阅读说明：本技术 降噪装置和抑制钝体绕流纯音噪声程度的确定方法 (Noise reduction device and determination method for inhibiting degree of pure-tone noise of blunt body streaming ) 是由 王晋军 段凡 郭沁峰 徐杨 冯立好 潘翀 于 2021-06-02 设计创作，主要内容包括：本发明提供了一种降噪装置和抑制钝体绕流纯音噪声程度的确定方法,涉及噪声控制技术领域,以解决现有技术对钝体绕流产生的纯音噪声抑制效果较差的技术问题。该降噪装置用于安装在钝体上,且该降噪装置包括柔性板,柔性板的一端设于钝体上；沿气流的来流方向,柔性板位于钝体的后方。本发明提供的降噪装置对钝体绕流产生的纯音噪声具有更好的抑制效果。(The invention provides a noise reduction device and a determination method for inhibiting the degree of pure tone noise of blunt body streaming, relates to the technical field of noise control, and aims to solve the technical problem that the pure tone noise generated by the blunt body streaming in the prior art is poor in inhibition effect. The noise reduction device is used for being installed on the blunt body and comprises a flexible plate, and one end of the flexible plate is arranged on the blunt body; the flexible plate is positioned behind the blunt body along the incoming flow direction of the airflow. The noise reduction device provided by the invention has a better suppression effect on pure tone noise generated by the bypass flow of the bluff body.)

1. A noise reduction device for mounting on a blunt body, characterized in that: the noise reduction device comprises a flexible plate, and one end of the flexible plate is arranged on the blunt body;

the flexible plate is positioned behind the blunt body along the incoming flow direction of the airflow.

2. The noise reduction device according to claim 1, characterized in that: the flexible board is provided with a rigid mounting part which is fixedly connected to the blunt body.

3. The noise reduction device according to claim 2, characterized in that: the installation department includes two clamping pieces, two the clamping piece is followed the thickness direction interval of flexbile plate sets up, the flexbile plate is located two between the clamping piece.

4. The noise reduction device according to claim 3, characterized in that: the clamping piece is plate-shaped;

a length W1 of the clamping member in the air flow direction, and a ratio of a characteristic length D of the blunt body to the length W is below 20%;

and/or the ratio of the thickness W2 of the clamping piece to the characteristic length D of the blunt body is less than 5%.

5. The noise reduction device according to any one of claims 1 to 4, wherein: the material of the flexible plate comprises one or more of a fiber reinforced polyvinyl chloride-based flexible film material, a PET-based composite film material or a nylon woven film material.

6. The noise reduction device according to any one of claims 1 to 4, wherein: the ratio of the thickness W3 of the flexible plate to the characteristic length D of the blunt body is below 3%;

and/or the ratio of the length L of the flexible plate in the airflow direction to the characteristic length D of the blunt body is 0.5-2.0.

7. The noise reduction device according to claim 1, characterized in that: the elastic modulus of the flexible plate is between 1 and 1500 MPa.

8. A method for determining the noise level of a blunt body bypass flow pure sound, which is applied to the noise reduction device according to any one of claims 1 to 7, the method comprising the steps of:

acquiring a velocity field of the passive body streaming of the airflow flowing through the passive body;

determining the wake width of the blunt body streaming around of the blunt body and the turbulent kinetic energy distribution of a wake region according to the velocity field;

determining the integral intensity of pulsation in the wake according to the width of the wake and the turbulence kinetic energy distribution of the wake area;

and determining the suppression degree of the flexible plate on pure tone noise generated by the bypass of the blunt body according to the integral strength of the pulsation in the wake.

9. The method for determining the noise suppression degree of pure acoustic streaming around the blunt body according to claim 8, wherein the step of determining the overall intensity of the pulsation in the wake according to the width of the wake and the distribution of the turbulent kinetic energy of the wake region specifically comprises:

integrating the turbulent kinetic energy vertically within the wake width to determine the overall intensity I of the pulsations in the wake_TKEIn the flow direction x/L_rAnd the flow direction coordinate x adopts the length L of the reflux area_rAnd (4) dimensionless.

10. The method for determining the suppression degree of the pure acoustic noise of the blunt body bypass according to claim 9, wherein the step of determining the suppression degree of the pure acoustic noise of the blunt body bypass by the flexible board according to the integral strength of the pulsation in the wake specifically comprises:

overall intensity of pulsation in the wake I_TKEIn the flow direction x/L_rPerforming power law fitting on the attenuation stage of the change curve;

wherein the power law fitted model is: i is_TKE＝A×(x/L_r)^β(ii) a β is a decay index associated with the structure of the bluff body;

determining a degree coefficient A according to the power law fitted model;

and determining the suppression degree of the pure tone noise of the passive bypass flow according to the degree coefficient A.

Technical Field

The invention relates to the technical field of noise control, in particular to a noise reduction device and a determination method for inhibiting the noise degree of pure sound of blunt body streaming.

Background

The body circumfluence phenomenon is widely existed in daily life and engineering application, and is influenced by the body, and a periodic vortex shedding phenomenon can be generated when fluid flows through the body, so that periodic strong pressure fluctuation is induced on the surface of the body, and a dipole sound source is generated. Pure tone noise radiated by a dipole sound source in the far field appears as a concentrated and sharp noise peak in the frequency spectrum, causing the noise level in the surrounding space to increase dramatically. For example, aircraft landing gear systems, high-speed rail pantograph systems, and passenger car rearview mirrors all generate pure-tone noise due to the streaming of bluff bodies.

