JP3139587B2 - Airflow outlet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wind tunnel device for passing low-noise airflow to a measuring unit, a tunnel ventilation tower outlet for low-noise exhaust to an external space, and low-noise ventilation air to a large space. It is used for the air supply port that flows out and the air discharge port of a low-noise air conditioner that supplies air to the room, and can further reduce the noise (outflow airflow noise) generated when the airflow flows out into the space. The present invention relates to a low-noise airflow outlet that can be used.

[0002]

2. Description of the Related Art A low-noise wind tunnel in which noise generated by a blower or a compressor of an airflow source is reduced is a wind tunnel that can measure aerodynamic noise generated from a test object in an airflow of a measuring section together with aerodynamic characteristics of an object. Yes, it is a wind tunnel that will be increasingly used in the future.

[0003] In an open or semi-open type wind tunnel having a measuring section in an open space between an airflow outlet and a bell mouth portion, and a wind tunnel in which an airflow is directly blown into an open space,
The main components of the noise generated in the measuring unit are the vortex emission sound from the airflow outlet and the jet noise.

[0004] Similarly, a tunnel ventilation tower exhaust port for taking out exhaust gas from the inside of the tunnel to the outside space, an air supply port for ventilating air to the large space with low noise, or a low noise type air conditioner for supplying air to the room. Even at the air discharge port, even if the noise generated by the blower or the like is sufficiently reduced by the silencer, the main component of the noise generated at the place where the air current is blown out into the space is the vortex emission sound from the air flow outlet and the jet noise. .

FIG. 16 shows a state of a jet jet from an air flow outlet (hereinafter referred to as a nozzle) 11 used in a device such as a wind tunnel or a ventilation tower which blows out an air current with low noise. The jet 1 ejected from the nozzle 11 is composed of a main flow (core flow) region 2, a turbulent mixing region 3 generated downstream thereof, and a shear flow region 4 surrounding these regions.

The shear flow region 4 is based on a vortex (not shown in FIG. 10) discharged from the nozzle tip or the outlet 5 and a speed difference between the main flow region 2 and a stationary fluid existing around the main flow region 2. It is caused by unstable momentum and the like. Since the local flow velocity and the pressure fluctuate greatly in this area, the shear flow region 4 has jet noise (reference numeral 6)
). In addition, since a vortex caused by the boundary layer on the inner surface of the nozzle 11 is emitted from the nozzle tip 5, a sound (indicated by reference numeral 7) based on the vortex emission is radiated around the nozzle and causes noise. Other sources of the outflow airflow noise include noise generated from a turbulence region on the downstream side, and the outflow airflow noise (nozzle) from the airflow outlet (nozzle) includes the jet noise 6 and the vortex emission noise. 7 has a significant effect.

In the conventional low-noise wind tunnel, tunnel ventilation tower, large space ventilation device, or low-noise air conditioner, only the noise generated by the blower or compressor of the air flow source is reduced, and the air flow to the wind tunnel measurement unit or space is reduced. No effective reduction technology has been proposed for the outflow airflow noise from the nozzle generated at the air supply / exhaust port. Jet noise 6 and vortex shedding noise 7 from shear flow
If this can be prevented, it is possible to greatly reduce the outflow airflow noise at the airflow supply / exhaust port to the wind tunnel measurement section and the space.

[0008]

However, in the prior art, there is an effective nozzle outlet airflow for further reducing noise generated from a low noise wind tunnel, a tunnel ventilation tower, a large space ventilation system or a low noise type air conditioner. No noise reduction technology was provided.

For example, it is well known to those skilled in the art that the jet noise 6 can be reduced by forming a coaxial double jet using a double nozzle, but complicated devices and pipes for providing the sub jet are known. There is the problem that the system is essential.

It has also been proposed to add a special adapter for preventing jet noise at the tip of the nozzle 11, but the adapter itself generates high-frequency air current noise (wind noise). There was a problem.

Further, in the case of a high-speed jet, the vortex emission sound 7 from the nozzle tip is small and inconspicuous as compared with the jet noise 6, so that the technology for preventing the vortex emission sound 7 is compared with the technology for the jet noise 6. Has not been studied. Therefore, as the technology for reducing the jet noise 6 is researched, the vortex emission sound 7 from the nozzle tip will be brought up as a noise source in the future.

