JP2005252575A - Coating structure of microphone and wind tunnel testing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating structure of a microphone and a wind tunnel testing apparatus with which hissing sound can be reduced and aerodynamic sound generated from an object of a test can highly accurately be measured. <P>SOLUTION: A thin film part 7 is fixed on the almost same face as a wall face of a fixed wall part 3a by leaving an interval between the film part and a vibration face 5d. The thin film part 7 is formed by stacking and bonding a plurality of thin films 8 and 9. The thin films 8 and 9 are adhesive tapes made of synthetic resin, which consist of films made from polypropylene. An adhesive layer 9b of the thin film 9 is stuck to the wall face of the fixed wall part 3a. The vibration face 5d is covered with the thin film part 7. Thus, when air flows into a wind tunnel measuring part 3, the thin film part 7 suppresses the disturbance of flow of air near the vibration face 5d, and the thin film part 7 prevents air flowing in the wind tunnel measuring part 3 from directly striking the vibration face 5d. Consequently, noise such as hissing sound and wind noise and the like generated by air passing near the vibration faces 5d is suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a microphone covering structure in which a vibrating surface of a microphone is covered with a thin film portion, and a wind tunnel for measuring the behavior of the test object generated by the flow of the gas when the gas flows through the test object in the wind tunnel. It relates to a test apparatus.

  A conventional wind tunnel test apparatus includes a wind tunnel measuring unit for installing a test object, an air outlet for blowing air into the wind tunnel measuring unit, a suction port for sucking air from the wind tunnel measuring unit, and a test object disposed in the wind tunnel measuring unit. A microphone for measuring noise generated from an object is provided (see, for example, Patent Document 1). This conventional wind tunnel test apparatus is an open-drum type wind tunnel test apparatus in which the wind tunnel measuring section between the air outlet and the suction opening is opened, and this test object is applied when an air flow is applied to the test object. Noise such as aerodynamic sound generated from objects is measured with a microphone. In such a conventional wind tunnel test apparatus, the microphone is disposed at a position away from the air flow so that the air flow does not directly hit the microphone.

Special Table 2000-507360

  On the other hand, in the conventional wind tunnel testing apparatus, there is a sealed-tunnel type wind tunnel testing apparatus in which a wind tunnel measuring unit is surrounded by a trunk and a flow path forms a closed circuit. In such a closed-pipe type wind tunnel test apparatus, if a microphone is arranged in the wind tunnel measurement section like the open-pipe type wind tunnel test apparatus, accurate measurement becomes difficult because the air flow directly hits the microphone. For this reason, in a closed-body type wind tunnel testing device, a recess is formed in the fixed wall of the wind tunnel measuring unit, and the microphone is installed in this recess so that the tip surface of the microphone and the wall surface of the fixed wall are substantially flush with each other. doing. For example, the microphone may be installed so that the front end surface of the protective cap portion that protects the vibration surface of the microphone is substantially flush with the wall surface of the fixed wall portion, or the front end surface of the urethane covering portion that covers this protective cap may be A microphone is installed so as to be substantially flush with the wall surface of the fixed wall portion.

  In the conventional closed-core type wind tunnel testing device, since many through-grooves are formed on the front end surface of the protective cap portion, the front end surface of the protective cap portion has an uneven portion, and the surface of the urethane covering portion is also present. There are minute uneven parts. For this reason, when the air flow hits these uneven portions, the air flow is disturbed, and the air flow directly hits the vibration surface of the microphone through the through groove of the protective cap portion. Noise components due to wind noise and the like increase. As a result, there is a problem that aerodynamic sound generated from the test object cannot be measured with a microphone with high accuracy.

  An object of the present invention is to provide a microphone covering structure and a wind tunnel test apparatus capable of reducing wind noise and the like and measuring aerodynamic sound generated from a test object with high accuracy.

The present invention solves the above-mentioned problems by the solving means described below.
In addition, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this embodiment.
The invention of claim 1 is a microphone covering structure in which the vibrating surface (5d) of the microphone (5) is covered with the thin film portion (7; 10), and the vibrating surface is formed from the wall surface of the fixed wall portion (3a). The microphone covering structure (6) is characterized in that the thin film portion is disposed substantially flush with the wall surface of the fixed wall portion.

  According to a second aspect of the present invention, there is provided the microphone covering structure according to the first aspect, wherein the thin film portion is fixed to a wall surface of the fixed wall portion.

