JPH056128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a wind tunnel apparatus having a circulation type pipe line with an open space, and the open space serving as a measurement section.

[Prior Art] As is well known, wind tunnel apparatuses for conducting experiments on aerodynamics, thermal forces, noise characteristics, etc. of air passage systems are known.
However, of course, noise is generated when the airflow is blown out of the nozzle into the open space.

Conventionally, this type of airflow noise is mainly caused by jet noise.
s or more) For airflow nozzles, the cross section of the nozzle is made into a chrysanthemum shape, or a double nozzle is used with two coaxial
The jet noise was reduced by creating a heavy jet flow.

However, nozzles for low-speed airflow (wind speed of about 50 m/s or less) generate very little jet noise, and it is said that using a straight duct or nozzle is the method to minimize noise. Therefore, it has been generally accepted that it is difficult to reduce the airflow noise generated from the low-velocity nozzle jet compared to the current situation.

Further, it is desired that the open space minimizes airflow interference and makes it convenient to measure acoustics such as noise, but due to space considerations, the open space cannot be made wide enough to prevent airflow interference.

Patent No. 156476 discloses a technique for adjusting the static pressure gradient in a wind tunnel. However, in the nozzle of such known technology, in order to adjust the static pressure gradient, the opening angle of the adjustment piece must be 15 degrees or less to achieve the purpose, and this technology cannot be applied to reduce noise.

[Problems to be Solved] Accordingly, an object of the present invention is to provide a wind tunnel device that has less interference with airflow and can reduce noise generated by airflow.

[Principle of the Invention] As a result of various experimental studies, the present inventor has found that the noise generated when a low-velocity airflow is blown out from a straight nozzle can be divided into the noise generated by the jet itself and the noise emitted from the vortex from the end of the nozzle. We discovered that most of these noises are vortex shedding noises, and that by reducing this vortex shedding noise, we can reduce airflow generated noise. Here, the vortex shedding sound is the sound generated from the nozzle end due to the discontinuity of the flow velocity distribution inside and outside the nozzle at the nozzle end.

[Means for Solving the Problems] According to the present invention, in a wind tunnel apparatus having a recirculation type conduit with an open space, and the open space serving as a measurement section, a nozzle is provided at one end of the conduit. a bell mouth is provided at the opposite end thereof, and a blower is provided in the conduit, a straight part is provided at the end of the nozzle, and a bell mouth is provided at the opposite end of the nozzle. A tapered flange portion is formed, and the angle at which the flange opens outward is 30° to 60°.

[Description of Effects] Therefore, when the blower in the conduit is driven, air is sucked into the bell mouth from the open space, passes through the conduit, and is discharged from the nozzle into the open space. In this way, the amount of air taken in and the amount of air released in the open space are approximately equal, so there is no interference and the space is compact.

When air flows from the straight section to the flange section, separation of the airflow occurs at the corners of the flange, making it possible to randomize the size and emission period of the vortex emitted from the end of the nozzle section. , the amount of vortex shedding sound generated can be reduced to reduce airflow generated noise. If the opening angle of the taper is in the range of 30° to 60° with respect to the blowing direction,
Airflow generated noise can be most effectively reduced.

In addition, in the present invention, only a flange portion that opens outward is provided at the end of the nozzle.
Applying the present invention to a nozzle does not cause any obstruction to the airflow blown out from the nozzle, and does not become a factor that deteriorates the aerodynamic performance of the wind tunnel device.

Experiments have shown that when the angle of the flange is 30 degrees or less, the noise is louder than a straight nozzle without a flange. This is because the generation of vortex shedding noise becomes large. Also, at angles above 60°, almost the same noise as a straight nozzle is generated. This is because the flange does not play that role. Therefore, the opening angle of the flange portion must be between 30° and 60°.

[Examples] Examples of the present invention will be described below with reference to the drawings.

The semi-open type wind tunnel apparatus shown in FIG. and a bell mouth 5 are provided facing each other. The airflow (indicated by arrows in FIG. 1) from the axial blower 2 is guided by the first corner vane 3a and the second corner vane 3b and blows out from the nozzle 10. The airflow enters from the bell mouth 5, is guided by the third corner vane 3c and the fourth corner vane 3d, and is refluxed. In the figure, reference numeral 6 is a traverse device, 7 is an air supply/exhaust device, and 8 is a breather hole, but since these are not directly related to the gist of the present invention, detailed explanations will be omitted.

