JP2019138977A - Resonance type sound absorption panel - Google Patents

Abstract

To provide a resonance type sound absorption panel which improves sound absorption performance with a simple shape change as much as possible, does not remarkably increase weight due to the shape change and can be easily applied to an existing sound absorption panel.SOLUTION: A resonance type sound absorption panel 1 comprises: a cell structure which is constituted from partitions 12 for partitioning cells 11 and a surface plate 20 where through holes 21 are formed and a back wall 30, which are arranged on upper and lower portions of the partitioned cells 11; and protrusions protruding in a center axis direction of the through holes 21 from a wall side of at least one of a surface side end and a back side end of the through holes 21 and having protrusion length which is 20% or less of diameters of the through holes 21.SELECTED DRAWING: Figure 1

Description

  The present invention relates to noise reduction (noise reduction in noise propagation path) for automobiles, aircraft and marine engines, noise reduction in buildings, public facilities, automobile roads, railway facilities (sound insulation in noise propagation path), vehicles, The present invention relates to a resonance type sound absorbing panel used for reducing noise in a vehicle such as an automobile and an aircraft, reducing noise in a cabin (sound reduction in a closed space), and reducing noise vibration in a fairing that houses precision equipment (sound reduction in a closed space).

  In general, a resonance type sound absorbing panel is formed by attaching a surface plate and a back wall on the front and back of a panel having a cell structure, and providing a through hole in the surface plate that leads to each small space surrounded by partition walls partitioning the cells.

  Several techniques related to the resonance type sound absorbing panel have been proposed.

  Patent Document 1 has a sound absorbing structure in which a hole is extended inside a cell, and proposes to shift the resonance frequency to a lower frequency side. This can shift the frequency at which the sound absorption rate is maximized to a low frequency, but does not lead to positively increasing the sound absorption rate.

  In Patent Document 2, another cell is provided inside the cell via an intermediate communication hole, and the second layer cell of the so-called double layer resonance type sound absorbing panel is arranged between the first layer cells. It is thought that. If so, the sound absorption effect of the unit unit is equivalent to the double layer sound absorption panel, but the cell area of the first layer is relatively reduced. It is inferred that the performance will decrease.

  Patent Document 3 forms a sound absorbing panel having a two-dimensional slit-shaped hole. It seems that the resonance frequency is adjusted by fitting a complicated cell shape and hole shape into the rectangular sound absorbing structure.

JP2013-8012A JP 2001-92468 A Japanese Patent Laid-Open No. 9-3833

  These conventional techniques adjust the hole length and cell shape by paying attention to the resonance frequency of the sound absorbing panel, and do not actively suggest the problem of increasing the sound absorption volume.

  Moreover, examination according to the amplitude of the sound incident on the sound absorbing panel has not been made. However, when the sound absorbing panel is applied with various requirements, it is required to improve the sound absorbing performance without a significant shape change with respect to the existing sound absorbing panel. For example, when it is used for the inner wall of a duct, since there is an air flow on the surface of the sound absorbing panel, a large change in the panel shape appears as a pressure loss in the duct and affects design requirements other than the acoustic surface.

  Furthermore, for example, adding a member that extends the through hole leads to an increase in the weight of the sound absorbing panel, which is disadvantageous in an aircraft engine or the like that requires light weight.

  Although the bent hole shape suggested in Patent Document 3 may be a two-dimensional slit, it is difficult to realize a three-dimensional hole shape or an increase in manufacturing cost is expected.

  In view of the circumstances as described above, the object of the present invention is to improve the sound absorption performance by changing the shape as simple as possible, without significantly increasing the weight due to the shape change, and easily applied to existing sound absorption panels. An object of the present invention is to provide a resonance type sound absorbing panel that can be used.

  In order to achieve the above object, a resonance type sound absorbing panel according to an embodiment of the present invention includes a partition wall that divides a cell, a surface plate that is provided above and below the partitioned cell, and at least one of which has a through-hole. A cell structure composed of a back wall and at least one wall side of the front-side end and the back-side end of the through-hole project in the direction of the central axis of the through-hole, and 20% or less of the diameter of the through-hole And a protruding portion having a protruding length.

  In the present invention, the sound absorbing performance can be enhanced by providing the protruding portion having the above-described configuration. Further, since the structure is simply provided with the protruding portion, it is possible to change the shape easily, without significantly increasing the weight due to the shape change, and to easily apply to the existing sound absorbing panel.

  The protrusion part based on this invention is realizable with various forms as follows.

  In the resonance type sound absorbing panel according to an aspect of the present invention, the protruding portion may protrude in an annular shape from the wall side toward the central axis of the through hole.