At present, in order to suppress the pure-tone noise generated by the turbulent flow of the bluff body, there are generally three ways, one of which is to install a rigid partition plate at the rear part of the bluff body along the incoming flow direction to suppress the vortex generated by the airflow flowing through the bluff body, so as to reduce the pure-tone noise generated by the turbulent flow. And secondly, the blunt body is wrapped by a porous material to reduce noise, so that the strength of a shear layer separated from the surface of the blunt body is effectively reduced, and the streaming pure-tone noise is finally reduced. And thirdly, a plasma exciter is arranged on the surface of the bluff body, and the plasma generated by the plasma exciter drives the ambient air to flow along the surface of the bluff body in an accelerating way to generate wall surface jet flow so as to control the streaming of the bluff body.

However, the existing methods have poor suppression degree of pure tone noise generated by the blunt body streaming.

Disclosure of Invention

In order to solve at least one of the problems mentioned in the background art, the present invention provides a noise reduction apparatus and a determination method for suppressing the degree of pure-tone noise of a blunt body bypass, so as to better suppress the pure-tone noise generated by the blunt body bypass.

In order to achieve the above object, in a first aspect, the present invention provides a noise reduction device for mounting on a blunt body, the noise reduction device comprising a flexible plate, one end of the flexible plate being provided on the blunt body;

the flexible plate is positioned behind the blunt body along the incoming flow direction of the airflow.

In a possible embodiment, the flexible plate is provided with a rigid mounting portion, and the mounting portion is fixedly connected to the blunt body.

In one possible embodiment, the mounting portion includes two clamping members, the two clamping members are spaced apart in a thickness direction of the flexible plate, and the flexible plate is located between the two clamping members.

In a possible embodiment, the clamping part is plate-shaped;

a length W1 of the clamping member in the air flow direction, and a ratio of a characteristic length D of the blunt body to the length W is below 20%;

and/or the ratio of the thickness W2 of the clamping piece to the characteristic length D of the blunt body is less than 5%.

In one possible embodiment, the material of the flexible board includes one or more of a fiber reinforced polyvinyl chloride based flexible film, a PET based composite film, or a nylon woven film.

In a possible embodiment, the ratio of the thickness W3 of the flexible plate to the characteristic length D of the blunt body is below 3%;

and/or the ratio of the length L of the flexible plate in the airflow direction to the characteristic length D of the blunt body is 0.5-2.0.

In a possible embodiment, the modulus of elasticity of the flexible sheet is between 1 and 1500 Mpa.

In a second aspect, the present invention provides a method for determining a noise level of a pure sound of a passive body bypass, which is applied to the above noise reduction apparatus, and the method for determining a noise level of a pure sound of a passive body bypass includes the following steps:

acquiring a velocity field of the passive body streaming of the airflow flowing through the passive body;

determining the wake width of the blunt body streaming around of the blunt body and the turbulent kinetic energy distribution of a wake region according to the velocity field;

determining the integral intensity of pulsation in the wake according to the width of the wake and the turbulence kinetic energy distribution of the wake area;

and determining the suppression degree of the flexible plate on pure tone noise generated by the bypass of the blunt body according to the integral strength of the pulsation in the wake.

In a possible implementation, the step of determining the overall intensity of the pulsation in the wake according to the width of the wake and the intensity of the turbulent kinetic energy of the wake region specifically includes:

integrating the turbulent kinetic energy vertically within the wake width to determine the overall intensity I of the pulsations in the wake_TKEIn the flow direction x/L_rAnd the flow direction coordinate x adopts the length L of the reflux area_rAnd (4) dimensionless.

In a possible implementation manner, the step of determining the suppression degree of the flexible plate to the pure-tone noise of the passive body streaming according to the overall intensity of the pulsation in the wake specifically includes:

overall intensity of pulsation in the wake I_TKEIn the flow direction x/L_rPerforming power law fitting on the attenuation stage of the change curve;

wherein the power law fitted model is: i is_TKE＝A×(x/L_r)^β(ii) a β is a decay index associated with the structure of the bluff body;

determining a degree coefficient A according to the power law fitted model;

and determining the suppression degree of the pure tone noise of the passive bypass flow according to the degree coefficient A.

According to the noise reduction device provided by the invention, the flexible plate is arranged behind the bluff body, the flexible plate can inhibit vortex shedding of bluff body streaming, the overall pulse intensity of a tail region of the bluff body streaming is reduced, and therefore, the noise reduction device has a strong inhibition effect on pure-tone noise generated by bluff body streaming.

