Sonic absorption device for an air pipeline of an aircraft, in particular of an air conditioning system of an aircraft

Reference to related applications

This application claims the benefit of the filing date of German Patent Application No. 10 2006 050 869.6 filed October 27, 2006 and of United States Provisional Patent Application No. 60/863,195 filed October 27, 2006, the disclosure of which applications is hereby incorporated herein by reference.

Technical Area

The present invention relates to a sonic absorption device for an air pipeline of an aircraft, which sonic absorption device comprises at least one curved pipe section whose respective interior wall is clad with sound absorption material, wherein within the curved pipe section at least one air guidance means is arranged for flow optimisation.

Background of the invention Air pipelines used in aircraft construction are subject to particularly stringent requirements relating to sound protection and flow dynamics. At the same time, air pipelines in an aircraft are to be dimensioned such that flow losses are kept to the minimum possible, for example in order to minimise the energy required for conveying the conditioned air. As a result of the confined space within an aircraft, air pipelines comprise a substantial number of curved pipe sections. In these positions preferably dispersion sound absorbers are used, because they are particularly efficient in these circumstances. Furthermore, the change in direction of the airflow results in turbulence, which among other things reduces the flow speed of the air.

For the purpose of dispersion sound absorption, usually in particular the curved pipe sections of the air pipeline comprise or are lined with a sound absorption material. Furthermore, in particular in the case of highly curved pipe sections, turbulence in

the airstream occurs which has a negative effect on efficiency, with air guidance means counteracting said turbulence.

However, a combination of air guidance means and sound absorption cladding in a curved pipe section can have a negative effect on the efficiency of sound absorption. The reason for this is because, for example, two air baffles, arranged parallel in relation to each other, as air guidance means within a curved pipe section produce three separate channel sections which when individually considered, are not fully clad with sound absorption materials. In particular the middle duct, which is formed by two air baffles that are arranged al a distance from each other, is unprotected in this regard.

Attempts have already been made to counteract this problem by using an increase in the bending radius of the curved pipe section so that at the most one air guidance means within the curved pipe section is required. However, this measure requires more installation space within an aircraft, which design space is again at a premium. Furthermore, attempts have already been made to design air guidance means in the form of acoustic separators. λn acoustic separator is an aerodynamieally shaped air guidance means comprising a wing shape, with the interior space of said separator comprising a filling of a sound absorption material. The connection to the sound absorption materia] is established by way of conventional perforations of an extent of perforation of approximately 20%. The term "extent of perforation" refers to the area of the surface that is taken up by perforations. While such an acoustic separator itself acts as a sonic absorption device, due to the thickness of the acoustic separator, this solution, however, requires a correspondingly large installation space in the interior of the curved pipe section, which in turn increases the drop in pressure in a disadvantageous manner. Furthermore, it has been shown that an extent of perforation exceeding 10% in itself may form a source of sound.

Description of the invention

Accordingly, there may be a need to create a sonic absorption device for a curved pipe section of an air pipeline of an aircraft, which sonic absorption device distinguishes itself by high efficiency while at the same time requiring a minimum of installation space.

The need may be met with a sonic absorption device according to the preamble of claim 1 together with its characterising features. The subsequent dependent claims show advantageous improvements of the invention.

The invention includes the technical teaching that for further weight-neutral sound absorption the air guidance means arranged within a curved pipe section comprises a micropcrforation on at least one side surface.

The solution according to the invention is associated in particular with an advantage in that, thanks to the microperforation, only a slight turbulence in the airstrcam arises when said airstream moves along the air guidance means so that the air guidance means does not become a source of noise, or so there is no danger of a significant decrease in pressure occurring. In addition, the aerodynamic beha\ iour of the microperfo rated air guidance means according to the invention is similar to that of non-perforated conventional air guidance means. The solution according to the invention thus combines the aerodynamic advantages of conventional air guidance means on the one hand, with optimal sound absorption on the other hand. The coefficient of absorption of the sound absorption solution according to the invention can be set to the required frequency by changing the si/c and/or the distance of the openings of the micropcrforation. The measure according to the invention of microperforation of air guidance means has no influence on (he weight and design space when compared to those of conventional solutions.

The air guidance means can be of various designs. For example, it is imaginable to design them in the manner of at least one air baffle or in the manner of an acoustic separator. In the former case the microperforations extend through the entire thickness of the air baffle. In the case of an acoustic separator the sheet metal 5 housing enclosing the central absorption core of said separator comprises microperforations in the region of the inside or the outside of the acoustic separatoi . In the context of this document the term "inside" refers to the inwardly curved surface of the acoustic separator, whereas the term "outside" refers to the outw ardl) curved surface of the acoustic separator.

I O

According to a further measure improving the invention as far as the acoustic separator is concerned, it is proposed that inside, which has no micropcrlbralion. or outside, which has no microperforation, of the sheet metal housing comprises a conventional perforation to an extent of at least 20% per foration. In particular in the

1 5 case of larger radii of curvature of the curved pipe sections, with this measure it is possible to achieve optimum results with a view to sound absorption and flow guidance. Furthermore, trials have shown that the solution according to the invention is particularly successful in the case of How speeds exceeding 5m/s.

20 The microperforation according to the invention is preferably implemented by individual circular or oval openings with a diameter of less than 1 mm. The microperforations are thus distinct from conventional perforations whose individual openings have a diameter of more than 2 mm. Furthermore, with the microperforation according to the invention an extent of perforation of less than 5%

25 in relation to the entire surface is achieved.

P2007/061473

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Brief Description of the Drawings

Further measures that improve the invention are shown in more detail below, together with the description of preferred exemplary embodiments of the invention. The following are shown:

figure 1 a lateral view of a curved pipe section with air guidance means in a first embodiment; and

Figure 2 a lateral view of a curved pipe section with air guidance means in a second embodiment.

Detailed Description of Exemplary Embodiments

According to Figure I , conditioned air flows, in the direction shown by an arrow, through a curved pipe section 1 of an air pipeline (not further shown) of an aircraft. The interior wall of the pipe section is lined or clad with a sound absorption material 2, which in the embodiment shown is made from glass wool. Within the curved pipe section 1 two air baffles 4a and 4b, arranged parallel to the airflow, are installed. Over its entire thickness each of the air baffles 4a and 4b comprises through- microperforatson for the purpose of sound absorption.

According to Figure 2, in the interior of an also curved pipe section i ' with a lining of sound absorption material 2 an acoustic separator 5 as an air guidance means is arranged. The acoustic separator 5, which is formed in a wing-like manner, comprises an inner absorption core 6 made of sound absorption material, which absorption core 6 is enclosed by a sheet metal housing 7. The sheet metal housing 7 forms the two side surfaces 3a and 3b of the acoustic separator 5, which side surfaces 3a and 3b are approximately opposite each other. In this embodiment the inside of the acoustic separator comprises a micropcrforation. whereas the outside 3a comprises a conventional perforation.

The invention is not limited to the two preferred exemplary embodiments described above. Instead, modifications thereof are imaginable which arc covered by the scope of the following claims of the patent. For example, it is also possible to accommodate the acoustic separator and the air baffles together within a curved pipe section, should this be favoured for aerodynamic or sound-related reasons. The invention is not solely applicable to air pipelines of air conditioning systems, but also to inlet ducts or outlet ducts of turbines or the like.

List of reference numerals

1 Curved pipe section

2 Sound absorption material

3 Side surface

4 Direction of flow

5 Acoustic separator

6 Central absorption core