  In the present invention, the protrusions may not be uniform around the axis of the through hole, but may exist periodically or aperiodically. That is, in the resonance type sound absorbing panel according to an aspect of the present invention, the protruding portions are arranged at intervals along the radial direction of the through hole, and are protruded from the wall side toward the central axis of the through hole. You may comprise from a protrusion member.

  In the present invention, the protrusion is thin toward the tip (toward the central axis of the through hole), the tip has an acute angle, or the outside of the through hole (air layer side) or toward the tip. The shape may be warped inside the through hole. That is, in the resonance type sound absorbing panel according to an aspect of the present invention, the protruding portion may be thinner as it goes from the wall side toward the central axis of the through hole. In the resonance type sound absorbing panel according to an aspect of the present invention, the protruding portion may have a warp in any one of the axial directions of the through hole.

  In the present invention, the outer periphery of the protruding portion and the inner surface of the through hole may be joined in a polygonal shape or smoothly joined. That is, in the resonance type sound absorbing panel according to an aspect of the present invention, the protruding portion may have a polygonal shape or an R shape on the inner surface of the through hole.

  A resonance type sound absorbing panel according to an aspect of the present invention includes an annular member having the protruding portion, and a countersink is provided around the through hole in the surface plate or the back wall, and the ring is formed on the countersink. A member may be fitted.

  The resonance type sound absorbing panel according to an aspect of the present invention may include a cylindrical member having the protruding portion, and the cylindrical member may be fitted into the through hole.

  The resonance type sound absorbing panel according to an aspect of the present invention includes a thin sheet-like member having a hole having a smaller diameter than the through hole, and the small hole is positioned in the through hole. The protrusion may be configured such that the sheet-like member is attached to the surface of the surface plate or the back wall, and the sheet-like member protrudes into the through hole.

  In the resonance type sound absorbing panel according to an aspect of the present invention, the thickness of the protruding portion may be 5% or less of the hole length of the through hole.

  According to the present invention, it is possible to improve the sound absorption performance by changing the shape as simple as possible, without increasing the weight significantly by changing the shape, and to be easily applied to an existing sound absorption panel.

It is a disassembled perspective view of the resonance type sound absorption panel which concerns on one Embodiment of this invention. FIG. 2 is a partial cross-sectional view of the resonance type sound absorbing panel shown in FIG. 1. It is an expanded sectional view of the through-hole vicinity of the resonance type sound absorption panel shown in FIG.1 and FIG.2. FIG. 3 is a plan view of the vicinity of a through hole of the resonance type sound absorbing panel shown in FIGS. 1 and 2. FIG. 10 is a cross-sectional view showing a protrusion according to another embodiment of the present invention, wherein the protrusion is configured to become gradually thinner. FIG. 10 is a cross-sectional view illustrating a case where the protrusion is configured to have an acute angle at the tip of the protrusion according to another embodiment of the present invention. It is a protrusion part which concerns on other embodiment of this invention, Comprising: It is sectional drawing in case a protrusion part has curvature outside. It is a protrusion part which concerns on other embodiment of this invention, Comprising: It is sectional drawing in case a protrusion part has curvature inside. It is a protrusion concerning other embodiments of the present invention, and is a sectional view in case a protrusion has an R shape. It is a protrusion part which concerns on other embodiment of this invention, Comprising: It is sectional drawing in case a protrusion part has polygonal shape. FIG. 11 is a cross-sectional view illustrating a protrusion according to another embodiment of the present invention, in which the protrusion includes a plurality of protrusion members that protrude in the direction of the central axis of the through hole from the wall side of the through hole. FIG. 10B is a plan view of FIG. 10A. It is a protrusion part which concerns on other embodiment of this invention, Comprising: It is sectional drawing for demonstrating the case where a protrusion part is used as a ring member, and it fits into a seat. It is a protrusion part which concerns on other embodiment of this invention, Comprising: It is sectional drawing for demonstrating the case where a protrusion part is comprised from the cylindrical member. It is a protrusion part which concerns on other embodiment of this invention, Comprising: It is sectional drawing for demonstrating the case where a protrusion part is comprised from a sheet-like member. It is a figure for demonstrating the numerical-analysis result performed in order to confirm the effect of this invention. It is a figure which shows the particle velocity distribution and entropy distribution when there is no protrusion part. It is a figure which shows the particle velocity distribution and entropy distribution when the protrusion amount (protrusion length) of the protrusion is 0.2 mm. It is a figure which shows the particle velocity distribution and entropy distribution at the time of the protrusion amount (protrusion length) of a protrusion part being 0.4 mm. It is a figure which shows the particle velocity distribution and entropy distribution when the protrusion amount (protrusion length) of the protrusion is 0.6 mm. It is a figure which shows the particle velocity distribution and entropy distribution when the protrusion amount (protrusion length) of a protrusion part is 0.8 mm. It is the graph which showed the relationship between the protrusion amount (protrusion length) of a protrusion part, and a sound absorption rate. It is a figure which shows the particle velocity distribution and entropy distribution in case the thickness of a protrusion part is zero. It is a figure which shows the particle velocity distribution and entropy distribution in case the thickness of a protrusion part is 0.05 mm. It is a figure which shows the particle velocity distribution and entropy distribution in case the thickness of a protrusion part is 0.1 mm. It is a figure which shows the particle velocity distribution and entropy distribution in case the thickness of a protrusion part is 0.2 mm. The particle velocity distribution and entropy distribution when the thickness of the protrusion is zero are shown. The particle velocity distribution and entropy distribution when the thickness of the protrusion is 0.05 mm are shown. The particle velocity distribution and entropy distribution when the thickness of the protrusion is zero and the shape is a sharp edge are shown. The particle velocity distribution and entropy distribution when the thickness of the protrusion is 0.05 mm and the shape is a sharp edge are shown. It is a figure which shows the example of application of the resonance type sound absorption panel which concerns on this invention. It is sectional drawing of the protrusion part which concerns on the modification of this invention. It is sectional drawing of the protrusion part which concerns on another modification of this invention. It is sectional drawing of the protrusion part which concerns on another modification of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Configuration of resonance type sound absorbing panel>
1 is an exploded perspective view of a resonance type sound absorbing panel according to an embodiment of the present invention, FIG. 2 is a partial sectional view of the resonance type sound absorbing panel, and FIG. 3A is an enlarged cross section near the through hole of the resonance type sound absorbing panel. FIG. 3B is a plan view of the vicinity of the through hole of the resonance type sound absorbing panel.

