Wind tunnel nozzle and its contraction section, and manufacturing method of wind tunnel nozzle contraction section

Abstract

The present invention discloses a wind tunnel nozzle and its contraction section, and a method for manufacturing the contraction section of the wind tunnel nozzle, which are applied to the field of wind tunnel test technology, and include a cylindrical part, the cylindrical part including a contraction section body and a suction section arranged coaxially; at least one weld is provided on the cylindrical part, and the weld extends from one axial end of the cylindrical part to the other end; and an angle is provided between a generatrix intersecting with the weld on the suction section and the weld. The contraction section of the wind tunnel nozzle provided by the present invention reduces the area of ​​the weld on the suction section on a single generatrix by tilting the weld on the suction section relative to the generatrix, and effectively avoids the formation of a suction "dead zone" in the local part of the suction section on the basis of ensuring that the weld of the cylindrical part has good safety, reliability and service life, thereby effectively reducing or eliminating the influence of the weld on the suction efficiency of the turbulent boundary layer, and can effectively improve the suction efficiency of the wind tunnel nozzle in the contraction section, and increase the quality of the wind tunnel nozzle.

Description

Technical Field

[0001] The invention relates to the technical field of wind tunnel testing, and in particular to a wind tunnel nozzle and a contraction section thereof, and a method for manufacturing the contraction section of the wind tunnel nozzle. Background Art

[0002] Hypersonic wind tunnels can be used to examine the aerodynamic thermal effects and aero-optical effects of aircraft in flight. In order to make the wind tunnel background disturbance close to the actual flight environment and accurately predict the aerodynamic thermal effects and aero-optical effects of high-speed aircraft, it is necessary to develop a hypersonic silent wind tunnel with a low-noise level quiescent flow test area. Assembling a silent wind tunnel nozzle is one of the key technologies to realize the quiescent flow test area. The wind tunnel nozzle includes a contraction section and an expansion section, which are connected to form a whole.

[0003] In the early days, in order to reduce the disturbance entering the throat of the wind tunnel nozzle, the contraction section of the wind tunnel nozzle generally has a large contraction ratio, but this cannot completely eliminate the impact of the upstream disturbance wave on the downstream. Therefore, in the design process of the wind tunnel nozzle, boundary layer suction devices, such as suction slots, have been used very early to suck the turbulent boundary layer at the throat of the contraction section to achieve the purpose of weakening or even eliminating the disturbance entering the expansion section. However, although the suction slot can effectively eliminate the incoming flow boundary layer, it has high requirements for the flow field and flow control at the throat. Once the suction flow control has deviations (suction intensity deviation, separation bubble generation, etc.), additional disturbances are also brought about accordingly. In particular, when the suction slot is not working, the disturbance caused by the existence of the suction slot causes the nozzle pressure pulsation to reach an order of magnitude of more than 1%, which makes the wind tunnel index far higher than the requirements of the low-noise wind tunnel index.

[0004] In the related art, in order to improve the problem of the suction seam being not robust, a subsonic contraction section is used for overall suction to achieve the purpose of removing or weakening the turbulent boundary layer on the contraction section wall. The specific method is to set a boundary layer suction device on the subsonic contraction section body to eliminate or weaken the influence of the contraction section wall boundary layer on the boundary layer flow of the wind tunnel nozzle expansion section; the contraction section is pressed from a special metal material, and in the process of forming a rotationally symmetrical contraction profile, the metal material needs to be welded to achieve circumferential connection of the metal material, such as Figure 1 However, since the weld 113 formed by the welded metal material is not air permeable, a suction "dead zone" will be formed in the area where the weld 113 is located, making the local suction ineffective, which will significantly affect the suction efficiency of the suction device, especially when the size of the contraction section 100 is relatively large, it is necessary to use multiple pieces of special metal materials for splicing, the number of welds 113 is further increased, and the impact of the weld 113 is more significant.