The construction of the present invention and other objects and advantages thereof will be more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic view illustrating an arrangement of a flexible board on a cylindrical blunt body according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a flexible board disposed on a square-cylindrical blunt body according to an embodiment of the present invention;

FIG. 3 is a schematic view of an arrangement of a flexible board on an I-shaped blunt body according to an embodiment of the present invention;

FIG. 4 is an enlarged view of a portion of FIG. 1 at A;

FIG. 5 is a schematic view of a fiber reinforced polyvinyl chloride-based flexible film according to an embodiment of the present invention;

FIG. 6 is a schematic structural diagram of a multi-layer fiber-reinforced polyvinyl chloride-based flexible film according to an embodiment of the present invention;

FIG. 7a shows that the ratio L/D of the length L of the flexible plate to the characteristic length D of the blunt body is 0.5, and the Reynolds number Re is 5.74 × 10⁴Measuring results of a pneumatic noise experiment;

FIG. 7b shows that the ratio L/D of the length L of the flexible plate to the characteristic length D of the blunt body is 1, and the Reynolds number Re is 5.74 × 10⁴Measuring results of a pneumatic noise experiment;

FIG. 7c shows the ratio L/D of the length L of the flexible plate to the characteristic length D of the blunt body is 2, and the Reynolds number Re is 5.74 × 10⁴Measuring results of a pneumatic noise experiment;

FIG. 7D shows that the ratio L/D of the length L of the flexible plate to the characteristic length D of the blunt body is 1, and the Reynolds number Re is 3.83 × 10⁴Measuring results of a pneumatic noise experiment;

FIG. 8a shows pure tone noise intensity I when a rigid partition is mounted on a bluff body_AA curve of variation with length L/D;

FIG. 8b shows pure tone noise intensity I when the flexible board is mounted on the blunt body_AA curve of variation with length L/D;

FIG. 8c shows the pure tone noise intensity I_AA variation curve with Reynolds number Re;

FIG. 9a is a graph of the kinetic energy TKE of turbulent flow in the wake of a bluff body winding without flexible plates and rigid baffles;

FIG. 9b is a graph of the kinetic energy of turbulence TKE in the wake of the bluff body flow when the rigid partition plate with L/D equal to 1.0 is installed;

FIG. 9c is a graph of the kinetic energy of turbulence TKE in the wake of the bluff body winding when the flexplate with L/D equal to 1.0 is installed;

fig. 10 is a schematic flowchart of a method for determining a degree of noise of pure sound of a passive bypass flow suppressed by a flexible board according to a second embodiment of the present invention;

FIG. 11 is a schematic illustration of the trail width w;

FIG. 12 is a flow direction x/L of a dimensionless trail width w/D_rThe variation curve of (d);

FIG. 13 is the integral I of turbulent kinetic energy over the wake width_TKE。

Description of reference numerals:

1-bluff body; 2-a flexible plate; 21-a reinforcing fiber; 22-PVC films; 3-clamping part.

Detailed Description

When the airflow flows through the blunt body, a periodic vortex shedding phenomenon is generated, and further, periodic strong pressure fluctuation is induced on the surface of the blunt body, so that a dipole sound source is generated. Pure tone noise radiated by a dipole sound source in the far field appears as a concentrated and sharp noise peak in the frequency spectrum, causing the noise level in the surrounding space to increase dramatically. For example: aircraft landing gear systems, high-speed rail pantograph systems and passenger car rearview mirrors. During the takeoff and landing of an aircraft, airframe noise is increasingly the dominant source of noise for modern large passenger aircraft. The aerodynamic noise generated by an aircraft landing gear system consisting of various columnar bluff bodies (beams, struts, cables and the like) is the main component of the noise of an aircraft body, and accounts for over 70 percent;

for a high-speed rail, the aerodynamic noise increases by the power of 6 of the running speed, while the structural noise increases only by the power of 3 of the running speed, so that the main noise source of the high-speed rail is mechanical noise when running at a low speed, and the aerodynamic noise gradually becomes the main component of the noise of the high-speed rail after the speed of the high-speed rail exceeds 250km/h, wherein the noise generated by a pantograph system consisting of a beam and a column is extremely remarkable and sharp.

For a car for home use, noise is an important criterion for evaluating the comfort thereof, and after the car has traveled over 80km/h, the wind noise generated by the rear view mirror becomes quite noticeable.

At present, three suppression methods are generally used for pure-tone noise generated by the streaming of a bluff body, one of the suppression methods is to mount a rigid partition plate at the rear part of the bluff body along the incoming flow direction of an airflow to suppress vortex shedding generated by the airflow flowing through the bluff body, so that the pure-tone noise generated by the streaming can be reduced. However, the rigid partition is generally made of metal material to ensure the rigidity of the partition, which can significantly increase the weight of the structure where the bluff body is located, for example, in the field of civil aviation, the passenger aircraft design is very sensitive to the increase of the weight of the structure, and the increase of the weight means higher oil consumption, higher cost and shorter voyage; and the rigid partition plate has poor effect of inhibiting pure-tone noise generated by the bypass flow of the bluff body.

And secondly, the blunt body is wrapped by a porous material for noise reduction, wherein the porous material is a general term for a breathable loose material, and typical porous materials comprise polyurethane foam, porous metal foam and the like. However, when the porous material is used for noise reduction, the thicker the porous material is, the better the noise reduction effect is, so in practical engineering application, to realize a good noise reduction effect, the thicker porous material needs to be wrapped outside the bluff body, which can significantly change the appearance of the bluff body, increase the volume of the bluff body, increase the resistance on one hand, and influence the operation of a transmission component, such as an aircraft landing gear, possibly needing to perform structure and mechanism design again. Moreover, the porous material wrapped the blunt body has a poor effect of inhibiting pure-tone noise generated by the flow around the blunt body.

