JP2002070799A - Apparatus for reducing rotation noise - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus which can reduce noises, in particular, a low frequency noise, generated when a rotary impeller of a blower and a screw or a propeller of a propulsion apparatus rotate. SOLUTION: The rotary apparatus for feeding fluid by rotating an impeller having several blades comprises a first sound reflecting plate arranged at an upstream side in the neighborhood of the outer periphery of the rotary impeller and a second sound reflecting plate arranged at a downstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reducing noise generated when a rotary impeller of a blower or a screw or a propeller of a propulsion device rotates, particularly a low frequency noise.

[0002]

2. Description of the Related Art Noise of ventilation blowers and air conditioner outdoor units, O
A device that forcibly sends out air for ventilation or waste heat, such as a low-frequency noise from a fan for cooling the A device, may have a problem with noise from a fan or a motor that sends out air. In general, these devices are often required to be small and light, and are housed in a limited space. It is often not easy to take countermeasures while satisfying various conditions such as The same applies to the case where it is desired to reduce the propeller sound in a screw or aircraft underwater.

[0003]

Various methods have been devised as a method for reducing the noise generated when the blower blows air, for example, by devising the shape of a blower fan. Difficulty and problems often remain. In general, in order to reduce low-frequency noise, it is necessary to increase the structure of the device for reducing noise and increase the thickness of the sound absorbing material. Therefore, effective measures are scarce because it is necessary to take measures without reducing the attractiveness of products such as miniaturization and weight reduction in order to reduce the blowing noise used in various consumer devices as described above. That is the current situation. Further, even in a screw of a ship or a propeller of an aircraft, if an attempt is made to reduce the noise without reducing the thrust, it is difficult to find any effective means.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an apparatus for exaggerating noise generated by a rotary impeller for moving fluid such as an air blower, a screw or a propeller rotating for obtaining thrust, or the like. It is an object of the present invention to provide a rotational noise reduction device that effectively reduces low-frequency noise, which is particularly difficult to reduce, without using a motor.

[0005]

SUMMARY OF THE INVENTION In a rotating device that moves a fluid flow by rotating an impeller composed of several impellers, a first sound wave reflecting plate is provided on an upstream side near an outer peripheral portion of the rotating impeller, and a first sound wave reflecting plate is provided on a downstream side. By providing a second sound wave reflecting plate on the side,
The vibration of the fluid on the upstream and downstream sides near the outer periphery of the rotary impeller, the vibration on the upstream side is sent to the downstream side, and the vibration on the downstream side is sent to the upstream side, thereby suppressing the vibration of the rotary impeller,
Reduce the noise generated by the rotating impeller.

[0006]

The air flow from the rotating impeller of the blower will now be considered with the fluid being air. When a moving object comes into contact with stationary air, a velocity gradient is generated between the flow layers of the airflow flowing near the surface of the object, and frictional noise is generated due to the viscous drag between the air flow layers and the pressure increase applied to the airflow by the blower. It is generally said that the frequency of the aerodynamic noise generated at this time is proportional to the flow velocity, and the loudness of the sound is proportional to the fourth to eighth power of the flow velocity.

When the impeller rotates, the peripheral speed increases as the distance from the center of the impeller toward the outer periphery increases. The noise output from the tip of the impeller when the impeller is rotating is larger than the magnitude of the noise output from the other part toward the center from the tip by the 4 to 8 power rule of the ratio of the distance from the center. Therefore, when noise reduction measures are taken into account, noise output from portions other than the outer peripheral portion of the impeller can be ignored and handled.

When a rotary impeller of a small axial flow blower is used as a surface sound source, the wavefront of a sound wave radiated from the surface sound source is the same as when a linear sound source is placed in a ring shape around the rotary impeller. Can be considered. It is considered that the wavefront of the sound wave emitted from the ring-shaped linear sound source spreads in a cylindrical shape, and the direction of the energy flow of the sound wave is distributed similarly to the spread of the wavefront.

[0009] Of the energy flow of the sound wave radiated from the rotating impeller of the blower, which spreads in a cylindrical shape, the upstream energy flow radiated outward from the outer periphery of the rotating impeller surface is:
The energy flow on the downstream side proceeds in the direction of the first sound wave reflecting plate provided along the outer periphery of the rotary impeller, and the energy flow on the downstream side proceeds in the direction of the second sound wave reflecting plate provided along the outer periphery of the rotating impeller. The reflection surface of each of the first and second sound wave reflectors is shaped like, for example, a spheroid or a paraboloid of revolution, and the first focal point of the first sound wave reflector is a ring at the outer periphery of the rotating impeller surface. The first focal point of the second sound wave reflecting plate is located at a position coincident with the downstream side of the ring-shaped linear sound source on the outer peripheral surface of the rotary impeller. The upstream energy flow radiated outward from the outer periphery of the rotating impeller surface is reflected by the first sound wave reflecting plate, and further reflected by the second sound wave reflecting plate.
The light is reflected by the sound wave reflection plate and travels in the direction of the downstream ring-shaped linear sound source on the outer peripheral portion of the rotating impeller surface. Similarly, the energy flow on the downstream side is reflected by the second sound wave reflecting plate, reflected by the first sound wave reflecting plate, and proceeds toward the upstream ring-shaped linear sound source on the outer periphery of the rotary impeller surface.

It is considered that the noise generated when the blower rotates depends on the speed gradient of the air flow and the pressure increase given to the air flow. The noise generated by the rotation of the impeller constituted by a plurality of blades is considered. , A portion having a higher pressure and a portion having a lower pressure than the surroundings are alternately generated near the upstream and downstream surfaces of the blade, which is considered to be the main mechanism of the noise source. When the vicinity of the upstream surface of any rotary impeller is a high pressure portion, the pressure near the downstream surface of the rotary impeller is low portion. The surface of the upstream side of the rotary impeller and the surface of the downstream side of the rotary impeller act on the first and second reflectors to act as pressure energy of the downstream and upstream sound waves, that is, interference with the opposite-phase sound waves. As a result, the rotating impeller at that position cannot maintain large acoustic vibrations that generate noise due to the rotational motion. In this effect, the lower the frequency, the longer the wavelength, the longer the time required for one cycle, and the pressure near the upstream and downstream surfaces of the rotary impeller affects the pressure near the downstream and upstream surfaces. Since the ratio of the error added in the process of sound wave propagation until the application is reduced, the interference effect in the inverse phase relationship appears remarkably. In this way, without using a large device, it is possible to effectively reduce the propagation energy as a wave of noise, particularly in a low frequency band,
This is to reduce the generation of rotational noise, but the same applies to the case where the fluid transmitting the sound is, for example, water.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An embodiment of a rotation noise reduction device according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing the configuration and operation of a rotation noise reduction device according to a first embodiment of the present invention. Example 1
This device was used as a ventilation fan. In FIG. 1, 1 is an impeller, 2 is a motor, 3 is an outer frame of the impeller 1, 4 is a reflector cover, 5 is an upstream end of the impeller 1,
6 is a first sound wave reflector, 7 is a first focus, 8 is a second focus, 15 is a downstream tip of the impeller 1, 16 is a second sound wave reflector, 17 is a first focus, and 18 is a first focus. This is the second focus. The impeller 1, the motor 2, and the outer frame 3 of the impeller 1 constitute a ventilation blower. The first sound wave reflecting plate 6 is a reflecting plate having a first focal point 7 and a second focal point 8 and is made of a member having a high sound reflectance, and the inner diameter of the outer frame 3 of the impeller 1 that covers the rotating impeller 1. A ring-shaped reflector having an inner diameter equal to
The sound wave reflecting plate is provided on the upstream side in the vicinity of the outer peripheral portion, and has a reflecting surface having a spheroidal shape. The first focal point 7 is set in accordance with the position of the upstream end 5 of the impeller 1. The second sound wave reflecting plate 16 has a first focal point 17 and a second focal point 18.
A ring-shaped reflector having an inner diameter equal to the inner diameter of the outer frame 3 of the impeller 1 which covers the rotary impeller 1 and which is made of a member having a high sound reflectivity and near the outer peripheral portion of the impeller 1 This is a sound wave reflection plate provided on the downstream side and having a reflection surface shape of a spheroid. The first focal point 17 is set in accordance with the position of the downstream end portion 15 of the impeller 1. The first sound wave reflector 6 and the second sound wave reflector 16 are housed in the reflector cover 4, and the second focal point 8 of the first sound wave reflector 6 and the second focal point 18 of the second sound wave reflector 16 are Set at the same position.

The operation will be described below with reference to the diagram shown in FIG. When the motor 2 is energized, the impeller 1 integrated with the motor 2 rotates, and the air around the impeller 1 flows from left to right in FIG. The noise of the impeller 1 is radiated from each part of the impeller 1 irrespective of the direction of the flow of the air flow sent out by the impeller 1. When the impeller 1 rotates, the peripheral speed increases as the distance from the center of the impeller 1 toward the tip increases. Considering that the magnitude of the noise output by the impeller 1 during rotation increases with the 4 to 8th power rule of the ratio of the distance from the center toward the tip of the impeller 1, the outer peripheral portion of the impeller 1 is considered. Noise output from other parts can be ignored and handled. Therefore, the wavefront of the sound wave of the noise output from the impeller 1 is the upstream end 5 and the downstream end 15 of the impeller 1.
Is radially diffused from each part as a ring-shaped line sound source.
A part of the energy flow of the sound that spreads radially around the ring-shaped line sound source part proceeds in the direction of the first sound wave reflection plate 6 and the second sound wave reflection plate 16 and is reflected by the respective sound flow. Most are collected at the second focus 8 and the second focus 18. The energy of the sound waves collected at the second focal point 8 and the second focal point 18 travels further straight due to the independence of the wave motion, and the second sound wave reflector 1
The light is reflected by the first acoustic wave reflecting plate 6 and the first sound wave reflecting plate 6, and collected at the downstream end portion 15 of the impeller 1 and the upstream end portion 5 of the impeller 1.

When a portion near the surface of the upstream end portion 5 of the arbitrary impeller 1 is a high pressure portion, the portion near the surface of the downstream tip portion 15 of the rotary impeller 1 is a low pressure portion. Therefore, the surface of the upstream end portion 5 of the rotary impeller 1 and the surface of the downstream end portion 15 of the rotary impeller 1 are located on the downstream side by the action of the first sound wave reflecting plate 6 and the second sound wave reflecting plate 16, respectively. And the interference of the sound pressure energy on the upstream side, that is, the sound wave of the opposite phase, causes no repetitive pressure change as the noise source, and the impeller 1 cannot maintain the vibration as the noise source. Becomes The effect of this action is that as the frequency becomes lower, the wavelength becomes longer and the time required for one cycle becomes longer, and the pressure near the surface of the upstream end portion 5 and the downstream end portion 15 of the rotary impeller 1 is reduced by the downstream end portion 15 and Since the ratio of the error added in the process of sound wave propagation until the pressure near the surface of the upstream end portion 5 is affected is reduced, the interference effect in the inverse phase relationship appears remarkably, and the generation of rotational noise is generated. Is effectively reduced.