The present invention has been proposed in view of the above-mentioned various problems of the prior art, and has a low-noise wind tunnel capable of effectively reducing both jet noise and vortex emission noise generated from an outflow airflow from a nozzle. It is an object of the present invention to provide a low-noise airflow outlet used for a measuring unit, a low-noise air outlet of a tunnel ventilation tower, a low-noise air supply port of a large space ventilation device, or an air discharge port of a low-noise air conditioner.

[0013]

As a result of various studies and studies, the inventor has found the following.

The magnitude of the jet noise depends on the strength of the shear flow around the jet (the rate of change of the flow velocity), and the strength of the shear flow is affected by the state of the boundary layer on the inner surface of the nozzle. In this boundary layer, the laminar boundary layer has a property that it is easy to create a shear flow having a synchronicity in the circumferential direction as compared with the turbulent boundary layer, and the turbulent boundary layer also has a vortex discharge with the synchronism. There is a property that it is easier to perform.

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, the circumferential synchronism in the boundary layer is weakened, or By increasing the thickness of the boundary layer (to the extent that the main flow is not significantly affected), the strength of the shear flow can be reduced, and the jet noise 6 and the vortex emission noise 7 based on the shear flow can be reduced. In order to realize such a phenomenon, it is general to lengthen the length L of the straight duct 13 attached to the downstream side of the contraction duct 12 which is the main part of the nozzle 11 shown in FIG. FIG. 18 shows the result of experimentally confirming how noise generated around the nozzle changes when the length L of the straight duct 13 is changed. In this figure, the nozzle diameter is D, the horizontal axis is the ratio of the length L to the diameter D, and the vertical axis is the relative noise level where OdB (A) is the generated noise level when L = 0 without a straight duct. The nozzle outflow velocity is 80m / s and 4
The results for the two cases of 0 m / s are shown. As L increases from L = 0, the nozzle outflow airflow generation noise decreases, and becomes minimum when L = 1.5D-2.0D, and then increases again. The reason why the generated sound becomes larger as the length becomes longer than 2.0D is that the turbulent boundary layer on the inner surface of the nozzle becomes larger and stronger, and the noise generated by the boundary layer increases. The situation where the sound is reduced is the above-mentioned phenomenon. However, a nozzle whose straight duct after contraction is longer than 1.5D will increase the size of each device such as a low-noise wind tunnel, a tunnel ventilation tower, a large space ventilation system or a low-noise air conditioner more than necessary. Not practical.

[0016] While the length L of the general and practical nozzle straight duct remains at about 0.5D, the straight duct has a length of 1.5D.
It is an object of the present invention to propose a technique for reducing the nozzle outflow airflow generation sound as in the case of D to 2.0D.

Further, if means for controlling the boundary layer on the inner surface of the nozzle is directly attached to the inner surface of the nozzle, the means itself generates wind noise (separation flow noise) and becomes a new noise source. There is a proposal that a method of providing a boundary layer control mechanism on the inner surface of a contraction duct having a low flow velocity is good. (Japanese Patent Application No. 2-228107 by the present applicant). However, the present invention is apparently considered to be able to sufficiently solve the same problem as the problem to be solved by the present invention,
There are many unknown items that need to be elucidated at the stage of determining the boundary layer control method that will produce the expected effect in implementation, and this is considered to be a technology that will be slowed down to practical use.

Further, as a method of providing a boundary layer control mechanism on the inner surface (air flow contact surface) of the straight duct near the nozzle outlet in such a manner that the generation of wind noise is very small, the inner surface is partially irradiated with ultrasonic waves, Partially heat the inner surface, create a stripe-shaped portion with large surface roughness parallel to the flow direction on the inner surface, attach multiple thin wire-shaped protrusions on the inner surface parallel to the flow direction, There is a proposal that it is preferable to provide a plurality of slit-shaped grooves or notches parallel to the flow direction (Japanese Patent Application No. 3-178122 by the present applicant).
issue). These methods use the inner surface of the nozzle duct (airflow contact surface)
Although the above flow promotes the partial transition to the turbulent boundary layer, it does not lead to the effect of partially changing the thickness of the boundary layer, so that the vortex emission sound and the jet sound are greatly reduced. It is difficult to do. On the other hand, when the dimensions and the like of the boundary layer control mechanism are increased in order to greatly change the thickness of the boundary layer, there is a disadvantage in that wind noise generated from each member or its additional material increases accordingly.