And thirdly, the plasma exciter is adopted to control the bypass noise of the bluff body, the plasma exciter generates plasma covering the surface of the bluff body, the generation of the plasma can apply force to surrounding air, the air is driven to flow backwards in an accelerated mode from the rear edge of the exposed electrode along the surface of the bluff body, wall surface jet flow is generated, and accordingly generation of bypass of the bluff body is restrained. However, the plasma exciter is an active control technology, and depends on continuous input of external energy, so that the energy consumption is increased; the plasma exciter needs an additional control system, which reduces the reliability of the system; when the plasma exciter is installed, the surface of the metal blunt body needs to be subjected to multilayer insulation treatment, so that the difficulty of a manufacturing process is greatly increased, and the weight of the structure is increased; moreover, when the bluff body where the plasma exciter is located is a cylinder, the suppression effect of the plasma exciter on pure-tone noise generated by the streaming of the bluff body is poor.

The invention provides a noise reduction device, which is characterized in that a flexible plate is arranged at the rear part of a blunt body along the flow direction, the flexible plate is used for inhibiting vortex shedding generated by airflow flowing through the blunt body, the integral pulsation intensity of a tail region of a flow winding of the blunt body can be well reduced, and therefore, the noise reduction device has a strong inhibition effect on pure-tone noise generated by the flow winding of the blunt body. Moreover, the flexible plate has a simple structure, has small influence on the blunt body, does not need external energy input, is convenient to arrange, and has small influence on the weight of the structure or/and mechanism where the blunt body is located.

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the preferred embodiments of the present invention. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are only some, but not all embodiments of the invention. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In the following mentioned directions of this embodiment, the flow direction refers to the direction along which the airflow comes, the span direction refers to the length direction of the blunt body, or the axial direction thereof, the vertical direction refers to the direction perpendicular to both the flow direction and the span direction, and the flow direction, the vertical direction and the span direction satisfy the right-hand spiral rule. In the following description, the flow direction coordinate is represented by x, the vertical coordinate is represented by y, and the origin of the coordinates is defined as the position of the centroid of the blunt body section.

Example one

Referring to fig. 1 to 3, a noise reduction device according to a first embodiment of the present invention is provided for being mounted on a blunt body 1, and includes a flexible plate 2, one end of the flexible plate 2 being fixed to the blunt body 1; and the flexible plate 2 is positioned behind the blunt body 1 along the incoming flow direction of the airflow.

It should be noted that the blunt body 1 may be a cylindrical body with a circular cross section as shown in fig. 1, a cylindrical body with a square cross section as shown in fig. 2, a cylindrical body with an i-shaped cross section as shown in fig. 3, or other blunt body structures known to those skilled in the art, such as a cylindrical body with a polygonal cross section.

When the air flow flows through the blunt body 1, the air flow cannot be completely attached to the surface of the blunt body 1, so that separation occurs, a sharp and wide wake is generated at the rear part of the blunt body 1, and a vortex shedding phenomenon, namely, the flow of the blunt body is formed. The vortex shedding means that the airflow is separated when flowing through the bluff body 1, and strong shear flow, namely a shear layer, is generated on two sides of the bluff body 1; the shear layer is periodically rolled up at the rear part of the blunt body 1 to form a large-scale vortex structure with opposite rotation directions, and then the vortex is separated and convected downstream in the wake.

Vortex shedding induces pure tone noise, which refers to a noise peak that is concentrated and sharp in a narrow frequency band in the noise spectrum.

The noise reduction device of this embodiment, through a flexplate 2 of rear installation at bluff body 1, can restrain the vortex of bluff body streaming and drop, reduce the holistic pulsating strength in streaming wake district to the realization is to the high-efficient suppression of the pure tone noise that bluff body streaming produced.

In the present embodiment, a structure for mounting the flexible board 2 on the blunt body 1 is provided, and referring to fig. 1 and 4, in the present embodiment, a mounting portion is provided at one end of the flexible board 2, and the mounting portion is made of a rigid material and is fixed on the blunt body 1.

Through set up the installation department of above-mentioned rigidity on flexible sheet 2, by the installation department and blunt body 1 fixed connection of rigidity, can be comparatively convenient fix flexible sheet 2 on blunt body 1.

In this embodiment, the mounting portion is provided to protrude from the blunt body 1. Through setting up installation department evagination in blunt body 1, can avoid causing the influence to the intensity of blunt body 1 self.

The present embodiment provides a mounting portion with a better structure, and referring to fig. 4, the mounting portion of the present embodiment includes two rigid clamping members 3, the two clamping members 3 are arranged at intervals along the thickness direction of the flexible board 2, and one end of the flexible board 2 is clamped and fixed between the two clamping members 3.

Referring to fig. 4, one way of clamping the flexible plate 2 between the two clamping members 3 is: the leading edge end of the flexible board 2 is clamped between two clamping pieces 3, and the flexible board 2 and the clamping pieces 3 are bonded through an adhesive.

The flexible board 2 may be fixed between the two clamping members 3 in a manner that: through vice fixed connection of bolt between two clamping pieces 3, perhaps through riveting fixed connection, only need can guarantee that clamping piece 3 and flexoplate 2 closely laminate can.

Referring to fig. 4, one way of fixing the two clamping members 3 to the blunt body 1 is: the two clamping members 3 are respectively welded and fixed on the blunt body 1.