[0005] Therefore, how to effectively reduce the impact of the weld of the contraction section on the boundary layer suction efficiency of the wind tunnel nozzle is a technical problem that technical personnel in this field currently need to solve. Summary of the invention

[0006] The purpose of the present invention is to provide a wind tunnel nozzle and its contraction section, and a method for manufacturing the contraction section of the wind tunnel nozzle, so as to improve the suction efficiency of the contraction section and the quality of the wind tunnel nozzle.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A wind tunnel nozzle contraction section comprises a cylindrical member, wherein the cylindrical member comprises a contraction section body and a suction section which are coaxially arranged, wherein the suction section is located downstream of the contraction section body, wherein the diameter of the suction section is smaller than the diameter of the contraction section body, and wherein the contraction section body and the suction section have a smooth transition; wherein at least one weld is provided on the cylindrical member, wherein the weld extends from one axial end of the cylindrical member to the other end; and wherein a generatrix on the suction section which intersects with the weld has an angle with the weld.

[0009] On the other hand, it also includes a skeleton, the cylindrical member is installed on the skeleton, and the cylindrical member is a porous material component.

[0010] On the other hand, a generatrix on the contraction section body that intersects with the weld has an angle with the weld.

[0011] On the other hand, the number of the welds is at least two, and the welds are arranged at intervals along the circumferential direction of the cylindrical member.

[0012] On the other hand, the weld on the suction section transitions smoothly with the weld on the contraction section body.

[0013] On the other hand, one of the welds is located in a welding plane, and the welding plane intersects with the axis of the cylindrical member, and the angle between the welding plane and the axis of the cylindrical member is an acute angle.

[0014] On the other hand, the angle between the welding plane and the axis of the cylindrical member is 15-35°.

[0015] A wind tunnel nozzle comprises the above-mentioned wind tunnel nozzle contraction section.

[0016] A method for manufacturing a wind tunnel nozzle contraction section comprises the following steps:

[0017] Step S1: obtaining a fan-shaped contraction section porous material plate, wherein a diameter direction on the contraction section porous material plate that intersects with the side of the contraction section porous material plate is provided with an angle with an extension direction of the side of the contraction section porous material plate;

[0018] Step S2: curling the contraction section porous material plate to obtain a truncated cone-shaped contraction section curled piece, and forming a weld between two side edges of the contraction section porous material plate;

[0019] Step S3: hot-pressing the shrinking section curled piece to form a shrinking section body and a suction section with a smooth transition on the shrinking section curled piece;

[0020] Step S4: The weld of the contraction section curled part is welded by cold welding process to obtain a finished cylindrical part.

[0021] On the other hand, the first side edge and the second side edge are respectively provided on both sides of the contraction section porous material plate, the first side edge and the second side edge extend in a straight line, and the first side edge and the second side edge are inclined toward the same side of the circumference of the contraction section porous material plate, and the inclination angles are the same.

[0022] The wind tunnel nozzle contraction section provided by the present invention comprises a cylindrical part, wherein the cylindrical part comprises a contraction section body and a suction section arranged coaxially, wherein the suction section is located downstream of the contraction section body, wherein the diameter of the suction section is smaller than the diameter of the contraction section body, and the contraction section body and the suction section have a smooth transition; wherein at least one weld is provided on the cylindrical part, wherein the weld extends from one axial end of the cylindrical part to the other end; and wherein an angle is provided between a generatrix intersecting with the weld on the suction section and the weld. The wind tunnel nozzle contraction section provided by the present invention reduces the area of ​​the weld on the suction section on a single generatrix by tilting the weld on the suction section relative to the generatrix, thereby effectively avoiding the formation of a suction "dead zone" in a part of the suction section while ensuring that the weld of the cylindrical part has good safety, reliability and service life, thereby effectively reducing or eliminating the influence of the weld on the suction efficiency of the turbulent boundary layer, and can effectively improve the suction efficiency of the wind tunnel nozzle in the contraction section and increase the quality of the wind tunnel nozzle.

[0023] In one embodiment, a weld is located in a welding plane, and the welding plane intersects the axis of the cylindrical member, and the angle between the welding plane and the axis of the cylindrical member is an acute angle. In the above arrangement, since the outer wall of the cylindrical member transitions in an arc shape in the axial direction, by limiting the single weld to be located in a welding plane, that is, under a certain viewing angle projection, the weld extends in a straight line, such an arrangement can facilitate the arrangement of welding equipment, simplify the welding process, and improve the welding efficiency.