In FIGS. 2 and 3, the nozzle 10 consists of a straight section 11 having a rectangular cross section (horizontally long rectangle) and a flange section 12 attached to the end of the straight section 11.

In FIG. 3, if α is the opening angle of the flange portion 12 with respect to the air blowing direction indicated by the arrow in the figure, then α=30° to 60° in the illustrated embodiment, and the length of the flange surface 12 is The length C is C≧0.2D, where D is the inner diameter dimension of the straight part (length in the vertical direction in the case of a rectangular cross section).

In this embodiment, the size and emission period of the vortices emitted from the straight portion 11 are different from those of the flange portion 11.
It is randomized by providing 2. As a result, the amount of vortex shedding noise is reduced, and airflow shedding noise is effectively reduced.

Figure 4 shows D=300mm, C=75mm, wind speed 36m/sec
This shows the 1/3 octave band spectrum and A-weighted noise level of the noise generated in
When the opening angle α is 15°, 30°, 60°, and 90°,
This shows the results of a comparative experiment with a straight nozzle without a flange. As can be seen from Fig. 4, when α = 15°, the sound pressure level is higher than that of the straight nozzle in the low frequency range.
It can be seen that when α=90°, the characteristics are almost the same as those of the straight nozzle, and when α is set in the range of 30° to 60°, the effect of reducing the sound pressure level is greatest.

Figure 5 shows the 1/3 octave band spectrum and A-weighted noise level of the generated noise, and shows the nozzle diameter D = 300 mm, opening angle α = 45°, and wind speed of 36 m/s. Figure 3)
When the length C is 0.1D or 0.2D or more,
The results of a comparative experiment with a straight nozzle are shown.
As can be seen from Fig. 5, in the case of C=0.1D, the sound pressure level is higher in the low frequency range than in the case of the straight nozzle, and the flange portion 12
It can be seen that the sound pressure level reduction effect is greatest when the length C=0.2D or more.

FIG. 6 shows another embodiment of the nozzle, nozzle 1
At the end of the straight part 11a with a circular cross section of 0a
An example is shown in which a flange portion 12a opened at 30° to 60° is provided. The embodiment shown in FIG. 6 also has the same effect as the embodiment shown in FIG. 2, and airflow generated noise is reduced.

[Effects of the Invention] As described above, the present invention provides the following excellent effects.

(1) The vortex of the airflow flowing from the straight part to the nozzle part separates from the flange corner, and as a result, the size and emission period of the vortex can be randomized.

(2) Therefore, the amount of vortex shedding sound that makes up most of the noise can be reduced.

(3) No airflow interference in open space.

(4) It is sufficient to provide a flange section that opens outward at a predetermined angle, and the vortices in the airflow will be separated from the flange section, and the flange section will not impede the blowing airflow, reducing aerodynamic characteristics. do not.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a wind tunnel device implementing the present invention,
FIG. 2 is a perspective view showing a nozzle implemented in the present invention, FIG. 3 is a side sectional view of FIG. 2, and FIGS. 4 and 5 are a 1/3 octave band spectrum and a FIG. 6 is a perspective view of another nozzle implemented in the present invention. 1... Wind tunnel main body, 2... Axial blower, 4... Measurement section, 10, 10a... Wind tunnel nozzle, 11, 1
1a... Straight part, 12, 12a... Flange part, α... Opening angle.

Claims (1)

[Claims] 1. In a wind tunnel device that has a circulation type pipe with an open space, and the open space serves as a measurement section,
A nozzle is provided at one end of the pipe, a bell mouth is provided at the opposite end thereof, a blower is provided in the pipe, and a straight part is provided at the end of the nozzle, and a bell mouth is provided at the opposite end of the pipe. A tapered flange portion that is connected and opens outward is formed, and the angle at which the flange opens outward is 30°.
A wind tunnel device characterized by an angle between 60° and 60°.