  The resonance type sound absorbing panel 1 includes a panel body 10, a surface plate 20, and a back wall 30.

  The panel body 10 has a large number of cells 11, and these cells 11 are partitioned by partition walls 12.

  A surface plate 20 is affixed to the front side of the panel body 10, and a back wall 30 is affixed to the back side of the panel body 10. Thereby, the resonance type sound absorbing panel 1 is provided on the upper and lower sides of the partition wall 12 partitioning the cell 11 and the partitioned cell 11, and constitutes a large number of cell structures 40 including the surface plate 20 and the back wall 30. .

  The surface plate 20 is provided with a through hole 21 that penetrates the external air layer and the cell 11. In the embodiment, seven through holes 21 are provided for one cell 11, but the present invention is not limited to this, and the number of through holes 21 may be one, or any of two or more. Also good.

A protruding portion 50 that protrudes in an annular shape in the central axis direction of the through hole 21 from the wall side is provided at the surface side end portion 21 a of the through hole 21. The protrusion length ε of the protrusion 50 is 20% or less of the diameter d of the through hole 21, that is,
ε / d ≦ 0.2
Have the relationship.
Thereby, compared with the case where the protrusion part 50 is not provided in the through-hole 21, a sound absorption rate becomes high. This point will be described later.

  The resonance type sound absorbing panel 1 has a function of absorbing energy of sound waves incident on the surface thereof. The surface of the resonance type sound absorbing panel 1 may have not only a flat surface but also a curved surface and an arbitrary shape as viewed from the space where the sound wave enters.

  The resonance type sound absorbing panel 1 has a three-layer structure from the panel surface. These are recognized as a surface plate 20, a panel body 10 composed of a large number of cells 11, and a back wall 30. A through-hole 21 is formed in the surface plate 20, and air that contacts the surface plate 20 communicates with the cell structure 40. The cell structure 40 is a small space surrounded by the surface plate 20, the back wall 30, and the partition wall 12 that partitions the cell 11. Depending on the application of the resonance type sound absorbing panel 1, a small hole for removing water that has entered the cell may be provided in a part of the partition wall 12 that partitions the cell 11. In addition, as will be described later, there is a so-called multi-layer sound absorbing panel structure in which a small hole is provided in the back wall 30 and the cell 11 and the back layer are provided behind the small hole. Since the cell structure 40 is sandwiched between the free surface plate 20 of the through-hole 21 and the back wall 30, it may be called a “sandwich structure”.

  The cross-sectional shape of each cell structure 40 is arbitrary, and may be triangular, quadrangular, polygonal or circular. Hexagonal ones are called “honeycomb” structures. The cell structure 40 communicates with the outside only through the through hole 21 provided in the surface plate 20 in principle. It is assumed that the back wall 30 is sufficiently rigid against air vibration. Further, in normal handling, all the partition walls 12 surrounding the cell structure 40 are treated as having sufficient rigidity as compared with the internal air.

  The resonance type sound absorbing panel 1 has a function of improving sound absorbing performance under an acoustic resonance frequency determined from the above structure. In general, sound propagating in the air forms a wave having time reproducibility depending on the frequency. In general, a sound includes a sound having a plurality of frequencies and accompanying amplitudes and phases. The resonance type sound absorbing panel 1 enhances sound absorbing performance in a frequency band centered on a specific frequency.