[0024] The wind tunnel nozzle provided in the present application is provided with the above-mentioned wind tunnel nozzle contraction section. Since the wind tunnel nozzle contraction section has the above-mentioned technical effects, the wind tunnel nozzle provided with the wind tunnel nozzle contraction section should also have corresponding technical effects.

[0025] The method for making the contraction section of a wind tunnel nozzle provided by the present invention comprises the following steps: Step S1: obtaining a fan-shaped contraction section porous material plate, wherein an angle is provided between a diameter direction on the contraction section porous material plate that intersects with the side of the contraction section porous material plate and an extension direction of the side of the contraction section porous material plate; Step S2: curling the contraction section porous material plate to obtain a truncated cone-shaped contraction section curled piece, wherein a weld is formed between two side edges of the contraction section porous material plate; Step S3: hot-pressing the contraction section curled piece to form a contraction section body and a suction section with a smooth transition on the contraction section curled piece; Step S4: cold-welding the weld of the contraction section curled piece to obtain a finished cylindrical piece. The method for making the contraction section of a wind tunnel nozzle provided by the present invention obtains the porous material plate of the contraction section, and adjusts the inclination angles of the two side edges of the porous material plate of the contraction section so that the two side edges of the porous material plate of the contraction section no longer extend radially along the porous material plate of the contraction section, so that after the porous material plate of the contraction section is curled to form the contraction section curled piece, the weld formed by the two side edges of the porous material plate of the contraction section only intersects with the busbar of the contraction section curled piece and does not overlap, thereby effectively reducing the area of ​​the weld on the busbar, effectively reducing or eliminating the influence of the weld on the suction efficiency of the turbulent boundary layer, and can effectively improve the suction efficiency of the wind tunnel nozzle in the contraction section and increase the quality of the wind tunnel nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a structural schematic diagram of the wind tunnel nozzle contraction section in the related technology.

[0028] Figure 2 The present invention is a partial structural schematic diagram of a specific implementation of the wind tunnel nozzle provided by the present invention.

[0029] Figure 3 The present invention is a schematic structural diagram of a specific implementation of a cylindrical member in a contraction section of a wind tunnel nozzle provided by the present invention.

[0030] Figure 4 This is a schematic structural diagram of another specific implementation of the cylindrical member in the contraction section of the wind tunnel nozzle provided by the present invention.

[0031] Figure 5 for Figure 3 Front view of the cylindrical part shown.

[0032] Figure 6 for Figure 4 Front view of the cylindrical part shown.

[0033] Figure 7 The present invention is a flow chart of a method for manufacturing a wind tunnel nozzle contraction section.

[0034] Figure 8 for Figure 7 Schematic diagram of the structure of the porous material plate in the contraction section in the manufacturing method shown.

[0035] Reference numerals:

[0036] 100-contraction section; 200-throat section; 300-expansion section;

[0037] 110 - cylindrical member; 111 - contraction section body; 112 - suction section; 113 - weld; 114 - busbar; 120 - contraction section porous material plate; 121 - first side edge; 122 - second side edge. DETAILED DESCRIPTION

[0038] The core of the present invention is to provide a wind tunnel nozzle and its contraction section, and a method for manufacturing the wind tunnel nozzle contraction section, which can significantly improve the suction efficiency of the wind tunnel nozzle contraction section and reduce the disturbance to the wind tunnel nozzle expansion section.

[0039] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0040] In this embodiment, if Figure 2 , Figure 3 and Figure 5 As shown, the wind tunnel nozzle contraction section 100 includes a cylindrical member 110, and the cylindrical member 110 includes a contraction section body 111 and a suction section 112 which are coaxially arranged. The suction section 112 is located downstream of the contraction section body 111, and the diameter of the suction section 112 is smaller than the diameter of the contraction section body 111, and the contraction section body 111 and the suction section 112 have a smooth transition; at least one weld 113 is provided on the cylindrical member 110, and the weld 113 extends from one axial end to the other end of the cylindrical member 110; and a generatrix 114 on the suction section 112 which intersects with the weld 113 has an angle with the weld 113.

