Patent ID: 12211477

DETAILED DISCLOSURE OF A FIRST EMBODIMENT

FIG.1illustrates an acoustic panel1for a turbomachine, according to the invention.

The acoustic panel1is a panel called “sandwich panel”. It comprises first and second substantially parallel skins2and3between which cavities forming Helmholtz resonators are disposed.

One of said skins, in this example the first skin2, is bored with orifices each opening into one of said cavities and forming a neck of the resonators.

Moreover, one or more of said cavities are formed by a hollow structure4in the shape of a right prism with a triangular base.

As visible inFIGS.2and3, the structure4in the shape of a right prism with a triangular base includes two opposite triangular bases4aand4band two opposite rectangular faces4cand4dextending from a shared square face4e. The junction of the two bases4aand4band of the two faces4cand4dforms an edge5disposed opposite to the square face4e. The structure4is hollow and thus encloses a cavity.

All the cavities are preferably formed by structures4in the shape of a right prism with a triangular base, forming a honeycomb configuration between the two skins2and3.

The cavities of the various structures4in the shape of a right prism with a triangular base are independent of each other and do not communicate.

Preferably, the structures4forming the cavities are defined in several assemblies or cells by lateral walls6. The acoustic panel is thus formed by a plurality of assemblies of structures4in the shape of a right prism with a triangular base.

InFIG.2, only two of the four lateral walls6of an assembly have been shown for easier comprehension of the arrangement of the structures4.

In the example illustrated inFIG.1, each assembly comprises four structures4in the shape of a right prism with a triangular base. A perspective view and a bottom view of an assembly are shown inFIGS.2and3.

The four structures4shown are disposed at 90° with respect to each other, with respect to an axis passing through the two skins2and3and perpendicular to the two skins3and3. This arrangement advantageously allows to optimise the space.

Moreover, the four structures4of an assembly are disposed so that each edge5is disposed facing the second skin3.

Each assembly also comprises a central cavity7formed between the structures4formed by a right prism with a triangular base. In other words, the central cavity7corresponds to the free space inside an assembly defined by the lateral walls6, between the structures4.

According to the first embodiment shown, the skin bored with orifices, which corresponds here to the first skin2, can comprise three orifices in the same assembly. A first orifice8aand a second orifice8brespectively open into a first cavity and into a second cavity out of the four cavities formed by a structure in the shape of a right prism with a triangular base, preferably at the square faces4e.

Moreover, a third orifice9opens into the central cavity7.

The first and second orifices8aand8bhave, in this example, different diameters. Moreover, the diameter of the third orifice9is greater than the diameters of the first and second orifices8aand8b.

For example, the first and second orifices8aand8bcan be disposed so that they open into two of the four structures4formed by a right prism with a triangular base, disposed diagonally inside the same assembly of structures4.

In this embodiment, two of the four structures4formed by a right prism with a triangular base are not used as a resonance cavity.

The structures4formed by a right prism with a triangular base are connected to one of said skins2and3, in this example the second skin3, by the edge5. Preferably, the interface between the edge5and the skin comprises an enlarged portion or border reinforcing the mechanical stability of the acoustic panel via the reinforcement of the connection between the structures4and the second skin.

The four cavities of the structures4in the shape of a right prism with a triangular base thus each form a Helmholtz resonator.

According to an alternative illustrated inFIG.4, the structures4in the shape of a right prism with a triangular base can be disposed according to a top-to-tail configuration in order to optimise the space inside the acoustic panel.

The graph ofFIG.5shows the change in the absorption coefficient according to the frequency, in Hz, measured on an acoustic panel having a configuration with three orifices, as illustrated inFIG.4, the structures disposed top to tail. In the example illustrated, the thickness of the first bored skin, and thus of the neck associated with the orifices8a,8band9, was chosen as equal to 4 mm and the diameter of the first, second and third orifices8a,8band9is respectively 2, 2.5 and 3 mm.

In this configuration, three well-defined absorption peaks can be observed in the drawing. In this configuration, the peaks can be observed around 500 Hz, 1100 Hz and 1400 Hz.

The resonators formed by the central cavity7, having a volume greater than the cavities of the structures4, generate the peak at low frequency around 500 Hz, while the resonators formed by the two structures4in the shape of a right prism with a triangular base into which the orifices8aand8bopen generate the two peaks at high frequencies, around 1100 and 1400 Hz.