The resonance frequency f of the resonance type sound absorbing panel 1 includes the volume V of the cell structure 40, the total area S of the surface through holes 21 corresponding to the cells 11, and the length of the through holes 21 (in other words, the thickness of the surface plate 20). Equivalent) d is defined as follows. Here, d ′ is obtained by adding an opening end correction amount to d.
f to c / 2π√ (s / Vd ′)

  When sound waves, that is, minute pressure fluctuations reach the surface plate 20 of the resonance type sound absorbing panel 1, the air inside the empty portion of the through hole 21 of the surface plate 20 is displaced. When the air inside the empty part of the through hole 21 is pushed toward the cell structure 40 side, the air inside the cell structure 40 is compressed, and when the air inside the empty part of the through hole 21 is pulled, the air inside the cell structure 40 is compressed. Expands. However, since the volume inside the through hole 21 is sufficiently smaller than the volume of the cell structure 40, the volume change amount due to the compression and expansion is sufficiently smaller than the volume of the cell structure 40. Since the incident sound fluctuates with the period (or frequency), the air inside the cavity of the through hole 21 is also displaced with the frequency of the incident sound wave, and as a result, the micro pressure inside the cell structure 40 also fluctuates with the frequency of the incident sound wave. It becomes.

  When the resonance type sound absorbing panel 1 is equivalent to a spring / mass / damper system, the energy dissipation (sound absorption) is carried by the damper, and is correlated with the time variation (particle velocity) of the displacement of the air inside the through hole 21. There is. When the incident sound wave has a frequency close to the resonance frequency of the panel, the particle velocity, which is the first time derivative of the displacement, is increased as in the frequency response of the spring-mass-damper system. In a macro system, an increase in particle velocity results in an increase in energy dissipation by the damper and an increase in energy dissipation of the incident sound wave, which is an external excitation, and appears as attenuation of the incident sound wave in the sound absorbing panel. .

  Thus, the resonance type sound absorbing panel 1 can be equivalent to a mechanical spring, mass, and damper model. The air in the through-hole 21 corresponds to a mass (mass) and is displaced with respect to incident sound that is an external force. In response to the displacement, the air inside the cell structure 40 plays a role of (spring) that compresses and expands and brings a restoring force to the air of the through hole 21. Since the damper does not occur as the air in the through hole 21 is displaced, the damper is generated by time differentiation (particle velocity) of the displacement. That is, theoretically, it can be said that the attenuation effect of the resonance type sound absorbing panel 1 is dominated by the fluctuation of the air in the through hole 21 of the surface plate 20 rather than the inside of the cell structure 40.

  The energy dissipation generated by the particle velocity excited by the movement of the air layer of the through-hole 21 and the sound absorption effect from a macro viewpoint are related to each other, and the particle velocity amplitude of the through-hole 21 in which the energy dissipation is dominant. Attention is paid to the hole shape of the opening portion (surface side end portion 21a) that is expected to increase. Typically, the present invention provides a slight change in the hole shape of the surface-side end portion 21a of the through-hole 21, that is, by providing the protruding portion 50, without changing the main properties of the sound-absorbing panel 1, the sound-absorbing sound. The performance (here, the sound absorption rate is taken as an example of the ratio of the energy of the reflected sound wave to the energy of the incident sound wave) is improved. Here, the main properties of the sound absorbing panel include resonance frequency, weight and bulk, surface roughness, and the like.

  Here, the case where the tangent of the inner surface of the through hole 21 is perpendicular to the front and back surfaces of the surface plate 20, that is, the case where there is no protrusion 50 in the resonance type sound absorbing panel 1 of FIGS. Baseline) shape. In other words, the base line is such that the through hole 21 is formed perpendicular to the surface plate 20, and when viewed from the side, the side surface of the through hole 21 and the surface of the surface plate 20 and the back surface of the surface plate form a right angle.

  With respect to this baseline shape, the resonance type sound absorbing panel 1 according to the present embodiment is such that the protruding portion 50 is provided in the through hole 21.

  That is, the resonance type sound absorbing panel 1 is a protrusion that forms protrusions on the back surface side end portion and / or the surface side end portion of the through hole 21 of the surface plate 20 or the through hole of the intermediate partition wall inside the cell of the panel as will be described later. The projecting length, which is the height of the projection that is the projecting portion 50, is 20% or less of the diameter of the through hole 21 (equivalent diameter for a non-circular hole). And

  For example, assuming that the through-hole 21 is circular, the diameter of the through-hole 21 is 1.65 mm, and a 12% -high protrusion, concentric minute protrusions (projections) having an inner diameter of 1.65 × 0.12 = 0.2 mm 50). The protrusion shape of the protrusion 50 may be smoothly connected in a direction perpendicular to the hole from the flow path (straight portion) of the through hole 21 or may be changed to a right angle.