[0041] Specifically, the wind tunnel nozzle is mainly used in model experiments of aircraft. The upstream of the wind tunnel nozzle is a contraction section 100, and the downstream is an expansion section 300. A throat section 200 is provided between the contraction section 100 and the expansion section 300. The diameter of the contraction section 100 decreases from the upstream to the downstream, and according to the shape of the contraction section 100, it is divided into a contraction section body 111 and a suction section 112. The suction section 112 is located downstream of the contraction section body 111, that is, the suction section 112 is close to the throat section 200, and the recessed portion of the contraction section body 111 faces the inner side of the contraction section 100, and the recessed portion of the suction section 112 faces the outer side of the contraction section 100.

[0042] The wind tunnel nozzle contraction section 100 provided by the present invention reduces the area of ​​the weld 113 on the suction section 112 on the single busbar 114 by tilting the weld 113 on the suction section 112 relative to the busbar 114. On the basis of ensuring that the weld 113 of the cylindrical part 110 has good safety, reliability and service life, it effectively avoids the formation of a suction "dead zone" in the part of the suction section 112, thereby effectively reducing or eliminating the influence of the weld 113 on the suction efficiency of the turbulent boundary layer, and can effectively improve the suction efficiency of the wind tunnel nozzle in the contraction section 100 and increase the quality of the wind tunnel nozzle.

[0043] In some embodiments, a frame is also included, and the cylindrical member 110 is installed on the frame; specifically, the expansion section 300 of the wind tunnel nozzle is a steel structure, and the expansion section 300 is connected to the frame by fasteners, and the fasteners can be flanges. The cylindrical member 110 is placed on the frame, and the cylindrical member 110 can be welded and fixed on the frame. The frame mainly provides support for the cylindrical member 110, ensures the strength of the cylindrical member 110, and improves the service life and good performance of the cylindrical member 110; a suction device is also provided inside the frame and outside the cylindrical member 110 to provide power. Of course, the location of the suction device can be selected as needed. Further, the cylindrical member 110 is a porous material component, and the cylindrical member 110 can be a porous metal material, such as a porous stainless steel material. Of course, the cylindrical member 110 can also be other high temperature and high pressure resistant porous materials; the ambient temperature allowed by the porous material component can reach 800k-1000k, and the ambient pressure can reach 10MPa.

[0044] In some embodiments, Figure 4 and Figure 6As shown, a busbar 114 on the contraction section body 111 intersecting with the weld 113 has an angle with the weld 113; specifically, the cylindrical member 110 is surrounded by a fan-shaped contraction section porous material plate 120, and the weld 113 is formed by the two side edges of the contraction section porous material plate 120 being close to each other; since the suction section 112 serves as the main structure for turbulent boundary layer suction, only the busbar 114 on the suction section 112 intersecting with the weld 113 may have an angle with the weld 113. Of course, in order to facilitate the formation of the weld 113, an angle is also provided between the busbar 114 on the contraction section body 111 intersecting with the weld 113 and the weld 113.

[0045] In some embodiments, the weld 113 on the suction section 112 and the weld 113 on the contraction section body 111 are smoothly transitioned, so that the weld 113 can be formed continuously during the formation process, and the operation is convenient.

[0046] In some embodiments, there are at least two welds 113, and each weld 113 is arranged at intervals along the circumference of the cylindrical member 110; specifically, when reprocessing the cylindrical member 110, a plurality of contraction section porous material plates 120 can be spliced ​​together. For example, when the size of the cylindrical member 110 is large, two or more contraction section porous material plates 120 can be selected, and the ends are connected in sequence, and then they are arranged around and welded and fixed; when there are multiple welds 113, each weld 113 should be set with an angle between the busbar 114 at the corresponding position, or at least on the suction section 112, the weld 113 should be set with an angle between the busbar 114 at the corresponding position, and an acute angle is preferably selected.

[0047] In some embodiments, a weld 113 is located in a welding plane, and the welding plane intersects with the axis of the cylindrical member 110 , and the angle between the welding plane and the axis of the cylindrical member 110 is an acute angle.

[0048] In some embodiments, the angle between the welding plane and the axis of the cylindrical member 110 is 15-35°. It should be noted that the angle between the weld 113 and the corresponding busbar 114, or the angle between the welding plane and the axis of the cylindrical member 110, should be an acute angle, preferably 15-35°. In this way, the length of the weld 113 will not be too large, reducing the process difficulty, and will not affect the strength of the cylindrical member 110 too much.