  According to a third aspect of the present invention, in the microphone covering structure according to the first or second aspect, the thin film portion (7) is formed by laminating and bonding a plurality of thin films (8, 9). A microphone covering structure characterized by the above.

  According to a fourth aspect of the present invention, there is provided the microphone covering structure according to the first or second aspect, wherein the thin film portion (10) is formed of a single thin film (11). Structure.

  The invention of claim 5 is a wind tunnel test apparatus for measuring the behavior of the test object (1) generated by the flow of the gas when the gas flows through the test object in the wind tunnel measuring section (4). A wind tunnel test apparatus (2) comprising the covering structure (6) of the microphone (5) according to any one of claims 1 to 4.

  According to the present invention, wind noise and the like can be reduced and aerodynamic sound generated from the test object can be measured with high accuracy.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a plan view of a wind tunnel testing apparatus according to the first embodiment of the present invention. FIG. 2 is a plan view seen from the II direction of FIG. FIG. 3 is a cross-sectional view of the microphone covering structure in the wind tunnel testing apparatus according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view of the thin film portion of the microphone covering structure in the wind tunnel testing apparatus according to the first embodiment of the present invention.
A test object 1 shown in FIG. 1 is a model or a real test body (specimen). The test object 1 is, for example, a model simulating (reducing) an actual railway vehicle, a current collector (pantograph), or the like.

  The wind tunnel test apparatus 2 is an apparatus that measures the behavior of the test object 1 generated by the flow of air when the air flows through the test object 1 in the wind tunnel measuring unit 3. For example, the wind tunnel test apparatus 2 causes the air to flow through the test object 1 in the wind tunnel measuring unit 3, and this air flow causes the aerodynamic sound generated from the test object 1 and / or the flow of the air. The pressure received by the test object 1 is measured. A wind tunnel test apparatus 2 shown in FIG. 1 is a hermetic trunk type wind tunnel test apparatus including a wind tunnel measuring unit 3, a wind tunnel 4, a microphone 5, a covering structure 6, and the like.

  The wind tunnel measuring part 3 is a part where the test object 1 is installed, and includes a fixed wall part 3a and a microphone housing part 3b as shown in FIGS. The fixed wall portion 3 a is a cylindrical portion surrounding the inside of the wind tunnel measuring unit 3. The microphone accommodating portion 3b is a concave portion that accommodates the microphone 5, and a plurality of microphone accommodating portions 3b are formed at intervals at positions retracted from the wall surface of the fixed wall portion 3a as shown in FIG.

  The wind tunnel 4 shown in FIG. 1 is a device that creates an artificial air flow to experimentally investigate various aerodynamic problems. The wind tunnel 4 includes a blower (not shown), a duct, a rectifying device, and the like that artificially blows wind with a certain property, and a nozzle portion 4a that blows air to create a uniform flow in the wind tunnel measurement unit 3. The nozzle part 4 a is connected to the wind tunnel measuring part 3.

  A microphone 5 shown in FIGS. 2 to 4 is a device that detects noise generated from the test object 1 when air is passed through the test object 1, and is an acoustoelectric converter that converts acoustic energy into electrical energy. Etc. As shown in FIG. 2, a plurality of microphones 5 are arranged at a predetermined interval, and each constitutes a two-dimensional microphone array. As shown in FIG. 3, the microphone 5 includes a diaphragm 5a, a vibration pickup section 5b, a main body section 5c, and the like. For example, the microphone 5 is accommodated in the microphone accommodating portion 3b in a state where the protective cap portion is removed from the tip portion and the vibration surface 5d is exposed.

  The diaphragm 5a is a part that converts sound waves into mechanical vibrations, and is formed of a polymer thin film or the like. The diaphragm 5a has a vibration surface (pressure receiving surface) 5d formed on the surface that receives sound from the sound source, and the vibration surface 5d is disposed at a position retracted from the wall surface of the fixed wall portion 3a. . The vibration pickup unit 5b is a mechanical / electrical converter that converts mechanical vibration of the diaphragm 5a into an electric signal, and is a piezoelectric element that outputs an electric signal corresponding to the magnitude of vibration. The main body 5c is a cylindrical case that accommodates the diaphragm 5a, the vibration pickup 5b, and the like, and a protective cap (not shown) that protects the diaphragm 5a can be detachably attached to the tip of the main body 5c. .