By fixing the clamping member 3 on the blunt body 1 in this way, the advantages are that firstly, the blunt body 1 does not need to be grooved or perforated, the rigidity and strength of the blunt body 1 are not changed, and in actual application, the strength of the blunt body 1 and the structure or/and mechanism where the blunt body 1 is located does not need to be checked further. Secondly, for the blunt body 1 which is already processed or put into use, the noise reduction device of the present embodiment can be directly installed in the above manner without redesigning and processing the blunt body 1.

It should be noted that the clamping member 3 may also be fixed to the blunt body 1 by means of bonding; the clamping member 3 may be integrally formed with the blunt body 1 when the blunt body 1 is manufactured.

In the present embodiment, the clamping member 3 is preferably made of a high-strength metal material, for example, 45# steel or 7-series aluminum alloy is used as the material of the clamping member 3. It should be noted that a high-strength composite material, such as an epoxy resin glass fiber board, may be used as the clamping member 3.

On the basis of the above, the present embodiment provides a preferable structure of the clamping member 3, and as shown in fig. 4, each clamping member 3 of the present embodiment has a plate shape, and the ratio of the length W1 of the clamping member 3 in the airflow direction to the characteristic length D of the blunt body 1 is 20% or less; the ratio of the thickness W2 of each clamping member 3 to the characteristic length D of the bluff body 1 is less than 5%. I.e., the ratio of W1/D is less than or equal to 20%; this ratio may be, for example, any of 5%, 8%, 11%, 14%, 17%, or 20%, or any other value of 20% or less. The ratio of W2/D is less than or equal to 5%; this ratio may be, for example, any of 2%, 3%, 4%, or 5%, or may be other values of 5% or less. It should be noted that both of the above ratios are preferably smaller values that satisfy the stable mounting of the flexible board 2 on the blunt body 1.

Wherein, the characteristic length D of the blunt body 1 refers to a length capable of representing a geometrical characteristic of the blunt body 1, for example, for a cylindrical blunt body 1 having a circular cross section as shown in fig. 1, the characteristic length D is a diameter of the circle; for the cylindrical blunt body 1 with a square cross section as shown in fig. 2, the characteristic length D is the side length of the square; for the columnar bluff body 1 with the polygonal section, the characteristic length is the diameter of a circumscribed circle of the polygon; for the cylindrical blunt body 1 having an i-shaped cross section as shown in fig. 3, the characteristic length D is the height of the i-shaped cross section. The definition of the characteristic length of the blunt body with other shapes is subject to the standard of the characteristic length recognized by researchers or technicians in the field.

By providing the clamping member 3 according to the above-described structure, it is possible to make the clamping member 3 have a light weight while satisfying the mounting of the flexible board 2 on the blunt body 1; meanwhile, the clamping piece 3 can be effectively prevented from reducing the suppression degree of pure-tone noise generated by the blunt body streaming by the flexible plate 2.

The embodiment provides a better flexible board 2, and specifically, the material of the flexible board 2 of the embodiment is one or more of a fiber-reinforced polyvinyl chloride-based flexible film material, a PET-based composite film material or a nylon woven film material; the material of the flexible board 2 is preferably a fiber-reinforced polyvinyl chloride-based flexible film material, and as shown in fig. 5, the fiber-reinforced polyvinyl chloride-based flexible film material is in a "sandwich" structure, and an inner interlayer thereof is made of warp-weft knitted reinforced fibers 21, and then is formed by laminating an upper layer and a lower layer of PVC films 22 (polyvinyl chloride). Adopt the flexbile plate 2 of fibre reinforcing polyvinyl chloride based flexible membrane material, its tensile strength and fatigue strength are showing and are being higher than pure PVC membrane material, can effectively prevent fatigue fracture when flexbile plate 2 swings in blunt body 1 wake.

On this basis, the embodiment further provides a fiber reinforced polyvinyl chloride based flexible film material with a better structure, which includes N layers of reinforcing fibers 21 and N +1 layers of PVC films 22, and the fiber layers 21 and the PVC film layers 22 are arranged in a spaced and stacked manner, as shown in fig. 6, fig. 6 specifically includes 3 layers of reinforcing fibers 21 and 4 layers of PVC films 22, and the flexible plate 2 made of the material can have higher tensile strength and fatigue strength.

In this embodiment, the ratio W3/D of the thickness W3 of the flexible board 2 to the characteristic length D of the blunt body 1 is 3% or less; the ratio L/D of the length L of the flexible plate 2 in the airflow direction to the characteristic length D of the bluff body 1 is 0.5-2; that is, the ratio of W3/D is less than or equal to 3%, which may be, for example, 1%, 1.5%, 2%, 2.5%, or 3%, or may be other values less than 3%, as long as the strength is sufficient. The ratio L/D is between 0.5 and 2, and may be, for example, any of 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 or 2.0, or it may be other values between 0.5 and 2. And the ratio of L/D is further preferably 1.

In this embodiment, the elastic modulus of the flexible board 2 is preferably between 1Mpa and 1500Mpa, which may be, for example, one of 1Mpa, 200Mpa, 400Mpa, 600Mpa, 800Mpa, 1000Mpa, 1200Mpa, and 1500Mpa, or any other value between 1Mpa and 1500 Mpa.

In this embodiment, the length of the flexible plate 2 in the span-wise direction of the blunt body 1 is preferably equal to the length in the span-wise direction of the blunt body 1.

