JPH1097261A - Sound absorbing structure for high temperature - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound absorbing structure which withstands hightemp. gas jets, is less thermally deformed, is capable of absorbing a broad frequency range of noises and is less deteriorated in performance by water absorption. SOLUTION: This sound absorbing structure is provided with a heat resistant foamed ceramic material 4 having open cells. The size of these cells is so set that the adhesion of moisture by surface tension attains <=50%. This heat resistant foamed ceramic material 4 is a ceramic composite material(CMC) reinforced with ceramic fibers. Further, the material has woven fabrics 6 made of heat resistant ceramics which is held on the surface of the ceramic material 4 and has the meshes large than the cells. The woven fabrics 6 made of the heat resistant ceramics consist of the two-dimensional weaves or three-dimensional weaves of the ceramic composite material(CMC) and are formed by thinning part of the fibers to form perforated woven fabrics and impregnating these fabrics with a matrix material or depositing this matrix material by evaporation thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature sound absorbing structure used for an exhaust nozzle or the like of a jet engine.

[0002]

2. Description of the Related Art A sound-absorbing silencer is a device in which a sound-absorbing material (sound-absorbing lining) is lined or inserted into a pipe to attenuate propagating sound waves to reduce sound power radiated from an outlet. . Porous layer for sound absorbing lining,
There are a resistance type formed of a fibrous layer and a reactive type having a Helmholtz resonator structure combining a honeycomb and a perforated plate.

The resistive lining dissipates energy based on the viscosity and heat conduction of the medium, and the reactive lining dissipates energy due to wall friction caused by the movement of the medium and loss due to momentum. .

[0004]

A conventional high-temperature sound absorbing structure used for an exhaust nozzle or the like of a jet engine includes a heat-resistant fiber (silica wool, rock fiber, stainless wool, etc.) supported by a front plate and a back plate. Alternatively, a reactive lining (illustrated in FIG. 7) composed of a heat-resistant alloy honeycomb and a perforated plate is used.

However, the sound absorbing structure has a problem in that the gap between the heat-resistant fibers is small, the water absorption by the capillary is high, and once water is absorbed, it is difficult to remove the water. Further, such a sound absorbing structure has a problem that the surface of the fiber (fiber) is easily scattered by a gas jet or the like.

On the other hand, in the sound absorbing structure (see FIG. 7), the perforated plate 1, the internal honeycomb 2 and its rear plate 3 are overheated or largely thermally deformed by high temperature (for example, 700 to 800K or more) exhaust gas. There was a problem. That is, since the perforated plate 1 is made of, for example, a plate of stainless steel or aluminum, it may be damaged or thermally deformed due to overheating, and the brazed portion with the honeycomb 2 may be peeled off. In addition, this sound absorbing structure has a problem that the band of noise that can be absorbed is narrow, and broadband noise such as jet cannot be eliminated. Further, in this sound absorbing structure, the hole diameter is increased when the plate thickness is increased to maintain the strength, and the aperture ratio of the hole is increased due to the restriction on the production of the hole by punching (hole diameter> plate thickness). It is difficult to design the frequency freely.

The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a high-temperature sound-absorbing structure that can withstand a high-temperature gas jet, has little thermal deformation, can absorb broadband noise, and has little performance deterioration due to water absorption.

[0008]

According to the present invention, there is provided a heat-resistant foamed ceramic material having continuous pores, and the size of the pores is set so that the amount of adhering water due to surface tension is 50% or less. , A high-temperature sound-absorbing structure is provided. With this configuration, since the foam material is a ceramic material having high heat resistance, it can withstand a high-temperature gas jet and reduce thermal deformation. Further, continuous pores of the heat-resistant foamed ceramic material can absorb a broadband noise. In addition, since the size of the pores is set so that the amount of water adhering due to surface tension is 50% or less, even if a large amount of water adheres due to rainwater or the like, the surface tension is weak and the water is immediately drained. In addition, the sound absorption coefficient can be kept high.

[0009] According to a preferred embodiment of the present invention, there is further provided a heat-resistant ceramic fabric having a mesh larger than the pores. With this configuration, the heat-resistant ceramic fabric on the surface can prevent the foamed ceramic material from being damaged by the gas jet.

According to a preferred embodiment of the present invention, the heat-resistant ceramic fabric is made of a two-dimensional weave or a three-dimensional weave of a ceramic composite material (CMC). Is formed and impregnated or vapor-deposited with a matrix material. With this configuration, since the fabric is a woven fabric, the degree of freedom of the aperture ratio and the hole diameter is high, and eyes for introducing noise into the interior can be easily formed. In addition, since the CMC is heat-resistant, has a large specific strength, and has a small expansion coefficient, damage to the foamed ceramic material inside can be stably prevented for a long period of time while being exposed to a high-temperature gas jet. Especially,
In the case of three-dimensional weaving, even if the surface plate is thickened, a sound absorber close to a bulk-type sound absorbing material itself can be obtained by increasing the number of internal voids, so that both the strength and the acoustic performance can be improved.