  The covering structure 6 is a structure in which the vibration surface 5 d of the microphone 5 is covered with the thin film portion 7. The covering structure 6 includes a flexible thin film portion (film portion) 7 as shown in FIGS. As shown in FIG. 4, the thin film portion 7 covers and protects the vibration surface 5d with a gap from the vibration surface 5d, and is disposed substantially on the same surface as the wall surface of the fixed wall portion 3a. In this embodiment, it is preferable to install the microphone 5 in the microphone housing portion 3b so that the gap between the thin film portion 7 and the vibration surface 5d is as small as possible. The thin film portion 7 is formed by superposing and bonding a plurality of thin films 8 and 9 and is fixed to the wall surface of the fixed wall portion 3a. As the thin film portion 7, it is preferable to select a material having a thickness and weight that can smooth the air flow and does not resonate due to the air flow. The thin films 8 and 9 have base materials 8a and 9a having smooth surfaces, and adhesive layers 8b and 9b formed by applying an adhesive to the back surfaces of the base materials 8a and 9a. This is an adhesive tape made of synthetic resin. The thin films 8 and 9 join the adhesive layer 8b and the adhesive layer 9b, and are fixed to the fixed wall 3a with the base material 8a side facing the vibration surface 5d and the base material 9a side facing the sound source side. ing. As shown in FIGS. 2 and 4, the thin film 9 is formed slightly longer and wider than the thin film 8, and the adhesive layer 9b of the thin film 9 is joined to the wall surface of the fixed wall 3a. The periphery of the thin film 8 is sandwiched and fixed between the wall surface of the fixed wall portion 3 a and the thin film 9.

Next, the operation of the wind tunnel testing apparatus according to the first embodiment of the present invention will be described.
As shown in FIG. 1, the test object 1 is installed in the wind tunnel measuring unit 3, and air is ejected from the nozzle part 4 a to flow the air through the test object 1. As a result, an aerodynamic sound is generated from the test object 1 when the air flow strikes the test object 1, and the aerodynamic sound is detected by the microphone 5 and measured.

Next, the operation of the microphone covering structure in the wind tunnel testing apparatus according to the first embodiment of the present invention will be described.
As shown in FIGS. 2 and 3, an adhesive layer 9b of the thin film 9 is attached to the wall surface of the fixed wall 3a so that the surface of the thin film portion 7 is substantially flush with the surface of the fixed wall 3a. Is covered by the thin film portion 7. For this reason, as shown in FIG. 1, when the air flows in the wind tunnel measuring unit 3, the thin film unit 7 prevents the air flow in the vicinity of the vibration surface 5 d from being disturbed and flows in the wind tunnel measuring unit 3. The thin film portion 7 prevents air from directly hitting the vibration surface 5d. As a result, noise such as wind noise and wind noise generated by the air passing near the vibration surface 5d is suppressed.

The wind tunnel test device and the microphone covering structure according to the first embodiment of the present invention have the following effects.
(1) In the first embodiment, the vibration surface 5d is disposed at a position retracted from the wall surface of the fixed wall portion 3a, and the thin film portion 7 is disposed substantially on the same wall surface as the fixed wall portion 3a. Yes. For this reason, the thin film portion 7 can prevent the air flow in the vicinity of the vibration surface 5d of the microphone 5 from being disturbed, and can also prevent the air flow from directly contacting the vibration surface 5d. As a result, generation of noise such as wind noise and wind noise generated near the vibration surface 5d can be suppressed, so that aerodynamic sound from the test object 1 to be originally measured can be accurately measured.

(2) In the first embodiment, the thin film portion 7 is fixed to the wall surface of the fixed wall portion 3a. As a result, since the wall surface of the fixed wall portion 3a and the surface of the thin film portion 7 are substantially the same surface, the air flow near the vibration surface 5d of the microphone 5 becomes smooth, and the air flow is disturbed near the vibration surface 5d. Can be prevented.

(3) In the first embodiment, the thin film portion 7 is formed by laminating and bonding a plurality of thin films 8 and 9. For this reason, the number of the thin films 8 and 9 is arbitrarily selected according to the velocity of the air flowing through the wind tunnel measuring section 3 and the size of the gap between the thin film section 7 and the vibration surface 5d, etc. The height, weight and rigidity can be easily adjusted.