The use of the two types of cavities is particularly advantageous and allows to obtain a plurality of peaks over a broad range of frequencies between 500 and 1500 Hz.

Detailed Disclosure of a Second Embodiment

FIG.6illustrates a second embodiment of an acoustic panel case10in which the bored skin comprises five orifices. Similarly to the first embodiment illustrated inFIG.1, the first skin2comprises a first orifice8aand a second orifice8brespectively opening into a first cavity and into a second cavity out of the four cavities formed by a structure4in the shape of a right prism with a triangular base, preferably at the square faces4e.

Moreover, the first skin2comprises a fourth orifice11aand a fifth orifice11brespectively opening into a third cavity and a fourth cavity out of the four cavities formed by a structure4in the shape of a right prism with a triangular base.

Preferably, the various orifices8a,8b,9,11aand11bhave four or five different diameters.

The graph ofFIG.7shows the change in the absorption coefficient according to the frequency, in Hz, measured on an acoustic panel having a configuration with five orifices, as illustrated inFIG.6. In the example illustrated, the thickness of the first bored skin, and thus of the neck associated with the orifices8a,8band9, was chosen as equal to 3 mm and the diameter of the first, second, third, fourth and fifth orifices8a,8band9is respectively 2, 2.5, 3.5, 3 and 3 mm.

Five well-defined absorption peaks can be observed in the drawing. In this configuration, the peaks are observed at low frequency around 500 Hz, and at a higher frequency around 800 Hz, 1100 Hz, 1400 Hz and 1500 Hz.

The resonators formed by the central cavity7, having a volume greater than the cavities of the structures4, generate the peak at low frequency around 500 Hz, while the resonators formed by the four structures4in the shape of a right prism with a triangular base into which the orifices8a,8b,11aand11bopen generate the four peaks at the higher frequencies.

The use of the two types of cavities is particularly advantageous and allows to obtain a plurality of peaks over a broad range of frequencies between 500 and 1500 Hz.

Such an acoustic panel allows to obtain an absorption greater than the panel including the three orifices, in particular between 600 and 1000 Hz. A broad range of absorption frequencies, between 500 and 1500 Hz, is obtained.

Of course, it is possible for the acoustic panel to comprise a number of different orifice diameters different than three or five, for example two, four or more than five.

Preferably, the acoustic panel1,10forms a monolithic structure.

Monolithic means in the sense of the invention a structure formed by a single block.

As elaborated on above, the acoustic panels1,10according to the invention allow an absorption of noise over a broad range of frequencies 600-1500 Hz, via multiple absorption peaks.

The invention also relates to a method for manufacturing an acoustic panel1,10. The method comprises a step of manufacturing by additive manufacturing. The additive manufacturing thus has the advantage of being able to manufacture an acoustic panel, for example the acoustic panels1and10, simply and quickly, in a single step.

Preferably, the step of manufacturing by additive manufacturing is carried out by the technique of Fused Filament Fabrication, FFF, particularly adapted to the production of a complex structure as described above, comprising structures4formed by right prisms with a triangular base.

Additive manufacturing means the manufacturing of a part by successive deposition or consolidation of the layers of material.

The acoustic elements are thus made in a single operation, and are thus monolithic.

The acoustic panel, preferably manufactured by additive manufacturing, can comprise at least one reinforced thermoplastic material and/or at least one non-reinforced thermoplastic material.

Reinforced material means a composite material in which fillers improve the properties, for example mechanical, of a matrix.

According to one example, the first and second skins2and3of an acoustic panel can be made from a reinforced thermoplastic material, for example carbon fibres, while simultaneously, the cavities are made from a non-reinforced thermoplastic material. The manufacturing by additive manufacturing of such an acoustic panel can be carried out in a single operation, by a device comprising two extrusion heads, preferably by the technique of Fused Filament Fabrication, FFF.

Preferably, the acoustic panel is manufactured from a thermoplastic polymer material, for example polyamide, or from a composite material with a polymer matrix, particularly advantageous for the additive manufacturing by fused filament fabrication and allowing both to reinforce and to lighten the structure. According to one embodiment, the composite material with a polymer matrix can include carbon fibre fillers.

The acoustic panel thus combines increased mechanical strength and noise absorption capacity.

It should be noted that it is also possible for the creation of the various orifices8a,8b,9,11aand11bto be carried out in a second step, after the step of manufacturing by additive manufacturing the acoustic panel1,10, by a mechanical method.