  More specifically, the protrusion 50 has a thin protrusion at the opening end of the through hole 21 of the surface plate 20, and the protrusion 50 extends from the corner of the end toward the central axis of the through hole 21. . The thickness of the protrusion 50 is assumed to be sufficiently thin in terms of engineering compared to the hole diameter. For example, the thickness is 5% or less of the diameter of the through hole 21, and the protrusion amount from the end corner is 20% of the diameter of the through hole 21 at the maximum. When the protrusion 50 is viewed from the central axis of the through hole 21, it is concentric with the through hole. That is, the protrusion 50 has an annular shape.

<Aspect of protrusion>
In this embodiment, the protrusion 50 has an annular shape, but the protrusion according to the present invention can be realized in various forms as shown in FIGS.

  For example, as shown in FIG. 4, the protrusion 50 may be configured to become thinner from the wall side of the through hole 21 toward the center axis direction of the through hole 21. In that case, you may comprise so that the front-end | tip of the protrusion part 50 may become an acute angle, as shown in FIG. Further, as shown in FIGS. 6 and 7, the protrusion 50 may have a warp in any one of the axial directions of the through hole 21. That is, as shown in FIG. 6, the protruding portion 50 may be warped on the outer side (air layer side) of the through hole 21, and as shown in FIG. 7, the protruding portion 50 is on the inner side of the through hole 21. It may be warped. Moreover, as for the surface inside the through-hole 21, the protrusion part 50 may be R shape as shown in FIG. 8, and may be polygonal shape as shown in FIG.

  As shown in FIG. 10A and FIG. 10B, a plurality of projecting members 50 are arranged at intervals along the radial direction of the through hole 21 and project from the wall side of the through hole 21 toward the central axis of the through hole 21. You may comprise from 51.

  As shown in FIG. 11, it has an annular member 52 having a protrusion 50, and a countersink 22 is provided around the through hole 21 of the surface plate 20 (FIG. 11A). 52 may be fitted (FIG. 11B).

  As shown in FIG. 12, a cylindrical member 53 having a protruding portion 50 may be prepared (FIG. 12 (a)), and the cylindrical member 53 may be fitted into the through hole 21 (FIG. 12 (b)).

  As shown in FIG. 13, a thin sheet-like member 54 having a hole 55 smaller in diameter than the through hole 21 is prepared (FIG. 13A), and the small hole 55 is positioned in the through hole 21. In addition, the sheet-like member 54 may be attached to the surface of the surface plate 20 (FIG. 13B), and the protruding portion 50 may be configured so that the sheet-like member 54 protrudes into the through hole 21.

<Effects of protrusions>
FIG. 14 shows an example in which the particle velocity fluctuation accompanying the incidence of sound waves is calculated by numerical fluid analysis when the protrusion 50 according to the present invention is provided.

  FIG. 14 shows a model of a resonance type sound absorbing panel 1 having a through hole 21 having a hole diameter of 1.65 mm, a protrusion 50 having a protrusion length of 0.4 mm (the thickness of the protrusion is 0) and a resonance frequency of 2150 Hz, and 120 dB. 3 is a result of numerical fluid analysis of the particle velocity around the through hole 21 and the generation enthalpy when a normal sound wave is vertically incident. The instantaneous particle velocity distribution is represented by arrows, and the instantaneous entropy generation is represented by grayscale shading.

The figure shows the vicinity of the through-hole 21 of the axis target cell structure, and the left side of the step means the through-hole 21. The lower part of the step is connected to a space called a cell 11, and the upper part of the step means a pipe line, that is, a sound wave passage, and a sound wave enters from the top toward the step.
At this moment, since the sound pressure of the cell 11 is in a high phase, a particle velocity vector is formed from the cell 11 toward the pipeline, and there is a portion that circulates in the protrusion 50. It can be seen that peeling occurs at the tip A of the protrusion 50. The large loss (sound absorption) is caused by the separation flow at the tip A of the protrusion 50.

15A to 15E show the particle velocity distribution and the entropy distribution when the hole diameter is increased while increasing the protrusion amount (protrusion length) of the protrusion 50 from zero to 0.8 mm by 0.2 mm. The diameter of the baseline through-hole 21 is 1.65 mm.
15A shows a protrusion amount (projection length) of the protrusion portion 50 of zero, FIG. 15B shows a protrusion amount (protrusion length) of the protrusion portion 50 of 0.2 mm, and FIG. 4D, FIG. 15D shows a case where the protrusion amount (protrusion length) of the protrusion 50 is 0.6 mm, and FIG. 15E shows a case where the protrusion amount (protrusion length) of the protrusion 50 is 0.8 mm. The table below summarizes the maximum sound absorption rate.

