WO1989008215A1

WO1989008215A1 - Soundproofing wall element

Info

Publication number: WO1989008215A1
Application number: PCT/EP1989/000214
Authority: WO
Inventors: Heinz Wieland; Ulrich Ackermann; Helmut Fuchs; Andreas Jacobs; Norbert Rambausek
Original assignee: Gebhardt Ventilatoren Gmbh & Co.
Priority date: 1988-03-04
Filing date: 1989-03-02
Publication date: 1989-09-08
Also published as: AU3189489A; EP0402423A1; DE3807128A1

Abstract

A soundproofing wall element for attenuating the pressure waves propagated in flow media in flow media channels comprises chambers which form cavities and are delimited on one side by a covering membrane (4) which can be made to vibrate in the audible frequency range. A perforated membrane (5) is arranged inside the chambers at a minimal distance from the covering membrane (4). Together, the two membranes form an absorber membrane. At least one side of the chambers forms, at least partially, a supporting wall (8). In addition, the covering membrane (4) forms, at least partially, the guiding rim (12) which guides the flow medium in a turbo-machine.

Description

Sound absorbing wall element

The invention relates to a sound-absorbing wall element according to the preamble of claim 1, and the use of this wall element according to claims 15-19.

The walls of containers in which a turbulent flow is carried, e.g. of fan housings or ventilation ducts are loaded by the flow both statically (stationary underpressures or overpressures with respect to the outside) and dynamically (unsteady pressure fluctuations). For their durability, it is therefore necessary to make them from a correspondingly thick, stable material. In order to achieve the highest possible rigidity with the lowest weight, a construction method has proven itself in vehicle and aircraft construction in which the walls consist of two relatively thin shells, which are attached to both sides of a honeycomb grid structure (e.g. glued on) ( see Fig. 1).

So that the sound waves in the interior of the housing and channels are not emitted too strongly into the environment, it is often necessary to attach a second (non-load-bearing) wall shell on the outside, which has no or the softest possible one with the first (load-bearing) Has connection. The air space is generally filled loosely with porous material 1 (see FIG. 2). In order to finally vaporize the sound propagation in the interior of the housings and channels, so that the noise of the flow, in particular from the turbomachines, is not radiated too strongly through any openings (air inlets and outlets), it is customary to line the walls 2 of flow channels from the inside with sound absorbers. Porous materials (see FIG. 3a) or membrane absorbers according to DE-OS 35 04 208 are again suitable for this. The latter can either be attached directly to the walls as a so-called peripheral backdrop (see FIG. 3b) or set into the channels as a central backdrop: a backdrop that is asymmetrically constructed and absorbs on both sides is shown in FIG. 3c.

If you want to meet all three requirements at the same time,

(a) constructive stiffening

(b) sound absorbing casing

(c) sound absorbing lining

of the walls, in particular that of the housings of the sound-producing flow machines (fans, blowers, pumps) themselves, this requires a conventional construction

- additional space requirements,

- higher cost of materials,

- increased wall weights,

so that especially the noise protection measures cause very considerable additional costs. The absorbers installed inside must also withstand the same static and dynamic loads from the flow as the walls. The mineral wool in FIG. 3a must be protected against discharge, for example by means of suitable covers 3 (foils, nonwovens), so that the penetration of the sound waves necessary for their effectiveness is thereby prevented or at least greatly reduced. The covering membranes 4 in FIGS. 3b and 3c can be pressed so strongly against the perforated membranes 5 by the flow that their vibrations necessary for sound absorption in connection with the air layer between the two membranes and the air plug in the holes 6 are no longer are stimulable and thus their effectiveness is destroyed or at least significantly reduced. Dynamic flow forces, for example in the area of flow separations and so-called dead water areas, can also use the relatively thin (typically 0.075-0.3 mm) membranes for transient bulging, denting and fluttering (in particular also at frequencies outside the damping range for which they are used designed) bring. On the one hand, this can result in a completely undesirable sound radiation from the membrane absorbers actually used for noise reduction (especially at frequencies above their design range). These deformations with large amplitudes (especially at frequencies below their design range) can finally tear off and completely destroy them after a prolonged load of this type, in particular in the area of the webs to which the membranes are attached. The object of the invention is to avoid the above-mentioned disadvantages of membrane absorbers in wall elements.

