JPH0581852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a wind tunnel nozzle that is used in a wind tunnel device that allows airflow to pass through a measuring section and is capable of reducing noise when airflow is generated.

[Prior Art] In open or semi-open wind tunnels that have a measuring section in the open space between the nozzle and the bell mouth, or in wind tunnels that blow air directly into the open space, it is difficult to reduce the noise generated in the measuring section. The main components are vortex shedding noise and jet noise from the nozzle.

FIG. 9 shows the state of a jet stream ejected from a nozzle used in such a wind tunnel. The jet flow ejected from the nozzle 1 includes a main stream (core flow) indicated by 2 and a shear flow indicated by 3.

This shear flow 3 is generated from a vortex emitted from the nozzle tip 4 (not shown in FIG. 9), instability of momentum due to the speed difference between the main flow 2 and the stationary fluid existing around it, etc. It is something to do. Since the local flow velocity and pressure fluctuate greatly inside the shear flow 3, the shear flow 3 generates jet noise (indicated by reference numeral 5) around it. Further, since vortices caused by the boundary layer on the inner surface of the nozzle 1 are emitted from the nozzle tip 4, sound (indicated by reference numeral 6) based on the vortex emission is emitted around the nozzle, causing noise.

Note that a secondary noise source is noise due to turbulence, which is radiated from the turbulent area downstream of the jet.

Here, if the jet noise from the wind tunnel nozzle can be prevented, especially the noise indicated by reference numerals 5 and 6 in FIG. 9, the jet noise will be significantly reduced.

[Problems to be Solved by the Invention] However, conventional techniques have not provided effective noise prevention technology.

For example, it is well known to those skilled in the art that jet noise can be reduced by forming a coaxial double airflow using a dual nozzle, but this requires complicated equipment and piping systems to provide a secondary jet. There is a problem.

It has also been proposed to add a special adapter to the tip of the nozzle 1 to prevent jet noise, but there is a problem in that the adapter itself generates high-frequency component airflow noise (wind noise). Ta.

Furthermore, in the case of high-speed jets, the vortex shedding noise from the nozzle tip is smaller and less noticeable than the jet noise, so research on prevention technology for this vortex shedding noise has not been conducted as compared to technology for jet noise. Therefore, the more research is done into techniques to reduce jet noise, the more the vortex shedding sound from the nozzle tip will be highlighted as a noise source.

The present invention was proposed in view of the various problems of the prior art described above, and an object of the present invention is to provide a wind tunnel nozzle that can effectively reduce the noise generated by the jet from the nozzle.

[Means for Solving the Problems] As a result of various studies and considerations, the inventor discovered the following.

The magnitude of the jet noise depends on the strength of the shear flow (rate of change in flow velocity) around the jet, and the strength of this shear flow is influenced by the boundary layer on the inner surface of the nozzle. In this boundary layer, compared to the turbulent boundary layer, the laminar boundary layer has the property that it is easier to create a shear flow that is simultaneous in the circumferential direction, and the turbulent boundary layer also has the property of creating simultaneous shear flow in the circumferential direction. It has the property of being easier to perform than

Therefore, by making the boundary layer on the inner surface of the nozzle a turbulent boundary layer and making the thickness of the circumferential boundary layer non-uniform, it is possible to improve the circumferential direction (of each hydrodynamic factor) within the boundary layer. It is possible to weaken the strength of the shear flow and reduce the jet noise and vortex shedding noise caused by the shear flow by weakening the simultaneity of the flow or increasing the thickness of the boundary layer (within a range that does not significantly affect the mainstream). becomes.

If a means for controlling the boundary layer is attached to the inner surface of the rear half (downstream half) of the nozzle where the airflow flows at high speed, the means itself will generate wind noise (separation flow noise) and generate new noise. It is also necessary to keep in mind that it may become a source of noise.

The wind tunnel nozzle of the present invention is a wind tunnel nozzle used in a wind tunnel apparatus that allows airflow to pass through to a measurement section, and is provided with a boundary layer control mechanism on the inner wall surface of a wind tunnel duct upstream of the nozzle.

In carrying out the present invention, the wind tunnel device may be of a type in which the measurement section is located in an open space or a type in which the measurement section is located in a semi-open space. Further, the present invention can be practiced in either a circulating type wind tunnel or a blowing type wind tunnel. Furthermore, the cross section of the nozzle outlet may be circular or polygonal.