(4) In the first embodiment, since the wind tunnel test apparatus 2 includes the covering structure 6, noise such as wind noise and wind noise near the vibration surface 5d of the microphone 5 is reduced, and aerodynamic force from the test object 1 is reduced. Sounds can be measured accurately.

(Second embodiment)
FIG. 5 is a plan view of a microphone covering structure in a wind tunnel testing apparatus according to the second embodiment of the present invention. FIG. 6 is a cross-sectional view of the microphone covering structure in the wind tunnel testing apparatus according to the second embodiment of the present invention. In the following, the same parts as those shown in FIGS. 1 to 4 are denoted by the same reference numerals and detailed description thereof is omitted.
The thin film portion 10 shown in FIGS. 5 and 6 includes a thin film 11 and an adhesive layer 12. The thin film 11 is a polypropylene film or the like similar to the thin film portion 7 shown in FIGS. 2 to 4, and the adhesive layer 12 covers the vibration surface 5 d of the microphone 5 as shown in FIGS. 5 and 6. It is affixed and fixed to the wall surface of the fixed wall part 3a. The adhesive layer 12 is applied to the wall surface of the fixed wall portion 3a so as to surround the microphone housing portion 3b. In the second embodiment, in addition to the effects of the first embodiment, since the thin film portion 10 is formed by one thin film 11, the thickness of the thin film portion 10 can be easily managed.

  Next, a microphone covering structure according to an embodiment of the present invention will be described. In order to verify the sound wave transmission characteristics by the thin film portion 7 shown in FIGS. 1 to 4 and the background noise reduction effect by the thin film portion 7, experiments on the characteristics of the thin film portion 7 were performed. First, two 50μm thick polypropylene films (transparent adhesive tape (product name: SCOTCH) manufactured by Sumitomo 3M Limited) with adhesive properties on one side are attached to each other as shown in FIGS. In addition, the vibrating surface 5d of the microphone 5 was covered and attached to the wall surface of the fixed wall portion 3a. The size of the rectangular area shown in FIG. 2 is 900 × 500 mm, and a film was attached so as to cover the microphone 5 in this area. The experiment was conducted using a closed-body type wind tunnel testing device in the Wind Tunnel Technology Center (Yonehara) of the Railway Technical Research Institute.

(Sound transmission characteristics)
FIG. 7 is a graph showing the test results of the sound wave transmission characteristics by the film in the microphone covering structure according to the embodiment of the present invention.
The vertical axis shown in FIG. 7 is the sound pressure level difference (dB) between when the film is applied and when the film is not applied, and the horizontal axis is the frequency (Hz). The sound transmission characteristic test was performed by generating a sound (white noise) having the same power in a certain frequency range from a speaker, which is a sound source for sound measurement, under no wind condition. The graph shown in FIG. 7 shows the difference between the sound pressure level measured by the microphone when the vibration surface is not covered with a film and the sound pressure level measured by the microphone when the vibration surface is covered with a film. This is an evaluation of the influence on the measurement result of the microphone by covering the vibration surface with a film. In general, when the vibration surface is covered with a film, it is desirable that the influence on the measurement result of the microphone be as small as possible, and even when the sound pressure level changes, it is preferable to change uniformly over a wide frequency band. As shown in FIG. 7, the effect of covering with the film is about 1.5 dB at the maximum, and it was confirmed that the influence on the measurement result of the microphone was very small.

(Dark noise reduction effect)
FIG. 8 is a graph showing measurement results of background noise by a film in the microphone covering structure according to the embodiment of the present invention.
The vertical axis shown in FIG. 8 is the sound pressure level (dB), and the horizontal axis is the frequency (Hz). The verification of the background noise reduction effect was performed by removing the test object 1 from the sealed cylinder and measuring the background noise in the sealed cylinder under a blowing condition of 50 m / s. Here, the background noise is a sound other than a specific sound when a plurality of sounds are present at the same time. For example, when considering aerodynamic sound in a sealed body, this aerodynamic sound is considered. The noise of the blower in the sealed body when there is no sound is called background noise against aerodynamic sound. As shown in Fig. 8, when the vibration surface is covered with a film (with film) compared to when the vibration surface is not covered with a film (without film), about 7 to 15 dB in the frequency range up to 5 kHz. Noise reduction effects such as wind noise and wind noise were confirmed.