FIG. 16 is a graph showing the relationship between the protrusion amount (protrusion length) of the protrusion 50 and the sound absorption rate based on these results.

  Compared to the case where there is no protrusion (Baseline), the maximum increase in the sound absorption coefficient is obtained at 10% of the hole diameter of the through-hole 21, and an increase in the sound absorption coefficient is recognized even when it is equivalent to 20%.

  In the analysis, a standing wave generated in the vertical incident tube when a sound wave incident on the surface plate 20 is assumed is obtained by simulating the vertical incident tube. Based on the amplitude ratio of the standing wave, the normal incident sound absorption coefficient in the sound absorption panel is obtained. According to the calculation result, in the case where the solution of the present invention was taken, the sound absorption coefficient was increased as compared with the case where the solution was not taken (that is, the case where the through hole 21 was simply provided perpendicular to the surface plate). 15A to 15E).

  Further, when attention is paid to the amount of entropy generated around the end portion of the through-hole 21, the amount of entropy generated is increased in the case where the protruding portion 50 according to the present invention is provided from the shades of FIGS. 15A to 15E. A trend is observed. This explains the increase in heat dissipation caused by the particle velocity and supports the increase in sound absorption from a macroscopic point of view. The same can be applied to the shape of the through-hole provided in the intermediate plate of the multilayer sound-absorbing panel.

From the above, the shape of the through-hole 21 of the surface plate 20 (the cross-sectional shape of the surface plate 20) in which the protruding portion 50 that is a minute protrusion is provided in the opening that is the surface side end of the through-hole 21 is a simple hole. This suggests that it has a function of promoting energy attenuation of the incident sound wave, that is, an effect of increasing the sound absorption rate, as compared with the case where a gap is made.
In addition, if a sound absorption rate increase of 20% or more from Baseline is taken as a guide, it is considered that a more significant increase in the sound absorption rate is expected if the protruding amount is at least 15%.

17A to 17D show the particle velocity distribution and entropy distribution when the protrusion length of the protrusion 50 is 0.4 mm and the thickness of the protrusion 50 is changed. The diameter of the through hole 21 is 1.65 mm.
17A shows zero thickness of the protrusion 50, FIG. 17B shows that the thickness of the protrusion 50 is 0.05 mm, FIG. 17C shows that the thickness of the protrusion 50 is 0.1 mm, and FIG. This is the case of 0.2 mm.
The table below summarizes the maximum sound absorption rate.

From the above, it can be seen that the sound absorption rate tends to decrease as the thickness of the protrusion 50 increases.

18A to 18D show the particle velocity distribution and entropy distribution when the protrusion shape of the protrusion 50 is changed to a realistic one. The diameter of the through hole 21 is 1.65 mm, and the protrusion height (protrusion length) of the protrusion 50 is 0.4 mm.
FIG. 18A shows the case where the thickness of the protrusion 50 is zero, and the sound absorption coefficient is 0.997. FIG. 18B shows the case where the thickness of the protrusion 50 is 0.05 mm, and the sound absorption coefficient is 0.991. FIG. 18C shows a case where the shoe edge is thinned toward the tip of the protrusion 50, and the sound absorption coefficient is 0.991 when the thickness of the base is zero. FIG. 18C shows a case where the shoe edge is thinned toward the tip of the protrusion 50, and the sound absorption coefficient is 0.977 when the thickness of the base is 0.05 mm. The thickness of the protrusion 50 is 0.05 mm (really thin) and the sharp edge (realistic shape) is the same sound absorption coefficient.

<Application example of resonance type sound absorbing panel according to the present invention>
The following types of application of the resonance type sound absorbing panel according to the present invention are conceivable. For simplicity, the resonance type sound absorbing panel is referred to as a sound absorbing panel.

  1) Install on the wall of the propagation path to prevent noise propagation.

  The propagation path is usually a flow path such as a duct. In this type, a perforated surface plate is installed on the wall surface of the propagation path, and the cell structure and the back wall exist behind it. An air flow may exist inside the propagation path, and a velocity distribution and a temperature distribution may exist in the path cross-sectional direction. Noise may propagate in the same direction as the airflow or in the opposite direction. Also, the acoustic mode corresponding to the cross-sectional shape of the noise (sound pressure distribution with the antinodes and nodes of the sound pressure, where there are multiple sound pressure distributions at the same frequency, and the spatial distribution of the sound pressure In some cases, including a time-varying position). Specifically, there is an example in which the sound pressure level is reduced before noise generated by the fan is released to the outside of the engine by installing a sound absorbing panel on the inner wall of the intake duct or exhaust duct of an aircraft turbofan engine. Can be mentioned. In the ground operation facility of a jet engine, there is an example in which high sound pressure noise due to jet noise is reduced by installing a sound absorbing panel on the inner wall of a duct that introduces a cooled high-speed exhaust jet and exhausts it to the outside. In a power plant, there is also an example in which a sound absorbing panel is installed on the inner wall of the air intake side duct to attenuate the noise generated from the blower or compressor before it is released to the outside.