According to the invention, this object is achieved by a wall element according to claim 1. Advantageous configurations are specified in the subclaims. New uses of the conversion elements according to the invention are specified in claims 15 to 19.

With regard to the design of the membrane absorber, express reference is made to DE-OS 35 04 208 and the corresponding, more detailed application PCT / EP 85/0039 or European application 86 901 369.8 and to the total disclosure content of these two applications.

The invention will be explained in more detail with reference to the accompanying drawing. In this show:

Fig. 1: a wall construction in lightweight construction

Fig. 2: a channel jacket

Fig. 3a: a wall lining with porous absorber

Fig. 3b: a wall lining with membrane absorber

3c: a silencer box (backdrop made of membrane absorber)

4a: a 90 ° flow deflection with an integrated membrane absorber

4b: an axial fan with integrated membrane absorbers

Fig. 4c: a radial fan with integrated membrane absorbers 5 shows a foam covering arranged on a covering membrane

Fig. 6 elastic spacer strips

Fig. 7 washers

Fig. 8 is an elastic fastening on a grid

Fig. 9 is a strip-shaped perforated membrane and

10: a further embodiment of the invention

Subject of the invention

The disadvantages of conventional sound absorbers for use as ■ wall linings in areas of highly unsteady (turbulent) flows,

- space requirements,

- cost of materials,

- weight increase,

- pressure loss,

- functional impairment,

- intrinsic noise,

- durability,

As indicated in the section on the prior art, can at least partially be avoided with the sound-absorbing wall element according to the invention

1. The main idea of the invention is to make the sound absorber itself a load-bearing construction element for flow-restricting walls or ends of any kind. The membrane absorber with its honeycomb structure is particularly suitable for this because it consists of From a sound-technical point of view, it can be configured as rigid and stiff and therefore can also be designed according to the respective static and dynamic requirements of the individual case. The sound absorber can thus completely or partially replace the flow boundary, for example housing or channel walls, that is, it can take over the flow guidance itself. The available space is thus optimally used, the additional material requirement is limited to the perforated and covering membrane, which hardly increase the weight of the system, and the noise protection measure does not require any additional pressure loss. This can even be reduced even more by shaping the membranes guiding the flow in a flow-favorable manner. In this way, the inherent noise generation of the sound absorbers is largely avoided, and the flow noise may even be reduced sustainably.

2. It is particularly advantageous to use the cavities, corners and cutouts present in flow channels and machine housings as chambers for the membrane absorbers according to DE-AS 35 04 208, as for example in FIG. 4a for a 90th ° channel bend and in Fig. 4b for an axial fan housing only to be used according to the principle. The additional space requirement indicated in FIG. 4 does not really mean a disadvantage, because the shape of the housing and the deflection was chosen only for practical reasons as drawn in the original state. The absorber chambers hardly require any additional space or weight during installation and assembly. The installation of the absorber exactly where Sound generation primarily takes place as a non-stationary interaction between turbulent flow and flow boundary, and can not only make the necessary silencers in the connected channels superfluous: since the membranes, which are kept vibratable instead of rigid flow contact, precisely affect the frequency range of the starches ¬ most sound excitation (eg rotating sound of the fans) can be adjusted, they reduce the interaction flow-wall and thus the sound excitation at the place of their origin from the outset due to their flexibility.

2a. At higher flow speeds it is of

The advantage of connecting the cover membrane and the perforated membrane in the area of the webs to one another at least in areas (16).