[0019]

The principle of the present invention is that the boundary layer on the airflow contact surface (inner surface) of the direct duct near the airflow outlet is partially turbulent while the wind noise from the component itself is hardly generated. Significantly changes the circumferential distribution of the boundary layer thickness, weakens the circumferential synchrony of vortex shedding from the nozzle tip, and the velocity difference in the shear flow region of the nozzle outflow. Can be reduced. As a result, vortex shedding noise is reduced, and jet noise from the shear flow is reduced, making it possible to provide a quieter nozzle exit airflow. The above-described problems can be solved by implementing the configuration of the present invention described below. Particularly, even in a region where the airflow is high and the wind noise from the control mechanism itself is likely to be a problem, the configuration is such that the boundary layer on the inner surface of the nozzle is directly controlled so that the wind noise is hardly generated. This is one of the notable principles of the invention.

[0020]

According to the present invention, in order to reduce the noise generated when an airflow flows out into a space, an airflow outlet provided with a straight duct near the outlet of the nozzle has an airflow contact with the straight duct. A partial turbulent boundary layer transition promoting means (micro longitudinal vortex generating mechanism) is provided on the surface, and the turbulent boundary layer transition promoting means continuously changes (decreases) the area of the outlet toward the outlet end. Or the length of the straight duct is 0.3 to 0.8 with respect to the outlet diameter.

In practicing the present invention, the low-noise wind tunnel device may be of a type in which the measuring unit is in an open space or a device in a semi-open space. Further, the present invention can be implemented in a circulating wind tunnel or a blowing wind tunnel. In addition to this, the present invention can be applied to a low-noise air outlet of a tunnel ventilation tower, and a low-noise air supply port of a large space facility or an air flow outlet such as an air discharge port of a low-noise air conditioner. . Further, the cross section of the nozzle outlet may be circular or polygonal.

The partial turbulent boundary layer transition promoting mechanism provided on the direct duct airflow contact surface near the airflow outlet is such that the area of the outlet gradually changes (decreases or increases) continuously toward the outlet end. For example, a plurality of semi-conical projections, triangular pyramid projections, or polygonal pyramid projections are formed in parallel with the flow direction so as to have a maximum cross-sectional area at the tip end of the outlet. preferable. In addition, it is preferable to form a plurality of triangular notches or semi-arcuate notches having the maximum width at the outlet end portion in parallel with the flow direction.

[0023]

According to the low-noise airflow outlet of the present invention having the above-described structure, the means for promoting the transition to the partial turbulent boundary layer is provided with a direct duct airflow contact surface near the air outlet. (The inner surface of the straight duct), the boundary layer on the inner surface of the airflow outlet partially transitions to the turbulent boundary layer. The transition to the partial turbulent boundary layer makes the thickness of the boundary layer in the circumferential direction non-uniform, and the cross-sectional area of the component changes continuously and gradually. The generation of wind noise is sufficiently suppressed, and the non-uniformity of the thickness of the boundary layer can be further increased within a range that does not affect the main flow (core flow). This corresponds to forcing the average thickness of the boundary layer to be greater than usual in short straight ducts.

As a result, circumferential synchronism of the hydrodynamic factors in the boundary layer is weakened, the strength of the shear flow is also weakened, and the vortex emission sound and the jet flow caused by the boundary layer and the shear flow are reduced. Noise can be reduced. Therefore, the outflow airflow noise generated from the vicinity of the nozzle outlet, which has been difficult to reduce practically, can be effectively reduced.

In the present invention, since the boundary layer control mechanism provided on the inner surface of the straight duct itself has a structure that does not generate wind noise (separation flow noise), the boundary layer control mechanism in the straight duct portion through which the high-speed airflow passes is provided. Even with control, the control mechanism itself does not become a new noise source. Furthermore, since it is important that this control mechanism is provided partially in the straight duct, the shape of the entire nozzle is not significantly deformed and the size of the nozzle is not increased. The structure does not become complicated as in the case where the boundary layer control is performed on the side.