Here, it is preferable to use a vortex generator type mechanism as the boundary layer control mechanism. It is also preferable to control the boundary layer by partially increasing the surface roughness of the inner surface of the nozzle. Furthermore, it is also preferable to configure the boundary layer to be controlled by a secondary air flow injection method.

In addition to this, when carrying out the present invention, it is necessary to create turbulence in the flow near the inner wall surface of the duct in the rectifier section upstream of the nozzle (contraction channel), or to make the flow velocity slower than the main flow. It is preferable to configure.

[Function] According to the wind tunnel nozzle of the present invention having the above-described configuration, the boundary layer on the inner surface of the nozzle becomes a turbulent boundary layer by the boundary layer control mechanism provided on the inner wall surface of the wind tunnel duct on the upstream side of the nozzle. . Make the boundary layer thickness non-uniform in the circumferential direction. Or the boundary layer is the mainstream (core flow)
The thickness can be increased within a range that does not have a large effect on the thickness. This weakens the circumferential simultaneity of each hydrodynamic factor in the boundary layer, weakens the strength of shear flow, and makes it possible to reduce jet noise and vortex shedding noise caused by shear flow. Become. Therefore, it is possible to effectively reduce the airflow noise generated from around the nozzle outlet, which has been difficult to reduce in the past.

In addition, in the present invention, the boundary layer control mechanism is provided on the inner wall surface of the wind tunnel duct upstream of the nozzle, and since the airflow velocity is relatively low in the wind tunnel duct upstream of the nozzle, the boundary layer control mechanism itself is Wind noise (separated flow noise) will not be generated and become a new noise source.

Furthermore, since the boundary layer control mechanism is provided on the inner wall surface of the wind tunnel duct upstream of the nozzle, the dimensions of the wind tunnel itself may be approximately the same as those of the conventional one. Further, since the configuration is relatively simple, the configuration does not become excessively complicated as would be the case if a double nozzle structure was used or a special adapter was added to the nozzle tip.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 8. In addition, in FIG. 1 to FIG. 8, the same members are given the same reference numerals and repeated explanations will be omitted.

1 to 4 show a first embodiment of the present invention, in which a wind tunnel apparatus, generally designated by the reference numeral 10, includes a wind tunnel nozzle 12 and a wind tunnel duct 14 upstream thereof. A plurality of boundary layer control mechanisms 18 in the form of vortex generators are arranged on the inner wall surface 16 of the wind tunnel duct 14. Specific examples of this vortex generator type boundary layer control mechanism 18 are shown in FIGS. 2-4.

A boundary layer control mechanism 20 in the form of a vortex generator shown in FIG.
and are rectangular. Further, the boundary layer control mechanism 26 shown in FIG. 3 has a circular base portion 28 and a cylindrical vertical portion 30. In the boundary layer control mechanism 32 shown in FIG. 4, the base portion 34 is rectangular, but the vertical portion 36 is triangular.

According to the first embodiment shown in FIGS. 1 to 4, a boundary layer control mechanism 18 (20, 26, 3
2), the boundary layer inside the wind tunnel duct 14 becomes a turbulent boundary layer, and the thickness of the boundary layer in the circumferential direction becomes non-uniform, or the main flow (arrow M in Fig. 1) is significantly affected. The boundary layer becomes thicker to the extent that it does not. As a result, the circumferential simultaneity of each hydrodynamic factor in the boundary layer on the inner periphery of the nozzle 14 is weakened, and the jet noise based on the shear flow (the sound whose propagation is indicated by reference numeral 5 in FIG. 1) is weakened.
and vortex shedding noise (the sound whose propagation is indicated by number 6 in Figure 1)
is reduced.

FIG. 5 shows a second embodiment of the invention. In this embodiment, a sheet-like material 40 is attached to the inner wall surface 16 of the wind tunnel duct 14. Although it is not so clear in FIG. 5, this sheet-like material 40 has a material with a large surface roughness. As the sheet-like material 40, metal steel, a punched metal plate, sand cloth, artificial turf, or a special resin film with a unidirectional surface treatment can be used.

Further, the sheet material 40 is nonuniformly bonded to the inner wall surface 16 of the wind tunnel duct 14 in the circumferential direction.