[0011] The heat-resistant foamed ceramic material may include about 1
It has a continuous cell diameter of ~ 2 mm. By providing the bubble diameter of this size, the gap can be made sufficiently smaller than the gap between the conventional heat-resistant fibers, the water-absorbing power of the capillary tube can be reduced, and the amount of adhering moisture due to surface tension can be greatly reduced.

Further, the heat-resistant foamed ceramic material may further comprise:
The bubble diameter on the front side is large and the bubble diameter on the back side is small. This configuration can be achieved by laminating materials having different cell diameters, a functionally graded material in which the cell diameter is partially changed, a wedge-shaped molded product, and the like. Since it can be a sound absorber close to a bulk-type sound absorbing material itself, high performance can be achieved in both strength and sound.

The heat-resistant foamed ceramic material is preferably a ceramic composite material (CMC) reinforced with ceramic fibers. With this configuration, since the CMC is heat-resistant, has a large specific strength, and has a small expansion coefficient, it is possible to prevent a decrease in strength due to an increase in bubbles by using a fiber-mixed CMC. , By molding (sound absorbing wedge type), it has high design flexibility.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, common parts are denoted by the same reference numerals. FIG. 1 is a high-temperature sound absorbing structure according to the present invention. In this figure, the high-temperature sound absorbing structure of the present invention includes a heat-resistant foamed ceramic material 4 having continuous pores. Further, a heat-resistant ceramic fabric 6 having eyes A larger than the pores of the heat-resistant ceramic foam material 4 is provided. The heat-resistant foamed ceramic material 4
The ceramic material 4 is attached to a back plate 8 and a ceramic fabric 6 is held on the surface of the ceramic material 4. The back plate 8 is, for example, a heat-resistant ceramic plate, and preferably has airtightness through which gas does not pass. It is particularly preferable that the back plate 8 is made of a ceramic composite material (CMC), but the present invention is not limited to this, and a metal plate similar to the conventional one may be used.

The heat-resistant ceramic fabric 6 is made of a two-dimensional weave or a three-dimensional weave of a ceramic composite material (CMC). A part of the fiber is thinned out to form a perforated fabric having a gap A, and a matrix material is formed on the perforated fabric. Can be formed by impregnation or vapor deposition. Back plate 8 and foamed ceramic material 4,
The ceramic foam material 4 and the ceramic fabric 6 are held in close contact with each other. This close contact holding may be performed by a ceramic bonding material or the like, or may be integrally formed by three-dimensional weaving or the like. Alternatively, they may be simply brought into close contact by a suitable mechanical means.

FIG. 2 shows the heat-resistant ceramic fabric 6 described above.
(A) is a test result comparing the sound absorption coefficient with and without the presence of
(B) shows the case where the heat-resistant ceramic fabric 6 of the present invention is used as the surface material. In each figure, the horizontal axis represents the frequency of the noise, and the vertical axis represents the sound absorption coefficient of the vertically incident noise. FIG. 2 shows that the heat-resistant ceramic fabric 6 of the present invention is used particularly in a high frequency region.
It can be seen that the use of ま る increases the sound absorption coefficient.

The above-mentioned heat-resistant foamed ceramic material 4 has continuous pores, and the size of the pores is set so that the amount of adhering water due to surface tension is 50% or less. For example, using a water-repellent ceramic material, about 1-2 mm
By foaming a large number of continuous air bubbles, the weight can be reduced and the sound absorbing properties can be improved, the surface tension can be reduced, and the amount of adhered water can be reduced to 50% or less.

FIG. 3 is a structural diagram of the heat-resistant foamed ceramic material of FIG. In this figure, (A) is a laminated structure,
(B) shows an inclined structure, and (C) shows a sound absorbing wedge type. With the various structures shown in this figure, it is possible to manufacture the heat-resistant foamed ceramic material 4 having a large cell diameter on the front side and a small cell diameter on the back side. The heat-resistant foamed ceramic material 4 is preferably a ceramic composite material (CMC) reinforced with ceramic fibers. By using such a CMC, C having a high heat resistance, a large specific strength and a small expansion coefficient can be obtained.
Because it is MC, it can prevent the strength decrease due to the increase of bubbles by the use of CMC mixed with fiber, and since it is a ceramic with self-supporting shape, high design flexibility by combination and molding (sound absorbing wedge type) Have.