[0049] The wind tunnel nozzle contraction section 100 improves the weld 113 of the cylindrical part 110, so that the influence of the weld 113 on the flow field suction capacity of the silent wind tunnel nozzle can be reduced or even eliminated, and the weld 113 will not introduce additional disturbances, which can effectively improve the quality of the wind tunnel; the weld 113 is inclined relative to the busbar 114 to minimize the area of ​​the weld 113 on the single busbar 114, so that the downstream of the weld 113, that is, the suction section 112, can still have the boundary layer suction function to the greatest extent.

[0050] In addition to the above-mentioned wind tunnel nozzle contraction section 100, the present application also provides a wind tunnel nozzle including the above-mentioned wind tunnel nozzle contraction section 100. For the structure of other parts of the wind tunnel nozzle, please refer to the relevant technology and will not be described in detail herein.

[0051] In addition to the above-mentioned wind tunnel nozzle and its contraction section 100, the present invention also provides a method for manufacturing the wind tunnel nozzle contraction section 100. Figure 7 As shown, the method for manufacturing the wind tunnel nozzle contraction section 100 comprises the following steps:

[0052] Step S1: obtaining a fan-shaped contraction section porous material plate 120, wherein a diameter direction of the contraction section porous material plate 120 intersecting with a side of the contraction section porous material plate 120 is provided with an angle with an extension direction of the side of the contraction section porous material plate 120;

[0053] Step S2: curling the contraction section porous material plate 120 to obtain a truncated cone-shaped contraction section curled piece, and forming a weld 113 between two side edges of the contraction section porous material plate 120;

[0054] Step S3: hot-pressing the contraction section curled piece to form a contraction section body 111 and a suction section 112 with a smooth transition on the contraction section curled piece;

[0055] Step S4: The weld seam 113 of the contraction section curled piece is welded by cold welding process to obtain the finished cylindrical piece 110 .

[0056] Specifically, the contraction section porous material plate 120 is a porous metal material plate, which has excellent welding performance, is easy to connect, and has a good suction effect on the turbulent boundary layer, which can reduce the impact on the turbulence downstream of the wind tunnel nozzle; the shapes of the two side edges of the contraction section porous material plate 120 should be adapted, that is, if the contraction section porous material plate 120 is curled, the side edge on one side of the contraction section porous material plate 120 should just be in contact with the side edge on the other side, and form a truncated cone-shaped contraction section curled part; the contraction section curled part is pressed into shape by a hot pressing mold, and the two curved surface structures of the contraction section body 111 and the suction section 112 are obtained, and then after processing by a cold welding process, the finished cylindrical part 110 can be obtained.

[0057] Furthermore, considering that the pores of porous material plates are relatively small, especially porous metal material plates, since metal materials are easily sintered and blocked by high temperatures, a cold welding process is selected during the welding process to minimize the width of the weld 113. Specifically, a cold welding process should be selected for the welding of the weld 113 and the welding between the cylindrical member 110 and the frame.

[0058] The manufacturing method of the wind tunnel nozzle contraction section 100 provided by the present invention obtains the contraction section porous material plate 120, and adjusts the inclination angles of the two side edges of the contraction section porous material plate 120 so that the two side edges of the contraction section porous material plate 120 no longer extend along the radial direction of the contraction section porous material plate 120, so that after the contraction section porous material plate 120 is curled to form a contraction section curled piece, the weld 113 formed by the two side edges of the contraction section porous material plate 120 only intersects with the busbar 114 of the contraction section curled piece and does not overlap, thereby effectively reducing the area of ​​the weld 113 on the busbar 114, effectively reducing or eliminating the influence of the weld 113 on the turbulent boundary layer suction efficiency, and can effectively improve the suction efficiency of the wind tunnel nozzle in the contraction section 100 and increase the quality of the wind tunnel nozzle.