  2) Install it on the wall where noise enters and prevent reflection of noise.

  In this type, panels are installed on the surfaces of walls, walls, and structures placed in open spaces. There may be airflow on the panel surface. The traveling direction of incident noise may not be perpendicular to the panel surface plate. As a specific example, a sound absorbing panel is installed on the wall surface of a room that requires quietness to suppress the echo in the room, a sound absorbing panel is installed on the surface of the fence provided on the route through which the high-speed vehicle passes, and the vehicle, road surface To reduce the reflection of noise generated from the incident and incident on the kite to reduce the amount of noise exposure to the surroundings, on the surface of the aircraft body (the fuselage surface, high lift devices such as flaps, landing devices such as legs and storage doors) By installing a sound-absorbing panel, aerodynamic noise and engine noise can be suppressed as much as possible with a noise generation source, and noise emission to a distant location can be exemplified.

  3) Install it on all or part of the boundary surface covering the closed space to reduce internal noise.

  It is assumed that the noise field is formed because it is a closed space and includes a noise source, and the case where a noise field that does not include a noise source but is introduced from an external noise source through vibration is formed. By installing a panel in all or part of the closed space, the noise amplitude propagating in the closed space is attenuated on the panel surface, thereby reducing the noise in the closed space compared to when there is no panel. Suppose. As a specific example, by installing a heat-resistant sound absorbing panel on the inner wall of a boiler or combustor and absorbing unstable combustion vibration and combustion noise generated inside the combustion chamber, it suppresses unstable vibration and combustion propagates outside. By reducing noise, installing a sound absorbing panel on the inner wall of the rocket fairing, reducing the sound field in which the external sound generated when launching the rocket is excited inside the fairing through the vibration of the fairing, For example, installing a sound absorbing panel on the inner wall to reduce engine noise, airframe noise, and boundary layer noise propagating from the outside.

Example 1
The sound absorbing panel 1 according to the present invention is installed in an aircraft jet engine intake and exhaust duct.

  As shown in FIG. 19, the sound absorbing panel 1 according to the present invention is installed on the inner wall surface of the duct 61. The inner wall of the duct 61 is usually circular, the sound absorbing panel 1 has a curvature, and the radius changes in the axial direction of the duct 61. In FIG. 19, reference numeral 62 denotes an air suction port of the engine, 63 denotes a fan rotor blade, and 64 denotes a fan stationary blade.

  When the surface plate 20, the cell structure 40, and the back wall 30 are single layers (in the case of a single layer sound absorbing panel), the through hole 21 according to the present invention is processed into the surface plate 20. In the case of multiple layers (double layer sound absorbing panel, triple layer sound absorbing panel, etc.), the through hole according to the present invention can be applied not only to the through hole 21 of the surface plate 20 but also to a through hole provided in an interlayer partition called a septum. Including. At this time, you may change the shape of the obstruction | occlusion part (protrusion part 50) of a hole with the through-hole 21 and septum of the surface board 20. FIG. Since the fan intake or exhaust passes through the surface plate 20, if the hole shape is significantly changed, the flow field changes, and the influence on the pressure loss in the duct is inevitable. As in the present invention, when a partial blockage of about 15% of the hole diameter of the through hole is applied using a straight line or other small protrusion, it is expected that the influence on the flow field is reduced. It is estimated that the sound absorption performance can be improved while maintaining the loss.

(Example 2)
The sound absorbing panel 1 according to the present invention is installed in an intake / exhaust duct of a power plant or the like.

  In power generation plants and general plants, outside air is introduced as a working fluid and exhausted after being used in a heat engine or the like. The sound absorbing panel 1 according to the present invention is installed on the inner wall of a flow path (duct) for sucking outside air or a flow path (duct) for discharging air. In this case, for example, by installing a perforated thin film on an existing sound absorbing panel as a retrofit (see FIG. 13), the sound absorbing performance can be improved.

(Example 3)
The sound absorbing panel 1 according to the present invention is installed on the wall of the room, the outer wall of the building, and the fence along the line.

  The sound absorbing panel 1 is installed on the wall or wall. The noise incident on the panel 1 is reduced, and the noise around the wall is reduced compared to the case where there is no sound absorbing panel. By installing the sound-absorbing panel 1 on the inner surface of the fence provided along the roads of automobiles and railways, the noise on the route is suppressed and the amount of noise exposure to the surrounding environment is reduced.