By arranging the flexible plate 2 according to the above structure and shape, it can be known by referring to the following experimental results that the scheme of the present embodiment can better suppress the pure-tone noise generated by the bypass flow of the bluff body.

Fig. 7a to 7d show the results of acoustic wind tunnel experiments for noise generated by the bypass of a blunt body under different conditions, where fig. 7a to 7d show the power spectral density of noise sound pressure. In fig. 7a to 7d, the line representing the cylinder indicates a condition where the rigid diaphragm and the flexible board 2 are not provided at the rear of the cylinder, the line representing the rigid board indicates a condition where the rigid diaphragm is provided at the rear of the cylinder, the line representing the flexible board indicates a condition where the flexible board 2 is provided at the rear of the cylinder, St indicates a dimensionless frequency, and PSD indicates a Power spectral Density (Power spectral Density).

In this example, the blunt body 1 used for the experiment was a cylinder having a diameter D of 30mm and an axial length of 1000mm, and was made of 7075 aluminum alloy. The reason why the cylinder is selected as the model in this embodiment is as follows: when the airflow flows through the cylinder, the separation point of the circumambient flow changes along with the change of the incoming flow speed, and when the airflow flows through the square column or the polygonal column, the separation point is generally fixed, so that the experiment taking the cylinder as a model is more representative.

The flexible plate 2 for carrying out the experiment adopts a fiber reinforced PVC flexible membrane material with the thickness of 0.45mm, the elastic modulus is 4.19Mpa, the rigid partition plate for carrying out the experiment adopts a metal plate material with the same thickness, and in the graphs from 7a to 7c, the ratio L/D of the length L of the flexible plate 2 and the rigid partition plate in the airflow direction to the diameter D of the bluff body 1 is 0.5, 1.0 and 2.0 in sequence.

In fig. 7a to 7c, the inflow velocity of the airflow is 30m/s, and at this time, the Reynolds number (Reynolds number) Re based on the diameter of the blunt body 1 is 5.74 × 10⁴. In fig. 7D, the ratio L/D of the flow direction length L of the flexible plate 2 and the rigid partition plate to the diameter D of the blunt body 1 is 1.0, and the incoming flow velocity of the air flow is 20m/s, and at this time, the reynolds number Re based on the diameter of the blunt body 1 is 3.83 × 10⁴。

As can be seen from fig. 7a to 7c, the flexible board 2 having a length in the range of L/D of 0.5 to 2.0 can significantly suppress the streaming pure sound noise peak compared to the case where the rigid partition board and the flexible board 2 are not provided at the rear portion of the cylinder under the same reynolds number, and the suppression effect is the best when L/D is 1.0. As can be seen from fig. 7a and 7b, the rigid partition plate having a length L/D of 0.5 and a length L/D of 1.0 has a suppression effect on pure-tone noise, and the rigid partition plate has a suppression effect on pure-tone noise weaker than that of the flexible plate 2 having the same length, and as can be seen from fig. 7c, the rigid partition plate having a length L/D of 2.0 does not have a suppression effect on pure-tone noise, but rather increases the peak value of pure-tone noise.

As can be seen from comparison of the characteristics of the frequency spectrums in fig. 7b and 7D, when the reynolds numbers are different, that is, the flow rates of the air flows are different, the effect of controlling the pure-tone noise by the flexible plate 2 having an L/D of 1.0 is substantially the same, and the effect of suppressing the pure-tone noise by the flexible plate 2 is always better than that of the rigid partition plate.

Therefore, the effect of the flexible plate 2 on suppressing the pure-tone noise generated by the bluff body streaming is better than that of the rigid partition plate on suppressing the pure-tone noise generated by the bluff body streaming under various conditions.

On the basis, the present embodiment further studies the intensity I of the pure-tone noise generated by the flexible board 2 with different lengths to the bypass of the blunt body 1 under the condition of different reynolds numbers, that is, under the condition of different flow velocities of the air flow_AThe inhibitory effect of (3). In the embodiment, the pure tone noise peak in the noise spectrum obtained under different Reynolds numbers is integrated and cut off at the position of 10dB less than the peak value, and the intensity I of the pure tone noise is quantitatively calculated_A. The reynolds numbers Re of 3.83 × 10 are given in fig. 8a and 8b, respectively⁴～9.57×10⁴In-range, pure tone noise intensity I_AThe values in the legend of fig. 8a and 8b represent specific reynolds number values for the corresponding curves as a function of length L/D. As can be seen from FIGS. 8a and 8b, the pure tone noise intensity I is shown at different Reynolds numbers_AThe variation trend along with the L/D is basically consistent, and the length of the two partition plates for generating the optimal noise reduction effect on pure tone noise is 1.0.

Fig. 8c further shows the pure-tone noise intensity I of the blunt body 1 without the rigid partition and the flexible plate, and the blunt body 1 with the rigid partition and the flexible plate 2 having an L/D of 1.0 mounted at the rear thereof_ACurve with reynolds number Re. Fig. 8c shows that the rigid partition and the flexible plate 2 with L/D of 1.0 significantly reduce the pure-tone noise of the body bypass, and the noise reduction effect of the flexible plate 2 is always better than that of the rigid partition. The rigid baffles reduced the pure tone noise intensity by an average of 14dB, while the flexible board 2 reduced the pure tone noise intensity flatness by 18 dB.