[0059] In some embodiments, Figure 8 As shown, a first side edge 121 and a second side edge 122 are respectively provided on both sides of the contraction section porous material plate 120, and the first side edge 121 and the second side edge 122 are both extended in a straight line, and the first side edge 121 and the second side edge 122 are inclined toward the same side of the circumference of the contraction section porous material plate 120, and the inclination angles are the same; that is, if the first side edge 121 is inclined toward the right relative to the diameter direction of the corresponding position, then the second side edge 122 should also be inclined to the right relative to the diameter direction of the corresponding position, and the inclination angles are the same; with such an arrangement, a complete cylindrical truncated cone structure can be formed when the contraction section porous material plate 120 is curled; the first side edge 121 and the second side edge 122 are both extended in a straight line to facilitate the processing of the contraction section porous material plate 120, and will also facilitate the subsequent welding process of the weld 113.

[0060] The wind tunnel nozzle and its contraction section 100, and the method for making the wind tunnel nozzle contraction section 100 provided by the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the present invention.

Claims

1. A wind tunnel nozzle contraction section, characterized in that: The invention comprises a cylindrical member (110), wherein the cylindrical member (110) is a porous material member, wherein the cylindrical member (110) comprises a contraction section body (111) and a suction section (112) which are coaxially arranged, wherein the suction section (112) is located downstream of the contraction section body (111), wherein the diameter of the suction section (112) is smaller than the diameter of the contraction section body (111), and wherein the contraction section body (111) and the suction section (112) are smoothly transitioned; wherein at least one weld (113) is provided on the cylindrical member (110), wherein the weld (113) extends from one axial end to the other end of the cylindrical member (110); and a generatrix (114) on the suction section (112) intersecting with the weld (113) forms an angle with the weld (113).

2. The wind tunnel nozzle contraction section according to claim 1, characterized in that: It also comprises a skeleton, on which the cylindrical member (110) is mounted.

3. The wind tunnel nozzle contraction section according to claim 1, characterized in that: A generatrix (114) on the contraction section body (111) intersecting with the weld (113) is provided with an angle between the generatrix and the weld (113).

4. The wind tunnel nozzle contraction section according to claim 1, characterized in that: The number of the weld seams (113) is at least two, and the weld seams (113) are arranged at intervals along the circumference of the cylindrical member (110).

5. The wind tunnel nozzle convergence section according to claim 1, characterized in that: The weld (113) on the suction section (112) and the weld (113) on the contraction section body (111) transition smoothly.

6. The wind tunnel nozzle convergence section according to any one of claims 1 to 5, characterized in that: The weld (113) is located in a welding plane, and the welding plane intersects with the axis of the cylindrical member (110), and the angle between the welding plane and the axis of the cylindrical member (110) is an acute angle.

7. The wind tunnel nozzle convergence section according to claim 6, characterized in that: The angle between the welding plane and the axis of the cylindrical member (110) is 15-35°.

8. A wind tunnel nozzle, comprising a wind tunnel nozzle contraction section (100), characterized in that: The wind tunnel nozzle convergence section (100) is the wind tunnel nozzle convergence section according to any one of claims 1 to 7.

9. A method for manufacturing a wind tunnel nozzle contraction section, characterized in that: The following steps are involved: Step S1: obtaining a fan-shaped contraction section porous material plate (120), wherein a diameter direction of the contraction section porous material plate (120) intersecting with a side edge of the contraction section porous material plate (120) is provided with an angle with a direction in which the side edge of the contraction section porous material plate (120) extends; Step S2: curling the contraction section porous material plate (120) to obtain a truncated cone-shaped contraction section curled piece, and forming a weld (113) between two side edges of the contraction section porous material plate (120); Step S3: hot-pressing the shrinking section curled piece to form a shrinking section body (111) and a suction section (112) with a smooth transition on the shrinking section curled piece; Step S4: welding the weld (113) of the shrinkage section curled piece using a cold welding process to obtain a finished cylindrical piece (110).

10. The method for manufacturing a wind tunnel nozzle contraction section according to claim 9, characterized in that: A first side edge (121) and a second side edge (122) are respectively provided on both sides of the contraction section porous material plate (120); the first side edge (121) and the second side edge (122) both extend in a straight line, and the first side edge (121) and the second side edge (122) are inclined toward the same side of the circumference of the contraction section porous material plate (120) and have the same inclination angle.

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