FIG. 4 is a comparison diagram of the sound absorbing performance. In this figure, the vertical axis indicates the noise level when flying at an altitude of 1000 ft at Mach 0.3. From this figure, it can be said that the foamed ceramic material constituting the high-temperature sound-absorbing structure according to the present invention has much higher sound-absorbing performance than the conventional honeycomb structure (sound-absorbing structure in FIG. 7), and is equivalent to a conventional fiber.

FIG. 5 is a graph showing the relationship between the water absorption ratio and the sound absorption coefficient.
5 is a test result obtained by measuring the sound absorption coefficient by changing the amount of adhered water using the method shown in FIG. Note that the water absorption ratio in this figure means water mass / (mass of foamed ceramic material + water mass), which is the same as the above-mentioned water adhesion amount (%). From this figure, it can be seen that as the water absorption ratio increases, the normal incidence sound absorption coefficient decreases, and when the water absorption ratio becomes 0.574 or more, it deteriorates rapidly. Therefore, in order to keep the noise absorption coefficient in a wide band high, it is necessary to reduce the amount of adhering water to 50% or less.

FIG. 6 is a graph showing the relationship between the water absorption ratio and the acoustic impedance, and shows the test results under the same conditions as in FIG. From this figure, it can be seen that the characteristics of the normal acoustic impedance change significantly when the water absorption ratio is 0.574 and 0.726. It is considered that this is because water enters the voids of the porous material due to water absorption and changes the properties of the material. Therefore, also from this result, the amount of water adhesion was 5%.
It is understood that it is important that the content is set to 0% or less.

According to the structure of the present invention described above, the heat-resistant ceramic fabric 6 on the surface can prevent the foamed ceramic material 4 from being damaged by the gas jet. Also,
Since both the inner foam material 4 and the fabric 6 on the surface are ceramic materials having high heat resistance, it can withstand a high-temperature gas jet and reduce thermal deformation. Further, the continuous pores of the heat-resistant foamed ceramic material 4 inside can absorb broadband noise. In addition, since the size of the pores is set so that the amount of water adhering due to surface tension is 50% or less, even if a large amount of water adheres due to rainwater or the like, the surface tension is weak and the water is immediately drained. In addition, the sound absorption coefficient can be kept high.

It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified without departing from the gist of the present invention.

[0024]

As described above, the high-temperature sound-absorbing structure of the present invention is excellent in that it withstands a high-temperature gas jet, has little thermal deformation, can absorb a broadband noise, and has little performance deterioration due to water absorption. Has an effect.

[Brief description of the drawings]

FIG. 1 is a diagram of a high-temperature sound absorbing structure according to the present invention.

FIG. 2 is a comparison diagram of the sound absorption coefficient depending on the presence or absence of a heat-resistant ceramic fabric.

FIG. 3 is a configuration diagram of the heat-resistant foamed ceramic material of FIG. 1;

FIG. 4 is a comparison diagram of sound absorption performance.

FIG. 5 is a relationship diagram between a water absorption ratio and a sound absorption coefficient.

FIG. 6 is a diagram showing a relationship between a water absorption ratio and acoustic impedance.

FIG. 7 is a conventional high-temperature sound absorbing structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Perforated plate 2 Honeycomb 3 Back plate 4 Heat-resistant foamed ceramic material 6 Heat-resistant ceramic fabric 8 Back plate

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tsutomu Oishi 229 Torogaya, Mizuho-cho, Nishitama-gun, Tokyo Ishikawajima-Harima Heavy Industries Co., Ltd. Mizuho Plant

Claims (6)

[Claims] 1. A heat-resistant foamed ceramic material having continuous pores, wherein the size of the pores is set so that the amount of water adhered by surface tension is 50% or less. High temperature sound absorbing structure. 2. The high-temperature sound absorbing structure according to claim 1, further comprising a heat-resistant ceramic fabric having eyes larger than the pores. 3. The heat-resistant ceramic fabric is made of a two-dimensional weave or a three-dimensional weave of a ceramic composite material (CMC). A part of the fibers is thinned out to form a perforated fabric, which is impregnated with a matrix material. The high-temperature sound absorbing structure according to claim 2, wherein the high-temperature sound absorbing structure is formed by vapor deposition. 4. The heat-resistant foamed ceramic material has a thickness of about 1-2.
The high-temperature sound-absorbing structure according to claim 1, having a continuous bubble diameter of 0.1 mm. 5. The high-temperature sound-absorbing structure according to claim 1, wherein the heat-resistant foamed ceramic material has a large cell diameter on the front side and a small cell diameter on the back side. 6. The ceramic composite material (CMC) reinforced with ceramic fibers, wherein the heat-resistant foamed ceramic material is a ceramic composite material (CMC).
The high-temperature sound absorbing structure according to claim 1, wherein: