JPH1010000A - Circular flow water tank equipped body with low loss sound pressure attenuating structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the adverse effect of fluid noise exerted on the evaluation of acoustic measurement in a measuring part to the utmost by attenuating the fluid noise generated when water is forcibly circulated to the utmost by the low loss sound pressure attenuating structure body and provided between an impeller and the corner part just near on the downstream side of the impeller. SOLUTION: In a circular flow water tank forcibly circulating water in a water tank by an impeller to generate water streams in a definite direction within a measuring part and measuring the sound generated by the matter placed in the water streams of the measuring part, a low loss sound pressure sound attenuating structure body 2 having a large number of low loss sound pressure attenuating cylindrical holes 2a formed thereto composed of a lattice structure or a honeycomb structure is provided between the impeller in the communication pipeline 1d of the circular flow water tank 1 and the corner part just near on downstream side of the impeller and the inner surfaces of the low loss sound pressure attenuating cylindrical holes 2a of the structure body are covered with a sound absorbing material 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the measurement of sound caused by an object placed in a water flow of a measuring unit by forcibly circulating water in a water tank with an impeller to generate a water flow in a fixed direction in the measuring unit. In particular, a low-loss sound pressure attenuating structure provided between the impeller and a corner portion immediately downstream of the impeller, for the fluid noise generated when the water is forcibly circulated. The present invention relates to a circulating water tank provided with a low-loss sound pressure attenuating structure that attenuates as much as possible and minimizes the adverse effect of fluid noise on the sound measured by a measuring unit.

[0002]

2. Description of the Related Art Conventionally, water in a water tank is forcibly circulated using, for example, an impeller or the like to generate a water flow in a fixed direction in a measurement unit, and a sound caused by an object placed in the water flow of the measurement unit is measured. A circulating water tank used to perform the water circulation is known.

The circulating water tank has a structure in which water in the water tank is forcibly circulated to generate a water flow in a fixed direction in the measuring section. That is, the circulation water tank is provided with a communication pipe for circulation, for example, below the bottom of the measurement unit, and both ends of the communication pipe are bent upward and connected to both side surfaces of the measurement unit, and the communication pipe is connected to the communication pipe. For example, an impeller that forcibly circulates water is installed inside the pipeline.

In the circulating water tank, the impeller is driven to force water to flow into the measuring section from one side of the measuring section, and to flow out of water from the other side of the measuring section. The water is circulated and flown again into the measuring section to generate a water flow in a fixed direction in the measuring section.

[0005]

By the way, in an experiment in which a sound caused by an object placed in the water flow of the measuring unit is measured using a circulating water tank, noise is generated. There are the following causes. (1) Noise generated by axial flow pumps (impeller and stator) for generating water flow (2) Fluid noise generated by guide vanes (guide vanes) (3) Turbulent noise generated in water tank (including boundary layer noise) (4) Noise generated by mechanical vibrations of guide vanes, tank outer plates, etc. (5) Noise generated by drive motor and drive shaft system Among these, (1), (2) and (3) are fluid noise, and (4),
(5) is mechanical noise. The largest noise level in the fluid noise is the fluid noise generated by the impeller in (1).

The sound wave of the noise generated by the impeller (also in the case of the stator) reaches the measuring section while mainly reflecting each corner of the circulating water tank, and adversely affects the evaluation of acoustic measurement in the measuring section. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in order to solve the problems. It is an object of the present invention to reduce the fluid noise generated when water is forcibly circulated by an impeller and the impeller. Attenuate as much as possible with a low-loss sound pressure attenuation structure provided between the impeller and the corner immediately downstream of the impeller to minimize the adverse effects of fluid noise on the acoustic measurement evaluation at the measurement unit. It is an object of the present invention to provide a circulating water tank provided with a low-loss sound pressure attenuating structure that can be used.

[0008]

In order to achieve the above object, the present invention forcibly circulates water in a water tank with an impeller to generate a water flow in a fixed direction in a measuring section, and In the circulating water tank that measures the sound caused by the object placed in the water flow, between the impeller in the communication conduit of the circulating water tank and the corner immediately downstream of the impeller,
A low loss sound pressure attenuating structure having a large number of low loss sound pressure attenuating cylindrical holes formed of a lattice structure or a honeycomb structure is provided, and the inner surface of each low loss sound pressure attenuating cylindrical hole of the structure is covered with a sound absorbing material. It consists of the means which did.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically based on embodiments of the invention shown in the drawings. Here, FIG. 1 is a schematic overall sectional side view of a circulation water tank, FIG. 2 is a schematic cutaway perspective view of a low-loss sound pressure attenuation structure having a lattice structure, and FIG. 3 is a schematic view of a low-loss sound pressure attenuation structure having a honeycomb structure. FIGS. 4A to 4D are cutaway perspective views showing the relationship between the transmission loss of the low-loss sound-pressure-attenuating cylindrical hole.

In the figure, a circulating water tank provided with a low-loss sound pressure attenuating structure is a device for forcibly circulating water in the water tank to generate a water flow in a certain direction in the water tank. Circulating water tank 1 for circulating water to generate a water flow in a certain direction in the water tank, and a fluid provided between impeller 3 in communication pipe 1d in which impeller 3 is installed and corner portion 1f immediately downstream of the impeller. It comprises a low-loss sound pressure attenuating structure 2 for attenuating noise.

The circulating water tank 1 is, for example, a vertical type, that is, a circulating water tank that circulates up and down. On the upper side of the circulating water tank, an acoustic object caused by an object placed in a water flow with an experimental object floating or submerged. Is provided.

An inlet for water circulating into the measuring section 1a is opened on one side in the longitudinal direction of the measuring section 1a.
Further, a discharge port for discharging water flowing through the inside of the measuring section 1a is opened on a side opposite to the inflow port. The inflow pipe 1 is located outside both ends of the measuring section 1a where the inlet and outlet are formed.
b and a discharge line 1c are provided respectively.

The inflow conduit 1b and the discharge conduit 1c are formed with corner portions 1e, 1e, each of which has a distal end curved downward by about 90 degrees, and are curved downward. Are formed with corner portions 1e and 1f curved approximately 90 degrees inward in the horizontal direction, respectively, and are connected to the end of a communication pipe 1d provided below the measuring section 1a.

The circulating water tank 1 is provided with a circulation path of water for causing a flow in the measuring section 1a by the inflow pipe 1b, the discharge pipe 1c, the communication pipe 1d, and the corners 1e and 1f. Is configured.

The low-loss sound pressure attenuating structure 2 is a structure for reducing fluid noise generated by rotation of the impeller 3 and the like as much as possible. It is provided inside the communication pipe line 1d between them. The low-loss sound-pressure attenuating structure 2 has a large number of low-loss sound-pressure attenuating cylindrical holes 2a having a lattice structure (see FIG. 2) or a honeycomb structure (see FIG. 3) formed in the vertical and horizontal directions.

The low-loss sound pressure attenuating structure 2 is attached to the communication pipe 1d so as to have a certain length in a direction in which the inside is shut off, that is, in a direction orthogonal to the water flow direction. Further, each low-loss sound-pressure-attenuating cylindrical hole 2a having a lattice structure or a honeycomb structure of the low-loss sound-pressure attenuating structure 2 is formed so that the hole core direction is parallel to the water flow direction. It also plays a rectifying function.

Each of the low-loss sound pressure attenuating cylindrical holes 2a of the lattice structure or the honeycomb structure of the low-loss sound pressure attenuating structure 2 has:
The inner surface of the hole is covered with a sound absorbing material 2b for absorbing sound. In other words, the sound absorbing material 2b is made of the low-loss sound pressure attenuating cylindrical
Fluid noise generated by the impeller 3 and the like is attenuated and absorbed while passing through each low-loss sound pressure attenuating cylindrical hole 2a, so that the damping effect is further enhanced. It has become.

Representative dimensions (diameter or length of short side) of the lattice structure or the honeycomb structure of each low-loss sound pressure attenuating cylindrical hole 2a.
Is obtained as follows according to the frequency f of the target noise. f = c / D Here, c: propagation speed of the sound wave D: diameter or length of the short side The sound pressure attenuation in the low-loss sound pressure attenuation structure 2 is effective in the vicinity of the frequency f (FIG. C)).

The transmission loss (attenuation sound pressure) T _L in the frequency range equal to or lower than the frequency f is expressed by the following equation. T _L = K · B / (S · L) where K: a constant determined from the combination of the sound absorbing materials and the sound absorption coefficient. B: the perimeter length of the cross section of the portion where the sound absorbing material is attached. S: the low-loss sound pressure attenuating cylinder. In the case of the circulating water tank 1, the frequency obtained by multiplying the number of blades of the impeller 3 by the maximum rotation speed is the target frequency. The size of the low-loss sound-pressure-attenuating cylindrical hole 2a is determined as a target.

An impeller 3 for generating a water flow is mounted inside the communication pipe 1d of the circulating water tank 1. The rotation shaft of the impeller 3 extends outside the communication line 1d, and is interlocked with a motor 3a installed below the outside of the discharge line 1c. The impeller 3 is one of the major causes of fluid noise.

A guide vane 4 is provided at each corner 1e, 1f of the circulating water tank 1. Guide vane 4
Functions to smoothly change the flow direction of water at the corners 1e and 1f. The guide vanes 4 have been subjected to a sound absorbing process so that sound waves are not reflected.

