Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
2001-06-20
2003-08-26
Lockett, Kim (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S293000
Reexamination Certificate
active
06609592
ABSTRACT:
The present invention relates to noise attenuation panels and to a method of manufacturing a noise attenuation panel.
Noise attenuation panels are widely used for attenuating noise produced by aircraft engines and are located at optimised positions in the flow ducts of aircraft engine nacelle structures. Such flow ducts primarily comprise the inlet duct, the fan duct and the nozzle assembly.
A typical noise attenuation panel comprises a sound reflecting solid backing plate or sheet, a perforate metal facing plate or sheet and a honeycomb or cellular core which is bonded between the backing and facing sheets and which partitions the air into a multiplicity of separate cells.
When the noise attenuation panel is mounted in a flow duct of an aircraft engine nacelle structure with the facing sheet exposed to sound waves generated in the duct, the sound waves become subjected to three mechanisms which result in a reduction of the sound energy by conversion thereof to heat energy, namely:
(i) friction in the facing sheet,
(ii) pressure loss when duct pressure sound waves expand into the cells of the honeycomb or cellular core, and
(iii) ‘reactive’ cancellation of the direct incident sound wave by the wave that is reflected from the solid backing sheet, the honeycomb cell depth being ‘tuned’ to the required frequency.
Noise attenuation panels are obviously important acoustically but, because of the hostile environment in which they operate, there is also an evident need for structural rigidity. As they form part of an aircraft engine nacelle structure it is important that the complete component is provided with adequate strength to withstand the inflight conditions to which an exposed area of a nacelle structure is susceptible. Moreover, noise attenuation panels are often so configured as to add strength to the nacelle structure into which they are to be installed.
The perforate facing sheets of noise attenuation panels heretofore proposed have commonly been perforated by punching or mechanical drilling. Current noise attenuation panel constructions use perforate facing sheets with holes typically of diameter between 0.020″ (0.508 mm) and 0.060″ (1.524 mm) positioned in an equi-spaced triangular array such as to provide open areas within the limits of 3 and 20%.
Early manufacturing procedures have included punching and drilling but they do not realistically allow for the provision of very small hole diameters and very small spacing. In metal sheets, punching for example dictates a minimum hole diameter of 0.020″ (0.508 mm). Mechanical drilling can produce holes with diameters as low as 0.010″ (0.254 mm), but this is highly impractical with the lowest practical hole diameter being 0.020″ (0.508 mm).
In prior patent specification GB 2314526, a method of manufacturing a noise attenuation panel has been proposed in which a blank facing sheet is subjected to electron beam drilling to produce a multiplicity of drilled holes with bore diameters not greater than 0.020″ (0.508 mm). The electron beam drilling it is stated may furthermore advantageously produce the multiplicity of drilled holes with bore diameters in the range of 0.002″ (0.0508 mm) to 0.020″ (0.508 mm).
It has furthermore been proposed in prior patent specification U.S. Pat. No. 4,850,093 to provide a perforated titanium facing sheet by laser drilling holes or perforations through the sheet. The holes are uniformly distributed over the sheet and constituted 3 to 6% of the total area of the sheet. The porosity of the facing sheet may, it is stated, be designed to meet specific flow resistances by either changing the hole size or the spacing between holes or by simultaneously changing both. A facing sheet considered to be suitable comprised holes with a hole diameter of 0.002 to 0.003″, a hole spacing of 0.008 to 0.016″, 11,000 to 16,000 holes per square inch and 3 to 6% open area.
In prior patent specification GB 2038410A it has been proposed to provide a noise attenuation panel for a fluid flow duct of a gas turbine aeroengine which is aimed at attenuating as many frequencies as possible by employing beneath the perforated facing sheet a Helmholtz-type resonator for frequencies at the lower end of the frequency range and tube-type resonators for higher frequencies. Attention is directed to varying the Helmholtz resonator characteristics to provide for a wide band absorption. The facing sheet has a regular array of uniformally-sized holes although it is proposed to increase the hole density by reducing the spacing between the holes at one location of the facing sheet for acoustic coupling purposes.
In prior patent specification U.S. Pat. No. 4,288,679 a laser microdrilling method is proposed which uses a power laser beam in which the surface finish and dimensional accuracy of the hole being formed is improved by heating the workpiece. The laser beam can, it is stated, be rotated about the axis of the beam to form holes having a surface finish with a dimensional accuracy better than those obtainable with conventional laser microdrilling technology.
It is an object of the present invention to provide a noise attenuation panel and a method of manufacturing the panel in which the holes in the facing sheet can, by virtue of their hole geometry and distribution, provide for noise attenuation over a wide range of frequencies to which the panel is subject when employed as a noise attenuation panel for gaseous flow ducts in gas turbine aeroengines.
The present invention according to its different aspects includes a noise attenuation panel or the manufacture of a noise attenuation panel which comprises: a cellular component part which has a front face and a rear face and a cell defining wall structure which defines a multiplicity of cells between the front face and the rear face; and a facing component part which has a front face and a rear face, extends across the ends of the cells of the cellular component part at the front face thereof with the rear face of the facing component part adjacent the front face of the cellular component part, and is provided with a multiplicity of holes which extend through the facing component part from the front face to the rear face to provide gaseous fluid communication between the cells of the cellular component part and the front face of the facing component part for the attenuation of noise generated by gaseous fluid flow at the surface of the front face of the facing component part.
According to a first aspect of the present invention, there is provided a method of manufacturing a noise attenuation panel as hereinbefore set forth, the method comprising producing, in a hole producing step, the multiplicity of holes through the facing component part in the form of an array of holes having a hole size which so varies over the facing component part as to provide optimum attenuating performance of the panel over a predetermined range of gaseous flow conditions at the front face of the facing component part.
According to a second aspect of the present invention, there is provided a method of manufacturing a noise attenuation panel as hereinbefore set forth, the method comprising producing, in a hole producing step, the multiplicity of holes through the facing component part in the form of an array of holes having a non-circular hole cross-section which is so chosen as to provide optimum combined structural strength and attenuating performance of the panel.
According to a third aspect of the present invention, there is provided a method of manufacturing a noise attenuation panel as hereinbefore set forth, wherein: the facing component part is in the form of a fibre reinforced composite comprising a matrix component and a fibre reinforcing component embodied within the matrix component; the fibre reinforcing component comprises arrays of fibres in which the fibres of each array extend in a predetermined direction in the matrix and in which the predetermined direction of the fibres of each array is different from that of the fibres of each of the ot
Fulbright & Jaworski L.L.P.
Lockett Kim
Short Brothers PLC
LandOfFree
Noise attenuation panel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Noise attenuation panel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Noise attenuation panel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3081510