Example 4
The sound-absorbing panel 1 according to the present invention is installed on the interior walls of the cabin and the vehicle.

  The sound absorbing panel 1 is installed on the inner wall of a closed space such as an aircraft cabin, a vehicle cabin, or a rocket fairing. Inside the aircraft or vehicle, noise from the prime mover, airflow sound, etc. propagates through the partition wall, resulting in internal noise remaining. It is expected to reduce noise by attaching the sound absorbing panel 1 to the inner wall, and it is expected to improve the effect of the existing sound absorbing panel.

  When launching a rocket, there are high-amplitude sound sources and vibration sources that propagate through the aircraft into the fairing. This results in unwanted vibrations in the payload inside the fairing. It is expected that the sound absorption volume of the inner wall of the fairing can be increased without increasing the weight by attaching the protruding portion 50 that is a slight protrusion to the through hole 21 of the surface plate 20 of the sound absorbing panel 1.

  As described above, it is possible to reduce environmental noise by applying the resonance type sound absorbing panel 1 according to the present invention to a noise propagation path of an automobile, a plant, and an aircraft.

  In addition, the resonance type sound absorbing panel 1 according to the present invention can be applied to the interior of a traffic machine, the interior wall of the cabin, etc., to reduce cabin noise and improve comfort.

  Furthermore, the resonance type sound absorbing panel 1 according to the present invention is applied to walls and walls of buildings, roads and the like to reduce environmental noise and improve the living and working environment.

  Further, the resonance type sound absorbing panel 1 according to the present invention is applied to a rocket fairing or a spacecraft to avoid damage to equipment.

<Others>
The present invention is not limited to the above embodiments, and various modifications are possible within the scope of the technical idea, and the scope of the modifications also belongs to the technical scope of the present invention.

  For example, as shown in FIG. 20, the protrusion 50 may be provided at the end on the back surface side of the through hole 21. Further, as shown in FIG. 21, the protrusions 50 may be provided at both the front surface side end portion and the back surface side end portion of the through hole 21.

  Moreover, as shown in FIG. 22, you may provide the protrusion part 50 in the surface side edge part of the through-hole 71 provided in the intermediate board 70 of the multilayer sound-absorption panel. The protruding portion 50 may be provided at the back surface side end portion of the through hole 71, or may be provided at both the front surface side end portion and the back surface side end portion of the through hole 71. The protrusion 50 may be provided in the through hole 21 of the surface plate 20, and the protrusion 50 may be provided in the through hole 71 of the intermediate plate 70.

DESCRIPTION OF SYMBOLS 1 Resonant type sound absorption panel 11 Cell 12 Partition 20 Surface plate 21 Through-hole 30 Back wall 40 Cell structure

Claims (10)

A cell structure composed of a partition wall that divides a cell, and a surface plate and a back wall that are provided above and below the partitioned cell and at least one of which has a through hole;
A resonance projecting from at least one wall side of the front-side end and the back-side end of the through-hole in the direction of the central axis of the through-hole and having a protruding length of 20% or less of the diameter of the through-hole. Type sound absorbing panel. The resonance type sound absorbing panel according to claim 1,
The projecting portion projects in an annular shape from the wall side toward the central axis of the through hole. The resonance type sound absorbing panel according to claim 1,
The said protrusion part is arrange | positioned at intervals along the central-axis direction of the said through-hole, and is comprised from the several protrusion member which protrudes in the central-axis direction of the said through-hole from the said wall side. The resonance type sound absorbing panel according to claim 2 or 3,
The projecting portion becomes thinner from the wall side toward the center axis direction of the through hole. The resonance type sound absorbing panel according to any one of claims 2 to 4,
The protrusion has a warp in any one of axial directions of the through hole. A resonance type sound absorbing panel according to any one of claims 2 to 5,
The protrusion has a polygonal shape or an R shape on the inner surface of the through hole. The resonance type sound absorbing panel according to any one of claims 1 to 6,
An annular member having the protrusion,
Provide a countersink around the through hole in the surface plate or back wall,
A resonance type sound absorbing panel in which the annular member is fitted into the seat. The resonance type sound absorbing panel according to any one of claims 1 to 6,
A cylindrical member having the protruding portion;
A resonance type sound absorbing panel in which the cylindrical member is fitted into the through hole. The resonance type sound absorbing panel according to any one of claims 1 to 6,
A thin sheet-like member having a hole having a smaller hole diameter than the through hole is provided,
The sheet-like member is attached to the surface of the surface plate or the back wall so that the small hole is positioned in the through-hole, and the sheet-like member protrudes into the through-hole. Resonance-type sound absorbing panel. A resonance type sound absorbing panel according to any one of claims 1 to 9,
The thickness of the protrusion is 5% or less of the hole length of the through hole.