,
including the following:-
`~`'
i (1) The cellular structure of the facing sheet when
produced by the powder sintering technique can be made to
meet permeability requirements over a wide range. The
cellular structure may be made permeable to gaseous flow
~, over a wide range of tightly controlled flow and
resistance requirements which will be engine dependent
and non permeable to a wide range of liquids and solid
contaminants. ~ ~
(2) The cellular structurè of the facing sheet whenproduced by the powder sintering technique provides a
highly complex interference flow path as a result of
which the noise attenuation properties are greatly
.
~ enhanced over other forms of perforate and porous
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(3) The very smooth surface of the facing sheet when
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~092/12854 PCT/GB92~00118
2~
produced by the powder sintering technique hassubstantial acoustic/air flow advantages over other
perforate and porous forms. There is a lower flow
resistance to high speed air flow, and therefore the
overall aero engine power plant efficiency is improved
over that obtained using the previously proposed panels;
(4) the sound attenuation is greater and covers a wider
frequency range than that of the previously proposed
panels; .
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~- (5) the thermoplastic component parts do not have the
~ problem of metal corrosion;
. (6) the panel is lighter than the previously proposed
panels;
:` (7) there is a improved "blacle-off" energy absorp~ion
~ compared with the previously proposed structures; and
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(8) there is an improved appearance.
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In addition to the above-mentioned advantages, the
acoustic absorbing properties of the panel are improved
by an appropriate inclining of the cells of the core to
the bac~ing and facing sheets, thereby extending the
~:; length of the cells without increasing the panel
thickness and thereby extènding the sound attenuation of
the panel to the lower frequencies generated in the large
diameter UHB ratio turbofan..engines.
Referring now to Fig. 3., a panel according to a second
embodiment of the invention is illustrated, in which the
: cellular core 12 of the embodiment of the invention
described with reference to Figs. l and 2 is replaced by
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W0~2t12854 ~ PCT/GB92/001l~
12
a split cellular core comprising an upper cellular
element 121 having a multiplicity of open-ended
juxtaposed inclined cells 151, a lower cellular element
122 having a further multiplicity of open-ended
` juxtaposed inclined cells 152~nd a septum sheet 24 which
7.
extends across the ends of thé cells 152 of the lower
cellular element 122 at the upper face thereof and the
ends of the cells 151 of the upper cellular element 121
at the lower face thereof. The cells of the two cellular
elements 121 and 122 form identical arrays of the
inclined cells as described with reference to Fig 1 and
are arranged one above the other. In Fig 3, the upper
open ends of the cells 151 and 152 are arranged one above
the other, as a consequence of which the lower open ends
of the cells 151 of the upper element 121 are not in
alignment with the upper open e.nds of the cel1s 152 of
the lower element 122. For some purposes, however, it
may be found advantageous so to mount the elements 121
and 122 that the cells 152 form a continuation of the
c~lls 151.
The backing sheet 11, the inner and outer facing sheets
13 and 14 and the upper and lower cellular elements 121
and 122 of the panel shown in Fig. 3 are constructed and
bonded together in the same manner as the sheet 11, core
12 and facing sheets 13 and 14 of the e~bodiment
described with reference to Figs. 1 and 2, with the
backing sheet 11 being secured to the lower face of the
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lower cellular element 122 and the inner and outer facing
sheets 13 and 14 being secured to the upper face of the
upper element 121.
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The septum sheet 24 is likewise bonded to adjacent faces
of the cellular elements 121 and 122. It is constructed
from a porous permeable thermoplast~cs materiel a~d may
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~92/12854 PCT/~B92/00118
12~92/~
take the same form as that of the outer facing sheet 14
of the panel described with reference to Figs. 1 and 2.
In a third embodiment of the invention illustrated in
Fig. 4, the inner facing sheet 13 of the panel described
with reference to Figs.1 and 2 is omitted and the outer
facing sheet 14, which is made of the porous
thermoplastics material, is adhered direct to the upper
face of the cellular core 12 using adhesive E2.
.
In Fig. 5, a fourth embodiment of the invention is
illustrated which corresponds to the embodiment of the
invention described with reference to Fig. 3, except that
the cells 151 of the upper cellular element 121 are
inclined in one direction and the cells 152 of the lower
element 122 are inclined in the opposite direction and
except insofar as the inner facing sheet 13 is omitted
and the outer facing sheet 14 is adhered direct to the
face of the upper cellular element 121 in the manner
described for the panel illustrated in Fig. 4.
In yet another embodiment of the invention (not
illustrated) the panel described with reference to Fig. 3
may be modified by making the upper cellular element 121
or the lower cellular element 132 or both of a porous
thermoplastics material and may be made'from:any of the
materials proposed for the outer facing sheet 14 of the
panel described with reference to Figs. 1 and 2.
The septum sheet 24 in the panels illustrated in Figs. 3
and 5 is described as being made of a porous -
thermoplastics material. It may however if desired be
made of a stainless steel fabric or any of the above-
mentioned materials which are suitable for the inner
facing sheet 13, the requirement of course being that the
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W092/12854 ~ PCT/GB92/0011
14
~-~ sheet is either porous and permeable, perforated or
apertured.
In the embodiments of the invention hereinbefore
described with reference to the drawings, cells 15 of
hexagonal cross section have been provided. It will
however be appreciated that cells of other cross
sections, for èxample conforming to an isogrid or
orthogrid pattern, can alternatively be used.
~`',~ .
In the embodiments of the invention hereinbefore
described with reference to the drawings, the cells 15
are prismatic in form, that is to say, are of constant
cross section with the lateral edges 16 of each cell 15
lying along lines parallel to each other. It will
however be appreciated that cells of non-constant cross
- section may be provided in which the lateral edges or
some of the lateral edges of each cell 15 are not equally
inclined, as for example where the cells are of pyramidal
form or in the form of truncated pyramids, so as to
provide cells in which the effective length varies within
the cell.
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Referring now to Fig 6, an aero engine 25 is
schematically illustrated and includes a turbofan power
unit 26 mounted within a nacelle 27 suspended from a
pylon 32. The nacelle 27 includes a nose cowl 28 having
an outer wall 29 and an inner wall 30. The inner wall 30
is in part formed by noise attenuation panels P which may
take the for~ of panels as described and illustrated with
reference to Figs. 1 to 5. The panels-P are arranged to
form part of the inner wall of the nose cowl 28 and serve
to reduce noise created by the high speed flow of air
passing through the duct 31 into the power unit 26, as
well as to reduce noise generated by the fan blades of
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- ~092t12854 PCT/GB92/OOlIB
2~2~ ~ ~
the unit 26.
It is to be emphasised that the panels in Fig. 6 are not
employed to reduce air noise by a reduction of the air
speed by passage of the air through the panels, but by
contrast acoustic attenuation is achieved without
affecting the speed of the air which generates the noise,
that is to say, the air does not pass through the noise
attenuation panels P.
In the aero engine mounting arrangement illustrated in
Fig. 6, the power unit is carried by the wing mounted
pylon 32. It will however be appreciated that the noise
attenuation panels according to the present invention may
be equally well be employed for reducing noise in other
aero engine installations.
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