Note that instead of the sheet material 40, solid fine particles (not shown) are used on the inner wall surface 1 of the wind tunnel duct 14.
You can also spray it onto No. 6 and fix it.

The operation of this second embodiment is substantially the same as that of the first embodiment, so a description thereof will be omitted.

FIG. 6 shows a third embodiment of the invention. This embodiment is configured such that a secondary airflow 46 is ejected into the duct through an opening 44 formed in the inner wall surface 16 of the wind tunnel duct 14. This opening 44
is connected to a sound-absorbing air storage tank 50 via a pipe 48, and the sound-absorbing air storage tank 50 is connected to an air source (for secondary airflow), not shown.

Here, although the secondary airflow 46 ejected and injected into the wind tunnel duct 14 has low noise due to the sound-absorbing air storage tank 50 and the like, it is not necessary to make it a low-turbulence flow.

According to this third embodiment, by blowing out the secondary airflow 46, the inner circumferential surface 16 inside the wind tunnel duct 14
The boundary layer becomes a turbulent boundary tank, and the thickness of the boundary layer in the circumferential direction becomes non-uniform, or the boundary layer becomes thick. Other functions are substantially the same as those in the first and second embodiments. In addition, this sound-absorbing air storage tank 5
A control mechanism (such as a control valve) for regulating the flow rate of the secondary airflow may be installed near the airflow point 0.

7 and 8 show a fourth embodiment of the present invention. In this fourth embodiment, a turbulence generator 5 is installed in a rectifier section 52 (FIG.
4.

This turbulence generator 54 has the effect of controlling the flow of the boundary layer in the wind tunnel duct 14 so that it becomes a turbulent flow instead of a laminar flow, or has the effect of slowing down the flow velocity of the surrounding flow by becoming a low antibody. . As understood from FIG. 8, in this embodiment, the turbulence generators 54 are randomly arranged in the direction of the wind tunnel duct 14.

According to this embodiment, the boundary layer on the inner circumferential surface 16 in the wind tunnel duct 14 becomes thick or becomes a turbulent boundary layer, so the circumferential simultaneity of the boundary layer in the nozzle 12 is weakened and the shear flow is increased. This reduces the strength and reduces jet noise and vortex shedding noise caused by shear flow.

[Effect of the invention] The effects of the present invention are listed below.

(1) By weakening the circumferential simultaneity in the boundary layer of the flow inside the nozzle, the strength of the shear flow of the jet can be reduced, and jet noise and vortex shedding noise caused by the shear flow can be reduced.

(2) Airflow noise generated from around the nozzle outlet can be effectively reduced.

(3) The boundary layer control mechanism itself is prevented from generating wind noise (separated flow noise) and becoming a new noise source.

(4) The dimensions of the wind tunnel itself may be approximately the same as conventional ones.

(5) Since the configuration is relatively simple, the configuration does not become excessively complicated as would be the case if a dual nozzle structure was used or a special adapter was added to the nozzle tip.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional side view showing a first embodiment of the present invention, FIG. 2 is a perspective view showing an example of a vortex generator-type boundary layer control mechanism used in the first embodiment, and FIG. FIG. 4 is a perspective view showing another example of the boundary layer control mechanism, FIG. 5 is a perspective view showing still another example of the boundary layer control mechanism, and FIG. 5 is a perspective view showing another example of the boundary layer control mechanism.
A cross-sectional side view showing the embodiment, FIG. 6 is the third embodiment of the present invention.
FIG. 7 and FIG. 8 are a cross-sectional side view and cross-sectional view showing a fourth embodiment of the present invention, respectively, and FIG. 9 is a side view showing a conventional technique. 1, 12... Nozzle 2... Main stream 5, 6...
Noise (propagating waves) 14...Wind tunnel duct 16...
...Wind tunnel duct inner peripheral surface 18, 20, 26, 32...
... Vortex generator type boundary layer control mechanism 40 ... Sheet-like material 44 ... Opening on the inner peripheral surface of the wind tunnel duct 46 ... Secondary airflow 52 ... Rectifier section in the wind tunnel duct 54 ... Turbulence generator .

Claims (1)

[Claims] 1. A wind tunnel nozzle for use in a wind tunnel device that allows airflow to pass through a measurement section, characterized in that a boundary layer control mechanism is provided on the inner wall surface of a wind tunnel duct on the upstream side of the nozzle.