The airflow outlet of the present invention has a function and an effect obtained by each of the above-mentioned components, and can be compared with an outflow airflow noise generated from a standard airflow outlet which is not provided with a partial transition promoting mechanism of a turbulent boundary layer. The maximum is about 5 dB quieter. This noise reduction amount is about 3 dB higher than the noise reduction effect of the case described in the prior art (Japanese Patent Application No. 3-178122), thereby reducing the outflow airflow noise at the outlet.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the inner surface of the straight duct 13 near the outlet 5 of the nozzle 11 at a pitch interval of 0.06 L to 0.12 L from the semi-conical projection 0.06 L to the turbulent boundary layer transition promoting mechanism is provided on the air flow contact surface. There are several mounted above. Here, L is the length of the straight duct 13 and is 0.3 to 0.1 times the diameter of the outlet.
Eight times is the length normally used.

FIGS. 2, 3 and 4 show a sketch of a nozzle having a semi-conical projection and the dimensions of the semi-conical projection. The length of this projection is preferably 0.1 L to 0.3 L, and the semicircular radius of the largest area at the rear end of the projection corresponding to the tip of the outlet is preferably 0.025 L to 0.05 L. With a row of protrusions of this size, it is possible to sufficiently suppress the generation of wind noise from the protrusions and promote the transition of the boundary layer on the inner surface of the straight duct to a turbulent boundary layer at multiple locations, and the vortex from the tip of the outlet The emission noise and jet noise generated from the shear flow region of the jet can be reduced.

FIGS. 5, 6, and 7 show an embodiment in which the protrusion (semi-conical shape) on the inner surface of the outlet end in the embodiment of FIGS. In addition, each constituent dimension of the triangular pyramid-shaped projection is determined. The protrusion is 0.05
Plural pieces are mounted on the inner circumference at a pitch interval of L to 0.1 L, and the length is preferably 0.1 L to 0.4 L. The width of the rear end of the triangular pyramid-shaped projection is preferably 0.05 L to 0.1 L, and the height (thickness) thereof is preferably 0.03 L to 0.1 L. According to the configuration as shown in FIGS. 5, 6, and 7, vortex emission noise from the outlet end and jet noise generated from the shear flow region of the jet can be reduced, and wind noise from the projections can be reduced. Very few.

FIGS. 8 and 9 show another embodiment of the present invention, in which a plurality of boundary layer control mechanisms constituted by pyramidal projections 17 are mounted on the inner surface of the straight duct 13 in parallel with the flow direction. It is. Here, the pitch interval between the polygonal pyramid-shaped projections 17 is 0.06 L to 0.12 L. The length K2 of the polygonal pyramid-shaped projection 17 is 0.1 L to 0.3 L, and the width of the rear end of the projection corresponding to the front end of the outlet is 0.06 L to 0.12.
L. Further, the height (thickness) h1 is preferably from 0.03 L to 0.1 L. In this embodiment, the generation of wind noise from the projection 17 itself is small, the partial transition of the inner surface of the nozzle 11 to the turbulent boundary layer is promoted by the generation of a turbulent mass, and the circumferential To reduce vortex shedding noise and jet noise.

FIGS. 10, 11 and 12 show another embodiment of the present invention, wherein the boundary layer control mechanism is constituted by a plurality of grooves 18 formed in the inner surface of the straight duct 13 in parallel with the flow direction. is there. The groove 18 is a triangular pyramidal groove (FIG. 11) or a semi-conical groove (FIG. 12), and a pitch interval between adjacent grooves 18 is 0.06 L to 0.12 L. The length K3 of the groove 18 is 0.1 L to 0.3 L, and the width b2 of the groove rear end corresponding to the front end of the outlet is 0.05 L to 0.1 L.
The depth h2 is preferably from 0.03 L to 0.06 L.
In this embodiment, the generation of wind noise from the triangular pyramidal groove or the semi-conical groove 18 itself is small, and the generation of a turbulent mass due to a minute step promotes a partial transition to a turbulent layer on the inner surface of the nozzle. Vortex shedding noise and jet noise are reduced by reducing the synchronism in the circumferential direction in the boundary layer.