On the basis, the present embodiment also studies the working condition that the bluff body 1 is not provided with the flexible plate 2 and the rigid partition plate, the working condition that the bluff body 1 is provided with the flexible plate 2, and the distribution of the turbulent kinetic energy TKE in the wake of the bluff body 1, and the results are shown in fig. 9a to 9c in sequence. FIG. 9a shows a condition where the flexible board 2 and the rigid partition board are not installed; FIG. 9b illustrates the installation of a rigid partition with an L/D of 1.0; fig. 9c shows the condition of mounting the flexible board 2 with L/D1.0; turbulent kinetic energy (Turbulent kinetic energy) is a statistic for describing the pulsation intensity in a flow field, and is marked as TKE after dimensionless, and in the bluff body wake, the Turbulent kinetic energy is mainly caused by vortex shedding; x/D and y/D represent the flow and vertical coordinates, respectively, non-dimensionalized by the cylinder diameter D.

As can be seen from fig. 9a to 9c, the peak value of the turbulent kinetic energy TKE in the wake of the flow is significantly reduced and the area of the region where the turbulent kinetic energy TKE is concentrated is significantly reduced after the flexible plate 2 and the rigid partition plate are installed, compared with the operating condition without the flexible plate 2 and the rigid partition plate; and the flexible plate 2 significantly narrows the vertical dimension of the turbulent kinetic energy distribution in the wake. In the passive body streaming, the turbulent kinetic energy represents the pulsating intensity induced by vortex shedding, and therefore, the results of fig. 9a to 9c show that the scheme of mounting the flexible plate at the rear part of the passive body in the streaming direction can effectively inhibit the pulsating intensity of the wake region of the passive body streaming while reducing streaming noise.

Example two

On the basis of the first embodiment of the present invention, the second embodiment of the present invention provides a method for determining a degree of noise of a pure sound of a passive bypass by a flexible board, which is shown in fig. 10 and includes the following steps:

s100, acquiring a velocity field of the passive body streaming of airflow flowing through the passive body;

s200, determining the wake width of the wake of the body streaming of the bluff body and the turbulent kinetic energy distribution of a wake region according to the velocity field;

s300, determining the integral intensity of pulsation in the wake according to the width of the wake and the turbulence kinetic energy distribution of the wake area;

s400, determining the suppression degree of the flexible plate to the pure tone noise generated by the passive body streaming according to the integral strength of the pulsation in the wake.

In this embodiment, in the step of obtaining the velocity field of the bluff body flow of the airflow flowing through the bluff body, the velocity field of the bluff body flow is measured by using a particle image velocimetry technique, where the velocity field refers to the velocity of each point in the flow field. For the same working condition, at least 2000 frame rate fields of continuous sampling at different time points need to be obtained. It should be noted that the manner of obtaining the velocity field of the flow field by the particle image velocimetry technology can adopt the existing mature technology, and the details thereof are not described herein.

The width of a wake of the flowing bluff body, the length of a backflow region and the turbulence kinetic energy distribution of the wake region can be calculated according to the velocity field of the flowing bluff body; in this embodiment, referring to FIG. 11, the wake width w of the bluff body streaming is defined as the velocity deficit reduced to the maximum deficit U_dAnd half of the width of the local velocity profile, the wake width w may be used to characterize the vertical dimension of the wake region's pulse distribution. It should be noted that the method for calculating the width w of the trail can be generalized as follows: speed loss is reduced to maximum loss U_dThe value range of k is 0-0.5 when the k is multiplied by the local speed type width, the smaller k is, the wider the calculated wake width w is, but the qualitative evaluation result of the algorithm on the noise reduction effect of different partition plates cannot be changed by the value of k.

Fig. 12 shows the variation curves of the wake width along the flow direction corresponding to three typical conditions, that is, the condition that the flexible plate and the rigid partition plate are not installed on the blunt body, and the condition that the rigid partition plate and the flexible plate are respectively installed with a length L/D equal to 1.0, where x represents the flow direction and y represents the vertical direction. As can be seen from FIG. 12, the wake width of the working condition with the rigid partition installed is significantly greater than the wake width of the working condition without the flexible board and the rigid partition installed; the wake width of the working condition of installing the flexible plate is smaller than that of the working condition of not installing the flexible plate and the rigid partition plate; this shows that the vertical dimension of the pulse distribution in the wake region is increased by mounting the rigid baffles, while the vertical dimension of the pulse distribution is effectively reduced by mounting the flexible plates. The turbulent kinetic energy distribution of the wake region corresponding to the three typical working conditions is shown in sequence in FIGS. 9a-9 c.

In fig. 12, the flow direction coordinate x is the recirculation zone length L_rTo proceed dimensionless processingThe reason is that: length L of reflux zone_rThe general rule of the tail feature of the blunt body 1 along the change of the flow direction can be better described; wherein, the reflux region refers to a countercurrent region formed at the rear part of the blunt body after the fluid flows through the blunt body, the flowing direction in the region is opposite to the main flowing direction, the fluid flows from the downstream to the upstream, the length of the reflux region is defined as the length of the reflux region along the flowing direction in the time-averaged flow field and is marked as L_r. By the length L of the reflux zone_rDimensionless flow direction coordinates are also given in fig. 9a-9 c. In the following description, unless otherwise specified, the flow direction coordinate x is the length L of the recirculation zone_rAnd carrying out dimensionless transformation.