3. In order to design the cover membrane (4) as a flow boundary, for example in detachment areas behind flow deflections, it is furthermore favorable to additionally cover the cover membrane which is in direct contact with the flow with a soft layer (for example made of fine-pored soft foam). to prove. As a result, the above-mentioned transient interaction can be further "cushioned", ie reduced. In addition, this additional coating (see FIG. 5) can reduce the flutter excitation of the cover membrane, vaporize it, and thereby further reduce the generation of intrinsic noise. 4. In some turbomachines (for example fans not too powerful), it may be advantageous to replace the covering membranes in whole or in part with a fine-pored soft foam mat that is kept open-pored over the entire layer thickness on the side facing the flow. but is hewn on the side facing the perforated membrane, so that the chambers of the membrane absorbers remain hermetically sealed from the fluid in the adjacent flow channels even with a cover membrane (4) designed in this way. Such a cover membrane can not only help to reduce the intrinsic noise. If necessary, it can also increase the damping of the vibration system, consisting of the membranes, the air cushion in the chambers and the air layers in between.

The measures according to 3 and 4 also have the effect that additional damping is possible even in a frequency range to which the membrane absorbers have not been tuned, e.g. above 1000 Hz. On the other hand, these measures according to FIGS. 3 and 4 are also suitable for reducing the non-stationary interaction between flow and boundary and thus the sound excitation at the point of their origin at frequencies below the tuning range.

5. With certain fluids that are contaminated with foreign substances, such as dust, aerosols, grease, etc., it can be advantageous to place between the perforated membranes on the webs of the honeycomb 6 are attached to the covering membranes according to FIG. 6 in the region of these webs, depending on the flow action, more or less soft strips (14), for example made of soft foam (so-called foam rubber) or other permanently elastic substances.

According to measures 3 - 5, an acoustic impairment of the function of the membrane absorbers by flow pressure on the covering membranes can be counteracted in this way. In addition, such soft spacing strips make it possible to achieve a similar requirement for the various vibration forms as with measures 3 and 4.

In order to increase the service life of the cover membranes and the perforated membranes, these can be at least partially reinforced in the region of the webs by means of washers 15, 15a according to FIG. 7. As a result of this measure, the covering and perforated membranes can be stiffened in the area of the webs, where they are activated relatively little acoustically but are highly stressed by the unsteady flow forces, so that their acoustic properties are within the scope of the vibration system described above are retained, but their durability is increased.

7. One way of designing the flow boundary in the event of high stress is to use perforated membranes on the webs of the honeycomb structure using a permanently elastic adhesive or sealant (19) instead of the stiffening strips 7, so that on the one hand the chambers of the honeycomb structure are sealed off from one another, but on the other hand a certain flexibility towards the pressure fluctuations of the flow is achieved (cf. FIG. 8).

8. From a manufacturing point of view, it can be advantageous to provide strip-shaped inner membranes 17 instead of the continuous perforated membranes, which usually lie over many chambers, between which a slot-shaped opening 18 remains. The slot 18 does not have to be parallel to the webs, but can also run obliquely to them. As a result, the vibration system on which the acoustic effect of the membrane absorber is based can be varied within still further limits, given the chamber size specified by the channel or housing geometry. The strip-shaped membranes 17 (see FIG. 9) can possibly. Manufacture cheaper, especially if they are made of high-strength material, e.g. Stainless steel.

As explained in the previous section, it is necessary to make the cover membrane (4) from high-strength and / or temperature-resistant material in the case of fluid channels carrying warm or hot fluid. In such turbomachines, the covering membrane can consist of metal or a material which is also resistant at higher temperatures, for example plastic or coated textiles (made of synthetic fibers). According to FIG. 4c, the membrane absorbers with their outer covering membrane are intended to emulate the inner contour of the spiral housing, the rear wall 8 of the chambers is then formed by the outer housing shell. Their form depends on the required volume of the membrane absorber which is matched for absorption. Since larger fans tend to have their maximum noise at lower frequencies, the membrane absorbers can be inexpensive and. U. be integrated into existing housings and the membrane absorbers are therefore designed to be approximately geometrically similar to the previously customary fan housings in order to achieve an optimal absorption effect.