FIGS. 13, 14 and 15 show another embodiment of the present invention. A boundary layer control mechanism is constituted by a triangular notch 19 having the maximum width at the end of the outlet of the straight duct 13. Things. The notches 19 are provided in parallel with the flow direction, and a plurality of the notches 19 are provided at a pitch interval of 0.06 L to 0.12 L. Length K4 of this notch 19
Is 0.1L to 0.3L, and the width b3 at the tip of the outlet is
Is preferably 0.05 L to 0.1 L. Although not shown, the same effect can be obtained even if the notch 19 is configured as a semi-arc-shaped notch of the same size.

In the embodiments shown in FIGS. 13, 14, and 15, the generation of wind noise from the triangular notch 19 itself is small. Then, a turbulent mass is generated by the flow with the outside air flow of the nozzle performed through the triangular notch 19, thereby promoting the transition of the inner surface of the nozzle 11 partially to the turbulent boundary layer. It reduces vortex shedding noise and jet noise by reducing synchronism.

[0035]

Since the present invention is configured as described above, it has the following effects.

(1) The strength of the shear flow around the outflowing jet is reduced by reducing the circumferential synchronization of the boundary layer flow on the inner surface of the nozzle immediately before the nozzle outlet, and the jet noise and vortex emission noise based on the shear flow are reduced. Can be reduced.

(2) Outflow airflow noise generated around the nozzle outlet can be effectively reduced.

(3) Wind noise from the boundary layer control mechanism itself can be prevented from becoming a new noise source.

(4) The external dimensions of the airflow outlet itself shown in the present invention are substantially the same as those of the conventional airflow outlet, and the space around the air outlet can be used effectively.

(5) The structure is relatively simpler than the conventionally proposed method of reducing jet noise, and can be easily implemented.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing one embodiment of the present invention.

FIG. 2 is a perspective view showing a main part of the embodiment of FIG. 1;

FIG. 3 is an enlarged side view showing a protrusion used in the embodiment of FIG. 1;

FIG. 4 is an enlarged end view showing a protrusion used in the embodiment of FIG. 1;

FIG. 5 is a perspective view showing an embodiment in which the protrusion of the embodiment of FIG. 1 is formed in another shape.

FIG. 6 is an enlarged side view showing a projection used in the embodiment of FIG. 5;

FIG. 7 is an enlarged end view showing a projection used in the embodiment of FIG. 5;

FIG. 8 is a side sectional view showing another embodiment of the present invention.

FIG. 9 is an enlarged perspective view showing a projection used in the embodiment of FIG. 8;

FIG. 10 is a side sectional view showing still another embodiment of the present invention.

FIG. 11 is an enlarged perspective view showing a groove used in the embodiment shown in FIG. 10;

FIG. 12 is an end view showing the arrangement of the grooves shown in FIG. 11;

FIG. 13 is a side sectional view showing an embodiment of the present invention.

FIG. 14 is a perspective view showing a notch used in the embodiment of FIG. 13;

FIG. 15 is an end view showing the arrangement of the notches shown in FIG. 14;

FIG. 16 is a side view for explaining a structure of a jet from an airflow outlet and a state of noise generated from the jet.

FIG. 17 is a side sectional view showing a basic configuration of an airflow outlet.

FIG. 18 is a view showing an experimental result showing a relationship between a ratio of a length of a nozzle straight duct to a nozzle diameter and a generated sound.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Jet part of measurement part 2 ... Main flow area 3 ... Turbulent mixing area 4 ... Shear flow 5 ... Outlet 6 ... Jet noise 7 ... Vortex emission sound 11 ... Nozzle 13 Projection 17 Projection 18 Groove 19 Hole

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-110630 (JP, A) JP-A-4-292518 (JP, A) JP-A-5-26762 (JP, A) 58262 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01M 9/00-9/08

Claims (1)

(57) [Claims] An airflow outlet provided with a straight duct near an outlet of a nozzle in order to reduce noise generated when an airflow flows out into a space. The flow boundary layer transition promoting means is provided, and the turbulent boundary layer transition promoting means has an area of the outlet gradually changing continuously toward the outlet end, and the length of the straight duct is
An airflow outlet having a diameter of 0.3 to 0.8 with respect to the outlet diameter.