  From the above, even if the vibration surface was covered with a film, the influence on the measurement result of the microphone was extremely small, and the effect of reducing wind noise and wind noise by the film was confirmed. When the number of films is small, there is a problem that is considered to be caused by resonance in a frequency range of 5 kHz or higher, and it is considered that the level of the sound pressure that is received increases by installing the film. This effect is reduced by increasing the number of films, but conversely, the performance in the high frequency band is lowered and it is considered difficult to pass sound waves. For this reason, it is necessary to pay sufficient attention to the relationship between the overall thickness of the stacked films and the performance. On the other hand, when a paper tape is used instead of the film, the sound is amplified at a specific frequency and the effect of reducing wind noise and the like is low.

(Other embodiments)
The present invention is not limited to the embodiment described above, and various modifications or changes can be made as described below, and these are also within the scope of the present invention.
(1) In this embodiment, the closed-tunnel type wind tunnel test apparatus 2 has been described as an example. However, the present invention can also be applied to an open-drum type wind tunnel test apparatus. For example, the fixed wall portion 3a may be disposed at a position away from the air flow of the open body, and the vibration surface 5d of the microphone 5 accommodated in the microphone accommodating portion 3b may be covered with the thin film portion 7. In this embodiment, the case where air is passed through the wind tunnel measuring unit 3 has been described as an example. However, the present invention can also be applied to the case where a gas other than air is passed through the wind tunnel measuring unit 3.

(2) In this embodiment, the case where the thin film portion 7 is fixed to the fixed wall portion 3a has been described as an example, but the present invention is not limited to this. For example, the covering structure of the microphone 5 including the thin film portion 7 that covers the vibration surface 5d can be configured by removing the protective cap portion from the tip without the fixed wall portion 3a and the like. In this case, not only when the microphone 5 is used in the open-tunnel type wind tunnel test apparatus, but also when the microphone is used outdoors, it is possible to prevent the air flow from directly hitting the vibration surface. . In this embodiment, the case where the adhesive tape having the adhesive layers 8b and 9b on one side of the base material 8a and 9a is bonded to the wall surface of the fixed wall 3a has been described as an example. A material may be applied and bonded to the wall surface of the fixed wall portion 3a.

1 is a plan view of a wind tunnel testing apparatus according to a first embodiment of the present invention. It is the top view seen from the II direction of FIG. It is sectional drawing of the covering structure of the microphone in the wind tunnel testing apparatus concerning 1st Embodiment of this invention. It is sectional drawing of the thin film part of the coating structure of the microphone in the wind tunnel testing apparatus concerning 1st Embodiment of this invention. It is a top view of the covering structure of the microphone in the wind tunnel testing apparatus concerning 2nd Embodiment of this invention. It is sectional drawing of the covering structure of the microphone in the wind tunnel testing apparatus concerning 2nd Embodiment of this invention. It is a graph which shows the test result of the sound wave transmission characteristic by the film in the covering structure of the microphone which concerns on the Example of this invention. It is a graph which shows the measurement result of the background noise by the film in the covering structure of the microphone which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test object 2 Wind tunnel test apparatus 3 Wind tunnel measuring part 3a Fixed wall part 3b Microphone accommodating part 4 Wind tunnel 5 Microphone 5a Diaphragm 5d Vibration surface 6 Covering structure 7 Thin film part 8, 9 Thin film 8a, 9a Base material 8b, 9b Adhesive material Layer 10 Thin film part 11 Thin film 12 Adhesive layer

Claims (5)

A microphone covering structure in which the vibration surface of the microphone is covered with a thin film portion,
The vibration surface is disposed at a position retracted from the wall surface of the fixed wall portion,
The thin film portion is disposed on substantially the same plane as the wall surface of the fixed wall portion;
A microphone covering structure characterized by The microphone covering structure according to claim 1,
The thin film portion is fixed to a wall surface of the fixed wall portion;
A microphone covering structure characterized by In the microphone covering structure according to claim 1 or 2,
The thin film portion is formed by laminating and bonding a plurality of thin films,
A microphone covering structure characterized by In the microphone covering structure according to claim 1 or 2,
The thin film portion is formed of a single thin film;
A microphone covering structure characterized by A wind tunnel test apparatus for measuring the behavior of a test object generated by the flow of the gas when the gas is flowed to the test object in a wind tunnel measuring unit,
A microphone covering structure according to any one of claims 1 to 4,
Wind tunnel testing device characterized by

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