Embodiment 2 Embodiment 2 of the rotation noise reduction device of the present invention will be described with reference to FIGS. 2 and 3 are views showing the configuration and operation of a rotation noise reduction device according to a second embodiment of the present invention.
In the second embodiment, the present device is used as a ventilation blower. 1 are denoted by the same reference numerals. 9
Denotes a ventilation blower mounting plate. In FIG. 2, the first sound wave reflecting plate 6 is a ring-shaped reflecting plate made of a member having a high sound reflectance and having an inner diameter equal to the inner diameter of the outer frame 3 of the impeller 1 that covers the rotating impeller 1. It is a sound wave reflection plate provided on the upstream side near the outer peripheral portion of the impeller 1 and having a reflection surface shape as a paraboloid of revolution. The first focal point 7 is set in accordance with the position of the upstream end 5 of the impeller 1. Second sound wave reflecting plate 16
Is a ring-shaped reflector having an inner diameter equal to the inner diameter of the outer frame 3 of the impeller 1 that covers the rotary impeller 1 and is provided on the downstream side near the outer peripheral portion of the impeller 1. And a sound wave reflecting plate having a reflecting surface in the form of a paraboloid of revolution. The first focal point 17 is set in accordance with the position of the downstream end portion 15 of the impeller 1. The first sound wave reflecting plate 6 and the second sound wave reflecting plate 16 are accommodated in the reflecting plate cover 4, and the first sound wave reflecting plate 6 and the second sound wave reflecting plate 16 are set at positions facing each other, and the blade The sound wave radiated from the upstream end portion 5 of the vehicle 1 is reflected by the first sound wave reflecting plate 6 and the second sound wave reflecting plate 16 and proceeds to the position of the downstream end portion 15 of the impeller 1. ing.

The operation will be described with reference to the diagram shown in FIG. In the second embodiment shown in FIG. 2, the ring-shaped reflecting surfaces of the first sound wave reflecting plate 6 and the second sound wave reflecting plate 16 of the first embodiment shown in FIG. It is a shape that is formed. The wavefront of the sound wave of the noise output from the impeller 1 spreads radially using the upstream end 5 and the downstream end 15 of the impeller 1 as a ring-shaped linear sound source, and a part of the energy flow of the sound is Most of the energy flow proceeds in the direction of the first sound wave reflecting plate 6 and the second sound wave reflecting plate 16 and is reflected by the second sound wave reflecting plate 16, respectively.
The light is reflected again by the sound wave reflecting plate 16 and the first sound wave reflecting plate 6 and collected at the downstream end portion 15 of the impeller 1 and the upstream end portion 5 of the impeller 1. In the following, near the surface of the upstream end portion 5 and the surface of the downstream end portion 15 of the rotary impeller 1, the sound pressure energy of the noise undergoes an interference action in an antiphase relationship, and the impeller 1 is a source of noise. The operation of each unit until the repeated pressure change as described above cannot be obtained and the vibration as the noise source cannot be maintained is the same as that of the first embodiment. FIG. 2 shows a shape in which the ring-shaped reflecting surfaces of the first sound wave reflecting plate 6 and the second sound wave reflecting plate 16 are paraboloids of revolution, while FIG. This is a ring-shaped reflecting plate, and the operation of each part is almost the same as in the case of FIG. Note that the ventilation blower mounting plate 9 is a member having a small sound transmission loss, and has a negligible acoustic effect.

[0016]

According to the present invention, since the structure is simple and the size of the device is not so large, the effect of reducing the sound particularly at a low frequency can be obtained, so that the cooling fan for waste heat of general OA equipment can be obtained. It is extremely practical because it can be easily disassembled and washed with water even if it is used as a ventilation fan for kitchens as well as noise reduction measures. One of the major features is that there is almost no pressure loss, and since it does not reduce the thrust even when used for the screw of a ship or the propeller of an aircraft, it is also effective as a measure to reduce the noise of ships and aircraft. It becomes something.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the configuration and operation of a first embodiment.

FIG. 2 is a diagram illustrating a configuration and an operation of the first embodiment.

FIG. 3 is a diagram illustrating the configuration and operation of a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, impeller 2, motor 3, outer frame of impeller 4 reflector cover 5 upstream end of impeller 6 first sound wave reflector 7, 17 first focus 8, 18 second focus 9, ventilation Blower mounting plate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G10K 11/16 G10K 11/16 B

Claims (1)

[Claims] 1. A rotating device for moving a fluid by rotating an impeller consisting of several impellers, wherein a first sound wave reflecting plate is provided on the upstream side near the outer periphery of the rotating impeller, and a second sound wave is provided on the downstream side. A rotating noise reduction device comprising a reflection plate.