According to claim 14, it can also be advantageous to optimize the wall element according to the invention at the same time as a sound insulation element for low and medium frequencies, so that the sound transmission from the flow medium into the environment is reduced.

In the exemplary embodiment according to FIG. 10, the hole membrane with holes 6 can be seen in plan view, furthermore some walls or webs 7, 9, 10, 11 and 13.

Claims

1. Sound-absorbing wall element for damping the pressure waves propagating in the fluid channels in the fluid, which consists of cavities forming chambers which are delimited on one side by a cover membrane which can be excited to vibrate in the hearing frequency range, the interior of the chamber a perforated membrane, which is arranged at a short distance from the covering membrane and which together form a membrane absorber, is provided, characterized in that at least partially

a) at least one side (7,8,9,10,11) of the chambers (4,7-11) as a supporting wall and b) the covering membrane (4) as the fluid boundary (12) of a turbomachine is.

2. Wall element according to claim 1, characterized in that the back (8) is designed as a supporting wall.

3. Wall element according to claims 1 and 2, characterized ge indicates that the chambers are designed as a load-bearing honeycomb structure.

4. Wall element according to claims 1 to 3, characterized ge indicates that cavities, corners, gaps and recesses of the turbomachine are formed with carrying and / or non-supporting chambers.

5. Wall element according to claim 1, characterized in that the cover membrane (4) is formed in its thickness such that it together with the thickness of the perforated membrane, the hole geometry and the chamber volume to the frequency range of the strongest sound excitation, the sound source in the turbomachine is matched.

6. Wall element according to claims 1 to 5, characterized in that the cover membrane (4) with a soft layer, e.g. is made of fine-pored foam rubber or PVC (Fig. 5).

7. Wall element according to claims 1 to 5, characterized ge indicates that the cover membrane consists of a soft foam mat, which is open-pored over the entire layer thickness on the side facing the flow, and on which the perforated membrane ( 5) facing skin is formed.

8. Wall element according to claims 1 to 5, characterized ge indicates that between the cover and the perforated membrane (4,5) in the region of the webs (13) of the chambers soft strips (14), e.g. made of foam rubber, are arranged.

9. Wall element according to claims 1 to 8, characterized ge indicates that the cover and perforated membrane (4,5) in the region of the webs (13) is reinforced (15, 15a).

10.Wall element according to claim 9, characterized in that the reinforcement consists of washers (15, 15a) which are glued or welded to the cover or perforated membrane or the webs.

11.Wall element according to claims 1 to 10, characterized ge indicates that the perforated membrane with the webs (13) is elastically connected by means of an adhesive or sealant (19).

12. Wall element according to claims 1 to 11, characterized in that the perforated membrane is replaced by oscillating strips (17) which leave slots (18) free in the region of the center.

13. Wall element according to claims 1 to 11, characterized ge indicates that the cover membrane (4) has at least partially small openings which allow pressure equalization between the chambers and the flow channel.

14. Wall element according to claims 1 to 13, characterized in that it is simultaneously optimized as an insulating element, for low and medium frequencies, for sound transmission from the fluid into the environment.

15. Use of membrane absorbers according to the claims

1 to 14 as load-bearing structural elements in flow machines.

16. Use of membrane absorbers according to claim 15, characterized in that the turbomachine is a fan, compressor or a pump.

17. Use of membrane absorbers according to claim 15, characterized in that the turbomachine is a turbine.

18. Use of membrane absorbers according to claim 15, characterized in that the turbomachine is a jacket screw.

19. Use of membrane absorbers according to claims 1 to 14, as load-bearing structural elements in throttle devices e.g. Control valves •