The step of determining the overall intensity of the pulsations in the wake according to the wake width and the turbulence kinetic energy distribution in the wake area comprises the following steps:

the integral of the turbulent kinetic energy distribution (FIGS. 9a-9c) of the bluff body 1 around the wake region along the vertical direction over the width of the wake is determined to determine the overall intensity I of the wake pulsation as shown in FIG. 13_TKEIn the flow direction x/L_rThe change curve of (2).

On the basis, the step of determining the suppression degree of the flexible plate 2 to the pure sound noise of the blunt body streaming according to the integral strength of the pulsation in the wake comprises the following steps:

integral intensity of pulse to trail I_TKEIn the flow direction x/L_rThe attenuation phase of the variation curve is power-law fitted, specifically in this embodiment, the attenuation phase is x/L_rStage > 2.

Wherein the power law fitted model is: i is_TKE＝A×(x/L_r)^β(ii) a Beta is a decay index related to the sectional shape of the blunt body; for the blunt bodies with different sections, the value range of beta is-1.2-0, and in the embodiment, the best fitting result can be obtained by taking-0.9 for the cylindrical blunt bodies.

Determining a degree coefficient A according to a power law fitting model;

and determining the degree of the flexible plate 2 for inhibiting the pure-tone noise of the blunt body streaming according to the degree coefficient A.

Specifically, the lower the degree coefficient a, the better the suppression degree of the pure-tone noise of the passive bypass is.

The blunt body used in aerodynamic noise experiment of the embodiment is adopted as the blunt body, the airflow speed is 20m/s, and the Reynolds number Re is 3.83 multiplied by 10⁴. For the working condition of not installing the rigid partition board and the flexible board, the working condition of installing the rigid partition board with L/D being 1, and the working condition of installing the flexible board with L/D being 1, according to the method of the present embodiment, the obtained values of the degree coefficient a are 0.398, 0.274, and 0.258, respectively, as shown in fig. 13, which illustrates that the installation of the flexible board 2 or the rigid partition board significantly suppresses the streaming pure tone noise compared to the working condition of the cylinder without installing the rigid partition board and the flexible board, and the suppression degree of the flexible board 2 on the pure tone noise is better than that of the rigid partition board on the pure tone noise, consistent with the result of the aerodynamic noise experiment of the embodiment (as shown in fig. 8 c).

The method is preferably applied to the case that the length of the partition board is short, such as the judgment of the degree of pure tone noise suppression of the partition board with the length L/D less than or equal to 1.0; the method is suitable for qualitatively judging the noise reduction effect of different partition plates on the same blunt body, and for the blunt bodies with different cross section shapes, the attenuation constants beta are different, so that comparison cannot be carried out through the degree coefficient A. The different partition boards may be made of different materials, have different lengths, have different thicknesses, and have different flexibility or/and rigidity.

The reason why the suppression degree of the flexible plate 2 and/or the rigid clapboard on the pure sound noise of the blunt body circumfluence can be determined by the overall strength of the pulsation in the wake is as follows: the pure-tone noise of the round-flow of the bluff body is derived from a dipole sound source induced on the surface of the bluff body by vortex shedding, so that the stronger the vortex shedding, the stronger the pure-tone noise radiated when the airflow flows through the bluff body. On the other hand, the flow field pulsation in the wake of the blunt body flow winding mainly originates from disturbance of vortex shedding to the flow field, and similarly, the stronger the vortex shedding, the stronger the overall intensity of the pulsation in the wake of the flow winding. Therefore, strong positive correlation exists between the vortex shedding strength, the pure tone noise strength and the overall strength of the pulsation in the wake; therefore, the noise reduction degree of the partition board can be approximately evaluated through the investigation of the overall strength of the pulsation in the wake.

Since measuring noise requires a specialized acoustic wind tunnel,but at present, professional acoustic wind tunnel equipment at home and abroad is few, and the use cost is very high. Therefore, compared with the method of directly measuring noise in an acoustic wind tunnel to evaluate the degree of pure tone noise generated by different partition plates for inhibiting the flow around the bluff body, the method of the embodiment obtains the continuous sampling velocity field of the wake flow field through the particle image velocimetry technology, and further calculates the overall strength I of pulsation in the wake_TKEIn the flow direction x/L_rThe attenuation degree coefficient A is used for evaluating the degree of pure tone noise generated by the baffle plate for inhibiting the blunt body bypass flow, and the method is not limited by an acoustic wind tunnel, is convenient and has lower cost.

In the description of the embodiments of the present invention, it should be understood that the terms "mounted," "connected," and "connected" are to be construed broadly and may include, for example, a fixed connection, an indirect connection through intervening media, a connection between two elements, or an interaction between two elements, unless expressly stated or limited otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations. The terms "upper", "lower", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience in describing and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. In the description of the present invention, "a plurality" means two or more unless specifically stated otherwise. The term "spacer" is to be understood broadly and refers to both the flexible plate 2 and/or rigid spacer described in the embodiments, as well as to the same or similar components or components having the same or similar functions as the flexible plate 2 or rigid spacer of the present invention.

The terms "first," "second," "third," "fourth," and the like in the description and in the claims of the present application and in the above-described drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.