Next, the operation based on the configuration of the embodiment of the present invention will be described below. Measuring part 1a of circulating water tank 1
The motor 3a is driven in order to generate a water flow. When the motor 3a is driven, the impeller 3 in the communication pipe 1d rotates to pump the water in the communication pipe 1d toward the inflow pipe 1b via the corner 1f. The water pumped from the communication pipe 1d to the inflow pipe 1b via the corner portion 1f flows through the inflow pipe 1b, and flows into the measuring section 1a from the inflow port on the downstream side of the inflow pipe 1b.

The water flowing into the measuring section 1a flows at a constant flow rate toward the discharge port on the opposite side. Therefore, the measuring unit 1
A water flow in a certain direction is generated in a. In the measurement unit 1a, acoustic measurement caused by an object placed in a water flow is performed in a state where the object for experiment is floating or submerged.

The water that has caused a constant flow in the measuring section 1a is discharged from the discharge port into the discharge line 1c, and is discharged from the discharge line 1c.
c, through the corner 1e, into the communication pipe 1d, where it is again circulated by the impeller 3 via the corner 1f to the inflow pipe 1b.

By the way, the sound wave of the noise generated during rotation of the impeller 3 for forcibly circulating the water in the circulating water tank 1 travels straight inside the communication pipe 1d toward the downstream side. A low-loss sound-pressure attenuating structure 2 is mounted inside a communication pipe 1d between the corner 1f and the corner 1f.

For this reason, the sound wave of the noise generated by the impeller 3 travels straight inside the communication pipe 1d toward the downstream side,
The low-loss sound pressure attenuating structure 2 enters the inside of each low-loss sound pressure attenuating cylindrical hole 2a having a lattice structure or a honeycomb structure.

The sound wave entering each low-loss sound-pressure-attenuating cylindrical hole 2a is absorbed by the sound-absorbing material 2b attached to the inner peripheral surface of the low-loss sound-pressure-attenuation structure 2, and formed into a predetermined size. The specific frequency generated in the impeller 3 is attenuated by the formed cylindrical hole.

It should be noted that the present invention is not limited to the above embodiment of the present invention, and it is needless to say that various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the case where the circulating water tank 1 is composed of a vertical type, that is, a circulating water tank that circulates vertically is described. However, the present invention is not limited to this, and the circulating water tank 1 circulates horizontally. A circulating water tank may be used.

[0029]

As is apparent from the above description, according to the circulating water tank provided with the low-loss sound pressure attenuating structure according to the present invention, the water in the water tank is forcibly circulated by the impeller, so that the water in the measuring section can be circulated. In the circulating water tank that generates a water flow in a certain direction and measures the sound caused by the object placed in the water flow of the measurement unit, between the impeller in the communication pipe of the circulating water tank and the corner immediately downstream of the impeller A low-loss sound-pressure-attenuating structure having a large number of low-loss sound-pressure-attenuating cylindrical holes formed of a lattice structure or a honeycomb structure, and the inner surface of each low-loss sound-pressure-attenuating cylindrical hole of the structure is provided with a sound absorbing material. By forming the coating, the fluid noise generated when the water is forcibly circulated is reduced by the low-loss sound-pressure-attenuating cylindrical member of the low-loss sound-pressure attenuating structure provided between the impeller and the corner immediately downstream of the impeller. As much as possible while passing through the hole By Attenuation can fluid noise is reduced as much as possible the adverse effect on the evaluation of the acoustic measurement in the measuring unit.

[Brief description of the drawings]

FIG. 1 is a schematic overall sectional side view of a circulating water tank showing an embodiment of the present invention.

FIG. 2 is a schematic cutaway perspective view of a low-loss sound pressure attenuation structure having a lattice structure according to the embodiment of the present invention.

FIG. 3 is a schematic cutaway perspective view of a low-loss sound pressure attenuation structure having a honeycomb structure according to an embodiment of the present invention.

FIGS. 4A to 4D are diagrams showing the relationship between transmission loss of a low-loss sound-pressure-attenuating cylindrical hole showing an embodiment of the present invention.

[Explanation of symbols]

 1 time water tank 1a measuring unit 1b inflow line 1c discharge line 1d communication line 1e corner part 1f corner part 2 low loss sound pressure attenuation structure 2a low loss sound pressure attenuation cylindrical hole 2b sound absorber 3 impeller 3a motor 4 guide Vane

Claims (1)

[Claims] 1. A circulating water tank for forcibly circulating water in a water tank with an impeller to generate a water flow in a fixed direction in the measurement unit and to measure a sound caused by an object placed in the water flow in the measurement unit. A low-loss sound-pressure attenuation structure having a large number of low-loss sound-pressure attenuation cylindrical holes formed of a lattice structure or a honeycomb structure between an impeller in a communication pipe of a circulation water tank and a corner portion immediately downstream of the impeller. A circulating water tank provided with a low-loss sound-pressure attenuation structure, wherein an inner surface of each low-loss sound-pressure attenuation cylindrical hole of the structure is covered with a sound-absorbing material.